Date of Award
Master of Science
Michael B. Zemel
Jay Whelan, Jean Skinner
Several recent reports from this laboratory demonstrate a regulatory role for intracellular Ca2+ ([Ca2+]1) in modulating lipid metabolism in both human and murine adipocytes, with increased [Ca2+]1 coordinately stimulating lipogenesis and inhibiting lipolysis, thereby expanding lipid mass. Further, we have recently demonstrated that 1,25-dihydroxyvitamin-D3 [1,25-(OH)2-D3] stimulates adipocyte membrane vitamin D receptor (mVDR)-mediated rapid Ca2+ influx into adipocytes, resulting in the stimulation of lipogenesis and inhibition of lipolysis. However, increasing [Ca2+]1 in the early stages of differentiation inhibits human adipocyte differentiation, whereas increasing [Ca2+]1 in the late stage promotes human adipocyte differentiation Accordingly, we have investigated the role of 1,25-(OH)2-D3 in the differentiation of 3T3-L1 preadipocytes, using triglyceride (TG) accumulation and glycerol-3-phosphate dehydrogenase (GPDH) as markers. 3T3-L1 preadipocytes were placed in differentiation media upon confluence, and exposed to varying amounts (0, 1nM, and 10nM) of 1,25-(OH)2-D3 for either one-hour pulses or for sustained (24 hrs or 48 hrs) amounts of time throughout the differentiation process Exposure to one-hour pulses of 1nM 1,25-(OH)2-D3 throughout differentiation caused modest decreases (31%-38%) in TG accumulation (p<0.0001), with one-hour pulse exposure to 10nM 1,25-(OH)2-D3 having little to no effect on TG accumulation. One-hour pulse exposure to both 1nM and 10nM 1,25-(OH)2-D3 suppressed GPDH activity early, but not late in differentiation. Sustained (24-hour) exposure to 1,25-(OH)2-D3 (1nM and 10nM) inhibited differentiation at 0-24 hrs, with decreases in both TG and GPDH of 41-81% (p<0.0001). Similarly, sustained exposure of 1,25-(OH)2-D3 resulted in marked inhibition of GPDH activity and TG accumulation early in differentiation. In contrast, sustained exposure late in differentiation exerted no significant effects on either marker of differentiation PPAR-γ and pref-1 expression were also used as markers of differentiation. One-hour pulses of 10nM 1,25-(OH)2-D3 did not cause any changes in PPAR-γ expression compared to control. Sustained exposure to 1,25-(OH)2-D3 throughout differentiation decreased PPAR-γ expression, with a 92% decrease from 0-48h (p<0.0001). One-hour pulses of 1,25-(OH)2-D3 had no effect on Pref-1 expression, with the exception of an increase in expression at 47-48 hr (p<0.0001). Sustained exposure to 10nM 1,25-(OH)2-D3 at 0-48 hrs, 24-48 hrs and 47- 48 hrs all caused significant increases (125%-146%) in the expression of Pref-1 (p<0.001). Thus, although 1,25-(OH)2-D3 stimulates lipogenesis, inhibits lipolysis and increases TG accumulation in mature human and murine adipocytes, it also modestly inhibits the differentiation of preadipocytes into mature adipocytes.
Coenen, Kimberly Ray Causey, "Effects of 1,25-Dihydroxyvitamin D₃ on adipocyte differentiation. " Master's Thesis, University of Tennessee, 2003.