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Keifi Bajestani A, Alavi MS, Etemad L, Roohbakhsh A. Role of orphan G-protein coupled receptors in tissue ischemia: A comprehensive review. Eur J Pharmacol 2024; 978:176762. [PMID: 38906238 DOI: 10.1016/j.ejphar.2024.176762] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2024] [Revised: 06/12/2024] [Accepted: 06/19/2024] [Indexed: 06/23/2024]
Abstract
Ischemic events lead to many diseases and deaths worldwide. Ischemia/reperfusion (I/R) occurs due to reduced blood circulation in tissues followed by blood reflow. Reoxygenation of ischemic tissues is characterized by oxidative stress, inflammation, energy distress, and endoplasmic reticulum stress. There are still no adequate clinical protocols or pharmacological approaches to address the consequences of I/R damage. G protein-coupled receptors (GPCRs) are important therapeutic targets. They compose a large family of seven transmembrane-spanning proteins that are involved in many biological functions. Orphan GPCRs are a large subgroup of these receptors expressed in different organs. In the present review, we summarized the literature regarding the role of orphan GPCRs in I/R in different organs. We focused on the effect of these receptors on modulating cellular and molecular processes underlying ischemia including apoptosis, inflammation, and autophagy. The study showed that GPR3, GPR4, GPR17, GPR30, GPR31, GPR35, GPR37, GPR39, GPR55, GPR65, GPR68, GPR75, GPR81, and GPR91 are involved in ischemic events, mainly in the brain and heart. These receptors offer new possibilities for treating I/R injuries in the body.
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Affiliation(s)
- Alireza Keifi Bajestani
- Department of Pharmacodynamics and Toxicology, School of Pharmacy, Mashhad University of Medical Sciences, Mashhad, Iran
| | - Mohaddeseh Sadat Alavi
- Department of Pharmacology, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran
| | - Leila Etemad
- Pharmaceutical Research Center, Pharmaceutical Technology Institute, Mashhad University of Medical Sciences, Mashhad, Iran
| | - Ali Roohbakhsh
- Department of Pharmacodynamics and Toxicology, School of Pharmacy, Mashhad University of Medical Sciences, Mashhad, Iran; Pharmaceutical Research Center, Pharmaceutical Technology Institute, Mashhad University of Medical Sciences, Mashhad, Iran.
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2
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Omodaka S, Kato Y, Sato Y, Falcone-Juengert J, Zhang H, Kanoke A, Eckalbar WL, Endo H, Hsieh CL, Aran D, Liu J. Defective interferon signaling in the circulating monocytes of type 2 diabetic mice. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.06.03.597050. [PMID: 38895236 PMCID: PMC11185546 DOI: 10.1101/2024.06.03.597050] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/21/2024]
Abstract
Type 2 diabetes mellitus (T2DM) is associated with poor outcome after stroke. Peripheral monocytes play a critical role in the secondary injury and recovery of damaged brain tissue after stroke, but the underlying mechanisms are largely unclear. To investigate transcriptome changes and molecular networks across monocyte subsets in response to T2DM and stroke, we performed single-cell RNA-sequencing (scRNAseq) from peripheral blood mononuclear cells and bulk RNA-sequencing from blood monocytes from four groups of adult mice, consisting of T2DM model db/db and normoglycemic control db/+ mice with or without ischemic stroke. Via scRNAseq we found that T2DM expands the monocyte population at the expense of lymphocytes, which was validated by flow cytometry. Among the monocytes, T2DM also disproportionally increased the inflammatory subsets with Ly6C+ and negative MHC class II expression (MO.6C+II-). Conversely, monocytes from control mice without stroke are enriched with steady-state classical monocyte subset of MO.6C+II+ but with the least percentage of MO.6C+II- subtype. Apart from enhancing inflammation and coagulation, enrichment analysis from both scRNAseq and bulk RNAseq revealed that T2DM specifically suppressed type-1 and type-2 interferon signaling pathways crucial for antigen presentation and the induction of ischemia tolerance. Preconditioning by lipopolysaccharide conferred neuroprotection against ischemic brain injury in db/+ but not in db/db mice and coincided with a lesser induction of brain Interferon-regulatory-factor-3 in the brains of the latter mice. Our results suggest that the increased diversity and altered transcriptome in the monocytes of T2DM mice underlie the worse stroke outcome by exacerbating secondary injury and potentiating stroke-induced immunosuppression. Significance Statement The mechanisms involved in the detrimental diabetic effect on stroke are largely unclear. We show here, for the first time, that peripheral monocytes have disproportionally altered the subsets and changed transcriptome under diabetes and/or stroke conditions. Moreover, genes in the IFN-related signaling pathways are suppressed in the diabetic monocytes, which underscores the immunosuppression and impaired ischemic tolerance under the T2DM condition. Our data raise a possibility that malfunctioned monocytes may systemically and focally affect the host, leading to the poor outcome of diabetes in the setting of stroke. The results yield important clues to molecular mechanisms involved in the detrimental diabetic effect on stroke outcome.
