Life without Proteinase Activated Receptor 2 (PAR2) Alters Body Composition and Glucose Tolerance in Mice.

The potential role of proteinase activated receptor 2 (PAR2) in the development of age-related obesity and insulin resistance is not well-understood. To address the hypothesis that deletion of PAR2 might ameliorate age-related obesity and impaired glucose homeostasis, we assessed body composition and insulin action in 18-month-old male PAR2 knockout (PAR2KO-AG), age-matched (AG) and young C57BL6 (YG, 6-month-old) mice. Body composition was measured by magnetic resonance spectroscopy (MRS) and insulin action was assessed by glucose tolerance (GT), insulin tolerance (IT) and AICAR tolerance (AT) testing. AG mice weighed significantly more than YG mice (p = 0.0001) demonstrating age-related obesity. However, PAR2KO-AG mice weighed significantly more than AG mice (p = 0.042), indicating that PAR2 may prevent a portion of age-related obesity. PAR2KO-AG and AG mice had greater fat mass and body fat percentage than YG mice. Similar to body weight, fat mass was greater in PAR2KO-AG mice compared to AG mice (p = 0.045); however, only a trend for greater body fat percentage in PAR2KO-AG compared to AG mice was observed (p = 0.09). No differences existed in lean body mass among the PAR2KO-AG, AG, and YG mice (p = 0.58). With regard to insulin action, the area under the curve (AUC) for GT was lower in PAR2KO-AG compared to AG mice (p = 0.0003) and YG mice (p = 0.001); however, no differences existed for the AUC for IT or AT. Our findings indicate that age-related obesity is not dependent on PAR2 expression.

The effect of succinic acid on the metabolic profile in high-fat diet-induced obesity and insulin resistance.

Obesity, insulin resistance, and poor metabolic profile are hallmarks of a high-fat diet (HFD), highlighting the need to understand underlying mechanisms. Therefore, we sought to determine the effect of succinic acid (SA) on metabolism in high-fat diet (HFD)-induced obesity. Animals were randomly assigned to either low-fat diet (LFD) or a high-fat diet (HFD). Mice consumed their respective diets for 4.5 months and then assigned to the following groups: (LFD)+vehicle, LFD + SA (0.75 mg/ml), HFD + vehicle, or HFD + SA. Body weight (BW), food, and water intake, were tracked weekly. After 6 weeks, insulin, glucose, and pyruvate tolerance tests were completed, and spontaneous physical activity was assessed. Epididymal white adipose tissue (EWAT) mass and in vitro measurements of oxidative skeletal muscle (soleus) respiration were obtained. Expectedly, the HFD increased BW and EWAT mass, and reduced glucose and insulin tolerance. SA significantly reduced EWAT mass, more so in HFD (p < .05), but had no effect on any in vivo measurements (BW, insulin, glucose, or pyruvate tolerance, nor physical activity, all p > .05). A significant (p < .05) interaction was observed between mitochondrial respiration and treatment, where SA increased respiration, likely owed to greater mitochondrial content, as assessed by complex IV activity in both LFD and HFD. In HFD-induced obesity, coupled with insulin desensitization, we found no favorable effect of succinic acid on glucose regulation, though adiposity was attenuated. In oxidative skeletal muscle, there was a tendency for increased respiratory capacity, likely owed to greater mitochondrial content, suggestive of a succinic acid-induced mitochondrial biogenesis.

High-fat diet induced obesity and age influence the telomere shelterin complex and telomerase gene expression in mouse adipose tissue.

