The lack of high-throughput methods to analyze the adipose tissue protein composition limits our understanding of the protein networks responsible for age and diet related metabolic response. We have developed an approach using multiple-dimension liquid chromatography tandem mass spectrometry and extended multiplexing (24 biological samples) with tandem mass tags (TMT) labeling to analyze proteomes of epididymal adipose tissues isolated from mice fed either low or high fat diet for a short or a long-term, and from mice that aged on low high fat diets. The peripheral metabolic health (as measured by body weight, adiposity, plasma fasting glucose, insulin, triglycerides, total cholesterol levels, and glucose and insulin tolerance tests) deteriorated with diet and advancing age, with long-term high fat diet exposure being the worst. In response to short-term high fat diet, 43 proteins representing lipid metabolism ( AACS, ACOX1, ACLY) and red-ox pathways ( CPD2, CYP2E, SOD3) were significantly altered (FDR < 10%). Long-term high fat diet significantly altered 55 proteins associated with immune response ( IGTB2, IFIT3, LGALS1) and rennin angiotensin system ( ENPEP, CMA1, CPA3, ANPEP). Age-related changes on low fat diet significantly altered only 18 proteins representing mainly urea cycle ( OTC, ARG1, CPS1), and amino acid biosynthesis ( GMT, AKR1C6). Surprisingly, high fat diet driven age-related changes culminated with alterations in 155 proteins involving primarily the urea cycle ( ARG1, CPS1), immune response/complement activation ( C3, C4b, C8, C9, CFB, CFH, FGA), extracellular remodeling ( EFEMP1, FBN1, FBN2, LTBP4, FERMT2, ECM1, EMILIN2, ITIH3) and apoptosis ( YAP1, HIP1, NDRG1, PRKCD, MUL1) pathways. Using our adipose tissue tailored approach we have identified both age-related and high fat diet specific proteomic signatures highlighting a pronounced involvement of arginine metabolism in response to advancing age, and branched chain amino acid metabolism in early response to high fat feeding. Data are available via ProteomeXchange with identifier PXD005953.

Recent studies into the physiology of the incretins glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) have added stimulation of ␤-cell growth, differentiation, and cell survival to well-documented, potent insulinotropic effects. Unfortunately, the therapeutic potential of these hormones is limited by their rapid enzymatic inactivation in vivo by dipeptidyl peptidase IV (DP IV). Inhibition of DP IV, so as to enhance circulating incretin levels, has proved effective in the treatment of type 2 diabetes both in humans and in animal models, stimulating improvements in glucose tolerance, insulin sensitivity, and ␤-cell function. We hypothesized that enhancement of the cytoprotective and ␤-cell regenerative effects of GIP and GLP-1 might extend the therapeutic potential of DP IV inhibitors to include type 1 diabetes. For testing this hypothesis, male Wistar rats, exposed to a single dose of streptozotocin (STZ; 50 mg/kg), were treated twice daily with the DP IV inhibitor P32/98 for 7 weeks. Relative to STZ-injected controls, P32/98-treated animals displayed increased weight gain (230%) and nutrient intake, decreased fed blood glucose (ϳ26 vs. ϳ20 mmol/l, respectively), and a return of plasma insulin values toward normal (0.07 vs. 0.12 nmol/l, respectively). Marked improvements in oral glucose tolerance, suggesting enhanced insulin secretory capacity, were corroborated by pancreas perfusion and insulin content measurements that revealed two-to eightfold increases in both secretory function and insulin content after 7 weeks of treatment. Immunohistochemical analyses of pancreatic sections showed marked increases in the number of small islets (؉35%) and total ␤-cells (؉120%) and in the islet ␤-cell fraction (12% control vs. D espite substantial advances in our understanding of type 1 diabetes, diagnosis of the condition still carries with it a sentence of lifelong daily insulin injection, a partially effective therapy at best (1). New therapeutic strategies under investigation include islet transplantation (and associated stem cell-derived and xenogeneic islet technologies necessary for treatment en masse), the development of improved insulin analogues and delivery systems, gene therapy, and the search for novel agents able to protect and/or stimulate the proliferation and regeneration of islet ␤-cells (1). The importance of the latter strategy is underscored by the need for an inexpensive, benign, preventive therapy that lacks the considerable profile of side effects of most therapies studied to date (e.g., immunosuppressants).A number of recent studies have highlighted the role of the incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) in ␤-cell function and development (2,3). Together, the incretins are responsible for Ͼ50% of nutrient-stimulated insulin release and make up the endocrine arm of the enteroinsular axis (4). Apart from their insulinotropic role, GIP and GLP-1 have been shown to enhance ␤-cell glucose competence and, ...

