Vascular and immune interactions in islets transplantation and 3D islet models.

The aim of regenerative medicine is to restore specific functions to damaged cells or tissues. A crucial aspect of success lies in effectively reintegrating these cells or tissues within the recipient organism. This is particularly pertinent for diabetes, where islet function relies on the close connection of beta cells to the bloodstream for glucose sensing and insulin release. Central to this approach is the need to establish a fast connection with the host's vascular system. In this review, we explore the intricate relationships between endocrine, vascular, and immune cell interactions in transplantation outcomes. We also delve into recent strategies aimed at enhancing engraftment, along with the utilization of in vitro platforms to model cellular interactions.

Delineating mouse ß-cell identity during lifetime and in diabetes with a single cell atlas.

Although multiple pancreatic islet single-cell RNA-sequencing (scRNA-seq) datasets have been generated, a consensus on pancreatic cell states in development, homeostasis and diabetes as well as the value of preclinical animal models is missing. Here, we present an scRNA-seq cross-condition mouse islet atlas (MIA), a curated resource for interactive exploration and computational querying. We integrate over 300,000 cells from nine scRNA-seq datasets consisting of 56 samples, varying in age, sex and diabetes models, including an autoimmune type 1 diabetes model (NOD), a glucotoxicity/lipotoxicity type 2 diabetes model (db/db) and a chemical streptozotocin ß-cell ablation model. The ß-cell landscape of MIA reveals new cell states during disease progression and cross-publication differences between previously suggested marker genes. We show that ß-cells in the streptozotocin model transcriptionally correlate with those in human type 2 diabetes and mouse db/db models, but are less similar to human type 1 diabetes and mouse NOD ß-cells. We also report pathways that are shared between ß-cells in immature, aged and diabetes models. MIA enables a comprehensive analysis of ß-cell responses to different stressors, providing a roadmap for the understanding of ß-cell plasticity, compensation and demise.

Human pluripotent stem cell-derived insulin-producing cells: A regenerative medicine perspective.

Tremendous progress has been made over the last two decades in the field of pancreatic beta cell replacement therapy as a curative measure for diabetes. Transplantation studies have demonstrated therapeutic efficacy, and cGMP-grade cell products are currently being deployed for the first time in human clinical trials. In this perspective, we discuss current challenges surrounding the generation, delivery, and engraftment of stem cell-derived islet-like cells, along with strategies to induce durable tolerance to grafted cells, with an eye toward a functional cellular-based therapy enabling insulin independence for patients with diabetes.

Pluripotent Stem Cell-Derived Pancreatic Progenitors and ß-Like Cells for Type 1 Diabetes Treatment.

In this review, we focus on the processes guiding human pancreas development and provide an update on methods to efficiently generate pancreatic progenitors (PPs) and ß-like cells in vitro from human pluripotent stem cells (hPSCs). Furthermore, we assess the strengths and weaknesses of using PPs and ß-like cell for cell replacement therapy for the treatment of Type 1 diabetes with respect to cell manufacturing, engrafting, functionality, and safety. Finally, we discuss the identification and use of specific cell surface markers to generate safer populations of PPs for clinical translation and to study the development of PPs in vivo and in vitro.

Direct Substrate Delivery Into Mitochondrial Fission-Deficient Pancreatic Islets Rescues Insulin Secretion.

In pancreatic ß-cells, mitochondrial bioenergetics control glucose-stimulated insulin secretion. Mitochondrial dynamics are generally associated with quality control, maintaining the functionality of bioenergetics. By acute pharmacological inhibition of mitochondrial fission protein Drp1, we demonstrate in this study that mitochondrial fission is necessary for glucose-stimulated insulin secretion in mouse and human islets. We confirm that genetic silencing of Drp1 increases mitochondrial proton leak in MIN6 cells. However, our comprehensive analysis of pancreatic islet bioenergetics reveals that Drp1 does not control insulin secretion via its effect on proton leak but instead via modulation of glucose-fueled respiration. Notably, pyruvate fully rescues the impaired insulin secretion of fission-deficient ß-cells, demonstrating that defective mitochondrial dynamics solely affect substrate supply upstream of oxidative phosphorylation. The present findings provide novel insights into how mitochondrial dysfunction may cause pancreatic ß-cell failure. In addition, the results will stimulate new thinking in the intersecting fields of mitochondrial dynamics and bioenergetics, as treatment of defective dynamics in mitochondrial diseases appears to be possible by improving metabolism upstream of mitochondria.

Impact of islet architecture on ß-cell heterogeneity, plasticity and function.

