Peroxisome proliferator-activated receptor δ (PPARδ) is a critical regulator of energy metabolism in the heart. Here, we propose a mechanism that integrates two deleterious characteristics of heart failure, hypoxia and a metabolic shift toward glycolysis, involving the microRNA cluster miR-199a∼214 and PPARδ. We demonstrate that under hemodynamic stress, cardiac hypoxia activates DNM3os, a noncoding transcript that harbors the microRNA cluster miR-199a∼214, which shares PPARδ as common target. To address the significance of miR-199a∼214 induction and concomitant PPARδ repression, we performed antagomir-based silencing of both microRNAs and subjected mice to biomechanical stress to induce heart failure. Remarkably, antagomir-treated animals displayed improved cardiac function and restored mitochondrial fatty acid oxidation. Taken together, our data suggest a mechanism whereby miR-199a∼214 actively represses cardiac PPARδ expression, facilitating a metabolic shift from predominant reliance on fatty acid utilization in the healthy myocardium toward increased reliance on glucose metabolism at the onset of heart failure.

A low fat oxidative capacity has been linked to muscle diacylglycerol (DAG) accumulation and insulin resistance. Alternatively, a low fat oxidation rate may stimulate glucose oxidation, thereby enhancing glucose disposal. Here, we investigated whether an ethyl-2-[6-(4-chlorophenoxy)hexyl]-oxirane-2-carboxylate (etomoxir)-induced inhibition of fat oxidation leads to muscle fat storage and insulin resistance. An intervention in healthy male subjects was combined with studies in human primary myotubes. Furthermore, muscle DAG and triacylglycerol (TAG), mitochondrial function, and insulin signaling were examined in etomoxir-treated C57bl6 mice. In humans, etomoxir administration increased glucose oxidation at the expense of fat oxidation. This effect was accompanied by an increased abundance of GLUT4 at the sarcolemma and a lowering of plasma glucose levels, indicative of improved glucose homeostasis. In mice, etomoxir injections resulted in accumulation of muscle TAG and DAG, yet improved insulin-stimulated GLUT4 translocation. Also in human myotubes, insulin signaling was improved by etomoxir, in the presence of increased intramyocellular lipid accumulation. These insulin-sensitizing effects in mice and human myotubes were accompanied by increased phosphorylation of AMP-activated protein kinase (AMPK). Our results show that a reduction in fat oxidation leading to accumulation of muscle DAG does not necessarily lead to insulin resistance, as the reduction in fat oxidation may activate AMPK.

Aims/hypothesis High-fat, high-sucrose diet (HF)-induced reactive oxygen species (ROS) levels are implicated in skeletal muscle insulin resistance and mitochondrial dysfunction. Here we investigated whether mitochondrial ROS sequestering can circumvent HF-induced oxidative stress; we also determined the impact of any reduced oxidative stress on muscle insulin sensitivity and mitochondrial function. Methods The Skulachev ion (plastoquinonyl decyltriphenylphosphonium) (SkQ), a mitochondria-specific antioxidant, was used to target ROS production in C2C12 muscle cells as well as in HF-fed (16 weeks old) male C57Bl/6 mice, compared with mice on low-fat chow diet (LF) or HF alone. Oxidative stress was measured as protein carbonylation levels. Glucose tolerance tests, glucose uptake assays and insulin-stimulated signalling were determined to assess muscle insulin sensitivity. Mitochondrial function was determined by high-resolution respirometry. Results SkQ treatment reduced oxidative stress in muscle cells (−23% p<0.05), but did not improve insulin sensitivity and glucose uptake under insulin-resistant conditions. In HF mice, oxidative stress was elevated (56% vs LF p<0.05), an effect completely blunted by SkQ. However, HF and HF+SkQ mice displayed impaired glucose tolerance (AUC HF up 33%, p<0.001; HF+SkQ up 22%; p<0.01 vs LF) and disrupted skeletal muscle insulin signalling. ROS sequestering did not improve mitochondrial function. Conclusions/interpretation SkQ treatment reduced muscle mitochondrial ROS production and prevented HF-induced oxidative stress. Nonetheless, whole-body glucose tolerance, insulin-stimulated glucose uptake, muscle insulin signalling and mitochondrial function were not improved. These results suggest that HF-induced oxidative stress is not a prerequisite for the development of muscle insulin resistance.

