Deletion of skeletal muscle SOCS3 prevents insulin resistance in obesity.

Obesity is associated with chronic low-grade inflammation that contributes to defects in energy metabolism and insulin resistance. Suppressor of cytokine signaling (SOCS)-3 expression is increased in skeletal muscle of obese humans. SOCS3 inhibits leptin signaling in the hypothalamus and insulin signal transduction in adipose tissue and the liver. Skeletal muscle is an important tissue for controlling energy expenditure and whole-body insulin sensitivity; however, the physiological importance of SOCS3 in this tissue has not been examined. Therefore, we generated mice that had SOCS3 specifically deleted in skeletal muscle (SOCS MKO). The SOCS3 MKO mice had normal muscle development, body mass, adiposity, appetite, and energy expenditure compared with wild-type (WT) littermates. Despite similar degrees of obesity when fed a high-fat diet, SOCS3 MKO mice were protected against the development of hyperinsulinemia and insulin resistance because of enhanced skeletal muscle insulin receptor substrate 1 (IRS1) and Akt phosphorylation that resulted in increased skeletal muscle glucose uptake. These data indicate that skeletal muscle SOCS3 does not play a critical role in regulating muscle development or energy expenditure, but it is an important contributing factor for inhibiting insulin sensitivity in obesity. Therapies aimed at inhibiting SOCS3 in skeletal muscle may be effective in reversing obesity-related glucose intolerance and insulin resistance.

Macrophage deletion of SOCS1 increases sensitivity to LPS and palmitic acid and results in systemic inflammation and hepatic insulin resistance.

OBJECTIVE: Macrophage secretion of proinflammatory cytokines contributes to the pathogenesis of obesity-related insulin resistance. An important regulator of inflammation is the suppressor of cytokine signaling-1 (SOCS1), which inhibits the JAK-STAT and toll-like receptor-4 (TLR4) pathways. Despite the reported role of SOCS1 in inhibiting insulin signaling, it is surprising that a SOCS1 polymorphism that increases SOCS1 promoter activity is associated with enhanced insulin sensitivity despite obesity. In the current study, we investigated the physiological role of myeloid and lymphoid cell SOCS1 in regulating inflammation and insulin sensitivity. RESEARCH DESIGN AND METHODS: We used mice generated by crossing SOCS1 floxed mice with mice expressing Cre recombinase under the control of the LysM-Cre promoter (SOCS1 LysM-Cre). These mice have deletion of SOCS1 in macrophages and lymphocytes. We assessed macrophage inflammation using flow cytometry and serum cytokine levels using Bioplex assays. We then measured insulin sensitivity using glucose tolerance tests and the euglycemic-hyperinsulinemic clamp. Using bone marrow-derived macrophages, we tested the effects of SOCS1 deletion in regulating responses to the TLR4 ligands: lipopolysaccharide (LPS) and palmitic acid. RESULTS: SOCS1 LysM-Cre mice had increased macrophage expression of CD11c, enhanced sensitivity to LPS, and palmitic acid and increased serum concentrations of tumor necrosis factor-α, interleukin-6, and monocyte chemoattractant protein. Increased inflammation was associated with impaired glucose tolerance and hyperinsulinemia as a result of reduced hepatic but not skeletal muscle insulin sensitivity. CONCLUSIONS: The expression of SOCS1 in hematopoietic cells protects mice against systemic inflammation and hepatic insulin resistance potentially by inhibiting LPS and palmitate-induced TLR4 signaling in macrophages.

Dual functions of ASCIZ in the DNA base damage response and pulmonary organogenesis.

Zn²(+)-finger proteins comprise one of the largest protein superfamilies with diverse biological functions. The ATM substrate Chk2-interacting Zn²(+)-finger protein (ASCIZ; also known as ATMIN and ZNF822) was originally linked to functions in the DNA base damage response and has also been proposed to be an essential cofactor of the ATM kinase. Here we show that absence of ASCIZ leads to p53-independent late-embryonic lethality in mice. Asciz-deficient primary fibroblasts exhibit increased sensitivity to DNA base damaging agents MMS and H2O2, but Asciz deletion knock-down does not affect ATM levels and activation in mouse, chicken, or human cells. Unexpectedly, Asciz-deficient embryos also exhibit severe respiratory tract defects with complete pulmonary agenesis and severe tracheal atresia. Nkx2.1-expressing respiratory precursors are still specified in the absence of ASCIZ, but fail to segregate properly within the ventral foregut, and as a consequence lung buds never form and separation of the trachea from the oesophagus stalls early. Comparison of phenotypes suggests that ASCIZ functions between Wnt2-2b/ß-catenin and FGF10/FGF-receptor 2b signaling pathways in the mesodermal/endodermal crosstalk regulating early respiratory development. We also find that ASCIZ can activate expression of reporter genes via its SQ/TQ-cluster domain in vitro, suggesting that it may exert its developmental functions as a transcription factor. Altogether, the data indicate that, in addition to its role in the DNA base damage response, ASCIZ has separate developmental functions as an essential regulator of respiratory organogenesis.

Whole body deletion of AMP-activated protein kinase {beta}2 reduces muscle AMPK activity and exercise capacity.

