Concise Review: Macrophages: Versatile Gatekeepers During Pancreatic β-Cell Development, Injury, and Regeneration

Harnessing beta cell regeneration biology for diabetes therapy

The pandemic scale of diabetes mellitus is alarming, its complications remain devastating, and current treatments still pose a major burden on those affected and on the healthcare system as a whole. As the disease emanates from the destruction or dysfunction of insulin-producing pancreatic β-cells, a real cure requires their restoration and protection. An attractive strategy is to regenerate β-cells directly within the pancreas; however, while several approaches for β-cell regeneration have been proposed in the past, clinical translation has proven challenging. This review scrutinizes recent findings in β-cell regeneration and discusses their potential clinical implementation. Hereby, we aim to delineate a path for innovative, targeted therapies to help shift from 'caring for' to 'curing' diabetes.

Reactive nitrogen species-mediated cell proliferation during tail regeneration and retinoic acid as a putative modulator of tissue regeneration in the geckos

Reactive nitrogen species (RNS), a mediator of nitrosative stress, plays a vital role during wound healing but its role during tissue regeneration is poorly understood. In the present study, the role of RNS was investigated post-tail autotomy and limb amputation in a gecko species, Hemidactylus murrayi Gleadow, 1887. Tail autotomy led to an increased expression of iNOS and nitrosative stress leading to protein S-nitrosylation that probably restricted the acute inflammatory response caused by wounding. Increased nitrosative stress was also associated with proliferation of the wound epithelium and the tail blastema. Nitric oxide synthase inhibitor (L-NAME) caused retarded growth and structural abnormalities in the regenerating tail while peroxynitrite inhibitor (FeTmPyp) arrested tail regeneration. Spermine NONOate and retinoic acid, used as NO donors generated small outgrowths post-amputation of limbs with an increased number of proliferating cells and s-nitrosylation indicating the role of nitric oxide signalling in cell proliferation during regeneration. Additionally, retinoic acid treatment caused regeneration of nerve, muscle and adipose tissue in the regenerated limb structure 105 days post-amputation suggesting it to be a putative modulator of tissue regeneration in the non-regenerating limbs.

Transfer of inflammatory mitochondria via extracellular vesicles from M1 macrophages induces ferroptosis of pancreatic beta cells in acute pancreatitis

Extracellular vesicles (EVs) exert a significant influence not only on the pathogenesis of diseases but also on their therapeutic interventions, contingent upon the variances observed in their originating cells. Mitochondria can be transported between cells via EVs to promote pathological changes. In this study, we found that EVs derived from M1 macrophages (M1-EVs), which encapsulate inflammatory mitochondria, can penetrate pancreatic beta cells. Inflammatory mitochondria fuse with the mitochondria of pancreatic beta cells, resulting in lipid peroxidation and mitochondrial disruption. Furthermore, fragments of mitochondrial DNA (mtDNA) are released into the cytosol, activating the STING pathway and ultimately inducing apoptosis. The potential of adipose-derived stem cell (ADSC)-released EVs in suppressing M1 macrophage reactions shows promise. Subsequently, ADSC-EVs were utilized and modified with an F4/80 antibody to specifically target macrophages, aiming to treat ferroptosis of pancreatic beta cells in vivo. In summary, our data further demonstrate that EVs secreted from M1 phenotype macrophages play major roles in beta cell ferroptosis, and the modified ADSC-EVs exhibit considerable potential for development as a vehicle for targeted delivery to macrophages.

Extracellular Vesicle Content Changes Induced by Melatonin Promote Functional Recovery of Pancreatic Beta Cells in Acute Pancreatitis

Aim

Acute pancreatitis is an inflammatory disorder of the pancreas, which causes abnormal activation of immune cells. The macrophages were accumulated in pancreas and infiltrated into islets during the AP process to induce abnormal glucose metabolism. However, the role of macrophages in abnormal glucose metabolism remains understood. Extracellular vesicles act in the regulation of intercellular function, but whether EVs secreted by macrophages contribute to β cell failure and apoptosis in AP is unclear. Based on this, the aim of this study was to reveal the role of macrophages-EVs in AP and develop a treatment for symptoms of hyperglycemia in AP.

Methods

The AP model was established and treated by various doses of melatonin to analyze the therapeutic effect. The accumulation and polarization of macrophages in the AP pancreas were observed, and the β cells were incubated with pancreatic derived EVs to analyze the role in β cell failure and apoptosis.

Results

The results showed that macrophages were recruited and polarized to M1 phenotype macrophages in the pancreas of AP mice, which obtained inflammatory EVs that contained specific miRNAs to induce β cell failure and apoptosis. Then, the EVs derived from M1 macrophages triggered β cell failure and apoptosis. Melatonin prevented polarization of macrophages to the M1 phenotype in vivo, which reduced the secretion of inflammatory EVs, changed the abundance of miRNAs in EVs, and therefore decreased inflammatory EV-mediated β cell failure and apoptosis.

