Novel strategies in diabetes therapy would obviously benefit from the use of beta (beta) cell stem/progenitor cells. However, whether or not adult beta cell progenitors exist is one of the most controversial issues in today's diabetes research. Guided by the expression of Neurogenin 3 (Ngn3), the earliest islet cell-specific transcription factor in embryonic development, we show that beta cell progenitors can be activated in injured adult mouse pancreas and are located in the ductal lining. Differentiation of the adult progenitors is Ngn3 dependent and gives rise to all islet cell types, including glucose responsive beta cells that subsequently proliferate, both in situ and when cultured in embryonic pancreas explants. Multipotent progenitor cells thus exist in the pancreas of adult mice and can be activated cell autonomously to increase the functional beta cell mass by differentiation and proliferation rather than by self-duplication of pre-existing beta cells only.

Identifying pathways for b-cell generation is essential for cell therapy in diabetes. We investigated the potential of 17b-estradiol (E 2 ) and estrogen receptor (ER) signaling for stimulating b-cell generation during embryonic development and in the severely injured adult pancreas. E 2 concentration, ER activity, and number of ERa transcripts were enhanced in the pancreas injured by partial duct ligation (PDL) along with nuclear localization of ERa in b-cells. PDL-induced proliferation of b-cells depended on aromatase activity. The activation of Neurogenin3 (Ngn3) gene expression and b-cell growth in PDL pancreas were impaired when ERa was turned off chemically or genetically (ERa 2/2 ), whereas in situ delivery of E 2 promoted b-cell formation. In the embryonic pancreas, b-cell replication, number of Ngn3 + progenitor cells, and expression of key transcription factors of the endocrine lineage were decreased by ERa inactivation. The current study reveals that E 2 and ERa signaling can drive b-cell replication and formation in mouse pancreas.Decreased functional b-cell mass is the major cause for hyperglycemia in diabetes. Restoration of the endogenous b-cell mass as a therapeutic strategy, however, requires a better understanding of signaling pathways that control b-cell growth and differentiation. Embryonic b-cells are generated by a developmental program executed through the timed action of a number of key transcription factors among which Neurogenin3 (Ngn3) is key for endocrine specification. Ngn3 + cells delaminate from pancreatic epithelium, are mitotically quiescent, and give rise to endocrine cells. Ngn3 cells appear maximally competent for driving b-cell formation at embryonic day (E) 14.5. Formed b-cells expand through self-replication, already evident at E18.5, and continue into early postnatal life (1). Also in adult mice with severely injured pancreas by partial duct ligation (PDL), Ngn3 + cells are generated near duct epithelium and can differentiate into b-cells (2). b-Cells are vastly generated through replication in PDL (3,4), but some derive from acinar (5) and duct (6) cells, apparently through an Ngn3 + stage (2,5) as in embryonic pancreas. How the numbers of Ngn3 + endocrine progenitors and replicating b-cells are controlled in the embryonic or mature pancreas is uncertain. Identifying factors that control these processes and manipulating them may be of therapeutic advantage. What is known is that 17b-estradiol (E 2 ) enhances b-cell survival and glycemic control in various animal models (7,8) by signaling through estrogen receptor (ER) a (8,9) and/or ERb (10).However, little is known about the importance of estrogen and ER signaling for b-cell proliferation and differentiation. So far, no in vivo effects on b-cell formation have been reported for the ER antagonist tamoxifen (TAM), although this compound is used to conditionally activate Cre recombinase activity (Cre ERT ) in genetic