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Glitsch MD. Recent advances in acid sensing by G protein coupled receptors. Pflugers Arch 2024; 476:445-455. [PMID: 38340167 PMCID: PMC11006784 DOI: 10.1007/s00424-024-02919-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2023] [Revised: 01/30/2024] [Accepted: 01/30/2024] [Indexed: 02/12/2024]
Abstract
Changes in extracellular proton concentrations occur in a variety of tissues over a range of timescales under physiological conditions and also accompany virtually all pathologies, notably cancers, stroke, inflammation and trauma. Proton-activated, G protein coupled receptors are already partially active at physiological extracellular proton concentrations and their activity increases with rising proton concentrations. Their ability to monitor and report changes in extracellular proton concentrations and hence extracellular pH appears to be involved in a variety of processes, and it is likely to mirror and in some cases promote disease progression. Unsurprisingly, therefore, these pH-sensing receptors (pHR) receive increasing attention from researchers working in an expanding range of research areas, from cellular neurophysiology to systemic inflammatory processes. This review is looking at progress made in the field of pHRs over the past few years and also highlights outstanding issues.
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Affiliation(s)
- Maike D Glitsch
- Medical School Hamburg, Am Sandtorkai 1, 20457, Hamburg, Germany.
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4
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Shore D, Griggs N, Graffeo V, Amin ARMR, Zha XM, Xu Y, McAleer JP. GPR68 limits the severity of chemical-induced oral epithelial dysplasia. Sci Rep 2023; 13:353. [PMID: 36611126 PMCID: PMC9825365 DOI: 10.1038/s41598-023-27546-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2022] [Accepted: 01/04/2023] [Indexed: 01/09/2023] Open
Abstract
Head and neck cancer is the sixth most common malignancy, and there is an urgent need to identify physiological processes contributing to tumorigenesis. Extracellular acidification caused by aerobic glycolysis within tumor microenvironments can stimulate proton-sensing receptors. GPR68, or ovarian cancer G protein-coupled receptor 1, responds to extracellular acidity and is highly expressed in head and neck squamous cell carcinoma (HNSCC) as well as normal esophageal tissue. To study the role of GPR68 in oral dysplasia, wild-type and GPR68-/- mice were treated with 4-Nitroquinoline N-oxide (4NQO) in drinking water for 11-13 weeks, followed by normal water for 11-12 weeks. 4NQO treatment resulted in 45 percent of GPR68-/- mice developing severe dysplasia or squamous cell carcinoma compared to only 10.5 percent of GPR68+/+ mice. This correlated with increased frequencies of regulatory T cells in the spleens of male GPR68-/- mice. Dysplastic regions of the tongue had increased CD31 staining compared to normal regions in both GPR68-/- and GPR68+/+ mice, suggesting that angiogenesis was GPR68-independent. RNA knockdown studies using HNSCC cell lines demonstrated no direct effect of GPR68 on survival or growth. Overall, we demonstrate that GPR68-deficiency worsens the severity of chemical-induced oral dysplasia, suggesting a protective role for this gene in tumorigenesis.
