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Immunological mechanisms have come into the focus of current translational stroke research, and the modulation of neuroinflammatory pathways has been identified as a promising therapeutic approach to protect the ischemic brain. However, stroke not only induces a local neuroinflammatory response but also has a profound impact on systemic immunity. In this review, we will summarize the consequences of ischemic stroke on systemic immunity at all stages of the disease, from onset to long‐term outcome, and discuss underlying mechanisms of systemic brain‐immune communication. Furthermore, since stroke commonly occurs in patients with multiple comorbidities, we will also overview the current understanding of the potential role of systemic immunity in common stroke‐related comorbidities, such as cardiac dysfunction, atherosclerosis, diabetes, and infections. Finally, we will highlight how targeting systemic immunity after stroke could improve long‐term outcomes and alleviate comorbidities of stroke patients. Graphical Abstract This Review discusses the impact of ischemic stroke on systemic immunity, its interaction with common comorbidities, and the underlying mechanisms of systemic brain‐immune communication.

Cytosolic double‐stranded DNA (dsDNA) is a danger signal that is tightly monitored and sensed by nucleic acid‐sensing pattern recognition receptors. We study the inflammatory cascade on dsDNA recognition and investigate the neuroprotective effect of cyclic GMP‐AMP (cGAMP) synthase (cGAS) antagonist A151 and its mechanisms of neuroprotection in a mouse model of experimental stroke. Here, we found that cerebral ischemia promoted the release of dsDNA into the cytosol, where it initiated inflammatory responses by activating the cGAS. A151 effectively reduced the expression of cGAS, absent in melanoma 2 (AIM2) inflammasome, and pyroptosis‐related molecules, including caspase‐1, gasdermin D, IL‐1β, and IL‐18. Furthermore, mice treated with A151 showed a dampened immune response to stroke, with reduced counts of neutrophils, microglia, and microglial production of IL‐6 and TNF‐α after MCAO. Moreover, A151 administration significantly reduced infarct volume, attenuated neurodeficits, and diminished cell death. Notably, the protective effect of A151 was blocked in a microglia‐specific cGAS knockout mouse. These findings offer unique perspectives on stroke pathogenesis and indicate that inhibition of cGAS could attenuate brain inflammatory burden, representing a potential therapeutic opportunity for stroke. Synopsis Inflammation is involved in the progression of ischemic brain injury. This study focuses on the inflammatory cascade on double‐strand DNA (dsDNA) recognition and highlights the possibility of inhibiting dsDNA‐sensing cyclic GMP‐AMP synthase (cGAS) for treatment of ischemic stroke. The release of dsDNA from necrotic tissue during brain infarction triggers an innate inflammatory cascade. A synthetic oligonucleotide A151 that antagonizes cGAS regulates the microglial immune response and pyroptosis after ischemic stroke. Inhibition of cGAS leads to a decline in neutrophil infiltration into the brain. Suppression of the dsDNA‐sensing cGAS pathway reduces ischemic brain injury via mitigating neuroinflammation. Graphical Abstract Inflammation is involved in the progression of ischemic brain injury. This study focuses on the inflammatory cascade on double‐strand DNA (dsDNA) recognition and highlights the possibility of inhibiting dsDNA‐sensing cyclic GMP‐AMP synthase (cGAS) for treatment of ischemic stroke.

Cardiac fibrosis is central to the pathology of heart failure, particularly heart failure with preserved ejection fraction (HFpEF). Irrespective of the underlying profibrotic condition (e.g. ageing, diabetes, hypertension), maladaptive cardiac fibrosis is defined by the transformation of resident fibroblasts to matrix‐secreting myofibroblasts. Numerous profibrotic factors have been identified at the molecular level (e.g. TGFβ, IL11, AngII), which activate gene expression programs for myofibroblast activation. A number of existing HF therapies indirectly target fibrotic pathways; however, despite multiple clinical trials in HFpEF, a specific clinically effective antifibrotic therapy remains elusive. Therapeutic inhibition of TGFβ, the master‐regulator of fibrosis, has unfortunately proven toxic and ineffective in clinical trials to date, and new approaches are needed. In this review, we discuss the pathophysiology and clinical implications of interstitial fibrosis in HFpEF. We provide an overview of trials targeting fibrosis in HFpEF to date and discuss the promise of potential new therapeutic approaches and targets in the context of underlying molecular mechanisms. Graphical Abstract This review discusses recent advances in novel therapeutic approaches against cardiac fibrosis in heart failure with preserved ejection fraction and their underlying molecular mechanisms.

