4 resultados para ARTHROGENIC MUSCLE INHIBITION
em Brock University, Canada
Resumo:
Resveratrol, a polyphenol found in red wine, has been reported to have
antithrombotic, antiatherogenic, and anticancer properties both in vitro and III VIVO.
However, possible antidiabetic properties of resveratrol have not been examined. The
objective of this study was to investigate the direct effects of resveratrol on basal and
insulin-stimulated glucose uptake and to elucidate its mechanism of action in skeletal
muscle cells. In addition, the effects of resveratrol on basal and insulin- stimulated amino
acid transport and mitogenesis were also examined.
Fully differentiated L6 rat skeletal muscle cells were incubated with resveratrol
concentrations ranging from 1 to 250 IlM for 15 to 120 min. Maximum stimulation, 201
± 8.90% of untreated control, (p<0.001), of2eH] deoxy- D- glucose (2DG) uptake was
seen with 100 IlM resveratrol after 120 min. Acute, 30 min, exposure of the cells to 100
nM insulin stimulated 2DG uptake to 226 ± 12.52% of untreated control (p<0.001). This
appears to be a specific property of resveratrol that is not shared by structurally similar
antioxidants such as quercetin and rutin, both of which did not have any stimulatory
effect. Resveratrol increased the response of the cells to submaximal insulin
concentrations but did not alter the maximum insulin response. Resveratrol action did not
require insulin and was not blocked by the protein synthesis inhibitor cycloheximide.
L Y294002 and wortmannin, inhibitors of PI3K, abolished both insulin and resveratrolstimulated
glucose uptake while phosphorylation of AktlPKB, ERK1I2, JNK1I2, and p38
MAPK were not increased by resveratrol. Resveratrol did not stimulate GLUT4
transporter translocation in GLUT4cmyc overexpressing cells, in contrast to the
significant translocation observed with insulin. Furthermore, resveratrol- stimulated glucose transport was not blocked by the presence of the protein kinase C (PKC)
inhibitors BIMI and G06983. Despite that, resveratrol- induced glucose transport
required an intact actin network, similar to insulin.
In contrast to the stimulatory effect seen with resveratrol for glucose transport,
e4C]methylaminoisobutyric acid (MeAIB) transport was inhibited. Significant reduction
of MeAIB uptake was seen only with 100uM resveratrol (74.2 ± 6.55% of untreated
control, p<0.05), which appeared to be maximum. In parallel experiments, insulin (100
nM, 30 min) increased MeAIB transport by 147 ± 5.77% (p<0.00l) compared to
untreated control. In addition, resveratrol (100 JlM, 120 min) completely abolished
insulin- stimulated amino acid transport (103 ± 7.35% of untreated control,p>0.05).
Resveratrol also inhibited cell proliferation in L6 myoblasts with maximal
inhibition of eH]thymidine incorporation observed with resveratrol at 50 J.LM after 24
hours (8 ± 1.59% of untreated control, p
Resumo:
Diabetes mellitus is a disorder of inadequate insulin action and consequent high blood glucose levels. Type 2 diabetes accounts for the majority of cases of the disease and is characterized by insulin resistance and relative insulin deficiency resulting in metabolic deregulation. It is a complex disorder to treat as its pathogenesis is not fully understood and involves a variety of defects including ~-cell failure, insulin resistance in the classic target tissues (adipose, muscle, liver), as well as defects in a-cells and kidney, brain, and gastrointestinal tissue. Present oral treatments, which aim at mimicking the effects of insulin, remain limited in their efficacy and therefore the study of the effects of novel compounds on insulin target tissues is an important area of research both for potentially finding more treatment options as well as for increasing our knowledge of metabolic regulation in health and disease. In recent years the extensively studied polyphenol, resveratrol, has been reported to have antidiabetic effects showing that it increases glucose uptake by skeletal muscle cells and prevents fatty acid-induced insulin resistance in vitro and in vivo. Naringenin, a citrus flavonoid with structural similarities to resveratrol, is reported to have antioxidan.t, antiproliferative, anticancer, and anti-inflammatory properties. Effects on glucose and lipid metabolism have