Carbon monoxide stimulates astrocytic mitochondrial biogenesis via L-type Ca²⁺ channel-mediated PGC-1α/ERRα activation

Carbon monoxide (CO), derived by the enzymatic reaction of heme oxygenase (HO), is a cellular regulator of energy metabolism and cytoprotection; however, its underlying mechanism has not been clearly elucidated. Astrocytes pre-exposed to the CO-releasing compound CORM-2 increased mitochondrial biogenesis, mitochondrial electron transport components (cytochrome c, Cyt c; cytochrome c oxidase subunit 2, COX2), and ATP synthesis. The increased mitochondrial function was correlated with activation of AMP-activated protein kinase α and upregulation of HO-1, peroxisome proliferators-activated receptor γ-coactivator-1α (PGC-1α), and estrogen-related receptor α (ERRα). These events elicited by CORM-2 were suppressed by Ca²⁺ chelators, a HO inhibitor, and an L-type Ca²⁺ channel blocker, but not other Ca²⁺ channel inhibitors. Among the HO byproducts, combined CORM-2 and bilirubin treatment effectively increased PGC-1α, Cyt c and COX2 expression, mitochondrial biogenesis, and ATP synthesis, and these increases were blocked by Ca²⁺ chelators. Moreover, cerebral ischemia significantly increased HO-1, PGC-1α, and ERRα levels, subsequently increasing Cyt c and COX2 expression, in wild-type mice, compared with HO-1^+/− mice. These results suggest that HO-1-derived CO enhances mitochondrial biogenesis in astrocytes by activating L-type Ca²⁺ channel-mediated PGC-1α/ERRα axis, leading to maintenance of astrocyte function and neuroprotection/recovery against damage of brain function.