Gene transfer of human neuregulin-1 attenuates ventricular remodeling in diabetic cardiomyopathy rats

Upregulated neuregulin-1 protects against optic nerve injury by regulating the RhoA/cofilin/F-actin axis

OBJECTIVE

In recent years, the roles of Neuregulin-1 (NRG-1) in optic nerve injury and retinal cells have been investigated. However, the molecular mechanism by which NRG-1 affects optic nerve injury remains elusive and merits deeper exploration. Hence, this study examined the specific function of NRG-1 in the RhoA/cofilin/F-actin axis in optic nerve injury.

METHODS

Retinal cells were isolated and identified for subsequent experimental uses. Reverse transcription quantitative polymerase chain reaction and Western blot assays were performed to measure NRG-1 expression in retinal cells which were cultured under elevated pressure. TUNEL staining was used to detect the cell apoptosis rate, and Western blot assay was performed to detect the expression of related genes. The axon growth was examined by immunofluorescence. The effects of NRG-1 on RhoA activity, cofilin phosphorylation, and F-actin were detected by Western blot assay. In other studies we established a rat model of acute optic nerve injury, and tested for beneficial effects of NRG-1 in vivo.

RESULTS

High expression of NRG-1 was evident in the retinal tissues of rats with optic nerve injury. Overexpressing NRG-1 successfully inhibited RhoA activity and the phosphorylation of cofilin and promoted F-actin expression. In cell experiments, overexpressed NRG-1 suppressed the apoptosis of retinal cells and promoted axon growth through the RhoA/cofilin/F-actin axis. In animal experiments, overexpressed NRG-1 relieved retinal injury.

CONCLUSION

Our results strongly suggest that overexpressed NRG-1 is highly effective in the protection of normal optic nerve function by suppressing RhoA activity and the phosphorylation of cofilin and rescuing F-actin function.

Neuregulin-1 attenuates right ventricular diastolic stiffness in experimental pulmonary hypertension

We have previously shown that treatment with recombinant human neuregulin-1 (rhNRG-1) improves pulmonary arterial hypertension (PAH) in a monocrotaline (MCT)-induced animal model, by decreasing pulmonary arterial remodelling and endothelial dysfunction, as well as by restoring right ventricular (RV) function. Additionally, rhNRG-1 treatment showed direct myocardial anti-remodelling effects in a model of pressure loading of the RV without PAH. This work aimed to study the intrinsic cardiac effects of rhNRG-1 on experimental PAH and RV pressure overload, and more specifically on diastolic stiffness, at both the ventricular and cardiomyocyte level. We studied the effects of chronic rhNRG-1 treatment on ventricular passive stiffness in RV and LV samples from MCT-induced PAH animals and in the RV from animals with compensated and decompensated RV hypertrophy, through a mild and severe pulmonary artery banding (PAB). We also measured passive tension in isolated cardiomyocytes and quantified the expression of myocardial remodelling-associated genes and calcium handling proteins. Chronic rhNRG-1 treatment decreased passive tension development in RV and LV isolated from animals with MCT-induced PAH. This decrease was associated with increased phospholamban phosphorylation, and with attenuation of the expression of cardiac maladaptive remodelling markers. Finally, we showed that rhNRG-1 therapy decreased RV remodelling and cardiomyocyte passive tension development in PAB-induced RV hypertrophy animals, without compromising cardiac function, pointing to cardiac-specific effects in both hypertrophy stages. In conclusion, we demonstrated that rhNRG-1 treatment decreased RV intrinsic diastolic stiffness, through the improvement of calcium handling and cardiac remodelling signalling.

Expression and secretion of neuregulin-1 in cardiac microvascular endothelial cells treated with angiogenic factors

Neuregulin-1 (NRG-1) is a positive regulator of angiogenesis, which suggests there may be an association between NRG-1 and angiogenic factors. The aim of the present study was to investigate the effect of treating human cardiac microvascular endothelial cells (HCMECs) with angiogenic factors on NRG-1 expression and secretion. HCMECs were cultured and stimulated with vascular endothelial growth factor (VEGF; 100 ng/ml), angiopoietin (Ang)-1 (100 ng/ml) or Ang-2 (100 ng/ml) under normal or hypoxia/serum deprivation (Hypo/SD) conditions for 24 h. The expression of ErbB receptors and NRG-1 in HCMECs was measured by western blot analysis and the secretion of NRG-1 in HCMECs was determined by ELISA. The results demonstrated that ErbB2, ErbB3 and ErbB4 were expressed in HCMECs and that ErbB2 expression levels were notably higher than those of ErbB3 and ErbB4. Under normal culture conditions the expression and secretion of NRG-1 was significantly increased in HCMECs treated with VEGF or Ang-1 (P<0.05), however levels significantly decreased in HCMECs treated with Ang-2 (P<0.05). Under Hypo/SD conditions the expression and secretion of NRG-1 significantly increased (P<0.05) and VEGF or Ang-1 treatment significantly increased these effects further (P<0.05). Conversely Ang-2 treatment significantly decreased these effects (P<0.05). The expression and release of NRG-1 were significantly increased in HCMECs with VEGF or Ang-1 treatment (P<0.05), which suggests that VEGF and Ang-1 may regulate myocardial angiogenesis and survival via the NRG-1/ErbB signaling pathway.