Pancreas injury by partial duct ligation (PDL) activates a healing response, encompassing β-cell neogenesis and proliferation. Macrophages (M s)were recently shown to promote β-cell proliferation after PDL, but they remain poorly characterized. We assessed myeloid cell diversity and the factors driving myeloid cell dynamics following acute pancreas injury by PDL. In naive and sham-operated pancreas, the myeloid cell compartment consisted mainly of two distinct tissue-resident M types, designated MHC-II lo and MHC-II hi M s, the latter being predominant. MHC-II lo and MHC-II hi pancreas M s differed at the molecular level, with MHC-II lo M s being more M2-activated. After PDL, there was an early surge of Ly6C hi monocyte infiltration in the pancreas, followed by a transient MHC-II lo M peak and ultimately a restoration of the MHC-II hi M -dominated steadystate equilibrium. These intricate M dynamics in PDL pancreas depended on monocyte recruitment by C-C chemokine receptor 2 and macrophage-colony stimulating factor receptor as well as on macrophage-colony stimulating factor receptor-dependent local M proliferation. Functionally, MHC-II lo M s were more angiogenic. We further demonstrated that, at least in C-C chemokine receptor 2-KO mice, tissue M s, rather than Ly6C hi monocyte-derived M s, contributed to β-cell proliferation. Together, our study fully characterizes the M subsets in the pancreas and clarifies the complex dynamics of M s after PDL injury.Keywords: M activation r M heterogeneity r M proliferation r Pancreas inflammation Additional supporting information may be found in the online version of this article at the publisher's web-site Correspondence: Prof. Harry Heimberg and Prof. Jo A. Van Ginderachter e-mail: harry.heimberg@vub.ac.be e-mail: jvangind@vub.ac.be * These authors contributed equally to this study as first co-authors. * * These authors contributed equally to this study as senior co-authors.C 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu Eur. J. Immunol. 2015. 45: 1482-1493 Innate immunity 1483Introduction M s display a tremendous plasticity in vivo depending on their microenvironment. Their activation status has been described using the conceptual framework of M1 (classical) and M2 (alternative) activation [1], although this model oversimplifies their true plasticity. In addition to their role as immune cells, the trophic role of M s during development, tissue repair, and regeneration is becoming increasingly appreciated [1,2]. Hence, efforts are being made to dissect specialized M subpopulations and to trace their origin in situations of sterile inflammation. Although tissueresident M s were traditionally believed to originate from bloodborne monocytes, recent evidence shows that such M s develop prenatally from dedicated precursors [3,4]. During adulthood, the pool of tissue-resident M s is maintained by low-level proliferation under steady-state [5] and can expand by enhanced in situ proliferation during pathologies [6][7][8][9]. Moreover, during sterile inflammat...

Diabetes mellitus is a pandemic metabolic disorder that results from either the autoimmune destruction or the dysfunction of insulin-producing pancreatic beta cells. A promising cure is beta cell replacement through the transplantation of islets of Langerhans. However, donor shortage hinders the widespread implementation of this therapy. Human pluripotent stem cells, including embryonic stem cells and induced pluripotent stem cells, represent an attractive alternative beta cell source for transplantation. Although major advances over the past two decades have led to the generation of stem cell-derived beta-like cells that share many features with genuine beta cells, producing fully mature beta cells remains challenging. Here, we review the current status of beta cell differentiation protocols and highlight specific challenges that are associated with producing mature beta cells. We address the challenges and opportunities that are offered by monogenic forms of diabetes. Finally, we discuss the remaining hurdles for clinical application of stem cell-derived beta cells and the status of ongoing clinical trials.

