A CCR2+ myeloid cell niche required for pancreatic β cell growth

The amazing impact of gut microbes on lifelong metabolic health

A new study published in Science1 reveals a crucial connection between our neonatal gut microbiota composition and the long-term health of our pancreas, specifically focusing on β-cell development and the subsequent lifelong impact microbe-induced β-cell expansion has on metabolic health, including prevention of, and even potential reversal of, diabetes.

Neonatal fungi promote lifelong metabolic health through macrophage-dependent β cell development

Loss of early-life microbial diversity is correlated with diabetes, yet mechanisms by which microbes influence disease remain elusive. We report a critical neonatal window in mice when microbiota disruption results in lifelong metabolic consequences stemming from reduced β cell development. We show evidence for the existence of a similar program in humans and identify specific fungi and bacteria that are sufficient for β cell growth. The microbiota also plays an important role in seeding islet-resident macrophages, and macrophage depletion during development reduces β cells. Candida dubliniensis increases β cells in a macrophage-dependent manner through distinctive cell wall composition and reduces murine diabetes incidence. Provision of C. dubliniensis after β cell ablation or antibiotic treatment improves β cell function. These data identify fungi as critical early-life commensals that promote long-term metabolic health.

Embryonic macrophages support endocrine commitment during human pancreatic differentiation

Organogenesis is a complex process that relies on a dynamic interplay between extrinsic factors originating from the microenvironment and tissue-specific intrinsic factors. For pancreatic endocrine cells, the local niche consists of acinar and ductal cells as well as neuronal, immune, endothelial, and stromal cells. Hematopoietic cells have been detected in human pancreas as early as 6 post-conception weeks, but whether they play a role during human endocrinogenesis remains unknown. To investigate this, we performed single-nucleus RNA sequencing (snRNA-seq) of the second-trimester human pancreas and identified a wide range of hematopoietic cells, including two distinct subsets of tissue-resident macrophages. Leveraging this discovery, we developed a co-culture system of human embryonic stem cell-derived endocrine-macrophage organoids to model their interaction in vitro. Here, we show that macrophages support the differentiation and viability of endocrine cells in vitro and enhance tissue engraftment, highlighting their potential role in tissue engineering strategies for diabetes.

Disruption of perinatal myeloid niches impacts the aging clock of pancreatic β cells

Perinatal expansion of pancreatic β cells is critical to metabolic adaptation. Yet, mechanisms surveying the fidelity by which proliferative events generate functional β cell pools remain unknown. We have previously identified a CCR2+ myeloid niche required for peri-natal β cell replication, with β cells dynamically responding to loss and repopulation of these myeloid cells with growth arrest and rebound expansion, respectively. Here, using a timed single-cell RNA-sequencing approach, we show that transient disruption of perinatal CCR2+ macrophages change islet β cell repertoires in young mice to resemble those of aged mice. Gene expression profiling and functional assays disclose prominent mitochondrial defects in β cells coupled to impaired redox states, NAD depletion, and DNA damage, leading to accelerated islets' dysfunction with age. These findings reveal an unexpected vulnerability of mitochondrial β cells' bioenergetics to the disruption of perinatal CCR2+ macrophages, implicating these cells in surveying early in life both the size and energy homeostasis of β cells populations.

