Insulin signaling: a possible pathogenesis of cardiac hypertrophy

Current understanding of structural and molecular changes in diabetic cardiomyopathy

Diabetic Mellitus has been characterized as the most prevalent disease throughout the globe associated with the serious morbidity and mortality of vital organs. Cardiomyopathy is the major leading complication of diabetes and within this, myocardial dysfunction or failure is the leading cause of the emergency hospital admission. The review is aimed to comprehend the perspectives associated with diabetes-induced cardiovascular complications. The data was collected from several electronic databases such as Google Scholar, Science Direct, ACS publication, PubMed, Springer, etc. using the keywords such as diabetes and its associated complication, the prevalence of diabetes, the anatomical and physiological mechanism of diabetes-induced cardiomyopathy, the molecular mechanism of diabetes-induced cardiomyopathy, oxidative stress, and inflammatory stress, etc. The collected scientific data was screened by different experts based on the inclusion and exclusion criteria of the study. This review findings revealed that diabetes is associated with inefficient substrate utilization, inability to increase glucose metabolism and advanced glycation end products within the diabetic heart resulting in mitochondrial uncoupling, glucotoxicity, lipotoxicity, and initially subclinical cardiac dysfunction and finally in overt heart failure. Furthermore, several factors such as hypertension, overexpression of renin angiotensin system, hypertrophic obesity, etc. have been seen as majorly associated with cardiomyopathy. The molecular examination showed biochemical disability and generation of the varieties of free radicals and inflammatory cytokines and becomes are the substantial causes of cardiomyopathy. This review provides a better understanding of the involved pathophysiology and offers an open platform for discussing and targeting therapy in alleviating diabetes-induced early heart failure or cardiomyopathy.

Assessment of left ventricular geometry in normotensive type II diabetic patients

Background

Abnormalities of glucose metabolism are associated with abnormal left ventricular geometry (LV) independent of atherosclerosis. Abnormal LV geometry, a predictor of premature cardiovascular events, indicates presence of subclinical target organ damages. Screening for abnormal LV geometry in diseases of abnormal glucose metabolism is desirable as part of their management protocol.

Aim

To assess the left ventricular geometry in normotensive type II diabetic patients. Cross-sectional, descriptive, hospital-based study. One hundred normotensive type II diabetic patients drawn from the Endocrinology and Family Medicine Clinics of a tertiary hospital were age- and gender-matched with 100 apparently healthy controls. Participants meeting the criteria and informed consent proceeded for clinical evaluation, biochemical assessment, electrocardiography, and echocardiography using the American Society of Echocardiography guideline.

Materials and Methods

Data were analyzed using the Statistical Package for Social Sciences [SPSS] version 25.0 (Chicago Illinois, USA).

Results

Mean age of study and control groups was (55.56 ± 9.89 versus 55.47 ± 10.7) years (χ2 = 0.062, P = 0.951). The mean duration of diabetes illness was 6.57 ± 6.26 years. Prevalence of abnormal LV geometry was 51% (study) versus 18% (control) FT, P < 0.001). Concentric remodeling was the predominant geometry in 36% of study versus 11% of controls, followed by eccentric hypertrophy in 11% (study) versus 4% (control) and concentric hypertrophy in 4% (study) versus 3% (control). Geometry was normal in 49% of study against 82% in the controls (FT, P < 0.001). Significant association existed between LV geometry and duration of diabetes (χ2 = 10.793, P = 0.005).

Conclusion

Abnormal LV geometry is highly prevalent in normotensive diabetic patients.

Therapeutic Stalemate in Heart Failure With Preserved Ejection Fraction

The findings of randomized trials of neurohormonal modulation have been neutral in heart failure with preserved ejection fraction and consistently positive in heart failure with reduced ejection. Left ventricular remodeling promotes the development and progression of heart failure with preserved and reduced ejection fraction. However, different stimuli mediate left ventricular remodeling that is commonly concentric in heart failure with preserved ejection fraction and eccentric in heart failure with reduced ejection. The stimuli that promote concentric left ventricular remodeling may account for the neutral findings of neuhormonal modulation in heart failure with preserved ejection fraction. Low‐grade systemic inflammation‐induced microvascular endothelial dysfunction is currently the leading hypothesis behind the development and progression of heart failure with preserved ejection fraction. The hypothesis provided the rationale for several randomized controlled trials that have led to neutral findings. The trials and their limitations are reviewed.