Conclusion

Our results demonstrate that similar to 20S proteasome inhibitor MG132, analyses indicated that melatonin prevented degradation of IκBα through the ubiquitylation pathway to restrict p50 subunits to the cytoplasm of macrophages, inhibited activation of the NF-κB pathway to downregulate the transcription of specific miRNAs, and reduced miRNA transport into EVs.

Lactobacillus Plantarum NC8 and its metabolite acetate alleviate type 1 diabetes via inhibiting NLRP3

A healthy organism is the result of host-microbiome co-evolution. Microbial metabolites can also stimulate immune cells to reduce intestinal inflammation and permeability. Gut dysbiosis will lead to a variety of autoimmune diseases, such as Type 1 diabetes (T1D). Most of probiotics, such as Lactobacillus casei, Lactobacillus reuteri, Bifidobacterium bifidium, and Streptococcus thermophiles, can improve the intestinal flora structure of the host, reduce intestinal permeability, and relieve symptoms of T1D patients if ingested above probiotics in sufficient amounts. Lactobacillus Plantarum NC8, a kind of Lactobacillus, whether it has an effect on T1D, and the mechanism of it regulating T1D is still unclear. As a member of the inflammatory family, NLRP3 inflammasome can enhance inflammatory responses by promoting the production and secretion of proinflammatory cytokines. Many previous studies had shown that NLRP3 also plays an important role in the development of T1D. When the NLRP3 gene is deleted, the disease progression of T1D will be delayed. Therefore, this study investigated whether Lactobacillus Plantarum NC8 can alleviate T1D by regulating NLRP3. The results demonstrated that Lactobacillus Plantarum NC8 and its metabolites acetate play a role in T1D by co-modulating NLRP3. Lactobacillus Plantarum NC8 and acetate can reduce the damage of T1D in the model mice, even if orally administered them in the early stage of T1D. The number of Th1/Th17 cells in the spleen and pancreatic lymph nodes (PLNs) of T1D mice were significantly reduced by oral Lactobacillus Plantarum NC8 or acetate. The expression of NLRP3 in the pancreas of T1D mice or murine macrophages of inflammatory model were significantly inhibited by treatment with Lactobacillus Plantarum NC8 or acetate. In addition, the number of macrophages in the pancreas were significantly reduced by the treatment with Lactobacillus Plantarum NC8 or acetate. In summary, this study indicated that the regulatory mechanism of Lactobacillus Plantarum NC8 and its metabolite acetate to T1D maybe via inhibiting NLRP3 and provides a novel insights into the mechanism of the alleviated role of probiotics to T1D.

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.

The research progress of anti-inflammatory and anti-fibrosis treatment of chronic pancreatitis

Chronic pancreatitis (CP) is a chronic progressive inflammatory disease of the pancreas, caused by multiple factors and accompanied by irreversible impairment of pancreatic internal and external secretory functions. Pathologically, atrophy of the pancreatic acini, tissue fibrosis or calcification, focal edema, inflammation, and necrosis are observed. Clinical manifestations include recurrent or persistent abdominal pain, diarrhea, emaciation, and diabetes. In addition, CP is prone to develop into pancreatic cancer(PC) due to persistent inflammation and fibrosis. The disease course is prolonged and the clinical prognosis is poor. Currently, clinical treatment of CP is still based on symptomatic treatment and there is a lack of effective etiological treatment. Encouragingly, experiments have shown that a variety of active substances have great potential in the etiological treatment of chronic pancreatitis. In this paper, we will review the pathogenesis of CP, as well as the research progress on anti-inflammatory and anti-fibrotic therapies, which will provide new ideas for the development of subsequent clinical studies and formulation of effective treatment programs, and help prevent CP from developing into pancreatic cancer and reduce the prevalence of PC as much as possible.

Polarized macrophages promote gestational beta cell growth through extracellular signal-regulated kinase 5 signalling

AIM

To show that depletion of pancreatic macrophages impairs gestational beta cell proliferation and leads to glucose intolerance.

MATERIALS AND METHODS

Genetic animal models were applied to study the effects of depletion of pancreatic macrophges on gestational beta-cell proliferaiton and glucose response. The crosstalk between macrophages and beta-cells was studied in vivo using beta-cell-specific extracellular-signal-regulated kinase 5 (ERK5) knockout and epidermal growth receptor (EGFR) knockout mice, and in vitro using a co-culture system.

RESULTS

Beta cell-derived placental growth factor (PlGF) recruited naïve macrophages and polarized them towards an M2-like phenotype. These macrophages then secreted epidermal growth factor (EGF), which activated extracellular signal-regulated kinase 5 (ERK5) signalling in beta cells to promote gestational beta cell proliferation. On the other hand, activation of ERK5 signalling in beta cells likely, in turn, enhanced the production and secretion of PlGF by beta cells.

