Mitochondrial dysfunction in skeletal muscle of fukutin deficient mice is resistant to exercise- and AICAR-induced rescue

Abstract

Disruptions in the dystrophin-glycoprotein complex (DGC) are clearly the primary basis underlying various forms of muscular dystrophies and dystroglycanopathies, but the cellular consequences of DGC disruption are still being investigated. Mitochondrial abnormalities are becoming an apparent consequence and contributor to dystrophy disease pathology. Herein, we demonstrate that muscle-specific deletion of the fukutin gene [Myf5/fktn-KO mice (KO)], a model of secondary dystroglycanopathy, results in ~30% lower muscle strength (P<0.001) and 16% lower mitochondrial function (P=0.002) compared to healthy littermate controls (LM). We also observed ~80% lower PGC-1α signaling (P=0.004), a primary transcription factor for mitochondrial biogenesis, in KO mice that likely contributes to the mitochondrial defects. PGC-1α is posttranslationally regulated via phosphorylation by AMPK. Treatment with the AMPK agonist AICAR (5-aminoimidazole-4-carboxamide ribonucleotide) failed to rescue mitochondrial deficits in KO mice (P=0.458) but did have beneficial (~30% greater) effects on recovery of muscle contractility following injury in both LM and KO mice compared to saline treatment (P=0.006).The beneficial effects of AMPK stimulation via AICAR on muscle function may be partially explained by AMPK's other role of regulating skeletal muscle autophagy, a cellular process critical for clearance of damaged and/or dysfunctional organelles. Two primary conclusions can be drawn from this data, 1) fukutin deletion produces intrinsic muscular metabolic defects that likely contribute to dystroglycanopathy disease pathology, and 2) AICAR treatment accelerates recovery of muscle function following injury suggesting AMPK signaling as a possible target for therapeutic strategies.