A Deeper Look into Type 1 Diabetes - Imaging Immune Responses during Onset of Disease

Single-cell RNA sequencing highlights the roles of C1QB and NKG7 in the pancreatic islet immune microenvironment in type 1 diabetes mellitus

Single-cell RNA sequencing (scRNA-seq) technology is a powerful tool for characterizing individual cells and elucidating biological mechanisms at the cellular level. Using this technology, this study focuses on the mechanism of C1QB and NKG7 in pancreatic islet immune microenvironment in type 1 diabetes mellitus (T1DM). T1DM-related scRNA-seq data were downloaded from GEO database, followed by batch effect removal, cluster analysis, cell annotation and enrichment analysis. Thereafter, T1DM-related Bulk RNA-seq data were downloaded from GEO database. The infiltrating immune cell abundance was estimated and its correlation with the expression of immune cell marker genes was determined. Functional assays were performed in a constructed rat model of T1DM and cultured monocytes and lymphocytes for further validation. A large number of highly variable genes were found in pancreatic islet samples in T1DM. T1DM islet-derived cells may consist of 14 cell types. Macrophages and T lymphocytes were the major cells in pancreatic islet immune microenvironment. C1QB and NKG7 may be the key genes affecting macrophages and T lymphocytes, respectively. Silencing C1QB inhibited the differentiation of monocytes into macrophages and reduced the number of macrophages. Silencing NKG7 prevented T lymphocyte activation and proliferation. In vivo data confirmed that silencing C1QB and NKG7 reduced the number of macrophages and T lymphocytes in the pancreatic islet of T1DM rats, respectively, and alleviated pancreatic islet β-cell damage. Overall, C1QB and NKG7 can increase the number of macrophages and T lymphocytes, respectively, causing pancreatic islet β-cell damage and promoting T1DM in rats.

Mouse models and human islet transplantation sites for intravital imaging

Human islet transplantations into rodent models are an essential tool to aid in the development and testing of islet and cellular-based therapies for diabetes prevention and treatment. Through the ability to evaluate human islets in an in vivo setting, these studies allow for experimental approaches to answer questions surrounding normal and disease pathophysiology that cannot be answered using other in vitro and in vivo techniques alone. Intravital microscopy enables imaging of tissues in living organisms with dynamic temporal resolution and can be employed to measure biological processes in transplanted human islets revealing how experimental variables can influence engraftment, and transplant survival and function. A key consideration in experimental design for transplant imaging is the surgical placement site, which is guided by the presence of vasculature to aid in functional engraftment of the islets and promote their survival. Here, we review transplantation sites and mouse models used to study beta cell biology in vivo using intravital microscopy and we highlight fundamental observations made possible using this methodology.

SWIP-a stabilized window for intravital imaging of the murine pancreas

Pancreatitis and pancreatic ductal adenocarcinoma (PDAC) are grave illnesses with high levels of morbidity and mortality. Intravital imaging (IVI) is a powerful technique for visualizing physiological processes in both health and disease. However, the application of IVI to the murine pancreas presents significant challenges, as it is a deep, compliant, visceral organ that is difficult to access, easily damaged and susceptible to motion artefacts. Existing imaging windows for stabilizing the pancreas during IVI have unfortunately shown poor stability for time-lapsed imaging on the minutes to hours scale, or are unable to accommodate both the healthy and tumour-bearing pancreata. To address these issues, we developed an improved stabilized window for intravital imaging of the pancreas (SWIP), which can be applied to not only the healthy pancreas but also to solid tumours like PDAC. Here, we validate the SWIP and use it to visualize a variety of processes for the first time, including (1) single-cell dynamics within the healthy pancreas, (2) transformation from healthy pancreas to acute pancreatitis induced by cerulein, and (3) the physiology of PDAC in both autochthonous and orthotopically injected models. SWIP can not only improve the imaging stability but also expand the application of IVI in both benign and malignant pancreas diseases.

The β-Cell Genomic Landscape in T1D: Implications for Disease Pathogenesis

PURPOSE OF REVIEW

Type 1 diabetes (T1D) develops as a consequence of a combination of genetic predisposition and environmental factors. Combined, these events trigger an autoimmune disease that results in progressive loss of pancreatic β cells, leading to insulin deficiency. This article reviews the current knowledge on the genetics of T1D with a specific focus on genetic variation in pancreatic islet regulatory networks and its implication to T1D risk and disease development.

