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Hirunpattarasilp C, James G, Kwanthongdee J, Freitas F, Huo J, Sethi H, Kittler JT, Owens RJ, McCoy LE, Attwell D. SARS-CoV-2 triggers pericyte-mediated cerebral capillary constriction. Brain 2023; 146:727-738. [PMID: 35867861 PMCID: PMC9384509 DOI: 10.1093/brain/awac272] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2022] [Revised: 07/04/2022] [Accepted: 07/11/2022] [Indexed: 11/21/2022] Open
Abstract
The SARS-CoV-2 receptor, ACE2, is found on pericytes, contractile cells enwrapping capillaries that regulate brain, heart and kidney blood flow. ACE2 converts vasoconstricting angiotensin II into vasodilating angiotensin-(1-7). In brain slices from hamster, which has an ACE2 sequence similar to human ACE2, angiotensin II evoked a small pericyte-mediated capillary constriction via AT1 receptors, but evoked a large constriction when the SARS-CoV-2 receptor binding domain (RBD, original Wuhan variant) was present. A mutated non-binding RBD did not potentiate constriction. A similar RBD-potentiated capillary constriction occurred in human cortical slices, and was evoked in hamster brain slices by pseudotyped virions expressing SARS-CoV-2 spike protein. This constriction reflects an RBD-induced decrease in the conversion of angiotensin II to angiotensin-(1-7) mediated by removal of ACE2 from the cell surface membrane and was mimicked by blocking ACE2. The clinically used drug losartan inhibited the RBD-potentiated constriction. Thus, AT1 receptor blockers could be protective in COVID-19 by preventing pericyte-mediated blood flow reductions in the brain, and perhaps the heart and kidney.
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Affiliation(s)
- Chanawee Hirunpattarasilp
- Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6BT, UK
- Princess Srisavangavadhana College of Medicine, Chulabhorn Royal Academy, Talat Bang Khen, Lak Si, Bangkok, 10210, Thailand
| | - Greg James
- Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6BT, UK
- Department of Neurosurgery, Great Ormond Street Hospital, London WC1N 3JH, UK
| | - Jaturon Kwanthongdee
- Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6BT, UK
- Princess Srisavangavadhana College of Medicine, Chulabhorn Royal Academy, Talat Bang Khen, Lak Si, Bangkok, 10210, Thailand
| | - Felipe Freitas
- Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6BT, UK
| | - Jiandong Huo
- Division of Structural Biology, Nuffield Department of Medicine, University of Oxford, Oxford OX3 7BN, UK
- Protein Production UK, The Research Complex at Harwell, and Rosalind Franklin Institute, Harwell Science and Innovation Campus, Didcot OX11 0GD, UK
| | - Huma Sethi
- Division of Neurosurgery, National Hospital for Neurology and Neurosurgery, Queen Square, London WC1N 3BG, UK
| | - Josef T Kittler
- Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6BT, UK
| | - Raymond J Owens
- Division of Structural Biology, Nuffield Department of Medicine, University of Oxford, Oxford OX3 7BN, UK
- Protein Production UK, The Research Complex at Harwell, and Rosalind Franklin Institute, Harwell Science and Innovation Campus, Didcot OX11 0GD, UK
| | - Laura E McCoy
- Division of Infection and Immunity, University College London, London NW3 2PP, UK
| | - David Attwell
- Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6BT, UK
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2
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Barkaway A, Attwell D, Korte N. Immune-vascular mural cell interactions: consequences for immune cell trafficking, cerebral blood flow, and the blood-brain barrier. NEUROPHOTONICS 2022; 9:031914. [PMID: 35581998 PMCID: PMC9107322 DOI: 10.1117/1.nph.9.3.031914] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/29/2021] [Accepted: 04/13/2022] [Indexed: 06/15/2023]
Abstract
Brain barriers are crucial sites for cerebral energy supply, waste removal, immune cell migration, and solute exchange, all of which maintain an appropriate environment for neuronal activity. At the capillary level, where the largest area of brain-vascular interface occurs, pericytes adjust cerebral blood flow (CBF) by regulating capillary diameter and maintain the blood-brain barrier (BBB) by suppressing endothelial cell (EC) transcytosis and inducing tight junction expression between ECs. Pericytes also limit the infiltration of circulating leukocytes into the brain where resident microglia confine brain injury and provide the first line of defence against invading pathogens. Brain "waste" is cleared across the BBB into the blood, phagocytosed by microglia and astrocytes, or removed by the flow of cerebrospinal fluid (CSF) through perivascular routes-a process driven by respiratory motion and the pulsation of the heart, arteriolar smooth muscle, and possibly pericytes. "Dirty" CSF exits the brain and is probably drained around olfactory nerve rootlets and via the dural meningeal lymphatic vessels and possibly the skull bone marrow. The brain is widely regarded as an immune-privileged organ because it is accessible to few antigen-primed leukocytes. Leukocytes enter the brain via the meninges, the BBB, and the blood-CSF barrier. Advances in genetic and imaging tools have revealed that neurological diseases significantly alter immune-brain barrier interactions in at least three ways: (1) the brain's immune-privileged status is compromised when pericytes are lost or lymphatic vessels are dysregulated; (2) immune cells release vasoactive molecules to regulate CBF, modulate arteriole stiffness, and can plug and eliminate capillaries which impairs CBF and possibly waste clearance; and (3) immune-vascular interactions can make the BBB leaky via multiple mechanisms, thus aggravating the influx of undesirable substances and cells. Here, we review developments in these three areas and briefly discuss potential therapeutic avenues for restoring brain barrier functions.
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Affiliation(s)
- Anna Barkaway
- University College London, Department of Neuroscience, Physiology and Pharmacology, London, United Kingdom
| | - David Attwell
- University College London, Department of Neuroscience, Physiology and Pharmacology, London, United Kingdom
| | - Nils Korte
- University College London, Department of Neuroscience, Physiology and Pharmacology, London, United Kingdom
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3
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Hartmann DA, Coelho-Santos V, Shih AY. Pericyte Control of Blood Flow Across Microvascular Zones in the Central Nervous System. Annu Rev Physiol 2022; 84:331-354. [PMID: 34672718 PMCID: PMC10480047 DOI: 10.1146/annurev-physiol-061121-040127] [Citation(s) in RCA: 70] [Impact Index Per Article: 35.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
The vast majority of the brain's vascular length is composed of capillaries, where our understanding of blood flow control remains incomplete. This review synthesizes current knowledge on the control of blood flow across microvascular zones by addressing issues with nomenclature and drawing on new developments from in vivo optical imaging and single-cell transcriptomics. Recent studies have highlighted important distinctions in mural cell morphology, gene expression, and contractile dynamics, which can explain observed differences in response to vasoactive mediators between arteriole, transitional, and capillary zones. Smooth muscle cells of arterioles and ensheathing pericytes of the arteriole-capillary transitional zone control large-scale, rapid changes in blood flow. In contrast, capillary pericytes downstream of the transitional zone act on slower and smaller scales and are involved in establishing resting capillary tone and flow heterogeneity. Many unresolved issues remain, including the vasoactive mediators that activate the different pericyte types in vivo, the role of pericyte-endothelial communication in conducting signals from capillaries to arterioles, and how neurological disease affects these mechanisms.
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Affiliation(s)
- David A Hartmann
- Department of Neurology and Neurological Sciences, Stanford University, Stanford, California, USA
| | - Vanessa Coelho-Santos
- Center for Developmental Biology and Regenerative Medicine, Seattle Children's Research Institute, Seattle, Washington, USA;
- Department of Pediatrics, University of Washington, Seattle, Washington, USA
| | - Andy Y Shih
- Center for Developmental Biology and Regenerative Medicine, Seattle Children's Research Institute, Seattle, Washington, USA;
- Department of Pediatrics, University of Washington, Seattle, Washington, USA
- Department of Bioengineering, University of Washington, Seattle, Washington, USA
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4
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Thébault S. Minireview: Insights into the role of TRP channels in the retinal circulation and function. Neurosci Lett 2021; 765:136285. [PMID: 34634394 DOI: 10.1016/j.neulet.2021.136285] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Revised: 08/25/2021] [Accepted: 08/28/2021] [Indexed: 12/17/2022]
Abstract
Consistent with their wide distribution throughout the CNS, transcripts of all transient receptor potential (TRP) cation channel superfamily members have been detected in both neuronal and non-neuronal cells of the mammalian retina. Evidence shows that members of the TRPC (canonical, TRPC1/4/5/6), TRPV (vanilloid, TRPV1/2/4), TRPM (melastatin, TRPM1/2/3/5), TRPA (ankyrin, TRPA1), and TRPP (polycystin, TRPP2) subfamilies contribute to retinal function and circulation in health and disease, but the relevance of most TRPs has yet to be determined. Their principal role in light detection is far better understood than their participation in the control of intraocular pressure, retinal blood flow, oxidative stress, ion homeostasis, and transmitter signaling for retinal information processing. Moreover, if the therapeutic potential of targeting some TRPs to treat various retinal diseases remains speculative, recent studies highlight that vision restoration strategies are very likely to benefit from the thermo- and mechanosensitive properties of TRPs. This minireview focuses on the evidence of the past 5 years about the role of TRPs in the retina and retinal circulation, raises some possibilities about the function of TRPs in the retina, and discusses the potential sources of endogenous stimuli for TRPs in this tissue, as a reflection for future studies.
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Affiliation(s)
- Stéphanie Thébault
- Instituto de Neurobiología, Universidad Nacional Autónoma de México (UNAM), Campus UNAM-Juriquilla, 76230 Querétaro, Mexico.
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5
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Fletcher EL, Phipps JA, Wilkinson-Berka JL. Dysfunction of retinal neurons and glia during diabetes. Clin Exp Optom 2021; 88:132-45. [PMID: 15926876 DOI: 10.1111/j.1444-0938.2005.tb06686.x] [Citation(s) in RCA: 59] [Impact Index Per Article: 19.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2004] [Revised: 04/15/2005] [Accepted: 04/23/2005] [Indexed: 12/27/2022] Open
Abstract
Diabetic retinopathy is the leading cause of blindness in those of working age. It is well known that the retinal vasculature is altered during diabetes. More recently, it has emerged that neuronal and glial dysfunction occurs in those with diabetes. Current research is directed at understanding these neuronal and glial changes because they may be an early manifestation of disease processes that ultimately lead to vascular abnormality. This review will highlight the recent advances in our understanding of the neuronal and glial changes that occur during diabetes.
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Affiliation(s)
- Erica L Fletcher
- Department of Anatomy and Cell Biology, The University of Melbourne, Grattan Street, Parkville, VIC 3010, Australia
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Lee LL, Khakoo AY, Chintalgattu V. Cardiac pericytes function as key vasoactive cells to regulate homeostasis and disease. FEBS Open Bio 2020; 11:207-225. [PMID: 33135334 PMCID: PMC7780101 DOI: 10.1002/2211-5463.13021] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2020] [Revised: 08/24/2020] [Accepted: 10/30/2020] [Indexed: 01/13/2023] Open
Abstract
Pericytes (PCs)—mural cells that envelop endothelial cells (ECs) of microvessels—regulate tissue‐specific vasculature development as well as maturation and maintenance of endothelial barrier integrity. However, little is known about their tissue‐specific function in the heart. Specifically, the mechanism by which cardiac PCs constrict coronary capillaries remains undetermined. To gain insights into the function of cardiac PCs at the cellular level, we isolated NG2+ PDGFRβ+ CD146+ CD34− CD31− CD45− PCs for detailed characterization. Functionally, we provide evidence that these PCs increased transepithelial electrical resistance and decreased endothelial permeability. We show for the first time that this population of PCs express contractile proteins, are stimulated by adrenergic signaling, and demonstrate stereotypical contraction and relaxation. Furthermore, we also studied for the first time, the PCs in in vitro models of disease. PCs in hypoxia activated the hypoxia‐inducible factor 1 alpha pathway, increased secretion of angiogenic factors, and caused cellular apoptosis. Supraphysiological levels of low‐density lipoprotein decreased PC proliferation and induced lipid droplet accumulation. Elevated glucose levels triggered a proinflammatory response. Taken together, our study characterizes cardiac PCs under in vitro disease conditions and supports the hypothesis that cardiac PCs are key vasoactive cells that can regulate blood flow in the heart.
