Proteomics and islet research

The Human Islet: Mini-Organ With Mega-Impact

This review focuses on the human pancreatic islet-including its structure, cell composition, development, function, and dysfunction. After providing a historical timeline of key discoveries about human islets over the past century, we describe new research approaches and technologies that are being used to study human islets and how these are providing insight into human islet physiology and pathophysiology. We also describe changes or adaptations in human islets in response to physiologic challenges such as pregnancy, aging, and insulin resistance and discuss islet changes in human diabetes of many forms. We outline current and future interventions being developed to protect, restore, or replace human islets. The review also highlights unresolved questions about human islets and proposes areas where additional research on human islets is needed.

Effects of bone marrow on the microenvironment of the human pancreatic islet: A Protein Profile Approach

Stem cells are a new therapeutic modality that may support the viability and function of human organs and tissue. Our previous studies have revealed that human allogeneic bone marrow (BM) sustains pancreatic β cell function and survival. This paper examines whether BM creates a microenvironment that supports human pancreatic islets in vitro by evaluating 107 proteins in culture media from BM, islet, and islet/bone marrow (IB) with mass spectrometry. Proteins were considered up- or down-regulated if p-values < 0.05 and fold change was greater than 2 fold I VS. IB. In addition, proteins identified that were uniquely found in islets co-cultured with bone marrow, but not in islets or bone marrow. A 95% protein probability was used as a threshold. Twenty three proteins were upregulated, and sixteen proteins were downregulated. The function of each protein is listed based on the protein database, which include structural proteins (9 upregulated, 4 downregulated); anti-protease and anti-endopeptidase enzymes (8 upregulated); cation binding proteins (6 up-regulated). Six proteins were uniquely identified in islet co-cultured with bone marrow. Three are anti-proteases or anti-endopeptidases, and 1 is a structural protein. These findings suggest that BM, by changing culture media proteins, may be one of mechanisms to maintain human islet function and survival.

Impact of exposure to low concentrations of nitric oxide on protein profile in murine and human pancreatic islet cells

Homeostatic levels of nitric oxide (NO) protect efficiently against apoptotic death in both human and rodent pancreatic β cells, but the protein profile of this action remains to be determined. We have applied a 2 dimensional LC-MS-MALDI-TOF/TOF-based analysis to study the impact of protective NO in rat insulin-producing RINm5F cell line and in mouse and human pancreatic islets (HPI) exposed to serum deprivation condition. 24 proteins in RINm5F and 22 in HPI were identified to undergo changes in at least one experimental condition. These include stress response mitochondrial proteins (UQCRC2, VDAC1, ATP5C1, ATP5A1) in RINm5F cells and stress response endoplasmic reticulum proteins (HSPA5, PDIA6, VCP, GANAB) in HPI. In addition, metabolic and structural proteins, oxidoreductases and chaperones related with protein metabolism are also regulated by NO treatment. Network analysis of differentially expressed proteins shows their interaction in glucocorticoid receptor and NRF2-mediated oxidative stress response pathways and eNOS signaling. The results indicate that exposure to exogenous NO counteracts the impact of serum deprivation on pancreatic β cell proteome. Species differences in the proteins involved are apparent.

Peptidomic profiling of secreted products from pancreatic islet culture results in a higher yield of full-length peptide hormones than found using cell lysis procedures

Peptide Hormone Acquisition through Smart Sampling Technique-Mass Spectrometry (PHASST-MS) is a peptidomics platform that employs high resolution liquid chromatography-mass spectrometry (LC-MS) techniques to identify peptide hormones secreted from in vitro or ex vivo cultures enriched in endocrine cells. Application of the methodology to the study of murine pancreatic islets has permitted evaluation of the strengths and weaknesses of the approach, as well as comparison of our results with published islet studies that employed traditional cellular lysis procedures. We found that, while our PHASST-MS approach identified fewer peptides in total, we had greater representation of intact peptide hormones. The technique was further refined to improve coverage of hydrophilic as well as hydrophobic peptides and subsequently applied to human pancreatic islet cultures derived from normal donors or donors with type 2 diabetes. Interestingly, in addition to the expected islet hormones, we identified alpha-cell-derived bioactive GLP-1, consistent with recent reports of paracrine effects of this hormone on beta-cell function. We also identified many novel peptides derived from neurohormonal precursors and proteins related to the cell secretory system. Taken together, these results suggest the PHASST-MS strategy of focusing on cellular secreted products rather than the total tissue peptidome may improve the probability of discovering novel bioactive peptides and also has the potential to offer important new insights into the secretion and function of known hormones.

Unraveling pancreatic islet biology by quantitative proteomics

The pancreatic islets of Langerhans play a critical role in maintaining blood glucose homeostasis by secreting insulin and several other important peptide hormones. Impaired insulin secretion due to islet dysfunction is linked to the pathogenesis underlying both Type 1 and Type 2 diabetes. Over the past 5 years, emerging proteomic technologies have been applied to dissect the signaling pathways that regulate islet functions and gain an understanding of the mechanisms of islet dysfunction relevant to diabetes. Herein, we briefly review some of the recent quantitative proteomic studies involving pancreatic islets geared towards gaining a better understanding of islet biology relevant to metabolic diseases.

Membrane Protein Profiling of Human Islets of Langerhans Using Several Extraction Methods

Introduction

Proteomic characterization of the human pancreatic islets, containing the insulin producing beta-cells, is likely to be of great importance for improved treatment and understanding of the pathophysiology of diabetes mellitus.

Objective

The focus of this study was to characterize the human islet membrane proteome.

Methods

In order to identify as many membrane proteins as possible, five different extraction procedures were used, i.e., phase separation using Triton X-114, a plasma membrane protein kit, cell surface protein biotinylation, total protein extraction, and lipid-based protein immobilization flow cell. Digested protein extracts were analyzed by nanoflow liquid chromatography tandem mass spectrometry. Then the identified proteins were categorized according to cellular location using their gene ontology annotation and by prediction of transmembrane helices in the sequence. This information was used to estimate the amount of membrane proteins identified.

Results

By combining the results from all extraction procedures, the total number of membrane proteins identified from the human islets was increased, accentuating that a combination of methods usually gives a higher coverage of the proteome. A total of 1,700 proteins were identified (≥2 unique peptides), and 735 of these proteins were annotated as membrane proteins while 360 proteins had at least one predicted transmembrane helix. The extraction method using phase separation with Triton X-114 yielded both the highest number and the highest proportion of membrane proteins.

Conclusion

This study gave an enhanced characterization of the human islet membrane proteome which may contribute to a better understanding of islet biology.

Characterization of seedling proteomes and development of markers to distinguish the Brassica A and C genomes

The diploid species Brassica rapa (genome AA) and B. oleracea (genome CC) were compared by full-scale proteome analyses of seedling. A total of 28.2% of the proteins was common to both species, indicating the existence of a basal or ubiquitous proteome. However, a number of discriminating proteins (32.0%) and specific proteins (39.8%) of the Brassica A and C genomes, respectively, were identified, which could represent potentially species-specific functions. Based on these A or C genome-specific proteins, a number of PCR-based markers to distinguish B. rapa and B. oleracea species were also developed.