Regulation and mechanism of action of miRNAs on insulin resistance in skeletal muscles

The term "insulin resistance" is commonly understood as a decrease in the response of insulin-sensitive tissues to insulin at its sufficient concentration, leading to chronic compensatory hyperinsulinemia. Type 2 diabetes mellitus is based on mechanisms consisting in the development of resistance to insulin in target cells (hepatocytes, adipocytes, skeletal muscle cells), resulting in the termination of an adequate response of these tissues to interaction with insulin. Since in healthy people 75-80% of glucose is utilized by skeletal muscle, it is more likely that the main cause of insulin resistance is impaired insulin-stimulated glucose utilization by skeletal muscle. With insulin resistance, skeletal muscles do not respond to insulin at its normal concentration, thereby determining an increase in glucose levels and a compensatory increase in insulin production in response to this. Despite many years of studying diabetes mellitus (DM) and insulin resistance, the molecular genetic basis for the development of these pathological conditions is still the subject of numerous studies. Recent studies point to the involvement of microRNAs (miRNAs) as dynamic modifiers in the pathogenesis of various diseases. MiRNAs are a separate class of RNA molecules that play a key role in the post-transcriptional regulation of gene expression. Recent studies have shown that miRNAs dysregulation in DM is closely related to miRNAs regulatory abilities in skeletal muscle insulin resistance. This gave grounds to consider an increase or decrease in the expression of individual microRNAs in muscle tissue and consider them as new biomarkers for diagnosing and monitoring insulin resistance and promising directions for targeted therapy. This review presents the results of scientific studies examining the role of miRNAs in skeletal muscle insulin resistance.

MicroRNAs' role in the environment-related non-communicable diseases and link to multidrug resistance, regulation, or alteration

The discovery of microRNAs (miRNAs) 20 years ago has advocated a new era of "small molecular genetics." About 2000 miRNAs are present that regulate one third of the genome. MiRNA dysregulated expression arising as a response to our environment insult or stress or changes may contribute to several diseases, namely non-communicable diseases, including tumor growth. Their presence in body fluids, reflecting level alteration in various cancers, merit circulating miRNAs as the "next-generation biomarkers" for early-stage tumor diagnosis and/or prognosis. Herein, we performed a comprehensive literature search focusing on the origin, biosynthesis, and role of miRNAs and summarized the foremost studies centering on miR value as non-invasive biomarkers in different environment-related non-communicable diseases, including various cancer types. Moreover, during chemotherapy, many miRNAs were linked to multidrug resistance, via modulating numerous, environment triggered or not, biological processes and/or pathways that will be highlighted as well.

Energy, Entropy and Quantum Tunneling of Protons and Electrons in Brain Mitochondria: Relation to Mitochondrial Impairment in Aging-Related Human Brain Diseases and Therapeutic Measures

Adult human brains consume a disproportionate amount of energy substrates (2-3% of body weight; 20-25% of total glucose and oxygen). Adenosine triphosphate (ATP) is a universal energy currency in brains and is produced by oxidative phosphorylation (OXPHOS) using ATP synthase, a nano-rotor powered by the proton gradient generated from proton-coupled electron transfer (PCET) in the multi-complex electron transport chain (ETC). ETC catalysis rates are reduced in brains from humans with neurodegenerative diseases (NDDs). Declines of ETC function in NDDs may result from combinations of nitrative stress (NS)-oxidative stress (OS) damage; mitochondrial and/or nuclear genomic mutations of ETC/OXPHOS genes; epigenetic modifications of ETC/OXPHOS genes; or defects in importation or assembly of ETC/OXPHOS proteins or complexes, respectively; or alterations in mitochondrial dynamics (fusion, fission, mitophagy). Substantial free energy is gained by direct O2-mediated oxidation of NADH. Traditional ETC mechanisms require separation between O2 and electrons flowing from NADH/FADH2 through the ETC. Quantum tunneling of electrons and much larger protons may facilitate this separation. Neuronal death may be viewed as a local increase in entropy requiring constant energy input to avoid. The ATP requirement of the brain may partially be used for avoidance of local entropy increase. Mitochondrial therapeutics seeks to correct deficiencies in ETC and OXPHOS.