Although ß-cell heterogeneity was discovered more than 50 years ago, the underlying principles have been explored only during the past decade. Islet-cell heterogeneity arises during pancreatic development and might reflect the existence of distinct populations of progenitor cells and the developmental pathways of endocrine cells. Heterogeneity can also be acquired in the postnatal period owing to ß-cell plasticity or changes in islet architecture. Furthermore, ß-cell neogenesis, replication and dedifferentiation represent alternative sources of ß-cell heterogeneity. In addition to a physiological role, ß-cell heterogeneity influences the development of diabetes mellitus and its response to treatment. Identifying phenotypic and functional markers to discriminate distinct ß-cell subpopulations and the mechanisms underpinning their regulation is warranted to advance current knowledge of ß-cell function and to design novel regenerative strategies that target subpopulations of ß cells. In this context, the Wnt/planar cell polarity (PCP) effector molecule Flattop can distinguish two unique ß-cell subpopulations with specific transcriptional signatures, functional properties and differential responses to environmental stimuli. In vivo targeting of these ß-cell subpopulations might, therefore, represent an alternative strategy for the future treatment of diabetes mellitus.

Targeting insulin-producing beta cells for regenerative therapy.

Pancreatic beta cells differ in terms of glucose responsiveness, insulin secretion and proliferative capacity; however, the molecular pathways that regulate this cellular heterogeneity are unknown. We have identified the Wnt-planar cell polarity (PCP) effector Flattop (FLTP) as a biomarker that identifies mature beta cells in the islets of Langerhans. Interestingly, three-dimensional architecture and Wnt-PCP ligands are sufficient to trigger mouse and human beta cell maturation. These results highlight the fact that novel biomarkers shed light on the long-standing mystery of beta cell heterogeneity and identify the Wnt-PCP pathway as triggering beta cell maturation. Understanding heterogeneity in the islets of Langerhans might allow targeting of beta cell subpopulations for regenerative therapy and provide building principles for stem cell-derived islets. This review 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 Harry Heimberg and colleagues, DOI: 10.1007/s00125-016-3879-6 ) and a commentary by the Session Chair, Shanta Persaud (DOI: 10.1007/s00125-016-3870-2 ).

Identification of proliferative and mature ß-cells in the islets of Langerhans.

Insulin-dependent diabetes is a complex multifactorial disorder characterized by loss or dysfunction of ß-cells. Pancreatic ß-cells differ in size, glucose responsiveness, insulin secretion and precursor cell potential; understanding the mechanisms that underlie this functional heterogeneity might make it possible to develop new regenerative approaches. Here we show that Fltp (also known as Flattop and Cfap126), a Wnt/planar cell polarity (PCP) effector and reporter gene acts as a marker gene that subdivides endocrine cells into two subpopulations and distinguishes proliferation-competent from mature ß-cells with distinct molecular, physiological and ultrastructural features. Genetic lineage tracing revealed that endocrine subpopulations from Fltp-negative and -positive lineages react differently to physiological and pathological changes. The expression of Fltp increases when endocrine cells cluster together to form polarized and mature 3D islet mini-organs. We show that 3D architecture and Wnt/PCP ligands are sufficient to trigger ß-cell maturation. By contrast, the Wnt/PCP effector Fltp is not necessary for ß-cell development, proliferation or maturation. We conclude that 3D architecture and Wnt/PCP signalling underlie functional ß-cell heterogeneity and induce ß-cell maturation. The identification of Fltp as a marker for endocrine subpopulations sheds light on the molecular underpinnings of islet cell heterogeneity and plasticity and might enable targeting of endocrine subpopulations for the regeneration of functional ß-cell mass in diabetic patients.

Analysis of nucleic acid-induced nonimmune cell death in vitro.

Foreign nucleic acids are recognized by germ-line-encoded receptors expressed in immune and nonimmune cells. Activation of the nucleic acid-specific pattern recognition receptors by foreign nucleic acid promotes production of inflammatory cytokines (mostly type I IFNs) and at the later stage leads to cell death. Here, we describe reliable and simple methods to quantify cell death caused by nucleic acid recognition. Additionally, we report two different methods to discriminate between two cell death modalities: apoptosis and necrosis.

Islet cell plasticity and regeneration.