RECENT FINDINGS

Accumulating evidence suggest an active role of β cells in T1D pathogenesis. Based on such observation several studies aimed in mapping T1D risk variants acting at the β cell level. Such studies unravel T1D risk loci shared with type 2 diabetes (T2D) and T1D risk variants potentially interfering with β-cell responses to external stimuli. The characterization of regulatory genomics maps of disease-relevant states and cell types can be used to elucidate the mechanistic role of β cells in the pathogenesis of T1D.

Altered expression of SIRPγ on the T-cells of relapsing remitting multiple sclerosis and type 1 diabetes patients could potentiate effector responses from T-cells

Factors regulating self-antigen directed immune-responses in autoimmunity are poorly understood. Signal regulatory protein gamma (SIRPγ) is a human T-cell specific protein with genetic variants associated with type 1 diabetes (T1D). SIRPγ's function in the immune system remains unclear. We show that T1D and relapsing remitting multiple sclerosis (RRMS) subjects have significantly greater frequency of rs2281808 T genetic variant, that correlates with reduced SIRPγ-expression in T-cells. Importantly, reduced SIRPγ-expression in RRMS and T1D subjects was not restricted to T variant, suggesting SIRPγ-expression is also regulated by disease specific factors in autoimmunity. Interestingly, increased frequencies of SIRPγlow T-cells in RRMS and T1D positively correlated with proinflammatory molecules from T-cells. Finally, we show that SIRPγlow T-cells have enhanced pathogenecity in vivo in a GVHD model. These findings suggest that decreased-SIRPγ expression, either determined by genetic variants or through peripherally acquired processes, may have a mechanistic link to autoimmunity through induction of hyperactive T-cells.

Mouse Models of Virus-Induced Type 1 Diabetes

Virus infections have been linked to the induction of autoimmunity and disease development in human type 1 diabetes. Experimental models have been instrumental in deciphering processes leading to break of immunological tolerance and type 1 diabetes development. Animal models have also been useful for proof-of-concept studies and for preclinical testing of new therapeutic interventions. This chapter describes two robust and clinically relevant mouse models for virus-induced type 1 diabetes; acceleration of disease onset in prediabetic nonobese diabetic (NOD) mice following Coxsackievirus infection and diabetes induction by lymphocytic choriomeningitis virus (LCMV) infection of transgenic mice expressing viral neo-antigens under control of the rat insulin promoter (RIP).

A Versatile, Portable Intravital Microscopy Platform for Studying Beta-cell Biology In Vivo

The pancreatic islet is a complex micro-organ containing numerous cell types, including endocrine, immune, and endothelial cells. The communication of these systems is lost upon isolation of the islets, and therefore the pathogenesis of diabetes can only be fully understood by studying this organized, multicellular environment in vivo. We have developed several adaptable tools to create a versatile platform to interrogate β-cell function in vivo. Specifically, we developed β-cell-selective virally-encoded fluorescent protein biosensors that can be rapidly and easily introduced into any mouse. We then coupled the use of these biosensors with intravital microscopy, a powerful tool that can be used to collect cellular and subcellular data from living tissues. Together, these approaches allowed the observation of in vivo β-cell-specific ROS dynamics using the Grx1-roGFP2 biosensor and calcium signaling using the GcAMP6s biosensor. Next, we utilized abdominal imaging windows (AIW) to extend our in vivo observations beyond single-point terminal measurements to collect longitudinal physiological and biosensor data through repeated imaging of the same mice over time. This platform represents a significant advancement in our ability to study β-cell structure and signaling in vivo, and its portability for use in virtually any mouse model will enable meaningful studies of β-cell physiology in the endogenous islet niche.

