Islets from patients with type 2 diabetes exhibit β cell dysfunction, amyloid deposition, macrophage infiltration, and increased expression of proinflammatory cytokines and chemokines. We sought to determine whether human islet amyloid polypeptide (hIAPP), the main component of islet amyloid, might contribute to islet inflammation by recruiting and activating macrophages. Early aggregates of hIAPP, but not nonamyloidogenic rodent islet amyloid polypeptide, caused release of CCL2 and CXCL1 by islets and induced secretion of TNF-α, IL-1α, IL-1β, CCL2, CCL3, CXCL1, CXCL2, and CXCL10 by C57BL/6 bone marrow-derived macrophages. hIAPP-induced TNF-α secretion was markedly diminished in MyD88-, but not TLR2- or TLR4-deficient macrophages, and in cells treated with the IL-1R antagonist (IL-1Ra) anakinra. To determine the significance of IL-1 signaling in hIAPP-induced pancreatic islet dysfunction, islets from wild-type or hIAPP-expressing transgenic mice were transplanted into diabetic NOD/SCID recipients implanted with mini-osmotic pumps containing IL-1Ra (50 mg/kg/d) or saline. IL-1Ra significantly improved the impairment in glucose tolerance observed in recipients of transgenic grafts 8 wk following transplantation. Islet grafts expressing hIAPP contained amyloid deposits in close association with F4/80-expressing macrophages. Transgenic grafts contained 50% more macrophages than wild-type grafts, an effect that was inhibited by IL-1Ra. Our results suggest that hIAPP-induced islet chemokine secretion promotes macrophage recruitment and that IL-1R/MyD88, but not TLR2 or TLR4 signaling is required for maximal macrophage responsiveness to prefibrillar hIAPP. These data raise the possibility that islet amyloid-induced inflammation contributes to β cell dysfunction in type 2 diabetes and islet transplantation.

The liver and pancreas share a common origin and coexpress several transcription factors. To gain insight into the transcriptional networks regulating the function of these tissues, we globally identify binding sites for FOXA2 in adult mouse islets and liver, PDX1 in islets, and HNF4A in liver. Because most eukaryotic transcription factors bind thousands of loci, many of which are thought to be inactive, methods that can discriminate functionally active binding events are essential for the interpretation of genome-wide transcription factor binding data. To develop such a method, we also generated genome-wide H3K4me1 and H3K4me3 localization data in these tissues. By analyzing our binding and histone methylation data in combination with comprehensive gene expression data, we show that H3K4me1 enrichment profiles discriminate transcription factor occupied loci into three classes: those that are functionally active, those that are poised for activation, and those that reflect pioneer-like transcription factor activity. Furthermore, we demonstrate that the regulated presence of H3K4me1-marked nucleosomes at transcription factor occupied promoters and enhancers controls their activity, implicating both tissue-specific transcription factor binding and nucleosome remodeling complex recruitment in determining tissue-specific gene expression. Finally, we apply these approaches to generate novel insights into how FOXA2, PDX1, and HNF4A cooperate to drive islet-and liver-specific gene expression.

Type 1 diabetes is characterized by destruction of insulin-producing β cells in the pancreatic islets by effector T cells. Tregs, defined by the markers CD4 and FoxP3, regulate immune responses by suppressing effector T cells and are recruited to sites of action by the chemokine CCL22. Here, we demonstrate that production of CCL22 in islets after intrapancreatic duct injection of double-stranded adeno-associated virus encoding CCL22 recruits endogenous Tregs to the islets and confers long-term protection from autoimmune diabetes in NOD mice. In addition, adenoviral expression of CCL22 in syngeneic islet transplants in diabetic NOD recipients prevented β cell destruction by autoreactive T cells and thereby delayed recurrence of diabetes. CCL22 expression increased the frequency of Tregs, produced higher levels of TGF-β in the CD4 + T cell population near islets, and decreased the frequency of circulating autoreactive CD8 + T cells and CD8 + IFN-γ-producing T cells. The protective effect of CCL22 was abrogated by depletion of Tregs with a CD25-specific antibody. Our results indicate that islet expression of CCL22 recruits Tregs and attenuates autoimmune destruction of β cells. CCL22-mediated recruitment of Tregs to islets may be a novel therapeutic strategy for type 1 diabetes.

Islet amyloid polypeptide (IAPP; amylin) is a peptide hormone that is cosecreted with insulin from beta-cells. Impaired processing of proIAPP, the IAPP precursor, has been implicated in islet amyloid formation in type 2 diabetes. We previously showed that proIAPP is processed to IAPP by the prohormone convertases PC1/3 and PC2 at its carboxyl (COOH) and amino (NH(2)) termini, respectively. In this study, we investigated the role of carboxypeptidase E (CPE) in the processing of proIAPP using mice lacking active CPE (Cpe(fat)/Cpe(fat)) and NIT-2 cells, a beta-cell line derived from their islets. Western blot analysis demonstrated that an approximately 6-kDa NH(2)-terminally unprocessed form of proIAPP was elevated approximately 86% in islets from Cpe(fat)/Cpe(fat) mice, compared with wild type. This increase was independent of the development of hyperglycemia (8 wk male) or obesity (18 wk female). Impaired proIAPP processing was associated with a decrease in PC2 (but not PC1/3) and both the 21- and 27-kDa forms of the PC2 chaperone protein 7B2, suggesting that PC2-mediated processing of proIAPP at its NH(2) terminus was impaired in the absence of CPE. Formation of COOH-terminally amidated (pro)IAPP was reduced approximately 75% in NIT-2, compared with NIT-1 beta-cells, supporting a direct role for CPE in maturation of IAPP by removal of its COOH-terminal dibasic residues, the step essential for IAPP amidation. We conclude that lack of CPE in islet beta-cells results in a marked decrease in processing of proIAPP at its NH(2) (but not COOH) terminus that is associated with attenuated levels of PC2 and (pro)7B2 and a great reduction in formation of mature amidated IAPP.