Angiotensin-induced EGF receptor transactivation inhibits insulin signaling in C9 hepatic cells

Angiotensin II Inhibits Insulin Receptor Signaling in Adipose Cells

Angiotensin II (Ang II) is a critical regulator of insulin signaling in the cardiovascular system and metabolic tissues. However, in adipose cells, the regulatory role of Ang II on insulin actions remains to be elucidated. The effect of Ang II on insulin-induced insulin receptor (IR) phosphorylation, Akt activation, and glucose uptake was examined in 3T3-L1 adipocytes. In these cells, Ang II specifically inhibited insulin-stimulated IR and insulin receptor substrate-1 (IRS-1) tyrosine-phosphorylation, Akt activation, and glucose uptake in a time-dependent manner. These inhibitory actions were associated with increased phosphorylation of the IR at serine residues. Interestingly, Ang II-induced serine-phosphorylation of IRS was not detected, suggesting that Ang II-induced desensitization begins from IR regulation itself. PKC inhibition by BIM I restored the inhibitory effect of Ang II on insulin actions. We also found that Ang II promoted activation of several PKC isoforms, including PKCα/βI/βII/δ, and its association with the IR, particularly PKCβII, showed the highest interaction. Finally, we also found a similar regulatory effect of Ang II in isolated adipocytes, where insulin-induced Akt phosphorylation was inhibited by Ang II, an effect that was prevented by PKC inhibitors. These results suggest that Ang II may lead to insulin resistance through PKC activation in adipocytes.

Sera from women with different metabolic and menopause states differentially regulate cell viability and Akt activation in a breast cancer in-vitro model

Obesity is associated with an increased incidence and aggressiveness of breast cancer and is estimated to increment the development of this tumor by 50 to 86%. These associations are driven, in part, by changes in the serum molecules. Epidemiological studies have reported that Metformin reduces the incidence of obesity-associated cancer, probably by regulating the metabolic state. In this study, we evaluated in a breast cancer in-vitro model the activation of the IR-β/Akt/p70S6K pathway by exposure to human sera with different metabolic and hormonal characteristics. Furthermore, we evaluated the effect of brief Metformin treatment on sera of obese postmenopausal women and its impact on Akt and NF-κB activation. We demonstrated that MCF-7 cells represent a robust cellular model to differentiate Akt pathway activation influenced by the stimulation with sera from obese women, resulting in increased cell viability rates compared to cells stimulated with sera from normal-weight women. In particular, stimulation with sera from postmenopausal obese women showed an increase in the phosphorylation of IR-β and Akt proteins. These effects were reversed after exposure of MCF-7 cells to sera from postmenopausal obese women with insulin resistance with Metformin treatment. Whereas sera from women without insulin resistance affected NF-κB regulation. We further demonstrated that sera from post-Metformin obese women induced an increase in p38 phosphorylation, independent of insulin resistance. Our results suggest a possible mechanism in which obesity-mediated serum molecules could enhance the development of luminal A-breast cancer by increasing Akt activation. Further, we provided evidence that the phenomenon was reversed by Metformin treatment in a subgroup of women.

ACE2 and energy metabolism: the connection between COVID-19 and chronic metabolic disorders

The renin-angiotensin system (RAS) has currently attracted increasing attention due to its potential function in regulating energy homeostasis, other than the actions on cellular growth, blood pressure, fluid, and electrolyte balance. The existence of RAS is well established in metabolic organs, including pancreas, liver, skeletal muscle, and adipose tissue, where activation of angiotensin-converting enzyme (ACE) - angiotensin II pathway contributes to the impairment of insulin secretion, glucose transport, fat distribution, and adipokines production. However, the activation of angiotensin-converting enzyme 2 (ACE2) - angiotensin (1-7) pathway, a novel branch of the RAS, plays an opposite role in the ACE pathway, which could reverse these consequences by improving local microcirculation, inflammation, stress state, structure remolding, and insulin signaling pathway. In addition, new studies indicate the protective RAS arm possesses extraordinary ability to enhance brown adipose tissue (BAT) activity and induces browning of white adipose tissue, and consequently, it leads to increased energy expenditure in the form of heat instead of ATP synthesis. Interestingly, ACE2 is the receptor of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is threating public health worldwide. The main complications of SARS-CoV-2 infected death patients include many energy metabolism-related chronic diseases, such as diabetes. The specific mechanism leading to this phenomenon is largely unknown. Here, we summarize the latest pharmacological and genetic tools on regulating ACE/ACE2 balance and highlight the beneficial effects of the ACE2 pathway axis hyperactivity on glycolipid metabolism, as well as the thermogenic modulation.

