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:Pancreatic endocrine-exocrine crosstalk plays a key role in normal physiology and disease and can be altered by host metabolic states, such as obesity. Classically, endocrine islet beta (β) cell secretion of insulin is thought to promote the development of obesity-associated pancreatic adenocarcinoma (PDAC), an exocrine cell-derived tumor. Here, we show that β cell expression of the peptide hormone cholecystokinin (CCK) is necessary and sufficient for obesity-associated PDAC progression in mice and that CCK expression – rather than insulin – correlates strongly with enhanced tumorigenesis. Single-cell RNA-sequencing, in silico latent-space archetypal and trajectory analysis, and experimental lineage tracing in vivo reveal that obesity induces the expansion of postnatal immature β cells, which adapt to express CCK via stress-responsive JNK/cJun signaling. Finally, obesity perturbs CCK-dependent peri-islet exocrine cell transcriptional states and enhances islet-proximal tumor formation. These results define endocrine-exocrine CCK signaling as a bona fide driver of obesity-associated PDAC development and uncover new avenues to target the endocrine pancreas to subvert exocrine tumorigenesis.
Project description:Pancreatic endocrine-exocrine crosstalk plays a key role in normal physiology and disease and can be altered by host metabolic states, such as obesity. Classically, endocrine islet beta (β) cell secretion of insulin is thought to promote the development of obesity-associated pancreatic adenocarcinoma (PDAC), an exocrine cell-derived tumor. Here, we show that β cell expression of the peptide hormone cholecystokinin (CCK) is necessary and sufficient for obesity-associated PDAC progression in mice and that CCK expression – rather than insulin – correlates strongly with enhanced tumorigenesis. Single-cell RNA-sequencing, in silico latent-space archetypal and trajectory analysis, and experimental lineage tracing in vivo reveal that obesity induces the expansion of postnatal immature β cells, which adapt to express CCK via stress-responsive JNK/cJun signaling. Finally, obesity perturbs CCK-dependent peri-islet exocrine cell transcriptional states and enhances islet-proximal tumor formation. These results define endocrine-exocrine CCK signaling as a bona fide driver of obesity-associated PDAC development and uncover new avenues to target the endocrine pancreas to subvert exocrine tumorigenesis.
Project description:Pancreatic endocrine-exocrine crosstalk plays a key role in normal physiology and disease and can be altered by host metabolic states, such as obesity. Classically, endocrine islet beta (β) cell secretion of insulin is thought to promote the development of obesity-associated pancreatic adenocarcinoma (PDAC), an exocrine cell-derived tumor. Here, we show that β cell expression of the peptide hormone cholecystokinin (CCK) is necessary and sufficient for obesity-associated PDAC progression in mice and that CCK expression – rather than insulin – correlates strongly with enhanced tumorigenesis. Single-cell RNA-sequencing, in silico latent-space archetypal and trajectory analysis, and experimental lineage tracing in vivo reveal that obesity induces the expansion of postnatal immature β cells, which adapt to express CCK via stress-responsive JNK/cJun signaling. Finally, obesity perturbs CCK-dependent peri-islet exocrine cell transcriptional states and enhances islet-proximal tumor formation. These results define endocrine-exocrine CCK signaling as a bona fide driver of obesity-associated PDAC development and uncover new avenues to target the endocrine pancreas to subvert exocrine tumorigenesis.
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:In response to obesity-related metabolic stress, islet beta-cells adapt (or compensate) by increasing their secretory function and mass. Yet, for unknown reasons, this compensation is reversed in some individuals at some point to induce beta-cell failure and overt type 2 diabetes. We have previously shown that transcription factor Myt3 (St18) and its paralogs, Myt1 and Myt2, prevent beta-cell failure. Myt3 was induced at post-transcriptional levels by obesity-related stress in both mouse and human beta cells and its downregulation accompanied beta-cell dysfunction during type 2 diabetes development. Single-nucleotide polymorphisms in MYT3 were associated with an increased risk of developing human diabetes. We now demonstrate that Myt3 translation is regulated by an upstream open-reading frame that overlaps with the main Myt3 open-reading frame in mice. Disrupting this overlap enhances Myt3 translation in mouse beta cells without metabolic stress but decreases it under high-fat-diet challenges. Consequently, this deregulation results in beta-cell dysfunction and glucose intolerance in mice, accompanied by compromised expression of several beta-cell function genes, demonstated by sc-RNAseq studies here. These findings suggest that stress-induced Myt3 translation is part of the compensation mechanism that prevents beta-cell failure.
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.