Beneficial islet inflammation in health depends on pericytic TLR/MyD88 signaling

While inflammation is beneficial for insulin secretion during homeostasis, its transformation adversely affects β cells and contributes to diabetes. However, the regulation of islet inflammation for maintaining glucose homeostasis remains largely unknown. Here, we identified pericytes as pivotal regulators of islet immune and β cell function in health. Islets and pancreatic pericytes express various cytokines in healthy humans and mice. To interfere with the pericytic inflammatory response, we selectively inhibited the TLR/MyD88 pathway in these cells in transgenic mice. The loss of MyD88 impaired pericytic cytokine production. Furthermore, MyD88-deficient mice exhibited skewed islet inflammation with fewer cells, an impaired macrophage phenotype, and reduced IL-1β production. This aberrant pericyte-orchestrated islet inflammation was associated with β cell dedifferentiation and impaired glucose response. Additionally, we found that Cxcl1, a pericytic MyD88-dependent cytokine, promoted immune IL-1β production. Treatment with either Cxcl1 or IL-1β restored the mature β cell phenotype and glucose response in transgenic mice, suggesting a potential mechanism through which pericytes and immune cells regulate glucose homeostasis. Our study revealed pericyte-orchestrated islet inflammation as a crucial element in glucose regulation, implicating this process as a potential therapeutic target for diabetes.

Pancreas and islet morphology in cystic fibrosis: clues to the etiology of cystic fibrosis-related diabetes

Cystic fibrosis (CF) is a multi-organ disease caused by loss-of-function mutations in CFTR (which encodes the CF transmembrane conductance regulator ion channel). Cystic fibrosis related diabetes (CFRD) occurs in 40-50% of adults with CF and is associated with significantly increased morbidity and mortality. CFRD arises from insufficient insulin release from β cells in the pancreatic islet, but the mechanisms underlying the loss of β cell function remain understudied. Widespread pathological changes in the CF pancreas provide clues to these mechanisms. The exocrine pancreas is the epicenter of pancreas pathology in CF, with ductal pathology being the initiating event. Loss of CFTR function results in ductal plugging and subsequent obliteration. This in turn leads to destruction of acinar cells, fibrosis and fatty replacement. Despite this adverse environment, islets remain relatively well preserved. However, islet composition and arrangement are abnormal, including a modest decrease in β cells and an increase in α, δ and γ cell abundance. The small amount of available data suggest that substantial loss of pancreatic/islet microvasculature, autonomic nerve fibers and intra-islet macrophages occur. Conversely, T-cell infiltration is increased and, in CFRD, islet amyloid deposition is a frequent occurrence. Together, these pathological changes clearly demonstrate that CF is a disease of the pancreas/islet microenvironment. Any or all of these changes are likely to have a dramatic effect on the β cell, which relies on positive signals from all of these neighboring cell types for its normal function and survival. A thorough characterization of the CF pancreas microenvironment is needed to develop better therapies to treat, and ultimately prevent CFRD.

CSF1R-dependent macrophages in the salivary gland are essential for epithelial regeneration after radiation-induced injury

The salivary glands often become damaged in individuals receiving radiotherapy for head and neck cancer, resulting in chronic dry mouth. This leads to detrimental effects on their health and quality of life, for which there is no regenerative therapy. Macrophages are the predominant immune cell in the salivary glands and are attractive therapeutic targets due to their unrivaled capacity to drive tissue repair. Yet, the nature and role of macrophages in salivary gland homeostasis and how they may contribute to tissue repair after injury are not well understood. Here, we show that at least two phenotypically and transcriptionally distinct CX3CR1+ macrophage populations are present in the adult salivary gland, which occupy anatomically distinct niches. CD11c+CD206-CD163- macrophages typically associate with gland epithelium, whereas CD11c-CD206+CD163+ macrophages associate with blood vessels and nerves. Using a suite of complementary fate mapping systems, we show that there are highly dynamic changes in the ontogeny and composition of salivary gland macrophages with age. Using an in vivo model of radiation-induced salivary gland injury combined with genetic or antibody-mediated depletion of macrophages, we demonstrate an essential role for macrophages in clearance of cells with DNA damage. Furthermore, we show that epithelial-associated macrophages are indispensable for effective tissue repair and gland function after radiation-induced injury, with their depletion resulting in reduced saliva production. Our data, therefore, provide a strong case for exploring the therapeutic potential of manipulating macrophages to promote tissue repair and thus minimize salivary gland dysfunction after radiotherapy.

