TMEM175 mediates Lysosomal function and participates in neuronal injury induced by cerebral ischemia-reperfusion
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As the main organelles for the clearance of damaged proteins and damaged organelles, the function of lysosomes is crucial for maintaining the intracellular homeostasis of long-lived neurons. A stable acidic environment is essential for lysosomes to perform their functions. TMEM175 has been identified as a new K+ channel that is responsible for regulating lysosomal membrane potential and pH stability in neurons. This study aimed to understand the role of TMEM175 in lysosomal function of neurons and neuronal injury following cerebral ischemia-reperfusion (I/R). A middle-cerebral-artery occlusion/reperfusion (MCAO/R) model was established in adult male Sprague-Dawley rats in vivo, and cultured neurons were exposed to oxygen-glucose deprivation/reoxygenation (OGD/R) to mimic ischemia-reperfusion (I/R) injury in vitro. We found that the protein level of TMEM175 decreased after cerebral I/R injury and that TMEM175 overexpression ameliorated MCAO/R-induced brain-cell death and neurobehavioral deficits in vivo. Furthermore, these results were recapitulated in cultured neurons. Acridine orange (AO) staining, as well as LysoSensor Green DND-189, cathepsin-B (CTSB), and cathepsin-D (CTSD) activities, showed that TMEM175 deficiency inhibited the hydrolytic function of lysosomes by affecting lysosomal pH. In contrast, TMEM175 upregulation reversed OGD/R-induced lysosomal dysfunction and impaired mitochondrial accumulation in cultured neurons. TMEM175 deficiency induced by cerebral I/R injury leads to compromised lysosomal pH stability, thus inhibiting the hydrolytic function of lysosomes. Consequently, lysosomal-dependent degradation of damaged mitochondria is suppressed and thereby exacerbates brain damage. Exogenous up-regulation of TMEM175 protein level could reverse the neuronal lysosomal dysfunction after ischemia-reperfusion.
Keywords: Ischemia-reperfusion injury; Ischemic stroke; Lysosome; Neuron; TMEM175.