Severe burn-induced endoplasmic reticulum stress and hepatic damage in mice

Severe burn injury results in liver dysfunction and damage, with subsequent metabolic derangements contributing to patient morbidity and mortality. On a cellular level, significant postburn hepatocyte apoptosis occurs and likely contributes to liver dysfunction. However, the underlying mechanisms of hepatocyte apoptosis are poorly understood. The endoplasmic reticulum (ER) stress response/ unfolded protein response (UPR) pathway can lead to hepatocyte apoptosis under conditions of liver dysfunction. Thus, we hypothesized that ER stress/UPR may mediate hepatic dysfunction in response to burn injury. We investigated the temporal activation of hepatic ER stress in mice after a severe burn injury. Mice received a scald burn over 35% of their body surface and were killed at 1, 7, 14, and 21 d postburn. We found that severe burn induces hepatocyte apoptosis as indicated by increased caspase-3 activity ( P< 0.05). Serum albumin levels decreased postburn and remained lowered for up to 21 d, indicating that constitutive secretory protein synthesis was reduced. Significantly, upregulation of the ER stress markers glucose-related protein 78 (GRP78)/BIP, protein disulfide isomerase (PDI), p-protein kinase R-like endoplasmic reticulum kinase (p-PERK), and inositol-requiring enzyme 1α (IRE-1α) were found beginning 1 d postburn ( P< 0.05) and persisted up to 21 d postburn ( P< 0.05). Hepatic ER stress induced by burn injury was associated with compensatory upregulation of the calcium chaperone/storage proteins calnexin and calreticulin ( P< 0.05), suggesting that ER calcium store depletion was the primary trigger for induction of the ER stress response. In summary, thermal injury in mice causes long-term adaptive and deleterious hepatic function alterations characterized by significant upregulation of the ER stress response.