Cochlear Capillary Pericytes

Research advances in cochlear pericytes and hearing loss

Pericytes are specialized mural cells surrounding endothelial cells in microvascular beds. They play a role in vascular development, blood flow regulation, maintenance of blood-tissue barrier integrity, and control of angiogenesis, tissue fibrosis, and wound healing. In recent decades, understanding of the critical role played by pericytes in retina, brain, lung, and kidney has seen significant progress. The cochlea contains a large population of pericytes. However, the role of cochlear pericytes in auditory pathophysiology is, by contrast, largely unknown. The present review discusses recent progress in identifying cochlear pericytes, mapping their distribution, and defining their role in regulating blood flow, controlling the blood-labyrinth barrier (BLB) and angiogenesis, and involvement in different types of hearing loss.

Pericytes control vascular stability and auditory spiral ganglion neuron survival

The inner ear has a rich population of pericytes, a multi-functional mural cell essential for sensory hair cell heath and normal hearing. However, the mechanics of how pericytes contribute to the homeostasis of the auditory vascular-neuronal complex in the spiral ganglion are not yet known. In this study, using an inducible and conditional pericyte depletion mouse (PDGFRB-CreERT2; ROSA26iDTR) model, we demonstrate, for the first time, that pericyte depletion causes loss of vascular volume and spiral ganglion neurons (SGNs) and adversely affects hearing sensitivity. Using an in vitro trans-well co-culture system, we show pericytes markedly promote neurite and vascular branch growth in neonatal SGN explants and adult SGNs. The pericyte-controlled neural growth is strongly mediated by pericyte-released exosomes containing vascular endothelial growth factor-A (VEGF-A). Treatment of neonatal SGN explants or adult SGNs with pericyte-derived exosomes significantly enhances angiogenesis, SGN survival, and neurite growth, all of which were inhibited by a selective blocker of VEGF receptor 2 (Flk1). Our study demonstrates that pericytes in the adult ear are critical for vascular stability and SGN health. Cross-talk between pericytes and SGNs via exosomes is essential for neuronal and vascular health and normal hearing.

Neuronal Cytoglobin in the Auditory Brainstem of Rat and Mouse: Distribution, Cochlear Projection, and Nitric Oxide Production

Cytoglobin (Cygb), a hemoprotein of the globin family, is expressed in the supportive tissue cells of the fibroblast lineage and in distinct neuronal cell populations. The expression pattern and regulatory parameters of fibroblasts and related cells were studied in organs such as the kidney and liver in a variety of animal models. In contrast, knowledge about cytoglobin-expressing neurons is sparse. Only a few papers described the distribution in the brain as ubiquitous with a restricted number of neurons in focal regions. Although there is evidence for cytoglobin involvement in neuronal hypoxia tolerance, its presence in the auditory system was not studied despite high metabolism rates and oxygen demands of the cochlea and related brainstem centers. In a continuation of a previous study demonstrating Cygb-neurons in, inter alia, auditory regions of the mouse brain, we concentrated on the superior olivary complex (SOC) in the present study. We sought to investigate the distribution, projection pattern and neurochemistry of Cygb-neurons in the SOC. We conducted immunohistochemistry using a Cygb antibody and found that this brainstem region, functionally competent for bilateral hearing and providing cochlear hair cell innervation, contains a considerable number of Cygb-expressing neurons (averaging 2067 ± 211 making up 10 ±1% percent of total neuron number) in rats, and 514 ± 138 (6 ± 1%) in mice. They were observed in all regions of the SOC. Retrograde neuronal tract tracing with Fluorogold injected into the cochlea demonstrated that 1243 ± 100 (6 ± 1% of total neuron number in rat SOC)) were olivocochlear neurons. Approximately 56% of total Cygb neurons were retrogradely labelled, while the majority of olivocochlear neurons of both lateral and medial systems were Cygb-immunoreactive. We also conducted double immunofluorescence staining for Cygb and neuronal nitric oxide synthase (nNOS), the enzyme responsible for nitric oxide production, and observed that cytoglobin in the SOC frequently co-localized with nNOS. Our findings suggest that cytoglobin plays an important physiologic role in the oxygen homeostasis of the peripheral and central auditory nervous system. Further studies, also including transgenic animal models, are required to shed more light on the function(s) of Cygb in neurons, in particular of the auditory system.

