Previous studies in burn injury by the Project 3 PI have demonstrated that alterations in post-receptor insulin signaling may be responsible for the insulin resistance of burn injury. The preliminary data are consistent with the hypothesis that burn-induced insulin resistance may be related to changes in IRS-1 phosphorylation and not alterations in insulin production and/or insulin clearance. Thus, alterations in phosphorylation of IRS-1 related to activation of the stress kinase enzymes may alter IRS-1 function and/or degradation and contribute to the development of burn-induced insulin resistance.

Hypothesis Guiding the Research

Alterations in the phosphorylation and/or degradation of insulin receptor substrate 1 (IRS-1) produced by burn injury may be responsible for burn-induced insulin resistance. Specifically, the reduction in glucose transport in skeletal muscle following burn injury may be secondary to altered abundance and/or phosphorylation of IRS-1. It is proposed that altered serine phosphorylation of IRS-1 following burn injury – mediated by the activation of the stress kinases (p38, MAPK or SAPK intermediate pathway) by cytokines such as interleukin-6 or Tumor Necrosis Factor – can alter IR/IRS-1 interaction as well as IRSI/PI 3-kinase interaction. Moreover, the abundance of IRS-1 is a major determinant of insulin signaling and the degradation of IRS-1 is controlled, in part, through altered IRS-1 ser/thr phosphorylation, for example, by an mTOR-dependent pathway. Therefore, it is proposed that burn injury may increase the turnover of IRS-1.

Specific Aims

Specific Aim 1 determines in vivo skeletal muscle glucose transport/phosphorylation and protein synthesis/catabolism under the effects of insulin resistance of burn injury. The study also uses PET technology combined with isotope tracer techniques to determine glucose and protein metabolic rates.

Specific Aim 2 evaluates the activities of the stress kinase enzymes involved in IRS-1 phosphorylation after injury.

Specific Aim 3 determines the phosphorylation sites on IRS-1 using a newly developed monoclonal antibody. In vivo phosphorylation sites are compared with in vitro phosphorylation site using purified recombinant kinases, such as p39, MAPK, SAPK and mTOR.

Innovation

The investigations into the mechanisms of insulin receptor dysfunction in proximal receptor events via an integrated set of studies in human subjects and model systems should help us to further characterize and understand changes in glucose and protein metabolism during burn injury. Alteration in IRS-1 phosphorylation status as the potential underlying cause of burn-associated insulin resistance is an original and novel concept. Utilization of PET technology should provide new information, not currently available. New knowledge from this project would serve as the basis for the rational design of interventions aimed at minimizing the untoward consequences of impaired glucose metabolism and homeostasis.

For more information about this project, please contact Dr. Edward Carter.