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Affiliation(s)
- David Shore
- grid.259676.90000 0001 2214 9920Marshall University School of Pharmacy, Huntington, WV USA
| | - Nosakhere Griggs
- grid.259676.90000 0001 2214 9920Marshall University School of Pharmacy, Huntington, WV USA
| | - Vincent Graffeo
- grid.36425.360000 0001 2216 9681Marshall University Joan C. Edwards School of Medicine, Huntington, WV USA
| | - A. R. M. Ruhul Amin
- grid.259676.90000 0001 2214 9920Marshall University School of Pharmacy, Huntington, WV USA
| | - Xiang-ming Zha
- grid.266756.60000 0001 2179 926XUniversity of Missouri-Kansas City School of Pharmacy, Kansas City, MO USA
| | - Yan Xu
- grid.257413.60000 0001 2287 3919Indiana University School of Medicine, Indianapolis, IN USA
| | - Jeremy P. McAleer
- grid.259676.90000 0001 2214 9920Marshall University School of Pharmacy, Huntington, WV USA
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Zha XM, Xiong ZG, Simon RP. pH and proton-sensitive receptors in brain ischemia. J Cereb Blood Flow Metab 2022; 42:1349-1363. [PMID: 35301897 PMCID: PMC9274858 DOI: 10.1177/0271678x221089074] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/13/2021] [Revised: 02/11/2022] [Accepted: 02/28/2022] [Indexed: 01/01/2023]
Abstract
Extracellular proton concentration is at 40 nM when pH is 7.4. In disease conditions such as brain ischemia, proton concentration can reach µM range. To respond to this increase in extracellular proton concentration, the mammalian brain expresses at least three classes of proton receptors. Acid-sensing ion channels (ASICs) are the main neuronal cationic proton receptor. The proton-activated chloride channel (PAC), which is also known as (aka) acid-sensitive outwardly rectifying anion channel (ASOR; TMEM206), mediates acid-induced chloride currents. Besides proton-activated channels, GPR4, GPR65 (aka TDAG8, T-cell death-associated gene 8), and GPR68 (aka OGR1, ovarian cancer G protein-coupled receptor 1) function as proton-sensitive G protein-coupled receptors (GPCRs). Though earlier studies on these GPCRs mainly focus on peripheral cells, we and others have recently provided evidence for their functional importance in brain injury. Specifically, GPR4 shows strong expression in brain endothelium, GPR65 is present in a fraction of microglia, while GPR68 exhibits predominant expression in brain neurons. Here, to get a better view of brain acid signaling and its contribution to ischemic injury, we will review the recent findings regarding the differential contribution of proton-sensitive GPCRs to cerebrovascular function, neuroinflammation, and neuronal injury following acidosis and brain ischemia.
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Affiliation(s)
- Xiang-ming Zha
- Division of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Missouri-Kansas City, Kansas City, MO, USA
| | - Zhi-Gang Xiong
- Department of Neurobiology, Morehouse School of Medicine, Atlanta, GA, USA
| | - Roger P Simon
- Department of Neurobiology, Morehouse School of Medicine, Atlanta, GA, USA
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Li L, Chen Y, Sluter MN, Hou R, Hao J, Wu Y, Chen GY, Yu Y, Jiang J. Ablation of Siglec-E augments brain inflammation and ischemic injury. J Neuroinflammation 2022; 19:191. [PMID: 35858866 PMCID: PMC9301848 DOI: 10.1186/s12974-022-02556-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2022] [Accepted: 07/14/2022] [Indexed: 11/10/2022] Open
Abstract
Sialic acid immunoglobulin-like lectin E (Siglec-E) is a subtype of pattern recognition receptors found on the surface of myeloid cells and functions as a key immunosuppressive checkpoint molecule. The engagement between Siglec-E and the ligand α2,8-linked disialyl glycans activates the immunoreceptor tyrosine-based inhibitory motif (ITIM) in its intracellular domain, mitigating the potential risk of autoimmunity amid innate immune attacks on parasites, bacteria, and carcinoma. Recent studies suggest that Siglec-E is also expressed in the CNS, particularly microglia, the brain-resident immune cells. However, the functions of Siglec-E in brain inflammation and injuries under many neurological conditions largely remain elusive. In this study, we first revealed an anti-inflammatory role for Siglec-E in lipopolysaccharide (LPS)-triggered microglial activation. We then found that Siglec-E was induced within the brain by systemic treatment with LPS in mice in a dose-dependent manner, while its ablation exacerbated hippocampal reactive microgliosis in LPS-treated animals. The genetic deficiency of Siglec-E also aggravated oxygen-glucose deprivation (OGD)-induced neuronal death in mouse primary cortical cultures containing both neurons and glial cells. Moreover, Siglec-E expression in ipsilateral brain tissues was substantially induced following middle cerebral artery occlusion (MCAO). Lastly, the neurological deficits and brain infarcts were augmented in Siglec-E knockout mice after moderate MCAO when compared to wild-type animals. Collectively, our findings suggest that the endogenous inducible Siglec-E plays crucial anti-inflammatory and neuroprotective roles following ischemic stroke, and thus might underlie an intrinsic mechanism of resolution of inflammation and self-repair in the brain.