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Affiliation(s)
- Linda L Lee
- Department of Cardiometabolic Disorders, Amgen Research and Discovery, Amgen Inc., South San Francisco, CA, USA
| | - Aarif Y Khakoo
- Department of Drug Development, Calico Labs, South San Francisco, CA, USA
| | - Vishnu Chintalgattu
- Department of Cardiometabolic Disorders, Amgen Research and Discovery, Amgen Inc., South San Francisco, CA, USA
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Abstract
Diabetic retinopathy (DR) is a frequent complication of diabetes mellitus and an increasingly common cause of visual impairment. Blood vessel damage occurs as the disease progresses, leading to ischemia, neovascularization, blood-retina barrier (BRB) failure and eventual blindness. Although detection and treatment strategies have improved considerably over the past years, there is room for a better understanding of the pathophysiology of the diabetic retina. Indeed, it has been increasingly realized that DR is in fact a disease of the retina's neurovascular unit (NVU), the multi-cellular framework underlying functional hyperemia, coupling neuronal computations to blood flow. The accumulating evidence reveals that both neurochemical (synapses) and electrical (gap junctions) means of communications between retinal cells are affected at the onset of hyperglycemia, warranting a global assessment of cellular interactions and their role in DR. This is further supported by the recent data showing down-regulation of connexin 43 gap junctions along the vascular relay from capillary to feeding arteriole as one of the earliest indicators of experimental DR, with rippling consequences to the anatomical and physiological integrity of the retina. Here, recent advancements in our knowledge of mechanisms controlling the retinal neurovascular unit will be assessed, along with their implications for future treatment and diagnosis of DR.
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Nelson AR, Sagare MA, Wang Y, Kisler K, Zhao Z, Zlokovic BV. Channelrhodopsin Excitation Contracts Brain Pericytes and Reduces Blood Flow in the Aging Mouse Brain in vivo. Front Aging Neurosci 2020; 12:108. [PMID: 32410982 PMCID: PMC7201096 DOI: 10.3389/fnagi.2020.00108] [Citation(s) in RCA: 52] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2019] [Accepted: 03/30/2020] [Indexed: 01/02/2023] Open
Abstract
Brains depend on blood flow for the delivery of oxygen and nutrients essential for proper neuronal and synaptic functioning. French physiologist Rouget was the first to describe pericytes in 1873 as regularly arranged longitudinal amoeboid cells on capillaries that have a muscular coat, implying that these are contractile cells that regulate blood flow. Although there have been >30 publications from different groups, including our group, demonstrating that pericytes are contractile cells that can regulate hemodynamic responses in the brain, the role of pericytes in controlling cerebral blood flow (CBF) has not been confirmed by all studies. Moreover, recent studies using different optogenetic models to express light-sensitive channelrhodopsin-2 (ChR2) cation channels in pericytes were not conclusive; one, suggesting that pericytes expressing ChR2 do not contract after light stimulus, and the other, demonstrating contraction of pericytes expressing ChR2 after light stimulus. Since two-photon optogenetics provides a powerful tool to study mechanisms of blood flow regulation at the level of brain capillaries, we re-examined the contractility of brain pericytes in vivo using a new optogenetic model developed by crossing our new inducible pericyte-specific CreER mouse line with ChR2 mice. We induced expression of ChR2 in pericytes with tamoxifen, excited ChR2 by 488 nm light, and monitored pericyte contractility, brain capillary diameter changes, and red blood cell (RBC) velocity in aged mice by in vivo two-photon microscopy. Excitation of ChR2 resulted in pericyte contraction followed by constriction of the underlying capillary leading to approximately an 8% decrease (p = 0.006) in capillary diameter. ChR2 excitation in pericytes substantially reduced capillary RBC flow by 42% (p = 0.03) during the stimulation period compared to the velocity before stimulation. Our data suggests that pericytes contract in vivo and regulate capillary blood flow in the aging mouse brain. By extension, this might have implications for neurological disorders of the aging human brain associated with neurovascular dysfunction and pericyte loss such as stroke and Alzheimer's disease.
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Affiliation(s)
| | | | | | | | | | - Berislav V. Zlokovic
- Department of Physiology and Neuroscience, Zilkha Neurogenetic Institute, University of Southern California, Los Angeles, CA, United States
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Cınar E, Yuce B, Zengin MO, Kucukerdonmez C. The Effect of Nicotine on Macular Microcirculation in Healthy Subjects. Ophthalmic Surg Lasers Imaging Retina 2019; 50:691-700. [DOI: 10.3928/23258160-20191031-04] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2018] [Accepted: 03/25/2019] [Indexed: 01/23/2023]
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10
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Phipps JA, Dixon MA, Jobling AI, Wang AY, Greferath U, Vessey KA, Fletcher EL. The renin-angiotensin system and the retinal neurovascular unit: A role in vascular regulation and disease. Exp Eye Res 2019; 187:107753. [PMID: 31408629 DOI: 10.1016/j.exer.2019.107753] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2019] [Revised: 07/31/2019] [Accepted: 08/05/2019] [Indexed: 01/16/2023]
Abstract
The retina is known to have a local renin-angiotensin system (RAS) and dysfunction in the RAS is often associated with diseases of the retinal vasculature that cause irreversible vision loss. Regulation of the retinal vasculature to meet the metabolic needs of the tissues occurs through a mechanism called neurovascular coupling, which is critical for maintaining homeostatic function and support for neurons. Neurovascular coupling is the process by which support cells, including glia, regulate blood vessel calibre and blood flow in response to neural activity. In retinal vascular diseases, this coupling mechanism is often disrupted. However, the role that angiotensin II (Ang II), the main effector peptide of the RAS, has in regulating both the retinal vasculature and neurovascular coupling is not fully understood. As components of the RAS are located on the principal neurons, glia and blood vessels of the retina, it is possible that Ang II has a role in regulating communication and function between these three cell types, and therefore the capacity to regulate neurovascular coupling. This review focuses on components of the RAS located on the retinal neurovascular unit, and the potential of this system to contribute to blood flow modulation in the healthy and compromised retina.
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Affiliation(s)
- Joanna A Phipps
- Department of Anatomy and Neuroscience, The University of Melbourne, Parkville, 3010, Victoria, Australia
| | - Michael A Dixon
- Department of Anatomy and Neuroscience, The University of Melbourne, Parkville, 3010, Victoria, Australia
| | - Andrew I Jobling
- Department of Anatomy and Neuroscience, The University of Melbourne, Parkville, 3010, Victoria, Australia
| | - Anna Y Wang
- Department of Anatomy and Neuroscience, The University of Melbourne, Parkville, 3010, Victoria, Australia
| | - Ursula Greferath
- Department of Anatomy and Neuroscience, The University of Melbourne, Parkville, 3010, Victoria, Australia
| | - Kirstan A Vessey
- Department of Anatomy and Neuroscience, The University of Melbourne, Parkville, 3010, Victoria, Australia
| | - Erica L Fletcher
- Department of Anatomy and Neuroscience, The University of Melbourne, Parkville, 3010, Victoria, Australia.
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11
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Bertlich M, Ihler F, Weiss BG, Freytag S, Strupp M, Jakob M, Canis M. Role of capillary pericytes and precapillary arterioles in the vascular mechanism of betahistine in a guinea pig inner ear model. Life Sci 2017; 187:17-21. [DOI: 10.1016/j.lfs.2017.08.015] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2017] [Revised: 08/03/2017] [Accepted: 08/14/2017] [Indexed: 10/19/2022]
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12
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Glial Cell Calcium Signaling Mediates Capillary Regulation of Blood Flow in the Retina. J Neurosci 2017; 36:9435-45. [PMID: 27605617 DOI: 10.1523/jneurosci.1782-16.2016] [Citation(s) in RCA: 102] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2016] [Accepted: 07/26/2016] [Indexed: 01/27/2023] Open
Abstract
UNLABELLED The brain is critically dependent on the regulation of blood flow to nourish active neurons. One widely held hypothesis of blood flow regulation holds that active neurons stimulate Ca(2+) increases in glial cells, triggering glial release of vasodilating agents. This hypothesis has been challenged, as arteriole dilation can occur in the absence of glial Ca(2+) signaling. We address this controversy by imaging glial Ca(2+) signaling and vessel dilation in the mouse retina. We find that sensory stimulation results in Ca(2+) increases in the glial endfeet contacting capillaries, but not arterioles, and that capillary dilations often follow spontaneous Ca(2+) signaling. In IP3R2(-/-) mice, where glial Ca(2+) signaling is reduced, light-evoked capillary, but not arteriole, dilation is abolished. The results show that, independent of arterioles, capillaries actively dilate and regulate blood flow. Furthermore, the results demonstrate that glial Ca(2+) signaling regulates capillary but not arteriole blood flow. SIGNIFICANCE STATEMENT We show that a Ca(2+)-dependent glial cell signaling mechanism is responsible for regulating capillary but not arteriole diameter. This finding resolves a long-standing controversy regarding the role of glial cells in regulating blood flow, demonstrating that glial Ca(2+) signaling is both necessary and sufficient to dilate capillaries. While the relative contributions of capillaries and arterioles to blood flow regulation remain unclear, elucidating the mechanisms that regulate capillary blood flow may ultimately lead to the development of therapies for treating diseases where blood flow regulation is disrupted, including Alzheimer's disease, stroke, and diabetic retinopathy. This finding may also aid in revealing the underlying neuronal activity that generates BOLD fMRI signals.
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Ivanova E, Yee CW, Sagdullaev BT. Leveraging Optogenetic-Based Neurovascular Circuit Characterization for Repair. Neurotherapeutics 2016; 13:341-7. [PMID: 26758692 PMCID: PMC4824015 DOI: 10.1007/s13311-015-0419-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
Abstract
Optogenetic techniques are a powerful tool for determining the role of individual functional components within complex neural circuits. By genetically targeting specific cell types, neural mechanisms can be actively manipulated to gain a better understanding of their origin and function, both in health and disease. The potential of optogenetics is not limited to answering biological questions, as it is also a promising therapeutic approach for neurological diseases. An important prerequisite for this approach is to have an identified target with a uniquely defined role within a given neural circuit. Here, we examine the retinal neurovascular unit, a circuit that incorporates neurons and vascular cells to control blood flow in the retina. We highlight the role of a specific cell type, the cholinergic amacrine cell, in modulating vascular cells, and demonstrate how this can be targeted and controlled with optogenetics. A better understanding of these mechanisms will not only extend our understanding of neurovascular interactions in the brain, but ultimately may also provide new targets to treat vision loss in a variety of retinal diseases.
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Affiliation(s)
- Elena Ivanova
- Department of Ophthalmology, Brain and Mind Research Institute, Weill Cornell Medical College, Burke Medical Research Institute, White Plains, NY, 10605, USA
| | - Christopher W Yee
- Department of Ophthalmology, Brain and Mind Research Institute, Weill Cornell Medical College, Burke Medical Research Institute, White Plains, NY, 10605, USA
| | - Botir T Sagdullaev
- Department of Ophthalmology, Brain and Mind Research Institute, Weill Cornell Medical College, Burke Medical Research Institute, White Plains, NY, 10605, USA.
