Muscle Of Diet-induced Obese Mice Research Articles

High-intensity interval training attenuates impairment in regulatory protein machinery of mitochondrial quality control in skeletal muscle of diet-induced obese mice.

Mitochondrial quality control processes are essential in governing mitochondrial integrity and function. The purpose of the study was to examine the effects of 10 weeks of high-intensity interval training (HIIT) on the regulatory protein machinery of skeletal muscle mitochondrial quality control and whole-body glucose homeostasis in diet-induced obese mice. Male C57BL/6 mice were assigned to low-fat diet (LFD) or high-fat diet (HFD) group. After 10 weeks, HFD-fed mice were divided into sedentary and HIIT (HFD+HIIT) groups for another 10 weeks (n=9/group). Graded exercise test, glucose and insulin tolerance tests, mitochondrial respiration, and protein markers of mitochondrial quality control processes were determined. HFD-fed mice exhibited lower ADP-stimulated mitochondrial respiration (p<0.05). However, 10 weeks of HIIT prevented this impairment (p<0.05). Importantly, the ratio of Drp1(Ser616) over Drp1(Ser637) phosphorylation, an indicator of mitochondrial fission, was significantly higher in HFD-fed mice (p<0.05), but such increase was attenuated in HFD-HIIT compared to HFD (-35.7%, p<0.05). Regarding autophagy, skeletal muscle p62 content was lower in the HFD group than the LFD group (-35.1%, p<0.05); however, such reduction was disappeared in the HFD+HIIT group. In addition, LC3B II/I ratio was higher in the HFD group than the LFD group (15.5%, p<0.05) but was ameliorated in the HFD+HIIT group (-29.9%, p<0.05). Overall, our study demonstrated that 10 weeks of HIIT was effective in improving skeletal muscle mitochondrial respiration and the regulatory protein machinery of mitochondrial quality control in diet-induced obese mice through the alterations of mitochondrial fission protein Drp1 phosphorylations and p62/LC3B-mediated regulatory machinery of autophagy.

A web-based integrative transcriptome analysis, RNAseqChef, uncovers the cell/tissue type-dependent action of sulforaphane

RNA sequencing (RNA-seq) is a powerful technique for understanding cellular state and dynamics. However, comprehensive transcriptomic characterization of multiple RNA-seq datasets is laborious without bioinformatics training and skills. To remove the barriers to sequence data analysis in the research community, we have developed "RNAseqChef" (RNA-seq data controller highlighting expression features), a web-based platform of systematic transcriptome analysis that can automatically detect, integrate, and visualize differentially expressed genes and their biological functions. To validate its versatile performance, we examined the pharmacological action of sulforaphane (SFN), a natural isothiocyanate, on various types of cells and mouse tissues using multiple datasets invitro and invivo. Notably, SFN treatment upregulated the ATF6-mediated unfolded protein response in the liver and the NRF2-mediated antioxidant response in the skeletal muscle of diet-induced obese mice. In contrast, the commonly downregulated pathways included collagen synthesis and circadian rhythms in the tissues tested. On the server of RNAseqChef, we simply evaluated and visualized all analyzing data and discovered the NRF2-independent action of SFN. Collectively, RNAseqChef provides an easy-to-use open resource that identifies context-dependent transcriptomic features and standardizes data assessment.

Lack of adipocyte IP3R1 reduces diet-induced obesity and greatly improves whole-body glucose homeostasis

