Long-term objectives and Specific Aims- Skeletal muscle wasting in humans is a critically important manifestation of a number of conditions including, but not limited to, aging, physical inactivity, nutrient imbalance or insufficiency, hormonal imbalance or insufficiency, and a variety of disease states. Loss of muscle protein in these conditions is due largely to development of an imbalance between rates of protein synthesis and degradation. Previous work in the Sponsor's laboratory has demonstrated that the initiation of mRNA translation plays a key role in regulating protein synthesis under a number of these conditions. It has also demonstrated that this process is highly important in regulating protein expression patterns through mechanisms that mediate discrimination in the selection of mRNAs for translation. A particular focus of the work has been to develop therapeutic strategies for abrogating or reversing the loss of muscle mass associated with these conditions. Work proposed in this application builds upon insights gained from the previous studies. In particular, the work builds upon the observation that the resistance exercise-induced stimulation of protein synthesis may be mediated by a rapamycin-sensitive increased expression of the e- subunit of the guanine nucleotide exchange factor, elF2B, through unregulated translation of the mRNA for its e-subunit. This observation suggests a novel link between mTOR signaling and elF2Be protein expression, and has broader implications on the role of mTOR in translational regulation of a subset of pro-growth mRNAs that might play a role in the acute regulation of protein synthesis and ultimately hypertrophy of skeletal muscle. Therefore, the specific aims of the project are to characterize upstream signaling proteins that play a role in mTOR activation following resistance exercise, establish whether mTOR signaling is sufficient to increase elF2Be translation/protein expression, determine what target downstream of mTOR is involved in this regulation, and characterize functional elements in the mRNA that mediate translational regulation.
These aims are to be accomplished by performing proof-of-concept studies in a cell culture model in which mTOR signaling responds rapidly to physiological changes in hormones and nutrients and in which molecular manipulations can be easily accomplished through transfection strategies. Once proof-of-concept is demonstrated, selected studies will be extended to the resistance exercise model to establish physiological relevance. Lay Summary- The proposed project aims to discover specific events that can be targeted for intervention to prevent the muscle wasting that occurs during aging, physical inactivity, and a number of disease states. It builds upon important and novel previous work form the Sponsor's laboratory. ? ? ?