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Affiliation(s)
- Lexiao Li
- Department of Pharmaceutical Sciences, Drug Discovery Center, College of Pharmacy, University of Tennessee Health Science Center, Memphis, TN, USA
| | - Yu Chen
- Department of Pharmaceutical Sciences, Drug Discovery Center, College of Pharmacy, University of Tennessee Health Science Center, Memphis, TN, USA
| | - Madison N Sluter
- Department of Pharmaceutical Sciences, Drug Discovery Center, College of Pharmacy, University of Tennessee Health Science Center, Memphis, TN, USA
| | - Ruida Hou
- Department of Pharmaceutical Sciences, Drug Discovery Center, College of Pharmacy, University of Tennessee Health Science Center, Memphis, TN, USA
| | - Jiukuan Hao
- Department of Pharmacological and Pharmaceutical Sciences, College of Pharmacy, University of Houston, Houston, TX, USA
| | - Yin Wu
- Children's Foundation Research Institute at Le Bonheur Children's Hospital, Department of Pediatrics, College of Medicine, University of Tennessee Health Science Center, Memphis, TN, USA
| | - Guo-Yun Chen
- Children's Foundation Research Institute at Le Bonheur Children's Hospital, Department of Pediatrics, College of Medicine, University of Tennessee Health Science Center, Memphis, TN, USA
| | - Ying Yu
- Department of Pharmaceutical Sciences, Drug Discovery Center, College of Pharmacy, University of Tennessee Health Science Center, Memphis, TN, USA
| | - Jianxiong Jiang
- Department of Pharmaceutical Sciences, Drug Discovery Center, College of Pharmacy, University of Tennessee Health Science Center, Memphis, TN, USA.
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Subbarayan K, Massa C, Leisz S, Steven A, Bethmann D, Biehl K, Wickenhauser C, Seliger B. Biglycan as a potential regulator of tumorgenicity and immunogenicity in K-RAS-transformed cells. Oncoimmunology 2022; 11:2069214. [PMID: 35529675 PMCID: PMC9067524 DOI: 10.1080/2162402x.2022.2069214] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2021] [Revised: 04/16/2022] [Accepted: 04/17/2022] [Indexed: 11/30/2022] Open
Abstract
The extracellular matrix component biglycan (BGN) plays an essential role in various physiological and pathophysiological processes. A deficient BGN expression associated with reduced immunogenicity was found in HER-2/neu-overexpressing cells. To determine whether BGN is suppressed by oncogene-driven regulatory networks, the expression and function of BGN was analyzed in murine and human BGNlow/BGNhigh K-RASG12V-transformed model systems as well as in different patients' datasets of colorectal carcinoma (CRC) lesions. K-RAS-mutated CRC tissues expressed low BGN mRNA and protein levels when compared to normal colon epithelial cells, which was associated with a reduced patients' survival. Transfection of BGN in murine and human BGNlow K-RAS-expressing cells resulted in a reduced growth and migration of BGNhigh vs BGNlow K-RAS cells. In addition, increased MHC class I surface antigens as a consequence of an enhanced antigen processing machinery component expression was found upon restoration of BGN, which was confirmed by RNA-sequencing of BGNlow vs. BGNhigh K-RAS models. Furthermore, a reduced tumor formation of BGNhigh versus BGNlow K-RAS-transformed fibroblasts associated with an enhanced MHC class I expression and an increased frequency of tumor-infiltrating lymphocytes in tumor lesions was found. Our data provide for the first time an inverse link between BGN and K-RAS expression in murine and human K-RAS-overexpressing models and CRC lesions associated with altered growth properties, reduced immunogenicity and worse patients' outcome. Therefore, reversion of BGN might be a novel therapeutic option for K-RAS-associated malignancies.