Microglial cells of the aged brain manifest signs of dysfunction that could contribute to the worse neurological outcome of stroke in the elderly. Treatment with colony‐stimulating factor 1 receptor antagonists enables transient microglia depletion that is followed by microglia repopulation after treatment interruption, causing no known harm to mice. We tested whether this strategy restored microglia function and ameliorated stroke outcome in old mice. Cerebral ischemia/reperfusion induced innate immune responses in microglia highlighted by type I interferon and metabolic changes involving lipid droplet biogenesis. Old microglia accumulated lipids under steady state and displayed exacerbated innate immune responses to stroke. Microglia repopulation in old mice reduced lipid‐laden microglia, and the cells exhibited reduced inflammatory responses to ischemia. Moreover, old mice with renewed microglia showed improved motor function 2 weeks after stroke. We conclude that lipid deposits in aged microglia impair the cellular responses to ischemia and worsen functional recovery in old mice. Synopsis Stroke outcome is impaired in old subjects. Here, microglia of aged mice are shown to accumulate lipids and display exacerbated inflammation after stroke. The microglia lipid droplet content was reduced by microglia depletion/repopulation in old mice, and motor function was improved after stroke. Ischemic stroke induced acute lipid droplet biogenesis in microglia. Aging caused lipid droplet accumulation in microglia and changes in lipid pathways under a steady state. Old mice showed worse outcomes after stroke, and their microglia displayed exaggerated innate immune reactions. Renewal of microglia in old mice by transient treatment with a CSF1R inhibitor reduced lipid droplets. Renewed microglia of old mice showed less inflammation after stroke, and motor function was improved. Graphical Abstract Stroke outcome is impaired in old subjects. Here, microglia of aged mice are shown to accumulate lipids and display exacerbated inflammation after stroke. The microglia lipid droplet content was reduced by microglia depletion/repopulation in old mice, and motor function was improved after stroke.

Low‐flow vascular malformations are congenital overgrowths composed of abnormal blood vessels potentially causing pain, bleeding and obstruction of different organs. These diseases are caused by oncogenic mutations in the endothelium, which result in overactivation of the PI3K/AKT pathway. Lack of robust in vivo preclinical data has prevented the development and translation into clinical trials of specific molecular therapies for these diseases. Here, we demonstrate that the Pik3ca H1047R activating mutation in endothelial cells triggers a transcriptome rewiring that leads to enhanced cell proliferation. We describe a new reproducible preclinical in vivo model of PI3K‐driven vascular malformations using the postnatal mouse retina. We show that active angiogenesis is required for the pathogenesis of vascular malformations caused by activating Pik3ca mutations. Using this model, we demonstrate that the AKT inhibitor miransertib both prevents and induces the regression of PI3K‐driven vascular malformations. We confirmed the efficacy of miransertib in isolated human endothelial cells with genotypes spanning most of human low‐flow vascular malformations. SYNOPSIS This work describes a robust preclinical model of PI3K‐driven vascular malformations using the postnatal mouse retina. We show that AKT inhibition by miransertib is an effective therapeutic strategy for these diseases. Pik3ca H1047R mutation in endothelial cells leads to enhanced cell cycle progression. Active angiogenesis is required for the formation of PI3K‐driven vascular malformations. PI3K‐driven vascular malformations are prevented and regressed upon miransertib treatment. Graphical Abstract This work describes a robust preclinical model of PI3K‐driven vascular malformations using the postnatal mouse retina. We show that AKT inhibition by miransertib is an effective therapeutic strategy for these diseases.

Cardiosphere‐derived cells (CDCs) reduce myocardial infarct size via secreted extracellular vesicles (CDC‐EVs), including exosomes, which alter macrophage polarization. We questioned whether short non‐coding RNA species of unknown function within CDC‐EVs contribute to cardioprotection. The most abundant RNA species in CDC‐EVs is a Y RNA fragment (EV‐YF1); its relative abundance in CDC‐EVs correlates with CDC potency in vivo . Fluorescently labeled EV‐YF1 is actively transferred from CDCs to target macrophages via CDC‐EVs. Direct transfection of macrophages with EV‐YF1 induced transcription and secretion of IL‐10. When cocultured with rat cardiomyocytes, EV‐YF1‐primed macrophages were potently cytoprotective toward oxidatively stressed cardiomyocytes through induction of IL‐10. In vivo, intracoronary injection of EV‐YF1 following ischemia/reperfusion reduced infarct size. A fragment of Y RNA, highly enriched in CDC‐EVs, alters Il10 gene expression and enhances IL‐10 protein secretion. The demonstration that EV‐YF1 confers cardioprotection highlights the potential importance of diverse exosomal contents of unknown function, above and beyond the usual suspects (e.g., microRNAs and proteins). Synopsis A Y RNA fragment enriched in extracellular vesicles from cardiosphere‐derived cells was identified and found to increase IL‐10 expression and secretion in macrophages. The fragment confers cardioprotection after ischemic injury in a rat model. A Y RNA fragment is the most abundant small RNA species in extracellular vesicles secreted from cardiosphere‐derived cells. When overexpressed in macrophages, this Y RNA fragment increases Il‐10 gene expression and secretion of IL‐10 protein, rendering macrophages cardioprotective. When administrated in a rat model of myocardial infarction, this Y RNA fragment confers cardioprotection. Graphical Abstract A Y RNA fragment enriched in extracellular vesicles from cardiosphere‐derived cells was identified and found to increase IL‐10 expression and secretion in macrophages. The fragment confers cardioprotection after ischemic injury in a rat model.

