Modulación de la masa de la célula alfa pancreática en un modelo murino de diabetes autoinmune experimental

La pérdida de la población beta pancreática y su regeneración han sido los temas centrales en la investigación de la diabetes mellitus tipo 1 (DM1). A pesar de la importancia de la célula alfa en la etiología y complicaciones de la DM1, existe poca información acerca de la masa de este tipo celular y su modulación en esta enfermedad. Además, investigaciones recientes han evidenciado que este tipo celular constituye un potencial reservorio celular para la regeneración de la población beta pancreática. El estudio de la regulación de la masa de la célula alfa en la DM1 constituye una importante fuente de información a la hora de elucidar los mecanismos que contribuyen a la fisiopatología de la DM y de crear estrategias para la regeneración de las células beta . En la presente tesis doctoral, se ha caracterizado la masa de la célula alfa así como los procesos que la modulan en dos estadios de diabetes autoinmune: diabetes temprana, una semana tras el comienzo de la enfermedad, y diabetes avanzada, cuatro semanas tras el debut. Para ello, se empleó el modelo murino inducible de diabetes autoinmune experimental RIPB7.1. Todos los animales diabéticos presentaron insulitis, hiperglicemia, hipoinsulinemia e hiperglucagonemia, junto a una marcada disminución del contenido total pancreático de insulina. En la diabetes temprana, la masa de la célula alfa y el contenido total pancreático de glucagón no presentaron cambios significativos respecto al grupo control, mientras que en la fase avanzada ambos parámetros sufrieron una disminución. En ambos estadios, el tamaño de la célula alfa, la proliferación y la neogénesis ductal se encontraron aumentados, mientras que la tasa de apoptosis en este tipo celular fue insignificante. El estudio de potenciales marcadores de transdiferenciación celular reveló un incremento, en ambos estadios, de la proporción de células bi-hormonales, positivas tanto para insulina como para glucagón, y de células positivas para glucagón con expresión del factor de transcripción PDX1, específico de las células beta. Estos hallazgos sugieren que la célula alfa experimenta diversos procesos de remodelación durante el transcurso de la diabetes autoinmune experimental, que puede estar ligado al mantenimiento de la población funcional de células alfa y/o a la regeneración de la población beta pancreática mediante transdiferenciación de las células alfa.Type 1 diabetes (T1D) studies have been focused on the loss and regenerative strategies of the pancreatic beta-cell population. Nevertheless, despite the role of the alpha-cell in the etiology and complications of T1D, there is a lack of knowledge about the modulation of the pancreatic alpha-cell mass in this pathology. Additionally, recent findings have presented the alpha-cell as a plastic cell with great potential as a reservoir for beta-cell regeneration. Thus, the understanding of the modulation of the alpha-cell mass could be of outstanding importance for the elucidation of contributive factors involved in T1D pathophysiology and for the implementation of beta-cell regeneration strategies. In the present doctoral thesis, the pancreatic alpha-cell mass and its modulatory processes have been characterized in two stages of the disease: early-onset, one-week after diabetes debut, and an advanced stage, four weeks after the onset. The transgenic RIP-B7.1 mice model of experimental autoimmune diabetes (EAD) was employed in this study. In both stages, diabetic mice presented insulitis, hyperglycaemia, hypoinsulinemia and high plasmatic glucagon levels along with a significative reduction of the pancreatic insulin content. In the early-onset of EAD, alpha-cell mass and pancreatic glucagon content were preserved, while both parameters were reduced in the advanced phase. At both diabetic phases, alpha-cell size, proliferation and ductal neogenesis were increased, whereas apoptosis was almost negligible. Interestingly, we found an increase in markers of alpha-cell transdifferentiation into beta-cells during EAD. In both the early-onset and advanced stages, diabetic mice showed an increase in the proportion of bihormonal cells positive for insulin and glucagon or positive for both glucagon and the beta-cell transcription factor PDX1. Our findings suggest that alpha-cell renewal mechanisms are up-regulated during the natural course of EAD, possibly as an attempt to maintain a functional alpha-cell population and/or to increase beta-cell regeneration via alpha-cell transdifferentiation

Pancreatic alpha-cell mass in the early-onset and advanced stage of a mouse model of experimental autoimmune diabetes