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Affiliation(s)
- Karthikeyan Subbarayan
- Institute of Medical Immunology, Martin Luther University Halle-Wittenberg, Halle, Germany
| | - Chiara Massa
- Institute of Medical Immunology, Martin Luther University Halle-Wittenberg, Halle, Germany
| | - Sandra Leisz
- Institute of Medical Immunology, Martin Luther University Halle-Wittenberg, Halle, Germany
| | - André Steven
- Institute of Medical Immunology, Martin Luther University Halle-Wittenberg, Halle, Germany
| | - Daniel Bethmann
- Institute of Pathology, Martin Luther University Halle-Wittenberg, Halle, Germany
| | - Katharina Biehl
- Institute of Medical Immunology, Martin Luther University Halle-Wittenberg, Halle, Germany
| | - Claudia Wickenhauser
- Institute of Pathology, Martin Luther University Halle-Wittenberg, Halle, Germany
| | - Barbara Seliger
- Institute of Medical Immunology, Martin Luther University Halle-Wittenberg, Halle, Germany
- Fraunhofer Institute for Cell Therapy and Immunology, Leipzig, Germany
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8
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Imenez Silva PH, Wagner CA. Physiological relevance of proton-activated GPCRs. Pflugers Arch 2022; 474:487-504. [PMID: 35247105 PMCID: PMC8993716 DOI: 10.1007/s00424-022-02671-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2021] [Revised: 02/07/2022] [Accepted: 02/08/2022] [Indexed: 12/12/2022]
Abstract
The detection of H+ concentration variations in the extracellular milieu is accomplished by a series of specialized and non-specialized pH-sensing mechanisms. The proton-activated G protein–coupled receptors (GPCRs) GPR4 (Gpr4), TDAG8 (Gpr65), and OGR1 (Gpr68) form a subfamily of proteins capable of triggering intracellular signaling in response to alterations in extracellular pH around physiological values, i.e., in the range between pH 7.5 and 6.5. Expression of these receptors is widespread for GPR4 and OGR1 with particularly high levels in endothelial cells and vascular smooth muscle cells, respectively, while expression of TDAG8 appears to be more restricted to the immune compartment. These receptors have been linked to several well-studied pH-dependent physiological activities including central control of respiration, renal adaption to changes in acid–base status, secretion of insulin and peripheral responsiveness to insulin, mechanosensation, and cellular chemotaxis. Their role in pathological processes such as the genesis and progression of several inflammatory diseases (asthma, inflammatory bowel disease), and tumor cell metabolism and invasiveness, is increasingly receiving more attention and makes these receptors novel and interesting targets for therapy. In this review, we cover the role of these receptors in physiological processes and will briefly discuss some implications for disease processes.
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Affiliation(s)
- Pedro H Imenez Silva
- Institute of Physiology, University of Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland. .,National Center of Competence in Research NCCR Kidney.CH, Zurich, Switzerland.
| | - Carsten A Wagner
- Institute of Physiology, University of Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland. .,National Center of Competence in Research NCCR Kidney.CH, Zurich, Switzerland.
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Zhao D, Zhang M, Yang L, Zeng M. GPR68 Improves Nerve Damage and Myelination in an Immature Rat Model Induced by Sevoflurane Anesthesia by Activating cAMP/CREB to Mediate BDNF. ACS Chem Neurosci 2022; 13:423-431. [PMID: 35025202 DOI: 10.1021/acschemneuro.1c00830] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Ovarian cancer G-protein-coupled receptor 1 (OGR1, also known as GPR68) is a member of proton-sensing G-protein-coupled receptors, involved in cardiovascular physiology, tumor biology, and asthma, and exerts a neuroprotective effect against brain ischemia. The effects of GPR68 on anesthesia-induced nerve damage and myelination were investigated in this study. First, 2-day old postnatal rats were exposed to 4.9% sevoflurane for 2 h. Data from hematoxylin and eosin staining and Nissl staining showed that sevoflurane induced pathological changes in the hippocampus with a reduced number of neurons. GPR68 was downregulated in the hippocampus of sevoflurane-induced rats. Second, sevoflurane-induced rats were injected with adeno-associated virus (AAV)-mediated overexpression of GPR68, and overexpression of GPR68 ameliorated sevoflurane-induced pathological changes, enhanced the number of neurons, and improved the learning and memory function. Moreover, overexpression of GPR68 increased the number of BrdU-positive and Olig2-positive cells and enhanced protein expression of Olig2 in sevoflurane-induced rats. Third, the number of myelin basic protein (MBP) positive cells and protein expression of MBP in sevoflurane-induced rats were also enhanced by injection with AAV-GPR68. Overexpression of GPR68 attenuated sevoflurane-induced neuronal apoptosis and oxidative stress in rats. Lastly, overexpression of GPR68 upregulated protein expression of the brain-derived neurotrophic factor (BDNF) by increasing cAMP and phosphorylated cAMP response element-binding protein (CREB). In conclusion, GPR68 alleviated sevoflurane-induced nerve damage and myelination through BDNF-mediated activation of the cAMP/CREB pathway.
