Project description:The short chain fatty acid (SCFA) receptor (free fatty acid receptor-3; FFAR3) is expressed in pancreatic beta cells; however, its role in insulin secretion is not clearly defined. Here, we examined the role of FFAR3 in insulin secretion. Using islets from global knockout FFAR3 (Ffar3-/-) mice, we explored the role of FFAR3 and ligand-induced FFAR3 signaling on glucose stimulated insulin secretion. RNA sequencing was also performed to gain greater insight into the impact of FFAR3 deletion on the islet transcriptome. First exploring insulin secretion, it was determined that Ffar3-/- islets secrete more insulin in a glucose-dependent manner as compared to wildtype (WT) islets. Next, exploring its primary endogenous ligand, propionate, and a specific agonist for FFAR3, signaling by FFAR3 inhibited glucose-dependent insulin secretion, which occurred through a Gαi/o pathway. To help understand these results, transcriptome analyses by RNA-sequencing of Ffar3-/- and WT islets observed multiple genes with well known roles in islet biology to be altered by genetic knockout of FFAR3. Our data shows that FFAR3 signaling mediates glucose stimulated insulin secretion through Gαi/o sensitive pathway. Future studies are needed to more rigorously define the role of FFAR3 by in vivo approaches. Analysis of total RNA from 3 biological replicates of pancreatic islets isolated from free fatty acid receptor 3 knockout (Ffar3 KO) and wildtype (Ffar3 WT) male mice
Project description:Pancreatic beta-cell dysfunction and death are central in the pathogenesis of type 2 diabetes. Saturated fatty acids cause beta-cell failure and contribute to diabetes development in genetically predisposed individuals. Here we used RNA-sequencing to map transcripts expressed in five palmitate-treated human islet preparations, observing 1,325 modified genes. Palmitate induced fatty acid metabolism and endoplasmic reticulum (ER) stress. Functional studies identified novel mediators of adaptive ER stress signaling. Palmitate modified genes regulating ubiquitin and proteasome function, autophagy and apoptosis. Inhibition of autophagic flux and lysosome function contributed to lipotoxicity. Palmitate inhibited transcription factors controlling beta-cell phenotype including PAX4 and GATA6. 59 type 2 diabetes candidate genes were expressed in human islets, and 11 were modified by palmitate. Palmitate modified expression of 17 splicing factors and shifted alternative splicing of 3,525 transcripts. Ingenuity Pathway Analysis of modified transcripts and genes confirmed that top changed functions related to cell death. DAVID analysis of transcription binding sites in palmitate-modified transcripts revealed a role for PAX4, GATA and the ER stress response regulators XBP1 and ATF6. This human islet transcriptome study identified novel mechanisms of palmitate-induced beta-cell dysfunction and death. The data point to crosstalk between metabolic stress and candidate genes at the beta-cell level. 5 human islet of Langerhans preparations examined under 2 conditions (control and palmitate treatment)
Project description:The short chain fatty acid (SCFA) receptor (free fatty acid receptor-3; FFAR3) is expressed in pancreatic beta cells; however, its role in insulin secretion is not clearly defined. Here, we examined the role of FFAR3 in insulin secretion. Using islets from global knockout FFAR3 (Ffar3-/-) mice, we explored the role of FFAR3 and ligand-induced FFAR3 signaling on glucose stimulated insulin secretion. RNA sequencing was also performed to gain greater insight into the impact of FFAR3 deletion on the islet transcriptome. First exploring insulin secretion, it was determined that Ffar3-/- islets secrete more insulin in a glucose-dependent manner as compared to wildtype (WT) islets. Next, exploring its primary endogenous ligand, propionate, and a specific agonist for FFAR3, signaling by FFAR3 inhibited glucose-dependent insulin secretion, which occurred through a Gαi/o pathway. To help understand these results, transcriptome analyses by RNA-sequencing of Ffar3-/- and WT islets observed multiple genes with well known roles in islet biology to be altered by genetic knockout of FFAR3. Our data shows that FFAR3 signaling mediates glucose stimulated insulin secretion through Gαi/o sensitive pathway. Future studies are needed to more rigorously define the role of FFAR3 by in vivo approaches.
Project description:Here we harnessed the potential of RNA sequencing in 89 human pancreatic islet donors to identify genes and exons regulated in this relevant tissue for T2D. mRNA profiles of 89 human pancreatic islet donors having different levels of blood glucose (HbA1c) with and without T2D. The data was generated by deep sequencing using Illumina HiSeq 2000.
