Leptin reduces microRNA-122 level in hepatic stellate cells in vitro and in vivo

Key events in cancer: Dysregulation of SREBPs

Lipid metabolism reprogramming is an important hallmark of tumor progression. Cancer cells require high levels of lipid synthesis and uptake not only to support their continued replication, invasion, metastasis, and survival but also to participate in the formation of biological membranes and signaling molecules. Sterol regulatory element binding proteins (SREBPs) are core transcription factors that control lipid metabolism and the expression of important genes for lipid synthesis and uptake. A growing number of studies have shown that SREBPs are significantly upregulated in human cancers and serve as intermediaries providing a mechanistic link between lipid metabolism reprogramming and malignancy. Different subcellular localizations, including endoplasmic reticulum, Golgi, and nucleus, play an indispensable role in regulating the cleavage maturation and activity of SREBPs. In this review, we focus on the relationship between aberrant regulation of SREBPs activity in three organelles and tumor progression. Because blocking the regulation of lipid synthesis by SREBPs has gradually become an important part of tumor therapy, this review also summarizes and analyzes several current mainstream strategies.

A novel regulatory facet for hypertriglyceridemia: The role of microRNAs in the regulation of triglyceride-rich lipoprotein biosynthesis

Atherosclerotic cardiovascular disease (ASCVD) is one of the major leading global causes of death. Genetic and epidemiological studies strongly support the causal association between triacylglycerol-rich lipoproteins (TAGRL) and atherogenesis, even in statin-treated patients. Recent genetic evidence has clarified that variants in several key genes implicated in TAGRL metabolism are strongly linked to the increased ASCVD risk. There are several triacylglycerol-lowering agents; however, new therapeutic options are in development, among which are miRNA-based therapeutic approaches. MicroRNAs (miRNAs) are small non-coding RNAs (18-25 nucleotides) that negatively modulate gene expression through translational repression or degradation of target mRNAs, thereby reducing the levels of functional genes. MiRNAs play a crucial role in the development of hypertriglyceridemia as several miRNAs are dysregulated in both synthesis and clearance of TAGRL particles. MiRNA-based therapies in ASCVD have not yet been applied in human trials but are attractive. This review provides a concise overview of current interventions for hypertriglyceridemia and the development of novel miRNA and siRNA-based drugs. We summarize the miRNAs involved in the regulation of key genes in the TAGRLs synthesis pathway, which has gained attention as a novel target for therapeutic applications in CVD.

microRNA-122 inhibits hepatic stellate cell proliferation and activation in vitro and represses carbon tetrachloride-induced liver cirrhosis in mice

OBJECTIVE

This study aimed to determine the roles of microRNA (miR)-122 in the activation of hepatic stellate cells (HSCs) and liver cirrhosis.

METHODS

Rat primary HSCs were incubated with transforming growth factor-beta (TGF-β), during which miR-122 and EphB2 expression was measured. miR-122 mimic and/or pcDNA3.1 EphB2 was transfected into TGF-β-induced HSCs. A mouse model of liver cirrhosis was established via an intraperitoneal injection of carbon tetrachloride (CCl₄), followed by the injection of miR-122 agomir. Levels of serum alanine transaminase (ALT) and aspartate aminotransferase (AST) were measured. Fibronectin (FN), alpha smooth muscle actin (α-SMA), Collagen I, miR-122, and EphB2 expression was evaluated in liver tissues and HSCs. Cell proliferation was measured using CCK-8 assay. Interactions between miR-122 and EphB2 were assessed using dual luciferase reporter assay.

RESULTS

miR-122 (0.15-fold) was downregulated and EphB2 (mRNA: 5.06-fold; protein: 2.35-fold) was upregulated after TGF-β induction of HSCs. Overexpressed miR-122 decreased proliferation and EphB2 (mRNA: 0.46-fold; protein: 0.62-fold), FN (mRNA: 0.45-fold; protein: 0.64-fold), α-SMA (mRNA: 0.48-fold; protein: 0.51-fold), and Collagen I (mRNA: 0.44-fold; protein: 0.51-fold) expression in HSCs, which was abrogated by EphB2 upregulation. miR-122 expression was reduced by 0.21-fold and serum ALT and AST levels were enhanced in mice following 8-week CCl₄ induction along with increased expression of FN, α-SMA, and Collagen I in liver tissues, which was blocked by miR-122 overexpression. Moreover, EphB2 was a target gene of miR-122.