Mitochondrial dysfunction, mitophagy, and role of dynamin-related protein 1 in Alzheimer's disease

Alzheimer's disease (AD) is the most common type of dementia and progressive neurodegenerative disease. The presence of β-amyloid (Aβ) plaques and phosphorylated Tau tangles are considered to be the two main hallmarks of AD. Recent findings have shown that different changes in the structure and dynamics of mitochondria play an important role in AD pathology progression. Mitochondrial changes in AD are expressed as enhanced mitochondrial fragmentation, altered mitochondrial dynamics, and changes in the expression of mitochondrial biogenesis genes in vitro and in vivo models. Therefore, targeting mitochondria and associated mitochondrial proteins seems to be a promising alternative instead of targeting Aβ and Tau in the prevention of Alzheimer's disease. The dynamin-related protein (Drp1) is one such protein that plays an important role in the regulation of mitochondrial division and maintenance of mitochondrial structures. Few researchers have shown that inhibition of Drp1 GTPase activity in neuronal cells rescues excessive mitochondrial fragmentation. In addition, the growing evidence revealed that Drp1 can interact with both Aβ and Tau protein in human brain tissues and mouse models. In this review, we would like to update existing knowledge about various changes in and around mitochondria related to the pathogenesis of Alzheimer's disease, with particular emphasis on mitophagy and autophagy.

MicroRNAs facilitate skeletal muscle maintenance and metabolic suppression in hibernating brown bears

Hibernating brown bears, Ursus arctos, undergo extended periods of inactivity and yet these large hibernators are resilient to muscle disuse atrophy. Physiological characteristics associated with atrophy resistance in bear muscle have been examined (e.g., muscle mechanics, neural activity) but roles for molecular signaling/regulatory mechanisms in the resistance to muscle wasting in bears still require investigation. Using quantitative reverse transcription PCR (RT-qPCR), the present study characterized the responses of 36 microRNAs linked with development, metabolism, and regeneration of skeletal muscle, in the vastus lateralis of brown bears comparing winter hibernating and summer active animals. Relative levels of mRNA of selected genes (mef2a, pax7, id2, prkaa1, and mstn) implicated upstream and downstream of the microRNAs were examined. Results indicated that hibernation elicited a myogenic microRNA, or "myomiR", response via MEF2A-mediated signaling. Upregulation of MEF2A-controlled miR-1 and miR-206 and respective downregulation of pax7 and id2 mRNA are suggestive of responses that promote skeletal muscle maintenance. Increased levels of metabolic microRNAs, such as miR-27, miR-29, and miR-33, may facilitate metabolic suppression during hibernation via mechanisms that decrease glucose uptake and fatty acid oxidation. This study identified myomiR-mediated mechanisms for the promotion of muscle regeneration, suppression of ubiquitin ligases, and resistance to muscle atrophy during hibernation mediated by observed increases in miR-206, miR-221, miR-31, miR-23a, and miR-29b. This was further supported by the downregulation of myomiRs associated with a muscle injury and inflammation (miR-199a and miR-223) during hibernation. The present study provides evidence of myomiR-mediated signaling pathways that are activated during hibernation to maintain skeletal muscle functionality in brown bears.

The Role of PGC-1α and Mitochondrial Biogenesis in Kidney Diseases

Chronic kidney disease (CKD) is one of the fastest growing causes of death worldwide, emphasizing the need to develop novel therapeutic approaches. CKD predisposes to acute kidney injury (AKI) and AKI favors CKD progression. Mitochondrial derangements are common features of both AKI and CKD and mitochondria-targeting therapies are under study as nephroprotective agents. PGC-1α is a master regulator of mitochondrial biogenesis and an attractive therapeutic target. Low PGC-1α levels and decreased transcription of its gene targets have been observed in both preclinical AKI (nephrotoxic, endotoxemia, and ischemia-reperfusion) and in experimental and human CKD, most notably diabetic nephropathy. In mice, PGC-1α deficiency was associated with subclinical CKD and predisposition to AKI while PGC-1α overexpression in tubular cells protected from AKI of diverse causes. Several therapeutic strategies may increase kidney PGC-1α activity and have been successfully tested in animal models. These include AMP-activated protein kinase (AMPK) activators, phosphodiesterase (PDE) inhibitors, and anti-TWEAK antibodies. In conclusion, low PGC-1α activity appears to be a common feature of AKI and CKD and recent characterization of nephroprotective approaches that increase PGC-1α activity may pave the way for nephroprotective strategies potentially effective in both AKI and CKD.

