B r i e f r e p o r t4 IntroductionStroke is a leading cause of morbidity and mortality, whose prevalence increases dramatically with age. Despite its substantial heritable basis, only a small number of causative genes have so far been identified, generally for severe early-onset phenotypes (cerebral autosomal dominant or recessive arteriopathy with subcortical infarcts and leukoencephalopathy: CADASIL [NOTCH3], CARASIL [HTRA1], and porencephaly [COL4A1]) (1-3). Such cases have revealed important pathways that contribute to stroke, including the roles of Notch and TGF-β signaling.In the same way, the vascular basement membrane's contribution (COL4A1 and COL4A2) (3, 4) to juvenile stroke phenotypes further stimulated investigation of the cellular components (endothelial and mural cells) upon which brain vascular integrity depends. The demonstration that Notch signaling regulates pericyte numbers (5, 6) has in turn provided a mechanistic explanation for disorders such as CADASIL. These examples of juvenile stroke resulting from severe alterations in brain vascular development raise the intriguing possibility that milder changes contribute to late-onset disease and that a larger proportion of strokes have embryonic origins. It is therefore notable that the same genes regulate cerebral structural development and angiogenesis (7) and that the cell populations essential for cerebral vascular homeostasis (pericytes and vascular smooth muscle) are predominantly derived from the neural crest (8, 9). The increasing prevalence of stroke exerts disproportionately severe effects on the quality of life of affected individuals and their families. Consequently, phenotypes predictive of future stroke merit investigation, with the goal of developing treatments targeting causative pathways and preventing a frequently preterminal disease. One such phenotype is cerebral small-vessel disease (CSVD), which represents a major risk factor for both ischemic and hemorrhagic stroke (10-13). Characterized by perturbed perforating end-artery function, CSVD results in lesions apparent on MRI that encompass white matter hyperintensities (WMHs), dilated perivascular spaces, microbleeds, and lacunar infarcts. These markers of cerebrovascular pathology provide opportunities for gene discovery and for defining the mechanisms that contribute to subsequent stroke.Our study evaluated the hypothesis that the forkhead box transcription factor FOXC1, which patterns multiple organs including the CNS, contributes to CSVD. It was prompted by a higher incidence of self-reported stroke in some of our local pedigrees with FOXC1 mutations and supported experimentally by: (a) blood-stained hydrocephalus in murine Foxc1 -/-mutants, (b) related zebrafish foxc1 morphant phenotypes, and (c) the extenPatients with cerebral small-vessel disease (CSVD) exhibit perturbed end-artery function and have an increased risk for stroke and age-related cognitive decline. Here, we used targeted genome-wide association (GWA) analysis and defined a CSVD locus adjacent to the forkh...

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Background The transmembrane receptor Notch1 is a critical regulator of arterial differentiation and blood vessel sprouting. Recent evidence shows that functional blockade of Notch1 and its ligand, Dll-4, leads to postnatal lymphatic defects in mice. However, the precise role of the Notch signaling pathway in lymphatic vessel development has yet to be defined. Here we show the developmental role of Notch1 in lymphatic vascular morphogenesis by analyzing lymphatic endothelial cell (LEC)-specific conditional Notch1 knockout mice crossed with an inducible Prox1CreERT2 driver. Results LEC-specific Notch1 mutant embryos exhibited enlarged lymphatic vessels. The phenotype of lymphatic overgrowth accords with increased LEC sprouting from the lymph sacs and increased filopodia formation. Furthermore, cell death was significantly reduced in Notch1-mutant LECs, whereas proliferation was increased. RNA-seq analysis revealed that expression of cytokine/chemokine signaling molecules was upregulated in Notch1-mutant LECs isolated from E15.5 dorsal skin, whereas VEGFR3, VEGFR2, VEGFC, and Gja4 (Connexin 37) were downregulated. Conclusions The lymphatic phenotype of LEC-specific conditional Notch1 mouse mutants indicates that Notch activity in LECs controls lymphatic sprouting and growth during development. These results provide evidence that similar to postnatal and pathological lymphatic vessel formation, the Notch signaling pathway plays a role in inhibiting developmental lymphangiogenesis.

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