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Cardiomyocyte proliferation stops at birth when the heart is no longer exposed to maternal blood and, likewise, to regulatory T cells (Tregs) that are expanded to promote maternal tolerance towards the fetus. Here, we report a role of Tregs in promoting cardiomyocyte proliferation. Treg-conditioned medium promotes cardiomyocyte proliferation, similar to the serum from pregnant animals. Proliferative cardiomyocytes are detected in the heart of pregnant mothers, and Treg depletion during pregnancy decreases both maternal and fetal cardiomyocyte proliferation. Treg depletion after myocardial infarction results in depressed cardiac function, massive inflammation, and scarce collagen deposition. In contrast, Treg injection reduces infarct size, preserves contractility, and increases the number of proliferating cardiomyocytes. The overexpression of six factors secreted by Tregs (Cst7, Tnfsf11, Il33, Fgl2, Matn2, and Igf2) reproduces the therapeutic effect. In conclusion, Tregs promote fetal and maternal cardiomyocyte proliferation in a paracrine manner and improve the outcome of myocardial infarction. Regulatory T cells (Tregs) expand during pregnancy to promote tolerance towards the fetus. Here the authors show that Tregs induce proliferation of fetal and maternal cardiomyocytes during pregnancy and enhance myocardial repair via proliferation-promoting paracrine actions.

Despite the high prevalence of ischemic heart diseases worldwide, no antibody-based treatment currently exists. Starting from the evidence that a specific isoform of the Bone Morphogenetic Protein 1 (BMP1.3) is particularly elevated in both patients and animal models of myocardial infarction, here we assess whether its inhibition by a specific monoclonal antibody reduces cardiac fibrosis. We find that this treatment reduces collagen deposition and cross-linking, paralleled by enhanced cardiomyocyte survival, both in vivo and in primary cultures of cardiac cells. Mechanistically, we show that the anti-BMP1.3 monoclonal antibody inhibits Transforming Growth Factor β pathway, thus reducing myofibroblast activation and inducing cardioprotection through BMP5. Collectively, these data support the therapeutic use of anti-BMP1.3 antibodies to prevent cardiomyocyte apoptosis, reduce collagen deposition and preserve cardiac function after ischemia. Here the authors show that a monoclonal antibody against a soluble isoform of Bone Morphogenetic Protein 1 prevents cardiac cell death, reducing fibrosis and preserving cardiac function after myocardial ischemia.

Arrhythmogenic cardiomyopathy (ACM) is a cardiac disorder manifesting through electrical and contractile dysfunction of the ventricles, characterized by fibro-fatty substitution of the myocardium. Cardiac mesenchymal stromal cells (CMSCs) are key contributors to this remodeling. In clinical management, several pharmacological approaches address ACM arrhythmias and heart failure, but, to date, none specifically target fibro-adipose replacement. Despite genetic origin, several studies have reported that non-genetic aspects influence ACM phenotype, including epigenetic factors. Little is known about their mechanisms in ACM and their potential therapeutic applications. In this work, we aimed to test whether, by perturbing the epigenetic landscape of ACM CMSCs, we could influence their propensity to fibro-fatty differentiation. We conducted a hypothesis-free screening of 157 epigenetic drugs on CMSCs, isolated from ACM patients. Through fluorescence assays, we evaluated lipid droplet accumulation, collagen deposition, and cell viability. Of the 157 drugs screened, five (splitomicin, suberohydroxamic acid, CPTH6, BVT-948, and PBIT) attenuated adipogenic differentiation of ACM CMSCs, with BVT-948 and CPTH6 also reducing collagen production. Overall, this study identified specific epigenetic drugs that were effective in reducing the fibro-fatty phenotype of ACM stromal cells, thus offering potential for adjunctive therapies in the clinical management of ACM patients.

