Downregulation of diaphragm electron transport chain and glycolytic enzyme gene expression in sepsis

Abstract

Cellular energy metabolism is altered in sepsis as a consequence of dysfunction of mitochondrial electron transport and glycolytic pathways. The purpose of the present study was to determine whether sepsis is associated with compensatory increases in gene expression of electron transport chain and glycolytic pathway proteins or, alternatively, whether gene expression decreases in sepsis, contributing to abnormalities in energy metabolism. Studies were performed using diaphragms from control and endotoxin-treated (8 mg x kg(-1) x day(-1)) rats; at 48 h after endotoxin administration, animals were killed. Microarrays and RNAse protection assays were used to assess the expression of several electron transport chain components (cytochrome-c oxidase subunits Cox 5A, Cox 5B, and Cox 6A, ATP synthase, and ATP synthase subunit 5B) and of the rate-limiting enzyme for glycolysis, phosphofructokinase (PFK). Western blotting was used to assess protein levels for these electron transport chain subunits and PFK. Activity assays were used to assess electron transport chain and phosphofructokinase function. We found that sepsis evoked 1) a downregulation of genes encoding all examined electron transport chain components (e.g., cytochrome-c oxidase 5A decreased 45 + 7%, P < 0.01) and PFK (P < 0.001), 2) reductions in protein levels for these electron transport chain subunits and PFK (P < 0.05 for each), and 3) decreases in mitochondrial state 3 respiration rates and phosphofructokinase enzyme activity (P < 0.01 for each comparison). We speculate that these sepsis-induced reductions in the expression of genes encoding critical electron transport and glycolytic proteins contribute to the development and persistence of sepsis-induced abnormalities in cellular energy metabolism.