Micro-Ribonucleic Acid-216a Regulates Bovine Primary Muscle Cells Proliferation and Differentiation via Targeting SMAD Nuclear Interacting Protein-1 and Smad7

MicroRNAs (miRNAs), belonging to a class of evolutionarily conserved small noncoding RNA of ∼22 nucleotides, are widely involved in skeletal muscle growth and development by regulating gene expression at the post-transcriptional level. While the expression feature and underlying function of miR-216a in mammal skeletal muscle development, especially in cattle, remains to be further elucidated. The aim of this study was to investigate the function and mechanism of miR-216a during bovine primary muscle cells proliferation and differentiation. Herein, we found that the expression level of miR-216a both presented a downward trend during the proliferation and differentiation phases, which suggested that it might have a potential role in the development of bovine skeletal muscle. Functionally, during the cells proliferation phase, overexpression of miR-216a inhibited the expression of proliferation-related genes, reduced the cell proliferation status, and resulted in cells G1 phase arrest. In cells differentiation stages, overexpression of miR-216a suppressed myogenic maker genes mRNA, protein, and myotube formation. Mechanistically, we found that SNIP1 and smad7 were the directly targets of miR-216a in regulating bovine primary muscle cells proliferation and differentiation, respectively. Altogether, these findings suggested that miR-216a functions as a suppressive miRNA in development of bovine primary muscle cells via targeting SNIP1 and smad7.

Effect of miR-19b on the protective effect of Exendin-4 on islet cells in non-obese diabetic mice

This study analyzed the effect of miR-19b on the protective effect of Exendin-4 on islet cells in non-obese diabetic (NOD) mice. Twenty-four NOD/LT mice were randomized, according to the random number table, into a control group (4 µg/kg•day), a low-dose group (2 µg/kg•day Exendin-4), a medium-dose group (4 µg/kg•day Exendin-4) and a high-dose group (8 µg/kg•day Exendin-4) (n=6), with miR-19b expression interfered (an interference group) except for the control group. RT-qPCR was used to detect interference results and different doses of Exendin-4 were given for 8 weeks of intervention after the interference. CD4⁺ and CD8⁺ cell levels were detected by flow cytometry, IL-2 and IL-10 levels in the peripheral blood by enzyme-linked immunosorbent assay, and the apoptosis rate of islet cells in the pancreatic tissue by TUNEL. After 4 and 8 weeks of Exendin-4 intervention, mice in the high-dose group had lower blood glucose level than the medium-dose group (P<0.05). The medium-dose group had lower CD4⁺ cell level than the high-dose group (P<0.05), while the medium-dose group had higher CD8⁺ cell level than the high-dose group (P<0.05). After 8 weeks of intervention, compared with the medium-dose group, the high-dose group had lower IL-2 level (P<0.05), but higher IL-10 level (P<0.05). After 8 weeks of intervention, the medium-dose group had a higher apoptosis rate than the high-dose group (P<0.05). In conclusion, the decrease in miR-19b expression can improve the therapeutic effect of Exendin-4 on NOD, control blood glucose effectively and improve inflammatory response and immune function, as well as reduce islet cell injury. The increase in the dose of Exendin-4 can further improve its therapeutic effect on NOD.