CONCLUSIONS

Our study shows a regulatory loop between macrophages and beta cells through PlGF/EGF/ERK5 signalling cascades to regulate gestational beta cell growth.

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.

Emerging roles of Galectin-3 in diabetes and diabetes complications: A snapshot

Galectin-3 is a member of the galectin family, widely expressed in immune cells and plays a role mainly in inflammation, autoimmunity, apoptosis, and chemotaxis. We summarized the roles of Galectin-3 in diabetes and its complications, as well as the underlying mechanisms. Clinical research has determined that the circulating level of Galectin-3 is closely related to diabetes and its complications, thus it is promising to use Galectin-3 as a predictor and biomarker for those diseases. Galectin-3 also may be considered as an ideal therapeutic target, which has broad prospects in the prevention and treatment of diabetes and its complications, especially macrovascular and microvascular complications.

The Human Islet: Mini-Organ With Mega-Impact

This review focuses on the human pancreatic islet-including its structure, cell composition, development, function, and dysfunction. After providing a historical timeline of key discoveries about human islets over the past century, we describe new research approaches and technologies that are being used to study human islets and how these are providing insight into human islet physiology and pathophysiology. We also describe changes or adaptations in human islets in response to physiologic challenges such as pregnancy, aging, and insulin resistance and discuss islet changes in human diabetes of many forms. We outline current and future interventions being developed to protect, restore, or replace human islets. The review also highlights unresolved questions about human islets and proposes areas where additional research on human islets is needed.

Stage-specific transcriptomic changes in pancreatic α-cells after massive β-cell loss

Background

Loss of pancreatic insulin-secreting β-cells due to metabolic or autoimmune damage leads to the development of diabetes. The discovery that α-cells can be efficiently reprogrammed into insulin-secreting cells in mice and humans has opened promising avenues for innovative diabetes therapies. β-cell loss triggers spontaneous reprogramming of only 1–2% of α-cells, limiting the extent of regeneration. Most α-cells are refractory to conversion and their global transcriptomic response to severe β-cell loss as well as the mechanisms opposing their reprogramming into insulin producers are largely unknown. Here, we performed RNA-seq on FAC-sorted α-cells to characterize their global transcriptional responses at different time points after massive β-cell ablation.

Results

Our results show that α-cells undergo stage-specific transcriptional changes 5- and 15-days post-diphtheria toxin (DT)-mediated β-cell ablation. At 5 days, α-cells transiently upregulate various genes associated with interferon signaling and proliferation, including Interferon Induced Protein with Tetratricopeptide Repeats 3 (Ifit3). Subsequently, at 15 days post β-cell ablation, α-cells undergo a transient downregulation of genes from several pathways including Insulin receptor, mTOR and MET signaling.

Conclusions

The results presented here pinpoint novel markers discriminating α-cells at different stages after acute β-cell loss, and highlight additional signaling pathways that are modulated in α-cells in this context.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07812-x.

High mRNA expression of LY6 gene family is associated with overall survival outcome in pancreatic ductal adenocarcinoma

Pancreatic cancer ranks one of the worst in overall survival outcome with a 5 year survival rate being less than 10%. Pancreatic cancer faces unique challenges in its diagnosis and treatment, such as the lack of clinically validated biomarkers and the immensely immunosuppressive tumor microenvironment. Recently, the LY6 gene family has received increasing attention for its multi-faceted roles in cancer development, stem cell maintenance, immunomodulation, and association with more aggressive and hard-to-treat cancers. A detailed study of mRNA expression of LY6 gene family and its association with overall survival (OS) outcome in pancreatic cancers is lacking. We used publicly available clinical datasets to analyze the mRNA expression of a set of LY6 genes and its effect on OS outcome in the context of the tumor microenvironment and immunomodulation. We used web-based tools Kaplan-Meier Plotter, cBioPortal, Oncomine and R-programming to analyze copy number alterations, mRNA expression and its association with OS outcome in pancreatic cancer. These analyses demonstrated that high expression of LY6 genes is associated with OS and disease free survival (DFS) outcome. High expression of LY6 genes and their association with OS outcome is dependent on the composition of tumor microenvironment. Considering that LY6 proteins are anchored to the outer cell membrane or secreted, making them readily accessible, these findings highlight the potential of LY6 family members in the future of pancreatic cancer diagnosis and treatment.

