Zhidan Luo

Activation of TRPV1 by Dietary Capsaicin Improves Endothelium-Dependent Vasorelaxation and Prevents Hypertension

Some plant-based diets lower the cardiometabolic risks and prevalence of hypertension. New evidence implies a role for the transient receptor potential vanilloid 1 (TRPV1) cation channel in the pathogenesis of cardiometabolic diseases. Little is known about impact of chronic TRPV1 activation on the regulation of vascular function and blood pressure. Here we report that chronic TRPV1 activation by dietary capsaicin increases the phosphorylation of protein kinase A (PKA) and eNOS and thus production of nitric oxide (NO) in endothelial cells, which is calcium dependent. TRPV1 activation by capsaicin enhances endothelium-dependent relaxation in wild-type mice, an effect absent in TRPV1-deficient mice. Long-term stimulation of TRPV1 can activate PKA, which contributes to increased eNOS phosphorylation, improves vasorelaxation, and lowers blood pressure in genetically hypertensive rats. We conclude that TRPV1 activation by dietary capsaicin improves endothelial function. TRPV1-mediated increase in NO production may represent a promising target for therapeutic intervention of hypertension.

Activation of the cold-sensing TRPM8 channel triggers UCP1-dependent thermogenesis and prevents obesity

Brown adipose tissue (BAT) is an energy-expending organ that produces heat. Expansion or activation of BAT prevents obesity and diabetes. Chronic cold exposure enhances thermogenesis in BAT through uncoupling protein 1 (UCP1) activation triggered via a β-adrenergic pathway. Here, we report that the cold-sensing transient receptor potential melastatin 8 (TRPM8) is functionally present in mouse BAT. Challenging brown adipocytes with menthol, a TRPM8 agonist, up-regulates UCP1 expression and requires protein kinase A activation. Upon mimicking long-term cold exposure with chronic dietary menthol application, menthol significantly increased the core temperatures and locomotor activity in wild-type mice; these effects were absent in both TRPM8(-/-) and UCP1(-/-) mice. Dietary obesity and glucose abnormalities were also prevented by menthol treatment. Our results reveal a previously unrecognized role for TRPM8, suggesting that stimulation of this channel mediates BAT thermogenesis, which could constitute a promising way to treat obesity.

Increased Transient Receptor Potential Canonical Type 3 Channels in Vasculature From Hypertensive Rats

We tested the hypothesis that transient receptor potential canonical type 3 (TRPC3) channels are increased in vascular smooth muscle cells and aortic tissue from spontaneously hypertensive rats (SHR) compared with normotensive Wistar Kyoto rats. Expression of TRPC3 was analyzed by immunohistochemistry and Western blotting. TRPC3 gene knockdown was performed by specific small interfering RNA and TRPC3 overexpression using the pAdEasy-1 system. Cytosolic calcium was measured using fluorescence spectrophotometry and vasoconstriction of aortic rings using a force transducer. In SHR, the expression of TRPC3 channel protein was significantly higher in aortic rings (1.48±0.05 versus 1.00±0.06; each n=6; P<0.01) and vascular smooth muscle cells (1.28±0.08 versus 1.00±0.03; each n=6; P<0.05) compared with Wistar Kyoto rats. Knockdown of TRPC3 gene expression by specific small interfering RNA significantly reduced the angiotensin II–induced calcium influx by 30±3% (n=6; P<0.01), whereas TRPC3 overexpression significantly increased it by 55±3% (n=6; P<0.01). The angiotensin II–induced calcium increase was significantly enhanced in vascular smooth muscle cells from SHR compared with Wistar Kyoto rats, even in the presence of the calcium channel blocker amlodipine. Angiotensin II significantly elevated the TRPC3 channel protein expression in vascular smooth muscle cells from SHR from 1.28±0.08 to 1.61±0.08 (each n=6; P<0.01). Angiotensin II–induced TRPC3 expression was prevented by telmisartan. Administration of telmisartan to SHR for 4 weeks significantly reduced blood pressure, angiotensin II–induced vasoconstriction, and TRPC3 channel protein expression in aortic tissue. TRPC3 expression was not significantly reduced after reduction of blood pressure in SHR using amlodipine. In conclusion, we give experimental evidence that increased TRPC3 channel protein expression in the vasculature is important for elevated blood pressure.

