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1,25‐Dihydroxyvitamin D Regulates Energy Substrate Metabolism to Reduce Triacylglycerol Accumulation in 3T3‐L1 Adipocytes
Author(s) -
Larrick Brienna M,
KeeHong Kim,
Donkin Shawn S,
Teegarden Dorothy
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.128.2
Subject(s) - chemistry , lipolysis , adipose tissue , oleic acid , palmitic acid , adipocyte , palmitoleic acid , medicine , endocrinology , fatty acid , vitamin , lipogenesis , lipid metabolism , metabolism , vitamin d and neurology , biochemistry , lipid droplet , biology
It is well established that vitamin D is sequestered in adipose tissue. Many studies have demonstrated vitamin D regulation of adipocyte differentiation, inflammation, and energy metabolism, highlighting the multifaceted role that vitamin D plays in adipose tissue physiology. However, whether vitamin D impacts lipid metabolism in terminally differentiated adipocytes is not yet known. To study this, 3T3‐L1 adipocytes were differentiated for 9 days, followed by stimulation with 1,25‐dihydroxyvitamin D (1,25(OH) 2 D, 10 nM) or vehicle for the times indicated. All data are normalized to protein content, determined using the bicinchoninic acid (BCA) assay. We previously demonstrated that 1,25(OH) 2 D, the bioactive vitamin D metabolite, stimulates a 21% reduction in TAG accumulation in differentiated 3T3‐L1 adipocytes after 4 days (p=0.01). This occurs despite a significant increase in fatty acid uptake, assessed using BODIPY FL C16, following 1–4 days of treatment (p<0.01), and with concomitant stimulation of PKA‐dependent lipolysis (p<0.01). In our current studies, we demonstrate that 1,25(OH) 2 D stimulates a 2.5‐fold increase in complete fatty acid oxidation (p<0.01), assessed by quantifying the production of 14 CO 2 from [1‐ 14 C] palmitic acid. Further, 1,25(OH) 2 D stimulates slight inhibition of de novo fatty acid synthesis, evidenced by a 10% reduction in [ 13 C 2 ]acetate incorporation into palmitic, palmitoleic, stearic, and oleic acids (p=0.03), determined by liquid chromatography‐mass spectrometry (LC‐MS). Interestingly, D‐[U‐ 13 C]glucose incorporation into these fatty acids was reduced by 30% in response to 1,25(OH) 2 D (p<0.01), indicating a reduced contribution of glucose as a substrate for de novo lipogenesis. Consistent with these results, the mRNA expression of pyruvate carboxylase (PC) is reduced by 40% in response to 1,25(OH) 2 D (p<0.01). PC catalyzes the carboxylation of pyruvate to form the tricarboxylic acid (TCA) cycle intermediate oxaloacetate, which may then be used to synthesize acetyl‐CoA and glycerol for triacylglycerol synthesis. In summary, 1,25(OH) 2 D stimulates fatty acid turnover in 3T3‐L1 adipocytes, characterized by stimulation of PKA‐dependent lipolysis and fatty acid uptake. Further, 1,25(OH) 2 D stimulates fatty acid oxidation, while reducing glucose utilization as a substrate for fatty acid synthesis, possibly through reduced flux of pyruvate into the TCA cycle. Collectively, these changes in lipid metabolism may contribute to the reduction in TAG accumulation that is stimulated by 1,25(OH) 2 D, and may be protective against excessive fat mass accumulation and associated metabolic disorders. Support or Funding Information Supported by the Purdue University Center for Cancer Research: Obesity and Cancer Discovery Group (CA023168) and a Project Development Team within the ICTSI NIH/NCRR (UL1TR001108).