Role of microRNA-122 in hepatic lipid metabolism of the weanling female rat offspring exposed to prenatal and postnatal caloric restriction

miR-743b-3p promotes hepatic lipogenesis via branched-chain amino acids (BCAA) metabolism by targeting PPM1K in aged mice

BACKGROUND

Lipid metabolism disorders appear to play an important role in the ageing process, thus understanding the cellular and molecular mechanisms underlying the association of ageing with elevated vulnerability to lipid metabolism related diseases is crucial towards promoting quality of life in old age. MicroRNAs (miRNAs) have emerged as crucial regulators of lipid metabolism, and some miRNAs have key roles in ageing.

METHODS

In this study, we investigated changes in liver lipid metabolism of ageing mice and the mechanisms of the altered expression of miRNAs in the ageing liver which contributes to the age-dependent increase in lipid synthesis. Here we found that miR-743b-3p was higher expressed in the liver tissues of ageing mice through the small RNA sequencing and bioinformatics analysis, and its target PPM1K was predicted and confirmed the target relationship of miR-743b-3p with PPM1K in the aged mouse liver tissues and the cultured senescent hepatocytes in vitro. Moreover, using the transfected miR-743b-3p mimics/inhibitors into the senescent hepatocyte AML12.

RESULTS

We found that miR-743b-3p inhibition reversed the hepatocyte senescence, and finally decreased the expression of genes involved in lipid synthesis(Chrebp, Fabp4, Acly and Pparγ) through increasing the target gene expression of PPM1K which regulated the expression of branched-chain amino acids (BCAA) metabolism-related genes (Bckdhα, Bckdk, Bcat2, Dbt).

CONCLUSIONS

These results identify that age-induced expression of miR-743b-3p inhibits its target PPM1K which induces BCAA metabolic disorder and regulates hepatocyte lipid accumulation during ageing.

miR-122/PPARβ axis is involved in hypoxic exercise and modulates fatty acid metabolism in skeletal muscle of obese rats

Hypoxic exercise is an effective intervention for obesity, because it promotes weight loss by regulating fatty acid (FA) metabolism. The regulation of peroxisome proliferator-activated receptor β (PPARβ) by miR-122 may be involved in this process, but the detailed mechanisms are unknown. In order to address this issue, we probed how miR-122 affected the expression of factors associated with FA metabolism in skeletal muscle of obese rats undergoing hypoxic training. By injecting adeno-associated virus 9 containing miR-122 overexpression vector or miR-122 inhibitor into skeletal muscles of rats with a 4-week hypoxic exercise regimen, the miR-122 expression level can be regulated. Body composition and blood lipid levels were analyzed, and PPARβ, carnitine palmitoyltransferase 1b (CPT1b), acetylCoA carboxylase 2 (ACC2), and FA synthase (FAS) mRNA and protein levels were evaluated using quantitative reverse transcription quantitative PCR(RT-qPCR) and Western blot analysis. We found that miR-122 overexpression increased low-density lipoprotein cholesterol (LDL-C) and triglyceride (TG) levels and decreased PPARβ, ACC2, and FAS expression. Conversely, miR-122 inhibition decreased TG level, increased high-density lipoprotein cholesterol (HDL-C) level, and upregulated PPARβ, ACC2, FAS, and CPT1b. These data indicated that the negative regulation of PPARβ by miR-122 promotes FA metabolism by altering the levels of the factors related to FA metabolism in skeletal muscle of obese rat under hypoxic training, thus providing molecular-level insight into the beneficial effects of this intervention.

Non-coding RNAs: The link between maternal malnutrition and offspring metabolism

Early life nutrition is associated with the development and metabolism in later life, which is known as the Developmental Origin of Health and Diseases (DOHaD). Epigenetics have been proposed as an important explanation for this link between early life malnutrition and long-term diseases. Non-coding RNAs (ncRNAs) may play a role in this epigenetic programming. The expression of ncRNAs (such as long non-coding RNA H19, microRNA-122, and circular RNA-SETD2) was significantly altered in specific tissues of offspring exposed to maternal malnutrition. Changes in these downstream targets of ncRNAs lead to abnormal development and metabolism. This review aims to summarize the existing knowledge on ncRNAs linking the maternal nutrition condition and offspring metabolic diseases, such as obesity, type 2 diabetes (T2D) and non-alcoholic fatty liver disease (NAFLD).