G protein-coupled receptors as promising cancer targets

G protein-coupled receptors (GPCRs) regulate an array of fundamental biological processes, such as growth, metabolism and homeostasis. Specifically, GPCRs are involved in cancer initiation and progression. However, compared with the involvement of the epidermal growth factor receptor in cancer, that of GPCRs have been largely ignored. Recent findings have implicated many GPCRs in tumorigenesis, tumor progression, invasion and metastasis. Moreover, GPCRs contribute to the establishment and maintenance of a microenvironment which is permissive for tumor formation and growth, including effects upon surrounding blood vessels, signaling molecules and the extracellular matrix. Thus, GPCRs are considered to be among the most useful drug targets against many solid cancers. Development of selective ligands targeting GPCRs may provide novel and effective treatment strategies against cancer and some anticancer compounds are now in clinical trials. Here, we focus on tumor related GPCRs, such as G protein-coupled receptor 30, the lysophosphatidic acid receptor, angiotensin receptors 1 and 2, the sphingosine 1-phosphate receptors and gastrin releasing peptide receptor. We also summarize their tissue distributions, activation and roles in tumorigenesis and discuss the potential use of GPCR agonists and antagonists in cancer therapy.

Aliskiren attenuates steatohepatitis and increases turnover of hepatic fat in mice fed with a methionine and choline deficient diet

Background & Aims

Activation of the renin-angiotensin-system is known to play a role in nonalcoholic steatohepatitis. Renin knockout mice manifest decreased hepatic steatosis. Aliskiren is the first direct renin inhibitor to be approved for clinical use. Our study aims to evaluate the possible therapeutic effects and mechanism of the chronic administration of aliskiren in a dietary steatohepatitis murine model.

Methods

Male C57BL/6 mice were fed with a methionine and choline-deficient (MCD) diet to induce steatohepatitis. After 8 weeks of feeding, the injured mice were randomly assigned to receive aliskiren (50 mg_·kg^-1 per day) or vehicle administration for 4 weeks. Normal controls were also administered aliskiren (50 mg_·kg^-1 per day) or a vehicle for 4 weeks.

Results

In the MCD mice, aliskiren attenuated hepatic steatosis, inflammation and fibrosis. Aliskiren did not change expression of lipogenic genes but increase turnover of hepatic fat by up-regulating peroxisome proliferator-activated receptor α, carnitine palmitoyltransferase 1a, cytochrome P450-4A14 and phosphorylated AMP-activated protein kinase. Furthermore, aliskiren decreased the hepatic expression of angiotensin II and nuclear factor κB. The levels of oxidative stress, hepatocyte apoptosis, activation of Kupffer cells and hepatic stellate cells, and pro-fibrotic markers were also reduced in the livers of the MCD mice receiving aliskiren.

Conclusions

Aliskiren attenuates steatohepatitis and fibrosis in mice fed with a MCD diet. Thus, the noted therapeutic effects might come from not only the reduction of angiotensin II but also the up-regulation of fatty acid oxidation-related genes.

Angiotensin II signaling in human preadipose cells: participation of ERK1,2-dependent modulation of Akt

The renin-angiotensin system expressed in adipose tissue has been implicated in the modulation of adipocyte formation, glucose metabolism, triglyceride accumulation, lipolysis, and the onset of the adverse metabolic consequences of obesity. As we investigated angiotensin II signal transduction mechanisms in human preadipose cells, an interplay of extracellular-signal-regulated kinases 1 and 2 (ERK1,2) and Akt/PKB became evident. Angiotensin II caused attenuation of phosphorylated Akt (p-Akt), at serine 473; the p-Akt/Akt ratio decreased to 0.5±0.2-fold the control value without angiotensin II (p<0.001). Here we report that the reduction of phosphorylated Akt associates with ERK1,2 activities. In the absence of angiotensin II, inhibition of ERK1,2 activation with U0126 or PD98059 resulted in a 2.1±0.5 (p<0.001) and 1.4±0.2-fold (p<0.05) increase in the p-Akt/Akt ratio, respectively. In addition, partial knockdown of ERK1 protein expression by the short hairpin RNA technique also raised phosphorylated Akt in these cells (the p-Akt/Akt ratio was 1.5±0.1-fold the corresponding control; p<0.05). Furthermore, inhibition of ERK1,2 activation with U0126 prevented the reduction of p-Akt/Akt by angiotensin II. An analogous effect was found on the phosphorylation status of Akt downstream effectors, the forkhead box (Fox) proteins O1 and O4. Altogether, these results indicate that angiotensin II signaling in human preadipose cells involves an ERK1,2-dependent attenuation of Akt activity, whose impact on the biological functions under its regulation is not fully understood.

