Histopathology of Type 1 Diabetes: Old Paradigms and New Insights

Although our knowledge on the various aspects of diabetes development in the NOD mouse model is substantial and keeps expanding at a dramatic pace, the dataset on histopathologic features of type 1 diabetes (T1D) in patients remains largely stagnant. Early work has established an array of common aspects that have become epitomic in the absence of new patient material. There is a growing consensus that an updated and more detailed view is required that challenges and expands our understanding. Comprehensive initiatives are currently ongoing to address these issues in pre-diabetic, recent onset and longstanding type 1 diabetic individuals, and some of the old data have been recently revisited. In this review article, we wish to provide an overview of where we stand today and how we can correlate the various cross-sectional studies from the past with contemporary models of the disease. We believe an enhanced understanding of the many histopathological particularities in patients as compared to animal models will ultimately lead, not only to more fundamental insights, but also to an improved ability to translate pre-clinical data from bench to bedside

Virus Infections in Type 1 Diabetes

The precise etiology of type 1 diabetes (T1D) is still unknown, but viruses have long been suggested as a potential environmental trigger for the disease. However, despite decades of research, the body of evidence supporting a relationship between viral infections and initiation or acceleration of islet autoimmunity remains largely circumstantial. The most robust association with viruses and T1D involves enterovirus species, of which some strains have the ability to induce or accelerate disease in animal models. Several hypotheses have been formulated to mechanistically explain how viruses may affect islet autoimmunity and β-cell decay. The recent observation that certain viral infections, when encountered at the right time and infectious dose, can prevent autoimmune diabetes illustrates that potential relationships may be more complex than previously thought. Here, we provide a concise summary of data obtained in mouse models and humans, and identify future avenues toward a better characterization of the association between viruses and T1D

Beta cells under attack: toward a better understanding of type 1 diabetes immunopathology

Transplantation and autoimmunit

Genetic evidence implicating natriuretic peptide receptor-3 in cardiovascular disease risk:a Mendelian randomization study

Abstract Background: C-type natriuretic peptide (CNP) is a known target for promoting growth and has been implicated as a therapeutic opportunity for the prevention and treatment of cardiovascular disease (CVD). This study aimed to explore the effect of CNP on CVD risk using the Mendelian randomization (MR) framework. Methods: Instrumental variables mimicking the effects of pharmacological intervention on CNP were identified as uncorrelated genetic variants located in the genes coding for its primary receptors, natriuretic peptide receptors-2 and 3 (NPR2 and NPR3), that associated with height. We performed MR and colocalization analyses to investigate the effects of NPR2 signalling and NPR3 function on CVD outcomes and risk factors. MR estimates were compared to those obtained when considering height variants from throughout the genome. Results: Genetically-proxied reduced NPR3 function was associated with a lower risk of CVD, with odds ratio (OR) 0.74 per standard deviation (SD) higher NPR3-predicted height, and 95% confidence interval (95% CI) 0.64–0.86. This effect was greater in magnitude than observed when considering height variants from throughout the genome. For CVD subtypes, similar MR associations for NPR3-predicted height were observed when considering the outcomes of coronary artery disease (0.75, 95% CI 0.60–0.92), stroke (0.69, 95% CI 0.50–0.95) and heart failure (0.77, 95% CI 0.58–1.02). Consideration of CVD risk factors identified systolic blood pressure (SBP) as a potential mediator of the NPR3-related CVD risk lowering. For stroke, we found that the MR estimate for NPR3 was greater in magnitude than could be explained by a genetically predicted SBP effect alone. Colocalization results largely supported the MR findings, with no evidence of results being driven by effects due to variants in linkage disequilibrium. There was no MR evidence supporting effects of NPR2 on CVD risk, although this null finding could be attributable to fewer genetic variants being identified to instrument this target. Conclusions: This genetic analysis supports the cardioprotective effects of pharmacologically inhibiting NPR3 receptor function, which is only partly mediated by an effect on blood pressure. There was unlikely sufficient statistical power to investigate the cardioprotective effects of NPR2 signalling