Barbaloin Treatment Contributes to the Rebalance of Glucose and Lipid Homeostasis of Gestational Diabetes Mellitus Mice

Aloe vera L has been shown to possess hypoglycemic and hypolipidemic effects on type 2 diabetic patients, and its major benefits may be linked to barbaloin, which is a major component of Aloe vera L. This study focused on investigating the potential effects and underlying mechanisms of barbaloin on gestational diabetes mellitus (GDM). The db/+ diabetic mice with GDM were daily orally administered with barbaloin or metformin during the gestational period. The results demonstrated that administration of barbaloin significantly reduced blood glucose levels and increased insulin levels in GDM mice. We further found that barbaloin treatment reduced inflammatory response and ROS levels in the liver. Finally, we revealed that the AMP-activated protein kinase (AMPK) / peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) signaling pathway was involved in BAT-mediated beneficial effects on mice with GDM. Our study suggested that barbaloin exerted hypoglycemic and hypolipidemic effects on GDM mice, via, at least in part, modulation of AMPK/ PGC-1α signaling in GDM mice.

Towards a Functional Cure for Diabetes Using Stem Cell-Derived Beta Cells: Are We There Yet?

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.

Pathological Mechanisms in Diabetes of the Exocrine Pancreas: What's Known and What's to Know

The clinical significance of diabetes arising in the setting of pancreatic disease (also known as diabetes of the exocrine pancreas, DEP) has drawn more attention in recent years. However, significant improvements still need to be made in the recognition, diagnosis and treatment of the disorder, and in the knowledge of the pathological mechanisms. The clinical course of DEP is different from type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM). DEP develops in patients with previous existing exocrine pancreatic disorders which damage both exocrine and endocrine parts of pancreas, and lead to pancreas exocrine insufficiency (PEI) and malnutrition. Therefore, damage in various exocrine and endocrine cell types participating in glucose metabolism regulation likely contribute to the development of DEP. Due to the limited amount of clinical and experimental studies, the pathological mechanism of DEP is poorly defined. In fact, it still not entirely clear whether DEP represents a distinct pathologic entity or is a form of T2DM arising when β cell failure is accelerated by pancreatic disease. In this review, we include findings from related studies in T1DM and T2DM to highlight potential pathological mechanisms involved in initiation and progression of DEP, and to provide directions for future research studies.

Good Cop, Bad Cop: The Opposing Effects of Macrophage Activation State on Maintaining or Damaging Functional β-Cell Mass

Loss of functional β-cell mass is a hallmark of Type 1 and Type 2 Diabetes. Macrophages play an integral role in the maintenance or destruction of pancreatic β-cells. The effect of the macrophage β-cell interaction is dependent on the activation state of the macrophage. Macrophages can be activated across a spectrum, from pro-inflammatory to anti-inflammatory and tissue remodeling. The factors secreted by these differentially activated macrophages and their effect on β-cells define the effect on functional β-cell mass. In this review, the spectrum of macrophage activation is discussed, as are the positive and negative effects on β-cell survival, expansion, and function as well as the defined factors released from macrophages that impinge on functional β-cell mass.

Macrophages in the pancreas: Villains by circumstances, not necessarily by actions

Introduction

Mounting evidence suggest that macrophages play crucial roles in disease and tissue regeneration. However, despite much efforts during the past decade, our knowledge about the extent of macrophages' contribution to adult pancreatic regeneration after injury or during pancreatic disease progression is still limited. Nevertheless, it is generally accepted that some macrophage features that normally would contribute to healing and regeneration may be detrimental in pancreatic cancer. Altogether, the current literature contains conflicting reports on whether macrophages act as friends or foe in these conditions.

Methods and Results

In this review, we briefly review the origins of tissue resident and infiltrating macrophages and the importance of cellular crosstalking between macrophages and other resident cells in tissue regeneration. The primary objective of this review is to summarize our knowledge of the distinct roles of tissue resident and infiltrating macrophages, the impact of M1 and M2 macrophage phenotypes, and emerging evidence on macrophage crosstalking in pancreatic injury, regeneration, and disease.

Conclusion

Macrophages are involved with various stages of pancreatic cancer development, pancreatitis, and diabetes. Elucidating their role in these conditions will aid the development of targeted therapeutic treatments.

Exercise and Type 1 Diabetes

Diabetes mellitus (DM) is the most common endocrine and metabolic disease caused by absolute or insufficient insulin secretion. Under the context of an aging population worldwide, the number of diabetic patients is increasing year by year. Most patients with diabetes have multiple complications that severely threaten their survival and living quality. DM is mainly divided into type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM). T1DM is caused by absolute lack of insulin secretion, so the current treatment for T1DM patients is exogenous insulin replacement therapy. At present, exercise therapy has been widely recognized in the prevention and treatment of diabetes, and regular aerobic exercise has become an important part of T1DM treatment. At the same time, exercise therapy is also used in conjunction with other treatments in the prevention and treatment of diabetic complications. However, for patients with T1DM, exercise still has the risk of hypoglycemia or hyperglycemia. T1DM Patients and specialist physician need to fully understand the effects of exercise on metabolism and implement individualized exercise programs. This chapter reviews the related content of exercise and T1DM.