Telmisartan Prevents Weight Gain and Obesity Through Activation of Peroxisome Proliferator-Activated Receptor-δ–Dependent Pathways

Telmisartan shows antihypertensive and several pleiotropic effects that interact with metabolic pathways. In the present study we tested the hypothesis that telmisartan prevents adipogenesis in vitro and weight gain in vivo through activation of peroxisome proliferator-activated receptor (PPAR)-&dgr;-dependent pathways in several tissues. In vitro, telmisartan significantly upregulated PPAR-&dgr; expression in 3T3-L1 preadipocytes in a time- and dose-dependent manner. Other than enhancing PPAR-&dgr; expression by 68.2±17.3% and PPAR-&dgr; activity by 102.0±9.0%, telmisartan also upregulated PPAR-&ggr; expression, whereas neither candesartan nor losartan affected PPAR-&dgr; expression. In vivo, long-term administration of telmisartan significantly reduced visceral fat and prevented high-fat diet-induced obesity in wild-type mice and hypertensive rats but not in PPAR-&dgr; knockout mice. Administration of telmisartan did not influence food intake in mice. Telmisartan influenced several lipolytic and energy uncoupling related proteins (UCPs) and enhanced phosphorylated protein kinase A and hormone sensitive lipase but reduced perilipin expression and finally inhibited adipogenesis in 3T3-L1 preadipocytes. Telmisartan-associated reduction of adipogenesis in preadipocytes was significantly blocked after PPAR-&dgr; gene knockout. Chronic telmisartan treatment upregulated the expressions of protein kinase A, hormone-sensitive lipase, and uncoupling protein 1 but reduced perilipin expression in adipose tissue and increased uncoupling protein 2 and 3 expression in skeletal muscle in wild-type mice but not in PPAR-&dgr; knockout mice. We conclude that telmisartan prevents adipogenesis and weight gain through activation of PPAR-&dgr;-dependent lipolytic pathways and energy uncoupling in several tissues.

TRPV1 activation improves exercise endurance and energy metabolism through PGC-1α upregulation in mice

Impaired aerobic exercise capacity and skeletal muscle dysfunction are associated with cardiometabolic diseases. Acute administration of capsaicin enhances exercise endurance in rodents, but the long-term effect of dietary capsaicin is unknown. The capsaicin receptor, the transient receptor potential vanilloid 1 (TRPV1) cation channel has been detected in skeletal muscle, the role of which remains unclear. Here we report the function of TRPV1 in cultured C2C12 myocytes and the effect of TRPV1 activation by dietary capsaicin on energy metabolism and exercise endurance of skeletal muscles in mice. In vitro, capsaicin increased cytosolic free calcium and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) expression in C2C12 myotubes through activating TRPV1. In vivo, PGC-1α in skeletal muscle was upregulated by capsaicin-induced TRPV1 activation or genetic overexpression of TRPV1 in mice. TRPV1 activation increased the expression of genes involved in fatty acid oxidation and mitochondrial respiration, promoted mitochondrial biogenesis, increased oxidative fibers, enhanced exercise endurance and prevented high-fat diet-induced metabolic disorders. Importantly, these effects of capsaicin were absent in TRPV1-deficient mice. We conclude that TRPV1 activation by dietary capsaicin improves energy metabolism and exercise endurance by upregulating PGC-1α in skeletal muscles. The present results indicate a novel therapeutic strategy for managing metabolic diseases and improving exercise endurance.

