[Show abstract][Hide abstract] ABSTRACT: The rising prevalence of gestational diabetes mellitus (GDM) affects up to 18% of pregnant women with immediate and long-term metabolic consequences for both mother and infant. Abnormal glucose uptake and lipid oxidation are hallmark features of GDM prompting us to use an exploratory proteomics approach to investigate the cellular mechanisms underlying differences in skeletal muscle metabolism between obese pregnant women with GDM (OGDM) and obese pregnant women with normal glucose tolerance (ONGT). Functional validation was performed in a second cohort of obese OGDM and ONGT pregnant women. Quantitative proteomic analysis in rectus abdominus skeletal muscle tissue collected at delivery revealed reduced protein content of mitochondrial complex I (C-I) subunits (NDUFS3, NDUFV2) and altered content of proteins involved in calcium homeostasis/signaling (calcineurin A, α1-syntrophin, annexin A4) in OGDM (n = 6) vs. ONGT (n = 6). Follow-up analyses showed reduced enzymatic activity of mitochondrial complexes C-I, C-III, and C-IV (-60-75%) in the OGDM (n = 8) compared with ONGT (n = 10) subjects, though no differences were observed for mitochondrial complex protein content. Upstream regulators of mitochondrial biogenesis and oxidative phosphorylation were not different between groups. However, AMPK phosphorylation was dramatically reduced by 75% in the OGDM women. These data suggest that GDM is associated with reduced skeletal muscle oxidative phosphorylation and disordered calcium homeostasis. These relationships deserve further attention as they may represent novel risk factors for development of GDM and may have implications on the effectiveness of physical activity interventions on both treatment strategies for GDM and for prevention of type 2 diabetes postpartum.
PLoS ONE 09/2014; 9(9):e106872. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Proteomics techniques have revealed that lysine acetylation is abundant in mitochondrial proteins. This study was undertaken 1) to determine the relationship between mitochondrial protein acetylation and insulin sensitivity in human skeletal muscle, identifying key acetylated proteins, and 2) to use molecular modeling techniques to understand the functional consequences of acetylation of adenine nucleotide translocase 1 (ANT1), which we found to be abundantly acetylated. Eight each lean and obese nondiabetic subjects had euglycemic clamps and muscle biopsies for isolation of mitochondrial proteins and proteomics analysis. A number of acetylated mitochondrial proteins were identified in muscle biopsies. Overall, acetylation of mitochondrial proteins was correlated with insulin action (r = 0.60, P < 0.05). Of the acetylated proteins, ANT1, which catalyzes ADP/ATP exchange across the inner mitochondrial membrane, was acetylated at lysines 10, 23, and 92. Acetylation of lysine 23 decreased following exercise, depending on insulin sensitivity. Molecular dynamics modeling and ensemble docking simulations predicted the ADP binding site of ANT1 to be a pocket of positively charged residues, including lysine 23. Calculated ADP/ANT1 binding affinities were physiologically relevant and predicted substantial reductions in affinity upon lysine 23 acetylation. Insertion of these derived binding affinities as parameters into a complete mathematical description of ANT1 kinetics predicted marked reductions in adenine nucleotide flux resulting from lysine 23 acetylation. Therefore, acetylation of ANT1 could have dramatic physiological effects on ADP/ATP exchange. Dysregulation of acetylation of mitochondrial proteins such as ANT1 therefore could be related to changes in mitochondrial function that are associated with insulin resistance.
[Show abstract][Hide abstract] ABSTRACT: Adipose triglyceride lipase (ATGL), the rate-limiting enzyme for triacylglycerol (TG) hydrolysis, is long known to be a phosphoprotein. However, the potential phosphorylation events that are involved in the regulation of ATGL function remain incompletely defined. Here, using a combinatorial proteomics approach, we obtained evidence that at least eight different sites of ATGL can be phosphorylated in adipocytes. Among them, Thr-372 resides within the hydrophobic region known to mediate lipid droplet (LD) targeting. While it had no impact on the TG hydrolase activity, substitution of phosphorylation-mimic Asp for Thr-372 eliminated LD localization and LD-degrading capacity of ATGL expressed in HeLa cells. In contrast, mutation of Thr-372 to Ala gave a protein that bound LDs and functioned the same as the wild type protein. In non-stimulated adipocytes, the Asp mutation led to decreased LD association and basal lipolytic activity of ATGL while the Ala mutation produced opposite effects. Moreover, the LD translocation of ATGL upon β-adrenergic stimulation was also compromised by the Asp mutation. In accordance, the Ala mutation promoted and the Asp mutation attenuated the capacity of ATGL to mediate lipolysis in adipocytes under both basal and stimulated conditions. Collectively, these studies identified Thr-372 as a novel phosphorylation site that may play a critical role in determining subcellular distribution as well as lipolytic action of ATGL.