Study question What is the prevalence of metabolic dysfunction, like insulin resistance, hyperglycaemia, hypertension, and/or dyslipidaemia, among subfertile women compared to healthy controls? Summary answer Signs of metabolic dysfunction were not observed more frequently in subfertile women than in controls. Overweight and obese patients were at risk for metabolic dysfunction. What is known already Metabolic dysfunction is known to impair female fecundity as it is linked to a longer time-to-pregnancy and to subfertility. Three times as many PCOS patients are diagnosed with metabolic syndrome than age matched controls. Moreover, a recent study showed a higher prevalence among the entire subfertile population. Metabolic disorders have been connected to the impairment of normal ovarian function and pituitary-hypothalamic axis. Obesity is correlated with menstrual irregularities, ovulation disorders and infertility. On top, it can increase risk of miscarriage and reduce chances with assisted reproductive technologies. Therefore, metabolic dysfunction might also be a driving factor behind unexplained subfertility. Study design, size, duration This cross-sectional observational case control study was performed in a secondary and tertiary care fertility clinic (MUMC+, Maastricht, The Netherlands). Patients were referred to the fertility clinic with either primary or secondary subfertility (inability to conceive after one year of regular unprotected intercourse), controls were healthy, parous women. All participants were aged between 18 and 41 years at time of inclusion. 119 patients and 68 controls were included over a time span of 3 years. Participants/materials, setting, methods A basic medical history was collected using questionnaires. Physical examination included measurement of weight, height, waist and hip circumference, blood pressure and pulse. Venipuncture was performed after an overnight fast on cycle day 2-4; including insulin, glucose, triglycerides, high-density lipid cholesterol, total cholesterol, glomerular filtration rate, urea, uric acid, creatinine, follicle stimulating hormone, estradiol and anti-Mullarian hormone. Urine was collected to measure protein and creatinine. Metabolic syndrome was diagnosed according to Adult Treatment Panel-III guidelines. Main results and the role of chance Body weight and BMI were similarly distributed between patients and controls. Main causes of subfertility comprised male factor (12%), anovulation (20%) and unexplained subfertility (47%). Comparing patients to controls, unexplained subfertility only had slightly higher HDL cholesterol levels (p = 0.046). Anovulatory patients showed 2% higher glucose (p = 0.003) and 133% higher AMH levels (p &lt; 0.001). Metabolic syndrome was diagnosed in 6% of unexplained subfertility patients, in 4% of male factor patients and in 5% of anovulatory patients. No controls were diagnosed with metabolic syndrome. In a comparison of overweight and obese patients to normal weight patients we observed resp. 16% and 37% higher waist circumference (p &lt; 0.001), 7% and 11% higher waist-to-hip ratio (p &lt; 0.01), 37% and 197% higher fasting insulin (p &lt; 0.01), 30% and 198% higher HOMA-IR (p &lt; 0.02) and 8% and 24% higher uric acid levels (p &lt; 0.03). Concomitantly, obese patients showed dyslipidemia with 98% higher triglyceride levels (p &lt; 0.001) and 24% lower HDL cholesterol (p &lt; 0.01). 181% higher AMH levels were found in obese patients (p &lt; 0.01). Metabolic syndrome was diagnosed in 1% of normal weight patients, 4% of overweight patients and in 25% of obese patients. Limitations, reasons for caution Participants were young and remarkably healthy, which might account for the low prevalence of metabolic disorders. It is known that the prevalence of metabolic dysfunction is strongly dependent on socioeconomic and geographic determinants in various populations. Our findings apply to a largely ethnically homogeneous Caucasian female population in the Netherlands. Wider implications of the findings We found that the presence or specific cause of subfertility per se, cannot be regarded as a reliable and strong predictor of metabolic dysfunction, even in anovulatory subfertility. As can be expected, metabolic dysfunction is highly associated with BMI and obese patients should consider lifestyle intervention to prevent future complications. Trial registration number Not applicable