Elizabeth K. McBee1, Jacob L. Brown1, Richard A. Perry, Jr1, Kevin L. Shimkus2,David E. Lee1, Megan E. Rosa1, Jessica M. Cardin2, Lemuel A. Brown1, Yasaman Shirazi-Fard2, Harry A. Hogan2, James D. Fluckey2, Tyrone A. Washington1, Nicholas P. Greene1,2 1University of Arkansas, Fayetteville, AR. 2Texas A&M University, College Station, TX; e-mail: emcbee@uark.edu

Muscular disuse affects an abundance of people with sedentary lifestyles and/or chronic diseases. Disuse has proven to cause severe muscular atrophy and disrupt mitochondrial quality. Autophagy is a cellular mechanism used to remove wasteful or damaged materials, mitophagy is the process of autophagically removing presumably damaged mitochondria. Beclin1 and Atg7 are machinery for autophagy, while Bnip3 specifically regulates mitophagy. Any dysregulation of autophagic processes may significantly impair cellular health following muscle disuse. PURPOSE: The purpose of this study was to investigate whether multiple bouts of muscle disuse (hindlimb unloading, HU) affect the expression of markers for autophagy. METHODS: Sprague-Dawley rats were subjected to chronic disuse atrophy by hindlimb unloading (28-d, 1HU) followed by ambulatory recovery (56-d) (1HU+REC). To mimic repeated bouts of disuse, the animals were subjected to a second bout of HU (28-d, 2HU) and then allowed ambulatory recovery (2HU+REC). Control (CON) animals were allowed normal cage activity throughout. Samples were analyzed for Beclin1, Atg7, and Bnip3 mRNA content by real time RT-PCR. To verify if HU impacted autophagy markers pre-planned T-tests were performed comparing CON and 1HU. To test if multiple bouts of disuse and reloading impacted regulators of autophagy, a one-way ANOVA across all groups was employed with α set at p<0.05. RESULTS: Beclin1, Atg7, and Bnip3 mRNA contents were not different, 270% greater, and ~50% lower following 1HU compared to CON, respectively. Across all conditions, Beclin1 was unchanged. Atg7 was not different from CON in 1HU+REC, 2HU, and 2HU+REC groups. Atg7 was ~30% of 1HU in 1HU+REC and 2HU groups. Bnip3 showed no further differences among conditions. CONCLUSION: A single bout of HU enhanced the capacity for general autophagy, while diminishing the capacity for mitophagy. Recovery from repeated bouts of HU did not alter mRNA levels of autophagic markers relative to CON. These data show that autophagic markers are dysregulated with HU, and that animals adapted to multiple bouts of HU, which dampened the impact of subsequent HU on autophagic markers.

Funding provided by NASA Grant Number NNX08AQ35G

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