Interleukin-6 and neuregulin-1 as regulators of utrophin expression via the activation of NRG-1/ErbB signaling pathway in mdx cells

Recombinant human neuregulin-1 alleviates immobilization-induced neuromuscular dysfunction via neuregulin-1/ErbB signaling pathway in rat

Immobilization-induced Neuromuscular Dysfunction (NMD) increases morbidity and mortality of patients in Intensive Care Units. However, the underlying mechanism of NMD remain poorly elucidated which limited the development of therapeutic method for NMD. Here we developed an immobilization rat model and tested the hypothesis that decreased expression of NRG-1, abnormal expression and distribution of nicotinic acetylcholine receptors (nAChRs) in skeletal muscle caused by immobilization can lead to NMD. To investigate the role of NRG-1/ErbB pathway on immobilization-induced NMD, exogenous recombinant human neuregulin-1 (rhNRG-1) was used to increase the expression of NRG-1 in skeletal muscle during immobilization. It was observed rhNRG-1 significantly alleviated the muscle loss and enhanced the expression of ε-nAChR, while diminished the expression of γ- and α7-nAChR and NMD. Interestingly, ErbB inhibitor PD158780 blocked the protective effects of rhNRG-1. Collectively, the results of present study suggested that rhNRG-1 attenuated immobilization-induced muscle loss and NMD, suppressed γ- and α7-nAChR production, enhanced ε-nAChR synthesis via activating NRG-1/ErbB pathway. Taken together, our findings provide novel insights into NMD contribution, suggesting that the rhNRG-1 is a promising therapy to protect against immobilization-induced myopathy.

Transcriptomic Profile of Primary Culture of Skeletal Muscle Cells Isolated from Semitendinosus Muscle of Beef and Dairy Bulls

The aim of the study was to identify differences in the transcriptomic profiles of primary muscle cell cultures derived from the semitendinosus muscle of bulls of beef breeds (Limousin (LIM) and Hereford (HER)) and a dairy breed (Holstein-Friesian (HF)) (n = 4 for each breed). Finding a common expression pattern for proliferating cells may point to such an early orientation of the cattle beef phenotype at the transcriptome level of unfused myogenic cells. To check this hypothesis, microarray analyses were performed. The analysis revealed 825 upregulated and 1300 downregulated transcripts similar in both beef breeds (LIM and HER) and significantly different when compared with the dairy breed (HF) used as a reference. Ontological analyses showed that the largest group of genes were involved in muscle organ development. Muscle cells of beef breeds showed higher expression of genes involved in myogenesis (including erbb-3, myf5, myog, des, igf-1, tgfb2) and those encoding proteins comprising the contractile apparatus (acta1, actc1, myh3, myh11, myl1, myl2, myl4, tpm1, tnnt2, tnnc1). The obtained results confirmed our hypothesis that the expression profile of several groups of genes is common in beef breeds at the level of proliferating satellite cells but differs from that observed in typical dairy breeds.

Interleukin-6 is required for Neuregulin-1 induced HER2 signaling in lung epithelium

A clear understanding of the mechanisms that regulate the alveolar epithelium's barrier is critical to develop new therapeutic strategies to mitigate lung injury. The HER2/HER3 receptor tyrosine kinase complex plays a central role in maintaining the alveolar-capillary barrier. This receptor complex is activated by its ligand, neuregulin-1 (NRG-1). Interleukin-6 (IL-6) is also known to induce HER2 signaling through HER2 transphosphorylation by the IL-6 receptor (IL-6R) complex (1). Due to this interaction, we hypothesized that NRG-1 and IL-6 cooperatively interacted to activate the HER2/HER3 complex. Studies were performed in cultured pulmonary epithelial cells measuring the HER2/IL-6/IL-6R/GP130 interaction and receptor activation by western blotting and confocal microscopy, IL-6 production by ELISA, and IL-6 inhibition using specific antibodies, small molecule inhibitors and shRNA. We found that IL-6 was required for NRG-1 induced activation of HER2 in pulmonary epithelial cells. IL-6 inhibition led to a decrease in NRG-1 induced HER2 activation. The IL-6R and GP130, a subunit of the IL-6R complex, were physically associated with HER2 and were required for NRG-1 induced HER2 activation. Inhibition of GP130, the β-subunit of the IL-6 receptor decreased NRG-1 induced HER2 activation lower than control by 38% Finally, HER2 activation increased IL-6 secretion more than two-fold over resting cells (526 ± 131 vs 231 ± 39.7 pg/ml), and inhibition of HER2 gene expression decreased basal IL-6 secretion over 80% (89 + 4.6 vs 1.3 + 0.8 pg/ml). These findings identify a requirement for IL-6 and the IL-6R complex to allow NRG-1 mediated HER2 activation, and a HER2 driven IL-6 production feedback loop.