Low-Dose Decitabine Assists Human Umbilical Cord-Derived Mesenchymal Stem Cells in Protecting β Cells via the Modulation of the Macrophage Phenotype in Type 2 Diabetic Mice

Background

Progressive β-cell dysfunction, a major characteristic of type 2 diabetes (T2D), is closely related to the infiltration of inflammatory macrophages within islets. Mesenchymal stem cells (MSCs) have been identified to alleviate β-cell dysfunction by modulating macrophage phenotype in T2D, but the restoration of β-cells by a single MSC infusion is relatively transient. Decitabine (DAC) has been reported to polarize macrophages towards the anti-inflammatory phenotype at low doses. We therefore investigated whether low-dose decitabine could enhance the antidiabetic effect of MSCs and further promote the restoration of β-cell function.

Methods

We induced a T2D mice model by high-fat diets and streptozotocin (STZ) injection. Mice were divided into five groups: the normal group, the T2D group, the DAC group, the MSC group, and the MSC plus DAC group (MD group). We examined the blood glucose and serum insulin levels of mice 1, 2, and 4 weeks after MSC and/or DAC treatment. Dynamic changes in islets and the phenotype of intraislet macrophages were detected via immunofluorescence. In vitro, we explored the effect of MSCs and DAC on macrophage polarization.

Results

The blood glucose and serum insulin levels revealed that DAC prolonged the antidiabetic effect of MSCs to 4 weeks in T2D mice. Immunofluorescence staining demonstrated more sustainable morphological and structural amelioration in islets of the MD group than in the MSC group. Interestingly, further analysis showed more alternatively activated macrophages (M2, anti-inflammatory) and fewer classically activated macrophages (M1, proinflammatory) in islets of the MD group 4 weeks after treatment. An in vitro study demonstrated that DAC together with MSCs further polarized macrophages from the M1 to M2 phenotype via the PI3K/AKT pathway.

Conclusion

These data unveiled that DAC prolonged the antidiabetic effect of MSCs and promoted sustainable β-cell restoration, possibly by modulating the macrophage phenotype. Our results offer a preferable therapeutic strategy for T2D.

Evidence of Tissue Repair in Human Donor Pancreas After Prolonged Duration of Stay in Intensive Care

M2 macrophages play an important role in tissue repair and regeneration. They have also been found to modulate β-cell replication in mouse models of pancreatic injury and disease. We previously reported that β-cell replication is strongly increased in a subgroup of human organ donors characterized by prolonged duration of stay in an intensive care unit (ICU) and increased number of leukocytes in the pancreatic tissue. In the present study we investigated the relationship between duration of stay in the ICU, M2 macrophages, vascularization, and pancreatic cell replication. Pancreatic organs from 50 donors without diabetes with different durations of stay in the ICU were analyzed by immunostaining and digital image analysis. The number of CD68⁺CD206⁺ M2 macrophages increased three- to sixfold from ≥6 days' duration of stay in the ICU onwards. This was accompanied by a threefold increased vascular density and a four- to ninefold increase in pancreatic cells positive for the replication marker Ki67. A strong correlation was observed between the number of M2 macrophages and β-cell replication. These results show that a prolonged duration of stay in the ICU is associated with an increased M2 macrophage number, increased vascular density, and an overall increase in replication of all pancreatic cell types. Our data show evidence of marked levels of tissue repair in the human donor pancreas.

OX40 ligand is inhibitory during the effector phase of crescentic glomerulonephritis

BACKGROUND

The functional relevance of OX40 ligand (OX40L) in the effector phase of crescentic glomerulonephritis (GN) is unknown. These studies defined the role of endogenous OX40L during the effector stage of murine crescentic GN.

METHODS

GN was induced by immunization with sheep globulin/adjuvant on Day 0 and injection of sheep anti-mouse glomerular basement membrane immunoglobulin (Ig) on Day 10. Rat IgG or neutralizing anti-OX40L antibody was administered on Days 10-18 and immune responses and renal injury assessed on Day 20.

RESULTS

Compared with naïve animals, OX40L was upregulated in the lymph nodes (LNs) and on leucocytes and resident non-immune cells in the kidneys of mice with GN. Inhibition of OX40L in GN augmented renal injury, as indicated by increased crescent formation, proteinuria and glomerular leucocyte accumulation. In line with increased injury, anti-OX40L treatment increased proliferation and decreased apoptosis of CD4 T cells in the LNs, without affecting LN CD4 cytokine production and CD8 T-cell responses. Blockade of OX40L decreased LN regulatory T-cell (Treg) proliferation, transforming growth factor β production and foxp3 expression. OX40L inhibition did not affect B cell expansion or circulating antibody levels. In the kidney, neutralization of OX40L augmented interferon γ (IFNγ) expression by CD4 and CD8 T cells and shifted macrophage polarization towards the pro-inflammatory M1 phenotype.

