Testosterone and Long Pulse Width Stimulation for Denervated Muscles after Spinal Cord Injury

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Our long-term goal is to develop a rehabilitation strategy to mitigate the deleterious changes in muscle size and lower leg lean mass in persons with denervation following spinal cord injury (SCI). Currently, there is no available rehabilitation intervention following lower motor neuron (LMN) denervation. More than 46,000 Veterans are affected with SCI and may experience profound skeletal muscle atrophy and loss of lean mass and about 20-25% experience LMN denervation. Skeletal muscle cross-sectional area is 6 times smaller following LMN denervation compared to the innervated muscles. Denervation atrophy may be accompanied by several SCI health-related consequences. Twelve weeks of twice weekly of surface neuromuscular electrical stimulation (NMES) resistance training (RT) can elicit more than a 35% increase in skeletal muscle size, decreased ectopic adipose tissue accumulation, increased insulin sensitivity after SCI. Moreover, the applicant’s CDA-2 preliminary findings showed that 16 weeks of NMES-RT and testosterone replacement therapy (TRT) increased leg lean mass by 1.5 kg with no changes in the TRT group only. This was accompanied by an increase in the basal metabolic rate (BMR) of 218 kcal/day in the NMES-RT+TRT with no changes in the TRT group. During the course of recruitment for the study, 20% of individuals with SCI were excluded and could not benefit from exercising their lower extremity muscles, presumably because of LMN denervation. Long pulse width stimulation (LPWS; 120-150 ms) has the potential to stimulate denervated muscles and to restore muscle size in people with SCI. The previous paradigm has focused on daily activation of the denervated muscles without applying progressive loading similar to RT. Daily training is not a clinically feasible approach in persons with SCI. Moreover, previous trials did not focus on enhancing the neuromuscular homeostasis by promoting the increase in lean mass independent of LMN denervation. Testosterone replacement therapy (TRT) has been shown to increase lean mass and basal metabolic rate in hypogonadal men with SCI. We will determine if TRT+LPWS would increase skeletal muscle size, leg lean mass and improve overall metabolic health in SCI persons with LMN denervation. We hypothesize that the one year TRT+LPWS protocol will upregulate protein synthesis pathways, down- regulate protein degradation pathways and increase overall mitochondrial health. Three specific aims will address these hypotheses. Aim 1 will assess the effects of TRT+LPWS compared to TRT+ standard neuromuscular electrical stimulation (NMES; as a control group) on the size of thigh skeletal muscle, intramuscular fat (IMF) and leg lean mass. Aim 2 will determine the association between the changes in skeletal muscle size, leg lean mass and the metabolic profile as determined by measuring BMR, serum lipids and carbohydrate profile. Aim 3 will investigate the cellular mechanisms responsible for evoking skeletal muscle hypertrophy following TRT+LPWS. This study is novel because it provides a feasible rehabilitation intervention by combining two approaches; which are likely to improve the quality of life in SCI persons with LMN denervation. If proven successful, the intervention will be easily translated into clinical practice for persons with SCI.