Time courses of changes in hepatic and skeletal muscle insulin action and GLUT4 protein in skeletal muscle after STZ injection

β-arrestin-1 suppresses myogenic reprogramming of brown fat to maintain euglycemia

A better understanding of the signaling pathways regulating adipocyte function is required for the development of new classes of antidiabetic/obesity drugs. We here report that mice lacking β-arrestin-1 (barr1), a cytoplasmic and nuclear signaling protein, selectively in adipocytes showed greatly impaired glucose tolerance and insulin sensitivity when consuming an obesogenic diet. In contrast, transgenic mice overexpressing barr1 in adipocytes were protected against the metabolic deficits caused by a high-calorie diet. Barr1 deficiency led to a myogenic reprogramming of brown adipose tissue (BAT), causing elevated plasma myostatin (Mstn) levels, which in turn led to impaired insulin signaling in multiple peripheral tissues. Additional in vivo studies indicated that barr1-mediated suppression of Mstn expression by BAT is required for maintaining euglycemia. These findings convincingly identify barr1 as a critical regulator of BAT function. Strategies aimed at enhancing barr1 activity in BAT may prove beneficial for the treatment of type 2 diabetes.

Metabolic effects of skeletal muscle-specific deletion of beta-arrestin-1 and -2 in mice

Type 2 diabetes (T2D) has become a major health problem worldwide. Skeletal muscle (SKM) is the key tissue for whole-body glucose disposal and utilization. New drugs aimed at improving insulin sensitivity of SKM would greatly expand available therapeutic options. β-arrestin-1 and -2 (Barr1 and Barr2, respectively) are two intracellular proteins best known for their ability to mediate the desensitization and internalization of G protein-coupled receptors (GPCRs). Recent studies suggest that Barr1 and Barr2 regulate several important metabolic functions including insulin release and hepatic glucose production. Since SKM expresses many GPCRs, including the metabolically important β2-adrenergic receptor, the goal of this study was to examine the potential roles of Barr1 and Barr2 in regulating SKM and whole-body glucose metabolism. Using SKM-specific knockout (KO) mouse lines, we showed that the loss of SKM Barr2, but not of SKM Barr1, resulted in mild improvements in glucose tolerance in diet-induced obese mice. SKM-specific Barr1- and Barr2-KO mice did not show any significant differences in exercise performance. However, lack of SKM Barr2 led to increased glycogen breakdown following a treadmill exercise challenge. Interestingly, mice that lacked both Barr1 and Barr2 in SKM showed no significant metabolic phenotypes. Thus, somewhat surprisingly, our data indicate that SKM β-arrestins play only rather subtle roles (SKM Barr2) in regulating whole-body glucose homeostasis and SKM insulin sensitivity.

Profound Changes in Net Energy and Nitrogen Metabolites Fluxes within the Splanchnic Area during Overfeeding of Yucatan Mini Pigs That Remain Euglycemic

A dysregulation of nutrient exchange between tissues (gut, liver, muscles, adipose) occurs during overnutrition and could induce obesity and metabolic diseases. We aimed to evaluate how, in overfed mini pigs, nutrients use and partition were regulated in the gut and liver. Net nutrients fluxes were assessed in the fed (PP) and post absorptive (PA) states at 1, 14 and 60 days of adaptation to overfeeding in five adult Yucatan female multicatheterized minipigs. Pigs PA glycaemia and PP-induced hyperglycemia remained unchanged over the experimental period, suggesting that the management of the excess of energy intake allowed the maintenance of glucose levels. This was associated with (1) an increased PA plasma insulin, (2) an increased gut lactate production (increased lactate net release +89%, 1 h PP, D1 vs. D60) probably from an increased glucose oxidation, (3) a shift in utilization of gluconeogenic precursor (lactate, propionate) in the liver, and (4) a reduced gut utilization of nitrogen moieties for energy purposes (glutamine), a nitrogen sparing effect at the whole body level (decreased plasma urea in PA (−24% D1 vs. D60) and PP states) and a specific increased level of AA involved in lipids handling and bile recycling in the gut lumen (taurine and glycine).

DNA-PK Promotes the Mitochondrial, Metabolic, and Physical Decline that Occurs During Aging

Hallmarks of aging that negatively impact health include weight gain and reduced physical fitness, which can increase insulin resistance and risk for many diseases, including type 2 diabetes. The underlying mechanism(s) for these phenomena is poorly understood. Here we report that aging increases DNA breaks and activates DNA-dependent protein kinase (DNA-PK) in skeletal muscle, which suppresses mitochondrial function, energy metabolism, and physical fitness. DNA-PK phosphorylates threonines 5 and 7 of HSP90α, decreasing its chaperone function for clients such as AMP-activated protein kinase (AMPK), which is critical for mitochondrial biogenesis and energy metabolism. Decreasing DNA-PK activity increases AMPK activity and prevents weight gain, decline of mitochondrial function, and decline of physical fitness in middle-aged mice and protects against type 2 diabetes. In conclusion, DNA-PK is one of the drivers of the metabolic and fitness decline during aging, and therefore DNA-PK inhibitors may have therapeutic potential in obesity and low exercise capacity.

Mice lacking GPR3 receptors display late-onset obese phenotype due to impaired thermogenic function in brown adipose tissue

We report an unexpected link between aging, thermogenesis and weight gain via the orphan G protein-coupled receptor GPR3. Mice lacking GPR3 and maintained on normal chow had similar body weights during their first 5 months of life, but gained considerably more weight thereafter and displayed reduced total energy expenditure and lower core body temperature. By the age of 5 months GPR3 KO mice already had lower thermogenic gene expression and uncoupling protein 1 protein level and showed impaired glucose uptake into interscapular brown adipose tissue (iBAT) relative to WT littermates. These molecular deviations in iBAT of GPR3 KO mice preceded measurable differences in body weight and core body temperature at ambient conditions, but were coupled to a failure to maintain thermal homeostasis during acute cold challenge. At the same time, the same cold challenge caused a 17-fold increase in Gpr3 expression in iBAT of WT mice. Thus, GPR3 appears to have a key role in the thermogenic response of iBAT and may represent a new therapeutic target in age-related obesity.

Biologically active, high levels of interleukin-22 inhibit hepatic gluconeogenesis but do not affect obesity and its metabolic consequences

Background

Interleukin-22 (IL-22), a cytokine with important functions in anti-microbial defense and tissue repair, has been recently suggested to have beneficial effects in obesity and metabolic syndrome in some but not in other studies. Here, we re-examined the effects of IL-22 on obesity, insulin resistance, and hepatic glucose metabolism.