Obesity and aging are linked to inflammation and increased risk of chronic disease. Telomeres are the endcaps of chromosomes that are regulated by telomerase, the enzyme that elongates telomeres, as well as a protein complex known as shelterin. Telomere dysfunction is associated with inflammation, aging, and disease. However, the effect of high-fat diet (HFD) induced obesity and advancing age on the shelterin complex and telomerase in adipose tissue is unknown. The present study investigated the effects of obesity and aging on C57BL/6J mice adipose tissue mRNA expression of shelterin complex genes. Young (YG) mice (3 mo) were randomly assigned to be fed either a high-fat diet (YG + HFD; 60% kcal from fat) or a low-fat diet (YG + LFD; 10% kcal from fat). A subset of mice were aged until 16 months. Body weight and epididymal white adipose tissue (EWAT) weight increased with age or a HFD. There was a trend for increased Terf2 expression, as expression was increased in HFD + YG by ~47% and aged mice by ~80%. Pot1b expression was increased in aged mice by ~35%-60% compared to YG, independent of diet. mTert, the gene that codes for the catalytic subunit of telomerase, was significantly elevated in aged mice. Changes in telomere associated gene expression was accompanied by changes in expression of inflammatory markers Mcp1 and Tnfα. These findings suggest obesity and age impact expression of shelterin complex and telomerase related genes in adipose, perhaps altering telomere function in adipose tissue thereby increasing inflammation and risk of chronic disease.

The impact of age and sex on body composition and glucose sensitivity in C57BL/6J mice.

A paucity of data exists regarding sex differences in age-related obesity and insulin resistance, particularly in the preclinical murine model. The purpose of this study was to determine the effects of age and sex on insulin action and body composition in C57BL/6J mice. Aged (AG, 18 months old) male C57BL/6J mice, glucose tolerance was diminished compared to young (YG, 6 months old) male mice (Area Under Curve: 95,103 ± 6818 vs. 64,005 ± 2031, P = 0.002). However, there was no age-related decline in glucose or insulin tolerance in females. Body composition analysis revealed that AG males had significantly greater body mass (42.2 ± 1.9 vs. 30.0 ± 0.4 g, P < 0.0001), fat mass (18.7 ± 2.0 vs. 3.3 ± 0.4 g, P < 0.0001), body fat (43.0 ± 3.0 vs. 11.0 ± 1.5%, P < 0.0001) than YG males. In AG females, body mass (32.8 ± 1.6 vs. 26.3 ± 0.9 g, P = 0.02) was higher, but fat mass (13.3 ± 2.0 vs. 9.5 ± 1.3 g, P = 0.24) and body fat (37.8 ± 4.8 vs. 35.5 ± 3.8%, P = 0.67) were similar when compared to YG females. AG males had significantly higher body mass (42.2 ± 1.9 vs. 32.8 ± 1.6 g, P = 0.001) and fat mass (18.7 ± 2.0 vs. 13.3 ± 2.0 g, P = 0.04) compared to AG females; however, body fat (43.0 ± 3.0 vs. 37.8 ± 4.8%, P = 0.28) was similar. Six weeks of treatment with MitoQ, a mitochondrial-targeted antioxidant, did not reverse age-related obesity in male mice. Surprisingly, obesity and insulin resistance appear to be reversed in the oldest of the old male mice (28 vs. 20 months). Our findings indicate that female mice, unlike males, are protected from age-related obesity and insulin resistance.

Short-term succinic acid treatment mitigates cerebellar mitochondrial OXPHOS dysfunction, neurodegeneration and ataxia in a Purkinje-specific spinocerebellar ataxia type 1 (SCA1) mouse model.

Mitochondrial dysfunction plays a significant role in neurodegenerative disease including ataxias and other movement disorders, particularly those marked by progressive degeneration in the cerebellum. In this study, we investigate the role of mitochondrial oxidative phosphorylation (OXPHOS) deficits in cerebellar tissue of a Purkinje cell-driven spinocerebellar ataxia type 1 (SCA1) mouse. Using RNA sequencing transcriptomics, OXPHOS complex assembly analysis and oxygen consumption assays, we report that in the presence of mutant polyglutamine-expanded ataxin-1, SCA1 mice display deficits in cerebellar OXPHOS complex I (NADH-coenzyme Q oxidoreductase). Complex I genes are upregulated at the time of symptom onset and upregulation persists into late stage disease; yet, functional assembly of complex I macromolecules are diminished and oxygen respiration through complex I is reduced. Acute treatment of postsymptomatic SCA1 mice with succinic acid, a complex II (succinate dehydrogenase) electron donor to bypass complex I dysfunction, ameliorated cerebellar OXPHOS dysfunction, reduced cerebellar pathology and improved motor behavior. Thus, exploration of mitochondrial dysfunction and its role in neurodegenerative ataxias, and warrants further investigation.

