Maternal obesity promotes offspring non-alcoholic fatty liver disease (NAFLD) through disruption of endoplasmic reticulum homeostasis
Junpei Soeda1, Angelina Mouralidarane1, Esra Asilmaz1, Shuvra Ray1, Joaquim Pombo2, Lucilla Poston2, Paul D. Taylor2, Jude A. Oben1,3
1Institute for Liver and Digestive Health, University College London, London, United Kingdom; 2Division of Women's Healh, King's College London, London, United Kingdom; 3Gastroenterology and Hepatology, Guy's and St Thomas' Hospital, London, United Kingdom
We previously showed that maternal obesity (MO) programs offspring obesity and non-alcoholic fatty liver disease (NAFLD) with involved mechanisms unclear. Accumulating evidence suggests that endoplasmic reticulum (ER) stress induced unfolded protein response (UPR) plays a central role in the pathogenesis of steatosis and non-alcoholic steatohepatitis (NASH). It has recently been shown that one of the UPR pathways (IRE1α) follows a 12 hour period rhythmic activation in normal liver but demonstrates constant activation in obese, leptin deficient, ob/ob mice. However, little is known about the role of UPR in developmentally programmed NAFLD. AIMS & METHODS: C57BL6 mice were fed standard chow (SC) or an obesogenic diet (OD) for 6 weeks prior to pregnancy, throughout pregnancy and lactation. Litters were weaned onto standard or an OD to generate 4 groups. Animals were sacrificed at 4-hourly intervals over a 12: 12hr light- dark cycle periods at 6 months. We initially studied UPR pathway at one specific time point and then further characterised rhythmic expression of specific UPR markers at all time points. RESULTS: Offspring exposed to MO and a post-weaning OD (OffOb-OD) developed profound NAFLD compared to those exposed to post-partum OD alone (OffCon-OD) or the control group (OffCon-SC), as assessed by raised ALT (p<0.001) and NAFLD Activity Score (p<0.01). At a single time point, phospho eIF-2alpha was specifically increased in Offob-OD (p<0.05) compared to OffCon-SC. ATF6 cleavage and the spliced form of XBP-1 were most abundantly expressed in Offob-OD. Also, Phopho SAPK/JNK, and Lc3BII protein expression were significantly increased in Offob-OD compared to OffCon-SC. In parallel CHOP expression was significantly higher in OffOb-OD compared to OffCon-Sc and Offob-OD. Furthermore, hepatocyte apoptosis was detected in Offob-OD. These results indicate that unresolved UPR is significantly activated in OffCon-OD. However, GRP78, a major ER chaperone and central regulator for ER stress, was significantly downregulated in Offob-OD. UPR induced chaperone (GRP94) and ER-associated protein degradation (ERAD) related genes (HERP and EDEM) were downregulated in OffCon-OD and Offob-OD. Further analysis at all time points showed that all 3 proximal sensors of UPR were continuously activated in Offob-OD while 12h rhythmic expression of GRP78 was blunted in Offob-OD. Finally, UPR downstream ERAD genes showed either a 12h or 24h rhythmic expression which was attenuated in Offob-OD. CONCLUSION: MO and a post-natal OD profoundly disrupted ER homeostasis in offspring. We propose that disrupted ER homeostasis may be involved in the propagation of programmed of NAFLD.
The following people have nothing to disclose: Junpei Soeda, Angelina Mouralidarane, Esra Asilmaz, Shuvra Ray, Joaquim Pombo, Lucilla Poston, Paul D. Taylor, Jude A. Oben