Association between insulin resistance and left ventricular hypertrophy in asymptomatic, Black, sub-Saharan African, hypertensive patients: a case-control study

Background

Conflicting information exists regarding the association between insulin resistance (IR) and left ventricular hypertrophy (LVH). We described the associations between obesity, fasting insulinemia, homeostasis model assessment of insulin resistance (HOMA-IR), and LVH in Black patients with essential hypertension.

Methods

A case–control study was conducted at the Centre Médical de Kinshasa (CMK), the Democratic Republic of the Congo, between January and December 2019. Cases and controls were hypertensive patients with and without LVH, respectively. The relationships between obesity indices, physical inactivity, glucose metabolism and lipid disorder parameters, and LVH were assessed using linear and logistic regression analyses in simple and univariate exploratory analyses, respectively. When differences were observed between LVH and independent variables, the effects of potential confounders were studied through the use of multiple linear regression and in conditional logistic regression in multivariate analyses. The coefficients of determination (R²), adjusted odds ratios (aORs), and their 95% confidence intervals (95% CIs) were calculated to determine associations between LVH and the independent variables.

Results

Eighty-eight LVH cases (52 men) were compared against 132 controls (81 men). Variation in left ventricular mass (LVM) could be predicted by the following variables: age (19%), duration of hypertension (31.3%), body mass index (BMI, 44.4%), waist circumference (WC, 42.5%), glycemia (20%), insulinemia (44.8%), and HOMA-IR (43.7%). Hypertension duration, BMI, insulinemia, and HOMA-IR explained 68.3% of LVM variability in the multiple linear regression analysis. In the logistic regression model, obesity increased the risk of LVH by threefold [aOR 2.8; 95% CI (1.06–7.4); p = 0.038], and IR increased the risk of LVH by eightfold [aOR 8.4; 95 (3.7–15.7); p < 0.001].

Conclusion

Obesity and IR appear to be the primary predictors of LVH in Black sub-Saharan African hypertensive patients. The comprehensive management of cardiovascular risk factors should be emphasized, with particular attention paid to obesity and IR. A prospective population-based study of Black sub-Saharan individuals that includes the use of serial imaging remains essential to better understand subclinical LV deterioration over time and to confirm the role played by IR in Black sub-Saharan individuals with hypertension.

The role and molecular mechanism of FoxO1 in mediating cardiac hypertrophy

Cardiac hypertrophy can lead to heart failure and cardiovascular events and has become a research hotspot in the field of cardiovascular disease. Despite extensive and in-depth research, the pathogenesis of cardiac hypertrophy is far from being fully understood. Increasing evidence has shown that the transcription factor forkhead box protein O 1 (FoxO1) is closely related to the occurrence and development of cardiac hypertrophy. This review summarizes the current literature on the role and molecular mechanism of FoxO1 in cardiac hypertrophy. We searched the database MEDLINE via PubMed for available evidence on the effect of FoxO1 on cardiac hypertrophy. FoxO1 has many effects on multiple diseases, including cardiovascular diseases, diabetes, cancer, aging, and stem cell activity. Recent studies have shown that FoxO1 plays a critical role in the development of cardiac hypertrophy. Evidence for this relationship includes the following. (i) FoxO1 can regulate cardiac growth/protein synthesis, calcium homeostasis, cell apoptosis, and autophagy and (ii) is controlled by several upstream signalling molecules (e.g. phosphatidylinositol 3-kinase/Akt, AMP-activated protein kinase, and sirtuins) and regulates many downstream transcription proteins (e.g. ubiquitin ligases muscle RING finger 1/muscle atrophy F-box, calcineurin/nuclear factor of activated T cells, and microRNAs). In response to stress or external stimulation (e.g. low energy, oxidative stress, or growth factor signalling), FoxO1 undergoes post-translational modification and transfers from the cytoplasm to nucleus, thus regulating the expression of a series of target genes in myocardium that are involved in cardiac growth/protein synthesis, calcium homeostasis, cell apoptosis, and autophagy. (iii) Finally, targeted regulation of FoxO1 is an effective method of intervening in myocardial hypertrophy. The information reviewed here should be significant for understanding the roles of FoxO1 in cardiac hypertrophy and should contribute to the design of further studies related to FoxO1 and the hypertrophic response. It should also shed light on a potential treatment for cardiac hypertrophy.