Long term rebaudioside A treatment does not alter circadian activity rhythms, adiposity, or insulin action in male mice.

Obesity is a major public health problem that is highly associated with insulin resistance and type 2 diabetes, two conditions associated with circadian disruption. To date, dieting is one of the only interventions that result in substantial weight loss, but restricting caloric intake is difficult to maintain long-term. The use of artificial sweeteners, particularly in individuals that consume sugar sweetened beverages (energy drinks, soda), can reduce caloric intake and possibly facilitate weight loss. The purpose of the present study was to examine the effects of the artificial sweetener, rebaudioside A (Reb-A), on circadian rhythms, in vivo insulin action, and the susceptibility to diet-induced obesity. Six month old male C57BL/6 mice were assigned to a control or Reb-A (0.1% Reb-A supplemented drinking water) group for six months. Circadian wheel running rhythms, body weight, caloric intake, insulin action, and susceptibility to diet-induced obesity were assessed. Time of peak physical activity under a 12:12 light-dark (LD) cycle, mean activity levels, and circadian period in constant dark were not significantly different in mice that consumed Reb-A supplemented water compared to normal drinking water, indicating that circadian rhythms and biological clock function were unaltered. Although wheel running significantly reduced body weight in both Reb-A and control mice (P = 0.0001), consuming Reb-A supplemented water did not alter the changes in body weight following wheel running (P = 0.916). In vivo insulin action, as assessed by glucose, insulin, and pyruvate tolerance tests, was not different between mice that consumed Reb-A treated water compared to normal drinking water. Finally, Reb-A does not appear to change the susceptibility to diet-induced obesity as both groups of mice gained similar amounts of body weight when placed on a high fat diet. Our results indicate that consuming Reb-A supplemented water does not promote circadian disruption, insulin resistance, or obesity.

Manganese [III] Tetrakis [5,10,15,20]-Benzoic Acid Porphyrin Reduces Adiposity and Improves Insulin Action in Mice with Pre-Existing Obesity.

The superoxide dismutase mimetic manganese [III] tetrakis [5,10,15,20]-benzoic acid porphyrin (MnTBAP) is a potent antioxidant compound that has been shown to limit weight gain during short-term high fat feeding without preventing insulin resistance. However, whether MnTBAP has therapeutic potential to treat pre-existing obesity and insulin resistance remains unknown. To investigate this, mice were treated with MnTBAP or vehicle during the last five weeks of a 24-week high fat diet (HFD) regimen. MnTBAP treatment significantly decreased body weight and reduced white adipose tissue (WAT) mass in mice fed a HFD and a low fat diet (LFD). The reduction in adiposity was associated with decreased caloric intake without significantly altering energy expenditure, indicating that MnTBAP decreases adiposity in part by modulating energy balance. MnTBAP treatment also improved insulin action in HFD-fed mice, a physiologic response that was associated with increased protein kinase B (PKB) phosphorylation and expression in muscle and WAT. Since MnTBAP is a metalloporphyrin molecule, we hypothesized that its ability to promote weight loss and improve insulin sensitivity was regulated by heme oxygenase-1 (HO-1), in a similar fashion as cobalt protoporphyrins. Despite MnTBAP treatment increasing HO-1 expression, administration of the potent HO-1 inhibitor tin mesoporphyrin (SnMP) did not block the ability of MnTBAP to alter caloric intake, adiposity, or insulin action, suggesting that MnTBAP influences these metabolic processes independent of HO-1. These data demonstrate that MnTBAP can ameliorate pre-existing obesity and improve insulin action by reducing caloric intake and increasing PKB phosphorylation and expression.