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Trost A, Lange S, Schroedl F, Bruckner D, Motloch KA, Bogner B, Kaser-Eichberger A, Strohmaier C, Runge C, Aigner L, Rivera FJ, Reitsamer HA. Brain and Retinal Pericytes: Origin, Function and Role. Front Cell Neurosci 2016; 10:20. [PMID: 26869887 PMCID: PMC4740376 DOI: 10.3389/fncel.2016.00020] [Citation(s) in RCA: 158] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2015] [Accepted: 01/18/2016] [Indexed: 12/13/2022] Open
Abstract
Pericytes are specialized mural cells located at the abluminal surface of capillary blood vessels, embedded within the basement membrane. In the vascular network these multifunctional cells fulfil diverse functions, which are indispensable for proper homoeostasis. They serve as microvascular stabilizers, are potential regulators of microvascular blood flow and have a central role in angiogenesis, as they for example regulate endothelial cell proliferation. Furthermore, pericytes, as part of the neurovascular unit, are a major component of the blood-retina/brain barrier. CNS pericytes are a heterogenic cell population derived from mesodermal and neuro-ectodermal germ layers acting as modulators of stromal and niche environmental properties. In addition, they display multipotent differentiation potential making them an intriguing target for regenerative therapies. Pericyte-deficiencies can be cause or consequence of many kinds of diseases. In diabetes, for instance, pericyte-loss is a severe pathological process in diabetic retinopathy (DR) with detrimental consequences for eye sight in millions of patients. In this review, we provide an overview of our current understanding of CNS pericyte origin and function, with a special focus on the retina in the healthy and diseased. Finally, we highlight the role of pericytes in de- and regenerative processes.
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Affiliation(s)
- Andrea Trost
- Research Program for Ophthalmology and Glaucoma Research, Paracelsus Medical University/SALK, University Clinic of Ophthalmology and OptometrySalzburg, Austria; Molecular Regenerative Medicine, Paracelsus Medical UniversitySalzburg, Austria
| | - Simona Lange
- Molecular Regenerative Medicine, Paracelsus Medical UniversitySalzburg, Austria; Spinal Cord Injury and Tissue Regeneration Center Salzburg, Paracelsus Medical University SalzburgSalzburg, Austria
| | - Falk Schroedl
- Research Program for Ophthalmology and Glaucoma Research, Paracelsus Medical University/SALK, University Clinic of Ophthalmology and OptometrySalzburg, Austria; Anatomy, Paracelsus Medical UniversitySalzburg, Austria
| | - Daniela Bruckner
- Research Program for Ophthalmology and Glaucoma Research, Paracelsus Medical University/SALK, University Clinic of Ophthalmology and Optometry Salzburg, Austria
| | - Karolina A Motloch
- Research Program for Ophthalmology and Glaucoma Research, Paracelsus Medical University/SALK, University Clinic of Ophthalmology and Optometry Salzburg, Austria
| | - Barbara Bogner
- Research Program for Ophthalmology and Glaucoma Research, Paracelsus Medical University/SALK, University Clinic of Ophthalmology and Optometry Salzburg, Austria
| | - Alexandra Kaser-Eichberger
- Research Program for Ophthalmology and Glaucoma Research, Paracelsus Medical University/SALK, University Clinic of Ophthalmology and Optometry Salzburg, Austria
| | - Clemens Strohmaier
- Research Program for Ophthalmology and Glaucoma Research, Paracelsus Medical University/SALK, University Clinic of Ophthalmology and Optometry Salzburg, Austria
| | - Christian Runge
- Research Program for Ophthalmology and Glaucoma Research, Paracelsus Medical University/SALK, University Clinic of Ophthalmology and Optometry Salzburg, Austria
| | - Ludwig Aigner
- Spinal Cord Injury and Tissue Regeneration Center Salzburg, Paracelsus Medical University SalzburgSalzburg, Austria; Anatomy, Paracelsus Medical UniversitySalzburg, Austria
| | - Francisco J Rivera
- Spinal Cord Injury and Tissue Regeneration Center Salzburg, Paracelsus Medical University SalzburgSalzburg, Austria; Anatomy, Paracelsus Medical UniversitySalzburg, Austria
| | - Herbert A Reitsamer
- Research Program for Ophthalmology and Glaucoma Research, Paracelsus Medical University/SALK, University Clinic of Ophthalmology and OptometrySalzburg, Austria; Anatomy, Paracelsus Medical UniversitySalzburg, Austria
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Østergaard L, Engedal TS, Moreton F, Hansen MB, Wardlaw JM, Dalkara T, Markus HS, Muir KW. Cerebral small vessel disease: Capillary pathways to stroke and cognitive decline. J Cereb Blood Flow Metab 2016; 36:302-25. [PMID: 26661176 PMCID: PMC4759673 DOI: 10.1177/0271678x15606723] [Citation(s) in RCA: 177] [Impact Index Per Article: 22.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/20/2015] [Accepted: 07/30/2015] [Indexed: 01/18/2023]
Abstract
Cerebral small vessel disease (SVD) gives rise to one in five strokes worldwide and constitutes a major source of cognitive decline in the elderly. SVD is known to occur in relation to hypertension, diabetes, smoking, radiation therapy and in a range of inherited and genetic disorders, autoimmune disorders, connective tissue disorders, and infections. Until recently, changes in capillary patency and blood viscosity have received little attention in the aetiopathogenesis of SVD and the high risk of subsequent stroke and cognitive decline. Capillary flow patterns were, however, recently shown to limit the extraction efficacy of oxygen in tissue and capillary dysfunction therefore proposed as a source of stroke-like symptoms and neurodegeneration, even in the absence of physical flow-limiting vascular pathology. In this review, we examine whether capillary flow disturbances may be a shared feature of conditions that represent risk factors for SVD. We then discuss aspects of capillary dysfunction that could be prevented or alleviated and therefore might be of general benefit to patients at risk of SVD, stroke or cognitive decline.
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Affiliation(s)
- Leif Østergaard
- Center of Functionally Integrative Neuroscience and MINDLab, Institute of Clinical Medicine, Aarhus University, Aarhus, Denmark Department of Neuroradiology, Aarhus University Hospital, Aarhus, Denmark
| | - Thorbjørn S Engedal
- Center of Functionally Integrative Neuroscience and MINDLab, Institute of Clinical Medicine, Aarhus University, Aarhus, Denmark
| | - Fiona Moreton
- Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, UK
| | - Mikkel B Hansen
- Center of Functionally Integrative Neuroscience and MINDLab, Institute of Clinical Medicine, Aarhus University, Aarhus, Denmark
| | - Joanna M Wardlaw
- Centre for Clinical Brain Sciences, University of Edinburgh, Edinburgh, UK
| | - Turgay Dalkara
- Institute of Neurological Sciences and Psychiatry and Department of Neurology, Faculty of Medicine, Hacettepe University, Ankara, Turkey
| | - Hugh S Markus
- Department of Clinical Neuroscience, University of Cambridge, Cambridge, UK
| | - Keith W Muir
- Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, UK
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16
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Østergaard L, Granfeldt A, Secher N, Tietze A, Iversen NK, Jensen MS, Andersen KK, Nagenthiraja K, Gutiérrez‐Lizardi P, Mouridsen K, Jespersen SN, Tønnesen EK. Microcirculatory dysfunction and tissue oxygenation in critical illness. Acta Anaesthesiol Scand 2015; 59:1246-59. [PMID: 26149711 PMCID: PMC4758388 DOI: 10.1111/aas.12581] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2015] [Revised: 05/19/2015] [Accepted: 06/14/2015] [Indexed: 12/19/2022]
Abstract
Severe sepsis is defined by organ failure, often of the kidneys, heart, and brain. It has been proposed that inadequate delivery of oxygen, or insufficient extraction of oxygen in tissue, may explain organ failure. Despite adequate maintenance of systemic oxygen delivery in septic patients, their morbidity and mortality remain high. The assumption that tissue oxygenation can be preserved by maintaining its blood supply follows from physiological models that only apply to tissue with uniformly perfused capillaries. In sepsis, the microcirculation is profoundly disturbed, and the blood supply of individual organs may therefore no longer reflect their access to oxygen. We review how capillary flow patterns affect oxygen extraction efficacy in tissue, and how the regulation of tissue blood flow must be adjusted to meet the metabolic needs of the tissue as capillary flows become disturbed as observed in critical illness. Using the brain, heart, and kidney as examples, we discuss whether disturbed capillary flow patterns might explain the apparent mismatch between organ blood flow and organ function in sepsis. Finally, we discuss diagnostic means of detecting capillary flow disturbance in animal models and in critically ill patients, and address therapeutic strategies that might improve tissue oxygenation by modifying capillary flow patterns.
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Affiliation(s)
- L. Østergaard
- Department of Neuroradiology Aarhus University Hospital Aarhus Denmark
- Center of Functionally Integrative Neuroscience and MINDLab Aarhus University Aarhus Denmark
| | - A. Granfeldt
- Department of Anaesthesia and Intensive Care Medicine Aarhus University Hospital Aarhus Denmark
| | - N. Secher
- Department of Anaesthesia and Intensive Care Medicine Aarhus University Hospital Aarhus Denmark
| | - A. Tietze
- Department of Neuroradiology Aarhus University Hospital Aarhus Denmark
- Center of Functionally Integrative Neuroscience and MINDLab Aarhus University Aarhus Denmark
| | - N. K. Iversen
- Center of Functionally Integrative Neuroscience and MINDLab Aarhus University Aarhus Denmark
| | - M. S. Jensen
- Center of Functionally Integrative Neuroscience and MINDLab Aarhus University Aarhus Denmark
| | - K. K. Andersen
- Department of Anaesthesia and Intensive Care Medicine Aarhus University Hospital Aarhus Denmark
| | - K. Nagenthiraja
- Center of Functionally Integrative Neuroscience and MINDLab Aarhus University Aarhus Denmark
| | - P. Gutiérrez‐Lizardi
- Faculty of Dentistry University of Monterrey Monterrey Mexico
- Critical Care College of Nuevo León Monterrey Mexico
| | - K. Mouridsen
- Center of Functionally Integrative Neuroscience and MINDLab Aarhus University Aarhus Denmark
| | - S. N. Jespersen
- Center of Functionally Integrative Neuroscience and MINDLab Aarhus University Aarhus Denmark
- Department of Physics and Astronomy Aarhus University Aarhus Denmark
| | - E. K. Tønnesen
- Department of Anaesthesia and Intensive Care Medicine Aarhus University Hospital Aarhus Denmark
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17
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Yu J, Jiang C, Wang X, Zhu L, Gu R, Xu H, Jia Y, Huang D, Sun X. Macular perfusion in healthy Chinese: an optical coherence tomography angiogram study. Invest Ophthalmol Vis Sci 2015; 56:3212-7. [PMID: 26024105 DOI: 10.1167/iovs.14-16270] [Citation(s) in RCA: 208] [Impact Index Per Article: 23.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE To investigate macular perfusion in healthy Chinese individuals and examine its dependence on age and sex. METHODS Healthy adult Chinese individuals were recruited. Macular perfusion was measured by spectral-domain optical coherence tomography (OCT) using the split-spectrum amplitude-decorrelation angiography (SSADA) algorithm. The parafoveal flow index and vessel area density as well as the area of the foveal capillary-free zone (CFZ) were quantified. RESULTS A total of 76 eyes in 45 subjects were included (20 males and 25 females, mean age 36 ± 11 years). The mean parafoveal flow index was 0.099 ± 0.013; the mean vessel area density was 0.891 ± 0.073; and the mean CFZ area was 0.474 ± 0.172 mm2. All three parameters were significantly correlated with age (flow index: P = 0.00; vessel area density: P = 0.00; CFZ area: P = 0.02). The flow index and vessel area density decreased annually by 0.6% and 0.4%, respectively, and CFZ area increased by 1.48% annually. The CFZ area was larger in females than in males, while all three parameters seemed to change more rapidly with age in males than in females. CONCLUSIONS In healthy Chinese eyes, macular perfusion decreased with increasing age, and decreased more rapidly in males than in females. The application of OCT angiograms may provide a useful approach for monitoring macular perfusion, although caution must be exercised with regard to age- and sex-related variations.