Senescence: a double-edged sword in beta-cell health and failure?

Cellular senescence is a complex process marked by permanent cell-cycle arrest in response to a variety of stressors, and acts as a safeguard against the proliferation of damaged cells. Senescence is not only a key process underlying aging and development of many diseases, but has also been shown to play a vital role in embryogenesis as well as tissue regeneration and repair. In context of the pancreatic beta-cells, that are essential for maintaining glucose homeostasis, replicative senescence is responsible for the age-related decline in regenerative capacity. Stress induced premature senescence is also a key early event underlying beta-cell failure in both type 1 and type 2 diabetes. Targeting senescence has therefore emerged as a promising therapeutic avenue for diabetes. However, the molecular mechanisms that mediate the induction of beta-cell senescence in response to various stressors remain unclear. Nor do we know if senescence plays any role during beta-cell growth and development. In this perspective, we discuss the significance of senescence in beta-cell homeostasis and pathology and highlight emerging directions in this area that warrant our attention.

Pericytes modulate islet immune cells and insulin secretion through Interleukin-33 production in mice

Introduction

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.

Methods

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 Il33 gene selectively in pancreatic pericytes, in combination with the administration of recombinant IL-33. Glucose response was measured in vivo and in vitro, and morphometric and molecular analyses were used to measure β-cell mass and gene expression. Immune cells were analyzed by flow cytometry.

Resuts

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.

Discussion

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.

Lessons from neonatal β-cell epigenomic for diabetes prevention and treatment

Pancreatic β-cell expansion and functional maturation during the birth-to-weaning period plays an essential role in the adaptation of plasma insulin levels to metabolic needs. These events are driven by epigenetic programs triggered by growth factors, hormones, and nutrients. These mechanisms operating in the neonatal period can be at least in part reactivated in adult life to increase the functional β-cell mass and face conditions of increased insulin demand such as obesity or pregnancy. In this review, we will highlight the importance of studying these signaling pathways and epigenetic programs to understand the causes of different forms of diabetes and to permit the design of novel therapeutic strategies to prevent and treat this metabolic disorder affecting hundreds of millions of people worldwide.

The Potential Causes of Cystic Fibrosis-Related Diabetes

Cystic fibrosis (CF) is a genetic disease caused by mutations in the cystic fibrosis transmembrane conductance regulator gene (CFTR). Cystic fibrosis-related diabetes (CFRD) is the most common comorbidity, affecting more than 50% of adult CF patients. Despite this high prevalence, the etiology of CFRD remains incompletely understood. Studies in young CF children show pancreatic islet disorganization, abnormal glucose tolerance, and delayed first-phase insulin secretion suggesting that islet dysfunction is an early feature of CF. Since insulin-producing pancreatic β-cells express very low levels of CFTR, CFRD likely results from β-cell extrinsic factors. In the vicinity of β-cells, CFTR is expressed in both the exocrine pancreas and the immune system. In the exocrine pancreas, CFTR mutations lead to the obstruction of the pancreatic ductal canal, inflammation, and immune cell infiltration, ultimately causing the destruction of the exocrine pancreas and remodeling of islets. Both inflammation and ductal cells have a direct effect on insulin secretion and could participate in CFRD development. CFTR mutations are also associated with inflammatory responses and excessive cytokine production by various immune cells, which infiltrate the pancreas and exert a negative impact on insulin secretion, causing dysregulation of glucose homeostasis in CF adults. In addition, the function of macrophages in shaping pancreatic islet development may be impaired by CFTR mutations, further contributing to the pancreatic islet structural defects as well as impaired first-phase insulin secretion observed in very young children. This review discusses the different factors that may contribute to CFRD.

