Acute high‐intensity muscle contraction moderates AChR gene expression independent of rapamycin‐sensitive mTORC1 pathway in rat skeletal muscle

Abstract

The relationship between mechanistic target of rapamycin complex 1 (mTORC1) activation after resistance exercise and acetylcholine receptor (AChR) subunit gene expression remains largely unknown. Therefore, we aimed to investigate the effect of electrical stimulation‐induced intense muscle contraction, which mimics acute resistance exercise, on the mRNA expression of AChR genes and the signalling pathways involved in neuromuscular junction (NMJ) maintenance, such as mTORC1 and muscle‐specific kinase (MuSK). The gastrocnemius muscle of male adult Sprague–Dawley rats was isometrically exercised. Upon completion of muscle contraction, the rats were euthanized in the early (after 0, 1, 3, 6 or 24 h) and late (after 48 or 72 h) recovery phases and the gastrocnemius muscles were removed. Non‐exercised control animals were euthanized in the basal state (control group). In the early recovery phase, Agrn gene expression increased whereas LRP4 decreased without any change in the protein and gene expression of AChR gene subunits. In the late recovery phase, Agrn, Musk, Chrnb1, Chrnd and Chrne gene expression were altered and agrin and MuSK protein expression increased. Moreover, mTORC1 and protein kinase B/Akt‐histone deacetylase 4 (HDAC) were activated in the early phase but not in the late recovery phase. Furthermore, rapamycin, an inhibitor of mTORC1, did not disturb changes in AChR subunit gene expression after muscle contraction. However, rapamycin addition slightly increased AChR gene expression, while insulin did not impact it in rat L6 myotube. These results suggest that changes in the AChR subunits after muscle contraction are independent of the rapamycin‐sensitive mTORC1 pathway.

Abstract

• What is the central question of this study?

  Can muscle contraction‐induced activation of mechanistic target of rapamycin complex 1 (mTORC1) be linked to changes in acetylcholine receptor (AChR) gene expression and molecular signalling for maintaining neuromuscular junctions (NMJs)?

• What is the main finding and its importance?

  An acute high‐intensity muscle contraction dynamically changes AChR gene expression and muscle‐specific kinase (MuSK) signalling proteins at the late recovery phase of the contraction. Additionally, pharmacological inhibition of mTORC1 via rapamycin does not affect muscle contraction‐induced alterations in AChR genes. Our findings indicate that an acute high‐intensity muscle contraction induces changes in MuSK signalling and mTORC1‐independent changes in expression of AChR genes.