Identification of Biological Pathways Contributing to Marbling in Skeletal Muscle to Improve Beef Cattle Breeding

Red meat is an important dietary source that provides part of the nutritional requirements. Intramuscular fat, known as marbling, is located throughout skeletal muscle. Marbling is a trait of major economic relevance that positively influences sensory quality aspects. The aim of the present study was to identify and better understand biological pathways defining marbling in beef cattle. Pathway analysis was performed in PathVisio with publicly available transcriptomic data from semitendinosus muscle of well-marbled and lean-marbled beef. Moreover, for Bos taurus we created a gene identifier mapping database with bridgeDb and a pathway collection in WikiPathways. The regulation of marbling is possibly the result of the interplay between signaling pathways in muscle, fat, and intramuscular connective tissue. Pathway analysis revealed 17 pathways that were significantly different between well-marbled and lean-marbled beef. The MAPK signaling pathway was enriched, and the signaling pathways that play a role in tissue development were also affected. Interestingly, pathways related to immune response and insulin signaling were enriched.

Heart Failure With Preserved Ejection Fraction in Diabetes: Mechanisms and Management

Diabetes mellitus (DM) is a major cause of heart failure in the Western world, either secondary to coronary artery disease or from a distinct entity known as "diabetic cardiomyopathy." Furthermore, heart failure with preserved ejection fraction (HFpEF) is emerging as a significant clinical problem for patients with DM. Current clinical data suggest that between 30% and 40% of patients with HFpEF suffer from DM. The typical structural phenotype of the HFpEF heart consists of endothelial dysfunction, increased interstitial and perivascular fibrosis, cardiomyocyte stiffness, and hypertrophy along with advanced glycation end products deposition. There is a myriad of mechanisms that result in the phenotypical HFpEF heart including impaired cardiac metabolism and substrate utilization, altered insulin signalling leading to protein kinase C activation, advanced glycated end products deposition, prosclerotic cytokine activation (eg, transforming growth factor-β activation), along with impaired nitric oxide production from the endothelium. Moreover, recent investigations have focused on the role of endothelial-myocyte interactions. Despite intense research, current therapeutic strategies have had little effect on improving morbidity and mortality in patients with DM and HFpEF. Possible explanations for this include a limited understanding of the role that direct cell-cell communication or indirect cell-cell paracrine signalling plays in the pathogenesis of DM and HFpEF. Additionally, integrins remain another important mediator of signals from the extracellular matrix to cells within the failing heart and might play a significant role in cell-cell cross-talk. In this review we discuss the characteristics and mechanisms of DM and HFpEF to stimulate potential future research for patients with this common, and morbid condition.

Obesity-induced kidney injury is attenuated by amelioration of aberrant PHD2 activation in proximal tubules

The involvement of tissue ischemia in obesity-induced kidney injury remains to be elucidated. Compared with low fat diet (LFD)-mice, high fat diet (HFD)-fed mice became obese with tubular enlargement, glomerulomegaly and peritubular capillary rarefaction, and exhibited both tubular and glomerular damages. In HFD-fed mice, despite the increase in renal pimonidazole-positive areas, the expressions of the hypoxia-responsive genes such as Prolyl-hydroxylase PHD2, a dominant oxygen sensor, and VEGFA were unchanged indicating impaired hypoxic response. Tamoxifen inducible proximal tubules (PT)-specific Phd2 knockout (Phd2-cKO) mice and their littermate control mice (Control) were created and fed HFD or LFD. Control mice on HFD (Control HFD) exhibited renal damages and renal ischemia with impaired hypoxic response compared with those on LFD. After tamoxifen treatment, HFD-fed knockout mice (Phd2-cKO HFD) had increased peritubular capillaries and the increased expressions of hypoxia responsive genes compared to Control HFD mice. Phd2-cKO HFD also exhibited the mitigation of tubular damages, albuminuria and glomerulomegaly. In human PT cells, the increased expressions of hypoxia-inducible genes in hypoxic condition were attenuated by free fatty acids. Thus, aberrant hypoxic responses due to dysfunction of PHD2 caused both glomerular and tubular damages in HFD-induced obese mice. Phd2-inactivation provides a novel strategy against obesity-induced kidney injury.