Effects of a High Fat Diet and Voluntary Wheel Running Exercise on Cidea and Cidec Expression in Liver and Adipose Tissue of Mice.

Cidea and Cidec play an important role in regulating triglyceride storage in liver and adipose tissue. It is not known if the Cidea and Cidec genes respond to a high fat diet (HFD) or exercise training, two interventions that alter lipid storage. The purpose of the present study was to determine the effect of a HFD and voluntary wheel running (WR) on Cidea and Cidec mRNA and protein expression in adipose tissue and liver of mice. A HFD promoted a significant increase in Cidea and Cidec mRNA levels in adipose tissue and liver. The increase in Cidea and Cidec mRNAs in adipose tissue and liver in response to a HFD was prevented by WR. Similar to the changes in Cidea mRNA, Cidea protein levels in adipose tissue significantly increased in response to a HFD, a process that was, again, prevented by WR. However, in adipose tissue the changes in Cidec mRNA did not correspond to the changes in Cidec protein levels, as a HFD decreased Cidec protein abundance. Interestingly, in adipose tissue Cidea protein expression was significantly related to body weight (R=.725), epididymal adipose tissue (EWAT) mass (R=.475) and insulin resistance (R=.706), whereas Cidec protein expression was inversely related to body weight (R=-.787), EWAT mass (R=-.706), and insulin resistance (R=-.679). Similar to adipose tissue, Cidea protein expression in liver was significantly related to body weight (R=.660), EWAT mass (R=.468), and insulin resistance (R=.599); however, unlike adipose tissue, Cidec protein levels in liver were not related to body weight or EWAT mass and only moderately associated with insulin resistance (R=-.422, P=0.051). Overall, our findings indicate that Cidea is highly associated with adiposity and insulin resistance, whereas Cidec is related to insulin sensitivity. The present study suggests that Cide proteins might play an important functional role in the development of obesity, hepatic steatosis, as well as the pathogenesis of type 2 diabetes.

Disassociation of insulin action and Akt/FOXO signaling in skeletal muscle of older Akt-deficient mice.

The purpose of the present study was to determine the effect of Akt gene ablation on Akt/Forkhead Box O (FOXO) signaling and atrogene expression. This was accomplished by studying wild-type (WT) and isoform-specific Akt knockout (Akt1(-/-) and Akt2(-/-)) mice. The ability of insulin to promote Akt phosphorylation on Ser(473) was significantly lower in extensor digitorum longus (EDL) and soleus muscles from Akt1(-/-) and Akt2(-/-) mice compared with WT mice. Total Akt1 protein levels were significantly lower in EDL muscles of Akt2(-/-) mice compared with WT mice, a process that appears to be posttranscriptionally regulated as Akt1 mRNA levels were unchanged. The loss of Akt1 protein in EDL muscles of Akt2(-/-) mice does not appear to be due to insulin resistance because 4 mo of a high-fat diet failed to reduce Akt1 protein levels in muscles of WT mice. Although FOXO3a phosphorylation and atrogin-1 expression were unaltered in muscles of Akt1(-/-) and Akt2(-/-) mice, the expression of the atrogenes Bnip3 and gabarapl were significantly elevated in muscles of both Akt1 and Akt2 knockout mice. Finally, the expression of striated activator of Rho signaling was significantly increased in muscles of Akt2(-/-) mice compared with Akt1(-/-) and WT mice. Our results demonstrate that the ablation of Akt isoforms disassociates insulin action and Akt/FOXO signaling to atrogenes.

PKB signaling and atrogene expression in skeletal muscle of aged mice.