Results

Genetic deletion of IL-22 did not affect high-fat-diet (HFD)-induced obesity and insulin resistance. IL-22 transgenic mice with relatively high levels of circulating IL-22 (~600 pg/ml) were completely resistant to Concanavalin A-induced liver injury but developed the same degree of high fat diet (HFD)-induced obesity, insulin resistance, and fatty liver as the wild-type littermate controls. Similarly, chronic treatment with recombinant mouse IL-22 (rmIL-22) protein did not affect HFD-induced obesity and the associated metabolic syndrome. In vivo treatment with a single dose of rmIL-22 downregulated the hepatic expression of gluconeogenic genes and subsequently inhibited hepatic gluconeogenesis and reduced blood glucose levels both in HFD-fed and streptozotocin (STZ)-treated mice without affecting insulin production. In vitro exposure of mouse primary hepatocytes to IL-22 suppressed glucose production and the expression of gluconeogenic genes. These inhibitory effects were partially reversed by blocking STAT3 or the AMPK signaling pathway.

Conclusion

Biologically active, high levels of IL-22 do not affect obesity and the associated metabolic syndrome. Acute treatment with IL-22 inhibits hepatic gluconeogenesis, which is mediated via the activation of STAT3 and AMPK in hepatocytes.

Role of adiponectin in the metabolic effects of cannabinoid type 1 receptor blockade in mice with diet-induced obesity

The adipocyte-derived hormone adiponectin promotes fatty acid oxidation and improves insulin sensitivity and thus plays a key role in the regulation of lipid and glucose metabolism and energy homeostasis. Chronic cannabinoid type 1 (CB1) receptor blockade also increases lipid oxidation and improves insulin sensitivity in obese individuals or animals, resulting in reduced cardiometabolic risk. Chronic CB1 blockade reverses the obesity-related decline in serum adiponectin levels, which has been proposed to account for the metabolic effects of CB1 antagonists. Here, we investigated the metabolic actions of the CB1 inverse agonist rimonabant in high-fat diet (HFD)-induced obese adiponectin knockout (Adipo(-/-)) mice and their wild-type littermate controls (Adipo(+/+)). HFD-induced obesity and its hormonal/metabolic consequences were indistinguishable in the two strains. Daily treatment of obese mice with rimonabant for 7 days resulted in significant and comparable reductions in body weight, serum leptin, free fatty acid, cholesterol, and triglyceride levels in the two strains. Rimonabant treatment improved glucose homeostasis and insulin sensitivity to the same extent in Adipo(+/+) and Adipo(-/-) mice, whereas it reversed the HFD-induced hepatic steatosis, fibrosis, and hepatocellular damage only in the former. The adiponectin-dependent, antisteatotic effect of rimonabant was mediated by reduced uptake and increased β-oxidation of fatty acids in the liver. We conclude that reversal of the HFD-induced hepatic steatosis and fibrosis by chronic CB1 blockade, but not the parallel reduction in adiposity and improved glycemic control, is mediated by adiponectin.

Tracing fasting glucose fluxes with unstressed catheter approach in streptozotocin induced diabetic rats

OBJECTIVE

Blood glucose concentrations of type 1 diabetic rats are vulnerable, especially to stress and trauma. The present study aimed to investigate the fasting endogenous glucose production and skeletal muscle glucose uptake of Streptozotocin induced type 1 diabetic rats using an unstressed vein and artery implantation of catheters at the tails of the rats as a platform.

RESEARCH DESIGN AND METHODS

Streptozotocin (65 mg·kg⁻¹) was administered to induce type 1 diabetic state. The unstressed approach of catheters of vein and artery at the tails of the rats was established before the isotope tracer injection. Dynamic measurement of fasting endogenous glucose production was assessed by continuously infusing stable isotope [6, 6-²H₂] glucose, while skeletal muscle glucose uptake by bolus injecting radioactively labeled [1-¹⁴C]-2-deoxy-glucose.

RESULTS

Streptozotocin induced type 1 diabetic rats displayed polydipsia, polyphagia, and polyuria along with overt hyperglycemia and hypoinsulinemia. They also had enhanced fasting endogenous glucose production and reduced glucose uptake in skeletal muscle compared to nondiabetic rats.

CONCLUSIONS

The dual catheters implantation at the tails of the rats together with isotope tracers injection is a save time, unstressed, and feasible approach to explore the glucose metabolism in animal models in vivo.

Carnitine Palmitoyltransferase 1b Deficiency Protects Mice from Diet-Induced Insulin Resistance

Background

Carnitine Palmitoyl Transferase 1 (CPT1) is the rate-limiting enzyme governing long-chain fatty acid entry into mitochondria. CPT1 inhibitors have been developed and exhibited beneficial effects against type II diabetes in short-term preclinical animal studies. However, the long-term effects of treatment remain unclear and potential non-specific effects of these CPT1 inhibitors hamper in-depth understanding of the potential molecular mechanisms involved.

Methods

We investigated the effects of restricting the activity of the muscle isoform CPT1b in mice using heterozygous CPT1b deficient (Cpt1b^+/−) and Wild Type (WT) mice fed with a High Fat Diet (HFD) for 22 weeks. Insulin sensitivity was assessed using Glucose Tolerance Test (GTT), insulin tolerance test and hyperinsulinemic euglycemic clamps. We also examined body weight/composition, tissue and systemic metabolism/energetic status, lipid profile, transcript analysis, and changes in insulin signaling pathways.

Results

We found that Cpt1b^+/− mice were protected from HFD-induced insulin resistance compared to WT littermates. Cpt1b^+/− mice exhibited elevated whole body glucose disposal rate and skeletal muscle glucose uptake. Furthermore, Cpt1b^+/− skeletal muscle showed diminished ex vivo palmitate oxidative capacity by ~40% and augmented glucose oxidation capacity by ~50% without overt change in whole body energy metabolism. HFD feeding Cpt1b^+/− but not WT mice exhibited well-maintained insulin signaling in skeletal muscle, heart, and liver.

Conclusion

The present study on a genetic model of CPT1b restriction supports the concept that partial CPT1b inhibition is a potential therapeutic strategy.