Pericytes of Stria Vascularis Are Targets of Cisplatin-Induced Ototoxicity: New Insights into the Molecular Mechanisms Involved in Blood-Labyrinth Barrier Breakdown

The stria vascularis (SV) contributes to cochlear homeostasis and consists of three layers, one of which contains the blood-labyrinthic barrier (BLB), with a large number of bovine cochlear pericytes (BCPs). Cisplatin is a chemotherapeutic drug that can damage the SV and cause hearing loss. In this study, cell viability, proliferation rate, cytotoxicity and reactive oxygen species production were evaluated. The protein content of phospho-extracellular signal-regulated kinases (ERK) 1/2, total ERK 1/2, phospho-cytosolic phospholipase A₂ (cPLA₂), total cPLA₂ and cyclooxygenase 2 (COX-2) and the release of prostaglandin E2 (PGE2) and vascular endothelial growth factor (VEGF) from BCPs were analyzed. Finally, the protective effect of platelet-derived growth factor (PDGF-BB) on BCPs treated with cisplatin was investigated. Cisplatin reduced viability and proliferation, activated ERK 1/2, cPLA₂ and COX-2 expression and increased PGE2 and VEGF release; these effects were reversed by Dexamethasone. The presence of PDGF-BB during the treatment with cisplatin significantly increased the proliferation rate. No studies on cell regeneration in ear tissue evaluated the effect of the PDGF/Dex combination. The aim of this study was to investigate the effects of cisplatin on cochlear pericytes and propose new otoprotective agents aimed at preventing the reduction of their vitality and thus maintaining the BLB structure.

Development of the stria vascularis in the common marmoset, a primate model

Stria vascularis is a structure that generates potassium gradients in the cochlea, which is vital for hair cells to convert mechanical sound waves into electrical pulses. The precise development of the stria vascularis and subsequent generation of endocochlear potential are thus essential for hearing. Understanding the development of the stria vascularis is valuable for studying hearing loss caused by aging or genetics and designing regenerative therapy. Although inter-species differences have been reported between rodents and humans, most of our current knowledge regarding cochlear development has been obtained from rodent models because of the difficulty in using human fetal samples in this field of research. Therefore, we investigated the development of the cochlear stria vascularis in the common marmoset (Callithrix jacchus), a small monkey species native to the New World. Our study confirms that stria vascularis development in the common marmoset is similar to that in humans and is suitable for furthering our understanding of human cochlear development. The time course established in this report will aid in studying the primate-specific developmental biology of the inner ear, which could eventually lead to new treatment strategies for hearing loss in humans.

Application and prospect of quasi-targeted metabolomics in age-related hearing loss

Age-related hearing loss (ARHL) is a common sensory deficit in the elderly, which seriously affects physical and mental health. Therefore, understanding its underlying molecular mechanisms and taking interventions to treat ARHL are urgently needed. In our study, cochlea of 4-week-old C57BL/6 mice as the Youth group (n = 6) and 48-week-old cochlea as the Old group (n = 6) were subjected to quasi-targeted metabolomics analysis by Ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). In total, 208 differential metabolites were identified in 12 cochlea samples, which highlighted the following discriminant compounds: tryptophan, piperidine, methionine, L-arginine, histamine, serotonin, acetylcholine, and 4-aminobutyric acid. Differentially expressed metabolites were identified which were involved in KEGG pathways related to the digestion and absorption of oxidative stress associated amino acids, Synaptic vesicle cycle of serotonin, Pantothenate and CoA Biosynthesis. These findings are a first step toward elucidating the pathophysiological pathways involved in the etiology of ARHL and provide the possibility to further explore the mechanisms of ARHL using metabolomic analysis.