The normal function of skeletal muscle and adipose tissue ensures whole-body glucose homeostasis. Ca2+ release channel inositol 1,4,5-trisphosphate receptor 1 (IP3R1) plays a vital role in regulating diet-induced obesity and disorders, but its functions in peripheral tissue regulating glucose homeostasis remain unexplored. In this study, mice with Ip3r1 specific knockout in skeletal muscle or adipocytes were used for investigating the mediatory role of IP3R1 on whole-body glucose homeostasis under normal or high-fat diet. We reported that IP3R1 expression levels were increased in the white adipose tissue and skeletal muscle of diet-induced obese mice. Ip3r1 knockout in skeletal muscle improved glucose tolerance and insulin sensitivity of mice on a normal chow diet, but worsened insulin resistance in diet-induced obese mice. These changes were associated with the reduced muscle weight and compromised Akt signaling activation. Importantly, Ip3r1 deletion in adipocytes protected mice from diet-induced obesity and glucose intolerance, mainly due to the enhanced lipolysis and AMPK signaling pathway in the visceral fat. In conclusion, our study demonstrates that IP3R1 in skeletal muscle and adipocytes exerts divergent effects on systemic glucose homeostasis, and characterizes adipocyte IP3R1 as a promising target for treating obesity and type 2 diabetes.

Empagliflozin Lowers Mitochondrial Respiration and Skeletal Muscle Sphingolipid Content in Female Mice Fed Western Diet

Sodium-glucose cotransporter-2 (SGLT2) inhibitors are a frontline treatment for type 2 diabetes due to their ability to attenuate hyperglycemia (via glucosuria). Mounting evidence indicates SGLT2 inhibitors can also alter mitochondrial metabolism, enhance reliance upon fat oxidation and attenuate fat accumulation in a growing list of tissues. Nevertheless, the impact of SGLT2 inhibition on skeletal muscle remains largely unexplored. The objective of this study was to test the hypothesis that SGLT2 inhibition would promote enhanced mitochondrial capacity for fat oxidation and lower accumulation of harmful lipids in skeletal muscle of diet-induced obese mice. Female C57BL/6J mice, aged 26 weeks, were provided ad libitum access to either low-fat diet (LFD, n=9) or western diet (WD) for 8-weeks. WD mice were then randomized to 4-weeks of diet supplemented with 10mg/kg (0.01%) empagliflozin (WD+Emp, n=10) or untreated control (WD, n = 10). Dual-energy x-ray absorptiometry and glucose tolerance tests were performed in all groups pre- and post-empagliflozin treatment. At week 12, mitochondria were isolated from quadriceps muscle and measured by high-resolution respirometry using octanoyl-carnitine+malate (OCM) and other non-lipid substrates. Intramyocellular lipids were assessed using liquid chromatography, tandem mass spectrometry. As expected, WD mice had greater body weight and fat mass, as well as impaired glucose tolerance, when compared with LFD mice (all P<0.05). Four weeks of empagliflozin treatment improved glucose tolerance in WD+Emp mice (P<0.01 for week 12 vs. 8), despite no differences in body weight or fat mass compared with pre-treatment (both P>0.05 for week 12 vs. 8). Lipid-supported mitochondrial respiration and overall lipid content (e.g., triacylglycerols, select sphingolipids and ceramides) were greater in skeletal muscle from WD compared with LFD mice (all comparisons P<0.05). Such effects of WD on muscle lipid metabolism were largely reversed with empagliflozin treatment. There was overall main effect of lower mitochondrial respiration in WD+Emp compared with WD (P<0.001), and a tendency for lower concentration of numerous sphingolipid and ceramide species (mean difference = 9-34%). We interpret this as preliminary evidence that empagliflozin can reverse some WD-induced adaptations to skeletal muscle lipid metabolism, which may contribute to the improvement in glucose control.

Designer Receptors Exclusively Activated by Designer Drugs Approach to Treatment of Sleep-disordered Breathing.

