Dendritic cells (DCs) and macrophages are critical to innate and adaptive immunity to the intestinal bacterial microbiota. Here, we identify a myeloid-derived mucosal DC in mice, which populates the ...entire lamina propria of the small intestine. Lamina propria DCs were found to depend on the chemokine receptor CX₃CR1 to form transepithelial dendrites, which enable the cells to directly sample luminal antigens. CX₃CR1 was also found to control the clearance of entero-invasive pathogens by DCs. Thus, CX₃CR1-dependent processes, which control host interactions of specialized DCs with commensal and pathogenic bacteria, may regulate immunological tolerance and inflammation.
Immune cells were recently shown to support β-cells and insulin secretion. However, little is known about how islet immune cells are regulated to maintain glucose homeostasis. Administration of ...various cytokines, including Interleukin-33 (IL-33), was shown to influence β-cell function. However, the role of endogenous, locally produced IL-33 in pancreatic function remains unknown. Here, we show that IL-33, produced by pancreatic pericytes, is required for glucose homeostasis.
To characterize pancreatic IL-33 production, we employed gene expression, flow cytometry, and immunofluorescence analyses. To define the role of this cytokine, we employed transgenic mouse systems to delete the
gene selectively in pancreatic pericytes, in combination with the administration of recombinant IL-33. Glucose response was measured
and
, and morphometric and molecular analyses were used to measure β-cell mass and gene expression. Immune cells were analyzed by flow cytometry.
Our results show that pericytes are the primary source of IL-33 in the pancreas. Mice lacking pericytic IL-33 were glucose intolerant due to impaired insulin secretion. Selective loss of pericytic IL-33 was further associated with reduced T and dendritic cell numbers in the islets and lower retinoic acid production by islet macrophages.
Our study demonstrates the importance of local, pericytic IL-33 production for glucose regulation. Additionally, it proposes that pericytes regulate islet immune cells to support β-cell function in an IL-33-dependent manner. Our study reveals an intricate cellular network within the islet niche.
The developing pancreatic epithelium gives rise to all endocrine and exocrine cells of the mature organ. During organogenesis, the epithelial cells receive essential signals from the overlying ...mesenchyme. Previous studies, focusing on ex vivo tissue explants or complete knockout mice, have identified an important role for the mesenchyme in regulating the expansion of progenitor cells in the early pancreas epithelium. However, due to the lack of genetic tools directing expression specifically to the mesenchyme, the potential roles of this supporting tissue in vivo, especially in guiding later stages of pancreas organogenesis, have not been elucidated. We employed transgenic tools and fetal surgical techniques to ablate mesenchyme via Cre-mediated mesenchymal expression of Diphtheria Toxin (DT) at the onset of pancreas formation, and at later developmental stages via in utero injection of DT into transgenic mice expressing the Diphtheria Toxin receptor (DTR) in this tissue. Our results demonstrate that mesenchymal cells regulate pancreatic growth and branching at both early and late developmental stages by supporting proliferation of precursors and differentiated cells, respectively. Interestingly, while cell differentiation was not affected, the expansion of both the endocrine and exocrine compartments was equally impaired. To further elucidate signals required for mesenchymal cell function, we eliminated β-catenin signaling and determined that it is a critical pathway in regulating mesenchyme survival and growth. Our study presents the first in vivo evidence that the embryonic mesenchyme provides critical signals to the epithelium throughout pancreas organogenesis. The findings are novel and relevant as they indicate a critical role for the mesenchyme during late expansion of endocrine and exocrine compartments. In addition, our results provide a molecular mechanism for mesenchymal expansion and survival by identifying β-catenin signaling as an essential mediator of this process. These results have implications for developing strategies to expand pancreas progenitors and β-cells for clinical transplantation.
The maintenance and expansion of β-cell mass rely on their proliferation, which reaches its peak in the neonatal stage. β-cell proliferation was found to rely on cells of the islet microenvironment. ...We hypothesized that pericytes, which are components of the islet vasculature, support neonatal β-cell proliferation.
To test our hypothesis, we combined in vivo and in vitro approaches. Briefly, we used a Diphtheria toxin-based transgenic mouse system to specifically deplete neonatal pancreatic pericytes in vivo. We further cultured neonatal pericytes isolated from the neonatal pancreas and combined the use of a β-cell line and primary cultured mouse β-cells.
Our findings indicate that neonatal pancreatic pericytes are required and sufficient for β-cell proliferation. We observed impaired proliferation of neonatal β-cells upon in vivo depletion of pancreatic pericytes. Furthermore, exposure to pericyte-conditioned medium stimulated proliferation in cultured β-cells.
This study introduces pancreatic pericytes as regulators of neonatal β-cell proliferation. In addition to advancing current understanding of the physiological β-cell replication process, these findings could facilitate the development of protocols aimed at expending these cells as a potential cure for diabetes.
•Pancreatic pericytes support proliferation of neonatal β-cells in vivo.•Factors produced by neonatal pancreatic pericytes stimulate adult β-cell proliferation in vitro.•Pericyte-dependent β-cell expansion requires β1-integrin signaling.
