Rationale: Understanding the mechanisms that regulate arterial flow recovery is important to design treatment options for peripheral arterial disease (PAD) patients ineligible for invasive revascularization. Transcriptional orchestrators of this recovery process represent an appealing target for treatment design. We previously identified positive regulatory domain-containing protein (Prdm)16 as an arterial-specific endothelial transcription factor but its in vivo role in arteries remains completely unknown. Objective: To unravel the role of Prdm16 in arteries under physiological and pathological conditions, more specifically during PAD. Methods and Results: Methods and Results: Within the vasculature, Prdm16 expression was strictly expressed by arterial endothelial and smooth muscle cells. Heterozygous loss of Prdm16 caused a modest reduction of the inner arterial diameter and smooth muscle cell coating without compromising vasomotor function. Upon femoral artery ligation, Prdm16 +/- mice featured significantly impaired flow recovery to ischemic limbs. This impairment was recapitulated in mice with a Prdm16 deletion specifically in endothelial cells (EC-Prdm16 -/- ) but not smooth muscle cells. Structural ollateral remodeling was normal in both Prdm16 +/- and <EC-Prdm16 -/- mice, but significant endothelial dysfunction post-ligation was present in EC-Prdm16 -/- mice as evidenced by impaired endothelial-dependent relaxation. Upon ligation, endothelial Prdm16 deficiency altered the expression of genes encoding endothelial cell function regulators, many related to nitric oxide bioavailability and Ca2 + homeostasis. Accordingly, Prdm16 overexpression in cultured endothelial cells affected both total cellular Ca2 + levels and store-operated Ca2 + entry. Conclusions: Conclusions: We showed that Prdm16 is indispensable for arterial flow recovery under pathological challenge not because it affects structural remodeling but due to its role in maintaining endothelial function. It therefore represents an appealing target for designing novel therapeutic strategies for no-option patients with PAD.

Background: Chronic pressure overload predisposes to heart failure, but the pathogenic role of microvascular endothelial cells (MiVEC) remains unknown. We characterized transcriptional, metabolic, and functional adaptation of cardiac MiVEC to pressure overload in mice and patients with aortic stenosis (AS). Methods: In Tie2-Gfp mice subjected to transverse aortic constriction or sham surgery, we performed RNA sequencing of isolated cardiac Gfp + -MiVEC and validated the signature in freshly isolated MiVEC from left ventricle outflow tract and right atrium of patients with AS. We next compared their angiogenic and metabolic profiles and finally correlated molecular and pathological signatures with clinical phenotypes of 42 patients with AS (50% women). Results: In mice, transverse aortic constriction induced progressive systolic dysfunction, fibrosis, and reduced microvascular density. After 10 weeks, 25 genes predominantly involved in matrix-regulation were >2-fold upregulated in isolated MiVEC. Increased transcript levels of Cartilage Intermediate Layer Protein ( Cilp ), Thrombospondin-4 , Adamtsl-2 , and Collagen1a1 were confirmed by quantitative reverse transcription polymerase chain reaction and recapitulated in left ventricle outflow tract-derived MiVEC of AS ( P <0.05 versus right atrium-MiVEC). Fatty acid oxidation increased >2-fold in left ventricle outflow tract-MiVEC, proline content by 130% (median, IQR, 58%–474%; P =0.008) and procollagen secretion by 85% (mean [95% CI, 16%–154%]; P <0.05 versus right atrium-MiVEC for all). The altered transcriptome in left ventricle outflow tract-MiVEC was associated with impaired 2-dimensional-vascular network formation and 3-dimensional-spheroid sprouting ( P <0.05 versus right atrium-MiVEC), profibrotic ultrastructural changes, and impaired diastolic left ventricle function, capillary density and functional status, especially in female AS. Conclusions: Pressure overload induces major transcriptional and metabolic adaptations in cardiac MiVEC resulting in excess interstitial fibrosis and impaired angiogenesis. Molecular rewiring of MiVEC is worse in women, compromises functional status, and identifies novel targets for intervention.

