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The protective role of proton-sensing TDAG8 in the brain injury in a mouse ischemia reperfusion model
Koichi Sato1, Ayaka Tobo2, Chihiro Mogi2
1Laboratory of Signal Transduction, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, 371-8512, Japan. kosato@gunma-u.ac.jp.
Abstract:
Extracellular acidification in the brain has been observed in ischemia; however, the physiological and pathophysiological implications of the pH reduction remain largely unknown. Here, we analyzed the roles of proton-sensing G protein-coupled receptors, including T-cell death-associated gene 8 (TDAG8), ovarian cancer G protein-coupled receptor 1 (OGR1), and G protein-coupled receptor 4 (GPR4) in a mouse ischemia reperfusion model. Cerebral infarction and dysfunctional behavior with transient middle cerebral artery occlusion (tMCAO) and subsequent reperfusion were exacerbated by the deficiency of TDAG8, whereas no significant effect was observed with the deficiency of OGR1 or GPR4. We confirmed that the pH of the predicted infarction region was 6.5. TDAG8 mRNA was observed in Iba1-positive microglia in the mouse brain. The tMCAO increased the mRNA expression of tumor necrosis factor-α in the ipsilateral cerebral hemisphere and evoked morphological changes in microglia in an evolving cerebral injury. These tMCAO-induced actions were significantly enhanced by the TDAG8 deficiency. Administration of minocycline, which is known to inhibit microglial activation, improved the cerebral infarction and dysfunctional behavior induced by tMCAO in the TDAG8-deficient mouse. Thus, acidic pH/TDAG8 protects against cerebral infarction caused by tMCAO, at least due to the mechanism involving the inhibition of microglial functions.
Insights
Brain acidification during ischemia is linked to stroke severity. The T-cell death-associated gene 8 (TDAG8) receptor protects against cerebral infarction by inhibiting microglial activation, suggesting a therapeutic target.
Area of Science:
- Neuroscience
- Molecular Biology
- Pathophysiology
Background:
- Extracellular brain acidification occurs during ischemia, but its functional significance is unclear.
- Proton-sensing G protein-coupled receptors (TDAG8, OGR1, GPR4) are potential mediators of pH effects.
- Microglia play a critical role in neuroinflammation and brain injury.
Purpose of the Study:
- To investigate the role of proton-sensing G protein-coupled receptors in a mouse model of cerebral ischemia-reperfusion injury.
- To elucidate the specific contribution of T-cell death-associated gene 8 (TDAG8) in the context of ischemic stroke.
- To explore the underlying mechanisms involving microglial activation and inflammation.
Main Methods:
- Transient middle cerebral artery occlusion (tMCAO) model in mice to induce ischemia-reperfusion.
- Analysis of cerebral infarction volume and behavioral dysfunction in wild-type and gene-deficient mice.
- Measurement of brain tissue pH and gene expression (e.g., tumor necrosis factor-α).
- Immunohistochemical analysis of microglia (Iba1-positive cells) and administration of minocycline.
Main Results:
- TDAG8 deficiency exacerbated cerebral infarction and behavioral deficits following tMCAO, while OGR1 and GPR4 deficiencies had no significant effect.
- The pH in the infarction region was measured to be as low as 6.5.
- TDAG8 mRNA was detected in microglia, and its deficiency enhanced tMCAO-induced microglial activation and pro-inflammatory cytokine expression.
- Minocycline treatment ameliorated stroke outcomes in TDAG8-deficient mice, indicating the involvement of microglial pathways.
Conclusions:
- Acidic pH, acting through TDAG8, confers protection against cerebral ischemia-reperfusion injury.
- TDAG8 signaling in microglia inhibits inflammatory responses and reduces brain damage.
- Targeting the acidic pH/TDAG8 pathway may offer a novel therapeutic strategy for ischemic stroke.
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