ABSTRACT
We tested the hypothesis that activation of transient receptor potential vanilloid type-1 (TRPV1) by capsaicin prevents adipogenesis. TRPV1 channels in 3T3-L1-preadipocytes and visceral adipose tissue from mice and humans were detected by immunoblotting and quantitative real-time RT-PCR. The effect of TRPV1 on cytosolic calcium was determined fluorometrically in 3T3-L1-preadipocytes and in human visceral fat tissue. Adipogenesis in stimulated 3T3-L1-preadipocytes was determined by oil red O-staining of intracellular lipid droplets, triglyceride levels, expression of peroxisome proliferator-activated receptor-gamma, and expression of fatty acid synthase. Long-term feeding experiments were undertaken in wild-type mice and TRPV1 knockout mice. We detected TRPV1 channels in 3T3-L1-preadipocytes and visceral adipose tissue from mice and humans. In vitro, the TRPV1 agonist capsaicin dose-dependently induced calcium influx and prevented the adipogenesis in stimulated 3T3-L1-preadipocytes. RNA interference knockdown of TRPV1 in 3T3-L1-preadipocytes attenuated capsaicin-induced calcium influx, and adipogenesis in stimulated 3T3-L1-preadipocytes was no longer prevented. During regular adipogenesis TRPV1 channels were downregulated which was accompanied by a significant and time-dependent reduction of calcium influx. Compared with lean counterparts in visceral adipose tissue from obese db/db and ob/ob mice, and from obese human male subjects we observed a reduced TRVP1 expression. The reduced TRPV1 expression in visceral adipose tissue from obese humans was accompanied by reduced capsaicin-induced calcium influx. The oral administration of capsaicin for 120 days prevented obesity in male wild type mice but not in TRPV1 knockout mice assigned to high fat diet. We conclude that the activation of TRPV1 channels by capsaicin prevented adipogenesis and obesity.
Subject(s)
Capsaicin/pharmacology , Obesity/prevention & control , TRPV Cation Channels/metabolism , 3T3-L1 Cells , Adipocytes/metabolism , Adipogenesis , Adipose Tissue/metabolism , Animals , Calcium/metabolism , Humans , Male , Mice , Mice, Inbred C57BL , Mice, Inbred NOD , Mice, Knockout , Mice, Obese , RNA, Small Interfering/pharmacology , Stem Cells/metabolism , TRPV Cation Channels/agonists , TRPV Cation Channels/deficiency , TRPV Cation Channels/drug effects , TRPV Cation Channels/genetics , VisceraABSTRACT
Obesity is one major cardiovascular risk factor. We tested effects of endurance exercise on cannabinoid receptor type 1 (CB1) and peroxisome proliferator-activated receptor-delta (PPAR-delta)-dependent pathways in adipose tissue. Male Wistar rats were randomly assigned to standard laboratory chow or a high-fat diet without and with regular endurance exercise. Exercise in rats on high-fat diet significantly reduced visceral fat mass, blood pressure, and adipocyte size (each p<0.05). Adipocyte hypertrophy induced by high-fat diet was accompanied by increased CB1 expression in adipose tissue, whereas exercise significantly reduced CB1 expression (each p<0.05). CB1 receptor expression and adipocyte differentiation were directly regulated by PPAR-delta. Adipocyte hypertrophy induced by high-fat diet was accompanied by reduced PPAR-delta. Furthermore, selective silencing of PPAR-delta by RNA interference in 3T3-L1-preadipocyte cells significantly increased CB1 expression from 1.00+/-0.06 (n=3) to 1.91+/-0.06 (n=3; p<0.01) and increased adipocyte differentiation, whereas adenovirus-mediated overexpression of PPAR-delta significantly reduced CB1 expression to 0.39+/-0.03 (n=3; p<0.01) and reduced adipocyte differentiation. In the presence of the CB1 antagonist rimonabant adipocyte differentiation in stimulated 3T3 L1 preadipocyte cells was significantly reduced. The study indicates that high-fat diet-induced hypertrophy of adipocytes is associated with increased CB1 receptor expression which is directly regulated by PPAR-delta. Both CB1 and PPAR-delta are intimately involved in therapeutic interventions against a most important cardiovascular risk factor.
Subject(s)
Adipose Tissue/metabolism , PPAR delta/physiology , Physical Conditioning, Animal/physiology , Receptor, Cannabinoid, CB1/physiology , 3T3 Cells , Animals , Disease Models, Animal , Male , Metabolic Syndrome/metabolism , Mice , Obesity/metabolism , Rats , Rats, Wistar , Receptor, Cannabinoid, CB1/metabolismABSTRACT
OBJECTIVE: To investigate the renin-angiotensin system (RAS) in mesenteric adipose tissues and effect of angiotensin II on adipocyte differentiation. METHODS: Thirty normal 8-week-old male Wistar rats were divided into groups on normal diet and high-fat diet. The rats on high-fat diet for 24 weeks developed the metabolic syndrome respectively. The mRNA and protein expression of mesenteric adipose tissue were measured by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot. Lipid drop in 3T3-L1 preadipocytes and mature adipocytes were observed using oil-red O staining. The fluorescence microscope was used to detect cytosolic-free calcium in 3T3-L1 preadipocytes and mature adipocytes. RESULTS: The expressions of angiotensinogen, angiotensin converting enzyme, angiotensin II receptor type 1 in mesenteric adipose tissue were significantly increased in rats with metabolic syndrome compared with those in rats on normal diet (P <0. 05, P <0. 01). After administration of angiotensin II , no lipid droplet in 3T3 -L1 preadipocytes and adipocytes were observed, however, intensive lipid droplet in adipocyte was found after administration of captopril and candesartan. Angiotensin II increased the intracellular-free calcium concentration in preadipocytes (P < 0. 01 ) , which was blocked by captopril and candesartan; in contrast, angiotensin II effect was blunt in mature adipocyte. Captopril and candesartan partially recovered the angiotensin II -mediated increase of cytosolic-free calcium. CONCLUSION: RAS in the mesenteric adipose tissues is active in rats with metabolic syndrome, and antagonization of RAS can recover the lipogenesis of adipocyte.