The purpose of this study was to determine if PKB signaling is decreased and contractile protein degradation is increased in extensor digitorum longus (EDL) and soleus (SOL) muscles from middle-aged (MA) and aged (AG) mice. We also examined the effect of age on atrogene expression in quadriceps muscle. PKB activity, as assessed by Thr(308) and Ser(473) phosphorylation, was significantly higher in EDL and SOL muscles from AG than MA mice. The age-related increase in PKB activity appears to be due to an increase in expression of the kinase, as PKB-α and PKB-ß levels were significantly higher in EDL and SOL muscles from AG than MA mice. The phosphorylation of forkhead box 3a (FOXO3a) on Thr(32), a PKB target, was significantly higher in EDL muscles from AG than MA mice. The rate of contractile protein degradation was similar in EDL and SOL muscles from AG and MA mice. Atrogin-1 and muscle-specific RING finger protein 1 (MuRF-1) mRNA levels did not change in muscles from AG compared with MA mice, indicating that ubiquitin-proteasome proteolysis does not contribute to sarcopenia. A significant decrease in Bcl-2 and 19-kDa interacting protein 3 (Bnip3) and GABA receptor-associated protein 1 (Gabarap1) mRNA was observed in muscles from AG compared with MA mice, which may contribute to age-related contractile dysfunction. In conclusion, the mechanisms responsible for sarcopenia are distinct from experimental models of atrophy and do not involve atrogin-1 and MuRF-1 or enhanced proteolysis. Finally, a decline in autophagy-related gene expression may provide a novel mechanism for impaired contractile function and muscle metabolism with advancing age.

Insulin resistance without elevated mammalian target of rapamycin complex 1 activity in muscles of mice fed a high-fat diet.

The mammalian target of rapamycin complex 1 (mTORC1) appears to mediate the development of insulin resistance in cultured cells. We studied in vivo insulin action and mTORC1 signaling in skeletal muscles of mice fed a normal chow [control (CON)] diet or a high-fat diet (HFD) for 16 wk. We assessed in vivo insulin action by measuring glucose tolerance (GT), insulin tolerance (IT), and insulin-assisted GT (IAGT). Although GT was not altered, the HFD significantly reduced IT and IAGT. Acute treatment with rapamycin, a highly specific inhibitor of mTORC1, did not improve GT, IT, or IAGT in mice fed the CON diet or the HFD. Phosphorylation of S6 kinase (S6K) on Thr(389), a surrogate measure of mTORC1 kinase activity, was assessed in skeletal muscles of mice 15 min after an intraperitoneal injection of insulin or saline. In the basal state and after insulin stimulation, phosphorylation of S6K on Thr(389) was similar in muscles of mice fed the HFD and mice fed the CON diet, indicating that mTORC1 activity is not elevated. Furthermore, phosphorylation of insulin receptor substrate 1 on Ser(636), a site phosphorylated by mTORC1, was similar in muscles of mice fed the HFD and mice fed the CON diet. Taken together, these findings indicate that in vivo insulin resistance can occur without an increase in mTORC1 activity in skeletal muscle and that inhibition of mTORC1 with rapamycin does not improve insulin action.

Rapamycin does not improve insulin sensitivity despite elevated mammalian target of rapamycin complex 1 activity in muscles of ob/ob mice.

Studies of cultured cells have indicated that the mammalian target of rapamycin complex 1 (mTORC1) mediates the development of insulin resistance. Because a role for mTORC1 in the development of skeletal muscle insulin resistance has not been established, we studied mTORC1 activity in skeletal muscles of ob/ob (OB) mice and wild-type (WT) mice. In vivo insulin action was assessed in muscles of mice 15 min following an intraperitoneal injection of insulin or an equivalent volume of saline. In the basal state, the phosphorylation of S6K on Thr(389), mTOR on Ser(2448), and PRAS40 on Thr(246) were increased significantly in muscles from OB mice compared with WT mice. The increase in basal mTORC1 signaling was associated with an increase in basal PKB phosphorylation on Thr(308) and Ser(473). In the insulin-stimulated state, no differences existed in the phosphorylation of S6K on Thr(389), but PKB phosphorylation on Thr(308) and Ser(473) was significantly reduced in muscles of OB compared with WT mice. Despite elevated mTORC1 activity in OB mice, rapamycin treatment did not improve either glucose tolerance or insulin tolerance. These results indicate that the insulin resistance of OB mice is mediated, in part, by factors other than mTORC1.

