Effects of 1,25(OH)₂ D₃ on lipid droplet growth in adipocytes

This study aimed to explore the effects of 1,25(OH)₂ D₃ on lipid droplet (LD) growth in 3T3-L1 adipocytes of hypertrophy model. Cocktail method was used to induce differentiation in 3T3-L1 cells. After 8 days, the cells were modeled by 100, 300, 600, and 900 μM palmitic acid (PA) for 24 hr. The best concentration of modeling was screened by MTT results and triglycerides (TG) content. The model cells were intervened by 1, 10, and 100 nM 1,25(OH)₂ D₃ for 24 hr. Then, the TG content of cells were detected and stained by oil red O. The diameter and quantity of LDs were analyzed. mRNA relative expression levels of genes related to LD (CIDE-a, Fsp27, PLIN-1), upstream response factor (PPAR-α, PPAR-γ, and VDR), and TG metabolism (long chain acyl-CoA synthetase 3, 1-acylglycerol-3-phosphate O-acyltransferase 1, adipose triglyceride lipase, diacylglycerol acyltransferase 1, diacylglycerol acyltransferase 2, glycerol-3-phosphate O-acyltransferase 3, glycerol-3-phosphate O-acyltransferase 4, hormone-sensitive lipase, mannosyl (alpha-1,3-)-glycoprotein beta-1,2-N-acetyl glucosaminyl transferase, phosphatidic acid phosphatase, and uncoupling protein-1) were detected by RT-qPCR. A total of 300 μM PA was selected as the optimum concentration. Compared with model group, 10 and 100 nM 1,25(OH)₂ D₃ decreased the average diameter, increased the quantity of LDs, upregulated PPAR-α and PLIN-1 mRNA expression levels, and downregulated CIDE-a and Fsp27 mRNA expression levels significantly (p < .05). However, 1 nM 1,25(OH)₂ D₃ did not alter LD morphology and TG content. mRNA expression levels of long chain acyl-CoA synthetase 3, 1-acylglycerol-3-phosphate O-acyltransferase 1, diacylglycerol acyltransferase 2, glycerol-3-phosphate O-acyltransferase 3, and glycerol-3-phosphate O-acyltransferase 4 in 10 and 100 nM groups were significantly lower than those in the model group (p < .05); mRNA expression levels of adipose triglyceride lipase, diacylglycerol acyltransferase 1, hormone-sensitive lipase, mannosyl (alpha-1,3-)-glycoprotein beta-1,2-N-acetyl glucosaminyl transferase, phosphatidic acid phosphatase, and uncoupling protein-1 were significantly increased in the 100 nM group (p < .05). The 10 and 100 nM 1,25(OH)₂ D₃ can inhibit LD fusion, promote LD decomposition, reduce LD volume, and inhibit lipogenesis through the PPAR-α signaling pathway.