Principles of Exercise Prescription, and How They Influence Exercise-Induced Changes of Transcription Factors and Other Regulators of Mitochondrial Biogenesis

Physical inactivity represents the fourth leading risk factor for mortality, and it has been linked with a series of chronic disorders, the treatment of which absorbs ~ 85% of healthcare costs in developed countries. Conversely, physical activity promotes many health benefits; endurance exercise in particular represents a powerful stimulus to induce mitochondrial biogenesis, and it is routinely used to prevent and treat chronic metabolic disorders linked with sub-optimal mitochondrial characteristics. Given the importance of maintaining a healthy mitochondrial pool, it is vital to better characterize how manipulating the endurance exercise dose affects cellular mechanisms of exercise-induced mitochondrial biogenesis. Herein, we propose a definition of mitochondrial biogenesis and the techniques available to assess it, and we emphasize the importance of standardizing biopsy timing and the determination of relative exercise intensity when comparing different studies. We report an intensity-dependent regulation of exercise-induced increases in nuclear peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) protein content, nuclear phosphorylation of p53 (serine 15), and PGC-1α messenger RNA (mRNA), as well as training-induced increases in PGC-1α and p53 protein content. Despite evidence that PGC-1α protein content plateaus within a few exercise sessions, we demonstrate that greater training volumes induce further increases in PGC-1α (and p53) protein content, and that short-term reductions in training volume decrease the content of both proteins, suggesting training volume is still a factor affecting training-induced mitochondrial biogenesis. Finally, training-induced changes in mitochondrial transcription factor A (TFAM) protein content are regulated in a training volume-dependent manner and have been linked with training-induced changes in mitochondrial content.

MicroRNA-106b promotes the proliferation, migration and invasion of retinoblastoma cells by inhibiting the expression of ZBTB4 protein

The present study investigated the function of microRNA (miR)-106b in the proliferation, migration and invasion of retinoblastoma (RB) cells, and aimed to elucidate the underlying mechanism. A total of 56 patients with RB were enrolled in the present study. The expression of miR-106b in RB tissues was measured by reverse transcription quantitative polymerase chain reaction. After transfection with miR-106b mimics or miR-106b inhibitor, a Cell-Counting kit-8 assay was used to determine the proliferation of WERI-Rb-1 cells and a Transwell assay was employed to measure the migration and invasion of the cells. Western blot analysis was performed to determine the expression of zinc finger and BTB domain containing 4 (ZBTB4) protein. By silencing or overexpression of ZBTB4 protein, the biological functions of ZBTB4 in WERI-Rb-1 cells were studied. A dual luciferase reporter assay was performed to test whether ZBTB4 was a target gene of miR-106b. The expression of miR-106b in RB tissues was elevated and closely associated with the severity of the disease. Overexpression of miR-106b increased but inhibition of miR-106b expression decreased the proliferation, migration and invasion abilities of WERI-Rb-1 cells. In addition, overexpression of miR-106b decreased but inhibition of miR-106b expression increased ZBTB4 protein expression in WERI-Rb-1 cells. Similarly, overexpression of ZBTB4 reduced but inhibition of ZBTB4 expression promoted the proliferation, migration and invasion of WERI-Rb-1 cells. Finally, miR-106b regulated the expression of ZBTB4 by binding to the 3'-untranslated region of the ZBTB4 gene. The present study demonstrated that increased expression of miR-106b in RB tissues is positively associated with the metastasis and differentiation of RB cells. As an oncogene, miR-106b promotes the proliferation, migration and invasion of WERI-Rb-1 cells by inhibiting the expression of ZBTB4 protein.

MicroRNAs and type 2 diabetes mellitus: Molecular mechanisms and the effect of antidiabetic drug treatment

The incidence of type 2 diabetes mellitus (T2DM), the most prevalent metabolic disease, is rapidly growing worldwide. T2DM has several underlying causes involved in its development. In recent decades, there is compelling evidence demonstrating that microRNAs (miRs) are implicated in the pathophysiology of T2DM. miRs are small non-coding RNAs which serve as endogenous gene regulators by binding to specific sequences in RNA and modifying gene expression toward up- or down-regulation. T2DM occurrence and complications may be influenced by increasing or decreasing the activity of some miRs. In the present narrative review, we comment on four molecular pathways/mechanisms that mediate the link between T2DM and different forms of miRs. These mechanisms include involvement of miRs in beta cells development, insulin sensitivity/resistance, insulin production/secretion and insulin signaling. The effects of antidiabetic drugs on miRs are also discussed.

