Survival in critical illness is associated with early activation of mitochondrial biogenesis

Abstract

Rationale: We previously reported outcome-associated decreases in muscle energetic status and mitochondrial dysfunction in septic patients with multiorgan failure. We postulate that survivors have a greater ability to maintain or recover normal mitochondrial functionality.

Objectives: To determine whether mitochondrial biogenesis, the process promoting mitochondrial capacity, is affected in critically ill patients.

Methods: Muscle biopsies were taken from 16 critically ill patients recently admitted to intensive care (average 1-2 d) and from 10 healthy, age-matched patients undergoing elective hip surgery.

Measurements and main results: Survival, mitochondrial morphology, mitochondrial protein content and enzyme activity, mitochondrial biogenesis factor mRNA, microarray analysis, and phosphorylated (energy) metabolites were determined. Ten of 16 critically ill patients survived intensive care. Mitochondrial size increased with worsening outcome, suggestive of swelling. Respiratory protein subunits and transcripts were depleted in critically ill patients and to a greater extent in nonsurvivors. The mRNA content of peroxisome proliferator-activated receptor γ coactivator 1-α (transcriptional coactivator of mitochondrial biogenesis) was only elevated in survivors, as was the mitochondrial oxidative stress protein manganese superoxide dismutase. Eventual survivors demonstrated elevated muscle ATP and a decreased phosphocreatine/ATP ratio.

Conclusions: Eventual survivors responded early to critical illness with mitochondrial biogenesis and antioxidant defense responses. These responses may partially counteract mitochondrial protein depletion, helping to maintain functionality and energetic status. Impaired responses, as suggested in nonsurvivors, could increase susceptibility to mitochondrial damage and cellular energetic failure or impede the ability to recover normal function. Clinical trial registered with clinical trials.gov (NCT00187824).

Figure 1.

Ultrastructural features of muscles and their mitochondria. (A) Control muscle showing well-aligned sarcomeres with well-defined A, I, and M bands and Z lines. Clusters of dense mitochondria are seen between fibers. (B and C) Muscle from a sepsis survivor showing focal breakdown of muscle morphology with loss of sarcomere structural integrity and swollen or damaged mitochondria. (D and E) Muscle from a nonsurvivor showing that mitochondrial changes affect the subsarcolemmal and interfiber regions. Bar = 2 μm in all cases.

Figure 2.

Respiratory chain protein subunits and complex activities in critical illness. (A) Analysis of respiratory chain subunits and activities for Complex I (NADH dehydrogenase complex) and Complex IV (cytochrome c oxidase complex). Protein content of subunits NDUFA9, NDUFB8 and COX1, COX2, and COX4 was determined by immunoblotting and expressed semiquantitatively as pixel density relative to an internal standard, normalized to total protein stain. Sample blots are shown in Figure E1. Complex I activity is expressed as nmol NADH/min/mg protein; Complex IV is expressed as a first-order rate constant for cytochrome c (1/min/mg protein). Data are shown as median, 25th, and 75th percentiles with range (dotted line) from 9 control patients, 9 or 10 survivors, and 5 or 6 nonsurvivors. (B) Relationship of respiratory complex activities (Complexes I and IV) with citrate synthase activity (nmol/min/mg protein). Open circles, control subjects; gray diamonds, survivors; closed squares, nonsurvivors.

Figure 3.

Microarray analysis of muscle biopsies from critically ill patients versus control patients. (A) Heatmap depicting the bead-types (875 transcripts) with a mean fold-change greater than 1.5 between survivor and nonsurvivor, showing an overall P value < 0.05 (one-way analysis of variance). Red indicates increase in transcript abundance; blue indicates decrease, relative to the overall mean value (white). Details of biostatistics may be found in the online supplement. (B) Heatmaps showing relative expression of transcripts encoding subunits of OXPHOS I through V in muscle biopsies from different patient groups. I, NADH ubiquinone oxidoreductase complex; II, succinate Complexes dehydrogenase complex (includes nine bead-types for SDH-like protein SDHALP1); III, ubiquinol-cytochrome c oxidoreductase complex; IV, cytochrome c oxidase; V, ATP synthase. Mitochondrially encoded subunits were not measured. (C) Histogram showing OXPHOS transcripts meeting the set thresholds for P value and fold-change. Black bars, survivor versus nonsurvivor; light gray bars, survivor versus control; red bars, nonsurvivor versus control. Horizontal dotted lines represent the 1.5-fold change threshold. Data represent biopsies from four control subjects, five survivors, and three nonsurvivors.

Figure 4.

Changes in critical illness of the mitochondrial biogenesis factors peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α), nuclear respiratory factor-1 (NRF-1), and mitochondrial transcription factor-A (TFAM) and the mitochondrial oxidative stress protein manganese superoxide dismutase (MnSOD). (A) Transcript abundance for PGC-1α, NRF-1, and TFAM, normalized to content of 18S rRNA; median, 25th and 75th percentile and range for biopsies from 10 control patients, 9 survivors, 3 nonsurvivors. (B) Semiquantitative analysis of MnSOD (SOD2) protein from immunoblots, expressed semiquantitatively as pixel density relative to an internal standard, normalized to total protein stain. Median plus 25th and 75th percentile and range for biopsies from 10 control patients, 10 survivors, and 6 nonsurvivors. (C) Positive association between MnSOD protein and PGC-1α mRNA. Control (open circles), survivors (gray diamonds), nonsurvivors (closed squares).