Perivascular fat-mediated vascular dysfunction and remodeling through the AMPK/mTOR pathway in high-fat diet-induced obese rats

Perivascular adipose tissue (PVAT) is implicated in the regulation of vascular function in the physiological state, but the modulatory effect of PVAT on vasculature during obesity is poorly understood. Endothelial nitric oxide synthase (eNOS), AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) participate in the regulation of vascular function. We therefore investigated whether PVAT has a potential role through the AMPK/mTOR pathway in obesity-related vascular dysfunction. Wistar rats on a high-fat diet (HFD) for 6 months had higher periaortic fat mass compared with rats on a chow diet (3.31±0.56 vs. 2.34±0.28 g, P<0.05). Obesity-related impairment of endothelium-dependent relaxation of the aorta was markedly attenuated by temporary periaortic fat removal whereas obesity-related enhancement of contractile performance was unaffected. Rats on an HFD had thicker aortic tunica medias (180.06±7.56 vs. 128.14±13.21 μm for rats on a chow diet, P<0.01) and larger periaortic adipocytes than rats on a chow diet (1209.00±62.65 vs. 447.20±21.31 μm2, respectively, P<0.01). Furthermore, mesenteric arterial rings incubated with periaortic fat from rats on an HFD demonstrated lower endothelium-dependent relaxation. This effect was absent in mesenteric arterial rings incubated with periaortic fat from rats on a chow diet. Moreover, an HFD led to a downregulation of AMPK and eNOS in the aorta with a concurrent upregulation of mTOR. In a parallel in vitro study, culturing vascular smooth muscle cells with periaortic adipocytes from rats on an HFD reduced the AMPK phosphorylation and increased mTOR phosphorylation, and the latter one was blocked by the incubation of compound C. We conclude that PVAT likely impacts obesity-related vascular dysfunction and remodeling through impairment of eNOS-mediated vasodilatation and the AMPK/mTOR pathway.

Activation of TRPV1 reduces vascular lipid accumulation and attenuates atherosclerosis

AIMS Activation of transient receptor potential vanilloid type-1 (TRPV1) channels may affect lipid storage and the cellular inflammatory response. Now, we tested the hypothesis that activation of TRPV1 channels attenuates atherosclerosis in apolipoprotein E knockout mice (ApoE(-/-)) but not ApoE(-/-)TRPV1(-/-) double knockout mice on a high-fat diet. METHODS AND RESULTS Both TRPV1 mRNA and protein expression were identified in vascular smooth muscle cells (VSMC) and in aorta from C57BL/6J mice using RT-PCR, immunoblotting, and immunohistochemistry. In vitro, activation of TRPV1 by the specific agonists capsaicin and resiniferatoxin dose-dependently increased cytosolic calcium and significantly reduced the accumulation of lipids in VSMC from C57BL/6J mice but not from TRPV1(-/-) mice. TRPV1 activation increased ATP-binding cassette transporter A1 (ABCA1) expression and reduced low-density lipoprotein-related protein 1 (LRP1) expression in VSMC by calcium-dependent and calcineurin- and protein kinase A-dependent mechanisms. These results showed increased cellular cholesterol efflux and reduced cholesterol uptake. In vivo, long-term activation of TRPV1 by capsaicin for 24 weeks increased ABCA1 and reduced LRP1 expression in aorta from ApoE(-/-) mice on a high-fat diet. Long-term activation of TRPV1 significantly reduced lipid storage and atherosclerotic lesions in the aortic sinus and in the thoracoabdominal aorta from ApoE(-/-) mice but not from ApoE(-/-)TRPV1(-/-) mice on a high-fat diet. These findings indicated that TRPV1 activation ameliorates high-fat diet-induced atherosclerosis. CONCLUSION Activation of TRPV1 may be a novel therapeutic tool to attenuate atherosclerosis caused by a high-fat diet.

