Abstract

The Liver Kinase B1 (LKB1)/AMP-Activated Protein Kinase (AMPK) signaling pathway is a major regulator of skeletal muscle metabolic processes. During exercise, LKB1-mediated phosphorylation of AMPK leads to its activation, promoting mitochondrial biogenesis and glucose transport, among other effects. The roles of LKB1 and AMPK have not been fully characterized in the diaphragm. Two methods of AMPK activation were used to characterize LKB1/AMPK signaling in diaphragms from muscle-specific LKB1 knockout (KO) and littermate control (C) mice: (1) acute injection of 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) and (2) 5-min direct electrical stimulation (ES) of the diaphragm. Diaphragms were excised 60 minutes post-AICAR injection and immediately after ES. AMPK phosphorylation increased with AICAR and ES in C but not KO mice. Acetyl CoA carboxylase (ACC) phosphorylation increased with AICAR in C but not KO mice, but increased in both genotypes with ES. While the majority of mitochondrial enzyme levels were lower in KO diaphragms, uncoupling protein 3 (UCP-3) levels were not different between genotypes. A IIx to IIb fiber type switch was observed in KO diaphragms. While in vitro peak force generation was similar between genotypes, KO diaphragms fatigued more quickly and had an impaired ability to recover. In conclusion, LKB1 regulates AMPK phosphorylation, mitochondrial enzyme expression, fiber type distribution, as well as recovery of the diaphragm from fatigue.

Degree

College and Department

Life Sciences; Physiology and Developmental Biology

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