RESUMO
In type 2 diabetes, ß-cells endure various forms of cellular stress, including oxidative stress and endoplasmic reticulum stress, secondary to increased demand for insulin production and extracellular perturbations, including hyperglycemia. Chronic exposure to stress causes impaired insulin secretion, apoptosis, and loss of cell identity, and a combination of these processes leads to ß-cell failure and severe hyperglycemia. Therefore, a better understanding of the molecular mechanisms underlying stress responses in ß-cells promises to reveal new therapeutic opportunities for type 2 diabetes. In this perspective, we discuss posttranscriptional control of gene expression as a critical, but underappreciated, layer of regulation with broad importance during stress responses. Specifically, regulation of mRNA translation occurs pervasively during stress to activate gene expression programs; however, the convenience of RNA sequencing has caused translational regulation to be overlooked compared with transcriptional controls. We highlight the role of RNA binding proteins in shaping selective translational regulation during stress and the mechanisms underlying this level of regulation. A growing body of evidence indicates that RNA binding proteins control an array of processes in ß-cells, including the synthesis and secretion of insulin. Therefore, systematic evaluations of translational regulation and the upstream factors shaping this level of regulation are critical areas of investigation to expand our understanding of ß-cell failure in type 2 diabetes.
Assuntos
Diabetes Mellitus Tipo 2/metabolismo , Estresse do Retículo Endoplasmático/fisiologia , Células Secretoras de Insulina/metabolismo , Estresse Oxidativo/fisiologia , Processamento Pós-Transcricional do RNA/fisiologia , Proteínas de Ligação a RNA/metabolismo , Animais , Apoptose/fisiologia , Diabetes Mellitus Tipo 2/genética , Diabetes Mellitus Tipo 2/patologia , Regulação da Expressão Gênica , Humanos , Secreção de Insulina/fisiologia , Células Secretoras de Insulina/patologia , Processamento de Proteína Pós-Traducional/fisiologia , Proteínas de Ligação a RNA/genéticaRESUMO
The homeodomain transcription factor Pdx1 controls pancreas organogenesis, specification of endocrine pancreas progenitors, and the postnatal growth and function of pancreatic ß-cells. Pdx1 expression in human-derived stem cells is used as a marker for induced pancreatic precursor cells. Unfortunately, the differentiation efficiency of human pancreatic progenitors into functional ß-cells is poor. In order to gain insight into the genes that Pdx1 regulates during differentiation, we performed Pdx1 chromatin immunoprecipitation followed by high-throughput sequencing of embryonic day (e) 13.5 and 15.5 mouse pancreata. From this, we identified the transcription factor Teashirt zinc finger 1 (Tshz1) as a direct Pdx1 target. Tshz1 is expressed in developing and adult insulin- and glucagon-positive cells. Endocrine cells are properly specified in Tshz1-null embryos, but critical regulators of ß-cell (Pdx1 and Nkx6.1) and α-cell (MafB and Arx) formation and function are downregulated. Adult Tshz1(+/-) mice display glucose intolerance due to defects in glucose-stimulated insulin secretion associated with reduced Pdx1 and Clec16a expression in Tshz1(+/-) islets. Lastly, we demonstrate that TSHZ1 levels are reduced in human islets of donors with type 2 diabetes. Thus, we position Tshz1 in the transcriptional network of maturing ß-cells and suggest that its dysregulation could contribute to the islet phenotype of human type 2 diabetes.
Assuntos
Diferenciação Celular/genética , Diabetes Mellitus Tipo 2/metabolismo , Células Secretoras de Insulina/metabolismo , Organogênese/genética , Pâncreas/metabolismo , Proteínas Repressoras/metabolismo , Animais , Diabetes Mellitus Tipo 2/genética , Redes Reguladoras de Genes , Proteínas de Homeodomínio/genética , Proteínas de Homeodomínio/metabolismo , Humanos , Insulina/metabolismo , Células Secretoras de Insulina/citologia , Lectinas Tipo C/genética , Lectinas Tipo C/metabolismo , Camundongos , Proteínas de Transporte de Monossacarídeos/genética , Proteínas de Transporte de Monossacarídeos/metabolismo , Pâncreas/citologia , Proteínas Repressoras/genética , Transativadores/genética , Transativadores/metabolismoRESUMO
Islet-1 (Isl-1) is essential for the survival and ensuing differentiation of pancreatic endocrine progenitors. Isl-1 remains expressed in all adult pancreatic endocrine lineages; however, its specific function in the postnatal pancreas is unclear. Here we determine whether Isl-1 plays a distinct role in the postnatal ß-cell by performing physiological and morphometric analyses of a tamoxifen-inducible, ß-cell-specific Isl-1 loss-of-function mouse: Isl-1(L/L); Pdx1-CreER(Tm). Ablating Isl-1 in postnatal ß-cells reduced glucose tolerance without significantly reducing ß-cell mass or increasing ß-cell apoptosis. Rather, islets from Isl-1(L/L); Pdx1-CreER(Tm) mice showed impaired insulin secretion. To identify direct targets of Isl-1, we integrated high-throughput gene expression and Isl-1 chromatin occupancy using islets from Isl-1(L/L); Pdx1-CreER(Tm) mice and ßTC3 insulinoma cells, respectively. Ablating Isl-1 significantly affected the ß-cell transcriptome, including known targets Insulin and MafA as well as novel targets Pdx1 and Slc2a2. Using chromatin immunoprecipitation sequencing and luciferase reporter assays, we found that Isl-1 directly occupies functional regulatory elements of Pdx1 and Slc2a2. Thus Isl-1 is essential for postnatal ß-cell function, directly regulates Pdx1 and Slc2a2, and has a mature ß-cell cistrome distinct from that of pancreatic endocrine progenitors.