Project description:Background: Long-term exposure to elevated levels of free fatty acids (FFAs) is deleterious for beta-cell function and may contribute to development of type 2 diabetes mellitus (T2DM). Whereas mechanisms of impaired glucose-stimulated insulin secretion (GSIS) in FFA-treated beta-cells have been intensively studied, biological events preceding the secretory failure, when GSIS is accentuated, are poorly investigated. To identify these early events, we performed genome-wide analysis of gene expression in isolated human islets exposed to fatty acid palmitate for different time periods. Results: Palmitate-treated human islets showed decline in beta-cell function starting from day two. Affymetrix Human Transcriptome Array 2.0 identified 903 differentially expressed genes (DEGs). Mapping of the genes onto pathways using KEGG pathway enrichment analysis predicted four islet biology-related pathways enriched prior but not after the decline of islet function and three pathways enriched both prior and after the decline of islet function. DEGs from these pathways were analyzed at the transcript level. The results propose that in palmitate-treated human islets, at early time points, protective events, including up-regulation of metallothioneins, tRNA synthetases and fatty acid-metabolising proteins, dominate over deleterious events, including inhibition of fatty acid detoxification enzymes, which contributes to the enhanced GSIS. After prolonged exposure of islets to palmitate, the protective events are outweighed by the deleterious events, which leads to impaired GSIS. Conclusions: The study identifies temporal order between different cellular events, which either promote or protect from beta-cell failure. The sequence of these events should be considered when developing strategies for prevention and treatment of the disease.
Project description:Pancreatic beta-cell dysfunction and death are central in the pathogenesis of type 2 diabetes. Saturated fatty acids cause beta-cell failure and contribute to diabetes development in genetically predisposed individuals. Here we used RNA-sequencing to map transcripts expressed in five palmitate-treated human islet preparations, observing 1,325 modified genes. Palmitate induced fatty acid metabolism and endoplasmic reticulum (ER) stress. Functional studies identified novel mediators of adaptive ER stress signaling. Palmitate modified genes regulating ubiquitin and proteasome function, autophagy and apoptosis. Inhibition of autophagic flux and lysosome function contributed to lipotoxicity. Palmitate inhibited transcription factors controlling beta-cell phenotype including PAX4 and GATA6. 59 type 2 diabetes candidate genes were expressed in human islets, and 11 were modified by palmitate. Palmitate modified expression of 17 splicing factors and shifted alternative splicing of 3,525 transcripts. Ingenuity Pathway Analysis of modified transcripts and genes confirmed that top changed functions related to cell death. DAVID analysis of transcription binding sites in palmitate-modified transcripts revealed a role for PAX4, GATA and the ER stress response regulators XBP1 and ATF6. This human islet transcriptome study identified novel mechanisms of palmitate-induced beta-cell dysfunction and death. The data point to crosstalk between metabolic stress and candidate genes at the beta-cell level.
Project description:Pancreatic beta cell senescence occurs during the development of Type 1 Diabetes. To model the transcriptional responses of islet cells to DNA damage, we previously developed a human islet culture model in which the DNA damage response and senescence can be induced via double strand-breaks with the agent bleomycin. Here, we report the transcriptome-wide changes in human pancreatic islet cells following bleomycin exposure.
Project description:Aging-related degeneration of pancreatic islet cells contributes to impaired glucose tolerance and diabetes. Endocrine cells age heterogeneously, complicating the effort to unravel the molecular drives underlying endocrine aging. To overcome these obstacles, we undertook single-cell RNA sequencing of pancreatic islet cells obtained from young and aged non-diabetic cynomolgus monkeys. Despite sex differences and increased single-cell level transcriptional variations, aged β-cells showed increased unfolded protein response (UPR) along with the accumulation of protein aggregates. We observed transcriptomic dysregulation of UPR components linked to canonical ATF6 and IRE1 signaling, comprising adaptive UPR during pancreatic aging. Notably, we found age-related β-cell-specific upregulation of HSP90B1, an ER-located chaperone, impeded high glucose-induced insulin secretion. Our work decodes aging-associated transcriptomic changes that underlie pancreatic islet functional decay at the single-cell resolution and indicates that targeting UPR components may prevent loss of proteostasis, suggesting an avenue for therapies to delay β-cell aging and prevent aging-related diabetes.