Insulin-dependent diabetes is a complex multifactorial disorder characterized by loss or dysfunction of ß-cells resulting in failure of metabolic control. Even though type 1 and 2 diabetes differ in their pathogenesis, restoring ß-cell function is the overarching goal for improved therapy of both diseases. This could be achieved either by cell-replacement therapy or by triggering intrinsic regenerative mechanisms of the pancreas. For type 1 diabetes, a combination of ß-cell replacement and immunosuppressive therapy could be a curative treatment, whereas for type 2 diabetes enhancing endogenous mechanisms of ß-cell regeneration might optimize blood glucose control. This review will briefly summarize recent efforts to allow ß-cell regeneration where the most promising approaches are currently (1) increasing ß-cell self-replication or neogenesis from ductal progenitors and (2) conversion of α-cells into ß-cells.

Podocyte loss involves MDM2-driven mitotic catastrophe.

Podocyte apoptosis as a pathway of podocyte loss is often suspected but rarely detected. To study podocyte apoptosis versus inflammatory forms of podocyte death in vivo, we targeted murine double minute (MDM)-2 for three reasons. First, MDM2 inhibits p53-dependent apoptosis; second, MDM2 facilitates NF-κB signalling; and third, podocytes show strong MDM2 expression. We hypothesized that blocking MDM2 during glomerular injury may trigger p53-mediated podocyte apoptosis, proteinuria, and glomerulosclerosis. Unexpectedly, MDM2 blockade in early adriamycin nephropathy of Balb/c mice had the opposite effect and reduced intra-renal cytokine and chemokine expression, glomerular macrophage and T-cell counts, and plasma creatinine and blood urea nitrogen levels. In cultured podocytes exposed to adriamycin, MDM2 blockade did not trigger podocyte death but induced G2/M arrest to prevent aberrant nuclear divisions and detachment of dying aneuploid podocytes, a feature of mitotic catastrophe in vitro and in vivo. Consistent with these observations, 12 of 164 consecutive human renal biopsies revealed features of podocyte mitotic catastrophe but only in glomerular disorders with proteinuria. Furthermore, delayed MDM2 blockade reduced plasma creatinine levels, blood urea nitrogen, tubular atrophy, interstitial leukocyte numbers, and cytokine expression as well as interstitial fibrosis. Together, MDM2-mediated mitotic catastrophe is a previously unrecognized variant of podocyte loss where MDM2 forces podocytes to complete the cell cycle, which in the absence of cytokinesis leads to podocyte aneuploidy, mitotic catastrophe, and loss by detachment. MDM2 blockade with nutlin-3a could be a novel therapeutic strategy to prevent renal inflammation, podocyte loss, glomerulosclerosis, proteinuria, and progressive kidney disease.

The antiviral cytokines IFN-α and IFN-ß modulate parietal epithelial cells and promote podocyte loss: implications for IFN toxicity, viral glomerulonephritis, and glomerular regeneration.

Interferon (IFN)-α and IFN-ß are the central regulators of antiviral immunity but little is known about their roles in viral glomerulonephritis (eg, HIV nephropathy). We hypothesized that IFN-α and IFN-ß would trigger local inflammation and podocyte loss. We found that both IFNs consistently activated human and mouse podocytes and parietal epithelial cells to express numerous IFN-stimulated genes. However, only IFN-ß significantly induced podocyte death and increased the permeability of podocyte monolayers. In contrast, only IFN-α caused cell-cycle arrest and inhibited the migration of parietal epithelial cells. Both IFNs suppressed renal progenitor differentiation into mature podocytes. In Adriamycin nephropathy, injections with either IFN-α or IFN-ß aggravated proteinuria, macrophage influx, and glomerulosclerosis. A detailed analysis showed that only IFN-ß induced podocyte mitosis. This did not, however, lead to proliferation, but was associated with podocyte loss via podocyte detachment and/or mitotic podocyte death (mitotic catastrophe). We did not detect TUNEL-positive podocytes. Thus, IFN-α and IFN-ß have both common and differential effects on podocytes and parietal epithelial cells, which together promote glomerulosclerosis by enhancing podocyte loss while suppressing podocyte regeneration from local progenitors.

The danger control concept in kidney disease: mesangial cells.

Kidney remodeling is a response to intrinsic or extrinsic triggers of kidney injury. Injury initiates a set of universal response programs that were positively selected through evolution to control potentially life-threatening dangers and to regain homeostasis, including tissue repair. These danger control programs are (i) clotting, to control the risk of bleeding; (ii) inflammation, to control the risk of infection; (iii) epithelial repair; (iv) mesenchymal repair; and (v) scar resolution or minimization. In this review we focus on the role of mesangial cells in glomerular disorders and how their behaviors follow these danger control programs. We review the role of mesangial cells in glomerular coagulation and fibrinolysis, as well as their role in triggering glomerular inflammation and mesangioproliferative disorders. Furthermore, we discuss how the mesangium self-repairs, how podocyte injury triggers a "mesenchymal healing"-kind of response that leads to glomerular fibrosis and sclerosis. Thus, we can better appreciate the contribution of mesangial cells to glomerular pathology when we understand their behavior as an attempt to support the evolutionally conserved universal danger control programs. However, these mechanisms often result in maladaptive processes that destroy the complex glomerular ultrastructure rather than help to regain tissue homeostasis.

