Hepatic gluconeogenesis is essential for maintenance of normal blood glucose concentrations and is regulated by opposing stimulatory (cyclic adenosine monophosphate, cAMP) and inhibitory (insulin) signaling pathways. The cAMP signaling pathway leads to phosphorylation of cAMP response element-binding (CREB) protein, resulting in recruitment of the coactivators CREB-binding protein (CBP) and p300 and subsequent activation of gluconeogenesis. Insulin signaling leads to phosphorylation of CBP at serine 436, a residue near its CREB-interacting domain, but it is unknown whether this event modulates cAMP signaling. Here, we show in vitro and in 'knock-in' mice that a mutant CBP (S436A) is aberrantly recruited to CREB protein, resulting in inappropriate activation of gluconeogenesis in the fed state and glucose intolerance resulting from increased hepatic glucose production. We propose that insulin signaling may directly regulate many cAMP signaling pathways at the transcriptional level by controlling CBP recruitment.

The cyclic AMP (cAMP) signaling pathway is central in ␤-cell gene expression and function. In the nucleus, protein kinase A (PKA) phosphorylates CREB, resulting in recruitment of the transcriptional coactivators p300 and CREB binding protein (CBP). CBP, but not p300, is phosphorylated at serine 436 in response to insulin action. CBP phosphorylation disrupts CREB-CBP interaction and thus reduces nuclear cAMP action. To elucidate the importance of the cAMP-PKA-CREB-CBP pathway in pancreatic ␤ cells specifically at the nuclear level, we have examined mutant mice lacking the insulin-dependent phosphorylation site of CBP. In these mice, the CREB-CBP interaction is enhanced in both the absence and presence of cAMP stimulation. We found that islet and ␤-cell masses were increased twofold, while pancreas weights were not different from the weights of wild-type littermates. ␤-Cell proliferation was increased both in vivo and in vitro in isolated islet cultures. Surprisingly, glucose-stimulated insulin secretion from perfused, isolated mutant islets was reduced. However, ␤-cell depolarization with KCl induced similar levels of insulin release from mutant and wild-type islets, indicating normal insulin synthesis and storage. In addition, transcripts of pgc1a, which disrupts glucose-stimulated insulin secretion, were also markedly elevated. In conclusion, sustained activation of CBP-responsive genes results in increased ␤-cell proliferation. In these ␤ cells, however, glucose-stimulated insulin secretion was diminished, resulting from concomitant CREB-CBP-mediated pgc1a gene activation.Under circumstances of increased metabolic demand, such as pregnancy (2, 4), or in insulin-resistant states (3, 30), islet and ␤-cell masses increase to meet metabolic requirements. The failure of ␤ cells to adapt to metabolic requirements results in relative insulin deficiency and diabetes mellitus. Within the pancreas, three conceptual mechanisms may lead to an increase in ␤-cell mass: (i) neogenesis from nonendocrine pancreatic tissue, such as pancreatic-duct epithelium (2, 3, 27, 28), pancreatic acinar cells (␤ cells derived from non-␤ cells) (3, 38, 39), or undifferentiated cells within the islet (1, 9, 15, 44); (ii) proliferation of ␤ cells (␤ cells derived from existing ␤ cells) (6,11,38); and (iii) reduced ␤-cell apoptosis in the context of normal ␤-cell turnover (5, 26).Cyclic AMP (cAMP) signaling is critical in the physiologic function of ␤ cells. This is exemplified by the effects of the incretin hormone glucagon-like peptide-1 (GLP-1), which improves glucose-stimulated insulin secretion from pancreatic ␤ cells, in part by raising intracellular cAMP levels (13,18,28). In pharmacologic studies, GLP-1 also stimulated PDX-1 gene expression in pancreatic-duct epithelial cells and stimulates proliferation of ␤ cells (5,7,22,26,38). Binding of GLP-1 to its ␤-cell receptor elevates intracellular cAMP levels; cAMP in turn binds to the regulatory subunit of protein kinase A (PKA) and releases the PKA catalytic subunit. Elevation of cAMP als...

Background Pancreatic islet transplantation has the potential to cure Type 1 Diabetes (T1D), a chronic lifelong disease, but its clinical applicability is limited by allograft rejection. Nuclear factor κB (NF-κB) is a transcription factor important for survival and differentiation of T cells. In this study, we tested whether NF-κB in T cells is required for the rejection of islet allografts. Methods Mice expressing a super-repressor form of NF-κB selectively in T cell (IκBαΔN-Tg mice) with or without the anti-apoptotic factor Bcl-xL, or mice with impaired TCR-and BCR-driven NF-κB activity (CARMA1-KO mice) were rendered diabetic and transplanted with islet allografts. Secondary skin transplantation in long-term acceptors of islet allografts was used to test for development of donor-specific tolerance. Immune infiltration of the transplanted islets was examined by immunofluorescence. TCR-transgenic CD4+ T cells were used to follow T cell priming and differentiation. Results Islet allograft survival was prolonged in IκBαΔN-Tg mice, although the animals did not develop donor-specific tolerance. Reduced NF-κB activity did not prevent T cell priming or differentiation but rather reduced survival of activated T cells, as transgenic expression of Bcl-xL restored islet allograft rejection in IκBαΔN-Tg mice. Abolishing TCR- and BCR-driven activation of NF-κB selectively via CARMA1 deficiency prevented T cell priming and islet allograft rejection. Conclusions Our data suggest that T cell-NF-κB plays an important role in the rejection of islet allografts. Targeting NF-κB selectively in lymphocytes appears a promising approach to facilitate acceptance of transplanted islets.

INTRODUCCIÓN: Las enfermedades retinianas hereditarias (IRD por sus siglas en inglés), son un grupo heterogéneo de enfermedades visualmente debilitantes causadas por la variación patogénica en proteínas críticas para la función retiniana. El diagnóstico temprano y preciso es necesario para las personas con IRD para permitir la toma de decisiones del paciente, identificar estudios clínicos adecuados, oportunidades de tratamiento y mejorar los resultados del paciente. METODOLOGÍA: Se realizó una revisión bibliográfica en las bases de datos PUBMED y MEDLINE de MeSH: “Inherited Retinal Diseases”, “mutations”, “molecular diagnosis”. Se utilizó filtros de búsqueda para obtener estudios denominados como ensayos clínicos o multicéntricos, estudios observaciones y de revisión. RESULTADOS: IRD siguen patrones de herencia simples (autosómica dominante, autosómico recesivo, ligado al cromosoma X y mitocondrial) y están asociados con mutaciones en 280 genes. La compleja base molecular de las IRD refleja una gama igualmente heterogénea de fenotipos clínicos, que varían en términos de compromiso del tipo de célula/tejido, inicio de la enfermedad, gravedad y progresión. CONCLUSIÓN: El reconocimiento de estas mutaciones y su adecuada aplicabilidad en la práctica clínica supone un avance extraordinario en el abordaje de esta patología.