CONCLUSIONS

OX40L is protective during the effector phase of murine crescentic GN by reducing the expansion of CD4 T cells and enhancing Treg responses in the LNs, and by locally inhibiting T-cell IFNγ production and pro-inflammatory macrophage phenotype in the kidney.

Loss of ubiquitin-conjugating enzyme E2 (Ubc9) in macrophages exacerbates multiple low-dose streptozotocin-induced diabetes by attenuating M2 macrophage polarization

Type 1 diabetes (T1D) is characterized by the selective autoimmune destruction of the islet β cells, and macrophages play a significant role in this process. Small ubiquitin-like modification (SUMOylation) is an important posttranslational modification involved in T1D pathogenesis, but its function in macrophages remains unexplored. We presently developed and used macrophage-specific ubiquitin-conjugating enzyme E2 (Ubc9) knockout (LyzM-Cre-Ubc9^fl/fl, KO) mice to address the impact of SUMOylation on macrophage function in a T1D model. We observed that blocking Ubc9 in macrophages exacerbated multiple-low dose streptozotocin (MLD-STZ)-induced diabetes. Specifically, after STZ treatment, blood glucose levels were consistently elevated in the KO mice. The KO mice exhibited a higher diabetes incidence than WT controls (85% vs. 55%, P < 0.01) along with a higher insulitis severity. The loss of Ubc9 impaired macrophage energy metabolism and attenuated macrophage M2 program, thereby enhancing T cell activation. Pancreas-resident macrophages, rather than migrant macrophages, played a predominant role in MLD-STZ-induced diabetes. Mechanistically, Ubc9-mediated SUMOylation of interferon regulator factor 4 (IRF4) enhanced its nuclear localization and stability, thereby transcribing IL-4 and arginase 1 (Arg1) to promote the macrophage M2 program. Ubc9-mediated SUMOylation modulates T1D risk at least in part by regulating macrophage function. Modulation of disturbed SUMOylation process in macrophages, either through cell adoptive transfer or targeted drug-delivery, could help to establish a tolerant pancreatic microenvironment and promote inflammation resolution in early insulitis stage, thus hindering T1D progression.

Understanding the Metabolic Profile of Macrophages During the Regenerative Process in Zebrafish

In contrast to mammals, lower vertebrates, including zebrafish (Danio rerio), have the ability to regenerate damaged or lost tissues, such as the caudal fin, which makes them an ideal model for tissue and organ regeneration studies. Since several diseases involve the process of transition between fibrosis and tissue regeneration, it is necessary to attain a better understanding of these processes. It is known that the cells of the immune system, especially macrophages, play essential roles in regeneration by participating in the removal of cellular debris, release of pro- and anti-inflammatory factors, remodeling of components of the extracellular matrix and alteration of oxidative patterns during proliferation and angiogenesis. Immune cells undergo phenotypical and functional alterations throughout the healing process due to growth factors and cytokines that are produced in the tissue microenvironment. However, some aspects of the molecular mechanisms through which macrophages orchestrate the formation and regeneration of the blastema remain unclear. In the present review, we outline how macrophages orchestrate the regenerative process in zebrafish and give special attention to the redox balance in the context of tail regeneration.

Age-related diseases as vicious cycles

The mortality rates of age-related diseases (ARDs) increase exponentially with age. Processes described by the exponential growth function typically involve a branching chain reaction or, more generally, a positive feedback loop. Here I propose that each ARD is mediated by one or several positive feedback loops (vicious cycles). I then identify critical vicious cycles in five major ARDs: atherosclerosis, hypertension, diabetes, Alzheimer's and Parkinson's. I also propose that the progression of ARDs can be halted by selectively interrupting the vicious cycles and suggest the most promising targets.

Extracellular Vesicles from Amnion-Derived Mesenchymal Stem Cells Ameliorate Hepatic Inflammation and Fibrosis in Rats

Background

There are no approved drug treatments for liver fibrosis and nonalcoholic steatohepatitis (NASH), an advanced stage of fibrosis which has rapidly become a major cause of cirrhosis. Therefore, development of anti-inflammatory and antifibrotic therapies is desired. Mesenchymal stem cell- (MSC-) based therapy, which has been extensively investigated in regenerative medicine for various organs, can reportedly achieve therapeutic effect in NASH via paracrine action. Extracellular vesicles (EVs) encompass a variety of vesicles released by cells that fulfill functions similar to those of MSCs. We herein investigated the therapeutic effects of EVs from amnion-derived MSCs (AMSCs) in rats with NASH and liver fibrosis.

Methods

NASH was induced by a 4-week high-fat diet (HFD), and liver fibrosis was induced by intraperitoneal injection of 2 mL/kg 50% carbon tetrachloride (CCl₄) twice a week for six weeks. AMSC-EVs were intravenously injected at weeks 3 and 4 in rats with NASH (15 μg/kg) and at week 3 in rats with liver fibrosis (20 μg/kg). The extent of inflammation and fibrosis was evaluated with quantitative reverse transcription polymerase chain reaction and immunohistochemistry. The effect of AMSC-EVs on inflammatory and fibrogenic response was investigated in vitro.