also been reported including blood glucose and lipid lowering effects. However, whether naringenin has insulinlike effects is not clear. In the present study the effects of naringenin on glucose uptake in skeletal muscle cells are examined and compared with those of insulin. Naringenin treatment of L6 myotubes increased glucose uptake in a dose- and time dependent manner and independent of insulin. The effects of naringenin on glucose uptake achieved similar levels as seen with maximum insulin stimulation and its effect was additive with sub-maximal insulin treatment. Like insulin naringenin treatment did not increase glucose uptake in myoblasts. To elucidate the mechanism involved in naringenin action we looked at its effect on phosphatidylinositol 3-kinase (PI3K) and Akt, two signalling molecules that are involved in the insulin signalling cascade leading to glucose uptake. Naringenin did not stimulate basal or insulinstimulated Akt phosphorylation but inhibition of PI3K by wortmannin partially repressed the naringenin-induced glucose uptake. We also examined naringenin's effect on AMP-activated protein kinase (AMPK), a molecule that is involved in mediating glucose uptake by a variety of stimuli. Naringenin stimulated AMPK phosphorylation and this effect was not inhibited by wortmannin. To deduce the nature of the naringenin-stimulated AMPK phosphorylation and its impact on glucose uptake we examined the role of several molecules implicated in mod.ulating AMPK activity including SIRTl, LKB 1, and ca2+ Icalmodulin-dependent protein kinase kinase (CaMKK). Our results indicate that inhibition of SIRTI did not prevent the naringeninstimulated glucose uptake Of. AMPK phosphorylation; naringenin did not stimulate LKB 1 phosphorylation; and inhibition of CaMKK did not prevent naringeninstimulated glucose uptake. Inhibition of AMPK by compound C also did not prevent naringenin-stimulated glucose uptake but effectively inhibited the phosphorylation of AMPK suggesting that AMPK may not be required for the naringenin-stimulated glucose uptake.
Resumo:
Pyruvate dehydrogenase (PDH) plays an important role in regulating carbohydrate oxidation in skeletal muscle. PD H is deactivated by a set of PD H kinases (PD K 1-4) with PDK2 and 4 being the predominant isoforms in skeletal muscle. PDK2 is highly sensitive to pyruvate inhibition, and is the most abundant isoform, while PDKI and 4 protein content are normally lower. This study examined the PDK isoform content and PDHa activation in muscle at rest and 10 and 40 Hz stimulation from PDK2 knockout (PDK2KO) mice to delineate the role of PDK2 in activating the PDH complex during low and moderate intensity muscle contraction. PDHa activity was lower in PDK2KO mice during contraction while total PDK actitvity was -4 fold lower. PDK4 protein was not different, however PDKI partially compensated for the lack of PDK2 and was -56% higher than WT. PDKI is a very potent inhibitor of the PDH complex due to its phosphorylation site specificity and allosteric regulation. These results suggest that the site specificity and allosteric regulatory properties of the individual PDK isoforms are more important than total PDK activity in determining transformation of the complex and PDHa activity during acute muscle contraction.
Resumo:
The first and rate-limiting step of lipolysis is the removal of the first fatty acid from a triglyceride molecule; it is catalyzed by adipose triglyceride lipase (ATGL). ATGL is co-activated by comparative gene identification-58 (CGI-58) and inhibited by the G(0)/G(1) switch gene-2 protein (G0S2). G0S2 has also recently been identified as a positive regulator of oxidative phosphorylation within the mitochondria. Previous research has demonstrated in cell culture, a dose dependent mechanism for inhibition by G0S2 on ATGL. However our data is not consistent with this hypothesis. There was no change in G0S2 protein content during an acute lipolytic inducing set of contractions in both whole muscle, and isolated mitochondria yet both ATGL and G0S2 increase following endurance training, in spite of the fact that there should be increased reliance on intramuscular lipolysis. Therefore, inhibition of ATGL by G0S2 appears to be regulated through more complicated intracellular or post-translation regulation.