AMP-activated protein kinase (AMPK) ß subunits (ß1 and ß2) provide scaffolds for binding α and γ subunits and contain a carbohydrate-binding module important for regulating enzyme activity. We generated C57Bl/6 mice with germline deletion of AMPK ß2 (ß2 KO) and examined AMPK expression and activity, exercise capacity, metabolic control during muscle contractions, aminoimidazole carboxamide ribonucleotide (AICAR) sensitivity, and susceptibility to obesity-induced insulin resistance. We find that ß2 KO mice are viable and breed normally. ß2 KO mice had a reduction in skeletal muscle AMPK α1 and α2 expression despite up-regulation of the ß1 isoform. Heart AMPK α2 expression was also reduced but this did not affect resting AMPK α1 or α2 activities. AMPK α1 and α2 activities were not changed in liver, fat, or hypothalamus. AICAR-stimulated glucose uptake but not fatty acid oxidation was impaired in ß2 KO mice. During treadmill running ß2 KO mice had reduced maximal and endurance exercise capacity, which was associated with lower muscle and heart AMPK activity and reduced levels of muscle and liver glycogen. Reductions in exercise capacity of ß2 KO mice were not due to lower muscle mitochondrial content or defects in contraction-stimulated glucose uptake or fatty acid oxidation. When challenged with a high-fat diet ß2 KO mice gained more weight and were more susceptible to the development of hyperinsulinemia and glucose intolerance. In summary these data show that deletion of AMPK ß2 reduces AMPK activity in skeletal muscle resulting in impaired exercise capacity and the worsening of diet-induced obesity and glucose intolerance.

Protective effects of exercise and phosphoinositide 3-kinase(p110alpha) signaling in dilated and hypertrophic cardiomyopathy.

Physical activity protects against cardiovascular disease, and physiological cardiac hypertrophy associated with regular exercise is usually beneficial, in marked contrast to pathological hypertrophy associated with disease. The p110alpha isoform of phosphoinositide 3-kinase (PI3K) plays a critical role in the induction of exercise-induced hypertrophy. Whether it or other genes activated in the athlete's heart might have an impact on cardiac function and survival in a setting of heart failure is unknown. To examine whether progressive exercise training and PI3K(p110alpha) activity affect survival and/or cardiac function in two models of heart disease, we subjected a transgenic mouse model of dilated cardiomyopathy (DCM) to swim training, genetically crossed cardiac-specific transgenic mice with increased or decreased PI3K(p110alpha) activity to the DCM model, and subjected PI3K(p110alpha) transgenics to acute pressure overload (ascending aortic constriction). Life-span, cardiac function, and molecular markers of pathological hypertrophy were examined. Exercise training and increased cardiac PI3K(p110alpha) activity prolonged survival in the DCM model by 15-20%. In contrast, reduced PI3K(p110alpha) activity drastically shortened lifespan by approximately 50%. Increased PI3K(p110alpha) activity had a favorable effect on cardiac function and fibrosis in the pressure-overload model and attenuated pathological growth. PI3K(p110alpha) signaling negatively regulated G protein-coupled receptor stimulated extracellular responsive kinase and Akt (via PI3K, p110gamma) activation in isolated cardiomyocytes. These findings suggest that exercise and enhanced PI3K(p110alpha) activity delay or prevent progression of heart disease, and that supraphysiologic activity can be beneficial. Identification of genes important for hypertrophy in the athlete's heart could offer new strategies for treating heart failure.

Aberrant methylation of the HRPT2 gene in parathyroid carcinoma.

OBJECTIVES: The incidence of parathyroid carcinoma in hyperparathyroidism-jaw tumor syndrome (HPT-JT) is reported to be as high as 15%. We used a methylation-specific polymerase chain reaction (MS-PCR) technique to investigate whether hypermethylation is one mechanism of HRPT2 gene inactivation in parathyroid tumors. METHODS: DNA was extracted from samples of parathyroid tumors embedded in paraffin. MS-PCR was performed on 11 parathyroid carcinomas, 37 sporadic parathyroid adenomas from control subjects, and 6 parathyroid adenomas from 3 patients with HPT-JT. Methylated and unmethylated PCR products from 2 tumors (Nos. 2 and 6) were cloned. Clones containing inserts were sequenced. RESULTS: Two of 11 (18%) parathyroid carcinomas showed amplification patterns consistent with methylation, compared to 0 of 37 sporadic parathyroid adenomas, and 1 of 6 (17%) parathyroid tumor samples from 3 HPT-JT patients. These results were confirmed by sequencing multiple clones from each of these samples. CONCLUSIONS: There is increasing evidence that loss of HRPT2 gene expression is strongly associated with parathyroid carcinomas. Our data indicate that methylation of the HRPT2 promoter may be another mechanism by which HRPT2 gene inactivation gives rise to parathyroid carcinomas.

CD8 T cells expressing killer Ig-like receptors and NKG2A are present in cord blood and express a more naïve phenotype than their counterparts in adult blood.

We report that natural killer receptors (NKR) for major histocompatibility complex (MHC) class I molecules (MHC-NKR), the inhibitory killer immunoglobulin-like receptors (KIR), and the CD94/NKG2A receptor are present on a small proportion of CD8 T cells in cord blood. On average, 1.67% of CD8 T cells in cord blood express KIR, and 0.74% expresses NKG2A, approximately fivefold less than in adult blood. CD8 T cells expressing MHC-NKR were present at similar levels in cord blood from preterm and term infants, and it is important that their presence was independent of placental pathology or infection. Cord blood CD8 T cells expressing MHC-NKR were relatively homogeneous and entirely CD27+, mostly CC chemokine receptor 7- and granzyme B-, with a majority being CD45RA+ and with no evidence for a skewed distribution of T cell receptor-Vbeta when tested in KIR+ cells. This contrasted with adult blood, which was more heterogeneous, and where a majority of CD8 T cells expressing MHC-NKR was CD27- and granzyme B+. Functional studies revealed that cord blood KIR+ CD8 T cells were as capable as KIR- CD8 T cells in their ability to proliferate in response to CD3 ligation, yet it is interesting that they were more capable than KIR- CD8 T cells in their ability to secrete interferon-gamma. These data suggest that cord blood CD8 T cells expressing MHC-NKR are a unique subset of cells, distinct from those in adult blood, and may represent a less-differentiated population.