Regeneration of arterial endothelium after injury is critical for the maintenance of normal blood flow, cell trafficking, and vascular function. Using mouse models of carotid injury, we show that the transition from a static to a dynamic phase of endothelial regeneration is marked by a strong increase in endothelial proliferation, which is accompanied by induction of the chemokine CX 3 CL1 in endothelial cells near the wound edge, leading to progressive recruitment of Ly6C lo monocytes expressing high levels of the cognate CX 3 CR1 chemokine receptor. In Cx3cr1 ‐deficient mice recruitment of Ly6C lo monocytes, endothelial proliferation and regeneration of the endothelial monolayer after carotid injury are impaired, which is rescued by acute transfer of normal Ly6C lo monocytes. Furthermore, human non‐classical monocytes induce proliferation of endothelial cells in co‐culture experiments in a VEGFA‐dependent manner, and monocyte transfer following carotid injury promotes endothelial wound closure in a hybrid mouse model in vivo . Thus, CX 3 CR1 coordinates recruitment of specific monocyte subsets to sites of endothelial regeneration, which promote endothelial proliferation and arterial regeneration. Synopsis Ly6C lo monocytes with patrolling behavior are recruited to endothelial wounds after arterial injury and promote endothelial regeneration in vivo by stimulating endothelial proliferation, which is mediated in a paracrine fashion via secretion of VEGF. After arterial injury in mice, endothelial cells upregulate fractalkine (CX 3 CL1) and recruit CX 3 CR1 hi Ly6C lo patrolling monocytes, which coincides with the onset of endothelial proliferation. In CX 3 CR1 deficient mice, monocyte recruitment along with endothelial proliferation and wound closure is impaired, which is rescued by transfer of wildtype monocytes. Both the human and murine monocyte subsets express VEGFA, which mediates endothelial proliferation in vitro . Human monocytes enhance endothelial regeneration in hybrid transfer experiments. Graphical Abstract Ly6C lo monocytes with patrolling behavior are recruited to endothelial wounds after arterial injury and promote endothelial regeneration in vivo by stimulating endothelial proliferation, which is mediated in a paracrine fashion via secretion of VEGF.

Hypertrophic cardiomyopathy (HCM) is a cardiac genetic disease accompanied by structural and contractile alterations. We identified a rare c.740C>T (p.T247M) mutation in ACTN2 , encoding α‐actinin 2 in a HCM patient, who presented with left ventricular hypertrophy, outflow tract obstruction, and atrial fibrillation. We generated patient‐derived human‐induced pluripotent stem cells (hiPSCs) and show that hiPSC‐derived cardiomyocytes and engineered heart tissues recapitulated several hallmarks of HCM, such as hypertrophy, myofibrillar disarray, hypercontractility, impaired relaxation, and higher myofilament Ca 2+ sensitivity, and also prolonged action potential duration and enhanced L‐type Ca 2+ current. The L‐type Ca 2+ channel blocker diltiazem reduced force amplitude, relaxation, and action potential duration to a greater extent in HCM than in isogenic control. We translated our findings to patient care and showed that diltiazem application ameliorated the prolonged QTc interval in HCM‐affected son and sister of the index patient. These data provide evidence for this ACTN2 mutation to be disease‐causing in cardiomyocytes, guiding clinical therapy in this HCM family. This study may serve as a proof‐of‐principle for the use of hiPSC for personalized treatment of cardiomyopathies. Synopsis Disease modeling of a rare ACTN2 mutation in iPSC‐derived cardiomyocytes & heart tissues engineering revealed typical features of hypertrophic cardiomyopathy & electrophysiological anomalies. Diltiazem reversed the in vitro phenotypes & guided clinical therapy in the family, reducing QTc intervals. Modeling hypertrophic cardiomyopathy (HCM) with patient‐ and isogenic control‐derived hiPSC‐cardiomyocytes revealed higher cell area, myofibrillar disarray and higher LTCC density in 2D, and hypercontractility, prolonged relaxation and action potentials in 3D. Prolonged action potentials in 3D associated with higher LTCC currents in 2D, matching prolonged QT intervals and monophasic action potentials in HCM‐affected family members. Diltiazem normalized the electro‐mechanical phenotype in vitro and guided clinical therapy in the HCM affected family, reducing QTc intervals. This study may serve as proof‐of‐principle for the use of hiPSC‐cardiomyocytes and CRISPR/Cas9 for personalized treatment of cardiomyopathies. Graphical Abstract Disease modeling of a rare ACTN2 mutation in iPSC‐derived cardiomyocytes & heart tissues engineering revealed typical features of hypertrophic cardiomyopathy & electrophysiological anomalies. Diltiazem reversed the in vitro phenotypes & guided clinical therapy in the family, reducing QTc intervals.