Carnitine Palmitoyltransferase 1b Deficient Mice Develop Severe Insulin Resistance After Prolonged High Fat Diet Feeding

Background

Carnitine palmitoyltransferase 1 (CPT1) is the rate-limiting enzyme governing the entry of long-chain acyl-CoAs into mitochondria. Treatments with CPT1 inhibitors protect against insulin resistance in short-term preclinical animal studies. We recently reported that mice with muscle isoform CPT1b deficiency demonstrated improved insulin sensitivity when fed a High Fat-Diet (HFD) for up to 5 months. In this follow up study, we further investigated whether the insulin sensitizing effects of partial CPT1b deficiency could be maintained under a prolonged HFD feeding condition.

Methods

We investigated the effects of CPT1b deficiency on HFD-induced insulin resistance using heterozygous CPT1b deficient (Cpt1b^+/−) mice compared with Wild Type (WT) mice fed a HFD for a prolonged period of time (7 months). We assessed insulin sensitivity using hyperinsulinemic-euglycemic clamps. We also examined body composition, skeletal muscle lipid profile, and changes in the insulin signaling pathways of skeletal muscle, liver, and adipose tissue.

Results

We found that Cpt1b^+/− mice became severely insulin resistant after 7 months of HFD feeding. Cpt1b^+/− mice exhibited a substantially reduced glucose infusion rate and skeletal muscle glucose uptake. While Cpt1b^+/− mice maintained a slower weight gain with less fat mass than WT mice, accumulation of lipid intermediates became evident in the muscle of Cpt1b^+/− but not WT mice after 7 months of HFD feeding. Insulin signaling was impaired in the Cpt1b^+/− as compared to the WT muscles.

Conclusion

Partial CPT1b deficiency, mimicking CPT1b inhibition, may lead to impaired insulin signaling and insulin sensitivity under a prolonged HFD feeding condition. Therefore, further studies on the potential detrimental effects of prolonged therapy with CPT1 inhibition are necessary in the development of this potential therapeutic strategy.

Hepatic Sirt1 deficiency in mice impairs mTorc2/Akt signaling and results in hyperglycemia, oxidative damage, and insulin resistance

Insulin resistance is a major risk factor for type 2 diabetes mellitus. The protein encoded by the sirtuin 1 (Sirt1) gene, which is a mouse homolog of yeast Sir2, is implicated in the regulation of glucose metabolism and insulin sensitivity; however, the underlying mechanism remains elusive. Here, using mice with a liver-specific null mutation of Sirt1, we have identified a signaling pathway involving Sirt1, Rictor (a component of mTOR complex 2 [mTorc2]), Akt, and Foxo1 that regulates gluconeogenesis. We found that Sirt1 positively regulates transcription of the gene encoding Rictor, triggering a cascade of phosphorylation of Akt at S473 and Foxo1 at S253 and resulting in decreased transcription of the gluconeogenic genes glucose-6-phosphatase (G6pase) and phosphoenolpyruvate carboxykinase (Pepck). Liver-specific Sirt1 deficiency caused hepatic glucose overproduction, chronic hyperglycemia, and increased ROS production. This oxidative stress disrupted mTorc2 and impaired mTorc2/Akt signaling in other insulin-sensitive organs, leading to insulin resistance that could be largely reversed with antioxidant treatment. These data delineate a pathway through which Sirt1 maintains insulin sensitivity and suggest that treatment with antioxidants might provide protection against progressive insulin resistance in older human populations.

Wnt signaling regulates hepatic metabolism

The contribution of the Wnt pathway has been extensively characterized in embryogenesis, differentiation, and stem cell biology but not in mammalian metabolism. Here, using in vivo gain- and loss-of-function models, we demonstrate an important role for Wnt signaling in hepatic metabolism. In particular, β-catenin, the downstream mediator of canonical Wnt signaling, altered serum glucose concentrations and regulated hepatic glucose production. β-Catenin also modulated hepatic insulin signaling. Furthermore, β-catenin interacted with the transcription factor FoxO1 in livers from mice under starved conditions. The interaction of FoxO1 with β-catenin regulated the transcriptional activation of the genes encoding glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK), the two rate-limiting enzymes in hepatic gluconeogenesis. Moreover, starvation induced the hepatic expression of mRNAs encoding different Wnt isoforms. In addition, nutrient deprivation appeared to favor the association of β-catenin with FoxO family members, rather than with members of the T cell factor of transcriptional activators. Notably, in a model of diet-induced obesity, hepatic deletion of β-catenin improved overall metabolic homeostasis. These observations implicate Wnt signaling in the modulation of hepatic metabolism and raise the possibility that Wnt signaling may play a similar role in the metabolic regulation of other tissues.

Attenuated alpha-adrenoceptor-mediated arterial and venous constrictions in rat models of diabetes

Diabetes is associated with metabolic and vascular abnormalities. We investigated if arterial and venous constrictions are impaired in rat models of diabetes. Wistar rats (5 weeks old) were fed a normal or high-fructose diet (60% of caloric intake). On Day 14, half of the animals in each diet regimen were given streptozotocin (60 mg/kg, i.v.). On Day 35, plasma insulin and triglyceride were measured, and on Day 42, insulin sensitivity (via hyperinsulinemic euglycemic clamp), and pressor as well as mean circulatory filling pressure (index of venous tone) responses to noradrenaline were determined. The rats treated with streptozotocin or fructose-streptozotocin were hyperglycemic, hypoinsulinemic and insulin resistant, and they also had reduced potency (increased ED(50)) of pressor response and reduced venoconstriction to noradrenaline compared to the two groups not given streptozotocin. Plasma triglyceride was unchanged in streptozotocin-treated rats, moderately increased in fructose-fed rats, and markedly increased in fructose-streptozotocin-treated rats. Hyperglycemia, insulin resistance and alpha-adrenoceptor-mediated venous contractile dysfunction were more pronounced in the group given fructose-streptozotocin than that given streptozotocin alone. The presence of marked hypertriglyceridemia, insulin resistance and vascular dysfunction makes the fructose-streptozotocin-treated rats a suitable model for study of metabolic and vascular abnormalities in advanced type 2 diabetes.

