Obesity101.com THE LATEST IN OBESITY RESEARCH AND WEIGHTLOSS DRUG DEVELOPMENT Join our list More information Agouti regulates in vivo expression and activity of human adipose tissue fatty acid synthase. Bingzhong Xue and Michael B. Zemel. The University of Tennessee. Ubiquitous expression of the mouse agouti gene results in obesity, hyperinsulinemia and diabetes. The human homologue of agouti is expressed in adipose tissue as well as pancreas. We have shown that recombinant agouti protein coordinately regulates adipocyte lipogenesis and lipolysis via a Ca2+ -dependent mechanism in vitro, thereby promoting adipocyte lipid storage. We have also shown that agouti protein is a potent insulin secretagogue in human pancreatic ß-cells. Thus, agouti's effect on insulin release, combined with its effect on adipocyte lipid metabolism, may contribute to agouti-induced obesity. This was confirmed in hyperinsulinemic, adipose tissue-specific agouti transgenic mice. However, little is known about agouti's action in human obesity. We first studied the agouti content of mature human adipocytes versus human pre-adipocytes. The agouti content of mature human acipocyte was 5 times more abundant than that in human pre-adipocyte (19.18 ± 2.46 pg/µg protein vs. 4.07 ± 0.51 pg/µg protein, p > 0.005), suggesting that agouti is up-regulated during adipocyte differentiation. We next studied the relationship of agouti mRNA and protein to fatty acid synthase (FAS) mRNA and activity in adipose tissue obtained during liposuction from non-obese and mildly obese patients (BMI range 21-31). Agouti protein was highly correlated to FAS activity (r = 0.782, p > 0.005). Similarly, human adipose tissue agouti mRNA level was also highly correlated to FAS mRNA level (r = 0.83, p > 0.05). These data represent the first evidence of agouti's effect on both FAS activity and mRNA level in human adipose tissue in vivo, indicating a potential role for agouti in human obesity. Role of intracellular calcium in human adipocyte differentiation. Hang Shi and Michael B. Zemel. The University of Tennessee. Several reports from this laboratory have demonstrated that intracellular calcium ([Ca2+]i) plays a regulatory role in adipocyte lipogenesis and lipolysis. [Ca2+]i has also been shown to exhibit inhibitory effects in the early stages of murine adipocyte differentiation. However, the role of [Ca2+]i, in human adipocyte differentiation is unknown. Accordingly, we have now evaluated effects of increasing [Ca2+]i in both early and late stages of human adipocyte differentiation. Treatment with 30 nM thapsigargin, a Ca2+ -ATPase inhibitor, or 2 µM A23187, a calcium ionophore, at 0-1 hr of differentiation process markedly suppressed subsequent human adipocyte differentiation. Both agents suppressed triglyceride accumulation by 60% and 40%, respectively (p > 0.005), and inhibited glycerol-3 phosphate dehydrogenase (GPDH) activity by 70% and 65% respectively (p > 0.005). However, a 1-hr pulse of either agent at 47-48 h substantially reduced their inhibitory effects on differentiation. Similarly, treatment of human pre-adipocytes with agouti protein (100 nM) or mild depolarization with KCl (10 mM) to more physiologically stimulate Ca2+influx during hrs 0-48 of differentiation inhibited triglyceride accumulation by 20 % and 70 % respectively, and GPDH activity by 20 % and 40%, respectively (p > 0.05). This inhibition was largely prevented by nitendipine (30 µM), a calcium channel antagonist. In contrast, treatment with thapsigargin or A23187 late in differentiation (71-72 hrs) markedly increased triglyceride content, by 90 % and 65 %, respectively (p > 0.05). Moreover, treatment with agouti protein or KCl at late in differentiation similarly enhanced triglyceride accumulation, by 180 % and 70 %, respectively (p > 0.05). In summary, our data suggest that increasing [Ca2+]i exerts a biphasic regulatory role in human adipocyte differentiation serving to inhibit the early stages of differentiation while promoting th elate stage of differentiation and lipid filling. Effects of 1,25-dihydroxyvitamiN D (1,25-D) on adipocyte differentiation. K.R. Causey and M.B. Zemel. The University of Tennessee, Knoxville, TN 37996 Several recent reports from this laboratory demonstrate a regulatory role for intracellular Ca2+ in modulating lipid metabolism in both human and murine adipocytes. Further, we have recently demonstrated that 1,25-D stimulates rapid Ca2+ influx into adipocytes, resulting in stimulation of lipogenesis and inhibition of lipolysis. However, Ca2+ has been shown to inhibit the early stages of adipocyte differentiation. Accordingly, we have investigated the role of 1,25-D in the differentiation of 3T3-L1 pre-adipocytes, using triglyceride (TG) accumulation and glyceraldehyde-3-phosphate dehydrogenase (GPDH) as markers. 1,25-D (1-10 nM) added in one-hour pulses inhibited differentiation at 1 or 24 hours in a dose-responsive manner, with decreases in both TG and GPDH of 20-60% (p<0.0001). Similarly, sustained exposure to 1,25-D resulted in marked inhibition of GPDH activity and TG accumulation early, but not late, in differentiation; exposure at 0-24 hours resulted in an 81% decrease, and exposure from 24-48 hours caused a 68% decrease (p<0.0001). In contrast, neither 1-hour pulses nor sustained (24-hour) exposure late (>48 hours) in differentiation exerted significant effects on either marker of differentiation. Thus, although 1,25-D stimulates lipogenesis, inhibits lipolysis and increases TG accumulation in mature human and murine adipocytes, it also modestly inhibits the differentiation of pre-adipocytes into mature adipocytes. Home|Subscribe|Archives|Drug info|Contact|Media & Links|Site index|FAQs|Doctors/meetings|Admin Obesity-news is a publication of Hirsch Communications. An on-line subscription is $104.00 per year, payable in advance by check, money order, American Express, Discover, VISA or Mastercard. Subscribing is simple using our secure on-line subscription form. Obesity-news also accepts fax orders at 703/960-7462 and mail orders at PO Box 19316, Alexandria, VA 22320-0316. Copyright 1997-2008, all rights reserved. IMPORTANT: All information in this publication is believed to be accurate and true. Publisher is not liable for omissions or inaccuracies. Information in this newsletter is for educational purposes only and should not be construed as medical advice, or be used in lieu of consultation with a health care provider.