Fig. 2: Enhancing the UPR^mt improves mitochondrial function in stressed primary mouse chondrocytes.

a Compared with control chondrocytes, chondrocytes treated with NR (1 mmol/l) showed increased mRNA levels of Hsp10, Hsp60, mtDNAj, Atf5, ClpP, and LonP1. **p < 0.01, ***p < 0.001; NS = not significant; n = 3. b Electron micrographs of chondrocytes showing intact mitochondria (white arrow, control, and IL-1β + NR groups) with well-preserved double membranes and cristae structures and fragmented mitochondria (black arrow, IL-1β group) with deformed or absent cristae structures. Scale bar, 500 nm. c–f Mitochondrial respiratory chain complex I–IV activity in chondrocytes treated with IL-1β. *p < 0.05, **p < 0.01 compared with the control group; NS = not significant; n = 3. g Flow cytometric analysis of JC‑1 distribution in chondrocytes. h The JC-1 ratio was calculated as the number of green JC-1-positive mitochondria relative to the number of red JC-1-positive mitochondria. **p < 0.01; n = 3.