Nonobese, insulin-deficient Ins2Akita mice develop type 2 diabetes phenotypes including insulin resistance and cardiac remodeling

Although insulin resistance has been traditionally associated with type 2 diabetes, recent evidence in humans and animal models indicates that insulin resistance may also develop in type 1 diabetes. A point mutation of insulin 2 gene in Ins2(Akita) mice leads to pancreatic beta-cell apoptosis and hyperglycemia, and these mice are commonly used to investigate type 1 diabetes and complications. Since insulin resistance plays an important role in diabetic complications, we performed hyperinsulinemic-euglycemic clamps in awake Ins2(Akita) and wild-type mice to measure insulin action and glucose metabolism in vivo. Nonobese Ins2(Akita) mice developed insulin resistance, as indicated by an approximately 80% reduction in glucose infusion rate during clamps. Insulin resistance was due to approximately 50% decreases in glucose uptake in skeletal muscle and brown adipose tissue as well as hepatic insulin action. Skeletal muscle insulin resistance was associated with a 40% reduction in total GLUT4 and a threefold increase in PKCepsilon levels in Ins2(Akita) mice. Chronic phloridzin treatment lowered systemic glucose levels and normalized muscle insulin action, GLUT4 and PKCepsilon levels in Ins2(Akita) mice, indicating that hyperglycemia plays a role in insulin resistance. Echocardiography showed significant cardiac remodeling with ventricular hypertrophy that was ameliorated following chronic phloridzin treatment in Ins2(Akita) mice. Overall, we report for the first time that nonobese, insulin-deficient Ins2(Akita) mice develop type 2 diabetes phenotypes including peripheral and hepatic insulin resistance and cardiac remodeling. Our findings provide important insights into the pathogenesis of metabolic abnormalities and complications affecting type 1 diabetes and lean type 2 diabetes subjects.

Hyperglycemia, maturity-onset obesity, and insulin resistance in NONcNZO10/LtJ males, a new mouse model of type 2 diabetes

As a new mouse model of obesity-induced diabetes generated by combining quantitative trait loci from New Zealand Obese (NZO/HlLt) and Nonobese Nondiabetic (NON/LtJ) mice, NONcNZO10/LtJ (RCS10) male mice developed type 2 diabetes characterized by maturity onset obesity, hyperglycemia, and insulin resistance. To metabolically profile the progression to diabetes in preobese and obese states, a 2-h hyperinsulinemic euglycemic clamp was performed and organ-specific changes in insulin action were assessed in awake RCS10 and NON/LtJ (control) males at 8 and 13 wk of age. Prior to development of obesity and attendant increases in hepatic lipid content, 8-wk-old RCS10 mice developed insulin resistance in liver and skeletal muscle due to significant decreases in insulin-stimulated glucose uptake and GLUT4 expression in muscle. Transition to an obese and hyperglycemic state by 13 wk of age exacerbated insulin resistance in skeletal muscle, liver, and heart associated with organ-specific increases in lipid content. Thus, this polygenic mouse model of type 2 diabetes, wherein plasma insulin is only modestly elevated and obesity develops with maturity yet insulin action and glucose metabolism in skeletal muscle and liver are reduced at an early prediabetic age, should provide new insights into the etiology of type 2 diabetes.

Profiling of human mesangial cell subproteomes reveals a role for calmodulin in glucose uptake

Proteomics combined with cell fractionation was used to identify proteins regulated by high glucose (HG) in human mesangial cells (HMC). Total membrane and cytosolic fraction proteins derived from HMC after 7 days of HG exposure were resolved by a two-dimensional gel electrophoresis approach. DeCyder software was used to analyze the HG-induced protein spot dysregulation. In the membrane subproteome, of the 92 spots that were matched across all gels, HG induced significant downregulation of only 4 protein spots. The dysregulated spots from the membrane subproteome included binding protein (BiP), calreticulin precursor protein, a 63-kDa transmembrane protein from a ER/Golgi intermediate, and beta-subunit of collagen proline 4-hydroxylase. In the cytosolic subproteome, of the 122 spots that were matched across all gels, HG induced downregulation of 3 protein spots and upregulation of 2 protein spots significantly. Enolase 1, annexin VI, and gamma(2)-actin were decreased, whereas heat shock protein-70 kDa and calmodulin (CaM) were increased. Further confocal microscopy and Western immunoblotting of mesangial cells validated the increase in CaM. Immunoblotting of diabetic mouse and rat kidneys exhibited a marked increase in CaM at both early and late stages of diabetes, reflecting the potential physiological relevance of CaM upregulation. CaM-specific inhibitors blocked glucose transport stimulated by transforming growth factor-beta and insulin in mesangial cells. In conclusion, using a combination of cell fractionation and protein expression profiling, we identified a cohort of HG-dysregulated proteins in the HMC and identified a critical and as yet unrecognized role for CaM in glucose transport in mesangial cells.

Improvement of insulin sensitivity after peroxisome proliferator-activated receptor-alpha agonist treatment is accompanied by paradoxical increase of circulating resistin levels

We studied the effect of peroxisome proliferator-activated receptor-alpha (PPAR-alpha) activation on serum concentrations and tissue expression of resistin, adiponectin, and adiponectin receptor-1 and -2 (AdipoR1 and AdipoR2) mRNA in normal mice and mice with insulin resistance induced by lipogenic, simple-carbohydrate diet (LD). Sixteen weeks of LD feeding induced obesity with liver steatosis and increased insulin levels but did not significantly affect circulating adiponectin or resistin. Treatment with PPAR-alpha agonist fenofibrate decreased body weight and fat pad weight and ameliorated liver steatosis in LD-fed mice with concomitant reduction in blood glucose, free fatty acid, triglyceride, serum insulin levels, and homeostasis model assessment index values. Euglycemic-hyperinsulinemic clamp demonstrated the development of whole-body and liver insulin resistance in LD-fed mice, which were both normalized by fenofibrate. Fenofibrate treatment markedly increased circulating resistin levels on both diets and adiponectin levels in chow-fed mice only. Fat adiponectin mRNA expression was not affected by fenofibrate treatment. Resistin mRNA expression increased in subcutaneous but not gonadal fat after fenofibrate treatment. In addition to fat, a significant amount of adiponectin mRNA was also expressed in the muscle. This expression markedly increased after fenofibrate treatment in chow- but not in LD-fed mice. Adipose tissue expression of AdipoR1 mRNA was significantly reduced in LD-fed mice and increased after fenofibrate treatment. In conclusion, PPAR-alpha activation ameliorated the development of insulin resistance in LD-fed mice despite a major increase in serum resistin levels. This effect could be partially explained by increased AdipoR1 expression in adipose tissue after fenofibrate treatment.