Curcumin: A naturally occurring autophagy modulator

Autophagy is a self-degradative process that plays a pivotal role in several medical conditions associated with infection, cancer, neurodegeneration, aging, and metabolic disorders. Its interplay with cancer development and treatment resistance is complicated and paramount for drug design since an autophagic response can lead to tumor suppression by enhancing cellular integrity and tumorigenesis by improving tumor cell survival. In addition, autophagy denotes the cellular ability of adapting to stress though it may end up in apoptosis activation when cells are exposed to a very powerful stress. Induction of autophagy is a therapeutic option in cancer and many anticancer drugs have been developed to this aim. Curcumin as a hydrophobic polyphenol compound extracted from the known spice turmeric has different pharmacological effects in both in vitro and in vivo models. Many reports exist reporting that curcumin is capable of triggering autophagy in several cancer cells. In this review, we will focus on how curcumin can target autophagy in different cellular settings that may extend our understanding of new pharmacological agents to overcome relevant diseases.

Release of MicroRNAs into Body Fluids from Ten Organs of Mice Exposed to Cigarette Smoke

Purpose: MicroRNAs are small non-coding RNAs that regulate gene expression, thereby playing a role in a variety of physiological and pathophysiological states. Exposure to cigarette smoke extensively downregulates microRNA expression in pulmonary cells of mice, rats, and humans. Cellular microRNAs are released into body fluids, but a poor parallelism was previously observed between lung microRNAs and circulating microRNAs. The purpose of the present study was to validate the application of this epigenetic biomarker by using less invasive collection procedures. Experimental design: Using microarray analyses, we measured 1135 microRNAs in 10 organs and 3 body fluids of mice that were either unexposed or exposed to mainstream cigarette smoke for up to 8 weeks. The results obtained with selected miRNAs were validated by qPCR. Results: The lung was the main target affected by smoke (190 dysregulated miRNAs), followed by skeletal muscle (180), liver (138), blood serum (109), kidney (96), spleen (89), stomach (36), heart (33), bronchoalveolar lavage fluid (32), urine (27), urinary bladder (12), colon (5), and brain (0). Skeletal muscle, kidney, and lung were the most important sources of smoke-altered microRNAs in blood serum, urine, and bronchoalveolar lavage fluid, respectively. Conclusions: microRNA expression analysis was able to identify target organs after just 8 weeks of exposure to smoke, well before the occurrence of any detectable histopathological alteration. The present translational study validates the use of body fluid microRNAs as biomarkers applicable to human biomonitoring for mechanistic studies, diagnostic purposes, preventive medicine, and therapeutic strategies.

MicroRNA-133 overexpression promotes the therapeutic efficacy of mesenchymal stem cells on acute myocardial infarction

Background

Our study aim was to evaluate the therapeutic efficacy and mechanisms of miR-133-overexpressing mesenchymal stem cells (MSCs) on acute myocardial infarction.

Methods

Rat MSCs were isolated and purified by whole bone marrow adherent culturing. After transfection with the agomir or antagomir of miR-133, MSCs were collected for assay of cell vitality, apoptosis, and cell cycle progression. At the same time, exosomes were isolated from the supernatant to analyze the paracrine miR-133. For in-vivo studies, constitutive activation of miR-133 in MSCs was achieved by lentivirus-mediated miR-133 overexpression. A rat myocardial infarction model was created by ligating the left anterior descending coronary artery, while control MSCs (vector-MSCs) or miR-133-overexpressed MSCs (miR-133-MSCs) were injected into the zone around the myocardial infarction. Subsequently, myocardial function was evaluated by echocardiography on days 7 and 28 post infarction. Finally the infarcted hearts were collected on days 7 and 28 for myocardial infarct size measurement and detection of snail 1 expression.

Results

Hypoxia-induced apoptosis of MSCs obviously reduced, along with enhanced expression of total poly ADP-ribose polymerase protein, after miR-133 agomir transfection, while the apoptosis rate increased in MSCs transfected with miR-133 antagomir. However, no change in cell viability and cell-cycle distribution was observed in control, miR-133-overexpressed, and miR-133-interfered MSCs. Importantly, rats transplanted with miR-133-MSCs displayed more improved cardiac function after acute myocardial infarction, compared with those that received vector-MSC injection. Further studies indicated that cardiac expression of snail 1 was significantly repressed by adjacent miR-133-overexpressing MSCs, and both the inflammatory level and the infarct size decreased in miR-133-MSC-injected rat hearts.