The Role and Mechanism of Oxidative Stress and Nuclear Receptors in the Development of NAFLD

The overproduction of reactive oxygen species (ROS) and consequent oxidative stress contribute to the pathogenesis of acute and chronic liver diseases. It is now acknowledged that nonalcoholic fatty liver disease (NAFLD) is characterized as a redox-centered disease due to the role of ROS in hepatic metabolism. However, the underlying mechanisms accounting for these alternations are not completely understood. Several nuclear receptors (NRs) are dysregulated in NAFLD, and have a direct influence on the expression of a set of genes relating to the progress of hepatic lipid homeostasis and ROS generation. Meanwhile, the NRs act as redox sensors in response to metabolic stress. Therefore, targeting NRs may represent a promising strategy for improving oxidation damage and treating NAFLD. This review summarizes the link between impaired lipid metabolism and oxidative stress and highlights some NRs involved in regulating oxidant/antioxidant turnover in the context of NAFLD, shedding light on potential therapies based on NR-mediated modulation of ROS generation and lipid accumulation.

Maternal Serum Albumin Redox State Is Associated with Infant Birth Weight in Japanese Pregnant Women

Background: Plasma albumin (ALB) reflects protein nutritional status in rats, but it is not clear whether it is associated with dietary protein insufficiency in pregnant women and/or their risk of low birth weight delivery. This study aimed to investigate whether maternal serum ALB redox state reflects maternal protein nutritional status and/or is associated with infant birth weights. Methods: The relationship between the serum reduced ALB ratio and infant birth weight was examined in an observational study of 229 Japanese pregnant women. A rat model simulating fetal growth restriction, induced by protein-energy restriction, was used to elucidate the relationship between maternal nutritional status, maternal serum ALB redox state, and birth weight of the offspring. Results: In the human study, serum reduced ALB ratio in the third trimester was significantly and positively correlated with infant birth weight. In the rat study, serum reduced ALB ratio and birth weight in the litter decreased as the degree of protein-energy restriction intensified, and a significant and positive correlation was observed between them in late pregnancy. Conclusions: Maternal serum reduced ALB ratio in the third trimester is positively associated with infant birth weight in Japanese pregnant women, which would be mediated by maternal protein nutritional status.

Molecular mechanisms governing offspring metabolic programming in rodent models of in utero stress

The results of different human epidemiological datasets provided the impetus to introduce the now commonly accepted theory coined as 'developmental programming', whereby the presence of a stressor during gestation predisposes the growing fetus to develop diseases, such as metabolic dysfunction in later postnatal life. However, in a clinical setting, human lifespan and inaccessibility to tissue for analysis are major limitations to study the molecular mechanisms governing developmental programming. Subsequently, studies using animal models have proved indispensable to the identification of key molecular pathways and epigenetic mechanisms that are dysregulated in metabolic organs of the fetus and adult programmed due to an adverse gestational environment. Rodents such as mice and rats are the most used experimental animals in the study of developmental programming. This review summarises the molecular pathways and epigenetic mechanisms influencing alterations in metabolic tissues of rodent offspring exposed to in utero stress and subsequently programmed for metabolic dysfunction. By comparing molecular mechanisms in a variety of rodent models of in utero stress, we hope to summarise common themes and pathways governing later metabolic dysfunction in the offspring whilst identifying reasons for incongruencies between models so to inform future work. With the continued use and refinement of such models of developmental programming, the scientific community may gain the knowledge required for the targeted treatment of metabolic diseases that have intrauterine origins.

Roles of Regulatory RNAs in Nutritional Control

Small RNAs (sRNAs), including microRNAs (miRNAs), are noncoding RNA (ncRNA) molecules involved in gene regulation. sRNAs play important roles in development; however, their significance in nutritional control and as metabolic modulators is still emerging. The mechanisms by which diet impacts metabolic genes through miRNAs remain an important area of inquiry. Recent work has established how miRNAs are transported in body fluids often within exosomes, which are small cell-derived vesicles that function in intercellular communication. The abundance of other recently identified ncRNAs and new insights regarding ncRNAs as dietary bioactive compounds could remodel our understanding about how foods impact gene expression. Although controversial, some groups have shown that dietary RNAs from plants and animals (i.e., milk) are functional in consumers. In the future, regulating sRNAs either directly through dietary delivery or indirectly by altered expression of endogenous sRNA may be part of nutritional interventions for regulating metabolism.