Mafa expression enhances glucose-responsive insulin secretion in neonatal rat beta cells

Abstract

Aim/hypothesis Neonatal beta cells lack glucose-stimulated insulin secretion and are thus functionally immature. We hypothesised that this lack of glucose responsiveness results from a generalised low expression of genes characteristic of mature functional beta cells. Important glucose-responsive transcription factors, Mafa and Pdx1, regulate genes involved in insulin synthesis and secretion, and have been implicated in late beta cell development. The aim of this study was to assess whether Mafa and/or Pdx1 regulates the postnatal functional maturation of beta cells. Methods By quantitative PCR we evaluated expression of these and other beta cell genes over the first month compared with adult. After infection with adenovirus expressing MAFA, Pdx1 or green fluorescent protein (Gfp), P2 rat islets were evaluated by RT-PCR and insulin secretion with static incubation and reverse haemolytic plaque assay (RHPA). Results At P2 most beta cell genes were expressed at about 10% of adult, but by P7 Pdx1 and Neurod1 no longer differ from adult; by contrast, Mafa expression remained significantly lower than adult through P21. Overexpression of Pdx1 increased Mafa, Neurod1, glucokinase (Gck) mRNA and insulin content but failed to enhance glucose responsiveness. Similar overexpression of MAFA resulted in increased Neurod1, Nkx6-1, Gck and Glp1r mRNAs and no change in insulin content but, importantly, acquisition of glucose-responsive insulin secretion. Both the percentage of secreting beta cells and the amount of insulin secreted per beta cell increased, approaching that of adult beta cells. Conclusions/interpretation In the process of functional maturation acquiring glucose-responsive insulin secretion, neonatal beta cells undergo a coordinated gene expression programme in which Mafa plays a crucial role.

Growth arrest specific protein (GAS) 6: a role in the regulation of proliferation and functional capacity of the perinatal rat beta cell

“…Accordingly, Mafa overexpression enhances GSIS in neonatal rat beta cells [15]. In addition, MAFA induces insulin expression via binding to the insulin promoter [30]; however, total insulin content in beta cells was not affected in Mafa-deficient (−/−) mice [14], similar to the findings of the current study.…”

“…Diet-induced changes in the temporal expression of transcription factors important for beta cell differentiation and maturation, such as v-maf musculoaponeurotic fibrosarcoma oncogene (MAF) homologue A and B and pancreatic duodenal homeobox-1 (PDX1), very likely play a role in development of the phenotype of LP offspring [14][15][16]. The regulation of these factors is, however, not fully clarified.…”

Maturation of Stem Cell-Derived Beta-cells Guided by the Expression of Urocortin 3

“…These factors have been demonstrated as necessary for beta-cell development and/or function [42,[46][47][48][73][74][75]. The genes listed here provide merely a small sample.…”

“…The expression of the transcription factors MAFA and MAFB changes markedly during the early postnatal period: MAFA expression is activated in most beta-cells perinatally, followed by the gradual loss of MAFB expression in the first postnatal weeks [80]. This shift from MAFB to MAFA expression is considered a defining transition for beta-cell maturation in mice [80], as MAFA is an important transcription factor for the generation and maintenance of mature beta-cell phenotype and normal islet architecture [74,75]. Enhanced postnatal expression of MAFA plays a crucial role in the acquisition of glucose-responsive insulin secretion [75].…”

“…This shift from MAFB to MAFA expression is considered a defining transition for beta-cell maturation in mice [80], as MAFA is an important transcription factor for the generation and maintenance of mature beta-cell phenotype and normal islet architecture [74,75]. Enhanced postnatal expression of MAFA plays a crucial role in the acquisition of glucose-responsive insulin secretion [75]. In an interesting example of specie differences between mouse and human islets, MAFB expression is not lost during human beta-cell maturation [81].…”