Melatonin treatment reduces endoplasmic reticulum stress and modulates the unfolded protein response in rabbits with lethal fulminant hepatitis of viral origin

Hepatocyte apoptosis plays an important role in the development of fulminant hepatic failure (FHF). The objective of this study was to investigate whether endoplasmic reticulum (ER) stress and unfolded protein response (UPR) inhibition is an underlying mechanism of melatonin anti-apoptotic effects in an animal model of FHF of viral origin induced by the rabbit hemorrhagic disease virus (RHDV). Rabbits were experimentally infected with 2x10(4) hemagglutination units of a RHDV isolate and received melatonin at two concentrations of 10mg/kg and 20mg/kg at 0hr, 12hr and 24hr postinfection. RHDV infection induced increased expression of CCAAT/enhancer-binding protein homologous protein (CHOP), immunoglobulin heavy chain binding protein (BiP/GRP78), glucose-regulated protein 94 (GRP94), phospho-c-Jun N-terminal kinase (JNK) and caspase-12. These effects were attenuated by melatonin. Double immunofluorescence staining showed colocalization of CHOP and cleaved caspase-3 in liver sections of RHDV-infected rabbits, while immunostaining decreased markedly with melatonin treatment. RHDV infection resulted in significant increases in the mRNA levels of activating transcription factor 6 (ATF6), ATF4, inositol-requiring enzyme 1 (IRE1), spliced X-box binding protein-1 (XBP1s) and tumor necrosis factor receptor-associated factor 2 (TRAF2). Melatonin attenuated the extent of the changes. Data obtained provide evidence that in rabbits with experimental infection by RHDV, reduction in apoptotic liver damage by melatonin is associated with attenuation of ER stress through a modulation of the three arms of UPR signaling and further support a potential hepatoprotective role of melatonin in FHF.