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Affiliation(s)
- Jian Yu
- Department of Ophthalmology and Vision Science, Eye and ENT Hospital, Fudan University, Shanghai, People's Republic of China 2Key Laboratory of Myopia of State Health Ministry, and Key Laboratory of Visual Impairment and Restoration of Shanghai, Shanghai
| | - Chunhui Jiang
- Department of Ophthalmology and Vision Science, Eye and ENT Hospital, Fudan University, Shanghai, People's Republic of China 2Key Laboratory of Myopia of State Health Ministry, and Key Laboratory of Visual Impairment and Restoration of Shanghai, Shanghai
| | - Xiaolei Wang
- Department of Ophthalmology and Vision Science, Eye and ENT Hospital, Fudan University, Shanghai, People's Republic of China 2Key Laboratory of Myopia of State Health Ministry, and Key Laboratory of Visual Impairment and Restoration of Shanghai, Shanghai
| | - Li Zhu
- Department of Ophthalmology and Vision Science, Eye and ENT Hospital, Fudan University, Shanghai, People's Republic of China 2Key Laboratory of Myopia of State Health Ministry, and Key Laboratory of Visual Impairment and Restoration of Shanghai, Shanghai
| | - Ruiping Gu
- Department of Ophthalmology and Vision Science, Eye and ENT Hospital, Fudan University, Shanghai, People's Republic of China 2Key Laboratory of Myopia of State Health Ministry, and Key Laboratory of Visual Impairment and Restoration of Shanghai, Shanghai
| | - Huan Xu
- Department of Ophthalmology and Vision Science, Eye and ENT Hospital, Fudan University, Shanghai, People's Republic of China 2Key Laboratory of Myopia of State Health Ministry, and Key Laboratory of Visual Impairment and Restoration of Shanghai, Shanghai
| | - Yali Jia
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, United States
| | - David Huang
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, United States
| | - Xinghuai Sun
- Department of Ophthalmology and Vision Science, Eye and ENT Hospital, Fudan University, Shanghai, People's Republic of China 2Key Laboratory of Myopia of State Health Ministry, and Key Laboratory of Visual Impairment and Restoration of Shanghai, Shanghai
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18
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Chang L, Nguyen V, Nguyen A, Scott MA, James AW. Pericytes in sarcomas of bone. Med Oncol 2015; 32:202. [PMID: 26076804 DOI: 10.1007/s12032-015-0651-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2015] [Accepted: 06/06/2015] [Indexed: 12/13/2022]
Abstract
Pericytes are mesenchymal cells that closely enwrap small blood vessels, lying in intimate association with the endothelium. Pericytes have recently gained attention as an important mediator of vascular biology and angiogenesis in cancer. Although better studied in carcinoma, pericytes have known interaction with sarcomas of bone, including Ewing's sarcoma, osteosarcoma, and chondrosarcoma. Best studied is Ewing's sarcoma (ES), which displays a prominent perivascular growth pattern. Signaling pathways of known importance in intratumoral pericytes in ES include Notch, PDGF/PDGFR-β, and VEGF signaling. In summary, pericytes serve important functions in the tumor microenvironment. Improved understanding of pericyte biology may hold significant implications for the development of new therapies in sarcoma.
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Affiliation(s)
- Le Chang
- Department of Pathology and Laboratory Medicine, David Geffen School of Medicine, University of California, Los Angeles, 10833 Le Conte Ave., 13-145 CHS, Los Angeles, CA, 90095, USA
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19
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Østergaard L, Jespersen SN, Engedahl T, Gutiérrez Jiménez E, Ashkanian M, Hansen MB, Eskildsen S, Mouridsen K. Capillary dysfunction: its detection and causative role in dementias and stroke. Curr Neurol Neurosci Rep 2015; 15:37. [PMID: 25956993 PMCID: PMC4441906 DOI: 10.1007/s11910-015-0557-x] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
In acute ischemic stroke, critical hypoperfusion is a frequent cause of hypoxic tissue injury: As cerebral blood flow (CBF) falls below the ischemic threshold of 20 mL/100 mL/min, neurological symptoms develop and hypoxic tissue injury evolves within minutes or hours unless the oxygen supply is restored. But is ischemia the only hemodynamic source of hypoxic tissue injury? Reanalyses of the equations we traditionally use to describe the relation between CBF and tissue oxygenation suggest that capillary flow patterns are crucial for the efficient extraction of oxygen: without close capillary flow control, "functional shunts" tend to form and some of the blood's oxygen content in effect becomes inaccessible to tissue. This phenomenon raises several questions: Are there in fact two hemodynamic causes of tissue hypoxia: Limited blood supply (ischemia) and limited oxygen extraction due to capillary dysfunction? If so, how do we distinguish the two, experimentally and in patients? Do flow-metabolism coupling mechanisms adjust CBF to optimize tissue oxygenation when capillary dysfunction impairs oxygen extraction downstream? Cardiovascular risk factors such as age, hypertension, diabetes, hypercholesterolemia, and smoking increase the risk of both stroke and dementia. The capillary dysfunction phenomenon therefore forces us to consider whether changes in capillary morphology or blood rheology may play a role in the etiology of some stroke subtypes and in Alzheimer's disease. Here, we discuss whether certain disease characteristics suggest capillary dysfunction rather than primary flow-limiting vascular pathology and how capillary dysfunction may be imaged and managed.
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Affiliation(s)
- Leif Østergaard
- Center of Functionally Integrative Neuroscience and MINDLab, Institute of Clinical Medicine, Aarhus University, Aarhus, Denmark,
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20
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Oxidative stress in myopia. OXIDATIVE MEDICINE AND CELLULAR LONGEVITY 2015; 2015:750637. [PMID: 25922643 PMCID: PMC4397465 DOI: 10.1155/2015/750637] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/06/2015] [Revised: 03/10/2015] [Accepted: 03/17/2015] [Indexed: 12/25/2022]
Abstract
Myopia affected approximately 1.6 billion people worldwide in 2000, and it is expected to increase to 2.5 billion by 2020. Although optical problems can be corrected by optics or surgical procedures, normal myopia and high myopia are still an unsolved medical problem. They frequently predispose people who have them to suffer from other eye pathologies: retinal detachment, glaucoma, macular hemorrhage, cataracts, and so on being one of the main causes of visual deterioration and blindness. Genetic and environmental factors have been associated with myopia. Nevertheless, lack of knowledge in the underlying physiopathological molecular mechanisms has not permitted an adequate diagnosis, prevention, or treatment to be found. Nowadays several pieces of evidence indicate that oxidative stress may help explain the altered regulatory pathways in myopia and the appearance of associated eye diseases. On the one hand, oxidative damage associated with hypoxia myopic can alter the neuromodulation that nitric oxide and dopamine have in eye growth. On the other hand, radical superoxide or peroxynitrite production damage retina, vitreous, lens, and so on contributing to the appearance of retinopathies, retinal detachment, cataracts and so on. The objective of this review is to suggest that oxidative stress is one of the key pieces that can help solve this complex eye problem.
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21
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Østergaard L, Finnerup NB, Terkelsen AJ, Olesen RA, Drasbek KR, Knudsen L, Jespersen SN, Frystyk J, Charles M, Thomsen RW, Christiansen JS, Beck-Nielsen H, Jensen TS, Andersen H. The effects of capillary dysfunction on oxygen and glucose extraction in diabetic neuropathy. Diabetologia 2015; 58:666-77. [PMID: 25512003 PMCID: PMC4351434 DOI: 10.1007/s00125-014-3461-z] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/14/2014] [Accepted: 11/06/2014] [Indexed: 12/14/2022]
Abstract
Diabetic neuropathy is associated with disturbances in endoneurial metabolism and microvascular morphology, but the roles of these factors in the aetiopathogenesis of diabetic neuropathy remain unclear. Changes in endoneurial capillary morphology and vascular reactivity apparently predate the development of diabetic neuropathy in humans, and in manifest neuropathy, reductions in nerve conduction velocity correlate with the level of endoneurial hypoxia. The idea that microvascular changes cause diabetic neuropathy is contradicted, however, by reports of elevated endoneurial blood flow in early experimental diabetes, and of unaffected blood flow when early histological signs of neuropathy first develop in humans. We recently showed that disturbances in capillary flow patterns, so-called capillary dysfunction, can reduce the amount of oxygen and glucose that can be extracted by the tissue for a given blood flow. In fact, tissue blood flow must be adjusted to ensure sufficient oxygen extraction as capillary dysfunction becomes more severe, thereby changing the normal relationship between tissue oxygenation and blood flow. This review examines the evidence of capillary dysfunction in diabetic neuropathy, and whether the observed relation between endoneurial blood flow and nerve function is consistent with increasingly disturbed capillary flow patterns. The analysis suggests testable relations between capillary dysfunction, tissue hypoxia, aldose reductase activity, oxidative stress, tissue inflammation and glucose clearance from blood. We discuss the implications of these predictions in relation to the prevention and management of diabetic complications in type 1 and type 2 diabetes, and suggest ways of testing these hypotheses in experimental and clinical settings.
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Affiliation(s)
- Leif Østergaard
- Center of Functionally Integrative Neuroscience and MINDLab, Institute of Clinical Medicine, Aarhus University Hospital, Building 10G, Nørrebrogade 44, DK-8000, Aarhus C, Denmark,
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22
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Abstract
Functional magnetic resonance imaging (fMRI) provides a unique view of the working human mind. The blood-oxygen-level-dependent (BOLD) signal, detected in fMRI, reflects changes in deoxyhemoglobin driven by localized changes in brain blood flow and blood oxygenation, which are coupled to underlying neuronal activity by a process termed neurovascular coupling. Over the past 10 years, a range of cellular mechanisms, including astrocytes, pericytes, and interneurons, have been proposed to play a role in functional neurovascular coupling. However, the field remains conflicted over the relative importance of each process, while key spatiotemporal features of BOLD response remain unexplained. Here, we review current candidate neurovascular coupling mechanisms and propose that previously overlooked involvement of the vascular endothelium may provide a more complete picture of how blood flow is controlled in the brain. We also explore the possibility and consequences of conditions in which neurovascular coupling may be altered, including during postnatal development, pathological states, and aging, noting relevance to both stimulus-evoked and resting-state fMRI studies.
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Affiliation(s)
- Elizabeth M C Hillman
- Departments of Biomedical Engineering and Radiology and the Kavli Institute for Brain Science, Columbia University, New York, NY 10027;
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23
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MacVicar BA, Newman EA. Astrocyte regulation of blood flow in the brain. Cold Spring Harb Perspect Biol 2015; 7:cshperspect.a020388. [PMID: 25818565 DOI: 10.1101/cshperspect.a020388] [Citation(s) in RCA: 215] [Impact Index Per Article: 23.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Neuronal activity results in increased blood flow in the brain, a response named functional hyperemia. Astrocytes play an important role in mediating this response. Neurotransmitters released from active neurons evoke Ca(2+) increases in astrocytes, leading to the release of vasoactive metabolites of arachidonic acid from astrocyte endfeet onto blood vessels. Synthesis of prostaglandin E2 (PGE2) and epoxyeicosatrienoic acids (EETs) dilate blood vessels, whereas 20-hydroxyeicosatetraenoic acid (20-HETE) constricts vessels. The release of K(+) from astrocyte endfeet may also contribute to vasodilation. Oxygen modulates astrocyte regulation of blood flow. Under normoxic conditions, astrocytic Ca(2+) signaling results in vasodilation, whereas under hyperoxic conditions, vasoconstriction is favored. Astrocytes also contribute to the generation of vascular tone. Tonic release of both 20-HETE and ATP from astrocytes constricts vascular smooth muscle cells, generating vessel tone. Under pathological conditions, including Alzheimer's disease and diabetic retinopathy, disruption of normal astrocyte physiology can compromise the regulation of blood flow.