Alpha-lipoic acid increases insulin sensitivity by activating AMPK in skeletal muscle

Triglyceride accumulation in skeletal muscle contributes to insulin resistance in obesity. We recently showed that alpha-lipoic acid (ALA) reduces body weight and prevents the development of diabetes in diabetes-prone obese rats by reducing triglyceride accumulation in non-adipose tissues. AMP-activated protein kinase (AMPK) is a major regulator of cellular energy metabolism. We examined whether ALA lowers triglyceride accumulation in skeletal muscle by activating AMPK. Alpha2-AMPK activity was decreased in obese rats compared to control rats. Administration of ALA to obese rats increased insulin-stimulated glucose disposal in whole body and in skeletal muscle. ALA also increased fatty acid oxidation and activated AMPK in skeletal muscle. Adenovirus-mediated administration of dominant negative AMPK into skeletal muscle prevented the ALA-induced increases in fatty acid oxidation and insulin-stimulated glucose uptake. These results suggest that ALA-induced improvement of insulin sensitivity is mediated by activation of AMPK and reduced triglyceride accumulation in skeletal muscle.

Atorvastatin induces insulin sensitization in Zucker lean and fatty rats

BACKGROUND

The 3-hydroxy-3-methyl glutaryl coenzyme A (HMG-CoA) reductase inhibitors ('statins') have been implicated in preventing new onset type 2 diabetes, whereas the mechanism of this effect is not known. We investigated the effects of an HMG-CoA reductase inhibitor, atorvastatin, on insulin sensitization in Zucker lean and fatty rats.

METHODS AND RESULTS

In vivo studies of insulin sensitization were performed in chow fed Zucker lean and fatty rats treated with atorvastatin 50mg/kg/day (ATORVA_50) and results were compared to Zucker lean and fatty rats treated with drug vehicle only (CONT). Additional Zucker lean rats were treated with an intermediate dose of atorvastatin 25mg/kg/day (ATORVA_25). Treatment with atorvastatin resulted in a dose-dependent improvement in whole body insulin sensitivity in both lean and fatty rats, with an approximately two-fold increase in glucose infusion rate and glucose disposal (Rd) in ATORVA_50 versus CONT (p<0.01). Atorvastatin 50mg/kg/day resulted in an increase in 2-deoxyglucose (2-DOG) uptake by skeletal muscles (approximately two-fold increase in 2-DOG uptake in quadriceps (p=0.06) and gastrocnemius (p<0.01)) in lean Zucker rats. Insulin-stimulated phosphorylation of Akt/PKB was significantly increased in skeletal muscle of ATORVA_50 versus CONT in both lean and fatty rats.

CONCLUSION

Atorvastatin induces insulin sensitization in Zucker lean and fatty rats. This may be a clinically important pleiotropic effect if confirmed in insulin resistant humans.

Thiazolidinediones improve insulin sensitivity in adipose tissue and reduce the hyperlipidaemia without affecting the hyperglycaemia in a transgenic model of type 2 diabetes

AIM/HYPOTHESIS

The aim of this study was to examine the effects of thiazolidinediones on the MKR mouse model of type 2 diabetes.

METHODS

Six-week-old wild-type (WT) and MKR mice were fed with or without rosiglitazone or pioglitazone for 3 weeks. Blood was collected from the tail vein for serum biochemistry analysis. Hyperinsulinaemic-euglycaemic clamp analysis was performed to study effects of thiazolidinediones on insulin sensitivity of tissues in MKR mice. Northern blot analysis was performed to measure levels of target genes of PPAR gamma agonists in white adipose tissue and hepatic gluconeogenic genes.

RESULTS

Thiazolidinedione treatment of MKR mice significantly lowered serum lipid levels and increased serum adiponectin levels but did not affect levels of blood glucose and serum insulin. Hyperinsulinaemic-euglycaemic clamp showed that whole-body insulin sensitivity and glucose homeostasis failed to improve in MKR mice after rosiglitazone treatment. Insulin suppression of hepatic endogenous glucose production failed to improve in MKR mice following rosiglitazone treatment. This lack of change in hepatic insulin insensitivity was associated with no change in the ratio of HMW : total adiponectin, hepatic triglyceride content, and sustained hepatic expression of PPAR gamma and stearoyl-CoA desaturase 1 mRNA. Interestingly, rosiglitazone markedly enhanced glucose uptake by white adipose tissue with a parallel increase in CD36, aP2 and GLUT4 gene expression.

CONCLUSIONS/INTERPRETATION

These data suggest that potentiation of insulin action on tissues other than adipose tissue is required to mediate the antidiabetic effects of thiazolidinediones in our MKR diabetic mice.

Gosha-jinki-gan (a Herbal Complex) Corrects Abnormal Insulin Signaling

Previous studies have shown that the traditional herbal complex Gosha-jinki-gan (GJG) improves diabetic neuropathy and insulin resistance. The present study was undertaken to elucidate the molecular mechanisms related with the long-term effects of GJG administration on insulin action in vivo and the early steps of insulin signaling in skeletal muscle in streptozotocin (STZ) diabetes. Rats were randomized into five subgroups: (1) saline treated control, (2) GJG treated control, (3) 2-unit insulin + saline treated diabetic, (4) saline + GJG treated diabetic and (5) 2-unit insulin + GJG treated diabetic groups. After seven days of treatment, euglycemic clamp experiment at an insulin infusion rate of 6 mU/kg/min was performed in overnight fasted rats. Despite the 2-unit insulin treatment, the metabolic clearance rates of glucose (MCR, ml/kg/min) in diabetic rats were significantly lower compared with the controls (11.4 +/- 1.0 vs 44.1 +/- 1.5; P < 0.001), and were significantly improved by insulin combined with GJG or GJG alone (26 +/- 3.2 and 24.6 +/- 2.2, P < 0.01, respectively). The increased insulin receptor (IR)-beta protein content in skeletal muscle of diabetic rats was not affected by insulin combined with GJG administration. However, the decreased insulin receptor substrate-1 (IRS-1) protein content was significantly improved by treatment with GJG. Additionally, the increased tyrosine phosphorylation levels of IR-beta and IRS-1 were significantly inhibited in insulin combined with GJG treated diabetes. The present results suggest that the improvement of the impaired insulin sensitivity in STZ-diabetic rats by administration of GJG may be due, at least in part, to correction in the abnormal early steps of insulin signaling in skeletal muscle.

