Vegf And Hb-egf Expression And Localization In Chronically Overloaded Rat Plantaris And Soleus Muscle

Abstract

Skeletal muscle hypertrophy is mediated by local mitogens that promote fiber growth and structural reorganization during this anabolic state. Two biochemicals that may participate in this process include Heparin-Binding Epidermal Growth Factor (HB-EGF) and Vascular Endothelial Growth Factor (VEGF). PURPOSE: To determine the expression profile and localization of HB-EGF and VEGF following functional overload (FO) of rat hindlimb muscles. METHODS: Bilateral FO for 3 and 7d (n= 5/group) of the plantaris and soleus muscles in adult female Sprague-Dawley rats was induced through surgical ablation of the gastrocnemius muscle and compared to normal controls (Con). Temporal protein expression levels were assessed through immunoblot analysis and localization was determined using immunofluorescent histochemistry. RESULTS: Absolute and relative (mg/g) soleus and plantaris muscle mass was increased (p<0.05) at 3 and 7d FO compared to Con. HB-EGF levels during FO were similar to Con. A muscle-specific response for VEGF expression occurred in the soleus and plantaris muscles at 3d FO: soleus VEGF decreased (p<0.05); conversely, a trend (p = 0.12) for elevated VEGF occurred in the plantaris. VEGF at 7d FO were similar to Con in both muscles. Immnunohistochemistry revealed a strong fiber membrane-specific localization for VEGF in both FO muscles. VEGF also appeared to be localized to fiber ends. CONCLUSION: VEGF expression profiles during FO were muscle-specific. The transient decrease of VEGF in the soleus during early FO may indicate a saturated VEGF state in this highly oxidative and vascular muscle. VEGF localization in proximity to the membrane suggests a role for vascular remodeling of the capillary network.