Myocardial regeneration is restricted to early postnatal life, when mammalian cardiomyocytes still retain the ability to proliferate. The molecular cues that induce cell cycle arrest of neonatal cardiomyocytes towards terminally differentiated adult heart muscle cells remain obscure. Here we report that the miR-106b~25 cluster is higher expressed in the early postnatal myocardium and decreases in expression towards adulthood, especially under conditions of overload, and orchestrates the transition of cardiomyocyte hyperplasia towards cell cycle arrest and hypertrophy by virtue of its targetome. In line, gene delivery of miR-106b~25 to the mouse heart provokes cardiomyocyte proliferation by targeting a network of negative cell cycle regulators including E2f5, Cdkn1c, Ccne1 and Wee1. Conversely, gene-targeted miR-106b~25 null mice display spontaneous hypertrophic remodeling and exaggerated remodeling to overload by derepression of the prohypertrophic transcription factors Hand2 and Mef2d. Taking advantage of the regulatory function of miR-106b~ 25 on cardiomyocyte hyperplasia and hypertrophy, viral gene delivery of miR-106b~25 provokes nearly complete regeneration of the adult myocardium after ischemic injury. Our data demonstrate that exploitation of conserved molecular programs can enhance the regenerative capacity of the injured heart. Myocardial regeneration and proliferation of heart muscle cells is limited to a short period after birth early postnatal life, after which heart muscle cells can only grow in size and not in number. Here, the authors identified that the expression level of an endogenous microRNA cluster in heart muscle promotes the passage of the proliferative state to adult heart growth, and modulating the expression of this cluster can stimulate heart regeneration after myocardial infarction.

Diagnosis of Arrhythmogenic CardioMyopathy (ACM) is challenging and often late after disease onset. No circulating biomarkers are available to date. Given their involvement in several cardiovascular diseases, plasma microRNAs warranted investigation as potential non-invasive diagnostic tools in ACM. We sought to identify circulating microRNAs differentially expressed in ACM with respect to Healthy Controls (HC) and Idiopathic Ventricular Tachycardia patients (IVT), often in differential diagnosis. ACM and HC subjects were screened for plasmatic expression of 377 microRNAs and validation was performed in 36 ACM, 53 HC, 21 IVT. Variable importance in data partition was estimated through Random Forest analysis and accuracy by Receiver Operating Curves. Plasmatic miR-320a showed 0.53 ± 0.04 fold expression difference in ACM vs. HC (p < 0.01). A similar trend was observed when comparing ACM (n = 13) and HC (n = 17) with athletic lifestyle, a ACM precipitating factor. Importantly, ACM patients miR-320a showed 0.78 ± 0.05 fold expression change vs. IVT (p = 0.03). When compared to non-invasive ACM diagnostic parameters, miR-320a ranked highly in discriminating ACM vs. IVT and it increased their accuracy. Finally, miR-320a expression did not correlate with ACM severity. Our data suggest that miR-320a may be considered a novel potential biomarker of ACM, specifically useful in ACM vs. IVT differentiation.

Experimental and clinical evidence indicate that bone marrow cells participate in the process of new blood vessel formation. However, the molecular mechanisms underlying their recruitment and their exact role are still elusive. Here, we show that bone marrow cells are recruited to the sites of neoangiogenesis through the neuropilin-1 (NP-1) receptor and that they are essential for the maturation of the activated endothelium and the formation of arteries in mice. By exploiting adeno-associated virus vector-mediated, long-term in vivo gene expression, we show that the 165-aa isoform of VEGF, which both activates the endothelium and recruits NP-1+ myeloid cells, is a powerful arteriogenic agent. In contrast, neither the shortest VEGF121 isoform, which does not bind NP-1 and thus does not recruit bone marrow cells, nor semaphorin 3A, which attracts cells but inhibits endothelial activation, are capable of sustaining arterial formation. Bone marrow myeloid cells are not arteriogenic per se nor are they directly incorporated in the newly formed vasculature, but they contribute to arterial formation through a paracrine effect ensuing in the activation and proliferation of tissue-resident smooth muscle cells.