Chronic Neuregulin-1β Treatment Mitigates the Progression of Postmyocardial Infarction Heart Failure in the Setting of Type 1 Diabetes Mellitus by Suppressing Myocardial Apoptosis, Fibrosis, and Key Oxidant-Producing Enzymes

BACKGROUND

Type 1 diabetes mellitus (DM) patients surviving myocardial infarction (MI) have substantially higher cardiovascular morbidity and mortality compared to their nondiabetic counterparts owing to the more frequent development of subsequent heart failure (HF). Neuregulin (NRG)-1β is released from cardiac microvascular endothelial cells and acts as a paracrine factor via the ErbB family of tyrosine kinase receptors expressed in cardiac myocytes to regulate cardiac development and stress responses. Because myocardial NRG-1/ErbB signaling has been documented to be impaired during HF associated with type 1 DM, we examined whether enhancement of NRG-1β signaling via exogenous administration of recombinant NRG-1β could exert beneficial effects against post-MI HF in the type 1 diabetic heart.

METHODS AND RESULTS

Type 1 DM was induced in male Sprague Dawley rats by a single injection of streptozotocin (STZ) (65 mg/kg). Two weeks after induction of type 1 DM, rats underwent left coronary artery ligation to induce MI. STZ-diabetic rats were treated with saline or NRG-1β (100 µg/kg) twice per week for 7 weeks, starting 2 weeks before experimental MI. Residual left ventricular function was significantly greater in the NRG-1β-treated STZ-diabetic MI group compared with the vehicle-treated STZ-diabetic MI group 5 weeks after MI as assessed by high-resolution echocardiography. NRG-1β treatment of STZ-diabetic MI rats was associated with reduced myocardial fibrosis and apoptosis as well as decreased gene expression of key oxidant-producing enzymes.

CONCLUSIONS

These results suggest that recombinant NRG-1β may be a promising therapeutic for HF post-MI in the setting of type 1 DM.

Neuregulin-1 attenuates development of nephropathy in a type 1 diabetes mouse model with high cardiovascular risk

Neuregulin-1 (NRG-1) is an endothelium-derived growth factor with cardioprotective and antiatherosclerotic properties and is currently being tested in clinical trials as a treatment for systolic heart failure. In clinical practice, heart failure often coexists with renal failure, sharing an overlapping pathophysiological background. In this study, we hypothesized that NRG-1 might protect against cardiomyopathy, atherosclerosis, and nephropathy within one disease process. We tested this hypothesis in a hypercholesterolemic apolipoprotein E-deficient (apoE(-/-)) type 1 diabetes mouse model prone to the development of cardiomyopathy, atherosclerosis, and nephropathy and compared the effects of NRG-1 with insulin. Upon onset of hyperglycemia induced by streptozotocin, apoE(-/-)mice were treated with vehicle, insulin, or recombinant human (rh)NRG-1 for 14 wk and were compared with nondiabetic apoE(-/-)littermates. Vehicle-treated diabetic apoE(-/-)mice developed left ventricular (LV) dilatation and dysfunction, dense atherosclerotic plaques, and signs of nephropathy. Nephropathy was characterized by abnormalities including hyperfiltration, albuminuria, increased urinary neutrophil gelatinase-associated lipocalin (NGAL), upregulation of renal fibrotic markers, and glomerulosclerosis. rhNRG-1 treatment induced systemic activation of ErbB2 and ErbB4 receptors in both heart and kidneys and prevented LV dilatation, improved LV contractile function, and reduced atherosclerotic plaque size. rhNRG-1 also significantly reduced albuminuria, NGALuria, glomerular fibrosis, and expression of fibrotic markers. Regarding the renal effects of rhNRG-1, further analysis showed that rhNRG-1 inhibited collagen synthesis of glomerular mesangial cells in vitro but did not affect AngII-induced vasoconstriction of glomerular arterioles. In conclusion, systemic administration of rhNRG-1 in hypercholesterolemic type 1 diabetic mice simultaneously protects against complications in the heart, arteries and kidneys.

Signalling between microvascular endothelium and cardiomyocytes through neuregulin

Heterocellular communication in the heart is an important mechanism for matching circulatory demands with cardiac structure and function, and neuregulins (Nrgs) play an important role in transducing this signal between the hearts' vasculature and musculature. Here, we review the current knowledge regarding Nrgs, explaining their roles in transducing signals between the heart's microvasculature and cardiomyocytes. We highlight intriguing areas being investigated for developing new, Nrg-mediated strategies to heal the heart in acquired and congenital heart diseases, and note avenues for future research.