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Affiliation(s)
- Brian A MacVicar
- Djavad Mowafaghian Centre for Brain Health, Department of Psychiatry, University of British Columbia, Vancouver, British Columbia V6T 2B5, Canada
| | - Eric A Newman
- Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota 55455
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24
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Abstract
Light stimulation evokes neuronal activity in the retina, resulting in the dilation of retinal blood vessels and increased blood flow. This response, named functional hyperemia, brings oxygen and nutrients to active neurons. However, it remains unclear which vessels mediate functional hyperemia. We have characterized blood flow regulation in the rat retina in vivo by measuring changes in retinal vessel diameter and red blood cell (RBC) flux evoked by a flickering light stimulus. We found that, in first- and second-order arterioles, flicker evoked large (7.5 and 5.0%), rapid (0.73 and 0.70 s), and consistent dilations. Flicker-evoked dilations in capillaries were smaller (2.0%) and tended to have a slower onset (0.97 s), whereas dilations in venules were smaller (1.0%) and slower (1.06 s) still. The proximity of pericyte somata did not predict capillary dilation amplitude. Expression of the contractile protein α-smooth muscle actin was high in arterioles and low in capillaries. Unexpectedly, we found that blood flow in the three vascular layers was differentially regulated. Flicker stimulation evoked far larger dilations and RBC flux increases in the intermediate layer capillaries than in the superficial and deep layer capillaries (2.6 vs 0.9 and 0.7% dilation; 25.7 vs 0.8 and 11.3% RBC flux increase). These results indicate that functional hyperemia in the retina is driven primarily by active dilation of arterioles. The dilation of intermediate layer capillaries is likely mediated by active mechanisms as well. The physiological consequences of differential regulation in the three vascular layers are discussed.
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25
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Ji Y, Chen S, Xu C, Li L, Xiang B. The use of propranolol in the treatment of infantile haemangiomas: an update on potential mechanisms of action. Br J Dermatol 2014; 172:24-32. [PMID: 25196392 DOI: 10.1111/bjd.13388] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/30/2014] [Indexed: 02/05/2023]
Abstract
Currently, propranolol is the preferred treatment for problematic proliferating infantile haemangiomas (IHs). The rapid action of propranolol has been shown to be especially dramatic in IHs involving dyspnoea, haemodynamic compromise, palpebral occlusion or ulceration. Another remarkable aspect of propranolol treatment revealed that the growth of the IHs was not only stabilized, but also that the improvement continued until complete involution was achieved, leading to a considerable shortening of the natural course of IH. However, the mechanisms underlying the effects of propranolol have not been fully elucidated. Recent studies have offered evidence of a variety of mechanisms. These include the promotion of pericyte-mediated vasoconstriction, the inhibition of vasculogenesis and catecholamine-induced angiogenesis, the disruption of haemodynamic force-induced cell survival, and the inactivation of the renin-angiotensin system. This review summarizes these mechanisms and the new concepts that are emerging in this area of research. Moreover, several molecular mechanisms by which propranolol may modify neovascularization in IH have also been proposed. The antihaemangioma effect of propranolol may not be attributable to a single mechanism, but rather to a combination of events that have not yet been elucidated or understood. Further studies are needed to evaluate and verify these mechanisms to gain a greater understanding of the effects of the intake of propranolol on haemangioma involution.
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Affiliation(s)
- Y Ji
- Division of Oncology, Department of Pediatric Surgery, West China Hospital of Sichuan University, Chengdu, 610041, China
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26
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Stapor PC, Sweat RS, Dashti DC, Betancourt AM, Murfee WL. Pericyte dynamics during angiogenesis: new insights from new identities. J Vasc Res 2014; 51:163-74. [PMID: 24853910 DOI: 10.1159/000362276] [Citation(s) in RCA: 126] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2013] [Accepted: 03/11/2014] [Indexed: 12/13/2022] Open
Abstract
Therapies aimed at manipulating the microcirculation require the ability to control angiogenesis, defined as the sprouting of new capillaries from existing vessels. Blocking angiogenesis would be beneficial in many pathologies (e.g. cancer, retinopathies and rheumatoid arthritis). In others (e.g. myocardial infarction, stroke and hypertension), promoting angiogenesis would be desirable. We know that vascular pericytes elongate around endothelial cells (ECs) and are functionally associated with regulating vessel stabilization, vessel diameter and EC proliferation. During angiogenesis, bidirectional pericyte-EC signaling is critical for capillary sprout formation. Observations of pericytes leading capillary sprouts also implicate their role in EC guidance. As such, pericytes have recently emerged as a therapeutic target to promote or inhibit angiogenesis. Advancing our basic understanding of pericytes and developing pericyte-related therapies are challenged, like in many other fields, by questions regarding cell identity. This review article discusses what we know about pericyte phenotypes and the opportunity to advance our understanding by defining the specific pericyte cell populations involved in capillary sprouting.
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Affiliation(s)
- Peter C Stapor
- Department of Biomedical Engineering, Tulane University, Lindy Boggs Center, New Orleans, La., USA
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27
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Ostergaard L, Kristiansen SB, Angleys H, Frøkiær J, Michael Hasenkam J, Jespersen SN, Bøtker HE. The role of capillary transit time heterogeneity in myocardial oxygenation and ischemic heart disease. Basic Res Cardiol 2014; 109:409. [PMID: 24743925 PMCID: PMC4013440 DOI: 10.1007/s00395-014-0409-x] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/18/2014] [Revised: 03/30/2014] [Accepted: 03/31/2014] [Indexed: 01/18/2023]
Abstract
Ischemic heart disease (IHD) is characterized by an imbalance between oxygen supply and demand, most frequently caused by coronary artery disease (CAD) that reduces myocardial perfusion. In some patients, IHD is ascribed to microvascular dysfunction (MVD): microcirculatory disturbances that reduce myocardial perfusion at the level of myocardial pre-arterioles and arterioles. In a minority of cases, chest pain and reductions in myocardial flow reserve may even occur in patients without any other demonstrable systemic or cardiac disease. In this topical review, we address whether these findings might be caused by impaired myocardial oxygen extraction, caused by capillary flow disturbances further downstream. Myocardial blood flow (MBF) increases approximately linearly with oxygen utilization, but efficient oxygen extraction at high MBF values is known to depend on the parallel reduction of capillary transit time heterogeneity (CTH). Consequently, changes in capillary wall morphology or blood viscosity may impair myocardial oxygen extraction by preventing capillary flow homogenization. Indeed, a recent re-analysis of oxygen transport in tissue shows that elevated CTH can reduce tissue oxygenation by causing a functional shunt of oxygenated blood through the tissue. We review the combined effects of MBF, CTH, and tissue oxygen tension on myocardial oxygen supply. We show that as CTH increases, normal vasodilator responses must be attenuated in order to reduce the degree of functional shunting and improve blood-tissue oxygen concentration gradients to allow sufficient myocardial oxygenation. Theoretically, CTH can reach levels such that increased metabolic demands cannot be met, resulting in tissue hypoxia and angina in the absence of flow-limiting CAD or MVD. We discuss these predictions in the context of MVD, myocardial infarction, and reperfusion injury.
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Affiliation(s)
- Leif Ostergaard
- Department of Neuroradiology, Aarhus University Hospital, Building 10G, Nørrebrogade 44, 8000, Aarhus C, Denmark,
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28
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Rat choroidal pericytes as a target of the autonomic nervous system. Cell Tissue Res 2013; 356:1-8. [DOI: 10.1007/s00441-013-1769-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2013] [Accepted: 11/11/2013] [Indexed: 02/04/2023]
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29
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Østergaard L, Aamand R, Karabegovic S, Tietze A, Blicher JU, Mikkelsen IK, Iversen NK, Secher N, Engedal TS, Anzabi M, Jimenez EG, Cai C, Koch KU, Naess-Schmidt ET, Obel A, Juul N, Rasmussen M, Sørensen JCH. The role of the microcirculation in delayed cerebral ischemia and chronic degenerative changes after subarachnoid hemorrhage. J Cereb Blood Flow Metab 2013; 33:1825-37. [PMID: 24064495 PMCID: PMC3851911 DOI: 10.1038/jcbfm.2013.173] [Citation(s) in RCA: 122] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/22/2013] [Revised: 08/31/2013] [Accepted: 09/08/2013] [Indexed: 02/07/2023]
Abstract
The mortality after aneurysmal subarachnoid hemorrhage (SAH) is 50%, and most survivors suffer severe functional and cognitive deficits. Half of SAH patients deteriorate 5 to 14 days after the initial bleeding, so-called delayed cerebral ischemia (DCI). Although often attributed to vasospasms, DCI may develop in the absence of angiographic vasospasms, and therapeutic reversal of angiographic vasospasms fails to improve patient outcome. The etiology of chronic neurodegenerative changes after SAH remains poorly understood. Brain oxygenation depends on both cerebral blood flow (CBF) and its microscopic distribution, the so-called capillary transit time heterogeneity (CTH). In theory, increased CTH can therefore lead to tissue hypoxia in the absence of severe CBF reductions, whereas reductions in CBF, paradoxically, improve brain oxygenation if CTH is critically elevated. We review potential sources of elevated CTH after SAH. Pericyte constrictions in relation to the initial ischemic episode and subsequent oxidative stress, nitric oxide depletion during the pericapillary clearance of oxyhemoglobin, vasogenic edema, leukocytosis, and astrocytic endfeet swelling are identified as potential sources of elevated CTH, and hence of metabolic derangement, after SAH. Irreversible changes in capillary morphology and function are predicted to contribute to long-term relative tissue hypoxia, inflammation, and neurodegeneration. We discuss diagnostic and therapeutic implications of these predictions.
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Affiliation(s)
- Leif Østergaard
- 1] Department of Neuroradiology, Aarhus University Hospital, Aarhus, Denmark [2] Center of Functionally Integrative Neuroscience and MINDLab, Aarhus University, Aarhus, Denmark
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Giese MJ, Speth RC. The ocular renin-angiotensin system: a therapeutic target for the treatment of ocular disease. Pharmacol Ther 2013; 142:11-32. [PMID: 24287313 DOI: 10.1016/j.pharmthera.2013.11.002] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2013] [Accepted: 10/25/2013] [Indexed: 02/06/2023]
Abstract
The renin-angiotensin system (RAS) is most well-known for its role in regulation and dysregulation of blood pressure as well as fluid and electrolyte homeostasis. Due to its ability to cause cardiovascular disease, the RAS is the target of a multitude of drugs that antagonize its pathophysiological effects. While the "classical" RAS is a systemic hormonal system, there is an increasing awareness of the existence and functional significance of local RASs in a number of organs, e.g., liver, kidney, heart, lungs, reproductive organs, adipose tissue and adrenal. The eye is one of these organs where a compelling body of evidence has demonstrated the presence of a local RAS. Individual components of the RAS have been shown to be present in many structures of the eye and their potential functional significance in ocular disease states is described. Because the eye is one of the most important and complex organs in the body, this review also discusses the implications of dysregulation of the systemic RAS on the pathogenesis of ocular diseases and how pharmacological manipulation of the RAS might lead to novel or adjunctive therapies for ocular disease states.
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Affiliation(s)
| | - Robert C Speth
- Department of Pharmaceutical Sciences, College of Pharmacy, Nova Southeastern University, Fort Lauderdale, FL 33328, United States.
