Endoplasmic reticulum stress and Ca2+ dysregulation in response to ammonia nitrogen exposure could be alleviated by dietary fermented mulberry leaf meal in Megalobrama amblycephala

Abstract

The present work was conducted to investigate the protective mechanisms of mulberry leaf meal (ML) and fermented mulberry leaf meal (FML) on endoplasmic reticulum stress (ERS), Ca2+ transport, as well as oxidative stress, autophagy, and inflammation induced by ammonia nitrogen stress in the Megalobrama amblycephala juveniles. Control diet, ML2 diet (supplementary 2.2% ML2), and FML2 diet (supplementary 2.2% FML2) were fed to M. amblycephala juveniles for 8 weeks and then juveniles were exposed to a 40 h ammonia nitrogen (16 mg/L) stress experiment in the 240 L tanks. Typically, M. amblycephala juveniles fed the FML2 diet displayed better tolerance to ammonia nitrogen stress. Following ammonia nitrogen stress, the supplementation of FML2 significantly alleviated the deterioration of plasma biochemical parameters (ALT, GLU), decreased MDA content and enhanced the activities of antioxidant enzymes (CAT, T-SOD) in the liver and head kidney. Furthermore, it was observed that ERS in the liver and head kidney was inhibited in FML2 groups by selective inhibition of the different transmembrane receptors in atf6, perk, and ire1. Moreover, FML2 supplementation repressed il-6, and il-1β expressions by inhibiting the expression of chop and downstream activation of nf-κb. The imbalance expressions of Ca2+ transport-related gene from the endoplasmic reticulum to the mitochondria induced by ammonia nitrogen stress was restored in the liver and head kidney because of the dietary inclusion of ML2 and FML2. Subsequently, ML2 and FML2 supplementation effectively suppressed autophagy caused by the dysregulation of gene expressions associated with Ca2+ transport. Overall, the supplementation of FML2 in the diet of M. amblycephala juveniles helped to reduce autophagy and inflammation caused by ERS and imbalanced Ca2+ transport in response to exposure to ammonia nitrogen.