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BackgroundCardiac valve disease (CVD) is observed in 2.5% of the general population and 10% of the elderly people. Effective pharmacological treatments are currently not available, and patients with severe CVD require surgery. PROX1 and FOXC2 are transcription factors that are required for the development of lymphatic and venous valves. We found that PROX1 and FOXC2 are expressed in a subset of valvular endothelial cells (VECs) that are located on the downstream (fibrosa) side of cardiac valves. Whether PROX1 and FOXC2 regulate cardiac valve development and disease is not known.MethodsWe used histology, electron microscopy and echocardiography to investigate the structure and functioning of heart valves fromProx1ΔVECmice in whichProx1was conditionally deleted from VECs. Isolated valve endothelial cells and valve interstitial cells were used to identify the molecular mechanismsin vitro, which were testedin vivoby RNAScope, additional mouse models and pharmacological approaches. The significance of our findings was tested by evaluation of human samples of mitral valve prolapse (MVP) and aortic valve insufficiency.ResultsHistological analysis revealed that the aortic and mitral valves ofProx1ΔVECmice become progressively thick and myxomatous. Echocardiography revealed that the aortic valves ofProx1ΔVECmice are stenotic. FOXC2 was downregulated and platelet-derived growth factor-B (PDGF-B) was upregulated in the VECs ofProx1ΔVECmice. Conditional knockdown of FOXC2 and conditional overexpression of PDGF-B in VECs recapitulated the phenotype ofProx1ΔVECmice. PDGF-B was also increased in mice lacking FOXC2 and in human MVP and insufficient aortic valve samples. Pharmacological inhibition of PDGF-B signaling with imatinib partially ameliorated the valve defects ofProx1ΔVECmice.ConclusionPROX1 antagonizes PDGF-B signaling partially via FOXC2 to maintain the extracellular matrix composition and prevent myxomatous degeneration of cardiac valves.Novelty and SignificanceWhat Is Known?The transcription factors PROX1 and FOXC2 are critical regulators of lymphatic and venous valve development.PROX1 and FOXC2 are expressed in the downstream valvular endothelial cells of heart valves.What Is New?Deletion ofProx1from the valvular endothelial cells of mice results in enlarged and myxomatous aortic and mitral valves. Aortic valves of the mutant (Prox1ΔVEC) mice were stenotic.FOXC2 is partially responsible for the phenotype ofProx1ΔVECmice.PROX1 and FOXC2 inhibit the expression of the cytokine PDGF-B in heart valves.Hyperactivation of PDGF-B signaling results in aortic and mitral valve thickening.Inhibition of PDGF-B signaling ameliorates aortic valve stenosis inProx1ΔVECmice.PDGFBis overexpressed andPROX1is downregulated in human mitral valve prolapse (MVP) samples.Our findings suggest that PROX1 is an inhibitor of myxomatous valve disease that afflicts ~10% of the elderly population. We have also identified PDGF-B as a potential target for treating myxomatous valve disease.

Background: Endothelial-to-mesenchymal transition (EndMT) is a dynamic process in which endothelial cells acquire mesenchymal properties and in turn contribute to tissue remodeling and growth. Previously, we found EndMT associated with mitral valve adaptation after myocardial infarction. Furthermore, mitral valve endothelial cells collected at 6 months post-myocardial infarction expressed the pan-leukocyte marker CD45 and EndMT markers. Additionally, mitral valve endothelial cells induced to undergo EndMT with TGF (transforming growth factor)-β1 strongly coexpressed CD45 but not CD11b or CD14. Pharmacologic inhibition of the CD45 PTPase (protein tyrosine phosphatase) domain in mitral valve endothelial cells blocked TGFβ-induced EndMT. This prompted us to speculate that, downstream of TGFβ, CD45 induces EndMT. Methods: We activated the endogenous CD45 promoter in human endothelial colony forming cells (ECFCs) using CRISPR (cluster regularly interspaced short palindromic repeats)/inactive Cas9 (CRISPR-associated protein 9) transcriptional activation. Bulk RNA sequencing was performed on control ECFCs and CD45-positive ECFCs to identify transcriptomic changes. Three functional assays—cellular migration, collagen gel contraction, and transendothelial electrical resistance—were conducted to assess mesenchymal properties in CD45-positive ECFCs. Results: Activation of the endogenous CD45 promoter in ECFC and 3 additional sources of endothelial cells induced expression of several genes implicated in EndMT. In addition, CD45-positive ECFCs showed increased migration, a hallmark of EndMT, increased collagen gel contraction, a hallmark of mesenchymal cells, and decreased cell-cell barrier integrity, indicating reduced endothelial function. Conclusions: CD45 is sufficient to incite an EndMT phenotype and acquisition of mesenchymal cell properties in normal human ECFCs. We speculate that CD45, through its C-terminal PTPase domain, initiates signaling events that drive EndMT.

