Project description:Inflammation is a key component of the pathogenesis of obesity-associated type 2 diabetes (T2D). However, the nature of T2D-associated islet inflammation and its impacts on T2D-associated beta cell abnormalities remain poorly defined. Using both diet-induced and genetically modified T2D animal models, we explore immune components of islet inflammation and define their roles in regulating beta cell function and proliferation. Our studies show that T2D-associated islet inflammation is uniquely dominated by macrophages, without the involvement of adaptive immune cells. We identify two islet macrophage populations, characterized by their distinct phenotypes, anatomical distributions and functional properties. Obesity induces a local expansion of intra-islet macrophages, independent of the replenishment from circulating monocytes. In contrast, the abundance of peri-islet macrophages is negligibly affected by obesity. Functionally, intra-islet macrophages impair beta cell function in a cell-cell contact dependent manner. In contrast, both intra- and peri-islet macrophage populations are able to promote beta cell proliferation. Together, these data provide a definitive view of the genesis of T2D-associated islet inflammation and define specific roles of islet macrophages in regulating beta cell function and proliferation.
Project description:Adult pancreatic β cells are refractory to proliferation, a roadblock for the treatment of insulin-deficient diabetes. Consumption of energy-dense Western or high-fat diet (HFD) triggers mild adaptive β cell mass expansion to compensate for peripheral insulin resistance; however, the underlying molecular mechanism remains unclear. Here we show that Toll-like receptors (TLR) 2/TLR4 act as molecular “brakes” for diet-induced β cell replication in both mice and humans. The combined loss of TLR2/TLR4, but not individually, dramatically increases facultative β, not α, cell replication, leading to progressively enlarged islet mass and hyperinsulinemia in diet-induced obesity. Mechanistically, loss of TLR2/TLR4 increases β cell proliferation and nuclear abundance of Cyclin D2 and CDK4 in an extracellular signal-regulated kinase (ERK)-dependent manner. These data reveal a novel mechanism governing adaptive β cell mass expansion in diet-induced obesity and suggest that selective targeting of TLR2/TLR4 pathways may hold promise for reversing β cell failure in diabetic patients.
Project description:Transcriptional mechanisms of beta cell proliferation are incompletely understood. We used single-cell transcriptomics to identify gene networks and signaling pathways central to beta cell proliferation
Project description:We knocked out the critical autophagy enzyme, ATG7, in the β-cells of mice (ATG7Δβ-cell) then monitored blood glucose to assess the phenotype induced by this KO model. We found that all ATG7Δβ-cell mice developed diabetes between 11-15 weeks of age. We isolated islets from ATG7Δβ-cell and littermate control mice several weeks prior to diabetes development (7-10 weeks of age) and performed bulk islet proteomics. The purpose of this experiment was to understand the islet biological process pathways altered by dysfunctional β-cell autophagy in the ATG7Δβ-cell model.
Project description:We found that in rodents, b-cell mass expansion during pregnancy and obesity is associated with changes in the expression of a group of islet microRNAs. We were able to reproduce in isolated pancreatic islets the decrease of miR-338-3p level observed in gestation and obesity by activating the G-protein coupled estrogen receptor GPR30 and the GLP1 receptor. Blockade of miR-338-3p in b-cells using specific anti-miR molecules mimicked gene expression changes occurring during b-cell mass expansion and resulted in increased proliferation and improved survival both in vitro and in vivo. These findings point to a major role for miR-338-3p in compensatory b-cell mass expansion occurring under different insulin resistance states.
Project description:Type 2 diabetes (T2D) is associated with compromised identity of insulin-producing pancreatic islet beta (β) cells, characterized by inappropriate production of other islet cell-enriched hormones. Here we examined how hormone misexpression was influenced by the MAFA and MAFB transcription factors, closely related proteins that maintain islet cell function. Mice specifically lacking MafA in β cells demonstrated broad, population-wide changes in hormone gene expression with an overall gene signature closely resembling islet gastrin (Gast)-positive cells generated under conditions of chronic hyperglycemia and obesity. A human b cell line deficient in MAFB, but not one lacking MAFA, also produced a gastrin (GAST)-positive gene expression pattern. In addition, GAST was detected in human T2D β cells with low levels of MAFB. Moreover, evidence is provided that human MAFB can directly repress GAST gene transcription. These results support a novel, species-specific role for MafA and MAFB in maintaining adult mouse and human β cell identity, respectively, by repressing expression of Gast/GAST and other non-b cell hormones.
Project description:We found that in rodents, postnatal beta-cell maturation is associated with changes in the expression of several islet microRNAs and discovered that these modifications are driven by changes in the nutrient supply. Mimicking the microRNA changes observed during β-cell maturation in newborn rat islet cells was sufficient to promote glucose-induced insulin release and to achieve a mature β-cell secretory phenotype. Moreover, the modifications in the level of some of these microRNAs reduced the proliferation of newborn β-cells, suggesting that they contribute to the limited proliferative capacity of adult β-cells. These findings demonstrated that miRNAs contribute to postnatal beta-cell maturation and development. Their role is likely to promote beta-cell adaptation to fule supply and to maintain glucose homeostasis by regulating insulin release and proliferation. Islets from 10-day-old rats (P10) (n=3) or 3-month-old male rat (n=3) were taken. Total RNA was extracted and mRNA profiling via Illumina single-end sequencing of mRNA-seq libraries was performed.
Project description:Endocrine islet beta cells comprise heterogenous cell subsets. Yet the origin, stability, and physiological significance of these subsets remain largely unknown. Using combinatorial cell lineage tracing, scRNA-seq, and DNA methylation analysis, we show here that embryonic islet progenitors with differential gene expression and DNA methylation produce stable beta-cell subtypes of different function and viability in adult mice. Differentially expressed genes, including the Myt transcription factors, voltage-gated channels, and Ca2+-sensor synaptotagmins, contribute to the functional differences of these subtypes. Maternal overnutrition, a major diabetes risk factor, reduces the proportion of endocrine progenitors of the better-functionality beta-cell subtype. Intriguingly, the gene signature that defines mouse beta-cell subtypes can reliably divide human cells into two populations, with the proportion of better-functionality beta cells reduced in diabetic donors. These results establish that some beta-cell subtypes are determined via DNA methylation in embryonic islet progenitors, which is regulated by diabetes-causing maternal factors. The implication is that modulating DNA methylation in islet progenitors can be explored to improve beta-cell function in the prevention and therapy of diabetes.