APOPTOSIS IN SKELETAL MUSCLE FOLLOWING BURN INJURY

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Burn injury, with and without sepsis, is associated with many functional and metabolic aberrations. In skeletal muscle, the important functional change is muscle weakness resulting in hypoventilation, dependence on respirators, and decreased mobilization. The neuromuscular dysfunction and muscle weakness associated with burns prolongs hospital stay, increases cost, morbidity and mortality. The long-term goals of these studies are, therefore, to characterize the etiology of muscle weakness and design strategies to improve tension-generating capacity of muscle in humans. Based on convincing preliminary data, the hypotheses tested in the present proposal is that apoptosis or programmed cell death occurs in skeletal muscle, at sites distant and immediately local to burn, with activation of pro-apoptotic signaling pathways. The goals of the present studies, using rats, are to: (1) Confirm and study the evolution of apoptosis in skeletal muscle at local and distant sites from burn, and in different fiber types (slow vs. fast twitch muscles). (2) Characterize the putative signaling pathways leading to apoptosis, previously documented only in in vitro systems. (3) Effectively inhibit some of the activated pro-apoptotic pathways and decrease muscle wasting and muscle weakness. Apoptosis will be confirmed by three independent methods- the ladder, TUNEL and ELISA assays. The cell membrane and downstream signaling molecules modulating apoptosis (e.g., TNFalpha, Fas, FasL, phosphatidylinositol 3-kinase, ceramide, BCL-2, BCL-X and caspases) will be assessed for expression and/or activity by using molecular pharmacological or biochemical techniques. The importance of certain signaling molecules will be confirmed by the use of knock out or transgenic (TNF, lpr or Fas, ceramide, BC12, and caspase) mice. Specific exogenous modulators (e.g., IGF-1 and caspase inhibitors) of some of the apoptotic signaling molecules will be used in vivo to attenuate muscle wasting due to apoptosis. These "reversal of apoptosis" studies will be performed in conjunction with protein turnover and functional studies to test the efficacy of these drugs to reverse the neuromuscular dysfunction of burns. The proposed studies will, therefore, delineate the neuromuscular dysfunction associated with burns, the component contributed to by apoptosis, and the potential for attenuation of both the apoptosis and the neuromuscular dysfunction by pharmacotherapy. Information obtained from the rat studies will provide a scientific basis and rationale for therapeutic maneuvers to prevent and/or rectify neuromuscular complications of burns or critical illness in humans.