Genome-level expression profiles in pediatric septic shock indicate a role for altered zinc homeostasis in poor outcome

Abstract

Human septic shock involves multiple genome-level perturbations. We have conducted microarray analyses in children with septic shock within 24 h of intensive care unit admission, using whole blood-derived RNA. Based on sequential statistical and expression filters, there were 2,482 differentially regulated gene probes (1,081 upregulated and 1,401 downregulated) between patients with septic shock (n = 42) and controls (n = 15). Both gene lists encompassed several biologically relevant gene ontologies and canonical pathways. Notably, many of the genes downregulated in the patients with septic shock, relative to the controls, participate in gene ontologies related to metal or zinc homeostasis. Comparison of septic shock survivors (n = 33) and nonsurvivors (n = 9) demonstrated differential regulation of 63 gene probes. Among the 63 gene probes differentially regulated between septic shock survivors and nonsurvivors, two isoforms of metallothionein (MT) demonstrated increased expression in the nonsurvivors. Consistent with the ability of MT to sequester zinc in the intracellular compartment, nonsurvivors had lower serum zinc levels compared with survivors. In a corroborating study of murine sepsis, MT-null mice demonstrated a survival advantage compared with wild-type mice. These data represent the largest reported cohort of pediatric patients with septic shock that has undergone genome-level expression profiling based on microarray. The data are biologically plausible and demonstrate that genome-level alterations of zinc homeostasis may be prevalent in clinical pediatric septic shock.

Figure 1

Two dimensional gene cluster map representing 2,482 genes differentially regulated between patients with septic shock and control patients (see text for filtering strategy). Individual patients are oriented horizontally and individual genes are oriented vertically. The color coded bar at the bottom of the map represents controls in grey and the patients with septic shock in black.

Figure 2

Two dimensional gene cluster map representing 63 genes differentially regulated between septic shock survivors and nonsurvivors (see text for filtering strategy). Individual patients are oriented horizontally and individual genes are oriented vertically. The color coded bar at the bottom of the map represents survivors in grey and nonsurvivors in black.

Figure 3

ELISA data (mean ± SEM) verifying that nonsurvivors with septic shock have increased serum levels of IL-8 protein compared to survivors and control patients. * p < 0.05 versus controls and survivors.

Figure 4

Serum zinc levels (mean ± SEM) demonstrating that nonsurvivors with septic shock have decreased serum zinc levels compared to survivors. * p < 0.05 versus survivors.

Figure 5

Survival study demonstrating that MT-null mice have a survival advantage compared to wild-type mice 72 hours after CLP (p = 0.03, Fisher’s exact test, n = 11 animals per group).