AJP Endocrinology and Metabolism 05/2014; · 4.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Modern techniques have produced many sequence annotation databases and protein structure portals, but these web resources are rarely integrated in ways that permit straightforward exploration of protein functional residues and their co-localization.
We have created the AMASS Database, which maps 1D sequence annotation databases to 3D protein structures with an intuitive visualization interface. Our platform also provides an analysis service that screens mass spectrometry sequence data for post-translational modifications that reside in functionally-relevant locations within protein structures. The system is built upon the premise that functional residues such as active sites, cancer mutations, and post-translational modifications within proteins may co-localize and share common functions.
AMASS DB is implemented with Biopython and Apache as a freely-available web server at amass-db.org.
[Show abstract][Hide abstract] ABSTRACT: Objective: Lifestyle intervention can improve insulin sensitivity in obese youth yet few studies have examined the molecular signatures associated with these improvements. Therefore, the purpose of this study was to explore gene expression changes in whole-blood that are associated with intervention-induced improvements in insulin sensitivity. Design and Methods: Fifteen (7M/8F) overweight/obese (BMI percentile=96.3±1.1) Latino adolescents (15.0±0.9 years) completed a 12-week lifestyle intervention that included weekly nutrition education and 180 minutes of moderate-vigorous exercise per week. Insulin sensitivity was estimated by an oral glucose tolerance test and the Matsuda Index. Global microarray analysis profiling from whole blood was performed to examine changes in gene expression and to explore biological pathways that were significantly changed in response to the intervention. Results: A total of 1,459 probes corresponding to mRNA transcripts (717 up, 742 down) were differentially expressed with a fold change ≥1.2. These genes were mapped within 8 significant pathways identified, including insulin signaling, type 1 diabetes, and glycerophospholipid metabolism. Participants that increased insulin sensitivity exhibited five times the number of significant genes altered compared to non-responders (1,144 vs. 230). Conclusions: These findings suggest that molecular signatures from whole blood are associated with lifestyle-induced health improvements among high-risk Latino youth.
[Show abstract][Hide abstract] ABSTRACT: The increased occurrence of type 2 diabetes and its clinical correlates is a global public health issue, and there are continued efforts to find its genetic determinant across ethnically diverse populations. The aims of this study were to determine the heritability of diabetes and metabolic syndrome phenotypes in the Arizona Insulin Resistance (AIR) registry and to perform an association analysis of common single nucleotide polymorphisms (SNPs) identified by GWAS with these traits. All study participants were Mexican Americans from the AIR registry.
Human Heredity 01/2014; 78(1):47-58. · 1.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Although insulin resistance in skeletal muscle is well-characterized, the role of circulating whole blood in the metabolic syndrome phenotype is not well understood. We set out to test the hypothesis that genes involved in inflammation, insulin signaling and mitochondrial function would be altered in expression in the whole blood of individuals with metabolic syndrome. We further wanted to examine whether similar relationships that we have found previously in skeletal muscle exist in peripheral whole blood cells. All subjects (n=184) were Latino descent from the Arizona Insulin Resistance registry. Subjects were classified based on the metabolic syndrome phenotype according to the National Cholesterol Education Program's Adult Treatment Panel III. Of the 184 Latino subjects in the study, 74 were classified with the metabolic syndrome and 110 were without. Whole blood gene expression profiling was performed using the Agilent 4x44K Whole Human Genome Microarray. Whole blood microarray analysis identified 1,432 probes that were altered in expression ≥1.2 fold and P<0.05 after Benjamini-Hochberg in the metabolic syndrome subjects. KEGG pathway analysis revealed significant enrichment for pathways including ribosome, oxidative phosphorylation and MAPK signaling (all Benjamini-Hochberg P<0.05). Whole blood mRNA expression changes observed in the microarray data were confirmed by quantitative RT-PCR. Transcription factor binding motif enrichment analysis revealed E2F1, ELK1, NF-kappaB, STAT1 and STAT3 significantly enriched after Bonferroni correction (all P<0.05). The results of the present study demonstrate that whole blood is a useful tissue for studying the metabolic syndrome and its underlying insulin resistance although the relationship between blood and skeletal muscle differs.