Insulinotropic agent ID-1101 (4-hydroxyisoleucine) activates insulin signaling in rat

ID-1101 (4-hydroxyisoleucine), an amino acid extracted from fenugreek seeds, exhibits an interesting glucose-dependent insulin-stimulating activity. The present study was undertaken to investigate a possible extrapancreatic effect of ID-1101 on insulin signaling and action besides its previously described insulinotropic action. Insulin-sensitizing effects of ID-1101 were investigated in rat in vivo by three different approaches: 1) using euglycemic hyperinsulinemic clamps in two different rat models of insulin resistance, i.e., Zucker fa/fa rats and rats fed a sucrose-lipid diet; 2) measuring liver and muscle phosphatidylinositol (PI) 3-kinase activity after an acute injection of ID-1101 in normal and insulin-resistant diabetic rats; and 3) after chronic treatment in two rat models of insulin resistance. Euglycemic hyperinsulinemic clamp experiments revealed that ID-1101 can improve insulin resistance through an increase of peripheral glucose utilization rate in sucrose-lipid-fed rats and by decreasing hepatic glucose production in Zucker fa/fa rats. Moreover, we demonstrated that a single injection of ID-1101 activates the PI 3-kinase activity in liver and muscle from normal rats but also in muscle from diabetic rats. Finally, chronic ID-1101 treatment significantly reduced insulinemia in type 2 diabetic rats and reduced the progression of hyperinsulinemia in insulin-resistant obese Zucker fa/fa rats. These findings clearly demonstrate that ID-1101 can reduce insulin resistance through activation of the early steps of insulin signaling in peripheral tissues and in liver. In summary, ID-1101, besides its insulinotropic effect, directly improves insulin sensitivity, making it a potentially very valuable therapeutic agent for diabetes treatment.

Genetic background (C57BL/6J versus FVB/N) strongly influences the severity of diabetes and insulin resistance in ob/ob mice

We studied the effects of genetic background on the phenotype of ob/ob mice, a model of severe obesity, insulin resistance, and diabetes caused by leptin deficiency. Despite a comparable degree of obesity and hyperinsulinemia, C57BL/6J ob/ob mice had much milder hyperglycemia and, surprisingly, normal circulating adiponectin levels despite still-prominent signs of insulin resistance. Hyperinsulinemic-euglycemic clamp revealed relatively less whole-body and muscle insulin resistance in C57BL/6J ob/ob mice, whereas liver insulin resistance tended to be more severe than in FVB/N ob/ob mice. C57BL/6J ob/ob mice had also more rapid clearance of circulating triglycerides and more severe hepatic steatosis. We suggest that strain-related distinction in lipid handling is the most important player in the differences in diabetic phenotype and insulin sensitivity, whereas the impact of circulating adiponectin levels on the overall phenotype of ob/ob mice is less important.

Influence of plasma insulin levels on antinatriuretic and vasoconstrictor actions of angiotensin-II

The objective of the present study is to investigate whether plasma insulin levels play a role in the antinatriuretic and vasoconstrictor actions of angiotensin-II (Ang-II). We evaluated antinatriuretic function of endogenous Ang-II using an AT1 receptor antagonist, candesartan in anesthetized Sprague-Dawley rats. In control rats, candesartan produced significant increases in natriuresis and diuresis and these effects were abolished in streptozocin (STZ, 55 mg/kg i.p.) treated rats. Replacement of insulin restored these renal effects of candesartan. In a separate group of rats pretreated with an autonomic ganglionic blocker, pressor responses to Ang-II and norepinephrine (NE) before or after L-NNA, a nitric oxide synthase inhibitor were not affected by STZ treatment. However, insulin replacement greatly augmented these responses. These data provide evidence in vivo showing that insulin can enhance both antinatriuretic and vasoconstrictor actions of Ang-II. Hence exaggerated renal and vascular effects of Ang-II in the obese Zucker rats observed in our previous studies may be related to hyperinsulimemia and this phenomena could contribute to salt-sensitivity and development of sustained hypertension.

Vasopeptidase inhibitor omapatrilat induces profound insulin sensitization and increases myocardial glucose uptake in Zucker fatty rats: Studies comparing a vasopeptidase inhibitor, angiotensin-converting enzyme inhibitor, and angiotensin II type I receptor blocker

BACKGROUND

ACE inhibitors (ACEIs) improve insulin resistance and prevent type 2 diabetes, possibly mediated by inhibition of bradykinin (BK) degradation. The vasopeptidase inhibitor omapatrilat (OMA) raises BK to a greater extent than ACEIs by dual enzyme inhibition, whereas its insulin-sensitizing effects and mechanisms have not been investigated.

METHODS AND RESULTS

We compared the insulin-sensitizing effects of OMA, ramipril (an ACEI), losartan (an angiotensin II type 1 receptor blocker), and placebo by 2-step euglycemic hyperinsulinemic clamp in insulin-resistant Zucker fatty rats (n=6 to 7 in each group). OMA resulted in a lower rate of endogenous glucose production than placebo at baseline (35+/-5 versus 54+/-4 mmol x kg(-1) x min(-1), P<0.01), greater suppression of endogenous glucose production by low-dose insulin (73+/-11% versus 27+/-18%, P<0.05), and greater glucose disposal at high-dose insulin (135+/-5 versus 92+/-4 mmol x kg(-1) x min(-1), P<0.01). Ramipril tended to improve insulin sensitivity, but losartan did not. OMA significantly increased 2-deoxyglucose uptake by myocardium, fat, and skeletal muscle. Ramipril increased 2-deoxyglucose uptake only by some skeletal muscles, but losartan did not. The insulin-sensitizing effects of OMA were blocked significantly by HOE-140 (a BK, B2 receptor antagonist) and NG-nitro-L-arginine methyl ester (a nitric oxide synthase inhibitor) in all tissues except myocardium.

CONCLUSIONS

OMA induces profound insulin sensitization and increases myocardial glucose uptake in Zucker fatty rats. This effect is greater than that of ramipril and probably occurs at least in part via stimulation of the B2 receptor. OMA has the potential for greater type 2 diabetes prevention than ACEI.