CONCLUSION

miR-122 curtails HSC proliferation and activation by targeting EphB2 and suppresses liver cirrhosis in mice.

Post-Transcriptional Regulation of Gnrhr: A Checkpoint for Metabolic Control of Female Reproduction

The proper expression of gonadotropin-releasing hormone receptors (GnRHRs) by pituitary gonadotropes is critical for maintaining maximum reproductive capacity. GnRH receptor expression must be tightly regulated in order to maintain the normal pattern of expression through the estrous cycle in rodents, which is believed to be important for interpreting the finely tuned pulses of GnRH from the hypothalamus. Much work has shown that Gnrhr expression is heavily regulated at the level of transcription. However, researchers have also discovered that Gnrhr is regulated post-transcriptionally. This review will discuss how RNA-binding proteins and microRNAs may play critical roles in the regulation of GnRHR expression. We will also discuss how these post-transcriptional regulators may themselves be affected by metabolic cues, specifically with regards to the adipokine leptin. All together, we present evidence that Gnrhr is regulated post-transcriptionally, and that this concept must be further explored in order to fully understand the complex nature of this receptor.

Unraveling the Role of Leptin in Liver Function and Its Relationship with Liver Diseases

Since its discovery twenty-five years ago, the fat-derived hormone leptin has provided a revolutionary framework for studying the physiological role of adipose tissue as an endocrine organ. Leptin exerts pleiotropic effects on many metabolic pathways and is tightly connected with the liver, the major player in systemic metabolism. As a consequence, understanding the metabolic and hormonal interplay between the liver and adipose tissue could provide us with new therapeutic targets for some chronic liver diseases, an increasing problem worldwide. In this review, we assess relevant literature regarding the main metabolic effects of leptin on the liver, by direct regulation or through the central nervous system (CNS). We draw special attention to the contribution of leptin to the non-alcoholic fatty liver disease (NAFLD) pathogenesis and its progression to more advanced stages of the disease as non-alcoholic steatohepatitis (NASH). Likewise, we describe the contribution of leptin to the liver regeneration process after partial hepatectomy, the mainstay of treatment for certain hepatic malignant tumors.

Mechanistic insights into the effects of SREBP1c on hepatic stellate cell and liver fibrosis

Sterol regulatory element-binding protein 1c (SREBP1c) plays key roles in maintenance of hepatic stellate cell (HSC) quiescence. The present researches investigated the mechanisms underlying the effects of SREBP1c on HSCs and liver fibrogenesis by HSC-targeted overexpression of the active SREBP1c using adenovirus in vitro and in vivo. Results demonstrated that SREBP1c exerted inhibitory effects on TAA-induced liver fibrosis. SREBP1c down-regulated TGFβ1 level in liver, reduced the receptors for TGFβ1 and PDGFβ, and interrupted the signalling pathways of Smad3 and Akt1/2/3 but not ERK1/2 in HSCs. SREBP1c also led to the decreases in the protein levels of the bromodomain-containing chromatin-modifying factor bromodomain protein 4, methionine adenosyltransferase 2B (MAT2B) and TIMP1 in HSCs. In vivo activated HSCs did not express cyclin D1 and cyclin E1 but SREBP1c down-regulated both cyclins in vitro. SREBP1c elevated PPARγ and MMP1 protein levels in the model of liver fibrosis. The effect of SREBP1c on MAT2B expression was associated with its binding to MAT2B1 promoter. Taken together, the mechanisms underlying the effects of SREBP1c on HSC activation and liver fibrosis were involved in its influences on TGFβ1 level, the receptors for TGFβ1 and PDGFβ and their downstream signalling, and the molecules for epigenetic regulation of genes.

The Emerging Role of MicroRNAs in NAFLD: Highlight of MicroRNA-29a in Modulating Oxidative Stress, Inflammation, and Beyond

Non-alcoholic fatty liver disease (NAFLD) is a common cause of chronic liver disease and ranges from steatosis to steatohepatitis and to liver fibrosis. Lipotoxicity in hepatocytes, elevated oxidative stress and the activation of proinflammatory mediators of Kupffer cells, and fibrogenic pathways of activated hepatic stellate cells can contribute to the development of NAFLD. MicroRNAs (miRs) play a crucial role in the dysregulated metabolism and inflammatory signaling connected with NAFLD and its progression towards more severe stages. Of note, the protective effect of non-coding miR-29a on liver damage and its versatile action on epigenetic activity, mitochondrial homeostasis and immunomodulation may improve our perception of the pathogenesis of NAFLD. Herein, we review the biological functions of critical miRs in NAFLD, as well as highlight the emerging role of miR-29a in therapeutic application and the recent advances in molecular mechanisms underlying its liver protective effect.

