PACAP promotes mitochondrial biogenesis in rat primary chondrocytes via the SIRT1/PGC-1α pathway

Mitochondrial biogenesis is essential for maintaining energy homeostasis and chondrocyte function in articular cartilage, and its impairment contributes to cartilage degeneration and osteoarthritis pathogenesis. PACAP (pituitary adenylate cyclase-activating polypeptide) has recently emerged as a regulator of cellular metabolism, but its role in chondrocyte mitochondrial biology remains unclear. In this study, we investigated whether PACAP38 promotes mitochondrial biogenesis in rat primary chondrocytes. Cells were treated with PACAP38 (50 or 100 nM) for 48 h. PACAP38 enhanced mitochondrial function in a dose-dependent manner, as evidenced by increased complex I activity, maximal oxygen consumption rate (OCR), and ATP production. PACAP38 also increased the mtDNA/nDNA ratio and the protein expression of mitochondrial complex subunits NDUFB8 and MTCO2, indicating enhanced mitochondrial biogenesis. MitoTracker red staining further revealed that PACAP38 significantly increased mitochondrial mass. Mechanistically, PACAP38 upregulated the expression of Nrf1 and TFAM, two key transcription factors for mitochondrial biogenesis, at both mRNA and protein levels. Moreover, PACAP38 increased SIRT1 expression and decreased acetylated PGC-1α levels. Notably, shRNA-mediated silencing of either SIRT1 or its downstream target PGC-1α abolished the upregulation of Nrf1 and TFAM, the increase in mitochondrial mass, and the enhancement of ATP production. Collectively, these findings demonstrate that PACAP38 promotes mitochondrial biogenesis in rat primary chondrocytes through the SIRT1/PGC-1α signaling pathway, suggesting a potential therapeutic target for cartilage degenerative diseases.