Myocardial infarction (MI) is the leading cause of death in Western countries. Epidemiological studies show acute MI to be more prevalent in the morning and to be associated with a poorer outcome in terms of mortality and recovery. The mechanisms behind this association are not fully understood. Here, we report that circadian oscillations of neutrophil recruitment to the heart determine infarct size, healing, and cardiac function after MI. Preferential cardiac neutrophil recruitment during the active phase (Zeitgeber time, ZT13) was paralleled by enhanced myeloid progenitor production, increased circulating numbers of CXCR2 hi neutrophils as well as upregulated cardiac adhesion molecule and chemokine expression. MI at ZT13 resulted in significantly higher cardiac neutrophil infiltration compared to ZT5, which was inhibited by CXCR2 antagonism or neutrophil‐specific CXCR2 knockout. Limiting exaggerated neutrophilic inflammation at this time point significantly reduced the infarct size and improved cardiac function. Synopsis Expression levels of chemokine receptor CXCR2 on circulating neutrophils exhibit diurnal oscillations. This causes time‐of‐day‐dependent variations in the number of neutrophils infiltrating the heart after myocardial infarction, with major consequences for infarction healing. During the sleep‐to‐wake transition period, myeloid progenitor production in the bone marrow is enhanced and the heart expresses higher levels of neutrophil chemoattractants and adhesion molecules. A myocardial infarction at this time point leads to excessive cardiac neutrophil recruitment, larger infarct size, and worsened heart function. The enhanced cardiac neutrophil infiltration after myocardial infarction onset during the sleep‐to‐wake transition period is CXCR2‐dependent. Graphical Abstract Expression levels of chemokine receptor CXCR2 on circulating neutrophils exhibit diurnal oscillations. This causes time‐of‐day‐dependent variations in the number of neutrophils infiltrating the heart after myocardial infarction, with major consequences for infarction healing.

Gene therapy critically relies on vectors that combine high transduction efficiency with a high degree of target specificity and that can be administered through a safe intravenous route. The lack of suitable vectors, especially for gene therapy of brain disorders, represents a major obstacle. Therefore, we applied an in vivo screening system of random ligand libraries displayed on adeno‐associated viral capsids to select brain‐targeted vectors for the treatment of neurovascular diseases. We identified a capsid variant showing an unprecedented degree of specificity and long‐lasting transduction efficiency for brain microvasculature endothelial cells as the primary target of selection. A therapeutic vector based on this selected viral capsid was used to markedly attenuate the severe cerebrovascular pathology of mice with incontinentia pigmenti after a single intravenous injection. Furthermore, the versatility of this selection system will make it possible to select ligands for additional in vivo targets without requiring previous identification of potential target‐specific receptors. Synopsis A capsid AAV2 mutant, AAV‐BR1, with tropism for the neurovascular endothelium, generated by selecting an AAV2 display peptide library in vivo , holds promise as a gene therapy vector for neurovascular and potentially other central nervous system diseases. Capsid mutants with a specific redirected tropism can be selected from AAV display peptide libraries in vivo . One mutant, AAV‐BR1, effectively transduces neurovascular (blood–brain barrier‐associated) endothelial cells in vivo and in vitro . AAV‐BR1 can be used to ameliorate the severe neurological impairments in a mouse model of incontinentia pigmenti. Graphical Abstract A capsid AAV2 mutant, AAV‐BR1, with tropism for the neurovascular endothelium, generated by selecting an AAV2 display peptide library in vivo , holds promise as a gene therapy vector for neurovascular and potentially other central nervous system diseases.