[A review of gene therapy for Duchenne muscular dystrophy]

Duchenne muscular dystrophy (DMD) is an X-linked recessive hereditary disease caused by mutations in the DMD gene that encodes dystrophin. It is characterized by progressive muscle weakness and degeneration of skeletal muscle and myocardium due to the absence of dystrophin. The disease often occurs at the age of 2-5 years, and most children may die of heart failure or respiratory insufficiency at the age of around 20 years. At present, supportive therapy is often used in clinical practice to improve symptoms, but this cannot improve the outcome of this disease. The development of gene therapy brings new hope to the cure of this disease. This article summarizes gene replacement therapy for DMD, including the research advances in DMD gene transduction technology mediated by adeno-associated virus, utrophin protein upregulation technology, and clustered regularly interspaced short palindromic repeat gene editing technology, and reviews the recommendations to solve the issues of adeno-associated viral load, long-term effective expression of transgenic products, and utrophin protein expression, in order to provide a reference for further research.

A Novel Regulatory Mechanism of Smooth Muscle α-Actin Expression by NRG-1/circACTA2/miR-548f-5p Axis

RATIONALE

Neuregulin-1 (NRG-1) includes an extracellular epidermal growth factor-like domain and an intracellular domain (NRG-1-ICD). In response to transforming growth factor-β1, its cleavage by proteolytic enzymes releases a bioactive fragment, which suppresses the vascular smooth muscle cell (VSMC) proliferation by activating ErbB (erythroblastic leukemia viral oncogene homolog) receptor. However, NRG-1-ICD function in VSMCs remains unknown.

OBJECTIVE

Here, we characterize the function of NRG-1-ICD and underlying mechanisms in VSMCs.

METHODS AND RESULTS

Immunofluorescence staining, Western blotting, and quantitative real-time polymerase chain reaction showed that NRG-1 was expressed in rat, mouse, and human VSMCs and was upregulated and cleaved in response to transforming growth factor-β1. In the cytoplasm of HASMCs (human aortic smooth muscle cells), the NRG-1-ICD participated in filamentous actin formation by interacting with α-SMA (smooth muscle α-actin). In the nucleus, the Nrg-1-ICD induced circular ACTA2 (alpha-actin-2; circACTA2) formation by recruitment of the zinc-finger transcription factor IKZF1 (IKAROS family zinc finger 1) to the first intron of α-SMA gene. We further confirmed that circACTA2, acting as a sponge binding microRNA (miR)-548f-5p, interacted with miR-548f-5p targeting 3' untranslated region of α-SMA mRNA, which in turn relieves miR-548f-5p repression of the α-SMA expression and thus upregulates α-SMA expression, thereby facilitating stress fiber formation and cell contraction in HASMCs. Accordingly, in vivo studies demonstrated that the localization of the interaction of circACTA2 with miR-548f-5p is significantly decreased in human intimal hyperplastic arteries compared with normal arteries, implicating that dysregulation of circACTA2 and miR-548f-5p expression is involved in intimal hyperplasia.

CONCLUSIONS

These results suggest that circACTA2 mediates NRG-1-ICD regulation of α-SMA expression in HASMCs via the NRG-1-ICD/circACTA2/miR-548f-5p axis. Our data provide a molecular basis for fine-tuning α-SMA expression and VSMC contraction by transcription factor, circular RNA, and microRNA.