Leptin up-regulates microRNA-27a/b-3p level in hepatic stellate cells

The miR-23-27-24 cluster: an emerging target in NAFLD pathogenesis

The incidence of non-alcoholic fatty liver disease (NAFLD) is increasing globally, being the most widespread form of chronic liver disease in the west. NAFLD includes a variety of disease states, the mildest being non-alcoholic fatty liver that gradually progresses to non-alcoholic steatohepatitis, fibrosis, cirrhosis, and eventually hepatocellular carcinoma. Small non-coding single-stranded microRNAs (miRNAs) regulate gene expression at the miRNA or translational level. Numerous miRNAs have been shown to promote NAFLD pathogenesis and progression through increasing lipid accumulation, oxidative stress, mitochondrial damage, and inflammation. The miR-23-27-24 clusters, composed of miR-23a-27a-24-2 and miR-23b-27b-24-1, have been implicated in various biological processes as well as many diseases. Herein, we review the current knowledge on miR-27, miR-24, and miR-23 in NAFLD pathogenesis and discuss their potential significance in NAFLD diagnosis and therapy.

Leptin Enhances Hepatic Fibrosis and Inflammation in a Mouse Model of Cholestasis

Leptin is an adipokine with roles in food intake and energy metabolism through its actions on neurons in the hypothalamus. The role of leptin in obesity and cardiovascular disorders is well documented. However, its influence on liver conditions such as cholestasis is poorly understood. The effects of exogenous leptin and leptin-neutralizing antibody on biliary hyperplasia, hepatic fibrosis, and inflammation in the multidrug resistance protein 2 knockout (Mdr2KO) mouse model of cholestasis were assessed by quantifying markers specific for cholangiocytes, activated hepatic stellate cells (HSCs), and cytokines. Serum and hepatic leptin were increased in Mdr2KO mice compared with FVB/NJ (FVBN) controls, and exogenous leptin enhanced biliary hyperplasia and liver fibrosis in Mdr2KO and FVBN mice. Leptin administration increased hepatic expression of C-C motif chemokine ligand 2 and IL-6 in Mdr2KO mice. In contrast, leptin-neutralizing antibody reduced intrahepatic bile duct mass and decreased HSC activation in Mdr2KO mice compared with FVBN controls. Sex-related differences were noted, with female Mdr2KO mice having more leptin than males. In cholangiocytes and LX2 cells in vitro, leptin increased phosphorylated Akt and stimulated cell proliferation. Leptin receptor siRNA and inhibitors of Akt phosphorylation impaired leptin-induced cell proliferation and proinflammatory cytokines. The current data suggest that leptin is abnormally increased in cholestatic mice, and excess leptin increases ductular reaction, hepatic fibrosis, and inflammation via leptin receptor-mediated phosphorylation of Akt in cholangiocytes and HSCs.

Leptin: an entry point for the treatment of peripheral tissue fibrosis and related diseases

Leptin is a small peptide mainly secreted by adipocyte, which acts on the central nervous system of the hypothalamus to regulate the body's energy balance by inhibiting food intake, it also can directly act on specific cells through leptin receptors (for example, ObRa, which exists in the blood-brain barrier or kidneys), thereby affect cell metabolism. Excessive deposition of extracellular matrix (ECM) causes damage to normal tissues or destruction of organ structure, which will eventually lead to tissue or organ fibrosis. The sustainable development of fibrosis can lead to structural damage and functional decline of organs, and even exhaustion, which seriously threatens human health and life. In recent years, studies have found that leptin directly alleviates the fibrosis process of various tissues and organs in mammals. Therefore, we speculate that leptin may become a significant treatment for fibrosis of various tissues and organs in the future. So, the main purpose of this review is to explore the specific mechanism of leptin in the process of fibrosis in multiple tissues and organs, and to provide a theoretical basis for the treatment of various tissues and organs fibrosis and related diseases caused by it, which is of great significance in the future.