Regional differences in glucose clearance: effects of insulin and resistance training on arm and leg glucose clearance in older hypertensive individuals.

The purpose of this study was to compare insulin's ability to stimulate glucose uptake in the arm and leg in a group of older hypertensive individuals (n = 13, 66 +/- 2 yr old). We also examined the effect of a 4-mo whole body resistance-training (RT) program on arm and leg glucose clearance (GC) during a hyperinsulinemic-euglycemic clamp. During the hyperinsulinemic-euglycemic clamp, GC was assessed by simultaneous measurement of arm and leg blood flow (BF) and assessment of fractional glucose extraction (GE) in blood samples from the brachial artery, brachial vein, and popliteal vein. At baseline, a significant main effect (arm vs. leg) demonstrated greater GC and BF in the arm than in the leg (P = 0.006 for GC and P = 0.012 for BF). Insulin significantly increased GE, BF, and GC in the arm and leg (main effects: P = 0.0001 for GE, P = 0.0001 for BF, and P = 0.0001 for GC) at baseline. However, the effect of insulin was similar in the arm and leg. After RT, a significant main effect (baseline vs. RT) demonstrated greater GE and GC in the leg (P = 0.024 for GE and P = 0.053 for GE), but not in the arm (P = 0.31 for GE and P = 0.14 for GC). No significant main effect (baseline vs. RT) for BF in the arm or leg was observed after RT. In conclusion, the greater GC in the arm than in the leg at baseline is primarily due to enhanced arm BF. Furthermore, whole body RT appears to increase GC in the leg but not in the arm.

Effect of aerobic exercise training on renal responses to sodium in hypertensives.

INTRODUCTION: Aerobic exercise training has been shown to improve cardiovascular function and lower blood pressure (BP) in older adults. The exact mechanism(s) by which aerobic exercise training elicits these changes are unknown; however, it is possible that changes in renal hemodynamics may play a role. PURPOSE: The present study was undertaken to examine the effect of aerobic exercise training on renal hemodynamics in older hypertensive individuals. METHODS: Renal plasma flow (RPF) and glomerular filtration rate (GFR) were determined by plasma and urinary clearances of 131I-hippuran and 99mTc-DTPA after 8 d of low (20 mEq) and high (200 mEq) Na+ diets in 31 older (63 +/- 1 yr), hypertensive (152 +/- 2/88 +/- 1 mm Hg) individuals at baseline and following 6 months of aerobic exercise training (at 75% VO2max, three times a week, 40 min per session). RESULTS: Following 6 months of aerobic exercise training, a significant increase was seen in maximal aerobic capacity (VO2max: 18.3 +/- 0.7 vs 20.7 +/- 0.7 mL.kg.min(-1), P = 0.017) as well as a significant decrease in resting systolic (152 +/- 2 vs 145 +/- 2 mm Hg, P = 0.037) and mean arterial (109 +/- 1 vs 105 +/- 1 mm Hg, P = 0.021) BP. No significant (P < 0.05) effects were seen of aerobic exercise training on RPF (208.8 +/- 12.2 vs 197.1 +/- 13.1 mL.min(-1).1.73 m(-2)), GFR (68.9 +/- 3.6 vs 69.0 +/- 3.9 mL.min(-1).1.73 m(-2)), or filtration fraction (35.3 +/- 2.3 vs 37.1 +/- 2.4%) on the low Na+ diet or RPF (210.6 +/- 12.8 vs 212.1 +/- 11.7 mL.min(-1).1.73 m(-2)), GFR (72.9 +/- 4.1 vs 77.3 +/- 4.3 mL.min(-1).1.73 m(-2)), or filtration fraction (37.1 +/- 2.5 vs 37.7 +/- 3.0%) on the high Na+ diet. CONCLUSIONS: Our results suggest that changes in renal hemodynamics do not contribute to the reduction in resting BP in older hypertensive persons.

