Vitamin D₃ inhibits proliferation and the early stage of adipogenic differentiation but promotes gene expression and lipid accumulation during the late stage of adipogenic differentiation in intramuscular adipose cells of Korean native cattle

This study investigated the role of 1,25-dihydroxyvitamin D₃ (vitamin D₃) in regulating adipogenesis in stromal vascular (SV) cells derived from Korean native cattle (Hanwoo), focusing on its dose- (0, 1, 10, and 100 nM) and time-dependent effects across the growth phase and the early(day 3), mid (day 7), and late (day 14) stages of the differentiation phase. SV cells were isolated from the intramuscular fat of the Longissimus thoracis muscle of four female Hanwoo cattle (29 to 32 mo old) raised on the same farm. Vitamin D₃ treatment during the growth phase significantly suppressed preadipocyte proliferation in a dose-dependent manner. Hyperplasia was significantly reduced at 10 and 100 nM of treatment compared to the control group (P < 0.01). During the early differentiation phase, high concentrations of vitamin D₃ (10 and 100 nM) delayed differentiation by suppressing the expression of Zfp423 and PPARγ, key transcription factors involved in preadipocyte determination and commitment (P < 0.05). In the mid-differentiation phase, 10 and 100 nM of vitamin D₃ significantly upregulated the expression of FABP4 and PPARγ compared to the control (P < 0.01), while no significant differences were observed in lipid accumulation or droplet size. In the late differentiation phase, 10 nM significantly increased the expression of PPARγ and FABP4 compared to the control group (P < 0.01), while enhanced lipid accumulation was observed at 1 and 10 nM of treatment (P < 0.01). Notably, lipid droplet size was significantly increased only at 1 nM compared to all other treatments (P < 0.01). These findings demonstrate the dual role of vitamin D₃ in adipogenesis. During the growth phase, vitamin D₃ inhibits hyperplasia by suppressing preadipocyte proliferation in a dose-dependent manner. During the differentiation phase, vitamin D₃ exhibits stage-specific effects, delaying differentiation in the early phase while promoting adipocyte maturation in the late phase through enhanced lipid accumulation and hypertrophy.