Shuangtao Ma

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.

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.

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.

Increased rhythmicity in hypertensive arterial smooth muscle is linked to transient receptor potential canonical channels

Vasomotion describes oscillations of arterial vascular tone due to synchronized changes of intracellular calcium concentrations. Since increased calcium influx into vascular smooth muscle cells from spontaneously hypertensive rats (SHR) has been associated with variances of transient receptor potential canonical (TRPC) channels, in the present study we tested the hypothesis that increased vasomotion in hypertension is directly linked to increased TRPC expression. Using a small vessel myograph we observed significantly increased norepinephrine‐induced vasomotion in mesenteric arterioles from SHR compared to normotensive Wistar–Kyoto (WKY) rats. Using immunoblottings we obtained significantly increased expression of TRPC1, TRPC3 and TRPC5 in mesenteric arterioles from SHR compared to WKY, whereas TRPC4 and TRPC6 showed no differences. Norepinephrine‐induced vasomotion from SHR was significantly reduced in the presence of verapamil, SKF96365, 2‐aminoethoxydiphenylborane (2‐APB) or gadolinium. Pre‐incubation of mesenteric arterioles with anti‐TRPC1 and anti‐TRPC3 antibodies significantly reduced norepinephrine‐induced vasomotion and calcium influx. Control experiments with pre‐incubation of TRPC antibodies plus their respective antigenic peptide or in the presence of anti‐β‐actin antibodies or random immunoglobulins not related to TRPC channels showed no inhibitory effects of norepinephrine‐induced vasomotion and calcium influx. Administration of candesartan or telmisartan, but not amlodipine to SHR for 16 weeks significantly reduced either the expression of TRPC1, TRPC3 and TRPC5 as well as norepinephrine‐induced vasomotion in mesenteric arterioles. In conclusion we gave experimental evidence that the increased TRPC1, TRPC3 and TRPC5 expression in mesenteric arterioles from SHR causes increased vasomotion in hypertension.

Uncoupling Protein 2 Ablation Exacerbates High-Salt Intake-Induced Vascular Dysfunction

BACKGROUND Salt-induced vascular dysfunction in which underlying mechanisms involve reactive oxygen species (ROS)-mediated reduction of nitric oxide (NO) bioavailability has been well documented. Uncoupling protein 2 (UCP2) has been implicated in the vascular protection, specifically by decreasing ROS production. However, it is unclear how UCP2 affects vascular function in salt-loaded mice. METHODS UCP2-deficient (UCP2(-/-)) and wild-type (WT) mice were placed on either a normal-salt (NS, 0.5%) or a high-salt (HS, 8%) diet for 24 weeks. Blood pressure (BP), mesenteric arterial reactivity, superoxide production, and NO bioavailability in the intact vessels were measured in each group. RESULTS UCP2(-/-) mice on a HS diet had a higher BP than those on a NS diet (P < 0.01). However, BP in WT mice was not different between the NS and HS diet group. Phenylephrine (PE)-induced contraction was enhanced while acetylcholine (ACh)-elicited relaxation was impaired in mesenteric resistance arteries from the HS diet-fed WT mice. Importantly, the enhanced contraction and impaired relaxation were both further exacerbated in UCP2(-/-) mice. Similarly, the HS diet led to a moderate increase in superoxide production and a comparable decrease in NO availability in both aortas and mesenteric resistance vessels, and these effects were also remarkably enhanced in UCP2(-/-) mice. CONCLUSIONS These findings suggest that UCP2 plays an important role in preventing salt-sensitive hypertension, which may be achieved by suppressing superoxide production and reserving NO bioavailability in blood vessels.