Brain Pericytes Acquire Stemness via the Nrf2-Dependent Antioxidant System

Pericytes (PCs) are a mural support cell population elongated at intervals along the walls of capillaries. Recent studies reported that PCs are multipotent cells that are activated in response to tissue injury and contribute to the regenerative process. Using a C.B-17 mouse model of ischemic stroke, it has been proposed that normal brain pericytes (nPCs) are converted to ischemic pericytes (iPCs), some of which function as multipotent stem cells. Furthermore, oxygen-glucose deprivation (OGD) promoted mesenchymal-epithelial transition in nPCs; however, nestin was not induced under OGD conditions. Therefore, further studies are needed to elucidate the PC reprogramming phenomenon. We herein isolated nPCs from the cortex of C.B-17 mice, and compared the traits of iPCs and nPCs. The results obtained showed that nPCs and iPCs shared common pericytic markers. Furthermore, intercellular levels of reactive oxygen species and the nuclear accumulation of nuclear factor erythroid-2-related factor 2 (Nrf2), a key player in antioxidant defenses, were higher in iPCs than in nPCs. OGD/reoxygenation and a treatment with tBHQ, an Nrf2 inducer, increased nestin levels in nPCs. Moreover, epithelial marker levels, including nestin, Sox2, and CDH1 (E-cadherin) mRNAs, were elevated in Nrf2-overexpressing PCs, which formed neurosphere-like cell clusters that differentiated into Tuj1-positive neurons. The present results demonstrate that oxidative stress and Nrf2 are required for the generation of stem cells after stroke and will contribute to the development of novel therapeutic strategies for ischemic stroke.

Adenosine improves LPS-induced ROS expression and increasing in monolayer permeability of endothelial cell via acting on A2AR

Blood-labyrinth barrier (BLB) disruption plays a crucial role in the development of otitis media. The aims of our study was to explore the role and action mechanism of adenosine in LPS-induced endothelial cells (ECs) damage, which are one of the major principal cell type for blood-labyrinth barrier (BLB), and so as to assess the potential of adenosine to be used in the treatment of BLB disruption in animal experiment. In our study, ECs were treated with LPS to mimic BLB damage in vitro. Our data showed that adenosine at dosage of 1, 10, and 20 μM had no influence on the cell viability of ECs. LPS treatment obviously suppressed the expression of Occludin and Zonula occludens-1 (ZO-1) in ECs, which was partly recused by adenosine treatment. Meantime, LPS-induced increasing in reactive oxygen species (ROS) production and ECs permeability also was rescued by adenosine treatment. However, inhibition the A2A receptor (A2AR) could attenuate the influence of adenosine on LPS-treated ECs, indicating that adenosine alleviated LPS-induced BLB damage by activating A2AR. Moreover, the inhibition of adenosine to LPS-induced inactivation of AMPK/AKT signaling pathway was partly recused by A2AR suppression. In addition, Compound C (an AMPK inhibitor) decreased the expression of Occludin and ZO-1 in ECs following LPS combined with adenosine treatment. In conclusion, adenosine alleviates LPS-induced BLB damage via AMPK/AKT pathway through activation of A2AR. This work suggests that adenosine may be a candidate drug for the treatment of BLB dysfunction-related diseases.

Progenitor cell therapy for acquired pediatric nervous system injury: Traumatic brain injury and acquired sensorineural hearing loss

While cell therapies hold remarkable promise for replacing injured cells and repairing damaged tissues, cell replacement is not the only means by which these therapies can achieve therapeutic effect. For example, recent publications show that treatment with varieties of adult, multipotent stem cells can improve outcomes in patients with neurological conditions such as traumatic brain injury and hearing loss without directly replacing damaged or lost cells. As the immune system plays a central role in injury response and tissue repair, we here suggest that multipotent stem cell therapies achieve therapeutic effect by altering the immune response to injury, thereby limiting damage due to inflammation and possibly promoting repair. These findings argue for a broader understanding of the mechanisms by which cell therapies can benefit patients.

Pericytes on placental capillaries in terminal villi preferentially cover endothelial junctions in regions furthest away from the trophoblast

Introduction

Pericytes are a common feature in the placental microvasculature but their roles are not well understood. Pericytes may provide physical or endocrine support for endothelium and in some tissues mediate vasoconstriction.

Methods

This study uses serial block-face scanning electron microscopy (SBFSEM) to generate three-dimensional (3D) reconstructions of placental pericytes of the terminal villi and transmission electron microscopy (TEM) to study pericyte endothelial cell interactions. The proportion of endothelial cell junctions covered by pericytes was determined.

