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Altered macrophage infiltration upon tissue damage results in inadequate healing due to inappropriate remodeling and stem cell recruitment and differentiation. We investigated in vivo whether cells of endothelial origin phenotypically change upon heterotopic ossification induction and whether infiltration of innate immunity cells influences their commitment and alters the ectopic bone formation. Liposome-encapsulated clodronate was used to assess macrophage impact on endothelial cells in the skeletal muscle upon acute damage in the ECs specific lineage-tracing Cdh5CreER T2 :R26REYFP/dtTomato transgenic mice. Macrophage depletion in the injured skeletal muscle partially shifts the fate of ECs toward endochondral differentiation. Upon ectopic stimulation of BMP signaling, monocyte depletion leads to an enhanced contribution of ECs chondrogenesis and to ectopic bone formation, with increased bone volume and density, that is reversed by ACVR1/SMAD pathway inhibitor dipyridamole. This suggests that macrophages contribute to preserve endothelial fate and to limit the bone lesion in a BMP/injury-induced mouse model of heterotopic ossification. Therefore, alterations of the macrophage-endothelial axis may represent a novel target for molecular intervention in heterotopic ossification.

The ACVR1 gene encodes a type I receptor of bone morphogenetic proteins (BMPs). Activating mutations in ACVR1 are responsible for fibrodysplasia ossificans progressiva (FOP), a rare disease characterized by congenital toe malformation and progressive heterotopic endochondral ossification leading to severe and cumulative disability. Until now, no therapy has been available to prevent soft-tissue swelling (flare-ups) that trigger the ossification process. With the aim of finding a new therapeutic strategy for FOP, we developed a high-throughput screening (HTS) assay to identify inhibitors of ACVR1 gene expression among drugs already approved for the therapy of other diseases. The screening, based on an ACVR1 promoter assay, was followed by an in vitro and in vivo test to validate and characterize candidate molecules. Among compounds that modulate the ACVR1 promoter activity, we selected the one showing the highest inhibitory effect, dipyridamole, a drug that is currently used as a platelet anti-aggregant. The inhibitory effect was detectable on ACVR1 gene expression, on the whole Smad-dependent BMP signaling pathway, and on chondrogenic and osteogenic differentiation processes by in vitro cellular assays. Moreover, dipyridamole reduced the process of heterotopic bone formation in vivo. Our drug repositioning strategy has led to the identification of dipyridamole as a possible therapeutic tool for the treatment of FOP. Furthermore, our study has also defined a pipeline of assays that will be useful for the evaluation of other pharmacological inhibitors of heterotopic ossification.

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The signals that control endothelial plasticity in inflamed tissues have only been partially characterized. For example, it has been shown that inadequate vasculogenesis in systemic sclerosis (SSc) has been associated with an endothelial defect. We used a genetic lineage tracing model to investigate whether endothelial cells die or change phenotypically after fibrosis induction and whether signals released by cells of the innate immune system and in the blood of patients influence their commitment. We observed that in the lineage-tracing transgenic mice Cdh5-CreER T2 ::R26R-EYFP, endothelial-derived cells (EdCs) underwent fibrosis after treatment with bleomycin, and EdCs retrieved from the lung showed expression of endothelial-to-mesenchymal transition (EndoMT) markers. Liposome-encapsulated clodronate was used to assess macrophage impact on EdCs. Clodronate treatment affected the number of alternatively activated macrophages in the lung, with upregulated expression of EndoMT markers in lung EdCs. Endothelial fate and function were investigated in vitro upon challenge with serum signals from SSc patients or released by activated macrophages. Sera of SSc patients with anti-Scl70 Abs, at higher risk of visceral organ fibrosis, induced EndoMT and jeopardized endothelial function. In conclusion, EdCs in SSc might be defective because of commitment to a mesenchymal fate, which is sustained by soluble signals in the patient's blood. Macrophages contribute to preserve the endothelial identity of precursor cells. Altered macrophage-dependent plasticity of EdCs could contribute to link vasculopathy with fibrosis.

ObjectiveInsulin resistance, defined as tissue inflammation leading to type 2 diabetes, is a feature of obesity. The immune system has been implicated in its pathogenesis, but the role of adaptive immunity in humans remains uncertain. Here, we aim to determine whether specific phenotypic and functional properties of visceral adipose tissue (VAT)-derived CD4 conventional T cells (Tconv) and CD8 T cells are associated with dysglycemia in human obesity.Research design and methodsPeripheral blood and the stromal vascular fraction of obese patients without dysglycemia (n=23), with impaired fasting glucose or type 2 diabetes (n=17), and non-diabetic lean controls (n=11) were studied. Characterization of memory, activation profile, cytokine production, proliferative capacity, cytotoxic potential and transforming growth factor-β-mediated suppression of CD4 Tconv and CD8 T cells was performed. Correlation between anthropometric/metabolic parameters and VAT-derived T cell subsets was determined.ResultsIn the VAT of the overall obese population, reduced frequency of interferon-γ-producing or tumor necrosis factor-α-producing CD4 (ie, T helper 1, Th1) and CD8 (ie, cytotoxic type 1, Tc1) T cells, as well as interleukin-17-producing CD8 T cells (ie, Tc17), was evident when compared with lean controls. However, enrichment of Tc1 cells, together with the impaired ability of CD4 and CD8 T cells to be suppressed, distinguished the visceral fat of obese patients with dysglycemia from the one of non-diabetic obese patients. Moreover, accumulation of Th1 and Tc1 cells in the VAT correlated with anthropometric and metabolic parameters.ConclusionsHere, we define the VAT-specific characteristics of T cells in human obesity, showing that accumulation of Tc1 cells and T cell resistance to suppression can be harmful to the development of obesity-induced diabetes. These findings open new directions to investigate immunological targets in the obesity setting.

Purpose of Review Diabetes mellitus can be categorized into two major variants, type 1 and type 2. A number of traits such as clinical phenotype, age at disease onset, genetic background, and underlying pathogenesis distinguish the two forms. Recent Findings Recent evidence indicates that type 1 diabetes can be accompanied by insulin resistance and type 2 diabetes exhibits self-reactivity. These two previously unknown conditions can influence the progression and outcome of the disease. Unlike most conventional considerations, diabetes appears to consist of a spectrum of intermediate phenotypes that includes monogenic and polygenic loci linked to inflammatory processes including autoimmunity, beta cell impairment, and insulin resistance. Summary Here we discuss why a shift of the classical bi-modal view of diabetes (autoimmune vs. non-autoimmune) is necessary in favor of a model of an immunological continuum of endotypes lying between the two extreme “insulin-resistant” and “autoimmune beta cell targeting,” shaped by environmental and genetic factors which contribute to determine specific immune-conditioned outcomes.

There was an error concerning Fig. 4 in Dis. Model. Mech. 9, 685-696.The wrong figure was used for Fig. 4. The correct figure is shown in this Correction with its legend. The PDF and full-text version of this article have been corrected.The authors and DMM office apologise to the readers for this error. P<0.001.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed. 1067