Figure 3. Vitamin D activates autophagic flux. (A) Confocal microscopy images of LC3B and LAMP1 in untreated OA chondrocytes and vehicle-, 1,25(OH)₂D3 (20 nM)-, or metformin (1 mM)-treated OA chondrocytes incubated with 20 ng/ml of IL-1β. The bar graph shows the mean Pearson’s correlation coefficient between LC3B and LAMP1. (B) Representative confocal microscopy images demonstrating co-localization of LC3B and MTDR or LAMP1 and MTDR in untreated or IL-1β (20 ng/ml)-treated human OA chondrocytes in the presence or absence of 1,25(OH)₂D3 or metformin (scale bar: 20 µm) (C) Immunoblot showing LC3BI, LC3BII, LAPM1, and β-actin expression in the presence or absence of 1.25(OH)₂D3 in IL-1β-stimulated OA chondrocytes. Bar graph shows the LC3BII/LC3BI ratio, LC3B and LAMP1 activities. (E) OCR kinetics in control and vitamin-D-treated chondrocytes. Bar graphs show basal respiration, ATP-linked, maximal respiration, reserve capacity, and proton leak in control and vitamin-D-treated chondrocytes. Data are presented as means ± SD.

ns, not significant.

^*p<0.05; ^**p<0.005; ^***p<0.001.