Recovered COVID-19 patients often display cardiac dysfunction, even after a mild infection. Most current histological results come from patients that are hospitalized and therefore represent more severe outcomes than most COVID-19 patients face. To overcome this limitation, we investigated the cardiac effects of SARS-CoV-2 infection in a hamster model. SARS-CoV-2 infected hamsters developed diastolic dysfunction after recovering from COVID-19. Histologically, increased cardiomyocyte size was present at the peak of viral load and remained at all time points investigated. As this increase is too rapid for hypertrophic remodeling, we found instead that the heart was oedemic. Moreover, cardiomyocyte swelling is associated with the presence of ischemia. Fibrin-rich microthrombi and pericyte loss were observed at the peak of viral load, resulting in increased HIF1α in cardiomyocytes. Surprisingly, SARS-CoV-2 infection inhibited the translocation of HIF1α to the nucleus both in hamster hearts, in cultured cardiomyocytes, as well as in an epithelial cell line. We propose that the observed diastolic dysfunction is the consequence of cardiac oedema, downstream of microvascular cardiac ischemia. Additionally, our data suggest that inhibition of HIF1α translocation could contribute to an exaggerated response upon SARS-CoV-2 infection.

Aims: We aimed to study the long-term effect of neutrophils on cardiac health during the process of natural aging. We hypothesized that neutrophil PAD4, via its role in neutrophil extracellular trap (NET) formation, is involved in myocardial remodeling and cardiac fibrosis development, resulting in turn in impaired cardiac function. Methods and results: We generated mice with deletion of Padi4, a NET-essential gene, under the neutrophil-specific promoter S100A8 (PAD4fl/flMRP8Cre+). These mice and their littermate controls were aged for two years (coinciding with approximately 70 years of age in humans; the age at which HF is the number one cause of hospitalization), after which cardiac function and remodeling were evaluated. We performed a comprehensive echocardiography analysis including both structural and functional parameter measurements. Deletion of PAD4 in neutrophils resulted in a protection against both systolic, and diastolic dysfunction. Interestingly, these mice showed protection against age induced fibrosis, detected as through the absence of cardiac collagen deposition. To explore this further, cardiac gene expression and plasma cytokine levels were evaluated. Here we saw a clear impact of PAD4-deficiency on cardiac neutrophil recruitment, with both cardiac genes as well as plasma cytokines involved in neutrophil recruitment being downregulated in aged PAD4fl/flMRP8Cre+ animals in comparison to littermate PAD4fl/fl controls, including decreased plasma levels of C-X-C ligand 1 (CXCL1). Conclusion: Our data confirms neutrophil PAD4 involvement in heart failure progression by promoting cardiac remodeling, leading to cardiac dysfunction with old age. We saw that the deletion of PAD4 specifically in neutrophils had an influence on the CXCL1-CXCR2 axis, which is known to be involved in HF development.

Rationale: Proper functionality of the circulatory system requires correct arteriovenous (AV) endothelial cell (EC) differentiation. While Notch signaling and its downstream effector Hes-Related Family bHLH Transcription Factor with YRPW Motif (Hey)2 favor arterial specification, transcription factor (TF) chicken ovalbumin upstream transcription factor 2 (Coup-TFII) inhibits canonical Notch activity to induce venous identity. However, transcriptional programs that compete with Coup-TFII to orchestrate arterial specification upstream of Notch remain largely unknown. We identified positive regulatory domain-containing protein (Prdm)16 as an arterial EC-specific TF, but its role during arterial EC specification and development remains unexplored. Objective: To unravel the role of Prdm16 during arterial endothelial lineage specification and artery formation. Methods and Results: Transcriptomic data of freshly isolated arterial and venous ECs from humans and mice revealed that Prdm16 is exclusively expressed by arterial ECs throughout development. This expression pattern was independent of hemodynamic factors and conserved in zebrafish. Accordingly, loss of prdm16 in zebrafish perturbed AV endothelial specification and caused AV malformations in an EC-autonomous manner. This coincided with reduced canonical Notch activity in arterial ECs and was amplified when prdm16 and notch pathway members were concomitantly knocked down. In vitro studies further indicated that Prdm16 not only amplified Notch signaling, but also physically and functionally interacted with Hey2 to drive proper arterial specification. Conclusion: We showed that Prdm16 plays a pivotal role during arterial development through its physical and functional interaction with canonical Notch. As both Hey2 and Prdm16 have been associated with diverse vascular disorders including migraine and atherosclerosis, Prdm16 represents an attractive new target to treat these vascular disorders.