PLoS ONE 12/2013; 8(12):e84002. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Latinos are disproportionately impacted by obesity and type 2 diabetes but remain underrepresented in biomedical research. Therefore, the purpose of this project was to develop a research registry and biorepository to examine cardiometabolic disease risk in the Latino community of Phoenix, Arizona. The overarching goal was to establish the research infrastructure that would encourage transdisciplinary research regarding the biocultural mechanisms of obesity-related health disparities and facilitate access to this research for the Latino community.
Prior to recruitment, key stakeholders from the local Latino community were engaged to develop a broad rapport within the community and seek advice regarding recruitment, enrollment, and follow-up. Self-identified community-dwelling Latinos underwent a comprehensive cardiometabolic health assessment that included anthropometrics, a fasting laboratory panel, and a 2-hour oral glucose tolerance test with measures of insulin and glucose to estimate insulin action and secretion. Separate consent was requested for future contact and banking of serum, DNA, and RNA. Research collaborations were sought out based on the cultural and metabolic profile of participants, faculty research agendas, and the potential for generating hypotheses.
A total of 667 participants (20.4% children, and 79.6% adults) were enrolled with 97% consenting to the registry and 94% to banking of samples. The prevalence of overweight/obesity was 50% in children and 81% in adults. Nearly 20% of children and more than 45% of the adults exhibited some degree of hyperglycemia. To date, more than 15 research projects have been supported through this infrastructure and have included projects on the molecular biology of insulin resistance to the sociocultural determinants of health behaviors and outcomes.
The high prevalence of obesity and cardiometabolic disease risk factors coupled with the overwhelming majority of participants consenting to be re-contacted, highlights the importance of supporting research infrastructure to generate hypotheses about obesity-related health in Latinos. Future studies that stem from the initial project will likely advance the limited understanding regarding the biocultural determinants of health disparities in the Latino community.
Clinical and Translational Science 10/2013; · 2.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: PURPOSE: Exercise training alters protein abundance in muscle of healthy individuals, but the effect of exercise on these proteins in patients with type 2 diabetes (T2D) is unknown. The aim of this study was to determine how exercise training alters the skeletal muscle proteome in patients with T2D. METHODS: Biopsies of the vastus lateralis were obtained before and after 4 weeks of exercise training in six patients with T2D (54 ± 4 yrs, BMI 29± 2) and six age- and BMI- matched control subjects (48 ± 2, BMI 28 ± 3) studied at baseline. Proteins were identified and quantified using normalized spectral abundance factors (NSAF) by multidimensional high-resolution mass spectrometry. RESULTS: Of 1,329 proteins assigned at baseline, 438 were present in at least half of all muscle samples; of these, 15 proteins differed significantly between patients with T2D and control subjects (p<0.05). In the diabetic patients, exercise training altered the abundance of 17 proteins (p<0.05). Key training adaptations included an increase in proteins of the malate-aspartate shuttle and citric acid cycle, reduced abundance of glycolytic proteins, and altered abundance of cytoskeleton proteins. CONCLUSIONS: The data from this study support the ability of exercise training to alter the abundance of proteins that regulate metabolism and cytoskeletal structure in patients with T2D. These findings open new avenues for future research.
Medicine and science in sports and exercise 12/2012; · 4.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: : New-onset diabetes after transplantation independently increases the risk of cardiovascular disease, infections, and graft loss and decreases patient survival. The required balance between insulin sensitivity/resistance and insulin secretion is necessary to maintain normal glucose metabolism. Calcineurin inhibitors are standard immunosuppression drugs used after transplantation and have been implicated in the development of new-onset diabetes after transplantation partially by pancreatic β-cell apoptosis and resultant decrease in insulin secretion. The ability of muscle to take up glucose is critical to blood glucose homeostasis. Skeletal muscle is quantitatively the most important tissue in the body for insulin-stimulated glucose disposal and is composed of diverse myofibers that vary in their properties between healthy and insulin-resistant muscle. Various signaling pathways are responsible for remodeling of skeletal muscle, and among these is the calcineurin/nuclear factor of activated T-cell pathway. The mechanism of action of the calcineurin inhibitors is to bind in a complex with a binding protein to calcineurin and inhibit its dephosphorylation and activation of nuclear factor of activated T cells. In this review, we will provide a detailed discussion of the hypothesis that inhibition of calcineurin in tissues involved in insulin sensitivity/resistance could be at least partially responsible for the diabetogenicity seen with the use of calcineurin inhibitors.