Non-coding RNA crosstalk with nuclear receptors in liver disease

The dysregulation of nuclear receptors (NRs) underlies the pathogenesis of a variety of liver disorders. Non-coding RNAs (ncRNAs) are defined as RNA molecules transcribed from DNA but not translated into proteins. MicroRNAs (miRNAs) and long non-coding RNAs (lncRNAs) are two types of ncRNAs that have been extensively studied for regulating gene expression during diverse cellular processes. NRs as therapeutic targets in liver disease have been exemplified by the successful application of their pharmacological ligands in clinics. MiRNA-based reagents or drugs are emerging as flagship products in clinical trials. Advancing our understanding of the crosstalk between NRs and ncRNAs is critical to the development of diagnostic and therapeutic strategies. This review summarizes recent findings on the reciprocal regulation between NRs and ncRNAs (mainly on miRNAs and lncRNAs) and their implication in liver pathophysiology, which might be informative to the translational medicine of targeting NRs and ncRNAs in liver disease.

MicroRNA in cardio-metabolic disorders

Hyperlipidemia is correlated with several health problems that contain the combination of hypertension, obesity, and diabetes mellitus, which are grouped as metabolic syndrome. Though the lipid-lowering agents, such as statins, which aims to reduce serum low-density lipoprotein cholesterol (LDL-C) has been considered as one of the most effective therapeutics in treating hyperlipidemia and coronary artery diseases, the persistent high risk of atherosclerosis after intensive lipid-lowering therapy could not be simply explained by hyperlipidemia. Therefore, it is necessary to identify novel factors to manage treatment and to predict risk of cardio-metabolic events. Endeavor over the past several decades has demonstrated the important functions of microRNAs in modulating macrophage activation, lipid metabolism, and hyperlipidemia. In the present review, we summarized the recent findings which highlighted the contributions of microRNAs in regulating serum lipid metabolism. Furthermore, we also provided the potential mechanisms whereby microRNAs controlled lipid metabolism and the risk of cardio-metabolic disorders, which could help us to identify microRNAs as a promising therapeutic target for hyperlipidemia and its related cardiovascular diseases.

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.

microRNA27a-3p mediates reduction of the Wnt antagonist sFRP-1 in systemic sclerosis

Systemic Sclerosis (SSc) is an autoimmune connective tissue disease that leads to skin and lung fibrosis. The Wnt pathway is clearly elevated in SSc and is pro-fibrotic via activation of canonical Wnt signalling. sFRP-1 is a Wnt antagonist that acts as a negative regulator of Wnt signalling. We sought to measure the levels of serum sFRP-1 in early diffuse SSc patients compared to healthy controls and if this is regulated by microRNA27a-3p. Ten early diffuse SSc patients and healthy controls sera were taken and sFRP-1 quantified by ELISA. Skin biopsies were also taken in five SSc patients and controls. Fibroblasts were quantified for microRNA27-3p expression by Taqman qRT-PCR with an internal microRNA to normalize. 3'UTR luciferase assays were performed to confirm direct targets of microRNA27a-3p with microRNA overexpression. Fibroblasts were transfected with microRNA27a mimics or scramble controls and using ELISA sFRP-1 was quantified. Furthermore, Collagen, Axin-2, TIMP-1 and MMP-1 were measured. Serum sFRP-1 was significantly reduced in early diffuse SSc patients. We identified microRNA27a-3p-3p as regulating sFRP-1 in dermal fibroblasts. We found significantly elevated microRNA27a-3p in isolated dermal fibroblasts from SSc patients. We confirmed that sFRP-1 is a direct target of microRNA27a-3p through cloning of the 3'UTR into a luciferase vector. ECM genes were also upregulated by microRNA27a-3p-3p and the matrix-degrading enzyme MMP-1 was suppressed. Serum sFRP-1 is reduced in diffuse SSc patients and is regulated by microRNA27a-3p and this is a direct regulation. Modulation of microRNA27a-3p levels could mediate fibrosis regression.