Genetically engineered myeloid cells rebalance the core immune suppression program in metastasis

Metastasis is the leading cause of cancer-related deaths, and greater knowledge of the metastatic microenvironment is necessary to effectively target this process. Microenvironmental changes occur at distant sites prior to clinically detectable metastatic disease; however, the key niche regulatory signals during metastatic progression remain poorly characterized. Here, we identify a core immune suppression gene signature in pre-metastatic niche formation that is expressed predominantly by myeloid cells. We target this immune suppression program by utilizing genetically engineered myeloid cells (GEMys) to deliver IL-12 to modulate the metastatic microenvironment. Our data demonstrate that IL12-GEMy treatment reverses immune suppression in the pre-metastatic niche by activating antigen presentation and T cell activation, resulting in reduced metastatic and primary tumor burden and improved survival of tumor-bearing mice. We demonstrate that IL12-GEMys can functionally modulate the core program of immune suppression in the pre-metastatic niche to successfully rebalance the dysregulated metastatic microenvironment in cancer.

Islet Regeneration: Endogenous and Exogenous Approaches

Both type 1 and type 2 diabetes are characterized by a progressive loss of beta cell mass that contributes to impaired glucose homeostasis. Although an optimal treatment option would be to simply replace the lost cells, it is now well established that unlike many other organs, the adult pancreas has limited regenerative potential. For this reason, significant research efforts are focusing on methods to induce beta cell proliferation (replication of existing beta cells), promote beta cell formation from alternative endogenous cell sources (neogenesis), and/or generate beta cells from pluripotent stem cells. In this article, we will review (i) endogenous mechanisms of beta cell regeneration during steady state, stress and disease; (ii) efforts to stimulate endogenous regeneration and transdifferentiation; and (iii) exogenous methods of beta cell generation and transplantation.

Gland Macrophages: Reciprocal Control and Function within Their Niche

The human body contains dozens of endocrine and exocrine glands, which regulate physiological processes by secreting hormones and other factors. Glands can be subdivided into contiguous tissue modules, each consisting of an interdependent network of cells that together perform particular tissue functions. Among those cells are macrophages, a diverse type of immune cells endowed with trophic functions. In this review, we discuss recent findings on how resident macrophages support tissue modules within glands via the creation of mutually beneficial cell-cell circuits. A better comprehension of gland macrophage function and local control within their niche is essential to achieve a refined understanding of gland physiology in homeostasis and disease.

Beta cell dysfunction in diabetes: the islet microenvironment as an unusual suspect

Cells in different tissues, including endocrine cells in the pancreas, live in complex microenvironments that are rich in cellular and acellular components. Intricate interactions with their microenvironment dictate most cellular properties, such as their function, structure and size, and maintain tissue homeostasis. Pancreatic islets are populated by endocrine, vascular and immune cells that are immersed in the extracellular matrix. While the intrinsic properties of beta cells have been vastly investigated, our understanding of their interactions with their surroundings has only recently begun to unveil. Here, we review current research on the interplay between the islet cellular and acellular components, and the role these components play in beta cell physiology and pathophysiology. Although beta cell failure is a key pathomechanism in diabetes, its causes are far from being fully elucidated. We, thus, propose deleterious alterations of the islet niche as potential underlying mechanisms contributing to beta cell failure. In sum, this review emphasises that the function of the pancreatic islet depends on all of its components. Graphical abstract.

Immune regulation of islet homeostasis and adaptation

The islet of Langerhans produces endocrine hormones to regulate glucose homeostasis. The normal function of the islet relies on the homeostatic regulations of cellular composition and cell–cell interactions within the islet microenvironment. Immune cells populate the islet during embryonic development and participate in islet organogenesis and function. In obesity, a low-grade inflammation manifests in multiple organs, including pancreatic islets. Obesity-associated islet inflammation is evident in both animal models and humans, characterized by the accumulation of immune cells and elevated production of inflammatory cytokines/chemokines and metabolic mediators. Myeloid lineage cells (monocytes and macrophages) are the dominant types of immune cells in islet inflammation during the development of obesity and type 2 diabetes mellitus (T2DM). In this review, we will discuss the role of the immune system in islet homeostasis and inflammation and summarize recent findings of the cellular and molecular factors that alter islet microenvironment and β cell function in obesity and T2DM.

