# Acute Cold Exposure Cell-Autonomously Reduces mTORC1 Signaling and Protein Synthesis Independent of AMPK

## TL;DR

Cold exposure reduces protein production in muscle cells through mTORC1, regardless of AMPK activation, offering new insights into cryotherapy effects.

## Contribution

Demonstrates that mTORC1 inhibition by cold exposure occurs independently of AMPK activation in muscle cells.

## Key findings

- Cold exposure activates AMPK and reduces mTORC1 activity and protein synthesis in myoblasts.
- mTORC1 and protein synthesis are downregulated independently of AMPK activation.
- AMPK is required for cold-induced suppression of myoblast proliferation but not for mTORC1 inhibition.

## Abstract

Cryotherapy is a commonly used strategy for skeletal muscle recovery, although the efficacy of its use has been controversial. Therefore, more research is needed to understand under what circumstances it should be used. This study aimed to examine the cell-autonomous effects of acute cold exposure on primary mouse myoblasts, focusing on metabolic signaling through the AMPK/mTORC1 pathway. In it, we hypothesized that cold exposure (COLD) would impair myoblast proliferation, differentiation, and protein synthesis in an AMPK-dependent manner. Wild-type (WT) and AMPK double-knockout (dKO) myoblast cultures were treated at 37 °C or 26 °C to evaluate AMPK-dependent effects. As expected, 30 min of cold exposure activated AMPK and decreased mTORC1 activity and protein synthesis; however, mTORC1 and protein synthesis were downregulated independently of AMPK activation. Additionally, cold exposure suppressed proliferation 6 h post-treatment in WT, but not dKO, myoblasts. On the other hand, in differentiated WT and dKO cells, cold treatment did not influence myotube size, although dKO myotubes exhibited decreased fusion index and increased size compared to WT. These findings offer new insights into the cell-autonomous metabolic effects of cryotherapy in skeletal muscle and indicate that while COLD-induced AMPK activation contributes to impaired myoblast proliferation, AMPK is not necessary for the COLD-induced inhibition of the mTORC1 pathway and protein synthesis.