Enhanced insulin sensitivity in mice lacking ganglioside GM3

Gangliosides are sialic acid-containing glycosphingolipids that are present on all mammalian plasma membranes where they participate in recognition and signaling activities. We have established mutant mice that lack GM3 synthase (CMP-NeuAc:lactosylceramide alpha2,3-sialyltransferase; EC 2.4.99.-). These mutant mice were unable to synthesize GM3 ganglioside, a simple and widely distributed glycosphingolipid. The mutant mice were viable and appeared without major abnormalities but showed a heightened sensitivity to insulin. A basis for the increased insulin sensitivity in the mutant mice was found to be enhanced insulin receptor phosphorylation in skeletal muscle. Importantly, the mutant mice were protected from high-fat diet-induced insulin resistance. Our results show that GM3 ganglioside is a negative regulator of insulin signaling, making it a potential therapeutic target in type 2 diabetes.

Opposite effects of background genotype on muscle and liver insulin sensitivity of lipoatrophic mice. Role of triglyceride clearance

The metabolic phenotype of the A-ZIP/F-1 (AZIP) lipoatrophic mouse is different depending on its genetic background. On both the FVB/N (FVB) and C57BL/6J (B6) backgrounds, AZIP mice have a similarly severe lack of white adipose tissue and comparably increased insulin levels and triglyceride secretion rates. However, on the B6 background, the AZIP mice have less hyperglycemia, lower circulating triglyceride and fatty acid levels, and lower mortality. AZIP characteristics that are more severe on the B6 background include increased liver size and liver triglyceride content. A unifying hypothesis is that the B6 strain has higher triglyceride clearance into the liver, with lower triglyceride levels elsewhere. This may account for the observation that the B6 AZIP mice have less insulin-resistant muscles and more insulin-resistant livers, than do the FVB AZIP mice. B6 wild type, as well as B6 AZIP, mice have increased triglyceride clearance relative to FVB, which may be explained in part by higher serum lipase levels and liver CD36/fatty acid translocase mRNA levels. Thus, it is likely that increased triglyceride clearance in B6, as compared with FVB, mice contributes to the strain differences in insulin resistance and lipid metabolism.

Effect of BRX-220 against peripheral neuropathy and insulin resistance in diabetic rat models

Bimoclomol (BML), a symptomatic antidiabetic agent, has been developed by Biorex R & D Co. to treat diabetic neuropathy and retinopathy. BRX-220, an orally active member of the BRX family, has been developed to treat diabetic complications and insulin resistance (IR) as a follow-up compound. The effect of BRX-220 on peripheral neuropathy was examined in rats with diabetes (type 1) induced by administration of a beta-cell toxin, streptozotocin (STZ, 45 mg/kg iv). Nerve functions were evaluated by electrophysiological measurements of muscle motor and sensory nerve conduction velocities (MNCV and SNCV, respectively). MNCV and SNCV decreased in diabetic rats by 25% (p < 0.001). A 1-month preventive treatment with BRX-220 (2.5, 5, 10, and 20 mg/kg po) dose-dependently improved diabetes-related deficits in MNCV (51.3%, 71.3%, 86.1%, and 91.3%) and SNCV (48.9%, 68.5%, 86.1%, and 93.2%). Insulin sensitivity was measured using the insulin tolerance test (ITT), both in STZ diabetic and in Zucker diabetic fatty (ZDF) rats (model of type 2 diabetes). Severe IR was detected in STZ diabetic and ZDF rats. This resistance was significantly (p < 0.05) reduced by BRX-220 treatment.

Short-term K(+) deprivation provokes insulin resistance of cellular K(+) uptake revealed with the K(+) clamp

We aimed to test the feasibility of quantifying insulin action on cellular K(+) uptake in vivo in the conscious rat by measuring the exogenous K(+) infusion rate needed to maintain constant plasma K(+) concentration ([K(+)]) during insulin infusion. In this "K(+) clamp" the K(+) infusion rate required to clamp plasma [K(+)] is a measure of insulin action to increase net plasma K(+) disappearance. K(+) infusion rate required to clamp plasma [K(+)] was insulin dose dependent. Renal K(+) excretion was not significantly affected by insulin at a physiological concentration ( approximately 90 microU/ml, P > 0.05), indicating that most of insulin-mediated plasma K(+) disappearance was due to K(+) uptake by extrarenal tissues. In rats deprived of K(+) for 2 days, plasma [K(+)] fell from 4.2 to 3.8 mM, insulin-mediated plasma glucose clearance was normal, but insulin-mediated plasma K(+) disappearance decreased to 20% of control, even though there was no change in muscle Na-K-ATPase activity or expression, which is believed to be the main K(+) uptake route. After 10 days K(+) deprivation, plasma [K(+)] fell to 2.9 mM, insulin-mediated K(+) disappearance decreased to 6% of control (glucose clearance normal), and there were 50% decreases in Na-K-ATPase activity and alpha2-subunit levels. In conclusion, the present study proves the feasibility of the K(+) clamp technique and demonstrates that short-term K(+) deprivation leads to a near complete insulin resistance of cellular K(+) uptake that precedes changes in muscle sodium pump expression.

Mechanism of insulin resistance in A-ZIP/F-1 fatless mice

Insulin resistance is a major factor in the pathogenesis of type 2 diabetes and may be related to alterations in fat metabolism. Fatless mice have been created using dominant-negative protein (A-ZIP/F-1) targeted gene expression in the adipocyte and shown to develop diabetes. To understand the mechanism responsible for the insulin resistance in these mice, we conducted hyperinsulinemic-euglycemic clamps in awake fatless and wild type littermates before the development of diabetes and examined insulin action and signaling in muscle and liver. We found the fatless mice to be severely insulin-resistant, which could be attributed to defects in insulin action in muscle and liver. Both of these abnormalities were associated with defects in insulin activation of insulin receptor substrate-1 and -2-associated phosphatidylinositol 3-kinase activity and a 2-fold increase in muscle and liver triglyceride content. We also show that upon transplantation of fat tissue into these mice, triglyceride content in muscle and liver returned to normal as does insulin signaling and action. In conclusion, these results suggest that the development of insulin resistance in type 2 diabetes may be due to alterations in the partitioning of fat between the adipocyte and muscle/liver leading to accumulation of triglyceride in the latter tissues with subsequent impairment of insulin signaling and action.