How cardiomyocytes sense pathophysiological stresses for cardiac remodeling

In the past decades, the cardiovascular community has laid out the fundamental signaling cascades that become awry in the cardiomyocyte during the process of pathologic cardiac remodeling. These pathways are initiated at the cell membrane and work their way to the nucleus to mediate gene expression. Complexity is multiplied as the cardiomyocyte is subjected to cross talk with other cells as well as a barrage of extracellular stimuli and mechanical stresses. In this review, we summarize the signaling cascades that play key roles in cardiac function and then we proceed to describe emerging concepts of how the cardiomyocyte senses the mechanical and environmental stimuli to transition to the deleterious genetic program that defines pathologic cardiac remodeling. As a highlighting example of these processes, we illustrate the transition from a compensated hypertrophied myocardium to a decompensated failing myocardium, which is clinically manifested as decompensated heart failure.

miR-322 regulates insulin signaling pathway and protects against metabolic syndrome-induced cardiac dysfunction in mice

We identified murine miR-322, orthologous to human miR-424, as a new regulator of insulin receptor, IGF-1 receptor and sirtuin 4 mRNA in vitro and in vivo in the heart and found that miR-322/424 is highly expressed in the heart of mice. C57Bl/6N mice fed 10weeks of high fat diet (HFD) presented signs of cardiomyopathy and a stable miR-322 cardiac level while cardiac function was slightly affected in 11week-old ob/ob which overexpressed miR-322. We thus hypothesized that mmu-miR-322 could be protective against cardiac consequences of hyperinsulinemia and hyperlipidemia. We overexpressed or knocked-down mmu-miR-322 using AAV9 and monitored cardiac function in wild-type C57Bl/6N mice fed a control diet (CD) or a HFD and in ob/ob mice. The fractional shortening progressively declined while the left ventricle systolic diameter increased in HFD mice infected with an AAVcontrol or with an AAVsponge (decreasing miR-322 bioavailability) but also in ob/ob mice infected with AAVsponge. Similar observations were also found in CD-fed mice infected with AAVsponge. On the contrary over-expressing miR-322 with AAVmiR-322 was efficient in protecting the heart from HFD effects in C57Bl/6N mice. This cardioprotection could be associated with the regulation of identified targets IGF1R, INSR and CD1, a decrease in insulin signaling pathway and an enrichment of genes involved in mitochondrial function and fatty acid oxidation as demonstrated by transcriptome analysis. Altogether, these results emphasize miR-322 as a new potential therapeutic target against cardiac consequences of metabolic syndrome, which represents an increasing burden in the western countries.

Shensongyangxin protects against pressure overload‑induced cardiac hypertrophy

Shensongyangxin (SSYX) is a medicinal herb, which has long been used in traditional Chinese medicine. Various pharmacological activities of SSYX have been identified. However, the role of SSYX in cardiac hypertrophy remains to be fully elucidated. In present study, aortic banding (AB) was performed to induce cardiac hypertrophy in mice. SSYX (520 mg/kg) was administered by daily gavage between 1 and 8 weeks following surgery. The extent of cardiac hypertrophy was then evaluated by pathological and molecular analyses of heart tissue samples. In addition, in vitro experiments were performed to confirm the in vivo results. The data of the present study demonstrated that SSYX prevented the cardiac hypertrophy and fibrosis induced by AB, as assessed by measurements of heart weight and gross heart size, hematoxylin and eosin staining, cross‑sectional cardiomyocyte area and the mRNA expression levels of hypertrophic markers. SSYX also inhibited collagen deposition and suppressed the expression of transforming growth factor β (TGFβ), connective tissue growth factor, fibronectin, collagen Ⅰα and collagen Ⅲα, which was mediated by the inhibition of the TGFβ/small mothers against decapentaplegic (Smad) signaling pathway. The inhibitory action of SSYX on cardiac hypertrophy was mediated by the inhibition of Akt signaling. In vitro investigations in the rat H9c2 cardiac cells also demonstrated that SSYX attenuated angiotensin II‑induced cardiomyocyte hypertrophy. These findings suggested that SSYX attenuated cardiac hypertrophy and fibrosis in the pressure overloaded mouse heart. Therefore, the cardioprotective effect of SSYX is associated with inhibition of the Akt and TGFβ/Smad signaling pathways.

