RESUMO
The growth and function of organs such as pancreatic islets adapt to meet physiological challenges and maintain metabolic balance, but the mechanisms controlling these facultative responses are unclear. Diabetes in patients treated with calcineurin inhibitors such as cyclosporin A indicates that calcineurin/nuclear factor of activated T-cells (NFAT) signalling might control adaptive islet responses, but the roles of this pathway in beta-cells in vivo are not understood. Here we show that mice with a beta-cell-specific deletion of the calcineurin phosphatase regulatory subunit, calcineurin b1 (Cnb1), develop age-dependent diabetes characterized by decreased beta-cell proliferation and mass, reduced pancreatic insulin content and hypoinsulinaemia. Moreover, beta-cells lacking Cnb1 have a reduced expression of established regulators of beta-cell proliferation. Conditional expression of active NFATc1 in Cnb1-deficient beta-cells rescues these defects and prevents diabetes. In normal adult beta-cells, conditional NFAT activation promotes the expression of cell-cycle regulators and increases beta-cell proliferation and mass, resulting in hyperinsulinaemia. Conditional NFAT activation also induces the expression of genes critical for beta-cell endocrine function, including all six genes mutated in hereditary forms of monogenic type 2 diabetes. Thus, calcineurin/NFAT signalling regulates multiple factors that control growth and hallmark beta-cell functions, revealing unique models for the pathogenesis and therapy of diabetes.
Assuntos
Calcineurina/metabolismo , Células Secretoras de Insulina/citologia , Células Secretoras de Insulina/metabolismo , Fatores de Transcrição NFATC/metabolismo , Transdução de Sinais , Envelhecimento , Animais , Proliferação de Células , Diabetes Mellitus Tipo 2/genética , Diabetes Mellitus Tipo 2/metabolismo , Hiperinsulinismo/genética , Hiperinsulinismo/metabolismo , Camundongos , Camundongos Knockout , Fatores de Transcrição NFATC/genética , Monoéster Fosfórico Hidrolases/química , Monoéster Fosfórico Hidrolases/genética , Monoéster Fosfórico Hidrolases/metabolismo , Subunidades Proteicas/deficiência , Subunidades Proteicas/genética , Transporte ProteicoRESUMO
Identification of signaling pathways that maintain and promote adult pancreatic islet functions will accelerate our understanding of organogenesis and improve strategies for treating diseases like diabetes mellitus. Previous work has implicated transforming growth factor-beta (TGF-beta) signaling as an important regulator of pancreatic islet development, but has not established whether this signaling pathway is required for essential islet functions in the adult pancreas. Here we describe a conditional system for expressing Smad7, a potent inhibitor of TGF-beta signaling, to identify distinct roles for this pathway in adult and embryonic beta cells. Smad7 expression in Pdx1+ embryonic pancreas cells resulted in striking embryonic beta cell hypoplasia and neonatal lethality. Conditional expression of Smad7 in adult Pdx1+ cells reduced detectable beta cell expression of MafA, menin, and other factors that regulate beta cell function. Reduced pancreatic insulin content and hypoinsulinemia produced overt diabetes that was fully reversed upon resumption of islet TGF-beta signaling. Thus, our studies reveal that TGF-beta signaling is crucial for establishing and maintaining defining features of mature pancreatic beta cells.
Assuntos
Diabetes Mellitus/metabolismo , Regulação da Expressão Gênica no Desenvolvimento/genética , Ilhotas Pancreáticas/metabolismo , Transdução de Sinais , Proteína Smad7/metabolismo , Fator de Crescimento Transformador beta/metabolismo , Envelhecimento/fisiologia , Animais , Proteínas Morfogenéticas Ósseas/deficiência , Proteínas Morfogenéticas Ósseas/genética , Proteínas Morfogenéticas Ósseas/metabolismo , Diferenciação Celular , Diabetes Mellitus/genética , Diabetes Mellitus/patologia , Embrião de Mamíferos/embriologia , Embrião de Mamíferos/metabolismo , Fatores de Diferenciação de Crescimento , Proteínas de Homeodomínio/genética , Proteínas de Homeodomínio/metabolismo , Ilhotas Pancreáticas/patologia , Fatores de Transcrição Maf Maior/metabolismo , Camundongos , Camundongos Transgênicos , Proteína Smad7/genética , Transativadores/genética , Transativadores/metabolismoRESUMO
Identification of endogenous signals that regulate expansion and maturation of organ-specific progenitor cells is a major goal in studies of organ development. Here we provide evidence that growth differentiation factor 11 (GDF11), a member of the TGF-beta ligand family, governs the number and maturation of islet progenitor cells in mouse pancreas development. Gdf11 is expressed in embryonic pancreatic epithelium during formation of islet progenitor cells that express neurogenin 3. Mice deficient for Gdf11 harbor increased numbers of NGN3+ cells, revealing that GDF11 negatively regulates production of islet progenitor cells. Despite a marked expansion of these NGN3+ islet progenitors, mice lacking Gdf11 have reduced beta-cell numbers and evidence of arrested beta-cell development, indicating that GDF11 is also required for beta-cell maturation. Similar precursor and islet cell phenotypes are observed in mice deficient for SMAD2, an intracellular signaling factor activated by TGF-beta signals. Our data suggest that Gdf11 and Smad2 regulate islet cell differentiation in parallel to the Notch pathway, which previously has been shown to control development of NGN3+ cells. Thus, our studies reveal mechanisms by which GDF11 regulates the production and maturation of islet progenitor cells in pancreas development.