TRP channels and their implications in metabolic diseases

The transient receptor potential (TRP) channel superfamily is composed of 28 nonselective cation channels that are ubiquitously expressed in many cell types and have considerable functional diversity. Although changes in TRP channel expression and function have been reported in cardiovascular disease and renal disorders, the pathogenic roles of TRP channels in metabolic diseases have not been systemically reviewed. In this review, we summarised the distribution of TRP channels in several metabolic tissues and discussed their roles in mediating and regulating various physiological and pathophysiological metabolic processes and diseases including diabetes, obesity, dyslipidaemia, metabolic syndrome, atherosclerosis, metabolic bone diseases and electrolyte disturbances. This review provides new insight into the involvement of TRP channels in the pathogenesis of metabolic disorders and implicates these channels as potential therapeutic targets for the management of metabolic diseases.

Activation of Transient Receptor Potential Vanilloid 1 by Dietary Capsaicin Delays the Onset of Stroke in Stroke-Prone Spontaneously Hypertensive Rats

Background and Purpose— Previous studies show that endothelial nitric oxide synthase (eNOS) plays a prominent role in maintaining cerebral blood flow and preventing stroke. Capsaicin in hot pepper can increase the phosphorylation of eNOS in endothelial cells. We test the hypothesis that chronic dietary capsaicin can prevent stroke through activation of cerebrovascular transient receptor potential vanilloid 1 (TRPV1) channels in stroke-prone spontaneously hypertensive rats (SHRsp). Methods— SHRsp were fed dietary capsaicin, and their onset of stroke was examined. TRPV1 knockout and transgenic mice were used for determining the function of TRPV1 channels. Expression of eNOS and cerebrovascular reactivity were examined. Results— Immunofluorescence showed TRPV1 channels and eNOS coexpression in cerebral arterioles. Administration of capsaicin significantly increased phosphorylated eNOS in carotid arteries from wild-type mice but not in TRPV1 knockout mice. Inhibition of eNOS using NG-nitro-L-arginine methyl ester, removal of endothelium, or mutant TRPV1 significantly reduced capsaicin-induced endothelium-dependent relaxation of basilar arteries in mice. Chronic dietary capsaicin also remarkably increased eNOS expression in carotid arteries from SHRsp. Compared with Wistar-Kyoto rats, SHRsp had impaired endothelium-dependent relaxation of basilar arteries. Administration of capsaicin or L-arginine significantly improved the endothelium-dependent relaxation of basilar arteries in SHRsp. SHRsp had hypertrophy of cerebral arterioles, which was reversed by dietary capsaicin. Importantly, long-term administration of capsaicin significantly delayed the onset of stroke and increased the survival time in SHRsp. Conclusions— Activation of TRPV1 channels by dietary capsaicin mediated increases in phosphorylation of eNOS and could represent a novel target for dietary intervention of stroke.

Angiotensin II receptor blocker telmisartan enhances running endurance of skeletal muscle through activation of the PPAR-δ/AMPK pathway

Clinical trials have shown that angiotensin II receptor blockers reduce the new onset of diabetes in hypertensives; however, the underlying mechanisms remain unknown. We investigated the effects of telmisartan on peroxisome proliferator activated receptor γ (PPAR‐δ) and the adenosine monophosphate (AMP)‐activated protein kinase (AMPK) pathway in cultured myotubes, as well as on the running endurance of wild‐type and PPAR‐δ‐deficient mice. Administration of telmisartan up‐regulated levels of PPAR‐δ and phospho‐AMPKα in cultured myotubes. However, PPAR‐δ gene deficiency completely abolished the telmisartan effect on phospho‐AMPKαin vitro. Chronic administration of telmisartan remarkably prevented weight gain, enhanced running endurance and post‐exercise oxygen consumption, and increased slow‐twitch skeletal muscle fibres in wild‐type mice, but these effects were absent in PPAR‐δ‐deficient mice. The mechanism is involved in PPAR‐δ‐mediated stimulation of the AMPK pathway. Compared to the control mice, phospho‐AMPKα level in skeletal muscle was up‐regulated in mice treated with telmisartan. In contrast, phospho‐AMPKα expression in skeletal muscle was unchanged in PPAR‐δ‐deficient mice treated with telmisartan. These findings highlight the ability of telmisartan to improve skeletal muscle function, and they implicate PPAR‐δ as a potential therapeutic target for the prevention of type 2 diabetes.