The role of angiotensin II in nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is now considered the most prevalent chronic liver disease, affecting over 30% of the US adult population. NAFLD is strongly linked to insulin resistance and is considered the hepatic manifestation of the metabolic syndrome. Activation of the renin-angiotensin-aldosterone system (RAAS) is known to play a role in the hypertension observed in the metabolic syndrome and also is thought to play a central role in insulin resistance and NAFLD. Angiotensin II (AngII) is considered the primary effector of the physiological outcomes of RAAS signaling, both at the systemic and local tissue level. Herein, we review data describing the potential involvement of AngII-mediated signaling at multiple levels in the development and progression of NAFLD, including increased steatosis, inflammation, insulin resistance, and fibrosis. Additionally, we present recent work on the potential therapeutic benefits of RAAS and angiotensin II signaling inhibition in rodent models and patients with NAFLD.

Anti-proliferative effect of rosiglitazone on angiotensin II-induced vascular smooth muscle cell proliferation is mediated by the mTOR pathway

VSMC (vascular smooth muscle cell) proliferation contributes significantly to intimal thickening in atherosclerosis, restenosis and venous bypass graft diseases. Ang II (angiotensin II) has been implicated in VSMC proliferation though the activation of multiple growth-promoting signals. Although TZDs (thiazolidinediones) can inhibit VSMC proliferation and reduce Ang II-induced fibrosis, the mechanism underlying the inhibition of VSMC proliferation and fibrosis needs elucidation. We have used primary cultured rat aortic VSMCs and specific antibodies to investigate the inhibitory mechanism of rosiglitazone on Ang II-induced VSMC proliferation. Rosiglitazone treatment significantly inhibited Ang II-induced rat aortic VSMC proliferation in a dose-dependent manner. Western blot analysis showed that rosiglitazone significantly lowered phosphorylated ERK1/2 (extracellular-signal-regulated kinase 1/2), Akt (also known as protein kinase B), mTOR (mammalian target of rapamycin), p70S6K (70 kDa S6 kinase) and 4EBP1 (eukaryotic initiation factor 4E-binding protein) levels in Ang II-treated VSMCs. In addition, PPAR-γ (peroxisome-proliferator-activated receptor γ) mRNA increased significantly and CTGF (connective tissue growth factor), Fn (fibronectin) and Col III (collagen III) levels decreased significantly. The results demonstrate that the rosiglitazone directly inhibits the pro-atherosclerotic effect of Ang II on rat aortic VSMCs. It also attenuates Ang II-induced ECM (extracellular matrix) molecules and CTGF production in rat aortic VSMCs, reducing fibrosis. Importantly, PPAR-γ activation mediates these effects, in part, through the mTOR-p70S6K and -4EBP1 system.

The renin-angiotensin system in the breast and breast cancer

Much evidence now suggests that angiotensin II has roles in normal functions of the breast that may be altered or attenuated in cancer. Both angiotensin type 1 (AT1) and type 2 (AT2) receptors are present particularly in the secretory epithelium. Additionally, all the elements of a tissue renin-angiotensin system, angiotensinogen, prorenin and angiotensin-converting enzyme (ACE), are also present and distributed in different cell types in a manner suggesting a close relationship with sites of angiotensin II activity. These findings are consistent with the concept that stromal elements and myoepithelium are instrumental in maintaining normal epithelial structure and function. In disease, this system becomes disrupted, particularly in invasive carcinoma. Both AT1 and AT2 receptors are present in tumours and may be up-regulated in some. Experimentally, angiotensin II, acting via the AT1 receptor, increases tumour cell proliferation and angiogenesis, both these are inhibited by blocking its production or function. Epidemiological evidence on the effect of expression levels of ACE or the distribution of ACE or AT1 receptor variants in many types of cancer gives indirect support to these concepts. It is possible that there is a case for the therapeutic use of high doses of ACE inhibitors and AT1 receptor blockers in breast cancer, as there may be for AT2 receptor agonists, though this awaits full investigation. Attention is drawn to the possibility of blocking specific AT1-mediated intracellular signalling pathways, for example by AT1-directed antibodies, which exploit the possibility that the extracellular N-terminus of the AT1 receptor may have previously unsuspected signalling roles.

