Program 5-8-2019 ERG 1 A POTASSIUM CHANNEL ABUNDANCE VARIES WITHIN SPECIFIC SKELETAL MUSCLE AND FIBER TYPE

Luke Anderson: Presented to the SIU Honors Program on May 8, 2019 at Southern Illinois University Carbondale. TITLE: ERG1A POTASSIUM CHANNEL ABUNDANCE VARIES WITHIN SPECIFIC SKELETAL MUSCLE AND FIBER TYPE MAJOR PROFESSOR: Amber Pond, Ph. D. Skeletal muscle atrophy is defined as a 5% or greater loss of muscle mass that occurs with muscle disuse, muscle and neural injuries, disease (e.g., cancer, diabetes), and also happens naturally with aging. Atrophy results from an imbalance of protein degradation and protein synthesis which produces a net loss of protein. The protein loss occurs mostly through three proteolytic systems: Calpain enzymes, cathespin enzymes, and the largest contributor, the ubiquitin proteasome pathway (UPP). The ether-a-go-go related gene (ERG1A) is a voltage gated K channel that is upregulated in atrophying skeletal muscle. Expression of ERG1A in skeletal muscle increases UPP activity and induces atrophy. Initial immunohistochemistry suggested that ERG1A might be more abundant in certain muscle fibers. Indeed, skeletal muscle fibers vary in their composition of the myosin heavy chain (MyHC) proteins which participate in muscle contraction. MyHC composition determines muscle fiber contraction speed, producing a slow-twitch fiber type and a number of fast-twitch fiber types. Different muscles are composed of varying numbers of fast and slow-twitch fibers which produce their specific contraction speed. Because ERG1A appears variably expressed in muscles composed of mixed fiber types and is a K channel which has the potential to modulate contraction speed by enhancing repolarization, we hypothesized that ERG1A would be more abundant in slow-twitch fibers than in fast-twitch fibers in skeletal muscle. To test this hypothesis, we cryo-sectioned Soleus (SOL), Extensor Digitorum Longus (EDL), and Gastrocnemius muscles of rats. These muscles were chosen because the SOL and EDL have an abundance of slow and fast-twitch fibers, respectively, while the Gastrocnemius contains a more heterogeneous composition. The sections were co-immunostained for the ERG1A protein and either the fast or slow-twitch MyHC. ERG1A fluorescence was measured in the sarcolemma of each fiber type and compared. The data reveal that the ERG1A protein is more abundant in muscle fibers of the Sol than in the EDL; however, these muscles are very homogeneous in terms of fiber type so it was not possible to get enough data from both fiber types within a muscle to compare ERG1A composition in each. Therefore, we immunostained fibers from the heterogeneous Gastrocnemius muscle. The data reveal that ERG1A is 3.2-fold greater in slow than in fast fibers in this muscle. This knowledge will allow us to concentrate our investigations into the role of ERG1A in the development of atrophy on muscles in which ERG1A is most highly abundant. Indeed, atrophy is a potentially debilitating condition for which there is no truly effective pharmacological treatment. Currently, exercise and diet are the best treatments to combat atrophy; however, sick and elderly individuals may not be able to participate in this effectively. Thus, further research into the mechanism(s) that regulate muscle atrophy is necessary for developing new treatments or therapies to combat muscle atrophy for those sick or elderly individuals.