Results

AMSC-EVs significantly decreased the number of Kupffer cells (KCs) in the liver of rats with NASH and the mRNA expression levels of inflammatory cytokines such as tumor necrosis factor- (Tnf-) α, interleukin- (Il-) 1β and Il-6, and transforming growth factor- (Tgf-) β. Furthermore, AMSC-EVs significantly decreased fiber accumulation, KC number, and hepatic stellate cell (HSC) activation in rats with liver fibrosis. In vitro, AMSC-EVs significantly inhibited KC and HSC activation and suppressed the lipopolysaccharide (LPS)/toll-like receptor 4 (TLR4) signaling pathway.

Conclusions

AMSC-EVs ameliorated inflammation and fibrogenesis in a rat model of NASH and liver fibrosis, potentially by attenuating HSC and KC activation. AMSC-EV administration should be considered as a new therapeutic strategy for chronic liver disease.

Role of Monocyte/Macrophages during HIV/SIV Infection in Adult and Pediatric Acquired Immune Deficiency Syndrome

Monocytes/macrophages are a diverse group of cells that act as first responders in innate immunity and then as mediators for adaptive immunity to help clear infections. In performing these functions, however, the macrophage inflammatory responses can also contribute to pathogenesis. Various monocyte and tissue macrophage subsets have been associated with inflammatory disorders and tissue pathogeneses such as occur during HIV infection. Non-human primate research of simian immunodeficiency virus (SIV) has been invaluable in better understanding the pathogenesis of HIV infection. The question of HIV/SIV-infected macrophages serving as a viral reservoir has become significant for achieving a cure. In the rhesus macaque model, SIV-infected macrophages have been shown to promote pathogenesis in several tissues resulting in cardiovascular, metabolic, and neurological diseases. Results from human studies illustrated that alveolar macrophages could be an important HIV reservoir and humanized myeloid-only mice supported productive HIV infection and viral persistence in macrophages during ART treatment. Depletion of CD4+ T cells is considered the primary cause for terminal progression, but it was reported that increasing monocyte turnover was a significantly better predictor in SIV-infected adult macaques. Notably, pediatric cases of HIV/SIV exhibit faster and more severe disease progression than adults, yet neonates have fewer target T cells and generally lack the hallmark CD4+ T cell depletion typical of adult infections. Current data show that the baseline blood monocyte turnover rate was significantly higher in neonatal macaques compared to adults and this remained high with disease progression. In this review, we discuss recent data exploring the contribution of monocytes and macrophages to HIV/SIV infection and progression. Furthermore, we highlight the need to further investigate their role in pediatric cases of infection.

Natural Killer Cells in the Orchestration of Chronic Inflammatory Diseases

Inflammation, altered immune cell phenotype, and functions are key features shared by diverse chronic diseases, including cardiovascular, neurodegenerative diseases, diabetes, metabolic syndrome, and cancer. Natural killer cells are innate lymphoid cells primarily involved in the immune system response to non-self-components but their plasticity is largely influenced by the pathological microenvironment. Altered NK phenotype and function have been reported in several pathological conditions, basically related to impaired or enhanced toxicity. Here we reviewed and discussed the role of NKs in selected, different, and “distant” chronic diseases, cancer, diabetes, periodontitis, and atherosclerosis, placing NK cells as crucial orchestrator of these pathologic conditions.

Preservation Analysis of Macrophage Gene Coexpression Between Human and Mouse Identifies PARK2 as a Genetically Controlled Master Regulator of Oxidative Phosphorylation in Humans

Macrophages are key players involved in numerous pathophysiological pathways and an in-depth characterization of their gene regulatory networks can help in better understanding how their dysfunction may impact on human diseases. We here conducted a cross-species network analysis of macrophage gene expression data between human and mouse to identify conserved networks across both species, and assessed whether such networks could reveal new disease-associated regulatory mechanisms. From a sample of 684 individuals processed for genome-wide macrophage gene expression profiling, we identified 27 groups of coexpressed genes (modules). Six modules were found preserved (P < 10⁻⁴) in macrophages from 86 mice of the Hybrid Mouse Diversity Panel. One of these modules was significantly [false discovery rate (FDR) = 8.9 × 10⁻¹¹] enriched for genes belonging to the oxidative phosphorylation (OXPHOS) pathway. This pathway was also found significantly (FDR < 10⁻⁴) enriched in susceptibility genes for Alzheimer, Parkinson, and Huntington diseases. We further conducted an expression quantitative trait loci analysis to identify SNP that could regulate macrophage OXPHOS gene expression in humans. This analysis identified the PARK2 rs192804963 as a trans-acting variant influencing (minimal P-value = 4.3 × 10⁻⁸) the expression of most OXPHOS genes in humans. Further experimental work demonstrated that PARK2 knockdown expression was associated with increased OXPHOS gene expression in THP1 human macrophages. This work provided strong new evidence that PARK2 participates to the regulatory networks associated with oxidative phosphorylation and suggested that PARK2 genetic variations could act as a trans regulator of OXPHOS gene macrophage expression in humans.