Long-term abuse of a high-carbohydrate diet is as harmful as a high-fat diet for development and progression of liver injury in a mouse model of NAFLD/NASH

OBJECTIVES

Non-alcoholic fatty liver disease (NAFLD) has become the most common liver disease globally. It is caused by a complex network of factors, including diet. The hallmark of NAFLD is the benign accumulation of triacylglycerols, however, this condition may worsen into non-alcoholic steatohepatitis (NASH), a more severe form associated with inflammation and fibrosis. Currently, no therapies are available, and diet modifications are the only strategy. Although there is increasing evidence emerging about how an abuse of carbohydrates could be involved in the progression of liver injury, a comprehensive understanding of the damage induced by an enriched carbohydrate diet is still far from complete. The aim of this study was to investigate and compare the effects of a low-fat/high-carbohydrate diet (LF-HCD) with high-fat (HFD) and standard (SD) diets in a nutritional mouse model of NAFLD/NASH.

METHODS

Histologic, real-time polymerase chain reaction, and immunohistochemical evaluations were performed.

RESULTS

The results showed that the prolonged abuse of both LF-HCDs and HFDs induced a significant increase in hepatic steatosis, inflammation, and fibrosis scores compared with SD. At the same time, both LF-HCDs and HFDs led to significant increases in the expression of the molecules involved in the progression of NAFLD that we assessed (perilipin, CD68, TGF-β1, CTGF, leptin, leptin receptor, and α-SMA).

CONCLUSIONS

The present study highlighted that the simple substitution of fats with carbohydrates is not a proper strategy to prevent or mitigate the progression of NAFLD/NASH. Further studies are required to define the best nutritional strategy to prevent NAFLD and its related metabolic syndrome.

The cross-talk between adipokines and miRNAs in health and obesity-mediated diseases

BACKGROUND

Multiple studies have revealed a direct correlation between obesity and the development of multiple comorbidities, including metabolic diseases, cardiovascular disorders, chronic inflammatory disease, and cancers. However, the molecular mechanism underlying the link between obesity and the progression of these diseases is not completely understood. Adipokines are factors that are secreted by adipocytes and play a key role in whole body homeostasis. Collaboratively, miRNAs are suggested to have key functions in the development of obesity and obesity-related disorders. Based on recently emerging evidence, obesity leads to the dysregulation of both adipokines and obesity-related miRNAs. In the present study, we described the correlations between obesity and its related diseases that are mediated by the mutual regulatory effects of adipokines and miRNAs.

METHODS

We reviewed current knowledge of the modulatory effects of adipokines on miRNAs activity and their relevant functions in pathological conditions and vice versa.

RESULTS

Our research reveals the ability of adipokines and miRNAs to control the expression and activity of the other class of molecules, and their effects on obesity-related diseases.

CONCLUSIONS

This study may help researchers develop a roadmap for future investigations and provide opportunities to develop new therapeutic and diagnostic methods for treating obesity-related diseases.

Molecular Insight into the Interaction between Epigenetics and Leptin in Metabolic Disorders

Nowadays, it is well-known that the deregulation of epigenetic machinery is a common biological event leading to the development and progression of metabolic disorders. Moreover, the expression level and actions of leptin, a vast adipocytokine regulating energy metabolism, appear to be strongly associated with epigenetics. Therefore, the aim of this review was to summarize the current knowledge of the epigenetic regulation of leptin as well as the leptin-induced epigenetic modifications in metabolic disorders and associated phenomena. The collected data indicated that the deregulation of leptin expression and secretion that occurs during the course of metabolic diseases is underlain by a variation in the level of promoter methylation, the occurrence of histone modifications, along with miRNA interference. Furthermore, leptin was proven to epigenetically regulate several miRNAs and affect the activity of the histone deacetylases. These epigenetic modifications were observed in obesity, gestational diabetes, metabolic syndrome and concerned various molecular processes like glucose metabolism, insulin sensitivity, liver fibrosis, obesity-related carcinogenesis, adipogenesis or fetal/early postnatal programming. Moreover, the circulating miRNA profiles were associated with the plasma leptin level in metabolic syndrome, and miRNAs were found to be involved in hypothalamic leptin sensitivity. In summary, the evidence suggests that leptin is both a target and a mediator of epigenetic changes that develop in numerous tissues during metabolic disorders.