Most studies in type 1 diabetes (T1D) have focused on the loss of the pancreatic beta-cell population. However, despite the involvement of the alpha-cell in the aetiology and complications of T1D, little is known about the regulation of the pancreatic alpha-cell mass in this disease. The need for a better understanding of this process is further emphasized by recent findings suggesting that alpha-cells may constitute a potential reservoir for beta-cell regeneration. In this study, we characterized the pancreatic alpha-cell mass and its regulatory processes in the transgenic RIP-B7.1 mice model of experimental autoimmune diabetes (EAD). Diabetic mice presented insulitis, hyperglycaemia, hypoinsulinemia and hyperglucagonemia along with lower pancreatic insulin content. While alpha-cell mass and pancreatic glucagon content were preserved at the early-onset of EAD, both parameters were reduced in the advanced phase. At both stages, alpha-cell size, proliferation and ductal neogenesis were up-regulated, whereas apoptosis was almost negligible. Interestingly, we found an increase in the proportion of glucagon-containing cells positive for insulin or the beta-cell transcription factor PDX1. Our findings suggest that pancreatic alpha-cell renewal mechanisms are boosted during the natural course of EAD, possibly as an attempt to maintain the alpha-cell population and/or to increase beta-cell regeneration via alpha-cell transdifferentiation.This research was supported by grants from the Ministerio de Ciencia, Innovación y Universidades, Agencia Estatal de Investigación and Fondo Europeo de Desarrollo Regional (BFU2013-42789; BFU2017-86579-R; BFU2016-77125-R; BFU2017-83588-P), Generalitat Valenciana (PROMETEOII/2015/016) and the Juvenile Diabetes Research Foundation (17-2013-372 to B.R.G.). L.M. holds a Juan de la Cierva fellowship from the Ministerio de Ciencia, Innovación y Universidades (IJCI-2015-24482). CIBERDEM is an initiative of the Instituto de Salud Carlos III

GATA6 controls Insulin biosynthesis and secretion in Adult ß cell

GATA4 and GATA6 play essential, but redundant, roles in pancreas formation in mice, and GATA6 mutations cause pancreatic agenesis in humans. GATA6 mutations have also recently been linked to adult-onset diabetes, with subclinical or no exocrine insufficiency, suggesting an important role for GATA6 in human β-cell physiology. To investigate the role of GATA6 in the adult endocrine pancreas, we generated mice in which Gata6 is specifically inactivated in the pancreas. These mice develop glucose intolerance. Islets deficient in GATA6 activity display decreased insulin content and impaired insulin secretion. Gata6-deficient β-cells exhibit ultrastructural abnormalities, including increased immature insulin granules, swollen mitochondria, and disorganized endoplasmic reticulum. We also demonstrate that Pdx1 expression in adult β-cells depends on GATA sites in transgenic reporter mice and that loss of GATA6 greatly affects β-cell–specific gene expression. These findings demonstrate the essential role of GATA6 in β-cell functionL.V. was supported by a contract from Spanish Ministry of Economy and Competitiveness (RYC-2013-14533). E.R.-S. was supported by a “Juan de la Cierva” postdoctoral fellowship from Spanish Ministry of Economy and Competitiveness (IJCI-2014-19251). This work was supported by grants from ISCIII cofunded by Fondos FEDER (PI14/01015, RD/0019/0028, and RD16/0011/0034 to B.S. and PI14/ 0804 to A.R.) and “Ramón y Cajal” program from the Spanish Ministry of Economy and Competitiveness (PI14/0804, RYC-2013-14533 to A.R.). P.M. was supported by a Juan de la Cierva fellowship from Spanish Ministry of Science and Innovation and by a Stand-Alone Grant from the Austrian Science Fund (FWF P27361-B23). Work by I.Q. was supported by the Spanish Ministry of Economy and Competitiveness (BFU2016-77125-R). Work by D.A.C. was supported by the Nicolás Monardes program of Andalusian Ministry of Health (C-0015-2014) and the Andalusian Ministry of Science and Innovation (CTS-7478).Peer reviewe

Cortistatin regulates glucose-induced electrical activity and insulin secretion in mouse pancreatic beta-cells

Although there is growing evidence that cortistatin regulates several functions in different tissues, its role in the endocrine pancreas is not totally known. Here, we aim to study the effect of cortistatin on pancreatic beta-cells and glucose-stimulated insulin secretion (GSIS). Exposure of isolated mouse islets to cortistatin inhibited GSIS. This effect was prevented using a somatostatin receptor antagonist. Additionally, cortistatin hyperpolarized the membrane potential and reduced glucose-induced action potentials in isolated pancreatic beta-cells. Cortistatin did not modify ATP-dependent K+ (KATP) channel activity. In contrast, cortistatin increased the activity of a small conductance channel with characteristics of G protein-coupled inwardly rectifying K+ (GIRK) channels. The cortistatin effects on membrane potential and GSIS were largely reduced in the presence of a GIRK channel antagonist and by down-regulation of GIRK2 with small interfering RNA. Thus, cortistatin acts as an inhibitory signal for glucose-induced electrical activity and insulin secretion in the mouse pancreatic beta-cell.This work was supported by grants from the Ministerio de Economía, Industria y Competitividad (Spain), Agencia Estatal de Investigación (Spain) and Fondo Europeo de Desarrollo Regional (BFU2013-42789; BFU2017-86579-R; BFU2016-77125-R), Generalitat Valenciana (Spain, PROMETEOII/2015/016), CNPq (Brazil; 302261/2014-1; 306359/2017-0) and Junta de Andalucía (Spain; CTS-1406, BIO-0139). L.M. holds a Juan de la Cierva fellowship from the Ministry of Economy, Industry and Competitiveness (Spain; IJCI-2015-24482). CIBERDEM and CIBERobn are an initiative of the Instituto de Salud Carlos III (Spain)