Sources of beta cells inside the pancreas

The generation of beta(-like) cells to compensate for their absolute or relative shortage in type 1 and type 2 diabetes is an obvious therapeutic strategy. Patients first received grafts of donor islet cells over 25 years ago, but this procedure has not become routine in clinical practice because of a donor cell shortage and (auto)immune problems. Transplantation of differentiated embryonic and induced pluripotent stem cells may overcome some but not all the current limitations. Reprogramming exocrine cells towards functional beta(-like) cells would offer an alternative abundant and autologous source of beta(-like) cells. This review focuses on work by our research group towards achieving such a source of cells. It summarises a presentation given at the 'Can we make a better beta cell?' symposium at the 2015 annual meeting of the EASD. It is accompanied by two other reviews on topics from this symposium (by Amin Ardestani and Kathrin Maedler, DOI: 10.1007/s00125-016-3892-9 , and by Heiko Lickert and colleagues, DOI: 10.1007/s00125-016-3949-9 ) and a commentary by the Session Chair, Shanta Persaud (DOI: 10.1007/s00125-016-3870-2 ).

Insulin Resistance in Relation to Lipids and Inflammation in Type-2 Diabetic Patients and Non-Diabetic People

Background

We demonstrated in experimental studies that hypercholesterolaemia enhances the proliferation of haematopoietic stem cells and the subsequent differentiation to neutrophils, whereas HDL-cholesterol inhibits these processes. To translate our experimental findings to clinical practice, we investigated in Chinese type-2 diabetic patients and in Flemish non-diabetic people the independent and joint associations of insulin resistance with markers of dyslipidaemia and inflammation, while looking for consistency between ethnicities and across the spectrum of insulin resistance.

Methods

We studied 798 Chinese patients with type-2 diabetes (53.6% women; mean age, 60.6 years) admitted to a tertiary referral centre and 1060 white Flemish (50.5%; 51.1 years) randomly recruited in Northern Belgium. Fasting insulin resistance (HOMA-IR) was derived from C-peptide in Chinese and from insulin in Flemish using the Homeostasis Model of Assessment algorithm. In multivariable-adjusted analyses, HOMA-IR was regressed on triglycerides, HDL-cholesterol and neutrophil count.

Results

In Chinese patients, the percentage changes in HOMA-IR associated with triglycerides, HDL-cholesterol and neutrophils (per 1-SD increment) amounted to 8.1 (95% confidence interval, 3.0 to 13.4; p = 0.0015), -8.7 (-13.0 to -4.2; p = 0.0002) and 5.6 (1.0 to 10.4; p = 0.017). In non-diabetic Flemish, the corresponding estimates were 11.7 (8.3 to 15.1; p<0.0001), -1.7 (-4.6 to 1.4; p = 0.28) and 3.3% (0.5 to 6.3; p = 0.022), respectively. None of the interaction terms between the three explanatory variables reached significance in Chinese or Flemish (p≥0.10).

Conclusions

Insulin resistance increases with the serum level of triglycerides and the blood neutrophil count, but decreases with serum HDL-cholesterol concentration. These associations were consistent in Chinese type-2 diabetic patients and non-diabetic Flemish people and were independent from one another. The clinical implications are that future studies should focus on intervening with serum triglyceride and HDL-cholesterol levels or controlling inflammation as a way to prevent or treat insulin resistance.

Tissue-resident versus monocyte-derived macrophages in the tumor microenvironment

The tumor-promoting role of macrophages has been firmly established in most cancer types. However, macrophage identity has been a matter of debate, since several levels of complexity result in considerable macrophage heterogeneity. Ontogenically, tissue-resident macrophages derive from yolk sac progenitors which either directly or via a fetal liver monocyte intermediate differentiate into distinct macrophage types during embryogenesis and are maintained throughout life, while a disruption of the steady state mobilizes monocytes and instructs the formation of monocyte-derived macrophages. Histologically, the macrophage phenotype is heavily influenced by the tissue microenvironment resulting in molecularly and functionally distinct macrophages in distinct organs. Finally, a change in the tissue microenvironment as a result of infectious or sterile inflammation instructs different modes of macrophage activation. These considerations are relevant in the context of tumors, which can be considered as sites of chronic sterile inflammation encompassing subregions with distinct environmental conditions (for example, hypoxic versus normoxic). Here, we discuss existing evidence on the role of macrophage subpopulations in steady state tissue and primary tumors of the breast, lung, pancreas, brain and liver.