[Show abstract][Hide abstract] ABSTRACT: Insulin stimulates the mobilization of glucose transporter 4 (GLUT4) storage vesicles to the plasma membrane, resulting in an influx of glucose into target tissues such as muscle and fat. We present evidence that CLIP-associating protein 2 (CLASP2), a protein previously unassociated with insulin action, is responsive to insulin stimulation. Using mass spectrometry-based protein identification combined with phospho-antibody immunoprecipitation in L6 myotubes, we detected a 4.8-fold increase of CLASP2 in the anti-phosphoserine immunoprecipitates upon insulin stimulation. Western blotting of CLASP2 immunoprecipitates with the phospho-antibody confirmed the finding that CLASP2 undergoes insulin-stimulated phosphorylation, and a number of novel phosphorylation sites were identified. Confocal imaging of L6 myotubes revealed that CLASP2 colocalizes with GLUT4 at the plasma membrane within areas of insulin-mediated cortical actin remodeling. CLASP2 is responsible for directing the distal end of microtubules to the cell cortex, and it has been shown that GLUT4 travels along microtubule tracks. In support of the concept that CLASP2 plays a role in the delivery of GLUT4 to the cell periphery, CLASP2 knockdown by siRNA in L6 myotubes interfered with insulin-stimulated GLUT4 localization to the plasma membrane. Furthermore, siRNA mediated knockdown of CLASP2 in 3T3-L1 adipocytes inhibited insulin-stimulated glucose transport. We therefore propose a new model for CLASP2 in insulin action, where CLASP2 directs the delivery of GLUT4 to cell cortex landing zones important for insulin action.
Journal of Biological Chemistry 09/2012; · 4.60 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: OBJECTIVE: Older adults have exaggerated postprandial lipemia, which increases their risk for cardiovascular disease. We sought to determine the effects of increased plasma l-arginine (L-ARG) availability on the oxidation of ingested fat (enriched with [1,1,1-(13)C]-triolein) and plasma triacylglycerol (TG) concentrations during the postprandial period in older subjects. METHODS: On one day, eight healthy subjects (67.8 ± 1.3 y old) received an intravenous infusion of L-ARG during the first hour of the postprandial period (L-ARG trial), while on a separate day, and in a randomized order, they received saline (control trial). RESULTS: The 8-h area under the plasma concentration-time curve describing the postprandial plasma TG concentrations was considerably lower in the L-ARG trial than in the control trial (-4 ± 21 versus 104 ± 21 mg ∙ dL(-1) ∙ h(-1), P < 0.01). The rate of the postprandial oxidation of the ingested lipid was not different between the trials, but the average contribution of the ingested oleate to the oleate of the TG of the plasma small TG-rich lipoproteins (Svedberg flotation index 20-400) was lower in the L-ARG trial (11 ± 1 versus 18 ± 2%, P < 0.01). L-ARG infusion also decreased the 8-h area under the plasma concentration-time curve of the plasma free fatty acid concentrations derived from the ingested fat compared with the saline infusion (0.77 ± 0.09 versus 1.11 ± 0.08; mmol ∙ L(-1) ∙ h(-1), P < 0.01). CONCLUSION: Increasing the plasma L-ARG availability during the postprandial period decreases the postprandial lipemia in older adults, in association with a decrease in the postprandial contribution of ingested lipids into TGs of the plasma small TG-rich lipoproteins.
[Show abstract][Hide abstract] ABSTRACT: Adverse effects on health mediated by increased plasma FFA concentrations are well established and older individuals are particularly susceptible to these effects. We sought to determine the effects of the amount of dietary fat on increasing the plasma FFA concentrations as a result of "spillover" of dietary fat into the plasma FFA pool during the postprandial period in older men. Healthy, older participants (63-71 y old) were studied in a randomized, crossover design following ingestions of low (LF) and moderate (MF) amounts of [1,1,1-(13)C]-triolein-labeled fat, corresponding to 0.4 and 0.7 g of fat/kg body weight, respectively. Spillover of dietary fatty acids into plasma during the 8-h postprandial period (AUC; mmol L(-1) h) after MF ingestion was 1.2 times greater than that after LF ingestion (2.8 ± 0.4 vs. 1.2 ± 0.1; P < 0.05). The spillover of dietary fatty acids following the MF, but not the LF, ingestion was correlated with the percent body fat (r(s) = -0.89) and percent body fat-free mass (r(s) = 0.94) of the men (P < 0.05). After adjusting to the amount of ingested fat, the spillover of dietary fatty acids in the MF trial was disproportionally higher than that in the LF trial (P < 0.05), but the corresponding postprandial plasma TG responses did not differ between trials. In conclusion, spillover of dietary lipid into plasma is disproportionally increased at higher doses of dietary fat and this response is inversely related to adiposity in healthy men of advanced age.
