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. Author manuscript; available in PMC: 2020 Mar 1.
Published in final edited form as: J Nutr Biochem. 2018 Nov 22;65:83–92. doi: 10.1016/j.jnutbio.2018.11.002

Fig. 6. Graphical abstract and working hypothesis.

Fig. 6.

VitD treatment increases IMCL accumulation, mRNA associated with both lipid storage and lipolysis, and mitochondrial respiration in skeletal muscle, but increases in lipolytic gene expression and mitochondrial respiration are dependent on PLIN2 expression. Calcitriol treatment (VitD) increases gene expression of lipid droplet proteins PLIN2, ATGL, and CGI-58 (top). VitD also increases mRNA expression for DGAT proteins that localize to both the endoplasmic reticulum for new lipid droplet synthesis (DGAT1) and to mature lipid droplets (DGAT2). These genes together are associated with increased capacity for IMCL accumulation and lipolysis and correspond with increased mitochondrial respiration. PLIN2 knockdown with siRNA before VitD treatment (bottom) decreases the expression of not only PLIN2 but also lipolytic cofactor CGI-58 and lipid droplet refilling gene DGAT2 (indicated by faded shapes and hashed lines). This is associated with decreases in CPT1 mRNA expression and mitochondrial respiration. VitD = Calcitriol; PLIN2 = Perilipin 2; DGAT2 = diglyceride O-acyltransferase 2; DGAT1 = diglyceride O-acyltransferase 1; ATGL = adipose triglyceride lipase; CGI-58 = comparative gene identifier 58; CPT-1 = carnitine palmitoyltransferase 1.