The dystrophin-associated protein complex (DAPC) provides a mechanical link between the intracellular cytoskeleton and extracellular matrix, serving as a mechanosensor and signal transducer across the sarcolemma. Pharmacological stimulation of AMP-activated protein kinase (AMPK) induces the expression of DAPC components in skeletal muscle, whereas physiological reductions in AMPK are associated with DAPC dysfunction. We sought to determine whether AMPK was necessary for the maintenance of DAPC expression in skeletal muscle. Fast glycolytic extensor digitorum longus (EDL) and slow oxidative soleus (SOL) muscles from wild-type (WT) mice, as well as from littermates deficient in both isoforms of the AMPK-β subunit in skeletal muscle (MKO) were analyzed. DAPC mRNA levels, as well as protein expression and localization were similar between genotypes, with the exception of nNOS, which displayed a compensatory sarcolemmal enrichment in MKO muscles. The content of transcriptional and post-transcriptional regulators of the DAPC, such as PGC-1α and KSRP, were also not affected by the loss of AMPK. However, MyoD and myogenin expression was significantly diminished in MKO muscles, which is consistent with previous reports of myopathy in these animals. Furthermore, we observed decrements in extrasynaptic utrophin expression selectively in MKO SOL muscles, despite an adaptive accumulation of PGC-1α at the sarcolemmal compartment. Collectively the evidence indicates that AMPK is sufficient, but not essential for the maintenance of DAPC expression in skeletal muscle. However, AMPK is required for preserving extrasynaptic utrophin levels in slow, oxidative muscles, which underscores the role of AMPK in the gene expression of this disease modifying protein. / Thesis / Master of Science (MSc) / The dystrophin-associated protein complex (DAPC) connects the interior and exterior of muscle cells. Activation of AMP-activated protein kinase (AMPK) increases the expression of the DAPC in skeletal muscle. We sought to determine whether AMPK was necessary for DAPC expression in skeletal muscle. Fast and slow muscles from normal mice, as well as from those deficient in skeletal muscle AMPK (MKO) were analyzed. We found DAPC levels and localization were similar between both groups, with the exception of nNOS, which was enriched at the muscle membrane in MKO muscles. Regulators of the DAPC were also not affected by the loss of AMPK. However, genes important for the production of muscle were significantly diminished in MKO muscles. Furthermore, we observed decrements in utrophin at the muscle membrane selectively in slow MKO muscles. Our work indicates that AMPK is not essential for the DAPC expression in skeletal muscle, however it is required for preserving utrophin levels in slow, oxidative muscles.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/22227 |
| Date | January 2017 |
| Creators | Dial, Athan |
| Contributors | Ljubicic, Vladimir, Kinesiology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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