Multiple organ failure (MOF) is a leading cause of death in trauma patients. Even with success of acute trauma management with fluid resuscitation and organ support protocols, many patients who survive their initial trauma are at high risk to progress towards a persistent organ injury. Clinical evidence suggests that advanced age is a risk factor for persistence of MOF and mortality. The molecular mechanisms and the impact of age in the persistence of MOF are yet to be defined. Furthermore, therapeutic strategies to promote recovery of organ function remain unavailable. Scientific evidence suggests that mitochondrial dysfunction is a critical pathogenetic event of MOF. In preliminary studies, we have observed that autophagy, an important process which enables the cells to dispose defective mitochondria, is impaired during hemorrhagic shock in the kidney of old rats (18-24 months) when compared to younger animals (2-3 months). This age-dependent impairment of autophagy correlates with severity of kidney injury and inflammatory response. At molecular analysis, we have identified AMP-activated protein kinase (AMPK) as a key signaling molecule regulating organ function and potential recovery after hemorrhagic shock. This kinase is a crucial energy status sensor, which is known to negatively regulate the autophagy controller the mammalian target of rapamycin complex 1 (mTORC1). Conversely, AMPK activates the peroxisome proliferator-activated receptor (PPAR) coactivator 1-a (PGC-1a), the master regulator of mitochondrial biogenesis, i.e. the process of restoration of functional mitochondria. Of clinical relevance, we have also observed that treatment with metformin, a common drug used for type 2 diabetes that activates AMPK through the upstream liver kinase B1 (LKB1), reduces kidney inflammation and ameliorates cardiovascular function in old rats subjected to hemorrhagic shock. Thus, our preliminary data raise the novel hypothesis that an age-dependent dysregulation of AMPK causes impairment of autophagy and reduction of mitochondrial biogenesis, leading to persistence of organ injury during hemorrhagic shock. The long-term goal of this project is to identify target pathways and to evaluate pharmacological treatments for organ dysfunction by maintaining proper disposal of damaged organelle and promoting organ recovery.
Three aims are proposed to validate these novel concepts.
In aim 1 we will determine the age-dependent alterations of autophagy and mitochondrial biogenesis and their correlation with AMPK activation during hemorrhagic shock in major organs of rats of different ages.
In aim 2 we will adopt pharmacological studies to determine the role of AMPK on hemorrhage-induced systemic inflammatory response, MOF and lethality in rats of different ages.
In aim 3 we will use AMPKa knockout mice to define the molecular mechanisms by which AMPK activates autophagy and mitochondrial biogenesis through regulation of mTORC1, PGC-1a, and SIRT1, a deacetylase described for its anti-aging properties. These studies may unveil novel regulatory paradigms that impact organ metabolic recovery and may lead to new therapies in hemorrhagic shock.
The management of geriatric trauma patients in critical care is extremely challenging because of the high risk of morbidity and mortality in this population segment. Our project is aimed to the understanding of the molecular mechanisms that regulate recovery of organ function in aging and hemorrhagic shock. We will investigate the mechanisms of autophagy, an important process that enables the cells to dispose defective mitochondria, and the mechanisms of mitochondrial biogenesis, an important process that enables the cells to generate new functional mitochondria. Our multidisciplinary pharmacological and genetic studies in experimental rodent models of hemorrhagic shock will provide clinically relevant information on novel candidate molecules that promote organ recovery and may be used as new treatment strategies in hemorrhagic shock.
