Impact of moderate exercise on fatty acid oxidation in pancreatic ß-cells and skeletal muscle.

Fatty acids (FA) play a crucial role in glycaemia regulation in healthy and metabolic disorders conditions through various mechanisms. FA oxidation is one of the processes involved in lipid metabolism and can be modulated by exercise. Nowadays, physical activity is known to be an effective strategy for the prevention and treatment of Type 2 Diabetes. Moreover, its intensity, its duration, the sex-gender, the prandial state, exerkines… are as many parameters that can influence glycaemic control. However, the widely debated question is to determine the best type of exercise for patients with metabolic disorders. In this review, we will discuss the impact of exercise intensity, especially moderate activity, on glycaemic control by focussing on FA oxidation in pancreatic ß-cells and skeletal muscle. Finally, thanks to all the recent data, we will determine whether moderate physical activity is a good therapeutic strategy and if FA oxidation represents a target of interest to treat diabetic, obese and insulin-resistant patients.

Selective protein depletion impairs bone growth and causes liver fatty infiltration in female rats: prevention by Spirulina alga.

Chronic protein malnutrition leads to child mortality in developing countries. Spirulina alga (Spi), being rich in protein and growing easily, is a good candidate as supplementation. We showed that Spi completely prevents bone growth retardation and liver disturbances observed in young rats fed a low protein diet. This supports Spi as a useful source of vegetable protein to fight against protein malnutrition. INTRODUCTION: Chronic malnutrition is a main factor of child mortality in developing countries. A low protein diet impairs whole-body growth and leads to fatty liver in growing rats. Spi has great potential as a supplementation as it has a 60 % protein content and all essential amino acids. However, its specific impact on bone growth and the related secretion of hepatokines have not yet been studied. METHODS: To address this question, 6-week-old female rats were fed isocaloric diets containing 10 % casein, 5 % casein, or 5 % casein + 5 % protein from Spi during 9 weeks. Changes in tibia geometry, microarchitecture, BMC, BMD, and biomechanical properties were analyzed. Serum IGF-I, FGF21, follistatin, and activin A were assessed as well as their hepatic gene expressions in addition to those of Sirt1, Ghr, and Igf1r. Hepatic fat content was also assessed. RESULTS: A low protein diet altered bone geometry and reduced proximal tibia BMD and trabecular bone volume. In addition, it increased hepatic fat content and led to hepatic GH resistance by decreasing serum IGF-I and increasing serum FGF21 without altering serum activin A and follistatin. Spi prevented low protein diet-induced bone, hepatic, and hormonal changes, and even led to higher biomechanical properties and lower hepatic fat content in association with specific InhbA and Follistatin expression changes vs. the 10 % casein group. CONCLUSIONS: Altogether our results demonstrate the preventive impact of Spi on bone growth delay and hepatic GH resistance in conditions of isocaloric dietary protein deficiency.

Bimodal impact of skeletal muscle on pancreatic ß-cell function in health and disease.

Diabetes is a complex disease that affects many organs directly or indirectly. Type 2 diabetes mellitus is characterized by insulin resistance with a relative deficiency in insulin secretion. It has become apparent that inter-organ communication is of great importance in the pathophysiology of diabetes. Far from being an inert tissue in terms of inter-organ communication, it is now recognized that skeletal muscle can secrete so-called myokines that can impact on the function of distant organs/tissues both favourably and unfavourably. We have proposed that communication between insulin-resistant skeletal muscle and ß-cells occurs in diabetes. This is a novel route of communication that we further suggest is modified by the prevailing degree of insulin resistance of skeletal muscle. This review focuses on the various myokines [interleukin-6 (IL-6), tumor necrosis factor-α, CXCL10, follistatin and IL-8] which have been identified either after different types of exercise or in the secretome from control and insulin-resistant human skeletal myotubes. We will also summarize studies on the impact of several myokines on pancreatic ß-cell proliferation, survival and function.