The Epithelial-Myeloid-Transition (EMyeT) of cancer cells as a wrongly perceived primary inflammatory process eventually progressing to a bone remodeling malignancy: the alternative pathway for Epithelial- Mesenchymal-Transition hypothesis (EMT)?

Cancer cells express multiple markers expressed by mesenchymal as well as myeloid cells in common and in addition specific markers of the myeloid lineages, especially those of dendritic cells, macrophages and preosteoclasts. It has also been possible to identify monocyte-macrophage gene clusters in cancer cell specimens as well as in cancer cell lines.

Accordingly, like myeloid cells cancer cells often express pro-inflammatory cytokines, and consequently the carcinoma may be perceived by the organism as a primary inflammatory process comparable to the immune inflammatory reactions in the eye or in the case of arthritis. This would explain why a carcinoma may induce a certain alarm state in the organism by increasing a fatal sympathetic tone in the patient, supplying the carcinomas with nutrients at the cost of other requirements, inducing tolerance against the cancer cells mistaken as myeloid cells, provoking fibrosis and neoangiogenesis, and increasing inflammatory cells at the carcinoma site.

This seemingly inflammatory process of Epithelial-Myeloid-Transition (EMyeT) is superimposed by the progression of part of the myeloid cancer cells to stages comparable to preosteoclasts and osteoclasts, and their development to metastasizing carcinomas often at the site of bone.

This concept of carcinogenesis and malignant progression described here challenges the widely accepted EMT-hypotheses and could deliver the rationale for the various peculiar aspects of cancer and the variety of therapeutic antitumoral measures.

The Mononuclear Phagocyte System: The Relationship between Monocytes and Macrophages

The mononuclear phagocyte system (MPS) is defined as a cell lineage in which committed marrow progenitors give rise to blood monocytes and tissue macrophages. Here, we discuss the concept of self-proscribed macrophage territories and homeostatic regulation of tissue macrophage abundance through growth factor availability. Recent studies have questioned the validity of the MPS model and argued that tissue-resident macrophages are a separate lineage seeded during development and maintained by self-renewal. We address this issue; discuss the limitations of inbred mouse models of monocyte-macrophage homeostasis; and summarize the evidence suggesting that during postnatal life, monocytes can replace resident macrophages in all major organs and adopt their tissue-specific gene expression. We conclude that the MPS remains a valid and accurate framework for understanding macrophage development and homeostasis.

Innate immune priming of insulin secretion

Increasing evidence suggests a role for the immune system to finely tune metabolic homeostasis. The possibility that the immune system can likewise regulate islet endocrine function has only commenced drawing attention. Islet beta cells are the main producers of insulin and have to dynamically respond to fluctuating insulin demands of the body. While inflammation has long been considered as an important pathogenic feature of diabetes development, pioneer studies have shown that immune cells reside inside pancreatic islets under steady state and that components of the immune system can promote beta cell insulin production. The present review will thus highlight the recent research on specific immune pathways regulating beta cell function discussing the beneficial influence of innate immune cells.

Understanding the Biology of Self-Renewing Macrophages

Macrophages reside in specific territories in organs, where they contribute to the development, homeostasis, and repair of tissues. Recent work has shown that the size of tissue macrophage populations has an impact on tissue functions and is determined by the balance between replenishment and elimination. Macrophage replenishment is mainly due to self-renewal of macrophages, with a secondary contribution from blood monocytes. Self-renewal is a recently discovered trait of macrophages, which can have a major impact on their physiological functions and hence on the wellbeing of the organism. In this review, I discuss our current understanding of the developmental origin of self-renewing macrophages and the mechanisms used to maintain a physiologically stable macrophage pool.