Thrombogenicity remains a major issue in cardiovascular implants (CVIs). Complete surficial coverage of CVIs by a monolayer of endothelial cells (ECs) prior to implantation represents a promising strategy but is hampered by the overall logistical complexity and the high number of cells required. Consequently, extensive cell expansion is necessary, which may eventually lead to replicative senescence. Considering that micro-structured surfaces with anisotropic topography may promote endothelialization, we investigated the impact of gratings on the biomechanical properties and the replicative capacity of senescent ECs. After cultivation on gridded surfaces, the cells showed significant improvements in terms of adherens junction integrity, cell elongation, and orientation of the actin filaments, as well as enhanced yes-associated protein nuclear translocation and cell proliferation. Our data therefore suggest that micro-structured surfaces with anisotropic topographies may improve long-term endothelialization of CVIs.

The potential use of bone marrow-derived cells (BMCs) to promote new blood vessel formation, recapitulating vasculogenesis in the adult, has recently aroused much excitement, and a rapid transposition to the clinic. However, new experimental evidence has challenged this notion, demonstrating that BMCs transplanted into ischemic tissues still adopt mature hematopoietic fates and do not transdifferentiate into vascular structures. To better define the actual role of bone marrow-derived cells in the formation of new blood vessels, we developed a series of AAV vectors to drive the persistent expression of several factors, differing in their capacity to promote angiogenesis and to recruit BMCs.Mice were divided into three groups (n>=24 per group) and injected, into the tibialis anterior muscle, with AAV-VEGF165, AAV-VEGF121 and AAV-Sema3A.Injection of AAV-VEGF165 determined the formation of an impressive number of new capillaries and arteriolae with a 20-120 μm diameter, paralleled by a massive muscle infiltration with CD45+, CD11b+ mononuclear cells. These cells were found to derive from the bone marrow (as detected by bone marrow transplantation and FISH analysis), but were not incorporated in the newly formed vessels. In contrast, VEGF121 induced a potent angiogenic sprouting with the massive formation of new capillaries, but neither cellular infiltrates nor arterial vessels were evident. Leading from the consideration that the main difference between the two VEGF isoforms is their ability to bind the co-receptor NP-1, we looked at the effect of Sema3A, another ligand for NP-1. We found that Sema3A, although not angiogenic, is able to recruit mononuclear CD11b+ cells from the bone marrow similar to VEGF, and that this recruitment, in both cases, is mediated by NP-1. Consistent with these findings, we found that mononuclear BMCs were able to migrate in vitro in response to both VEGF and Sema3A, and that migration was impaired after NP-1 knock-down using a specific siRNA. Finally, we also showed that CD11b+ cells were able to stimulate the migration of smooth muscle cells in culture and to promote the maturation of VEGF121-induced capillaries to acquire an arterial phenotype in vivo.Together, these findings demonstrate that the different isoforms of VEGF are not redundant in their angiogenic properties, and that CD11b+ cells recruited from the bone marrow through NP-1, although not directly incorporated into the newly formed vessels, are required for proper arterial formation.

Myocardial regeneration is restricted to early postnatal life, when mammalian cardiomyocytes still retain the ability to proliferate. The molecular cues that induce cell cycle arrest of neonatal cardiomyocytes towards terminally differentiated adult heart muscle cells remain obscure. Here we report that the miR-106b∼25 cluster is higher expressed in the early postnatal myocardium and decreases in expression towards adulthood, especially under conditions of overload, and orchestrates the transition of cardiomyocyte hyperplasia towards cell cycle arrest and hypertrophy by virtue of its targetome. In line, gene delivery of miR-106b∼25 to the mouse heart provokes cardiomyocyte proliferation by targeting a network of negative cell cycle regulators including E2f5, Cdkn1c, Ccne1 and Wee1. Conversely, gene-targeted miR-106b∼25 null mice display spontaneous hypertrophic remodeling and exaggerated remodeling to overload by derepression of the prohypertrophic transcription factors Hand2 and Mef2d. Taking advantage of the regulatory function of miR-106b∼25 on cardiomyocyte hyperplasia and hypertrophy, viral gene delivery of miR-106b∼25 provokes nearly complete regeneration of the adult myocardium after ischemic injury. Our data demonstrate that exploitation of conserved molecular programs can enhance the regenerative capacity of the injured heart. Competing Interest Statement E.D., M.G. and L.D.W filed the data in the manuscript for patent protection. P.D.C.M. and L.D.W. are co-founders and stockholders of Mirabilis Therapeutics BV.