Effects of insulin and transgenic overexpression of UDP-glucose pyrophosphorylase on UDP-glucose and glycogen accumulation in skeletal muscle fibers.

UDP-glucose (UDP-Glc) and glycogen levels in skeletal muscle fibers of defined fiber type were measured using microanalytical methods. Infusing rats with insulin increased glycogen in both Type I and Type II fibers. Insulin was without effect on UDP-Glc in Type I fibers but decreased UDP-Glc by 35-40% in Type IIA/D and Type IIB fibers. The reduction in UDP-Glc suggested that UDP-Glc pyrophosphorylase (PPL) activity might limit glycogen synthesis in response to insulin. To explore this possibility, we generated mice overexpressing a UDP-Glc PPL transgene in skeletal muscle. The transgene increased both UDP-Glc PPL activity and levels of UDP-Glc in skeletal muscles by approximately 3-fold. However, overexpression of UDP-Glc PPL was without effect on either the levels of skeletal muscle glycogen or glucose tolerance in vivo. The transgene was also without effect on either control or insulin-stimulated rates of (14)C-glucose incorporation into glycogen in muscles incubated in vitro. The results indicate that UDP-Glc PPL activity is not limiting for glycogen synthesis.

Resistance training enhances insulin-mediated glucose disposal with minimal effect on the tumor necrosis factor-alpha system in older hypertensives.

The purpose of the present study was to determine if the improvement in insulin sensitivity after resistance training (RT) is associated with a decline in plasma levels of tumor necrosis factor-alpha (TNF-alpha), soluble TNF-alpha receptor 1 (sTNF R1), and soluble TNF receptor 2 (sTNF R2). Eleven older hypertensives (5 men/6 women, 67 +/- 2 years) participated in a 4-month RT program. Following RT there was a significant increase in upper body (P =.029) and lower body strength (P =.001), assessed by the bench press 1-repetition maximum (1RM) and leg press 1RM, respectively. The RT program produced a significant increase in lean body mass (LBM) (P =.029), a trend for a decline in percent body fat (P =.083), and no change in total body mass (P =.958). Insulin-mediated glucose disposal, assessed by the hyperinsulinemic euglycemic clamp procedure, significantly increased following RT (P =.026). Despite the increase in insulin action, plasma levels of TNF-alpha, sTNF R1, and sTNF R2 were not significantly altered by RT (TNF-alpha: P =.118, sTNF R1: P =.184, sTNF R2: P =.168). In conclusion, a 4-month RT program significantly increased insulin-mediated glucose disposal and LBM without a significant reduction in plasma levels of TNF-alpha, sTNF R1, and sTNF R2 in older hypertensive subjects.

Effects of aerobic exercise training on the protein kinase B (PKB)/mammalian target of rapamycin (mTOR) signaling pathway in aged skeletal muscle.

The protein kinase B (PKB)/mammalian target of rapamycin (mTOR) signaling pathway is thought to play a critical role in the regulation of protein synthesis and skeletal muscle mass. The purpose of the present study was to determine the effects of voluntary wheel running on the PKB/mTOR signaling pathway in muscles from aged mice (20-22 months). The total levels of mTOR were 65% higher in gastrocnemius muscles from aged mice subjected to wheel running compared to aged sedentary mice (p-0.002) PKB phosphorlation on Ser473 was 45% higher in gastrocnemius muscles from aged mice subjected to wheel running compared to aged sedentary mice (p=0.01) The total abundance of PKB was 50% higher in gastrocnemius muscles from wheel running mice compared to aged controls (p=0.005). Three months of wheel running did not alter the total amount of p70 S6K in gastrocnemius muscle. Protein synthesis, as assessed by [(14)C]phenylalanine incorporation into protein was significantly higher in soleus muscles from aged mice subjected to wheel running compared to aged sedentary mice (p-0.001) These findings indicate the aerobic exercise training may attenuate the age-related decline in protein synthesis, a process that appears to be due, in part, to increases in mTOR and PKB.