High-density lipoprotein (HDL), a lipid nanoparticle containing many different low abundance proteins, is an attractive target for clinical proteomics because its compositional heterogeneity is linked to its cardioprotective effects. Selected reaction monitoring (SRM) is currently the method of choice for targeted quantification of proteins in such a complex biological matrix. However, model system studies suggest that parallel reaction monitoring (PRM) is more specific than SRM because many product ions can be used to confirm the identity of a peptide. We therefore compared PRM and SRM for their abilities to quantify proteins in HDL, using 15N-labeled apolipoprotein A-I (HDL’s most abundant protein) as the internal standard. PRM and SRM exhibited comparable linearity, dynamic range, precision, and repeatability for protein quantification of HDL. Moreover, the single internal standard protein performed as well as protein-specific peptide internal standards when quantifying 3 different proteins. Importantly, PRM and SRM yielded virtually identical quantitative results for 26 proteins in HDL isolated from 44 subjects. Because PRM requires less method development than SRM and is potentially more specific, our observations indicate that PRM in concert with a single isotope-labeled protein is a promising new strategy for quantifying HDL proteins in translational studies.

Glucose-dependent insulinotropic polypeptide (GIP) is a peptide hormone that is released postprandially from the small intestine and acts in concert with glucagonlike peptide (GLP)-1 to potentiate glucose-induced insulin secretion from the pancreatic ␤-cell. In type 2 diabetes, there is a decreased responsiveness of the pancreas to GIP; however, the insulin response to GLP-1 remains intact. The literature suggests that the ineffectiveness of GIP in type 2 diabetes may be a result of chronic homologous desensitization of the GIP receptor. Yet, there has been no conclusive evidence suggesting that GIP levels are elevated in diabetes. The hypothesis of the present study is that one cause of decreased responsiveness to GIP in type 2 diabetes is an inappropriate expression of the GIP receptor in the pancreatic islet. This hypothesis was tested using a strain of diabetic fatty Zucker rats. The obese rats displayed basal GIP levels similar to the control animals; however, they were unresponsive to a GIP infusion (4 pmol ⅐ min -1 ⅐ kg -1 ), whereas the lean animals displayed a significant reduction in blood glucose (GIP levels, 50% control after 60 min, P < 0.05) as well as a significant increase in circulating insulin. GIP also potently stimulated firstphase insulin secretion from isolated perifused islets (10.3 ؎ 3.0 ؋ basal), and GIP and GLP-1 potentiated insulin secretion from the perfused pancreas (6 ؋ control area under the curve [AUC]) from lean animals. GIP yielded no significant effect in the Vancouver diabetic fatty Zucker (VDF) rat pancreases, whereas GLP-1 elicited an eightfold increase of insulin secretion from the perfused VDF pancreas. Islets from lean animals subjected to static incubations with GIP showed a 2.2-fold increase in cAMP, whereas GIP failed to increase islet cAMP in the VDF islets. Finally, the expression of both GIP receptor mRNA and protein was decreased in islets from VDF rats. These data suggest that the decreased effectiveness of GIP in the VDF rat and in type 2 diabetes may be a result of a decreased receptor expression in the islet. Diabetes 50

Background It is critical to develop new metrics to determine whether high density lipoprotein (HDL) is cardioprotective in humans. One promising approach is HDL particle concentration (HDL-P) – the size and concentration of HDL in plasma or serum. However, the two methods currently used to determine HDL-P yield concentrations that differ more than 5-fold. We therefore developed and validated an improved approach to quantify HDL-P, termed calibrated ion mobility analysis (calibrated IMA). Methods HDL was isolated from plasma by ultracentrifugation, introduced into the gas phase with electrospray ionization, separated by size, and quantified by particle counting. A calibration curve constructed with purified proteins was used to correct for the ionization efficiency of HDL particles. Results The concentrations of gold nanoparticles and reconstituted HDLs measured by calibrated IMA were indistinguishable from concentrations determined by orthogonal methods. In plasma of control (n=40) and cerebrovascular disease (n=40) subjects, three subspecies of HDL were reproducibility measured, with an estimated total HDL-P of 13.4±2.4 µM (mean±SD). HDL-C accounted for 48% of the variance in HDL-P. HDL-P was significantly lower in subjects with cerebrovascular disease, and this difference remained significant after adjustment for HDL cholesterol levels. Conclusions Calibrated IMA accurately and reproducibly determined the concentration of gold nanoparticles and synthetic HDL, strongly suggesting the method could accurately quantify HDL particle concentration. Importantly, the estimated stoichiometry of apoA-I determined by calibrated IMA was 3–4 per HDL particle, in excellent agreement with current structural models. Furthermore, HDL-P associated with cardiovascular disease status in a clinical population independently of HDL cholesterol.