Journal of Nutrition 09/2012; 142(10):1806-11. · 4.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In adults, the shape of the glucose response during an oral glucose tolerance test (OGTT) prospectively and independently predicts type 2 diabetes. However, no reports have described the utility of this indicator in younger populations. The purpose of this study was to compare type 2 diabetes risk factors in Latino adolescents characterized by either a monophasic or biphasic glucose response during an OGTT.
A total of 156 nondiabetic Latino adolescents completed a 2-h OGTT. Monophasic and biphasic groups were compared for the following type 2 diabetes risk factors: fasting and 2-h glucose, HbA(1c), glucose area under the curve (AUC), insulin sensitivity (Matsuda index), insulin secretion (insulinogenic index), and β-cell function as measured by the disposition index (insulin sensitivity × insulin secretion).
Of the participants, 107 youth were categorized as monophasic and 49 were biphasic. Compared with the monophasic group, participants with a biphasic response exhibited lower HbA(1c) (5.4 ± 0.3 vs. 5.6 ± 0.3%, P < 0.01) and lower glucose AUC (14,205 ± 2,382 vs. 16,230 ± 2,537 mg ⋅ dL(-1) ⋅ h(-1), P < 0.001) with higher insulin sensitivity (5.4 ± 3.2 vs. 4.6 ± 3.4, P ≤ 0.05), higher insulin secretion (2.1 ± 1.3 vs. 1.8 ± 1.3, P = 0.05), and better β-cell function (10.3 ± 7.8 vs. 6.0 ± 3.6, P < 0.001). Differences persisted after adjusting for age, sex, and BMI.
These data suggest that the glycemic response to an OGTT may differentiate risk for type 2 diabetes in youth. This response may be an early marker of type 2 diabetes risk among high-risk youth.
Diabetes care 06/2012; 35(9):1925-30. · 7.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Protein phosphatase 1 (PP1) is one of the major phosphatases responsible for protein dephosphorylation in eukaryotes. So far, only few specific phosphorylation sites of PP1 regulatory subunit 12A (PPP1R12A) have been shown to regulate the PP1 activity. The effect of insulin on PPP1R12A phosphorylation is largely unknown. Utilizing a mass spectrometry based phosphorylation identification and quantification approach, we identified 21 PPP1R12A phosphorylation sites (7 novel sites, including Ser20, Thr22, Thr453, Ser478, Thr671, Ser678, and Ser680) and quantified 16 of them under basal and insulin stimulated conditions in hamster ovary cells overexpressing the insulin receptor (CHO/IR), an insulin sensitive cell model. Insulin stimulated the phosphorylation of PPP1R12A significantly at Ser477, Ser478, Ser507, Ser668, and Ser695, while simultaneously suppressing the phosphorylation of PPP1R12A at Ser509 (more than 2-fold increase or decrease compared to basal). Our data demonstrate that PPP1R12A undergoes insulin stimulated/suppressed phosphorylation, suggesting that PPP1R12A phosphorylation may play a role in insulin signal transduction. The novel PPP1R12A phosphorylation sites as well as the new insulin-responsive phosphorylation sites of PPP1R12A in CHO/IR cells provide targets for investigation of the regulation of PPP1R12A and the PPP1R12A-PP1cδ complex in insulin action and other signaling pathways in other cell models, animal models, and humans.