Downregulation of miR‑141 deactivates hepatic stellate cells by targeting the PTEN/AKT/mTOR pathway

The activation of hepatic stellate cells (HSCs) caused by stimulating factors or fibrogenic cytokines is the critical stage of liver fibrosis. Recent studies have demonstrated the influence of microRNAs (miRNAs or miRs) on HSC activation and transformation; however, the function and underlying mechanisms of miRNAs in HSC activation have not yet been completely clarified. In the present study, transforming growth factor β1 (TGF‑β1) was used to treat human HSC lines (HSC‑T6 and LX2 cells) to simulate the activation of HSCs in vivo and whether the expression of miRNAs in HSCs was affected by TGF‑β1 treatment was examined using a miRNA microarray. It was observed that miR‑141 was one of the most upregulated miRNAs during HSC activation. Functional analyses revealed that miR‑141 knockdown suppressed the viability of HSCs and inhibited the expression levels of pro‑fibrotic markers. In addition, phosphatase and tensin homolog (PTEN), a well‑known suppressor of the AKT/mammalian target of rapamycin (mTOR) pathway, was found to be directly targeted by miR‑141 in HSCs. More importantly, the knockdown of PTEN markedly reversed the suppressive effects of miR‑141 inhibition on the viability of and the expression levels of pro‑fibrotic markers during HSC activation. Finally, it was observed that the downregulation of miR‑141 blocked the TGF‑β1‑induced activation of the AKT/mTOR pathway in HSCs. On the whole, the findings of the present study indicate that miR‑141 inhibition suppresses HSC activation via the AKT/mTOR pathway by targeting PTEN, highlighting that miR‑141 may serve as a novel therapeutic target for liver fibrosis.

Leptin Modulates the Expression of miRNAs-Targeting POMC mRNA by the JAK2-STAT3 and PI3K-Akt Pathways

The central control of energy balance involves a strongly regulated neuronal network within the hypothalamus and the brainstem. In these structures, pro-opiomelanocortin (POMC) neurons are known to decrease food intake and to increase energy expenditure. Thus, leptin, a peripheral signal that relays information regarding body fat content, modulates the activity of POMC neurons. MicroRNAs (miRNAs) are short non-coding RNAs of 22–26 nucleotides that post-transcriptionally interfere with target gene expression by binding to their mRNAs. It has been demonstrated that leptin is able to modulate the expression of miRNAs (miR-383, miR-384-3p, and miR-488) that potentially target POMC mRNA. However, no study has identified the transduction pathways involved in this effect of leptin on miRNA expression. In addition, miRNAs targeting POMC mRNAs are not clearly identified. In this work, using in vitro models, we have identified and confirmed that miR-383, miR-384-3p, and miR-488 physically binds to the 3′ untranslated (3′UTR) regions of POMC mRNA. Importantly, we show that leptin inhibits these miRNAs expression by different transduction pathways. Taken together, these results allowed us to highlight the miRNA involvement in the regulation of POMC expression downstream of the leptin signaling and satiety signal integration.

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.

Circular RNA in Liver: Health and Diseases

Circular RNA (circRNA) is an important class of noncoding RNA characterized by covalently closed continuous loop structures. In recent years, the various functions of circRNAs have been continuously documented, including effects on cell proliferation and apoptosis and nutrient metabolism. The liver is the largest solid organ in mammals, and it also performs many functions in the body, which is considered to be the busiest organ in the body. At the same time, the liver is vulnerable to multiple pathogenic factors, causing various acute and chronic liver diseases. The pathogenesis of liver disease is still not fully understood. As a rising star for the past few years, circRNAs have been proven involved in the regulation of liver homeostasis and disease. This chapter will explain the role of circRNAs in liver health and diseases and sort out the confusion in the present study.