Bioengineering with Endothelial Progenitor Cells Improves the Vascular Engraftment of Transplanted Human Islets

Pancreatic islets isolated for transplantation are disconnected from their vascular supply and need to establish a new functional network posttransplantation. Due to poor revascularization, prevailing hypoxia with correlating increased apoptosis rates in experimental studies can be observed for months posttransplantation. Endothelial progenitor cells (EPCs) are bone marrow-derived cells that promote neovascularization. The present study tested the hypothesis that EPCs, isolated from human umbilical cord blood, could be coated to human islet surfaces and be used to promote islet vascular engraftment. Control or EPC bioengineered human islets were transplanted into the renal subcapsular space of nonobese diabetic/severe combined immunodeficiency mice. Four weeks posttransplantation, graft blood perfusion and oxygen tension were measured using laser Doppler flowmetry and Clark microelectrodes, respectively. Vessel functionality was also assessed by in vivo confocal imaging. The vascular density and the respective contribution of human and recipient endothelium were assessed immunohistochemically by staining for human and mouse CD31. Islet grafts with EPCs had substantially higher blood perfusion and oxygen tension than control transplants. Furthermore, analysis of the vascular network of the grafts revealed that grafts containing EPC bioengineered islets had a superior vascular density compared with control grafts, with functional chimeric blood vessels. We conclude that a simple procedure of surface coating with EPCs provides a possibility to improve the vascular engraftment of transplanted human islets. Established protocols are also easily applicable for intraportal islet transplantation in order to obtain a novel directed cellular therapy at the site of implantation in the liver.

Deciphering the Pathogenesis of Human Type 1 Diabetes (T1D) by Interrogating T Cells from the "Scene of the Crime"

PURPOSE OF REVIEW

Autoimmune-mediated destruction of insulin-producing β-cells within the pancreas results in type 1 diabetes (T1D), which is not yet preventable or curable. Previously, our understanding of the β-cell specific T cell repertoire was based on studies of autoreactive T cell responses in the peripheral blood of patients at risk for, or with, T1D; more recently, investigations have included immunohistochemical analysis of some T cell specificities in the pancreas from organ donors with T1D. Now, we are able to examine live, islet-infiltrating T cells from donors with T1D.

RECENT FINDINGS

Analysis of the T cell repertoire isolated directly from the pancreatic islets of donors with T1D revealed pro-inflammatory T cells with targets of known autoantigens, including proinsulin and glutamic acid decarboxylase, as well as modified autoantigens. We have assayed the islet-infiltrating T cell repertoire for autoreactivity and function directly from the inflamed islets of T1D organ donors. Design of durable treatments for prevention of or therapy for T1D requires understanding this repertoire.

Surgical preparation of rats and mice for intravital microscopic imaging of abdominal organs

Intravital microscopy is a powerful research tool that can provide insight into cellular and subcellular events that take place in organs in the body. However, meaningful results can only be obtained from animals whose physiology is preserved during the process of microscopy. Here I discuss the importance of preserving the overall state of health of the animal, methods of anesthesia, surgical techniques for intravital microscopy of various abdominal organs, methods to maintain and monitor the physiology of the animal during microscopy and associated peri- and post-operative recovery considerations.

Bringing the human pancreas into focus: new paradigms for the understanding of Type 1 diabetes

Type 1 diabetes affects increasingly large numbers of people globally (including at least half a million children under the age of 14 years) and it remains an illness with life-long and often devastating consequences. It is surprising, therefore, that the underlying aetiology of Type 1 diabetes remains poorly understood. This is largely because the cellular and molecular processes leading to the loss of β cells in the pancreas have rarely been studied at, or soon after, the onset of disease. Where such studies have been undertaken, a number of surprises have emerged which serve to challenge conventional wisdom. In particular, it is increasingly understood that the process of islet inflammation (insulitis) is much less florid in humans than in certain animal models. Moreover, the profile of immune cells involved in the inflammatory attack on β cells is variable and this variation occurs at the level of individual patients. As a result, two distinct profiles of insulitis have now been defined that are differentially aggressive and that might, therefore, require specifically tailored therapeutic approaches to slow the progression of disease. In addition, the outcomes are also different in that the more aggressive form (termed 'CD20Hi') is associated with extensive β-cell loss and an early age of disease onset (<7 years), while the less aggressive profile (known as 'CD20Lo') is associated with later onset (>13 years) and the retention of a higher proportion of residual β cells. In the present review, these new findings are explained and their implications evaluated in terms of future therapies.