Roberto Serra

Exercise Training Induces Mitochondrial Biogenesis and Glucose Uptake in Subcutaneous Adipose Tissue Through eNOS-Dependent Mechanisms

Insulin resistance and obesity are associated with a reduction of mitochondrial content in various tissues of mammals. Moreover, a reduced nitric oxide (NO) bioavailability impairs several cellular functions, including mitochondrial biogenesis and insulin-stimulated glucose uptake, two important mechanisms of body adaptation in response to physical exercise. Although these mechanisms have been thoroughly investigated in skeletal muscle and heart, few studies have focused on the effects of exercise on mitochondria and glucose metabolism in adipose tissue. In this study, we compared the in vivo effects of chronic exercise in subcutaneous adipose tissue of wild-type (WT) and endothelial NO synthase (eNOS) knockout (eNOS−/−) mice after a swim training period. We then investigated the in vitro effects of NO on mouse 3T3-L1 and human subcutaneous adipose tissue–derived adipocytes after a chronic treatment with an NO donor: diethylenetriamine-NO (DETA-NO). We observed that swim training increases mitochondrial biogenesis, mitochondrial DNA content, and glucose uptake in subcutaneous adipose tissue of WT but not eNOS−/− mice. Furthermore, we observed that DETA-NO promotes mitochondrial biogenesis and elongation, glucose uptake, and GLUT4 translocation in cultured murine and human adipocytes. These results point to the crucial role of the eNOS-derived NO in the metabolic adaptation of subcutaneous adipose tissue to exercise training.

Changes in FAT=CD36, UCP2, UCP3 and GLUT4 gene expression during lipid infusion in rat skeletal and heart muscle

Objective: It has been reported that an increased availability of free fatty acids (NEFA) not only interferes with glucose utilization in insulin-dependent tissues, but may also result in an uncoupling effect of heart metabolism. We aimed therefore to investigate the effect of an increased availability of NEFA on gene expression of proteins involved in transmembrane fatty acid (FAT/CD36) and glucose (GLUT4) transport and of the uncoupling proteins UCP2 and 3 at the heart and skeletal muscle level.Study Design: Euglycemic hyperinsulinemic clamp was performed after 24 h Intralipid® plus heparin or saline infusion in lean Zucker rats. Skeletal and heart muscle glucose utilization was calculated by 2-deoxy-[1-3H]-D-glucose technique. Quantification of FAT/CD36, GLUT4, UCP2 and UCP3 mRNAs was obtained by Northern blot analysis or RT-PCR.Results: In Intralipid® plus heparin infused animals a significant decrease in insulin-mediated glucose uptake was observed both in the heart (22.62±2.04 vs 10.37±2.33 ng/mg/min; P<0.01) and in soleus muscle (13.46±1.53 vs 6.84±2.58 ng/mg/min; P<0.05). FAT/CD36 mRNA was significantly increased in skeletal muscle tissue (+117.4±16.3%, P<0.05), while no differences were found at the heart level in respect to saline infused rats. A clear decrease of GLUT4 mRNA was observed in both tissues. The 24 h infusion of fat emulsion resulted in a clear enhancement of UCP2 and UCP3 mRNA levels in the heart (99.5±15.3 and 80±4%) and in the skeletal muscle (291.5±24.7 and 146.9±12.7%).Conclusions: As a result of the increased availability of NEFA, FAT/CD36 gene expression increases in skeletal muscle, but not at the heart level. The augmented lipid fuel supply is responsible for the depression of insulin-mediated glucose transport and for the increase of UCP2 and 3 gene expression in both skeletal and heart muscle.

Hyperlactatemia reduces muscle glucose uptake and GLUT-4 mRNA while increasing (E1α)PDH gene expression in rat

An increased basal plasma lactate concentration is present in many physiological and pathological conditions, including obesity and diabetes. We previously demonstrated that acute lactate infusion in rats produced a decrease in overall glucose uptake. The present study was carried out to further investigate the effect of lactate on glucose transport and utilization in skeletal muscle. In chronically catheterized rats, a 24-h sodium lactate or bicarbonate infusion was performed. To study glucose uptake in muscle, a bolus of 2-deoxy-[3H]glucose was injected in basal condition and during euglycemic-hyperinsulinemic clamp. Our results show that hyperlactatemia decreased glucose uptake in muscles (i.e., red quadriceps; P< 0.05). Moreover in red muscles, both GLUT-4 mRNA (-30% in red quadriceps and -60% in soleus; P < 0.025) and protein (-40% in red quadriceps; P < 0.05) were decreased, whereas the (E1α)pyruvate dehydrogenase (PDH) mRNA was increased (+40% in red quadriceps; P< 0.001) in lactate-infused animals. PDH protein was also increased (4-fold in red gastrocnemius and 2-fold in red quadriceps). These results indicate that chronic hyperlactatemia reduces glucose uptake by affecting the expression of genes involved in glucose metabolism in muscle, suggesting a role for lactate in the development of insulin resistance.

