Nitric oxide and mitochondrial biogenesis in sepsis

Piantadosi, Claude

Abstract

This revised competitive renewal application seeks to understand how nitric oxide (NO) production in bacterial sepsis causes both mitochondrial damage and regulates mitochondrial quality control, which protects against organ failure. In the previous grant cycle, we discovered that toll-like receptor (TLR) activation of NF-kB- dependent NO synthase (iNOS/NOS2) is involved in the regulation of hepatic mitochondrial biogenesis through the major co-activator, PGC-11 and the adenosine monophosphate (AMP)-activated protein kinase (AMPK). Our preliminary data in mice with sepsis indicate that: NOS2 induction leads to AMPK activation, AMPK helps to activate mitochondrial biogenesis, but not always after ATP depletion, and NOS2 deficiency diminishes AMPK up-regulation and mitochondrial biogenesis and increases apoptosis and inflammation in response to TLR activation. Thus, AMPK appears to activate mitochondrial biogenesis while opposing apoptosis and inflammation in sepsis. In contrast, too much NO is independently associated with mitochondrial damage and loss of NO signal specificity by chemical attack of NO species (NOx) on proteins and nucleic acids. We hypothesize that NOS2, acting in part through AMPK, is required for apposite regulation of the transcriptional program of mitochondrial biogenesis before the failure of ATP production in order to maintain mitochondrial quality control and prevent cell death in sepsis. A test of this hypothesis requires definitions of NO-dependent transcriptional control mechanisms, the role of AMPK, and the chemical biology of mitochondrial NO in relevant model systems. Our approach will focus on the liver as a sentinel organ and on one genetic factor- NOS2- as a quantitative influence on mitochondrial turnover and cell survival. We plan to test these Specific Aims:
Aim 1 : To determine the role of NOS2 on hepatic mitochondrial biogenesis and cell survival during severe sepsis through quantitative NOS2 gene titration studies. 1A. Define the relationships between NOx-mediated mtDNA and protein damage, respiratory capacity, high-energy metabolite levels, and sepsis-induced hepatic cell death using NOS2 titration. 1B. Assess the importance of NOS2 expression on the regulation of mitochondrial biogenesis in sepsis through CREB and/or NRF-1 induction and regulation of NRF-21 (GABPA) and/or PGC-11 expression.
Aim 2 : To understand hepatic AMPK activation in sepsis in relation to NOS2, the transcriptional program of mitochondrial biogenesis, and prevention of apoptosis. 2A. Determine if NO-dependent AMPK activation promotes mitochondrial biogenesis in sepsis through CREB and/or prevents apoptosis by inhibitory phosphorylation of pro-apoptotic proteins, Bad and BNIP3. 2B. Determine if pharmacological activation of AMPK in sepsis can promote mitochondrial biogenesis and/or inhibit apoptosis independently of NOS2. These studies will provide new insights into NOx-induced mitochondrial damage in sepsis in the context of physiological mechanisms by which NOS2 regulates mitochondrial biogenesis and the extent to which it is orchestrated by AMPK. By implication, NO regulation of AMPK would play a critical salvage role in MODS, and this knowledge would allow rational new pharmacological approaches to support mitochondrial function while minimizing collateral damage by NOx.

Public Health Relevance

This application proposes to study mechanisms of how nitric oxide (NO) production during bacterial sepsis regulates the pro-survival transcriptional program of mitochondrial biogenesis. The prevalence and cost of sepsis is high, and the multiple organ dysfunction syndrome (MODS) has a high mortality in which damage to mitochondria, the cellular organelles responsible for making energy available for work, is an important, but poorly understood, component. Our research strategy is based on understanding how damage to mitochondria is resolved under genetic control by the nucleus and through a cytoplasmic kinase complex called AMPK. This new information on NO and AMPK is amenable to pharmacological manipulation and will be directly translatable to new therapeutic approaches to critically ill patients with severe infections.