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Hashitani H, Mitsui R, Shimizu Y, Higashi R, Nakamura K. Functional and morphological properties of pericytes in suburothelial venules of the mouse bladder. Br J Pharmacol 2013; 167:1723-36. [PMID: 22862143 DOI: 10.1111/j.1476-5381.2012.02125.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2012] [Revised: 06/19/2012] [Accepted: 07/26/2012] [Indexed: 01/16/2023] Open
Abstract
BACKGROUND AND PURPOSE In suburothelial venules of rat bladder, pericytes (perivascular cells) develop spontaneous Ca(2+) transients, which may drive the smooth muscle wall to generate spontaneous venular constrictions. We aimed to further explore the morphological and functional characteristics of pericytes in the mouse bladder. EXPERIMENTAL APPROACH The morphological features of pericytes were investigated by electron microscopy and fluorescence immunohistochemistry. Changes in diameters of suburothelial venules were measured using video microscopy, while intracellular Ca(2+) dynamics were visualized using Fluo-4 fluorescence Ca(2+) imaging. KEY RESULTS A network of α-smooth muscle actin immunoreactive pericytes surrounded venules in the mouse bladder suburothelium. Scanning electron microscopy revealed that this network of stellate-shaped pericytes covered the venules, while transmission electron microscopy demonstrated that the venular wall consisted of endothelium and adjacent pericytes, lacking an intermediate smooth muscle layer. Pericytes exhibited spontaneous Ca(2+) transients, which were accompanied by phasic venular constrictions. Nicardipine (1 μM) disrupted the synchrony of spontaneous Ca(2+) transients in pericytes and reduced their associated constrictions. Residual asynchronous Ca(2+) transients were suppressed by cyclopiazonic acid (10 μM), 2-aminoethoxydiphenyl borate (10 μM), U-73122 (1 μM), oligomycin (1 μM) and SKF96365 (10 μM), but unaffected by ryanodine (100 μM) or YM-244769 (1 μM), suggesting that pericyte Ca(2+) transients rely on Ca(2+) release from the endoplasmic reticulum via the InsP(3) receptor and also require Ca(2+) influx through store-operated Ca(2+) channels. CONCLUSIONS AND IMPLICATIONS The pericytes in mouse bladder can generate spontaneous Ca(2+) transients and contractions, and thus have a fundamental role in promoting spontaneous constrictions of suburothelial venules.
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Affiliation(s)
- Hikaru Hashitani
- Department of Cell Physiology, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan.
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Wittig D, Jászai J, Corbeil D, Funk RHW. Immunohistochemical localization and characterization of putative mesenchymal stem cell markers in the retinal capillary network of rodents. Cells Tissues Organs 2013; 197:344-59. [PMID: 23571553 DOI: 10.1159/000346661] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/20/2012] [Indexed: 11/19/2022] Open
Abstract
Perivascular cells of microvascular niches are the prime candidates for being a reservoire of mesenchymal stem cell (MSC)-like cells in many tissues and organs that could serve as a potential source of cells and a target of novel cell-based therapeutic approaches. In the present study, by utilising typical markers of pericytes (neuronal-glial antigen 2, NG2, a chondroitin sulphate proteoglycan) and those of MSCs (CD146 and CD105) and primitive pluripotent cells (sex-determining region Y-box 2, Sox2), the phenotypic traits and the distribution of murine and rat retinal perivascular cells were investigated in situ. Our findings indicate that retinal microvessels of juvenile rodents are highly covered by NG2-positive branching processes of pericytic (perivascular) cells that are less prominent in mature capillary networks of the adult retina. In the adult rodent retinal vascular bed, NG2 labeling is mainly confined to membranes of the cell body resulting in a pearl-chain-like distribution along the vessels. Retinal pericytes, which were identified by their morphology and NG2 expression, simultaneously express CD146. Furthermore, CD146-positive cells located at small arteriole-to-capillary branching points appear more intensely stained than elsewhere. Evidence for a differential expression of the two markers around capillaries that would hint at a clonal heterogeneity among pericytic cells, however, is lacking. In contrast, the expression of CD105 is exclusively restricted to vascular endothelial cells and Sox2 is detected neither in perivascular nor in endothelial cells. In dissociated retinal cultures, however, simultaneous expression of NG2 and CD105 was observed. Collectively, our data indicate that vascular wall resident retinal pericytes share some phenotypic features (i.e. CD146 expression) with archetypal MSCs, which is even more striking in dissociated retinal cultures (i.e. CD105 expression). These findings might have implications for the treatment of retinal pathologies.
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Affiliation(s)
- Dierk Wittig
- Institute of Anatomy, TU Dresden, Dresden, Germany.
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Puro DG. Retinovascular physiology and pathophysiology: new experimental approach/new insights. Prog Retin Eye Res 2012; 31:258-70. [PMID: 22333041 DOI: 10.1016/j.preteyeres.2012.01.001] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2011] [Revised: 01/28/2012] [Accepted: 01/31/2012] [Indexed: 01/09/2023]
Abstract
An important challenge in visual neuroscience is to understand the physiology and pathophysiology of the intra-retinal vasculature, whose function is required for ophthalmoception by humans and most other mammals. In the quest to learn more about this highly specialized portion of the circulatory system, a newly developed method for isolating vast microvascular complexes from the rodent retina has opened the way for using techniques such as patch-clamping, fluorescence imaging and time-lapse photography to elucidate the functional organization of a capillary network and its pre-capillary arteriole. For example, the ability to obtain dual perforated-patch recordings from well-defined sites within an isolated microvascular complex permitted the first characterization of the electrotonic architecture of a capillary/arteriole unit. This analysis revealed that this operational unit is not simply a homogenous synctium, but has a complex functional organization that is dynamically modulated by extracellular signals such as angiotensin II. Another recent discovery is that a capillary and its pre-capillary arteriole have distinct physiological differences; capillaries have an abundance of ATP-sensitive potassium (K(ATP)) channels and a dearth of voltage-dependent calcium channels (VDCCs) while the converse is true for arterioles. In addition, voltage transmission between abluminal cells and the endothelium is more efficient in the capillaries. Thus, the capillary network is well-equipped to generate and transmit voltages, and the pre-capillary arteriole is well-adapted to transduce a capillary-generated voltage into a change in abluminal cell calcium and thereby, a vasomotor response. Use of microvessels isolated from the diabetic retina has led to new insights concerning retinal vascular pathophysiology. For example, soon after the onset of diabetes, the efficacy of voltage transmission through the endothelium is diminished; arteriolar VDCCs are inhibited, and there is increased vulnerability to purinergic vasotoxicity, which is a newly identified pathobiological mechanism. Other recent studies reveal that K(ATP) channels not only have an essential physiological role in generating vasomotor responses, but their activation substantially boosts the lethality of hypoxia. Thus, the pathophysiology of the retinal microvasculature is closely linked with its physiology.
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Affiliation(s)
- Donald G Puro
- Department of Ophthalmology & Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA.
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Liu YP, Kuznetsova T, Thijs L, Jin Y, Schmitz B, Brand SM, Brand E, Manunta P, Bianchi G, Struijker-Boudier H, Staessen JA. Are retinal microvascular phenotypes associated with the 1675G/A polymorphism in the angiotensin II type-2 receptor gene? Am J Hypertens 2011; 24:1300-5. [PMID: 21850060 DOI: 10.1038/ajh.2011.151] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
BACKGROUND The X-linked angiotensin II type-2 receptor (AT2R) gene 1675G/A polymorphism is located in the short intron 1 of the AT2R gene within a sequence motif conforming to a splice branch site. AT2R is expressed in the human retina, but no previous study examined the association between retinal microvascular phenotypes and the AT2R 1675G/A polymorphism. METHODS In 340 subjects randomly selected from a Flemish population (mean age, 51.9 years; 51.5% women), we post-processed retinal images using IVAN software to generate the retinal arteriole and venule equivalents (central retinal arteriolar equivalent (CRAE) and central retinal venular equivalent (CRVE)) and the arteriole-to-venule ratio (AVR). DNA fragments including the AT2R 1675G/A polymorphism were amplified by PCR. We applied a mixed model to assess phenotype-genotype associations while accounting for relatedness and covariables. RESULTS CRAE, CRVE, and AVR averaged 151.9 µm, 215.2 µm, and 0.710, respectively. CRAE was 5.5 µm greater in women than men and decreased with age (P < 0.05). In multivariable-adjusted analyses, CRAE was higher in hemizygous and homozygous carriers of the AT2R A allele than in their G allele counterparts in both sexes combined (+4.49 µm; P = 0.014) and in men (+4.91 µm; P = 0.032) with a similar trend in women (+3.41 µm; P = 0.14). AVR was increased in the presence of the AT2R A allele compared with AT2R G hemizygotes and homozygotes (+0.024; P = 0.0082). The associations of CRAE and CRVE with other polymorphisms were not significant. CONCLUSIONS Pending confirmation in experimental and epidemiological studies, our findings suggest that diameter of the retinal arterioles might be associated with the AT2R 1675G/A polymorphism.
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Advanced glycation end products and diabetic retinopathy. Amino Acids 2011; 44:1397-407. [DOI: 10.1007/s00726-011-1071-3] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2011] [Accepted: 08/27/2011] [Indexed: 12/21/2022]
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Zhang T, Wu DM, Xu GZ, Puro DG. The electrotonic architecture of the retinal microvasculature: modulation by angiotensin II. J Physiol 2011; 589:2383-99. [PMID: 21486796 DOI: 10.1113/jphysiol.2010.202937] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The capillary/arteriole complex is the key operational unit regulating local perfusion to meet metabolic demand. However, much remains to be learned about how this multi cellular unit is functionally organized. To help address this challenge, we characterized the electrotonic architecture of the retinal microvasculature, which is particularly well adapted for the decentralized control of blood flow. In this study, we quantified the transmission of voltage between pairs of perforated-patch pipettes sealed onto abluminal cells located on microvascular complexes freshly isolated from the adult rat retina. These complexes consisted of capillaries,as well as tertiary and secondary arterioles. Dual recording experiments revealed that voltage spreading axially through a capillary, tertiary arteriole or secondary arteriole is transmitted very efficiently with a decay rate of only ∼5% per 100 μm. However, the retinal microvasculature is not simply a well-coupled syncytium since we detected significant voltage dissipation with radial abluminal cell-to-endothelium transmission and also at branch points between a capillary and its tertiary arteriole and between tertiary and secondary arterioles. Consistent with capillaries being particularly well-suited for the task of transmitting voltages induced by vasoactive signals, radial transmission is most efficient in this portion of the retinal microvasculature. Dual recordings also revealed that angiotensin II potently inhibits axial transmission. As a functional consequence, the geographical extent of the microvasculature's response to voltage-changing inputs is markedly restricted in the presence of angiotensin. In addition, this effect of angiotensin established that the electrotonic architecture of the retinal microvasculature is not static, but rather, is dynamically modulated by vasoactive signals.
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Affiliation(s)
- Ting Zhang
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA
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Pericytes in capillaries are contractile in vivo, but arterioles mediate functional hyperemia in the mouse brain. Proc Natl Acad Sci U S A 2010; 107:22290-5. [PMID: 21135230 DOI: 10.1073/pnas.1011321108] [Citation(s) in RCA: 284] [Impact Index Per Article: 20.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Modern functional imaging techniques of the brain measure local hemodynamic responses evoked by neuronal activity. Capillary pericytes recently were suggested to mediate neurovascular coupling in brain slices, but their role in vivo remains unexplored. We used two-photon microscopy to study in real time pericytes and the dynamic changes of capillary diameter and blood flow in the cortex of anesthetized mice, as well as in brain slices. The thromboxane A(2) analog, 9,11-dideoxy-9α,11α-methanoepoxy Prostaglandin F2α (U46619), induced constrictions in the vicinity of pericytes in a fraction of capillaries, whereas others dilated. The changes in vessel diameter resulted in changes in capillary red blood cell (RBC) flow. In contrast, during brief epochs of seizure activity elicited by local administration of the GABA(A) receptor antagonist, bicuculline, capillary RBC flow increased without pericyte-induced capillary diameter changes. Precapillary arterioles were the smallest vessels to dilate, together with penetrating and pial arterioles. Our results provide in vivo evidence that pericytes can modulate capillary blood flow in the brain, which may be important under pathological conditions. However, our data suggest that precapillary and penetrating arterioles, rather than pericytes in capillaries, are responsible for the blood flow increase induced by neural activity.