Little is known about the factors that regulate the asymmetric division of cancer stem–like cells (CSC). Here, we demonstrate that EGFL6, a stem cell regulatory factor expressed in ovarian tumor cells and vasculature, regulates ALDH+ ovarian CSC. EGFL6 signaled at least in part via the oncoprotein SHP2 with concomitant activation of ERK. EGFL6 signaling promoted the migration and asymmetric division of ALDH+ ovarian CSC. As such, EGFL6 increased not only tumor growth but also metastasis. Silencing of EGFL6 or SHP2 limited numbers of ALDH+ cells and reduced tumor growth, supporting a critical role for EGFL6/SHP2 in ALDH+ cell maintenance. Notably, systemic administration of an EGFL6-neutralizing antibody we generated restricted tumor growth and metastasis, specifically blocking ovarian cancer cell recruitment to the ovary. Together, our results offer a preclinical proof of concept for EGFL6 as a novel therapeutic target for the treatment of ovarian cancer. Cancer Res; 76(21); 6396–409. ©2016 AACR.

Supplementary Methods

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Background: Epsin endocytic adaptor proteins are implicated in the progression of atherosclerosis; however, the underlying molecular mechanisms have not yet been fully defined. In this study, we determined how epsins enhance endothelial-to-mesenchymal transition (EndoMT) in atherosclerosis and assessed the efficacy of a therapeutic peptide in a preclinical model of this disease. Methods: Using single-cell RNA sequencing combined with molecular, cellular, and biochemical analyses, we investigated the role of epsins in stimulating EndoMT using knockout in Apoe −/− and lineage tracing/proprotein convertase subtilisin/kexin type 9 serine protease mutant viral-induced atherosclerotic mouse models. The therapeutic efficacy of a synthetic peptide targeting atherosclerotic plaques was then assessed in Apoe −/− mice. Results: Single-cell RNA sequencing and lineage tracing revealed that epsins 1 and 2 promote EndoMT and that the loss of endothelial epsins inhibits EndoMT marker expression and transforming growth factor-β signaling in vitro and in atherosclerotic mice, which is associated with smaller lesions in the Apoe −/− mouse model. Mechanistically, the loss of endothelial cell epsins results in increased fibroblast growth factor receptor-1 expression, which inhibits transforming growth factor-β signaling and EndoMT. Epsins directly bind ubiquitinated fibroblast growth factor receptor-1 through their ubiquitin-interacting motif, which results in endocytosis and degradation of this receptor complex. Consequently, administration of a synthetic ubiquitin-interacting motif–containing peptide atheroma ubiquitin-interacting motif peptide inhibitor significantly attenuates EndoMT and progression of atherosclerosis. Conclusions: We conclude that epsins potentiate EndoMT during atherogenesis by increasing transforming growth factor-β signaling through fibroblast growth factor receptor-1 internalization and degradation. Inhibition of EndoMT by reducing epsin–fibroblast growth factor receptor-1 interaction with a therapeutic peptide may represent a novel treatment strategy for atherosclerosis.

BACKGROUNDEpsin endocytic adaptor proteins are implicated in the progression of atherosclerosis; however, the underlying molecular mechanisms have not yet been fully defined. In this study, we determined how epsins enhance endothelial-to-mesenchymal transition (EndoMT) in atherosclerosis and assessed the efficacy of a therapeutic peptide in a preclinical model of this disease.METHODSUsing single cell RNA sequencing (scRNA-seq), combined with molecular, cellular, and biochemical analyses, we investigated the role of epsins in stimulating EndoMT using knock-out mouse models. The therapeutic efficacy of a synthetic peptide targeting atherosclerotic plaques was then assessed inApoe−/−mice.RESULTSScRNA-seq and lineage tracing revealed that epsins 1 and 2 promote EndoMT, and the loss of endothelial epsins inhibits EndoMT marker expression as well as transforming growth factor-beta signalingin vitroand in atherosclerotic mice, which is associated with smaller lesions inApoe−/−mouse model. Mechanistically, the loss of endothelial cell epsins results in increased fibroblast growth factor receptor-1 (FGFR1) expression that inhibits TGF-β signaling and EndoMT. Epsins directly bind ubiquitinated FGFR1 through their ubiquitin-interacting motif (UIM), which results in endocytosis and degradation of this receptor complex. Consequently, administration of a synthetic UIM–containing peptide API significantly attenuates EndoMT and progression of atherosclerosis.CONCLUSIONSWe conclude that epsins potentiate EndoMT during atherogenesis by increasing TGF-β signaling through FGFR1 internalization and degradation. Inhibition of EndoMT by reducing epsin-FGFR1 interaction with a therapeutic peptide may represent a novel treatment strategy for atherosclerosis.