Exercise-induced changes in insulin action are associated with ACE gene polymorphisms in older adults.

We evaluated the association between insulin resistance and the angiotensin-converting enzyme (ACE) insertion (I)/deletion (D) gene polymorphism in a group of older hypertensive subjects (63 +/- 1 yr, n = 35) before and after a 6-mo aerobic exercise program (AEX). Insulin sensitivity index (S(I)), assessed by the frequently sampled intravenous glucose tolerance test, was significantly (P = 0.0001) increased following AEX. In addition, there was a significant (P = 0.001) interaction between AEX and ACE genotype. S(I) increased significantly (P < 0.05) more in those with the II (2.5 +/- 0.8 microU x 10(-4) x min(-1) x ml(-1)) ACE genotype compared with both the DD and ID (0.7 +/- 0.1 and 0.7 +/- 0.2 microU x 10(-4) x min(-1) x ml(-1), respectively) ACE genotypes. Similarly, there was a significant (P = 0.036) decrease in the acute insulin response to glucose (AIR(G)) and a significant (P = 0.05) interaction between AEX and ACE genotype. AIR(G) decreased significantly (P < 0.05) more in those with the II (-17.6 +/- 5.6 mU/ml) ACE genotype compared with both the DD and ID (-1.4 +/- 6.2 and -3.6 +/- 2.5 mU/ml) ACE genotypes. In conclusion, we demonstrated that those older hypertensives with the ACE II genotype have the greatest improvement in insulin action following AEX.

Aerobic exercise training improves insulin sensitivity independent of plasma tumor necrosis factor-alpha levels in older female hypertensives.

The purpose of the present study was to determine if the improvement in insulin sensitivity following aerobic exercise training (AEX) is associated with a decline in plasma tumor necrosis factor-alpha (TNF-alpha) levels. Fourteen older hypertensive females (age, 62 +/- 2 years) participated in a 6-month AEX program. Following AEX there was a significant increase in maximal aerobic capacity (VO(2)max) (P =.0001), and a significant decline in systolic (P =.01) and diastolic (P =.006) blood pressure. In addition, following AEX there was a significant decline in total body fat mass (P =.005), abdominal fat mass (P =.048), and percent body fat (P =.006). Insulin sensitivity, as assessed by the insulin-assisted frequently sampled intravenous glucose tolerance test (FSIVGTT), increased significantly following AEX (P =.007). Despite the increase in insulin sensitivity and the decline in body fat, plasma TNF-alpha levels were not altered by AEX (P =.223). No significant relationship existed among the changes in TNF-alpha levels and the changes insulin sensitivity or any measure of body composition following AEX. In conclusion, in this population of older hypertensive females, AEX improved insulin sensitivity and lowered blood pressure without a reduction in plasma TNF-alpha levels.

Effect of age on skeletal muscle proteolysis in extensor digitorum longus muscles of B6C3F1 mice.

The purpose of this study was to determine if age-related muscle atrophy is associated with an increased rate of protein degradation in extensor digitorum longus (EDL) muscles from young (YG; 2-4 months), middle-aged (MA; 12-17 months), and aged (AG; 22-24 months) B6C3F1 mice. EDL muscles from AG mice weighed less than EDL muscles from MA mice (p =.01). EDL muscles from MA mice weighed more than EDL muscles from YG mice (p =.02). The rate of protein degradation, as assessed by tyrosine release during in vitro incubations, was higher in EDL muscles from AG mice than it was in those from MA mice (p =.03). The rate of protein degradation was higher in EDL muscles from YG mice than it was in those from MA mice (p =.04). An inverse relationship existed between muscle mass and protein degradation (r = -.67; p =.0001). We conclude that skeletal muscle protein degradation rates decrease with maturation and increase with advancing age.