David M. Blodgett

Novel Observations From Next-Generation RNA Sequencing of Highly Purified Human Adult and Fetal Islet Cell Subsets.

Understanding distinct gene expression patterns of normal adult and developing fetal human pancreatic α- and β-cells is crucial for developing stem cell therapies, islet regeneration strategies, and therapies designed to increase β-cell function in patients with diabetes (type 1 or 2). Toward that end, we have developed methods to highly purify α-, β-, and δ-cells from human fetal and adult pancreata by intracellular staining for the cell-specific hormone content, sorting the subpopulations by flow cytometry, and, using next-generation RNA sequencing, we report the detailed transcriptomes of fetal and adult α- and β-cells. We observed that human islet composition was not influenced by age, sex, or BMI, and transcripts for inflammatory gene products were noted in fetal β-cells. In addition, within highly purified adult glucagon-expressing α-cells, we observed surprisingly high insulin mRNA expression, but not insulin protein expression. This transcriptome analysis from highly purified islet α- and β-cell subsets from fetal and adult pancreata offers clear implications for strategies that seek to increase insulin expression in type 1 and type 2 diabetes.

Analysis of self-antigen specificity of islet-infiltrating T cells from human donors with type 1 diabetes

A major therapeutic goal for type 1 diabetes (T1D) is to induce autoantigen-specific tolerance of T cells. This could suppress autoimmunity in those at risk for the development of T1D, as well as in those with established disease who receive islet replacement or regeneration therapy. Because functional studies of human autoreactive T cell responses have been limited largely to peripheral blood–derived T cells, it is unclear how representative the peripheral T cell repertoire is of T cells infiltrating the islets. Our knowledge of the insulitic T cell repertoire is derived from histological and immunohistochemical analyses of insulitis, the identification of autoreactive CD8+ T cells in situ, in islets of human leukocyte antigen (HLA)-A2+ donors and isolation and identification of DQ8 and DQ2–DQ8 heterodimer–restricted, proinsulin-reactive CD4+ T cells grown from islets of a single donor with T1D. Here we present an analysis of 50 of a total of 236 CD4+ and CD8+ T cell lines grown from individual handpicked islets or clones directly sorted from handpicked, dispersed islets from nine donors with T1D. Seventeen of these T cell lines and clones reacted to a broad range of studied native islet antigens and to post-translationally modified peptides. These studies demonstrate the existence of a variety of islet-infiltrating, islet-autoantigen reactive T cells in individuals with T1D, and these data have implications for the design of successful immunotherapies.

Analysis of Glucose Transporter Topology and Structural Dynamics

Homology modeling and scanning cysteine mutagenesis studies suggest that the human glucose transport protein GLUT1 and its distant bacterial homologs LacY and GlpT share similar structures. We tested this hypothesis by mapping the accessibility of purified, reconstituted human erythrocyte GLUT1 to aqueous probes. GLUT1 contains 35 potential tryptic cleavage sites. Fourteen of 16 lysine residues and 18 of 19 arginine residues were accessible to trypsin. GLUT1 lysine residues were modified by isothiocyanates and N-hydroxysuccinimide (NHS) esters in a substrate-dependent manner. Twelve lysine residues were accessible to sulfo-NHS-LC-biotin. GLUT1 trypsinization released full-length transmembrane helix 1, cytoplasmic loop 6–7, and the long cytoplasmic C terminus from membranes. Trypsin-digested GLUT1 retained cytochalasin B and d-glucose binding capacity and released full-length transmembrane helix 8 upon cytochalasin B (but not d-glucose) binding. Transmembrane helix 8 release did not abrogate cytochalasin B binding. GLUT1 was extensively proteolyzed by α-chymotrypsin, which cuts putative pore-forming amphipathic α-helices 1, 2, 4, 7, 8, 10, and 11 at multiple sites to release transmembrane peptide fragments into the aqueous solvent. Putative scaffolding membrane helices 3, 6, 9, and 12 are strongly hydrophobic, resistant to α-chymotrypsin, and retained by the membrane bilayer. These observations provide experimental support for the proposed GLUT1 architecture; indicate that the proposed topology of membrane helices 5, 6, and 12 requires adjustment; and suggest that the metastable conformations of transmembrane helices 1 and 8 within the GLUT1 scaffold destabilize a sugar translocation intermediate.

Disease allele-dependent small-molecule sensitivities in blood cells from monogenic diabetes

Even as genetic studies identify alleles that influence human disease susceptibility, it remains challenging to understand their functional significance and how they contribute to disease phenotypes. Here, we describe an approach to translate discoveries from human genetics into functional and therapeutic hypotheses by relating human genetic variation to small-molecule sensitivities. We use small-molecule probes modulating a breadth of targets and processes to reveal disease allele-dependent sensitivities, using cells from multiple individuals with an extreme form of diabetes (maturity onset diabetes of the young type 1, caused by mutation in the orphan nuclear receptor HNF4α). This approach enabled the discovery of small molecules that show mechanistically revealing and therapeutically relevant interactions with HNF4α in both lymphoblasts and pancreatic β-cells, including compounds that physically interact with HNF4α. Compounds including US Food and Drug Administration–approved drugs were identified that favorably modulate a critical disease phenotype, insulin secretion from β-cells. This method may suggest therapeutic hypotheses for other nonblood disorders.