Background:Lymphatic malformations (LMs) often pose treatment challenges due to a large size or a critical location that could lead to disfigurement, and there are no standardized treatment approaches for either refractory or unresectable cases.Methods:We examined the genomic landscape of a patient cohort of LMs (n = 30 cases) that underwent comprehensive genomic profiling using a large-panel next-generation sequencing assay. Immunohistochemical analyses were completed in parallel.Results:These LMs had low mutational burden with hotspot PIK3CA mutations (n = 20) and NRAS (n = 5) mutations being most frequent, and mutually exclusive. All LM cases with Kaposi sarcoma-like (kaposiform) histology had NRAS mutations. One index patient presented with subacute abdominal pain and was diagnosed with a large retroperitoneal LM harboring a somatic PIK3CA gain-of-function mutation (H1047R). The patient achieved a rapid and durable radiologic complete response, as defined in RECIST1.1, to the PI3Kα inhibitor alpelisib within the context of a personalized N-of-1 clinical trial (NCT03941782). In translational correlative studies, canonical PI3Kα pathway activation was confirmed by immunohistochemistry and human LM-derived lymphatic endothelial cells carrying an allele with an activating mutation at the same locus were sensitive to alpelisib treatment in vitro, which was demonstrated by a concentration-dependent drop in measurable impedance, an assessment of cell status.Conclusions:Our findings establish that LM patients with conventional or kaposiform histology have distinct, yet targetable, driver mutations.Funding:R.P. and W.A. are supported by awards from the Levy-Longenbaugh Fund. S.G. is supported by awards from the Hugs for Brady Foundation. This work has been funded in part by the NCI Cancer Center Support Grants (CCSG; P30) to the University of Arizona Cancer Center (CA023074), the University of New Mexico Comprehensive Cancer Center (CA118100), and the Rutgers Cancer Institute of New Jersey (CA072720). B.K.M. was supported by National Science Foundation via Graduate Research Fellowship DGE-1143953.Clinical trial number:NCT03941782

Objective: Capillary malformation (CM) occurs sporadically and is associated with Sturge-Weber syndrome. The somatic mosaic mutation in GNAQ (c.548G>A, p.R183Q) is enriched in endothelial cells (ECs) in skin CM and Sturge-Weber syndrome brain CM. Our goal was to investigate how the mutant Gαq (G-protein αq subunit) alters EC signaling and disrupts capillary morphogenesis. Approach and Results: We used lentiviral constructs to express p.R183Q or wild-type GNAQ in normal human endothelial colony forming cells (EC-R183Q and EC-WT, respectively). EC-R183Q constitutively activated PLC (phospholipase C) β3, a downstream effector of Gαq. Activated PLCβ3 was also detected in human CM tissue sections. Bulk RNA sequencing analyses of mutant versus wild-type EC indicated constitutive activation of PKC (protein kinase C), NF-κB (nuclear factor kappa B) and calcineurin signaling in EC-R183Q. Increased expression of downstream targets in these pathways, ANGPT2 (angiopoietin-2) and DSCR (Down syndrome critical region protein) 1.4 were confirmed by quantitative PCR and immunostaining of human CM tissue sections. The Gαq inhibitor YM-254890 as well as siRNA targeted to PLCβ3 reduced mRNA expression levels of these targets in EC-R183Q while the pan-PKC inhibitor AEB071 reduced ANGPT2 but not DSCR1.4. EC-R183Q formed enlarged blood vessels in mice, reminiscent of those found in human CM. shRNA knockdown of ANGPT2 in EC-R183Q normalized the enlarged vessels to sizes comparable those formed by EC-WT. Conclusions: Gαq-R183Q, when expressed in ECs, establishes constitutively active PLCβ3 signaling that leads to increased ANGPT2 and a proangiogenic, proinflammatory phenotype. EC-R183Q are sufficient to form enlarged CM-like vessels in mice, and suppression of ANGPT2 prevents the enlargement. Our study provides the first evidence that endothelial Gαq-R183Q is causative for CM and identifies ANGPT2 as a contributor to CM vascular phenotype.