WY-14643 and 9-cis-retinoic acid induce IRS-2/PI 3-kinase signalling pathway and increase glucose transport in human skeletal muscle cells: differential effect in myotubes from healthy subjects and Type 2 diabetic patients.

AIMS/HYPOTHESIS: To determine the effects of peroxisome proliferator-activated receptor α (PPARα) and retinoid X receptor (RXR) agonists on insulin action, we investigated the effects of Wy-14643 and 9-cis-retinoic acid (9-cis-RA) on insulin signalling and glucose uptake in human myotubes. METHODS: Primary cultures of differentiated human skeletal muscle cells, established from healthy subjects and Type 2 diabetic patients, were used to study the effects of Wy-14643 and 9-cis-RA on the expression and activity of proteins involved in the insulin signalling cascade. Glucose transport was assessed by measuring the rate of [3H]2-deoxyglucose uptake. RESULTS: Wy-14643 and 9-cis-RA increased IRS-2 and p85α phosphatidylinositol 3-kinase (PI 3-kinase) mRNA and protein expression in myotubes from non-diabetic and Type 2 diabetic subjects. This resulted in increased insulin stimulation of protein kinase B phosphorylation and increased glucose uptake in cells from control subjects. Myotubes from diabetic patients displayed marked alterations in the stimulation by insulin of the IRS-1/PI 3-kinase pathway. These alterations were associated with blunted stimulation of glucose transport. Treatment with Wy-14643 and 9-cis-RA did not restore these defects but increased the basal rate of glucose uptake. CONCLUSIONS/INTERPRETATION: These results demonstrate that PPARα and RXR agonists can directly affect insulin signalling in human muscle cells. They also indicate that an increase in the IRS-2/PI 3-kinase pathway does not overcome the impaired stimulation of the IRS-1-dependent pathway and does not restore insulin-stimulated glucose uptake in myotubes from Type 2 diabetic patients.

Regulation of p85alpha phosphatidylinositol-3-kinase expression by peroxisome proliferator-activated receptors (PPARs) in human muscle cells.

Regulation of p85a phosphatidylinositol-3-kinase (p85alphaPI-3K) expression by peroxisome proliferator-activated receptor (PPAR) activators was studied in human skeletal muscle cells. Activation of PPARgamma or PPARbeta did not modify the expression of p85alphaPI-3K. In contrast, activation of PPARalpha increased p85alphaPI-3K mRNA. This effect was potentiated by 9-cis-retinoic acid, an activator of RXR. Up-regulation of p85alphaPI-3K gene expression resulted in a rise in p85alphaPI-3K protein level and in an increase in insulin-induced PI3-kinase activity. According to the role of p85alphaPI-3K in insulin action, these results suggest that drugs with dual action on both PPARgamma and PPARalpha can be of interest for the treatment of insulin resistance.

Specific cleavage of insulin-like growth factor-binding protein-1 by a novel protease activity.

Insulin-like growth factor-binding protein-1 (IGFBP-1) is secreted in a highly phosphorylated form that binds IGF-I with high affinity and is resistant to proteolysis. We have purified IGFBP-1-specific protease activity from the urine of an individual with multiple myeloma. This protease efficiently cleaves both phosphorylated and non-phosphorylated IGFBP-1 at Ile130-Ser131, generating fragments that together have higher association and dissociation rates for IGFs compared with intact IGFBP-1. The proteolytic fraction contained azurocidin, a protease homologue hitherto considered inactive. After cleavage of IGFBP-1, there was a lower affinity, but higher capacity for IGF-I binding, suggesting both N- and C-terminal fragments may interact with ligand independently. There was decreased inhibition of IGF-II-stimulated cell growth and glucose uptake. Alone, proteolysed IGFBP-1 stimulated glucose uptake in muscle. We conclude that specific cleavage of IGFBP-1 at target tissues is important in cellular growth and metabolism and opens novel strategies for targeting IGFBP-1 in treatment of disease.