Rationale: Obstructive sleep apnea is recurrent upper airway obstruction caused by a loss of upper airway muscle tone during sleep. The main goal of our study was to determine if designer receptors exclusively activated by designer drugs (DREADD) could be used to activate the genioglossus muscle as a potential novel treatment strategy for sleep apnea. We have previously shown that the prototypical DREADD ligand clozapine-N-oxide increased pharyngeal diameter in mice expressing DREADD in the hypoglossal nucleus. However, the need for direct brainstem viral injections and clozapine-N-oxide toxicity diminished translational potential of this approach, and breathing during sleep was not examined.Objectives: Here, we took advantage of our model of sleep-disordered breathing in diet-induced obese mice, retrograde properties of the adeno-associated virus serotype 9 (AAV9) viral vector, and the novel DREADD ligand J60.Methods: We administered AAV9-hSyn-hM3(Gq)-mCherry or control AAV9 into the genioglossus muscle of diet-induced obese mice and examined the effect of J60 on genioglossus activity, pharyngeal patency, and breathing during sleep.Measurements and Main Results: Compared with control, J60 increased genioglossus tonic activity by greater than sixfold and tongue uptake of 2-deoxy-2-[18F]fluoro-d-glucose by 1.5-fold. J60 increased pharyngeal patency and relieved upper airway obstruction during non-REM sleep.Conclusions: We conclude that following intralingual administration of AAV9-DREADD, J60 can activate the genioglossus muscle and improve pharyngeal patency and breathing during sleep.

MicroRNA miR-222 mediates pioglitazone beneficial effects on skeletal muscle of diet-induced obese mice

Pioglitazone belongs to the class of drugs thiazolidinediones (TZDs) and is an oral hypoglycemic drug, used in the treatment of type 2 diabetes, which improves insulin sensitivity in target tissues. Adipose tissue is the main target of pioglitazone, a PPARg and PPARa agonist; however, studies also point to skeletal muscle as a target. Non-PPAR targets of TZDs have been described, thus we aimed to study the direct effects of pioglitazone on skeletal muscle and the possible role of microRNAs as targets of this drug. Pioglitazone treatment of obese mice increased insulin-mediated glucose transport as a result of increased fatty acid oxidation and mitochondrial activity. PPARg blockage by treatment with GW9662 nullified pioglitazone's effect on systemic and muscle insulin sensitivity and citrate synthase activity of obese mice. After eight weeks of high-fat diet, miR-221–3p expression in soleus muscle was similar among the groups and miR-23b-3p and miR-222–3p were up-regulated in obese mice compared to the control group, and treatment with pioglitazone was able to reverse this condition. In vitro studies in C2C12 cells suggest that inhibition of miR-222–3p protects C2C12 cells from insulin resistance and increased non-mitochondrial respiration induced by palmitate. Together, these data demonstrate a role of pioglitazone in the downregulation of microRNAs that is not dependent on PPARg. Moreover, miR-222 may be a novel PPARg-independent mechanism through which pioglitazone improves insulin sensitivity in skeletal muscle.

An MG53-IRS1-interaction disruptor ameliorates insulin resistance

Mitsugumin 53 (MG53) is an E3 ligase that induces insulin receptor substrate-1 (IRS-1) ubiquitination and degradation in skeletal muscle. We previously demonstrated that the pharmaceutical disruption of the MG53-IRS-1 interaction improves insulin sensitivity by abrogating IRS-1 ubiquitination and increasing IRS-1 levels in C2C12 myotubes. Here, we developed a novel MG53-IRS-1 interaction disruptor (MID-00935) that ameliorates insulin resistance in diet-induced obese (DIO) mice. MID-00935 disrupted the molecular interaction of MG53 and IRS-1, abrogated MG53-induced IRS-1 ubiquitination and degradation and improved insulin signaling in C2C12 myotubes. Oral administration of MID-00935 increased insulin-induced IRS-1, Akt, and Erk phosphorylation via increasing IRS-1 levels in the skeletal muscle of DIO mice. In DIO mice, MID-00935 treatment lowered fasting blood glucose levels and improved glucose disposal in glucose and insulin tolerance tests. These results suggest that MID-00935 may be a potential muscle-targeting drug candidate for treating insulin resistance.