Conclusions

miR-133-MSCs obviously improved cardiac function in a rat model of myocardial infarction. Transplantation of miR-133-overexpressing MSCs provides an effective strategy for cardiac repair and modulation of cardiac-related diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0722-z) contains supplementary material, which is available to authorized users.

Fenofibrate reverses changes induced by high-fat diet on metabolism in mice muscle and visceral adipocytes

The effect of fenofibrate on the metabolism of skeletal muscle and visceral white adipose tissue of diet-induced obese (DIO) mice was investigated. C57BL/6J male mice were fed either a control or high-fat diet for 8 weeks. Fenofibrate (50 mg/Kg BW, daily) was administered by oral gavage during the last two weeks of the experimental period. Insulin-stimulated glucose metabolism in soleus muscles, glucose tolerance test, insulin tolerance test, indirect calorimetry, lipolysis of visceral white adipose tissue, expression of miR-103-3p in adipose tissue, and miR-1a, miR-133a/b, miR-206, let7b-5p, miR-23b-3p, miR-29-3p, miR-143-3p in soleus muscle, genes related to glucose and fatty acid metabolism in adipose tissue and soleus muscle, and proteins (phospho-AMPKα2, Pgc1α, Cpt1b), intramuscular lipid staining, and activities of fatty acid oxidation enzymes in skeletal muscle were investigated. In DIO mice, fenofibrate prevented weight gain induced by HFD feeding by increasing energy expenditure; improved whole body glucose homeostasis, and in skeletal muscle, increased insulin dependent glucose uptake, miR-1a levels, reduced intramuscular lipid accumulation, and phospho-AMPKα2 levels. In visceral adipose tissue of obese mice, fenofibrate decreased basal lipolysis rate and visceral adipocytes hypertrophy, and induced the expression of Glut-4, Irs1, and Cav-1 mRNA and miR-103-3p suggesting a higher insulin sensitivity of the adipocytes. The evidence is presented herein that beneficial effects of fenofibrate on body weight, glucose homeostasis, and muscle metabolism might be related to its action in adipose tissue. Moreover, fenofibrate regulates miR-1a-3p in soleus and miR-103-3p in adipose tissue, suggesting these microRNAs might contribute to fenofibrate beneficial effects on metabolism.

Expression of microRNAs and target proteins in skeletal muscle of rats selectively bred for high and low running capacity

Impairments in mitochondrial function and substrate metabolism are implicated in the etiology of obesity and Type 2 diabetes. MicroRNAs (miRNAs) can degrade mRNA or repress protein translation and have been implicated in the development of such disorders. We used a contrasting rat model system of selectively bred high- (HCR) or low- (LCR) intrinsic running capacity with established differences in metabolic health to investigate the molecular mechanisms through which miRNAs regulate target proteins mediating mitochondrial function and substrate oxidation processes. Quantification of select miRNAs using the rat miFinder miRNA PCR array revealed differential expression of 15 skeletal muscles (musculus tibialis anterior) miRNAs between HCR and LCR rats (14 with higher expression in LCR; P < 0.05). Ingenuity Pathway Analysis predicted these altered miRNAs to collectively target multiple proteins implicated in mitochondrial dysfunction and energy substrate metabolism. Total protein abundance of citrate synthase (CS; miR-19 target) and voltage-dependent anion channel 1 (miR-7a target) were higher in HCR compared with LCR cohorts (~57 and ~26%, respectively; P < 0.05). A negative correlation was observed for miR-19a-3p and CS (r = 0.32, P = 0.015) protein expression. To determine whether miR-19a-3p can regulate CS in vitro, we performed luciferase reporter and transfection assays in C2C12 myotubes. MiR-19a-3p binding to the CS untranslated region did not change luciferase reporter activity; however, miR-19a-3p transfection decreased CS protein expression (∼70%; P < 0.05). The differential miRNA expression targeting proteins implicated in mitochondrial dysfunction and energy substrate metabolism may contribute to the molecular basis, mediating the divergent metabolic health profiles of LCR and HCR rats.