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Schmidt KG, Bergert H, Funk RHW. Neurodegenerative diseases of the retina and potential for protection and recovery. Curr Neuropharmacol 2010; 6:164-78. [PMID: 19305795 PMCID: PMC2647152 DOI: 10.2174/157015908784533851] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2007] [Revised: 10/29/2007] [Accepted: 11/11/2007] [Indexed: 12/27/2022] Open
Abstract
Recent advances in our understanding of the mechanisms in the cascade of events resulting in retinal cell death in ocular pathologies like glaucoma, diabetic retinopathy and age-related macular degeneration led to the common descriptive term of neurodegenerative diseases of the retina. The final common pathophysiologic pathway of these diseases includes a particular form of metabolic stress, resulting in an insufficient supply of nutrients to the respective target structures (optic nerve head, retina). During metabolic stress, glutamate is released initiating the death of neurones containing ionotropic glutamate (N-methyl-D-aspartat, NMDA) receptors present on ganglion cells and a specific type of amacrine cells. Experimental studies demonstrate that several drugs reduce or prevent the death of retinal neurones deficient of nutrients. These agents generally block NMDA receptors to prevent the action of glutamate or halt the subsequent pathophysiologic cycle resulting in cell death. The major causes for cell death following activation of NMDA receptors are the influx of calcium and sodium into cells, the generation of free radicals linked to the formation of advanced glycation endproducts (AGEs) and/or advanced lipoxidation endproducts (ALEs) as well as defects in the mitochondrial respiratory chain. Substances preventing these cytotoxic events are considered to be potentially neuroprotective.
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Affiliation(s)
- K-G Schmidt
- Department of Ophthalmology, Starnberg, Josef-Jägerhuberstr. 7, D-82319 Starnberg, Germany.
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Hamilton NB, Attwell D, Hall CN. Pericyte-mediated regulation of capillary diameter: a component of neurovascular coupling in health and disease. FRONTIERS IN NEUROENERGETICS 2010; 2. [PMID: 20725515 PMCID: PMC2912025 DOI: 10.3389/fnene.2010.00005] [Citation(s) in RCA: 333] [Impact Index Per Article: 23.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/11/2010] [Accepted: 04/28/2010] [Indexed: 12/18/2022]
Abstract
Because regional blood flow increases in association with the increased metabolic demand generated by localized increases in neural activity, functional imaging researchers often assume that changes in blood flow are an accurate read-out of changes in underlying neural activity. An understanding of the mechanisms that link changes in neural activity to changes in blood flow is crucial for assessing the validity of this assumption, and for understanding the processes that can go wrong during disease states such as ischaemic stroke. Many studies have investigated the mechanisms of neurovascular regulation in arterioles but other evidence suggests that blood flow regulation can also occur in capillaries, because of the presence of contractile cells, pericytes, on the capillary wall. Here we review the evidence that pericytes can modulate capillary diameter in response to neuronal activity and assess the likely importance of neurovascular regulation at the capillary level for functional imaging experiments. We also discuss evidence suggesting that pericytes are particularly sensitive to damage during pathological insults such as ischaemia, Alzheimer's disease and diabetic retinopathy, and consider the potential impact that pericyte dysfunction might have on the development of therapeutic interventions and on the interpretation of functional imaging data in these disorders.
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Affiliation(s)
- Nicola B Hamilton
- Department of Neuroscience, Physiology and Pharmacology, University College London London, UK
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Matsushita K, Fukumoto M, Kobayashi T, Kobayashi M, Ishizaki E, Minami M, Katsumura K, Liao SD, Wu DM, Zhang T, Puro DG. Diabetes-induced inhibition of voltage-dependent calcium channels in the retinal microvasculature: role of spermine. Invest Ophthalmol Vis Sci 2010; 51:5979-90. [PMID: 20484578 DOI: 10.1167/iovs.10-5377] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE Although decentralized control of blood flow is particularly important in the retina, knowledge of the functional organization of the retinal microvasculature is limited. Here, the authors characterized the distribution and regulation of L-type voltage-dependent calcium channels (VDCCs) within the most decentralized operational complex of the retinal vasculature--the feeder vessel/capillary unit--which consists of a capillary network plus the vessel linking it with a myocyte-encircled arteriole. METHODS Perforated-patch recordings, calcium-imaging, and time-lapse photography were used to assess VDCC-dependent changes in ionic currents, intracellular calcium, abluminal cell contractility, and lumen diameter, in microvascular complexes freshly isolated from the rat retina. RESULTS Topographical heterogeneity was found in the distribution of functional VDCCs; VDCC activity was markedly greater in feeder vessels than in capillaries. Experiments showed that this topographical distribution occurs, in large part, because of the inhibition of capillary VDCCs by a mechanism dependent on the endogenous polyamine spermine. An operational consequence of functional VDCCs predominantly located in the feeder vessels is that voltage-driven vasomotor responses are generated chiefly in this portion of the feeder vessel/capillary unit. However, early in the course of diabetes, this ability to generate voltage-driven vasomotor responses becomes profoundly impaired because of the inhibition of feeder vessel VDCCs by a spermine-dependent mechanism. CONCLUSIONS The regulation of VDCCs by endogenous spermine not only plays a critical role in establishing the physiological organization of the feeder vessel/capillary unit, but also may contribute to dysfunction of this decentralized operational unit in the diabetic retina.
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Affiliation(s)
- Kenji Matsushita
- Department of Ophthalmology and Visual Sciences, Fudan University, Shanghai, China
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Fletcher EL, Phipps JA, Ward MM, Vessey KA, Wilkinson-Berka JL. The renin-angiotensin system in retinal health and disease: Its influence on neurons, glia and the vasculature. Prog Retin Eye Res 2010; 29:284-311. [PMID: 20380890 DOI: 10.1016/j.preteyeres.2010.03.003] [Citation(s) in RCA: 99] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Renin-Angiotensin System is classically recognized for its role in the control of systemic blood pressure. However, the retina is recognized to have all the components necessary for angiotensin II formation, suggestive of a role for Angiotensin II in the retina that is independent of the systemic circulation. The most well described effects of Angiotensin II are on the retinal vasculature, with roles in vasoconstriction and angiogenesis. However, it is now emerging that Angiotensin II has roles in modulation of retinal function, possibly in regulating GABAergic amacrine cells. In addition, Angiotensin II is likely to have effects on glia. Angiotensin II has also been implicated in retinal vascular diseases such as Retinopathy of Prematurity and diabetic retinopathty, and more recently actions in choroidal neovascularizaiton and glaucoma have also emerged. The mechanisms by which Angiotensin II promotes angiogensis in retinal vascular diseases is indicative of the complexity of the RAS and the variety of cell types that it effects. Indeed, these diseases are not purely characterized by direct effects of Angiotensin II on the vasculature. In retinopathy of prematurity, for example, blockade of AT1 receptors prevents pathological angiogenesis, but also promotes revascularization of avascular regions of the retina. The primary site of action of Angiotensin II in this disease may be on retinal glia, rather than the vasculature. Indeed, blockade of AT1 receptors prevents glial loss and promotes the re-establishment of normal vessel growth. Blockade of RAS as a treatment for preventing the incidence and progression of diabetic retinopathy has also emerged based on a series of studies in animal models showing that blockade of the RAS prevents the development of a variety of vascular and neuronal deficits in this disease. Importantly these effects may be independent of actions on systemic blood pressure. This has culminated recently with the completion of several large multi-centre clinical trials that showed that blockade of the RAS may be of benefit in some at risk patients with diabetes. With the emergence of novel compounds targeting different aspects of the RAS even more effective ways of blocking the RAS may be possible in the future.
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Affiliation(s)
- Erica L Fletcher
- Department of Anatomy and Cell Biology, The University of Melbourne, Parkville 3010, Victoria, Australia.
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Matsuo J, Oku H, Kanbara Y, Kobayashi T, Sugiyama T, Ikeda T. Involvement of NADPH oxidase and protein kinase C in endothelin-1-induced superoxide production in retinal microvessels. Exp Eye Res 2009; 89:693-9. [PMID: 19576886 DOI: 10.1016/j.exer.2009.06.012] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2009] [Revised: 03/30/2009] [Accepted: 06/24/2009] [Indexed: 01/01/2023]
Abstract
Redox signaling has been implicated in pathophysiological changes in the vascular system. We examined whether endothelin-1 (ET-1) increases the formation of superoxide anions in retinal microvessels. Freshly isolated retinal microvessels from rats were exposed to ET-1 (100 nM), and the intracellular superoxide formation in the retinal pericytes was assessed semi-quantitatively by time-lapse fluorometric analyses using hydroethidine. The receptor mechanisms were determined by BQ-123 and BQ-788, receptor antagonists for ET(A) and ET(B) receptors, respectively, and also by IRL-1620, a selective agonist for ET(B) receptors. In addition, the changes induced by adding apocynin (10 microM), myr-PKC (1.0 microM), allopurinol (100 microM), rotenone (10 microM), or L-NAME (100 microM) with ET-1 were evaluated. Microvessels were incubated with phorbol 12-myristate 13-acetate (PMA, 10nM), a protein kinase C (PKC) activator. Fluorometric analyses showed ethidium fluorescence-positive regions that coincided well with the location of retinal pericytes. The intracellular superoxide levels were significantly increased after addition of ET-1 (100 nM), and this elevation was suppressed by apocynin or myr-PKC. Other enzyme inhibitors including L-NAME had no effect. The ET-1-induced increase of superoxide was significantly suppressed by BQ-123 (1.0 microM), while effects of adding BQ-788 (1.0 microM) were insignificant. IRL-1620 (100 nM) did not increase superoxide formation significantly. PMA (10nM) mimicked the effect of ET-1. These results suggest that ET-1 increases the formation of superoxides in the retinal microvascular pericytes most likely by activating NADPH oxidase through ET(A) receptors. The activation of PKC may be involved in the mechanism. Thus, ET-1 may augment its vasoconstrictive effects through the formation of superoxide, which may impair the bioavailability of nitric oxide in the retinal microvasculature.
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Affiliation(s)
- Junko Matsuo
- Department of Ophthalmology, Osaka Medical College, 2-7 Daigaku-machi, Takatsuki, Osaka 569-8686, Japan
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TGF-beta is required for vascular barrier function, endothelial survival and homeostasis of the adult microvasculature. PLoS One 2009; 4:e5149. [PMID: 19340291 PMCID: PMC2659748 DOI: 10.1371/journal.pone.0005149] [Citation(s) in RCA: 153] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2008] [Accepted: 03/11/2009] [Indexed: 12/22/2022] Open
Abstract
Pericyte-endothelial cell (EC) interactions are critical to both vascular development and vessel stability. We have previously shown that TGF-β signaling between EC and mural cells participates in vessel stabilization in vitro. We therefore investigated the role of TGF-β signaling in maintaining microvessel structure and function in the adult mouse retinal microvasculature. TGF-β signaling was inhibited by systemic expression of soluble endoglin (sEng) and inhibition was demonstrated by reduced phospho-smad2 in the adult retina. Blockade of TGF-β signaling led to increased vascular and neural cell apoptosis in the retina, which was associated with decreased retinal function, as measured by electroretinogram (ERG). Perfusion of the inner retinal vasculature was impaired and was accompanied by defective autoregulation and loss of capillary integrity. Fundus angiography and Evans blue permeability assay revealed a breakdown of the blood-retinal-barrier that was characterized by decreased association between the tight junction proteins zo-1 and occludin. Inhibition of TGF-β signaling in cocultures of EC and 10T1/2 cells corroborated the in vivo findings, with impaired EC barrier function, dissociation of EC from 10T1/2 cells, and endothelial cell death, supporting the role of EC-mesenchymal interactions in TGF-β signaling. These results implicate constitutive TGF-β signaling in maintaining the integrity and function of the adult microvasculature and shed light on the potential role of TGF-β signaling in vasoproliferative and vascular degenerative retinal diseases.