Effect of exendin-4 on lipid deposition in skeletal muscle of diet-induced obese mice and its underlying mechanism

Objective: To investigate the effect of exendin-4, a glucagon-like peptide-1 (GLP-1) receptor agonist, on reducing lipid deposition and improving insulin resistance in skeletal muscle and the underlying mechanisms in high-fat diet (HFD)-induced obese mice. Methods: Twelve male C57BL/6J mice were challenged with HFD for 12 weeks to induce obesity and then randomly divided into two groups: exendin-4 group (intraperitoneal injection of 24 nmol·kg-1·d-1 exendin-4 for 4 weeks) and HFD group (intraperitoneal injection of normal saline for 4 weeks), with 6 mice in each group. Additional 6 mice were also selected as control group. Body weight, fasting blood glucose were recorded. Serum triglyceride (TG), total cholesterol (TC), insulin and skeletal muscle triglyceride levels were measured by enzyme-linked immunosobent assay (ELISA). Oil red O staining was used for morphologic changes of frozen sections from skeletal muscle. The protein levels of lipid metabolic pathway mediated by AMP-activated protein kinase (AMPK) and insulin signailing pathway were determined by Western blot. Results: Compared with mice in HFD group, exendin-4 significantly decreased body weight[(37.68±1.80) vs (46.03±5.00) g, P<0.025], fasting blood glucose[(5.40±0.33) vs (7.65±1.92) mmol/L, P<0.025], serum TG[(37.78±7.14) vs (80.76±34.22) mg/dl, P<0.025], TC[(180.13±18.75) vs (217.57±22.52) mg/dl, P<0.025], insulin[(0.58±0.01) vs (1.67±1.23) ng/ml, P<0.025]and skeletal muscle TG levels[(9.84±1.08) vs (19.35±7.44) mg/g, P<0.025]of obese mice. Oil red O staining revealed that exendin-4 alleviated the accumulation of larger lipid droplets in skeletal muscle. The protein expressions of lipolysis and lipid oxidation mediated by AMPK and insulin signailing pathway were up-regulated, and the protein expressions of lipogenesis mediated by AMPK were down-regulated after intervention of exendin-4. Conclusion: Exendin-4 reduces lipid deposition and insulin resistance in skeletal muscle of HFD-induced obese mice via activating AMPK and up-regulating insulin signailing pathway.

MyomiRs as Markers of Insulin Resistance and Decreased Myogenesis in Skeletal Muscle of Diet-Induced Obese Mice.

High-fat diet (HFD) feeding causes insulin resistance (IR) in skeletal muscle of mice, which affects skeletal muscle metabolism and function. The involvement of muscle-specific microRNAs in the evolution of skeletal muscle IR during 4, 8, and 12 weeks in HFD-induced obese mice was investigated. After 4 weeks in HFD, mice were obese, hyperglycemic, and hyperinsulinemic; however, their muscles were responsive to insulin stimuli. Expressions of MyomiRs (miR-1, miR-133a, and miR-206) measured in soleus muscles were not different from those found in control mice. After 8 weeks of HFD feeding, glucose uptake was lower in skeletal muscle from obese mice compared to control mice, and we observed a significant decrease in miR-1a in soleus muscle when compared to HFD for 4 weeks. miR-1a expression continued to decay within time. After 12 weeks of HFD, miR-133a expression was upregulated when compared to the control group. Expression of miR-1a was negatively correlated with glycemia and positively correlated with the constant rate of plasma glucose disappearance. Pioglitazone treatment could not reverse decreases of miR-1a levels induced by HFD. Targets of myomiRs involved in insulin-growth factor (IGF)-1 pathway, such as Igf-1, Irs-1, Rheb, and follistatin, were reduced after 12 weeks in HFD and Mtor increased, when compared to the control or HFD for 4 or 8 weeks. These findings suggest for the first time that miR-1 may be a marker of the development of IR in skeletal muscle. Evidence was also presented that impairment in myomiRs expression contributes to decreased myogenesis and skeletal muscle growth reported in diabetes.