BDC12-4.1 T-Cell Receptor Transgenic Insulin-Specific CD4 T Cells Are Resistant to <i>In Vitro</i> Differentiation into Functional Foxp3⁺ T Regulatory Cells

<div><p>The infusion of ex vivo-expanded autologous T regulatory (Treg) cells is potentially an effective immunotherapeutic strategy against graft-versus-host disease (GvHD) and several autoimmune diseases, such as type 1 diabetes (T1D). However, <i>in vitro</i> differentiation of antigen-specific T cells into functional and stable Treg (iTreg) cells has proved challenging. As insulin is the major autoantigen leading to T1D, we tested the capacity of insulin-specific T-cell receptor (TCR) transgenic CD4⁺ T cells of the BDC12-4.1 clone to convert into Foxp3⁺ iTreg cells. We found that <i>in vitro</i> polarization toward Foxp3⁺ iTreg was effective with a majority (>70%) of expanded cells expressing Foxp3. However, adoptive transfer of Foxp3⁺ BDC12-4.1 cells did not prevent diabetes onset in immunocompetent NOD mice. Thus, <i>in vitro</i> polarization of insulin-specific BDC12-4.1 TCR transgenic CD4⁺ T cells toward Foxp3⁺ cells did not provide dominant tolerance in recipient mice. These results highlight the disconnect between an <i>in vitro</i> acquired Foxp3⁺ cell phenotype and its associated <i>in vivo</i> regulatory potential.</p></div

BDC12-4.1 T cells expand and display memory and Treg cell phenotypes in the periphery.

<p>(A and B) Age-associated increases in total CD4⁺ T cell numbers in the spleen and PLN of BDC12-4.1.RAG^KO mice. Splenocytes and PLN lymphocytes from BDC12-4.1.RAG^KO mice were analyzed at different ages by flow cytometry for the frequency of CD4⁺Vβ2⁺ T cells. The percentage of CD4⁺Vβ2⁺ cells was multiplied with the total number of cells isolated from the spleen or PLN to calculate the total number of CD4⁺ T cells. Trypan blue was used for the exclusion of dead cells prior to counting. (C and D) Representative FACS plots and data for activated T cells, CD44^hiCD62L^low, and Treg cells, CD25⁺Foxp3⁺, from the spleens of donor mice that were used to generate Foxp3⁺ Treg cells in vitro are shown.</p

<i>In vitro</i> polarization induces Foxp3 expression in memory BDC12-4.1 T cells but does not endow <i>in vivo</i> regulatory functions.

<p>CD4⁺CD25⁺ cells from splenocytes of BDC12-4.1 mice polarized into Treg cells (A) <i>in vitro</i> in the presence of a-CD3 (left panel) or InsB:9-23 peptide (right panel). Expanded T cells were gated on CD4⁺CD25⁺ cells (not shown) and expression of CD127 and Foxp3 were determined. (B). 1×10⁶ Tregs polarized with anti-CD3 (left panel) or InsB:9-23 peptide (right panel) were adoptively transferred into prediabetic 8-wk old NOD mice and diabetes development was monitored. Unmanipulated NOD mice monitored on a regular basis in our animal colony served as negative controls with cumulative diabetes incidence of ∼90% by 27 wks of age. Representative results from one of three independent experiments are shown.</p

T cells with InsB:9-23 specific responses increase in frequencies with age.

<p>Total splenocytes from BDC12-4.1.RAG^KO mice were obtained at different ages. 250,000 splenocytes per well were incubated with or without native InsB:9-23 peptide in triplicates. Following 3-day incubation, IFN-γ, IL-2, and IL-4 production were determined by ELISpot assay. Representative images of cytokine production from BDC12-4.1.RAG^KO T-cells with (bottom row) or without antigen (top row) stimulation is shown in A. Background (media) subtracted IFN-γ spot numbers produced in response to antigen stimulation, from BDC12-4.1.RAG^KO mice of different age groups are shown on the Y-axis in B. Representative means ± SEM data from one of two independent experiments with n = 3 per each group with similar results are shown.</p