Reduced glucose clearance as the major determinant of postabsorptive hyperglycemia in diabetic rats

The relationships between postabsorptive glucose concentration and hepatic glucose output (HGO) and glucose clearance were studied in rats one day after treatment with various doses of streptozotocin (STZ; 0, 15, 30, 40, 50, or 75 mg/kg; n = 6 per dose; study 1). Glucose fluxes were estimated using a prolonged (6-h) infusion of [3-3H]glucose to ensure complete tracer equilibration at hyperglycemia. Postabsorptive glucose was significantly increased at the high doses of STZ (50 and 75 mg/kg; P < 0.01) and was strongly correlated with glucose clearance across all doses (r = -0.85, P < 0.001) but less strongly with HGO (r = 0.46, P < 0.01). In the group treated with 50 mg/kg STZ, postabsorptive glucose was increased twofold compared with the control (i.e., zero dose) group, with no change in HGO and a 45% decrease in glucose clearance, indicating that the hyperglycemia was due to a decrease in glucose clearance. To understand the cellular mechanisms of decreased glucose clearance in STZ diabetic rats, skeletal muscle glucose clearance and intracellular glucose and glucose 6-phosphate (G-6-P) concentrations were determined in normal and STZ (50 mg/kg) diabetic rats at their postabsorptive glucose levels as well as at matched hyperglycemia (12 mM; study 2). Glucose clearance was significantly decreased in soleus (P < 0.05) muscles of the diabetic rats, and this was associated with significantly decreased intracellular glucose and G-6-P levels at matched hyperglycemia (P < 0.05), suggestive of decreased glucose transport. In conclusion, postabsorptive hyperglycemia in STZ diabetic rats was largely due to decreased glucose clearance, although increased HGO may also have been a contributing factor at the highest STZ dose. The decrease in postabsorptive glucose clearance in STZ diabetic rats appeared to be associated with an impairment of glucose transport in soleus (type I) muscles.

Impaired insulin secretion and excessive hepatic glucose production are both early events in the diabetic GK rat

Adult Goto-Kakisaki Wistar (GK) rats exhibit a spontaneous non-insulin-dependent diabetes characterized by impaired glucose-induced insulin secretion, decreased beta-cell mass, hepatic glucose overproduction, and moderate insulin resistance in muscles and adipose tissues. To elucidate the pathogenesis of hyperglycemia in this animal model, we have studied insulin secretion and insulin action in 4-wk-old GK pups, just before weaning. In the postabsorptive state, their basal plasma glucose level was elevated (P < 0.001), and their tolerance to intravenous glucose was impaired. Their kinetics of insulin release in response to glucose was impaired, with a low acute phase of insulin release in vivo and in vitro (perfused pancreas). Basal glucose production was increased in the GK pups by 40% (P < 0.05). During euglycemic clamp performed at submaximal hyperinsulinemia, suppression of liver glucose production was less effective (P < 0.01) in the GK rats, whereas their overall glucose utilization was similar to that of the control group. This was correlated with a normal insulin-stimulated glucose utilization by epitrochlearis, soleus, and extensor digitorum longus muscles, diaphragm, and white adipose tissues. These data give body to the primacy of the beta-cell defects in the etiology of non-insulin-dependent diabetes mellitus in the GK rat. They also highlight a possible primary role of the liver defect. Peripheral insulin resistance does not contribute to the development of postnatal glucose intolerance in this diabetes model.

GLP-1(7-36)amide binding in skeletal muscle membranes from streptozotocin diabetic rats

A higher specific binding of GLP-1(7-36)amide is found in skeletal muscle plasma membranes from adult streptozotocin (STZ)-treated rats (insulin-dependent diabetes mellitus model) and from neonatal STZ-treated rats (non insulin-dependent diabetes mellitus model), as compared to that in normal controls; no apparent change in the affinity was observed, that indicating the presence in both diabetic models of an increased number of high affinity binding sites for the peptide. The maximal specific GLP-1(7-16)amide binding in the non insulin-dependent diabetes mellitus model was found to be significantly higher than that in the insulin-dependent diabetes mellitus model. As GLP-1(7-36)amide exerts a glycogenic effect in the rat skeletal muscle, the present data suggest that the action of the peptide in the muscle glucose metabolism may be increased in states of insulin deficiency accompanied or not by insulin resistance.

Mechanisms and time course of impaired skeletal muscle glucose transport activity in streptozocin diabetic rats

Skeletal muscle glucose transport is altered in diabetes in humans, as well as in rats. To investigate the mechanisms of this abnormality, we measured glucose transport Vmax, the total transporter number, their average intrinsic activity, GLUT4 and GLUT1 contents in skeletal muscle plasma membrane vesicles from basal or insulin-stimulated streptozocin diabetic rats with different duration of diabetes, treated or not with phlorizin. The glucose transport Vmax progressively decreased with the duration of diabetes. In the basal state, this decrease was primarily associated with the reduction of transporter intrinsic activity, which appeared earlier than any change in transporter number or GLUT4 and GLUT1 content. In the insulin-stimulated state, the decrease of transport was mainly associated with severe defects in transporter translocation. Phlorizin treatment partially increased the insulin-stimulated glucose transport by improving the transporter translocation defects. In conclusion, in streptozocin diabetes (a) reduction of intrinsic activity plays a major and early role in the impairment of basal glucose transport; (b) a defect in transporter translocation is the mechanism responsible for the decrease in insulin-stimulated glucose transport; and (c) hyperglycemia per se affects the insulin-stimulated glucose transport by altering the transporter translocation.

Alterations in specific protein-tyrosine phosphatases accompany insulin resistance of streptozotocin diabetes

To test whether protein tyrosine phosphatases (PTPases) may play a role in the insulin resistance of insulinopenic diabetes, we assessed PTPase activity as well as the protein and mRNA abundance of three major candidate PTPases in subcellular fractions of liver and skeletal muscle of streptozotocin-diabetic rats before and after insulin treatment. PTPase activity against the insulin receptor in liver and muscle cytosol increased to 120-125% of control in the diabetic animals and by an additional 5-10% after insulin treatment. In the particulate fraction, PTPase activity decreased to 65-70% of control in diabetic liver and muscle and increased to 115-120% of control after insulin treatment. Protein for the leukocyte common antigen-related PTPase paralleled the changes in the PTPase activity in the particulate fraction. SH-PTP2/syp and PTPase 1B were both significantly increased in diabetes. SH-PTP2/syp also exhibited an increased ratio of particulate to cytosol distribution in diabetic tissues (1.8-1.9) that was reversed after insulin treatment (0.79-0.95). Northern analysis suggested that the PTPases were regulated at a pretranslational level. These changes in the abundance and distribution of specific PTPases may be involved in the pathogenesis of insulin resistance in insulinopenic diabetes.