The cardioprotection of the insulin-mediated PI3K/Akt/mTOR signaling pathway

Apoptosis occurs frequently in myocardial infarction, oxidative stress injury, and ischemia/reperfusion injury, and plays a pivotal role in the development of heart diseases. Inhibition of apoptosis alone does not necessarily lead to meaningful rescue in terms of either cardiomyocyte survival or function. Activation of the PI3K/Akt signaling pathway induced by insulin not only inhibits cardiomyocyte apoptosis but also substantially preserves and even improves regional and overall cardiac function. Insulin can protect cardiomyocytes from apoptosis by regulating a number of signaling molecules, such as eNOS, FOXOs, Bad, GSK-3β, mTOR, NDRG2, and Nrf2, through activating PI3K and Akt. This review focuses on the protective mechanisms and targets of insulin identified in the prevention and treatment of myocardial injury.

Insulin-resistance HCV infection-related affects vascular stiffness in normotensives

BACKGROUND AND AIMS. Arterial stiffness evaluated as pulse wave velocity, is an early marker of vascular damage and an independent predictor for cardiovascular events. We investigated if the insulin resistance/hyperinsulinemia chronic hepatitis C virus infection-related could influence arterial stiffness. METHODS. We enrolled 260 outpatients matched for age, body mass index, gender, ethnicity: 52 with never-treated uncomplicated chronic hepatitis C virus infection (HCV(+)), 104 never-treated hypertensives (HT) and 104 healthy subjects (NT). Pulse wave velocity was evaluated by a validated system employing high-fidelity applanation tonometry. We also measured: fasting plasma glucose and insulin, total, LDL- and HDL-cholesterol, triglyceride, creatinine, e-GFR-EPI, HOMA, quantitative HCV-RNA. RESULTS. HCV(+) patients with respect to NT had an increased pulse wave velocity (7.9 ± 2.1 vs 6.4 ± 2.1 m/s; P < 0.0001), similar to that observed in HT group (8.8 ± 3.2 m/s). HCV(+) patients, in comparison with NT, had higher triglyceride, creatinine, fasting insulin and HOMA (3.2 ± 1.3 vs 2.5 ± 1.0; P < 0.0001). At linear regression analysis, the correlation between pulse wave velocity and HOMA was similar in HT (r = 0.380, P < 0.0001) and HCV(+) (r = 0.369, P = 0.004) groups. At multiple regression analysis, HOMA resulted the major determinant of pulse wave velocity in all groups, explaining respectively 11.8%, 14.4% and 13.6% of its variation in NT, HT and HCV(+). At correlational analysis hepatitis C virus-RNA and HOMA demonstrated a strong and linear relationship between them, explaining the 72.4% of their variation (P = 0.022). CONCLUSIONS. We demonstrated a significant and direct correlation between HOMA and pulse wave velocity in HCV(+) patients, similar to that observed in hypertensives.

Chronic HCV infection increases cardiac left ventricular mass index in normotensive patients

BACKGROUND & AIMS

Left ventricular hypertrophy (LVH), is an independent predictor for cardiovascular events. We investigated if chronic hepatitis C virus (HCV) infection and the related insulin resistance (IR)/hyperinsulinemia could influence the increase of left ventricular mass (LVM).

METHODS

We enrolled 260 outpatients matched for age, body mass index, gender, ethnicity: 52 with never-treated uncomplicated chronic HCV infection (HCV(+)), 104 never-treated hypertensives (HT) and 104 healthy subjects (NT). LVM was calculated according to the Devereux formula and indexed for body surface area. The following laboratory parameters were measured: fasting plasma glucose and insulin, total, LDL- and HDL-cholesterol, triglyceride, creatinine, e-GFR-EPI, HOMA. Quantitative HCV-RNA was assessed by PCR.

