Metabolomics,Unknown,Transcriptomics,Genomics,Proteomics

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Increased SRF Transcriptional Activity is a Novel Signature of Insulin Resistance in Humans and Mice

ABSTRACT: Insulin resistance in skeletal muscle is a key phenotype associated with type 2 diabetes (T2D) and is even present in offspring of diabetic parents. However, molecular mediators of insulin resistance remain unclear. We find that the top-ranking gene set in expression analysis of muscle from humans with T2D and normoglycemic insulin resistant subjects with parental family history (FH+) of T2D is increased expression of actin cytoskeleton genes regulated by serum response factor (SRF) and its coactivator MKL1. Furthermore, the SRF activator STARS is upregulated in FH+ and T2D and inversely correlated with insulin sensitivity. These patterns are recapitulated in insulin resistant mice, and linked to alterations in two other regulators of this pathway: reduced G-actin and increased nuclear localization of MKL1. Both genetic and pharmacologic manipulation of STARS/MKL1/SRF pathway significantly alter insulin action: 1) Overexpression of MKL1 or reduction in G-actin decreased insulin-stimulated Akt phosphorylation; 2) reduced STARS expression increased insulin signalling and glucose uptake, and 3) SRF inhibition by CCG-1423 reduced nuclear MKL1, improved glucose uptake, and improved glucose tolerance in insulin resistant mice in vivo. Thus, SRF pathway alterations are a signature of insulin resistance which may also contribute to T2D pathogenesis and be a novel therapeutic target. Skeletal muscle samples were obtained from 10 subjects with type 2 diabetes, 25 subjects with a family history of type 2 diabetes (one or both parents), and 15 subjects with no family history of type 2 diabetes. In this analysis RNA was isolated for cRNA preparation and hybridized to Affymetrix Human Genome U133 Plus 2.0 microarrays.

ORGANISM(S): Homo sapiens

SUBMITTER: Mary Elizabeth Patti

PROVIDER: E-GEOD-25462 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Duchenne muscular dystrophy (DMD) is characterized by impaired cytoskeleton organization, cytosolic calcium handling oxidative stress and mitochondrial dysfunction. This results in progressive and fatal muscle damage, wasting and weakness. The Striated Muscle activator of Rho signalling (STARS) is an actin binding protein that activates the myocardin-related transcription factor-A (MRTFA)/serum response factor (SRF) transcriptional pathway; a pathway that regulates cytoskeletal structure, muscle function, growth and repair. Here we investigated the regulation of several members of the STARS signalling pathway in muscle from patients with DMD and the dystrophin-deficient mdx and dko (utrophin‐ and dystrophin‐null) mice. A reduction in protein levels of STARS, SRF and RHOA, and an increase in MRTFA were observed in quadriceps muscle of patients with DMD. STARS, SRF and MRTFA mRNA levels were also decreased in DMD muscle, while Stars mRNA levels were decreased in mdx tibialis anterior (TA) muscle and Srf and Mrtfa mRNAs were decreased in dko TA muscle. Overexpressing the human STARS (hSTARS) protein in mdx TA muscle increased maximal isometric specific force by 13%. This was not associated with changes in muscle mass, fibre cross-sectional area (CSA), fibre type, centralized nuclei or collagen deposition. Proteomics screening identified 31 upregulated and 22 downregulated proteins or individual peptides that were significantly regulated by hSTARS overexpression. Pathway enrichment analysis indicated that hSTARS overexpression regulated the keratin, NRF2 and oxidative phosphorylation (OXPHOS) pathways. These pathways are impaired in dystrophic muscle and regulate cytoskeleton organization, oxidative stress and mitochondrial energy production; processes that are vital for muscle function. We conclude that increasing the STARS protein in dystrophic muscle improves muscle force production, potentially via its regulation of multiple pathways that positively influence cytoskeletal structure, oxidative stress and energy production.

Project description:Objective: We hypothesized that type 1 diabetes (T1D) is accompanied by changes in gene expression in peripheral blood mononuclear cells (PBMCs) due to dysregulation of adaptive and innate immunity, counterregulatory responses to immune dysregulation, insulin deficiency and hyperglycemia. Research Design and Methods: Microarray analysis was performed on PBMCs from 43 patients with newly diagnosed T1D, 12 patients with newly diagnosed type 2 diabetes (T2D) and 24 healthy controls. One and four month follow-up samples were obtained from 20 of the T1D patients. Results: Microarray analysis identified 282 genes differing in expression between newlydiagnosed T1D patients and controls at a false discovery rate of 0.05. Changes in expression of interleukin-1Î² (IL1B), early growth response gene 3 (EGR3), and prostaglandin-endoperoxide; synthase 2 (PTGS2) resolved within four months of insulin therapy and were also observed in T2D suggesting that they resulted from hyperglycemia. With use of a knowledge base, 81/282 genes could be placed within a network of interrelated genes with predicted functions including apoptosis and cell proliferation. IL1B and the MYC oncogene were the most highly-connected genes in the network. IL1B was highly overexpressed in both T1D and T2D, whereas MYC was dysregulated only in T1D. Conclusion: T1D and T2D likely share a final common pathway for beta cell dysfunction that includes secretion of interleukin-1Î² and prostaglandins by immune effector cells, exacerbating existing beta cell dysfunction, and causing further hyperglycemia. The results identify several targets for disease-modifying therapy of diabetes and potential biomarkers for monitoring treatment efficacy. Experiment Overall Design: We obtained blood samples from 24 healthy volunteers, 43 newly diagnosed T1D patients and 12 newly diagnosed T2D patients. All study participants were between the ages of 2 and 18 years. We collected samples one and four months after diagnosis from the last 20 of the T1D patients. For each time point one sample did not pass quality control and was dropped from the analysis. Patients with T2D were distinguished from T1D on the basis of age, body habitus, Experiment Overall Design: presence (11/12 patients) of acanthosis nigricans, family history of type 2 diabetes (11/12 patients), and absence of autoantibodies to insulin, IA-2, and GAD65. We allowed low titers of insulin antibodies in T2D patients (< 4 U/mL), which have been previously reported. All but two Experiment Overall Design: of the T1D patients with positive anti-insulin antibodies were also positive for at least one additional autoantibody.

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Increased SRF Transcriptional Activity is a Novel Signature of Insulin Resistance in Humans and Mice

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