NF-κB is a well-characterized transcription factor, widely known for its roles in inflammation and immune responses, as well as in control of cell division and apoptosis. However, its function in ...β-cells is still being debated, as it appears to depend on the timing and kinetics of its activation. To elucidate the temporal role of NF-κB in vivo, we have generated two transgenic mouse models, the ToIβ and NOD/ToIβ mice, in which NF-κB activation is specifically and conditionally inhibited in β-cells. In this study, we present a novel function of the canonical NF-κB pathway during murine islet β-cell development. Interestingly, inhibiting the NF-κB pathway in β-cells during embryogenesis, but not after birth, in both ToIβ and NOD/ToIβ mice, increased β-cell turnover, ultimately resulting in a reduced β-cell mass. On the NOD background, this was associated with a marked increase in insulitis and diabetes incidence. While a robust nuclear immunoreactivity of the NF-κB p65-subunit was found in neonatal β-cells, significant activation was not detected in β-cells of either adult NOD/ToIβ mice or in the pancreata of recently diagnosed adult T1D patients. Moreover, in NOD/ToIβ mice, inhibiting NF-κB post-weaning had no effect on the development of diabetes or β-cell dysfunction. In conclusion, our data point to NF-κB as an important component of the physiological regulatory circuit that controls the balance of β-cell proliferation and apoptosis in the early developmental stages of insulin-producing cells, thus modulating β-cell mass and the development of diabetes in the mouse model of T1D.
Glucose homeostasis relies on tightly regulated insulin secretion from pancreatic beta-cells, and its loss in diabetes is associated with the dysfunction of these cells. Beta-cells reside in the ...islets of Langerhans, which are highly vascularized by a dense capillary network comprised of endothelial cells and pericytes. While the requirement of the endothelium for the proper pancreatic function is well established, the role of pancreatic pericytes has only recently begun to unveil. Recent studies described multiple roles for pancreatic pericytes in glucose homeostasis, highlighting their function as both regulators of islet blood flow and as a source of critical signals that support proper beta-cell function and mass. Furthermore, recent findings point to the contribution of pericytic abnormalities to beta-cell dysfunction in type 2 diabetes, implicating the involvement of pancreatic pericytes in both the initiation and the progression of this disease. This newly gained data implicate pancreatic pericytes as critical components of the cellular network required for glucose regulation.
Current approaches in human embryonic stem cell (hESC) to pancreatic beta cell differentiation have largely been based on knowledge gained from developmental studies of the epithelial pancreas, while ...the potential roles of other supporting tissue compartments have not been fully explored. One such tissue is the pancreatic mesenchyme that supports epithelial organogenesis throughout embryogenesis. We hypothesized that detailed characterization of the pancreatic mesenchyme might result in the identification of novel factors not used in current differentiation protocols. Supplementing existing hESC differentiation conditions with such factors might create a more comprehensive simulation of normal development in cell culture. To validate our hypothesis, we took advantage of a novel transgenic mouse model to isolate the pancreatic mesenchyme at distinct embryonic and postnatal stages for subsequent proteomic analysis. Refined sample preparation and analysis conditions across four embryonic and prenatal time points resulted in the identification of 21,498 peptides with high-confidence mapping to 1,502 proteins. Expression analysis of pancreata confirmed the presence of three potentially important factors in cell differentiation: Galectin-1 (LGALS1), Neuroplastin (NPTN), and the Laminin α-2 subunit (LAMA2). Two of the three factors (LGALS1 and LAMA2) increased expression of pancreatic progenitor transcript levels in a published hESC to beta cell differentiation protocol. In addition, LAMA2 partially blocks cell culture induced beta cell dedifferentiation. Summarily, we provide evidence that proteomic analysis of supporting tissues such as the pancreatic mesenchyme allows for the identification of potentially important factors guiding hESC to pancreas differentiation.
•The pancreas develops from the embryonic foregut endoderm.•Pancreas organogenesis depends on interactions between endoderm-derived epithelial cells and mesenchymal cells.•The mesenchyme provides ...cues to support the survival and expansion of pancreatic progenitors and differentiated cells.•The main approaches used to study mesenchymal-epithelial interactions are explant cultures and transgenic mouse systems.•Mesenchymal cues promote the generation of insulin-producing cells from stem cells as a potential therapy for diabetes.
Pancreas organogenesis depends on proper interactions of endoderm-derived epithelial cells, which will form the exocrine and endocrine cells of the adult organ, with their surrounding mesenchymal layer. Research on the role of pancreatic mesenchyme, pioneered by Golosow and Grobstein in the 1960’s, revealed these cells regulate multiple events during pancreas development. Still, much is unknown regards the molecular basis of epithelial-mesenchymal interactions in this process. Here, we review in vivo and ex vivo approaches to study mesenchymal requirements for mammal pancreas organogenesis, and how gained knowledge is being translated toward the development of cell replacement therapy for diabetes.
β-Cells rely on the islet microenvironment for their functionality and mass. Pericytes, along with endothelial cells, make up the dense islet capillary network. However, although the role of ...endothelial cells in supporting β-cell homeostasis has been vastly investigated, the role of pericytes remains largely unknown. Here, we focus on contribution of pericytes to β-cell function. To this end, we used a transgenic mouse system that allows diphtheria toxin-based depletion of pericytes. Our results indicate that islets depleted of their pericytes have reduced insulin content and expression. Additionally, isolated islets displayed impaired glucose-stimulated insulin secretion, accompanied by a reduced expression of genes associated with β-cell function. Importantly, reduced levels of the transcription factors MafA and Pdx1 point to β-cell dedifferentiation in the absence of pericytes. Ex vivo depletion of pericytes in isolated islets resulted in a similar impairment of gene expression, implicating their direct, blood flow-independent role in maintaining β-cell maturity. To conclude, our findings suggest that pericytes are pivotal components of the islet niche, which are required for β-cell maturity and functionality. Abnormalities of islet pericytes, as implicated in type 2 diabetes, may therefore contribute to β-cell dysfunction and disease progression.
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