RESULTS

HCV(+) patients with respect to healthy normotensive subjects had an increased LVMI (100 ± 23 vs. 83 ± 15 g/m(2); p < 0.0001), similar to that observed in HT group (103 ± 25 g/m(2)). Regarding biochemical variables, HCV(+) patients, in comparison with normotensive healthy subjects, had higher triglyceride, creatinine, fasting insulin and HOMA (3.2 ± 1.3 vs. 2.5 ± 1.0; p < 0.0001). At linear regression analysis, the correlation between LVMI and HOMA was similar in HT (r = 0.528, p < 0.0001) and HCV(+) (r = 0.489, p < 0.0001) groups. At multiple regression analysis, HOMA resulted the major determinant of LMVI in all groups, explaining respectively 21.8%, 27.8%, and 23.9% of its variation in NT, HT and HCV(+). At correlational analysis HCV-RNA and HOMA demonstrated a strong and linear relationship between them, explaining the 72.4% of their variation (p = 0.022).

CONCLUSIONS

We demonstrated a significant and direct correlation between HOMA and LVMI in patients with chronic HCV infection, similar to that observed in hypertensives.

Loss of NHE1 activity leads to reduced oxidative stress in heart and mitigates high-fat diet-induced myocardial stress

Acute inhibition of the NHE1 Na(+)/H(+) exchanger protects against ischemia-reperfusion injury and chronic inhibition attenuates development of cardiac hypertrophy and failure. To determine the cardiac effects of chronic inhibition of NHE1 under non-pathological conditions we used NHE1-null mice as a model of long-term NHE1 inhibition. Cardiovascular performance was relatively normal in Nhe1(-/-) mice although cardiac contractility and relaxation were slightly improved in mutant mice of the FVB/N background. GSH levels and GSH:GSSG ratios were elevated in Nhe1(-/-) hearts indicating an enhanced redox potential. Consistent with a reduced need for antioxidant protection, expression of heat shock proteins Hsp60 and Hsp25 was lower in Nhe1(-/-) hearts. Similarly, expression of mitochondrial superoxide dismutase 2 was reduced, with no increase in expression of other ROS scavenging enzymes. GLUT1 levels were increased in Nhe1(-/-) hearts, the number of lipid droplets in myocytes was reduced, and PDK4 expression was refractory to high-fat diet-induced upregulation observed in wild-type hearts. High-fat diet-induced stress was attenuated in Nhe1(-/-) hearts, as indicated by smaller increases in phosphorylation of Hsp25 and α-B crystallin, and there was better preservation of insulin sensitivity, as evidenced by PKB/Akt phosphorylation. Plasma glucose and insulin levels were lower and high-fat diet-induced hepatic lipid accumulation was reduced in Nhe1(-/-) mice, demonstrating extracardiac effects of NHE1 ablation. These data indicate that long-term ablation of NHE1 activity increases the redox potential, mitigates high-fat diet-induced myocardial stress and fatty liver disease, leads to better preservation of insulin sensitivity, and may alter both cardiac and systemic metabolic substrate handling in mice.

Sgk1 sensitivity of Na(+)/H(+) exchanger activity and cardiac remodeling following pressure overload

Sustained increase of cardiac workload is known to trigger cardiac remodeling with eventual development of cardiac failure. Compelling evidence points to a critical role of enhanced cardiac Na(+)/H(+) exchanger (NHE1) activity in the underlying pathophysiology. The signaling triggering up-regulation of NHE1 remained, however, ill defined. The present study explored the involvement of the serum- and glucocorticoid-inducible kinase Sgk1 in cardiac remodeling due to transverse aortic constriction (TAC). To this end, experiments were performed in gene targeted mice lacking functional Sgk1 (sgk1 (-/-)) and their wild-type controls (sgk1 (+/+)). Transcript levels have been determined by RT-PCR, cytosolic pH (pH( i )) utilizing 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF) fluorescence, Na(+)/H(+) exchanger activity by the Na(+)-dependent realkalinization after an ammonium pulse, ejection fraction (%) utilizing cardiac cine magnetic resonance imaging and cardiac glucose uptake by PET imaging. As a result, TAC increased the mRNA expression of Sgk1 in sgk1 (+/+) mice, paralleled by an increase in Nhe1 transcript levels as well as Na(+)/H(+) exchanger activity, all effects virtually abrogated in sgk1 (-/-) mice. In sgk1 (+/+) mice, TAC induced a decrease in Pgc1a mRNA expression, while Spp1 mRNA expression was increased, both effects diminished in the sgk1 (-/-) mice. TAC was followed by a significant increase of heart and lung weight in sgk1 (+/+) mice, an effect significantly blunted in sgk1 (-/-) mice. TAC increased the transcript levels of Anp and Bnp, effects again significantly blunted in sgk1 (-/-) mice. TAC increased transcript levels of Collagen I and III as well as Ctgf mRNA and CTGF protein abundance, effects significantly blunted in sgk1 (-/-) mice. TAC further decreased the ejection fraction in sgk1 (+/+) mice, an effect again attenuated in sgk1 (-/-) mice. Also, cardiac FDG-glucose uptake was increased to a larger extent in sgk1 (+/+) mice than in sgk1 (-/-) mice after TAC. These observations point to an important role for SGK1 in cardiac remodeling and development of heart failure following an excessive work load.

