Neurog3 misexpression in adult pancreatic duct cells reveals their plasticity

Le pancréas est constitué de deux tissus : exocrine et endocrine. Le tissu endocrine est organisé en îlots de Langerhans, comprenant 5 sous-types cellulaires dont les deux principaux (α et β) sécrètent respectivement le glucagon et l’insuline. Le diabète de type 1 est une maladie auto-immune caractérisée par la perte des cellules β et donc une hyperglycémie chronique. Les thérapies actuelles sont efficaces mais contraignantes, amenant une partie de la recherche actuelle à déchiffrer les mécanismes de la genèse des cellules β et/ou de leur régénération pour tenter d’établir des thérapies alternatives. Des études ont permis de caractériser la cascade de facteurs de transcription différentiant les cellules progénitrices pancréatiques durant le développement, dont Neurog3 spécifiant le lignage endocrine et le gène Pax4 favorisant le lignage β. De précédents résultats nous ont amenés à établir l’hypothèse que les cellules canalaires pancréatiques contiendraient une source potentielle de précurseurs, qui par la réexpression de Neurog3 pourraient devenir endocrine, ce que nous avons analysé in vivo après avoir généré les souris transgéniques correspondantes. Nous avons observé un accroissement considérable de la taille des îlots, dû à une augmentation du nombre de chaque sous-type cellulaire endocrine. Nous démontrons que ces cellules endocrines supplémentaires ont bien une origine canalaires, tandis que des études physiologiques indiquent une réponse fonctionnelle de l’insuline suite à une injection de glucose. Finalement, nos analyses apportent également la preuve que le devenir de ces nouvelles cellules endocrines peut être modulé en agissant sur l’activité du gène Pax4.The pancreas can be divided into two tissue types: exocrine and endocrine. The endocrine tissue is organized into clusters of cells named islets of Langerhans, comprising five cell subtypes of which the two main (α and β) secrete respectively glucagon and insulin. Type 1 diabetes is an auto-immune disease resulting in the loss of pancreatic β-cells and, consequently, in chronic hyperglycemia. Current therapies are efficient but remain highly binding, leading current research to aim at deciphering the β-cell genesis and/or regeneration to potentially establish new therapies. Many studies characterized the specific cascade of transcription factors differentiating pancreatic progenitor cells during development, including Neurog3 specifying the endocrine lineage and Pax4 favoring the β-cell lineage. Previous results obtained in the lab led us to establish the hypothesis that pancreatic ducts may contain a potential source of progenitor cells, which could become endocrine cells through re-expression of Neurog3. Thus, we investigated the consequences of the ectopic misexpression of Neurog3 in pancreatic duct cells in vivo. Using this strategy, we observed a dramatic increase in islet size, due to an augmentation in all endocrine cells types. Lineage tracing allowed us to demonstrate that the new endocrine cells have a ductal origin, while physiological studies displayed functional insulin response upon a glucose bolus. Finally, our analyses also demonstrated that the fate of these newly generated endocrine cells could be modulated by acting on the Pax4 gene

β-Cell Replacement Strategies: The Increasing Need for a “β-Cell Dogma”

Type 1 diabetes is an auto-immune disease resulting in the loss of pancreatic β-cells and, consequently, in chronic hyperglycemia. Insulin supplementation allows diabetic patients to control their glycaemia quite efficiently, but treated patients still display an overall shortened life expectancy and an altered quality of life as compared to their healthy counterparts. In this context and due to the ever increasing number of diabetics, establishing alternative therapies has become a crucial research goal. Most current efforts therefore aim at generating fully functional insulin-secreting β-like cells using multiple approaches. In this review, we screened the literature published since 2011 and inventoried the selected markers used to characterize insulin-secreting cells generated by in vitro differentiation of stem/precursor cells or by means of in vivo transdifferentiation. By listing these features, we noted important discrepancies when comparing the different approaches for the initial characterization of insulin-producing cells as true β-cells. Considering the recent advances achieved in this field of research, the necessity to establish strict guidelines has become a subject of crucial importance, especially should one contemplate the next step, which is the transplantation of in vitro or ex vivo generated insulin-secreting cells in type 1 diabetic patients

[Reprogramming pancreatic cells to β cells].