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Abstract
Diabetic macular edema is a major cause of visual impairment. The pathogenesis of macular edema appears to be multifactorial. Laser photocoagulation is the standard of care for macular edema. However, there are cases that are not responsive to laser therapy. Several therapeutic options have been proposed for the treatment of this condition. In this review we discuss several factors and mechanisms implicated in the etiology of macular edema (vasoactive factors, biochemical pathways, anatomical abnormalities). It seems that combined pharmacologic and surgical therapy may be the best approach for the management of macular edema in diabetic patients.
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Affiliation(s)
- Neelakshi Bhagat
- The Institute of Ophthalmology and Visual Science, New Jersey Medical School, Newark, New Jersey, USA
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Knels L, Worm M, Wendel M, Roehlecke C, Kniep E, Funk RHW. Effects of advanced glycation end products-inductor glyoxal and hydrogen peroxide as oxidative stress factors on rat retinal organ cultures and neuroprotection by UK-14,304. J Neurochem 2008; 106:1876-87. [PMID: 18624919 DOI: 10.1111/j.1471-4159.2008.05540.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Retinal ganglion cell degeneration is supposed to be mediated by reactive oxygen species (ROS) and advanced glycation end products (AGEs). The alpha2-adrenergic agonist, 5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine (brimonidine; UK-14,304), is said to exert a neuroprotective effect. To investigate these mechanisms in detail, we exposed rat whole mounts to glyoxal or H(2)O(2) and treated them with either UK-14,304 alone or additionally with the phosphatidylinositide 3 kinase (PI3) kinase inhibitor, 2-(4-Morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (Ly 294002). The accumulation of Nepsilon-[carboxymethyl] lysine (CML) was assessed immunohistochemically and changes in intracellular pH (pHi), mitochondrial transmembrane potential (MTMP) and ROS production in cell bodies of multipolar ganglion cell layer were studied by intravital fluorescence microscopy and confocal laser scanning microscopy. Ultrastructural changes in mitochondria of multipolar ganglion cell layer cell bodies were determined by transmission electron microscopy. We found that glyoxal and H(2)O(2) increased accumulation of CML-modified proteins and ROS production and decreased pHi and MTMP in cell bodies of multipolar ganglion cell layer. UK-14,304 could prevent production of ROS, accumulation of CML-modified proteins, ameliorate acidification, preserve MTMP and attenuate ultrastructural damages of ganglion cell mitochondria. Ly 294002 reversed the UK-14,304-mediated attenuation of CML and ROS production. We conclude that the protective effects of UK-14,304 seem partly to be mediated by PI3 kinase-dependent pathways.
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Affiliation(s)
- Lilla Knels
- Institute of Anatomy, Medical Faculty Carl Gustav Carus, Technische Universitat, Dresden, Germany.
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Pournaras CJ, Rungger-Brändle E, Riva CE, Hardarson SH, Stefansson E. Regulation of retinal blood flow in health and disease. Prog Retin Eye Res 2008; 27:284-330. [PMID: 18448380 DOI: 10.1016/j.preteyeres.2008.02.002] [Citation(s) in RCA: 387] [Impact Index Per Article: 24.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Optimal retinal neuronal cell function requires an appropriate, tightly regulated environment, provided by cellular barriers, which separate functional compartments, maintain their homeostasis, and control metabolic substrate transport. Correctly regulated hemodynamics and delivery of oxygen and metabolic substrates, as well as intact blood-retinal barriers are necessary requirements for the maintenance of retinal structure and function. Retinal blood flow is autoregulated by the interaction of myogenic and metabolic mechanisms through the release of vasoactive substances by the vascular endothelium and retinal tissue surrounding the arteriolar wall. Autoregulation is achieved by adaptation of the vascular tone of the resistance vessels (arterioles, capillaries) to changes in the perfusion pressure or metabolic needs of the tissue. This adaptation occurs through the interaction of multiple mechanisms affecting the arteriolar smooth muscle cells and capillary pericytes. Mechanical stretch and increases in arteriolar transmural pressure induce the endothelial cells to release contracting factors affecting the tone of arteriolar smooth muscle cells and pericytes. Close interaction between nitric oxide (NO), lactate, arachidonic acid metabolites, released by the neuronal and glial cells during neural activity and energy-generating reactions of the retina strive to optimize blood flow according to the metabolic needs of the tissue. NO, which plays a central role in neurovascular coupling, may exert its effect, by modulating glial cell function involved in such vasomotor responses. During the evolution of ischemic microangiopathies, impairment of structure and function of the retinal neural tissue and endothelium affect the interaction of these metabolic pathways, leading to a disturbed blood flow regulation. The resulting ischemia, tissue hypoxia and alterations in the blood barrier trigger the formation of macular edema and neovascularization. Hypoxia-related VEGF expression correlates with the formation of neovessels. The relief from hypoxia results in arteriolar constriction, decreases the hydrostatic pressure in the capillaries and venules, and relieves endothelial stretching. The reestablished oxygenation of the inner retina downregulates VEGF expression and thus inhibits neovascularization and macular edema. Correct control of the multiple pathways, such as retinal blood flow, tissue oxygenation and metabolic substrate support, aiming at restoring retinal cell metabolic interactions, may be effective in preventing damage occurring during the evolution of ischemic microangiopathies.
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Affiliation(s)
- Constantin J Pournaras
- Department of Ophthalmology, Vitreo-Retina Unit, University Hospitals of Geneva, 22 rue Alcide Jentzer, CH-1211 Geneva 14, Switzerland.
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Gastinger MJ, Tian N, Horvath T, Marshak DW. Retinopetal axons in mammals: emphasis on histamine and serotonin. Curr Eye Res 2006; 31:655-67. [PMID: 16877274 PMCID: PMC3351198 DOI: 10.1080/02713680600776119] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Since 1892, anatomical studies have demonstrated that the retinas of mammals, including humans, receive input from the brain via axons emerging from the optic nerve. There are only a small number of these retinopetal axons, but their branches in the inner retina are very extensive. More recently, the neurons in the brain stem that give rise to these axons have been localized, and their neurotransmitters have been identified. One set of retinopetal axons arises from perikarya in the posterior hypothalamus and uses histamine, and the other arises from perikarya in the dorsal raphe and uses serotonin. These serotonergic and histaminergic neurons are not specialized to supply the retina; rather, they are a subset of the neurons that project via collaterals to many other targets in the central nervous system, as well. They are components of the ascending arousal system, firing most rapidly when the animal is awake and active. The contributions of these retinopetal axons to vision may be predicted from the known effects of serotonin and histamine on retinal neurons. There is also evidence suggesting that retinopetal axons play a role in the etiology of retinal diseases.
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Affiliation(s)
- Matthew J Gastinger
- Graduate School of Biomedical Sciences, The University of Texas Health Science Center Houston, Houston, Texas 77225, USA
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Helmbold P, Lautenschläger C, Marsch WC, Nayak RC. Detection of a physiological juvenile phase and the central role of pericytes in human dermal microvascular aging. J Invest Dermatol 2006; 126:1419-21. [PMID: 16557234 DOI: 10.1038/sj.jid.5700275] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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Matsushita K, Puro DG. Topographical heterogeneity of K(IR) currents in pericyte-containing microvessels of the rat retina: effect of diabetes. J Physiol 2006; 573:483-95. [PMID: 16581863 PMCID: PMC1779733 DOI: 10.1113/jphysiol.2006.107102] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Although inwardly rectifying potassium (K(IR)) channels are known to have important functional roles in arteries and arterioles, knowledge of these channels in pericyte-containing microvessels is limited. A working hypothesis is that K(IR) channel activity affects the membrane potential and thereby the contractile tone of abluminal pericytes whose contractions and relaxations may regulate capillary perfusion. Because pericyte function is thought to be particularly important in the retina, we used the perforated-patch technique to monitor the ionic currents of pericytes located on microvessels freshly isolated from the rat retina. In addition, because changes in ion channel function may contribute to microvascular dysfunction in the diabetic retina, we also recorded from pericyte-containing microvessels of streptozotocin-injected rats. Using barium to identify K(IR) currents, we found that there is a topographical heterogeneity of these currents in the pericyte-containing microvasculature of the normal retina. Specifically, the K(IR) current detected at distal locations is strongly rectifying, but the proximal K(IR) current is weakly rectifying and has a smaller inward conductance. However, soon after the onset of diabetes, these differences diminish as the rectification and inward conductance of the proximal K(IR) current increase. These diabetes-induced changes were reversed by an inhibitor of polyamine synthesis and could be mimicked by spermine, whose concentration is elevated in the diabetic eye. Hence, spermine is a candidate for mediating the effect of diabetes on the function of microvascular K(IR) channels. In addition, our findings raise the possibility that functional changes in K(IR) channels contribute to blood flow dysregulation in the diabetic retina.
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Affiliation(s)
- Kenji Matsushita
- Department of Ophthalmology and Visual Sciences, University of Michigan, 1000 Wall Street, Ann Arbor, MI 48105, USA
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Yamanishi S, Katsumura K, Kobayashi T, Puro DG. Extracellular lactate as a dynamic vasoactive signal in the rat retinal microvasculature. Am J Physiol Heart Circ Physiol 2006; 290:H925-34. [PMID: 16299264 DOI: 10.1152/ajpheart.01012.2005] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We tested the hypothesis that extracellular lactate regulates the function of pericyte-containing retinal microvessels. Although abluminally positioned pericytes appear to adjust capillary perfusion by contracting and relaxing, knowledge of the molecular signals that regulate the contractility of these mural cells is limited. Here, we focused on lactate because this metabolic product is in the retinal extracellular space under both physiological and pathophysiological conditions. In microvessels freshly isolated from the adult rat retina, we used perforated-patch pipettes to monitor ionic currents, fura-2 to measure calcium levels, and time-lapse photography to visualize changes in mural cell contractility and lumen diameter. During lactate exposure, pericyte calcium rose; these cells contracted, and lumens constricted. This contractile response appears to involve a cascade of events resulting in the inhibition of Na+/Ca2+exchangers (NCXs), the decreased of which function causes pericyte calcium to increase and contraction to be triggered. On the basis of our observation that gap junction uncouplers minimized the lactate-induced rise in pericyte calcium, we propose that the NCXs inhibited by lactate are predominately located in the endothelium. Indicative of the importance of endothelial/pericyte gap junctions, uncouplers of these junctions switched the pericyte response to lactate from contraction to relaxation. In addition, we observed that hypoxia, which closes microvascular gap junctions, also switched lactate’s effect from vasocontraction to vasorelaxation. Thus the response of pericyte-containing retinal microvessels to extracellular lactate is metabolically modulated. The ability of lactate to serve as a vasoconstrictor when energy supplies are ample and a vasodilator under hypoxic conditions may be an efficient mechanism to link capillary function with local metabolic need.
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Affiliation(s)
- Shigeki Yamanishi
- Department of Ophthalmology and Visual Sciences, University of Michigan, 1000 Wall St., Ann Arbor, Michigan 48105, USA
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