Exercise training boosts eNOS-dependent mitochondrial biogenesis in mouse heart: role in adaptation of glucose metabolism

Endurance exercise training increases cardiac energy metabolism through poorly understood mechanisms. Nitric oxide (NO) produced by endothelial NO synthase (eNOS) in cardiomyocytes contributes to cardiac adaptation. Here we demonstrate that the NO donor diethylenetriamine-NO (DETA-NO) activated mitochondrial biogenesis and function, as assessed by upregulated peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), nuclear respiratory factor 1, and mitochondrial transcription factor A (Tfam) expression, and by increased mitochondrial DNA content and citrate synthase activity in primary mouse cardiomyocytes. DETA-NO also induced mitochondrial biogenesis and function and enhanced both basal and insulin-stimulated glucose uptake in HL-1 cardiomyocytes. The DETA-NO-mediated effects were suppressed by either PGC-1α or Tfam small-interference RNA in HL-1 cardiomyocytes. Wild-type and eNOS(-/-) mice were subjected to 6 wk graduated swim training. We found that eNOS expression, mitochondrial biogenesis, mitochondrial volume density and number, and both basal and insulin-stimulated glucose uptake were increased in left ventricles of swim-trained wild-type mice. On the contrary, the genetic deletion of eNOS prevented all these adaptive phenomena. Our findings demonstrate that exercise training promotes eNOS-dependent mitochondrial biogenesis in heart, which behaves as an essential step in cardiac glucose transport.

Substrate competition and insulin action in animal models.

Increased basal plasma FFA and lactate concentrations are often present in obesity and may deeply affect insulin action. The inhibition of glucose transport or phosphorylation is thought to be involved in this phenomenon, but the molecular mechanisms on the basis are still unknown. In our laboratory we observed that a chronic infusion of Intralipid plus heparin in rats significantly decreased the insulin dependent-glucose uptake, as well as GLUT4 gene expression in muscular tissue. On the other hand it has been shown that an enhanced plasma lactate concentration may increase insulin secretion and hepatic insulin clearance. Moreover we observed that chronic hyperlactatemia in rats is able to decrease glucose uptake in muscles, while reducing GLUT4 mRNA and protein in the same tissues. In obesity, lactate and FFA overproduction from visceral fat may therefore play a synergic role in reducing insulin sensitivity.

Presence of anti-ADAMTS13 antibodies in obesity

Eur J Clin Invest 2012; 42 (11): 1197–1204

Lactate infusion to normal rats during hyperglycemia enhances in vivo muscle glycogen synthesis

Both hyperglycemia and hyperinsulinemia stimulate whole body and muscle glucose disposal. To define the impact of increased lactate concentration (4-5 mM) on muscle glucose disposal during hyperglycemia, we studied anesthetized normal rats infused with either sodium lactate or sodium bicarbonate as control. Animals were studied under hyperglycemic clamp (13 mM) using [3-3H]glucose ( study 1) and 2-deoxy-[1-3H]glucose ( study 2) to assess glucose rate of disappearance (Rd), glycolytic flux (GF), glycogen synthesis, and glucose utilization index by different tissues. Moreover, in study 3, the effect of lactate on the pattern of plasma insulin response to hyperglycemia was evaluated. In study 1, lactate infusion resulted in an increased Rd (38.7 ± 1.7 vs. 32.3 ± 1.3 mg ⋅ min-1 ⋅ kg-1; P < 0.01), which was explained by an enhanced rate of glycogen synthesis (23.0 ± 1.7 vs. 14.7 ± 1.2 mg ⋅ min-1 ⋅ kg-1; P < 0.001), whereas GF was unchanged. In study 2, lactate-infused animals showed an increased 2-deoxy-glucose disposal and a stimulated glycogen synthase activity as well as an increased glycogen accumulation at the end of the study in several skeletal muscles. In study 3, lactate did not induce any change in either early or late insulin response to hyperglycemia. In conclusion, our results show that muscle glycogen deposition may be enhanced by elevated lactate levels under hyperglycemic conditions and support a role for lactate in the regulation of glucose homeostasis.

Definition, Epidemiology, and Social Implications of Obesity

Excess body weight is an important risk factor for mortality and morbidity from several chronic diseases, such as cardiovascular diseases, type 2 diabetes, chronic liver and gallbladder disease, some forms of cancer, osteoarthritis, and musculoskeletal disorders, causing nearly three million annual deaths worldwide. Beyond the health consequences, overweight and obesity can be associated to a number of problems such as low self-esteem and disturbance of body image. Weight loss improves obesity-related risk factors, and some evidence suggests that benefits can persist as long as weight loss is maintained.