The expression and function of gelatinolytic activity at the rat neuromuscular junction upon physical exercise.

Marine Yeghiazaryan,Anna M Cabaj,Urszula Sławińska,Grzegorz M Wilczyński

doi:10.1007/s00418-014-1273-3

Abstract

The gelatinases MMP-9 and MMP-2 have been implicated in skeletal muscle adaptation to training; however, their specific role(s) in the different muscle types are only beginning to be unraveled. Recently, we found that treadmill running increased the activity and/or expression of these enzymes in myonuclei and in activated satellite cells of the soleus (Sol), but not extensor digitorum longus (EDL) muscles on the fifth day of training of adult rats. Here, we asked whether the gelatinases can be involved in physical exercise-induced adaptation of the neuromuscular compartment. To determine the subcellular localization of the gelatinolytic activity, we used high-resolution in situ zymography and immunofluorescence techniques. In both control and trained muscles, strong gelatinolytic activity was associated with myelin sheaths within intramuscular nerve twigs. In EDL, but not Sol, there was an increase in the gelatinolytic activity at the postsynaptic domain of the neuromuscular junction (NMJ). The increased activity was found within punctate structures situated in the vicinity of synaptic cleft of the NMJ, colocalizing with a marker of endoplasmic reticulum. Our results support the hypothesis that the gelatinolytic activity at the NMJ may be involved in NMJ plasticity.

Highlights

Endurance exercise has been recognized as an important stimulus improving muscle contractile properties (Gollnick 1986)
In the study of Andonian and Fahim (1987), it was shown that 30 days of endurance treadmill exercise resulted in an increased nerve terminal area and a number of branches in the extensor digitorum longus (EDL) and Sol muscles of young adult rats, with greater magnitude of changes in the EDL
Similar results were established by Waerhaug et al (1992), who described the significant increase in the area and length of the nerve terminals after 6 weeks of treadmill running in EDL, but not in Sol of young adult rats

Summary

Introduction

Endurance exercise (repetitive, prolonged exercise of submaximal intensity) has been recognized as an important stimulus improving muscle contractile properties (Gollnick 1986). We reported that gelatinase activity of soleus (Sol) is enhanced after repetitive training, e.g., under this condition there is upregulation of MMP-2 in the myonuclei and upregulation of MMP-9 in Histochem Cell Biol (2015) 143:143–152 the cytoplasm of activated satellite cells/myoblasts in Sol [but not in extensor digitorum longus (EDL)] (Yeghiazaryan et al 2012). It is known, that muscle adaptation to training is associated with structural and functional changes in the neuromuscular compartment, including the neuromuscular junction (NMJ) (Nishimune et al 2014). We performed a detailed morphological analysis of the gelatinolytic activity at the NMJ in rat EDL and Sol muscle

Methods

Results

Conclusion