WY-14643 and 9- cis-retinoic acid induce IRS-2/PI 3-kinase signalling pathway and increase glucose transport in human skeletal muscle cells: differential effect in myotubes from healthy subjects and Type 2 diabetic patients.

AIMS/HYPOTHESIS: To determine the effects of peroxisome proliferator-activated receptor alpha (PPARalpha) and retinoid X receptor (RXR) agonists on insulin action, we investigated the effects of Wy-14643 and 9- cis-retinoic acid (9- cis-RA) on insulin signalling and glucose uptake in human myotubes. METHODS: Primary cultures of differentiated human skeletal muscle cells, established from healthy subjects and Type 2 diabetic patients, were used to study the effects of Wy-14643 and 9- cis-RA on the expression and activity of proteins involved in the insulin signalling cascade. Glucose transport was assessed by measuring the rate of [(3)H]2-deoxyglucose uptake. RESULTS: Wy-14643 and 9- cis-RA increased IRS-2 and p85alpha phosphatidylinositol 3-kinase (PI 3-kinase) mRNA and protein expression in myotubes from non-diabetic and Type 2 diabetic subjects. This resulted in increased insulin stimulation of protein kinase B phosphorylation and increased glucose uptake in cells from control subjects. Myotubes from diabetic patients displayed marked alterations in the stimulation by insulin of the IRS-1/PI 3-kinase pathway. These alterations were associated with blunted stimulation of glucose transport. Treatment with Wy-14643 and 9- cis-RA did not restore these defects but increased the basal rate of glucose uptake. CONCLUSIONS/INTERPRETATION: These results demonstrate that PPARalpha and RXR agonists can directly affect insulin signalling in human muscle cells. They also indicate that an increase in the IRS-2/PI 3-kinase pathway does not overcome the impaired stimulation of the IRS-1-dependent pathway and does not restore insulin-stimulated glucose uptake in myotubes from Type 2 diabetic patients.

The expression of the p85alpha subunit of phosphatidylinositol 3-kinase is induced by activation of the peroxisome proliferator-activated receptor gamma in human adipocytes.

AIMS/HYPOTHESIS: Thiazolidinediones are new oral antidiabetic drugs that activate the nuclear receptor PPARgamma. Our aim was to identify potential target genes of PPARgamma in the human adipocyte in order to clarify how thiazolidinediones improve insulin sensitivity. METHODS: The effect of BRL 49653 (Rosiglitazone) on the mRNA expression of insulin receptor, insulin receptor substrate-1, p85alpha, p110alpha and p110beta subunits of phosphatidylinositol 3-kinase, Glut 4 and hormone sensitive lipase was examined in isolated adipocytes. Target mRNA levels were determined by RT-competitive PCR. RESULTS: The BRL 49653 (1 micromol/l) increased the mRNA concentrations of p85alphaPI-3 K (264 +/- 46 vs 161 +/- 31 amol/microg total RNA, p = 0.003) whithout affecting the expression of the other mRNAs of interest. This effect was dose-dependent (K0.5 = 5 nmol/l) and was reproduced by a specific activator of RXR, indicating that it was probably mediated by the PPARgamma/RXR heterodimer. The BRL 49653 also increased the amount of p85alphaPI-3K protein in adipose tissue explants (71 +/- 19%). In addition, BRL 49653 produced a more than twofold increase in insulin stimulation of phosphatidylinositol 3-kinase activity and significantly enhanced the antilipolytic action of insulin. CONCLUSION/INTERPRETATION: This work demonstrates that the gene of p85alphaPI-3K is probably a target of PPARgamma and that thiazolidinediones can improve insulin action in normal human adipocytes. Although the precise mechanism of action of BRL 49653 on PI3-Kinase activity is not completely clear, these findings improve our understanding of the insulin-sensitizing effects of the thiazolidinediones, possible drugs for the treatment of Type II (non-insulin-dependent) diabetes mellitus.