Results

The detailed 3D models of placental pericytes show pericyte structure at a new level of detail. Placental pericytes have many fingers extending from the cell body which can span multiple capillary branches. The proportion of endothelial cell-cell junctions covered by pericytes was significantly higher than pericyte coverage of capillary endothelium as a whole (endothelium: 14%, junctions: 43%, p < 0.0001). However, the proportion of endothelial cell-cell junctions covered by pericytes in regions adjacent to trophoblast was reduced compared to regions >3 μm away from trophoblast (27% vs 62% respectively, p < 0.001). No junctional complexes were observed connecting pericytes and endothelial cells but there were regions of cell membrane with features suggestive of intercellular adhesions.

Discussion

These data suggest that the localisation of pericytes on the villous capillary is not random but organised in relation to both endothelial junctions and the location of adjacent trophoblast. This further suggests that pericyte coverage may favour capillary permeability in regions that are most important for exchange, but limit capillary permeability in other regions.

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Three-dimensional imaging highlights the structure of placental pericytes.

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Placental pericytes preferentially cover endothelial junctions.

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The proportion of covered junctions decreased in regions adjacent to trophoblasts.

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The localisation of placental pericytes suggests endothelial coverage is non-random.

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Junction coverage may alter capillary permeability in key regions of exchange.

Menière's disease caused by CGRP - A new hypothesis explaining etiology and pathophysiology. Redirecting Menière's syndrome to Menière's disease

This paper provides a new hypothetical explanation for the etiopathology and pathophysiology of Menière's Disease (MD), which to date remain unexplained, or incompletely understood. The suggested hypothesis will explain the close connection of MD and Migraine, the coexistence of endolymphatic hydrops (ELH) and Menière attacks and the signs of inflammation detected in the inner ears of MD patients. Although as yet unproven, the explanations provided appear highly plausible and could pave the way for the generation of the first animal model of MD - an invaluable asset for developing new treatment strategies. Furthermore, if proven correct, this hypothesis could redefine and also reset the actual name of Menière's Syndrome to Menière's Disease.

Serum Renin Levels in Sudden Sensorineural Hearing Loss

Objective:

The aim of this study was to investigate the serum renin levels of patients with idiopathic sudden sensorineural hearing loss (ISSNHL).

Material and Methods:

Twenty-four patients with ISSNHL and 24 asymptomatic healthy volunteers were included in the study. Subjects underwent pure-tone audiometry and serum renin levels were measured.

Results:

There were 14 women (mean age:42.35 ± 9.53) and 10 men (mean age:43.8 ± 6.87) in the patient group. There were 14 women (mean age:42.4 ± 4.7) and 10 men (mean age:41.4 ± 4.59) in the control group. ISSNHL was detected on the right side in 13 patients and on the left side in 11 patients. Serum renin levels of the patients and controls were 788.01 ± 327.8 and 282.37 ± 107.73 pg/mL, respectively. The serum renin levels were found to be significantly higher in the patient group compared to the control group ( P ≤ .001). There was a statistically significant strong positive correlation between serum renin level and the severity of hearing loss ( r = 0.77; P = .001).

Conclusion:

Serum renin levels of patients with ISSNHL were higher than controls. There was a statistically significant strong positive correlation between serum renin level and the severity of hearing loss.

Acoustic Trauma Modulates Cochlear Blood Flow and Vasoactive Factors in a Rodent Model of Noise-Induced Hearing Loss

Noise exposure affects the organ of Corti and the lateral wall of the cochlea, including the stria vascularis and spiral ligament. Although the inner ear vasculature and spiral ligament fibrocytes in the lateral wall consist of a significant proportion of cells in the cochlea, relatively little is known regarding their functional significance. In this study, 6-week-old male C57BL/6 mice were exposed to noise trauma to induce transient hearing threshold shift (TTS) or permanent hearing threshold shift (PTS). Compared to mice with TTS, mice with PTS exhibited lower cochlear blood flow and lower vessel diameter in the stria vascularis, accompanied by reduced expression levels of genes involved in vasodilation and increased expression levels of genes related to vasoconstriction. Ultrastructural analyses by transmission electron microscopy revealed that the stria vascularis and spiral ligament fibrocytes were more damaged by PTS than by TTS. Moreover, mice with PTS expressed significantly higher levels of proinflammatory cytokines in the cochlea (e.g., IL-1β, IL-6, and TNF-α). Overall, our findings suggest that cochlear microcirculation and lateral wall pathologies are differentially modulated by the severity of acoustic trauma and are associated with changes in vasoactive factors and inflammatory responses in the cochlea.