Functional interaction between cholinergic and adrenergic systems in the maintenance of muscle mass and motor endplate

Abstract

Although previous studies have revealed a major role of cAMP signaling in controlling the stabilization of the nicotinic acetylcholine receptors (AchRs) at the neuromuscular junction, the physiological regulators of this pathway remain elusive. We have recently demonstrated that the Sympathetic Nervous System (SNS) plays an important role in controlling the skeletal muscle protein metabolism through the activation of ²2-adrenoceptors and cAMP/PKA signaling. Thus, we hypothesize that beyond protective effects on muscle mass, the SNS mediates the stabilization of AchRs at motor endplate. For this purpose, mice will be treated with clenbuterol, a selective ²2-agonist and the kinetics of AchRs lifetimes upon pulse labeling of mouse muscles with ¹²uI-±-bungarotoxin in vivo (using innervated and denervated muscles). Additionaly, we will employ in vivo imaging of mouse neuromuscular synapses. To elucidate the molecular mechanisms related to these effects we will quantitate the PKA activity, cAMP content, and the expression of genes and proteins related to atrophy (atrogin-1 and MuRF1) and autophagy (GABARAP and LC3). In parallel, the phosphorylation levels of Akt, a key protein in the control of protein metabolism, will be estimated. We aim to further define the role of the cholinergic innervation in the control of protein metabolism. Following addition of cholinergic agonists in isolated rat muscles, we shall measure the activity of diverse proteolytic pathways and rates of protein synthesis, in the presence or absence of ²2-agonists. These results will contribute to a better understanding of the functional interaction between cholinergic and adrenergic systems in the maintenance of muscle mass and motor endplate. (AU)