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...