Insulin decreases myocardial adiponectin receptor 1 expression via PI3K/Akt and FoxO1 pathway

AIMS

Adiponectin is considered an important adipokine protecting against diabetes, atherosclerosis, and cardiovascular disease. Because adiponectin receptors (AdipoRs) are critical components in the adiponectin signalling cascade, we investigated the effect of insulin on the expression of myocardial AdipoRs and explored the possible molecular mechanism.

METHODS AND RESULTS

The hyperinsulinaemia rat model was induced by infusion of insulin (1 U/day) for 28 days: serum and myocardial adiponectin levels were increased, and skeletal muscle and myocardial AdipoR1 expression and AMP-activated protein kinase (AMPK) phosphorylation were decreased. In primary cultured neonatal rat ventricular myocytes (NRVMs), insulin decreased AdipoR1 but not AdipoR2 expression and AMPK phosphorylation; high glucose had no affect on AdipoRs expression. Akt and extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation was increased in insulin-treated hearts and in NRVMs. P13K inhibitor LY294002 and Akt1/2 kinase inhibitor but not the ERK1/2 kinase (MEK) inhibitors PD98059 and U0126 blocked the insulin-induced reduction in AdipoR1 expression and AMPK phosphorylation. Insulin induced forkhead/winged helix box gene group O-1 (FoxO1) phosphorylation and translocation from the nucleus to the cytosol, and this was blocked by LY294002. FoxO1 small interfering RNA reduced AdipoR1 expression and AMPK phosphorylation. In electrophoretic mobility shift assay and chromatin immunoprecipitation, FoxO1 bound to the putative site from -167 to -157 bp of the AdipoR1 promoter both in vitro and in living cells; insulin suppressed this binding, which was blocked by LY294002.

CONCLUSION

Insulin inhibits myocardial AdipoR1 expression via PI3K/Akt and FoxO1 pathways, and FoxO1 mediates AdipoR1 transcription by binding to its promoter directly.

Prolonged exposure to GH impairs insulin signaling in the heart

Acromegaly is associated with cardiac hypertrophy, which is believed to be a direct consequence of chronically elevated GH and IGF1. Given that insulin is important for cardiac growth and function, and considering that GH excess induces hyperinsulinemia, insulin resistance, and cardiac alterations, it is of interest to study insulin sensitivity in this tissue under chronic conditions of elevated GH. Transgenic mice overexpressing GH present cardiomegaly and perivascular and interstitial fibrosis in the heart. Mice received an insulin injection, the heart was removed after 2  min, and immunoblotting assays of tissue extracts were performed to evaluate the activation and abundance of insulin-signaling mediators. Insulin-induced tyrosine phosphorylation of the insulin receptor (IR) was conserved in transgenic mice, but the phosphorylation of IR substrate 1 (IRS1), its association with the regulatory subunit of the phosphatidylinositol 3-kinase (PI3K), and the phosphorylation of AKT were decreased. In addition, total content of the glucose transporter GLUT4 was reduced in transgenic mice. Insulin failed to induce the phosphorylation of the mammalian target of rapamycin (mTOR). However, transgenic mice displayed increased basal activation of the IR/IRS1/PI3K/AKT/mTOR and p38 signaling pathways along with higher serine phosphorylation of IRS1, which is recognized as an inhibitory modification. We conclude that GH-overexpressing mice exhibit basal activation of insulin signaling but decreased sensitivity to acute insulin stimulation at several signaling steps downstream of the IR in the heart. These alterations may be associated with the cardiac pathology observed in these animals.