Beyond the brain: disrupted in schizophrenia 1 regulates pancreatic β-cell function via glycogen synthase kinase-3β

Individuals with schizophrenia and their first‐degree relatives have higher rates of type 2 diabetes (T2D) than the general population (18–30 vs. 1.2–6.3%), independent of body mass index and antipsychotic medication, suggesting shared genetic components may contribute to both diseases. The cause of this association remains unknown. Mutations in disrupted in schizophrenia 1 (DISC1) increase the risk of developing psychiatric disorders [logarithm (base 10) of odds = 7.1]. Here, we identified DISC1 as a major player controlling pancreatic β‐cell proliferation and insulin secretion via regulation of glycogen synthase kinase‐3β (GSK3β). DISC1 expression was enriched in developing mouse and human pancreas and adult β‐ and ductal cells. Loss of DISC1 function, through siRNA‐mediated depletion or expression of a dominant‐negative truncation that models the chromosomal translocation of human DISC1 in schizophrenia, resulted in decreased β‐cell proliferation (3 vs. 1%; P< 0.01), increased apoptosis (0.1 vs. 0.6%; P< 0.01), and glucose intolerance in transgenic mice. Insulin secretion was reduced (0.5 vs. 0.1 ng/ml; P < 0.05), and critical β‐cell transcription factors Pdx1 and Nkx6.1 were significantly decreased. Impaired DISC1 allowed inappropriate activation of GSK3β in β cells, and antagonizing GSK3β (SB216763; IC50 = 34.3 nM) rescued the β‐cell defects. These results uncover an unexpected role for DISC1 in normal β‐cell physiology and suggest that DISC1 dysregulation contributes to T2D independently of its importance for cognition.—Jurczyk, A., Nowosielska, A., Przewozniak, N., Aryee, K.‐E., DiIorio, P., Blodgett, D., Yang, C., Campbell‐Thompson, M., Atkinson, M., Shultz, L., Rittenhouse, A., Harlan, D., Greiner, D., Bortell, R. Beyond the brain: disrupted in schizophrenia 1 regulates pancreatic β‐cell function via glycogen synthase kinase‐3β. FASEB J. 30, 983–993 (2016). www.fasebj.org

α Cell Function and Gene Expression Are Compromised in Type 1 Diabetes

SUMMARY Many patients with type 1 diabetes (T1D) have residual β cells producing small amounts of C-peptide long after disease onset but develop an inadequate glucagon response to hypoglycemia following T1D diagnosis. The features of these residual β cells and α cells in the islet endocrine compartment are largely unknown, due to the difficulty of comprehensive investigation. By studying the T1D pancreas and isolated islets, we show that remnant β cells appeared to maintain several aspects of regulated insulin secretion. However, the function of T1D α cells was markedly reduced, and these cells had alterations in transcription factors constituting α and β cell identity. In the native pancreas and after placing the T1D islets into a non-autoimmune, normoglycemic in vivo environment, there was no evidence of α-to-β cell conversion. These results suggest an explanation for the disordered T1D counterregulatory glucagon response to hypoglycemia.

The pancreatic β-cell transcriptome and integrated-omics.

Purpose of review&bgr; Cells represent one of many cell types in heterogeneous pancreatic islets and play the central role in maintaining glucose homeostasis, such that disrupting &bgr;-cell function leads to diabetes. This review summarizes the methods for isolating and characterizing &bgr; cells, and describes integrated ‘omics’ approaches used to define the &bgr; cell by its transcriptome and proteome. Recent findingsRNA sequencing and mass spectrometry-based protein identification have now identified RNA and protein profiles for mouse and human pancreatic islets and &bgr; cells, and for &bgr;-cell lines. Recent publications have outlined these profiles and, more importantly, have begun to assign the presence or absence of specific genes and regulatory molecules to &bgr;-cell function and dysfunction. Overall, researchers have focused on understanding the pathophysiology of diabetes by connecting genome, transcriptome, proteome, and regulatory RNA profiles with findings from genome-wide association studies. SummaryStudies employing these relatively new techniques promise to identify specific genes or regulatory RNAs with altered expression as &bgr;-cell function begins to deteriorate in the spiral toward the development of diabetes. The ultimate goal is to identify the potential therapeutic targets to prevent &bgr;-cell dysfunction and thereby better treat the individual with diabetes. Video abstracthttp://links.lww.com/COE/A5.

Surprising Heterogeneity of Pancreatic Islet Cell Subsets.

Two studies clearly demonstrate that pancreatic islets and, more specifically, their cellular constituents, display a much greater complexity than previously appreciated.

Corrigendum: Analysis of self-antigen specificity of islet-infiltrating T cells from human donors with type 1 diabetes

Corrigendum: Analysis of self-antigen specificity of islet-infiltrating T cells from human donors with type 1 diabetes