Activation of mTOR/p70S6 kinase by ANG II inhibits insulin-stimulated endothelial nitric oxide synthase and vasodilation

Elevated tissue levels of angiotensin II (ANG II) are associated with impairment of insulin actions in metabolic and cardiovascular tissues. ANG II-stimulated activation of mammalian target of rapamycin (mTOR)/p70 S6 kinase (p70S6K) in cardiovascular tissues is implicated in cardiac hypertrophy and vascular remodeling. However, the role of ANG II-stimulated mTOR/p70S6K in vascular endothelium is poorly understood. In the present study, we observed that ANG II stimulated p70S6K in bovine aortic endothelial cells. ANG II increased phosphorylation of insulin receptor substrate-1 (IRS-1) at Ser(636/639) and inhibited the insulin-stimulated phosphorylation of endothelial nitric oxide synthase (eNOS). An inhibitor of mTOR, rapamycin, attenuated the ANG II-stimulated phosphorylation of p70S6K and phosphorylation of IRS-1 (Ser(636/639)) and blocked the ability of ANG II to impair insulin-stimulated phosphorylation of eNOS, nitric oxide production, and mesenteric-arteriole vasodilation. Moreover, point mutations of IRS-1 at Ser(636/639) to Ala prevented the ANG II-mediated inhibition of insulin signaling. From these results, we conclude that activation of mTOR/p70S6K by ANG II in vascular endothelium may contribute to impairment of insulin-stimulated vasodilation through phosphorylation of IRS-1 at Ser(636/639). This ANG II-mediated impairment of vascular actions of insulin may help explain the role of ANG II as a link between insulin resistance and hypertension.

Functional relevance of biased signaling at the angiotensin II type 1 receptor

Angiotensin II type 1 receptor antagonists (AT1R blockers, or ARBs) are used commonly in the treatment of cardiovascular disorders such as heart failure and hypertension. Their clinical success arises from their ability to prevent deleterious Gα(q) protein activation downstream of AT1R, which leads to a decrease in morbidity and mortality. Recent studies have identified AT1R ligands that concurrently inhibit Gα(q) protein-dependent signaling and activate Gα(q) protein-independent/β-arrestin-dependent signaling downstream of AT1R, events that may actually improve cardiovascular performance more than conventional ARBs. The ability of such ligands to induce intracellular signaling events in an AT1R-β-arrestin-dependent manner while preventing AT1R-Gα(q) protein activity defines them as biased AT1R ligands. This mini-review will highlight recent studies that have defined biased signaling at the AT1R and discuss the possible clinical relevance of β-arrestin-biased AT1R ligands in the cardiovascular system.

GPCR agonist-induced transactivation of the EGFR upregulates MLC II expression and promotes hypertension in insulin-resistant rats

AIMS

The presence of metabolic abnormalities such as insulin resistance and elevated levels of various vasoconstrictor G-protein-coupled receptor (GPCR) agonists contributes to the development of hypertension. Recent studies have suggested a link between disease progression and activation of growth factor receptor signalling pathways such as the epidermal growth factor receptor (EGFR) by matrix metalloproteinases (MMPs). We hypothesized that excessive stimulation of GPCRs such as alpha(1)-adrenergic receptors activates MMP-dependent EGFR transactivation and contributes to the development of hypertension by promoting increased synthesis of contractile proteins in vascular smooth muscle (VSM).

METHODS AND RESULTS

We tested this concept in experiments using insulin-resistant VSM cells (VSMCs) and fructose hypertensive rats (FHRs), a model of acquired systolic hypertension and insulin resistance. We found that insulin resistance and agonist stimulation increased the expression and activity of MMPs (MMP-2 and MMP-7), the EGFR, contractile proteins such as myosin light chain kinase and MLC II, and their transcriptional activators including P90 ribosomal kinase (P90RSK) and serum response factor, possibly via the activation of extracellular signal-regulated kinase (ERK1/2) in VSMCs. Further, in insulin-resistant VSMCs and arteries from FHRs, disruption of MMP-EGFR signalling either by a pharmacological or small interfering RNA approach normalized the increased expression and activity of contractile proteins and their transcriptional activators and prevented the development of hypertension in FHRs.

CONCLUSION

Our data suggest that the MMP-EGFR pathway could be a potential target in the treatment of hypertension in insulin resistance and/or hyperglycaemic conditions such as type 2 diabetes.