TNF stimulation induces VHL overexpression and impairs angiogenic potential in skeletal muscle myocytes

Abstract

Decreased skeletal muscle capillarization is considered to significantly contribute to the development of pulmonary cachexia syndrome (PCS) and progressive muscle wasting in several chronic inflammatory diseases, including chronic obstructive pulmonary disease (COPD). It is unclear to which extent the concurrent presence of systemic inflammation contributes to decreased skeletal muscle capillarization under these conditions. The present study was designed to examine in vitro the effects of the pro-inflammatory cytokine, tumor necrosis factor (TNF), on the regulation of hypoxia-angiogenesis signal transduction and capillarization in skeletal muscles. For this purpose, fully differentiated C2C12 skeletal muscle myocytes were stimulated with TNF and maintained under normoxic or hypoxic conditions. The expression levels of the putative elements of the hypoxia-angiogenesis signaling cascade were examined using qPCR, western blot analysis and immunofluorescence. Under normoxic conditinos, TNF stimulation increased the protein expression of anti-angiogenic von-Hippel Lindau (VHL), prolyl hydroxylase (PHD)2 and ubiquitin conjugating enzyme 2D1 (Ube2D1), as well as the total ubiquitin content in the skeletal muscle myocytes. By contrast, the expression levels of hypoxia-inducible factor 1‑α (HIF1-α) and those of its transcriptional targets, vascular endothelial growth factor (VEGF)A and glucose transporter 1 (Glut1), were markedly reduced. In addition, hypoxia increased the expression of the VHL transcript and further elevated the VHL protein expression levels in C2C12 myocytes following TNF stimulation. Consequently, an impaired angiogenic potential was observed in the TNF-stimulated myocytes during hypoxia. In conclusion, TNF increases VHL expression and disturbs hypoxia-angiogenesis signal transduction in skeletal muscle myocytes. The current findings provide a mechanism linking systemic inflammation and impaired angiogenesis in skeletal muscle. This is particularly relevant to further understanding the mechanisms mediating muscle wasting and cachexia in patients with chronic inflammatory diseases, such as COPD.

Advances and challenges in skeletal muscle angiogenesis

“…Given that skeletal muscle comprises nearly 40% of body mass in humans, altering muscle CD has a significant impact on metabolism, endocrine function, and locomotion. Whereas an increased skeletal muscle CD likely indicates capillary growth (angiogenesis) linked with functional improvements, decreased skeletal muscle CD (i.e., capillary rarefaction) is associated with poor health outcomes and declining prognosis in association with many chronic diseases, such as peripheral arterial disease ( 77 , 87 ), diabetes ( 79 , 80 ), cachexia ( 7 ), and chronic obstructive pulmonary disease ( 74 ). It is therefore important to understand the mechanisms involved in the regulation of muscle capillaries to both optimize physiological outcomes and ameliorate pathological consequences.…”

Effects of oral N-acetylcysteine on walking capacity, leg reactive hyperemia, and inflammatory and angiogenic mediators in patients with intermittent claudication

“…Increased oxidative stress and inflammation have been linked to impaired angiogenic signaling and microvascular rarefaction in skeletal muscle (2,62). We anticipated that oral treatment with NAC would enhance exercise-induced increase in angiogenic mediators in PAD.…”

“…Among other consequences, repeated exposure to these injurious events is thought to promote functional and structural abnormalities in skeletal muscle (13,24,44) and endothelial dysfunction (57). In addition, increased inflammation and oxidative stress are associated with vascular rarefaction (22) and might impair the angiogenic potential of exercise (2,62). Thus strategies that prevent and/or minimize exercise-induced oxidative stress and inflammation can potentially restore skeletal muscle function, improve endothelial function, and enhance the benefits of exercise in patients with IC.…”

Effects of hereditary moderate high fat diet on metabolic performance and physical endurance capacity in C57BL/6 offspring

“…Subsequent to three repeats for acclimation, the exhaustion test was carried out until mice stayed on the shaker plate for more than 10 sec without attempting to run. The exhaustion time and distance were recorded for each subject (16,17).…”