Muscle weakness accompanies all forms of critical illnesses including burns, resulting in hypoventilation, dependence on respirators, and decreased mobilization, all of which lead to increased morbidity and mortality. The loss of muscle strength is out of proportion to loss of muscle mass. It is hypothesized (a) since prolonged open channel time of acetylcholine receptors (AChRs) due to congenital mutations of AChRs results in muscle weakness, the weakness of muscles in close proximity to bums is related to the expression of gamma subunits containing an """"""""immature"""""""" isoform of AChRs, which also have a longer mean open-channel time; (b) that akin to that seen in many congenital muscular dystrophies (CMDs), the weakness in muscles at sites distant from burn occurs as a result of changes in muscle membrane structural components termed dystrophin associated complexes (DACs). It is postulated that the pathophysiological bases for the neuromuscular changes following burns are related to (a) decreased signaling via agrin, important for clustering, expression, and maturation of the AChRs, and (b) decreased growth factor signaling via Akt/PKB, important for stabilization and maintenance of DACs, respectively. Related to the above:
Specific Aim 1 tests the hypotheses (1) that muscles in close proximity to burn injury express an immature isoform of AChRs at the neuromuscular junction (NMJ), resulting in aberrant neurotransmission, (2) that these AChR changes are related to increased expression of iNOS, resulting in decreased signaling of agrin, and (3) that iNOS inhibitors and/or exogenous agrin will reverse the AChR changes and enhance muscle function.
Specific Aim 2 tests the hypothesis that the diminished contractility of skeletal muscle at sites distant from bum is due to changes in muscle membrane DAC, independent of AChRs, since AChRs are unaltered at sites distant from burn. Muscle membrane costamere integrity will be determined by confocal microscope. Biochemical fractionation techniques (velocity gradients) will be utilized to detect molecular localization of each DAC component (dystrophin, dystroglycan, caveolin-3, and integrin), since abnormal localization of these membranes will result in disruption of costamere integrity.
Specific Aim 3 using the rat in vivo model and the in vitro cell culture model, tests the hypothesis that bum injury-induced malformation of DAC is due to decreased pro-anabolic signaling via Akt/PKB.
Specific Aim 4 tests the hypothesis that the attenuated Akt/PKB activity at sites distant from burn can be rectified by parenteral IGF-I or adenovirus transfer of Akt/PKB, both of which will restore the DAC integrity and function to normal. Delineation of the pathophysiology of burn-induced muscle dysfunction will provide a scientific rationale for therapeutic approaches to prevent muscular complications of burns. These mechanistic studies will also help to understand the molecular etiology of other acquired and congenital diseases of muscle, which affect muscle function in a vast number of adult and pediatric patients.
Showing the most recent 10 out of 27 publications