International audienceType 1 diabetes (T1DM) is a common metabolic disorder affecting an ever-increasing number of patients worldwide. T1DM is caused by the selective destruction of pancreatic insulin-producing β-cells by the immune system. Such loss results in chronic hyperglycemia and could induce a number of cardio-vascular complications. Despite the classical insulin-based therapy, compared to healthy people, patients with T1DM display a shortened life expectancy due to the treatment's inability to strictly regulate glycemic levels. An alternative therapy involves pancreatic islet transplantation but the shortage of donors and the required immuno-suppressive treatments limit the widespread use of this approach. Therefore, the search of new approaches to generate functional β-cells is of growing interest. In this review, we describe several novel strategies aiming at the conversion of diverse pancreatic cells into β-cells, such as acinar, ductal, and endocrine cells. Clearly, such promising results could open new research avenues in the context of type 1 diabetes research

Induction of multiple cycles of pancreatic β-cell replacement.

International audienc

GABA signaling stimulates α-cell-mediated β-like cell neogenesis

Diabetes is a chronic and progressing disease, the number of patients increasing exponentially, especially in industrialized countries. Regenerating lost insulin-producing cells would represent a promising therapeutic alternative for most diabetic patients. To this end, using the mouse as a model, we reported that GABA, a food supplement, could induce insulin-producing beta-like cell neogenesis offering an attractive and innovative approach for diabetes therapeutics

<i>Neurog3</i> misexpression unravels mouse pancreatic ductal cell plasticity

<div><p>In the context of type 1 diabetes research and the development of insulin-producing β-cell replacement strategies, whether pancreatic ductal cells retain their developmental capability to adopt an endocrine cell identity remains debated, most likely due to the diversity of models employed to induce pancreatic regeneration. In this work, rather than injuring the pancreas, we developed a mouse model allowing the inducible misexpression of the proendocrine gene <i>Neurog3</i> in ductal cells <i>in vivo</i>. These animals developed a progressive islet hypertrophy attributed to a proportional increase in all endocrine cell populations. Lineage tracing experiments indicated a continuous neo-generation of endocrine cells exhibiting a ductal ontogeny. Interestingly, the resulting supplementary β-like cells were found to be functional. Based on these findings, we suggest that ductal cells could represent a renewable source of new β-like cells and that strategies aiming at controlling the expression of <i>Neurog3</i>, or of its molecular targets/co-factors, may pave new avenues for the improved treatments of diabetes.</p></div

Lineage tracing experiments unravel the conversion of ductal cells into endocrine cells upon the sole <i>Neurog3</i> misexpression.

<p>(<b>A</b>) Taking advantage of the β-galactosidase tracer, we monitored the fate of the ductal cells ectopically expressing <i>Neurog3</i>. X-Gal staining reveals β-galactosidase-positive cells (previously ductal cells) within the islet of Langerhans (outlined with red lines) of Tam-treated HNFN3OE mice. (<b>B</b>) Quantitative RT-PCR analyses confirm the presence of <i>β-galactosidase</i> mRNA in the transcriptome of islets isolated from Tam-treated animals (n = 6 animals for each condition). Statistics were performed using the Mann-Whitney test (<b>C-D</b>) Immunohistochemical analyses combining β-galactosidase and insulin detection. While control pancreata are negative for β-galactosidase (<b>C</b>), their Tam-treated counterparts display cells positive for both insulin and β-galactosidase (<b>D</b>), indicating duct-to-endocrine cell conversion. Note that the apparent staining in the exocrine tissue is artefactual and caused by the antibody used. (<b>E-F</b>) Accordingly, several glucagon⁺ (<b>E</b>) or somatostatin⁺ (<b>F</b>) cells are also found labeled with the ductal cell tracer, β-galactosidase.</p