Macrophages are classically considered detrimental for pancreatic b-cell survival and function, thereby contributing to b-cell failure in both type 1 (T1D) and 2 (T2D) diabetes mellitus. In addition, adipose tissue macrophages negatively influence peripheral insulin signaling and promote obesityinduced insulin resistance in T2D. In contrast, recent data unexpectedly uncovered that macrophages are not only able to protect b cells during pancreatitis but also to orchestrate b-cell proliferation and regeneration after b-cell injury. Moreover, by altering their activation state, macrophages are able to improve insulin resistance in murine models of T2D. This review will elaborate on current insights in macrophage heterogeneity and on the evolving role of pancreas macrophages during organogenesis, tissue injury, and repair. Additional identification of macrophage subtypes and of their secreted factors might ultimately translate into novel therapeutic strategies for both T1D and T2D. STEM CELLS TRANSLATIONAL MEDICINE 2015;4:555-563 SIGNIFICANCEDiabetes mellitus is a pandemic disease, characterized by severe acute and chronic complications. Macrophages have long been considered prime suspects in the pathogenesis of both type 1 and 2 diabetes mellitus. In this concise review, current insights in macrophage heterogeneity and on the, as yet, underappreciated role of alternatively activated macrophages in insulin sensing and b-cell development/repair are reported. Further identification of macrophage subtypes and of their secreted factors might ultimately translate into novel therapeutic strategies for diabetes mellitus.

It is generally accepted that vascularization and oxygenation of pancreatic islets are essential for the maintenance of an optimal β-cell mass and function and that signaling by vascular endothelial growth factor (VEGF) is crucial for pancreas development, insulin gene expression/secretion, and (compensatory) β-cell proliferation. A novel mouse model was designed to allow conditional production of human sFlt1 by β-cells in order to trap VEGF and study the effect of time-dependent inhibition of VEGF signaling on adult β-cell fate and metabolism. Secretion of sFlt1 by adult β-cells resulted in a rapid regression of blood vessels and hypoxia within the islets. Besides blunted insulin release, β-cells displayed a remarkable capacity for coping with these presumed unfavorable conditions: even after prolonged periods of blood vessel ablation, basal and stimulated blood glucose levels were only slightly increased, while β-cell proliferation and mass remained unaffected. Moreover, ablation of blood vessels did not prevent β-cell generation after severe pancreas injury by partial pancreatic duct ligation or partial pancreatectomy. Our data thus argue against a major role of blood vessels to preserve adult β-cell generation and function, restricting their importance to facilitating rapid and adequate insulin delivery.

Aims/hypothesis As current islet-transplantation protocols suffer from significant graft loss and dysfunction, strategies to sustain the long-term benefits of this therapy are required. Rapid and adequate oxygen and nutrient delivery by blood vessels improves islet engraftment and function. The present report evaluated a potentially beneficial effect of adult human blood outgrowth endothelial cells (BOEC) on islet graft vascularisation and function. Methods Human BOEC, 5×10 5 , were co-transplanted with a rat marginal-islet graft under the kidney capsule of hyperglycaemic NOD severe combined immunodeficiency (SCID) mice, and the effect on metabolic outcome was evaluated. Results Although vessel density remained unaffected, cotransplantation of islets with BOEC resulted in a significant and specific improvement of glycaemia and increased plasma C-peptide. Moreover, in contrast to control mice, BOEC recipients displayed reduced beta cell death and increases in body weight, beta cell proliferation and graft-vessel and beta cell volume. In vivo cell tracing demonstrated that BOEC remain at the site of transplantation and do not expand. The potential clinical applicability was underscored by the observed metabolic benefit of co-transplanting islets with BOEC derived from a type 1 diabetes patient. Conclusions/interpretation The present data support the use of autologous BOEC in translational studies that aim to improve current islet-transplantation protocols for the treatment of brittle type 1 diabetes.

Reciprocal signalling between the endothelium and the pancreatic epithelium is crucial for coordinated differentiation of the embryonic endocrine and exocrine pancreas. In the adult pancreas, islets depend on their dense capillary network to adequately respond to changes in plasma glucose levels. Vascular changes contribute to the onset and progression of both type 1 and type 2 diabetes. Impaired revascularisation of islets transplanted in individuals with type 1 diabetes is linked to islet graft failure and graft loss. This review summarises our understanding of the role of vascular endothelial growth factor-A (VEGF-A) and endothelial cells in beta cell development, physiology and disease. In addition, the therapeutic potential of modulating VEGF-A levels in beta and beta-like cells for transplantation is discussed.