Dietary magnesium deficiency impaired intestinal structural integrity in grass carp (Ctenopharyngodon idella)

Shuo-Peng Wei,Yang Liu,Yong-An Zhang,Sheng-Yao Kuang,Wei-Dan Jiang,Pei Wu,Jun Jiang,Yun-Yun Zeng,Lin Feng,Ling Tang,Xiao-Qiu Zhou

doi:10.1038/s41598-018-30485-8

Abstract

Grass carp (223.85–757.33 g) were fed diets supplemented with magnesium (73.54–1054.53 mg/kg) for 60 days to explore the impacts of magnesium deficiency on the growth and intestinal structural integrity of the fish. The results demonstrated that magnesium deficiency suppressed the growth and damaged the intestinal structural integrity of the fish. We first demonstrated that magnesium is partly involved in (1) attenuating antioxidant ability by suppressing Nrf2 signalling to decrease antioxidant enzyme mRNA levels and activities (except CuZnSOD mRNA levels and activities); (2) aggravating apoptosis by activating JNK (not p38MAPK) signalling to upregulate proapoptotic protein (Apaf-1, Bax and FasL) and caspase-2, -3, -7, -8 and -9 gene expression but downregulate antiapoptotic protein (Bcl-2, IAP and Mcl-1b) gene expression; (3) weakening the function of tight junctional complexes (TJs) by promoting myosin light chain kinase (MLCK) signalling to downregulate TJ gene expression [except claudin-7, ZO-2b and claudin-15 gene expression]. Additionally, based on percent weight gain (PWG), against reactive oxygen species (ROS), against caspase-9 and claudin-3c in grass carp, the optimal dietary magnesium levels were calculated to be 770.38, 839.86, 856.79 and 811.49 mg/kg, respectively.

Highlights

Magnesium is an essential element well known for its role in activating enzymes for nutrition metabolism, energy metabolism and nucleic acid biochemistry in mammals[1]
Apart from systematic research on the relationship between magnesium deficiency and tight junctional complexes (TJs), we innovatively investigated the relationship between magnesium deficiency and oxidation, antioxidants, and cell apoptosis as well as the corresponding signalling molecules (Nrf[2], myosin light chain kinase (MLCK) and JNK) in animal intestines, aiming to determine the possible mechanism of fish intestinal structural integrity with magnesium treatment
We found that dietary magnesium downregulated ZO-2b gene expression only in grass carp proximal intestine (PI) and that dietary magnesium had no influence on claudin-7b and -7a gene expression in the intestines of this fish

Summary

Introduction

Magnesium is an essential element well known for its role in activating enzymes for nutrition metabolism, energy metabolism and nucleic acid biochemistry in mammals[1]. In animal livers, magnesium could activate the phosphatidylethanolamine N-methyltransferase pathway[21,22] to synthesize lecithin (an important lipid in the cytomembrane) in the liver (rather than in the intestine)[23] This evidence indicates that the effect of magnesium on the structural integrity of animal intestines is different from that in other organs. To date, there have been no studies on animal intestines focused on the relationship between magnesium deficiency and oxidation, antioxidants and cell apoptosis, and no reports have addressed the corresponding mechanisms in animals. In the 3T3-L1 adipocytes of rats, insulin could stimulate phosphorylation of MLCK39 According to these discoveries, it is imperative to systematically investigate the relationship between magnesium deficiency and TJs as well as the corresponding molecular mechanisms in animals. Studying the dietary magnesium requirements of grass carp (223.85–757.33 g) is imperative

Methods

Results

Discussion

Conclusion