Journal of proteomics 04/2012; 75(11):3342-50. · 5.07 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We sought to evaluate the reproducibility of a liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based approach to measure the stable-isotope enrichment of in vivo-labeled muscle ATP synthase β subunit (β-F1-ATPase), a protein most directly involved in ATP production, and whose abundance is reduced under a variety of circumstances. Muscle was obtained from a rat infused with stable-isotope-labeled leucine. The muscle was homogenized, β-F1-ATPase immunoprecipitated, and the protein was resolved using 1D-SDS PAGE. Following trypsin digestion of the isolated protein, the resultant peptide mixtures were subjected to analysis by HPLC-ESI-MS/MS, which resulted in the detection of multiple β-F1-ATPase peptides. There were three β-F1-ATPase unique peptides with a leucine residue in the amino acid sequence, and which were detected with high intensity relative to other peptides and assigned with >95% probability to β-F1-ATPase. These peptides were specifically targeted for fragmentation to access their stable-isotope enrichment based on MS/MS peak areas calculated from extracted ion chromatographs for selected labeled and unlabeled fragment ions. Results showed best linearity (R(2) = 0.99) in the detection of MS/MS peak areas for both labeled and unlabeled fragment ions, over a wide range of amounts of injected protein, specifically for the β-F1-ATPase(134-143) peptide. Measured stable-isotope enrichment was highly reproducible for the β-F1-ATPase(134-143) peptide (CV = 2.9%). Further, using mixtures of synthetic labeled and unlabeled peptides we determined that there is an excellent linear relationship (R(2) = 0.99) between measured and predicted enrichment for percent enrichments ranging between 0.009% and 8.185% for the β-F1-ATPase(134-143) peptide. The described approach provides a reliable approach to measure the stable-isotope enrichment of in-vivo-labeled muscle β-F1-ATPase based on the determination of the enrichment of the β-F1-ATPase(134-143) peptide.
PLoS ONE 10/2011; 6(10):e26171. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Insulin resistance in skeletal muscle is a prominent feature of obesity and type 2 diabetes. The association between mitochondrial changes and insulin resistance is well known. More recently, there is growing evidence of a relationship between inflammation, extracellular remodeling, and insulin resistance. The intent of this review is to propose a potentially novel mechanism for the development of insulin resistance, focusing on the underappreciated connections among inflammation, extracellular remodeling, cytoskeletal interactions, mitochondrial function, and insulin resistance in human skeletal muscle. Several sources of inflammation, including expansion of adipose tissue resulting in increased lipolysis and alterations in pro- and anti-inflammatory cytokines, contribute to the insulin resistance observed in obesity and type 2 diabetes. In the experimental model of lipid oversupply, an inflammatory response in skeletal muscle leads to altered expression extracellular matrix-related genes as well as nuclear encoded mitochondrial genes. A similar pattern also is observed in "naturally" occurring insulin resistance in muscle of obese nondiabetic individuals and patients with type 2 diabetes mellitus. More recently, alterations in proteins (including α-actinin-2, desmin, proteasomes, and chaperones) involved in muscle structure and function have been observed in insulin-resistant muscle. Some of these cytoskeletal proteins are mechanosignal transducers that allow muscle fibers to sense contractile activity and respond appropriately. The ensuing alterations in expression of genes coding for mitochondrial proteins and cytoskeletal proteins may contribute to the mitochondrial changes observed in insulin-resistant muscle. These changes in turn may lead to a reduction in fat oxidation and an increase in intramyocellular lipid, which contributes to the defects in insulin signaling in insulin resistance.
AJP Endocrinology and Metabolism 08/2011; 301(5):E749-55. · 4.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: IRS-1 serine phosphorylation is often elevated in insulin resistance models, but confirmation in vivo in humans is lacking. We therefore analysed IRS-1 phosphorylation in human muscle in vivo.
We used HPLC-electrospray ionisation (ESI)-MS/MS to quantify IRS-1 phosphorylation basally and after insulin infusion in vastus lateralis muscle from lean healthy, obese non-diabetic and type 2 diabetic volunteers.
Basal Ser323 phosphorylation was increased in type 2 diabetic patients (2.1 ± 0.43, p ≤ 0.05, fold change vs lean controls). Thr495 phosphorylation was decreased in type 2 diabetic patients (p ≤ 0.05). Insulin increased IRS-1 phosphorylation at Ser527 (1.4 ± 0.17, p ≤ 0.01, fold change, 60 min after insulin infusion vs basal) and Ser531 (1.3 ± 0.16, p ≤ 0.01, fold change, 60 min after insulin infusion vs basal) in the lean controls and suppressed phosphorylation at Ser348 (0.56 ± 0.11, p ≤ 0.01, fold change, 240 min after insulin infusion vs basal), Thr446 (0.64 ± 0.16, p ≤ 0.05, fold change, 60 min after insulin infusion vs basal), Ser1100 (0.77 ± 0.22, p ≤ 0.05, fold change, 240 min after insulin infusion vs basal) and Ser1142 (1.3 ± 0.2, p ≤ 0.05, fold change, 60 min after insulin infusion vs basal).
We conclude that, unlike some aspects of insulin signalling, the ability of insulin to increase or suppress certain IRS-1 phosphorylation sites is intact in insulin resistance. However, some IRS-1 phosphorylation sites do not respond to insulin, whereas other Ser/Thr phosphorylation sites are either increased or decreased in insulin resistance.