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Affiliation(s)
- Dan Zhao
- Department of Anesthesiology, Chengdu University of Traditional Chinese Medicine Hospital, Chengdu, Sichuan 610032, China
| | - Minli Zhang
- Department of Anesthesiology, Chengdu University of Traditional Chinese Medicine Hospital, Chengdu, Sichuan 610032, China
| | - Lingling Yang
- Department of Anesthesiology, Chengdu University of Traditional Chinese Medicine Hospital, Chengdu, Sichuan 610032, China
| | - Mingquan Zeng
- Department of Critical Care Medicine, Public Health Clinical Center of Chengdu, Chengdu, Sichuan 610000, China
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Zhou G, Zha XM. GPR68 Contributes to Persistent Acidosis-Induced Activation of AGC Kinases and Tyrosine Phosphorylation in Organotypic Hippocampal Slices. Front Neurosci 2021; 15:692217. [PMID: 34113235 PMCID: PMC8185064 DOI: 10.3389/fnins.2021.692217] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2021] [Accepted: 04/29/2021] [Indexed: 12/28/2022] Open
Abstract
Persistent acidosis occurs in ischemia and multiple neurological diseases. In previous studies, acidic stimulation leads to rapid increase in intracellular calcium in neurons. However, it remains largely unclear how a prolonged acidosis alters neuronal signaling. In our previous study, we found that GPR68-mediated PKC activities are protective against acidosis-induced injury in cortical slices. Here, we first asked whether the same principle holds true in organotypic hippocampal slices. Our data showed that 1-h pH 6 induced PKC phosphorylation in a GPR68-dependent manner. Go6983, a PKC inhibitor worsened acidosis-induced neuronal injury in wild type (WT) but had no effect in GPR68−/− slices. Next, to gain greater insights into acid signaling in brain tissue, we treated organotypic hippocampal slices with pH 6 for 1-h and performed a kinome profiling analysis by Western blot. Acidosis had little effect on cyclin-dependent kinase (CDK) or casein kinase 2 activity, two members of the CMGC family, or Ataxia telangiectasia mutated (ATM)/ATM and RAD3-related (ATR) activity, but reduced the phosphorylation of MAPK/CDK substrates. In contrast, acidosis induced the activation of CaMKIIα, PKA, and Akt. Besides these serine/threonine kinases, acidosis also induced tyrosine phosphorylation. Since GPR68 is widely expressed in brain neurons, we asked whether GPR68 contributes to acidosis-induced signaling. Deleting GPR68 had no effect on acidosis-induced CaMKII phosphorylation, attenuated that of phospho-Akt and phospho-PKA substrates, while abolishing acidosis-induced tyrosine phosphorylation. These data demonstrate that prolonged acidosis activates a network of signaling cascades, mediated by AGC kinases, CaMKII, and tyrosine kinases. GPR68 is the primary mediator for acidosis-induced activation of PKC and tyrosine phosphorylation, while both GPR68-dependent and -independent mechanisms contribute to the activation of PKA and Akt.
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Affiliation(s)
- Guokun Zhou
- Department of Physiology and Cell Biology, University of South Alabama College of Medicine, Mobile, AL, United States
| | - Xiang-Ming Zha
- Department of Physiology and Cell Biology, University of South Alabama College of Medicine, Mobile, AL, United States
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