Calcium oxalate crystals induce renal inflammation by NLRP3-mediated IL-1ß secretion.

Nephrocalcinosis, acute calcium oxalate (CaOx) nephropathy, and renal stone disease can lead to inflammation and subsequent renal failure, but the underlying pathological mechanisms remain elusive. Other crystallopathies, such as gout, atherosclerosis, and asbestosis, trigger inflammation and tissue remodeling by inducing IL-1ß secretion, leading us to hypothesize that CaOx crystals may induce inflammation in a similar manner. In mice, intrarenal CaOx deposition induced tubular damage, cytokine expression, neutrophil recruitment, and renal failure. We found that CaOx crystals activated murine renal DCs to secrete IL-1ß through a pathway that included NLRP3, ASC, and caspase-1. Despite a similar amount of crystal deposits, intrarenal inflammation, tubular damage, and renal dysfunction were abrogated in mice deficient in MyD88; NLRP3, ASC, and caspase-1; IL-1R; or IL-18. Nephropathy was attenuated by DC depletion, ATP depletion, or therapeutic IL-1 antagonism. These data demonstrated that CaOx crystals trigger IL-1ß-dependent innate immunity via the NLRP3/ASC/caspase-1 axis in intrarenal mononuclear phagocytes and directly damage tubular cells, leading to the release of the NLRP3 agonist ATP. Furthermore, these results suggest that IL-1ß blockade may prevent renal damage in nephrocalcinosis.

Plasma leakage through glomerular basement membrane ruptures triggers the proliferation of parietal epithelial cells and crescent formation in non-inflammatory glomerular injury.

Glomerular crescents are most common in rapidly progressive glomerulonephritis but also occur in non-inflammatory chronic glomerulopathies; thus, factors other than inflammation should trigger crescent formation, eg vascular damage and plasma leakage. Here we report that Alport nephropathy in Col4A3-deficient Sv129 mice is complicated by diffuse and global crescent formation in which proliferating parietal epithelial cells are the predominant cell type. Laminin staining and transmission and acellular scanning electron microscopy of acellular glomeruli documented disruptions and progressive disintegration of the glomerular basement membrane in Col4A3-deficient mice. FITC-dextran perfusion further revealed vascular leakage from glomerular capillaries into Bowman's space, further documented by fibrin deposits in the segmental crescents. Its pathogenic role was validated by showing that the fibrinolytic activity of recombinant urokinase partially prevented crescent formation. In addition, in vitro studies confirmed an additional mitogenic potential of serum on murine and human parietal epithelial cells. Furthermore, loss of parietal cell polarity and unpolarized secretion of extracellular matrix components were evident within fibrocellular crescents. Among 665 human Alport nephropathy biopsies, crescent formation was noted in 0.4%. We conclude that glomerular vascular injury and GBM breaks cause plasma leakage which triggers a wound healing programme involving the proliferation of parietal cells and their loss of polarity. This process can trigger cellular and fibrocellular crescent formation even in the absence of cellular inflammation and rupture of the Bowman's capsule.

A novel pathogenetic concept-antiviral immunity in lupus nephritis.

Lupus nephritis is a complication of systemic lupus erythematosus, a heterogeneous autoimmune syndrome involving multiple pathways. Accumulating data from the fields of genetics, clinical science, transcriptomics and basic immunology indicate that antiviral immunity has relevance in the pathogenesis of lupus nephritis. This idea is based on the existence of genetic variants that promote the persistence of nuclear particles in the extracellular space or inside lysosomes. Such nuclear particles mimic viral particles and their RNA or DNA components activate viral nucleic acid recognition receptors in antigen-presenting cells. These autoadjuvant effects of endogenous nucleic acids promote an inappropriate immune interpretation of the nuclear particles during antigen presentation. This process fosters the expansion of autoreactive T cells and B cells, which promotes autoantibody production and immune complex glomerulonephritis. The release of interferon α sets off an antiviral immune response with a coordinated induction of hundreds of antiviral genes both inside and outside the kidney. In this article we summarize the available data indicating that innate immunity triggers antiviral immunity in systemic lupus erythematosus. We also discuss the related implications for innovative therapeutic strategies.