Biology subjects

Larrivee, B.

Publications and source records attributed to Larrivee, B..

4 recordsLinked to original sources

bioRxiv2026

Rapid Vascular Activation Precedes Immune Cell Infiltration Following Corneal Alkali Burn

Under homeostatic conditions, the cornea is avascular and contains few immune cells, but this changes rapidly following injury. Although the long-term consequences of corneal damage are well characterized, the earliest vascular and immune responses remain poorly understood. Here, we used a murine corneal alkali-burn model to examine limbal vascular activation and leukocyte recruitment immediately and at 2, 6, and 24 hours after injury. Limbal blood vessels underwent immediate dilation; however, vascular leakage into the corneal stroma occurred only in males. Lymphatic capillaries rapidly formed directed extensions toward the injury without significantly increasing their total vascular area, with males exhibiting longer extensions than females. Fluorescent dextran uptake provided evidence that these lymphatic vessels were functionally engaged in early tracer drainage. Despite pronounced vascular activation, early recruitment of neutrophils, monocytes, dendritic cells, macrophages, T cells, B cells, and natural killer cells remained limited. Thus, limbal blood and lymphatic vessels initiate the earliest response to corneal alkali injury before substantial leukocyte infiltration. These findings reveal sex-dependent differences in vascular permeability and lymphatic remodeling and identify the limbal vasculature as an early regulator of corneal inflammation and tissue repair.

pathology↗

bioRxiv2026

SOX9 regulates endothelial tip cell specification to promote cerebral and neuroretinal vascularization

BackgroundTissue vascularization relies on the organotypic specification of endothelial tip cells to interpret local cues and guide angiogenic sprouts into specific tissue compartments. However, the molecular regulators controlling brain and retinal endothelial tip cell identity remain poorly understood. MethodsEndothelial-specific Sox9 loss-of-function mouse was combined with single-cell, spatial, and bulk RNA sequencing analyses of developing mouse brain and retinal vasculature, as well as experimental ischemic stroke. Transcriptomic findings were validated using in situ hybridization, immunofluorescence, and functional angiogenesis assays. ResultsTranscription factor activity analysis of single-cell RNA-sequencing datasets identified SOX9 as a candidate regulator selectively enriched in developing brain and retinal endothelial tip cells. Endothelial-specific deletion of Sox9 impaired brain and neuroretina vascularization and disrupted the tip cell transcriptomic program, resulting in reduced sprouting angiogenesis and matrix-remodeling pathways. Conversely, SOX9 overexpression in HUVECs promoted neuro-tip-like signatures and enhanced endothelial invasion and sprouting. Following ischemic stroke, single-cell and spatial transcriptomic analyses identified a transient angiogenic endothelial population within the ischemic area. However, these cells failed to express Sox9 and lacked key developmental brain tip cell features. ConclusionsSOX9 is a key regulator of endothelial tip cell identity and neuronal angiogenesis. These findings reveal fundamental differences between developmental and injury-induced vascular responses and identify SOX9 as a potential therapeutic target to promote functional vascular regeneration.

developmental biology↗

bioRxiv2025

Loss of endothelial ALK1 signaling induces the emergence of a KIT+ angiogenic endothelial cluster driving brain arteriovenous malformations

BackgroundHereditary Hemorrhagic Telangiectasia type 2 (HHT2) is a genetic disorder caused by mutations in the ALK1 (ACVRL1) gene, encoding a receptor for Bone Morphogenetic Proteins 9 and 10 (BMP9/BMP10). HHT2 patients frequently develop brain arteriovenous malformations (bAVMs), which are abnormal connections between arteries and veins. Currently, surgical resection is the only treatment, associated with significant risks and complications. Despite evidence suggesting endothelial cell (EC) heterogeneity in bAVMs, it remains poorly characterized, limiting our ability to identify new therapeutic avenues. MethodsWe employed endothelial cell-specific and inducible Alk1 knockout mice (Alk1iECKO) with tamoxifen-induced deletion at postnatal day 6 (P6). We separately analyzed the P8 perineural (PNVP) and intraneural (INVP) vascular plexuses, which differ in vessel composition and flow dynamics. Single-cell RNA sequencing (scRNAseq) was performed to characterize EC heterogeneity and identify transcriptomic changes in both vascular plexuses of mutant versus wild type mice. ResultsLoss of endothelial ALK1 signaling triggered bAVM formation predominantly in the PNVP vascular network. scRNAseq revealed that Alk1 deletion promoted brain capillaries differentiation into angiogenic-1 ECs, whereas it drove PNVP venules EC proliferation and the emergence of the unique angiogenic-2 cluster. The latter shares transcriptomic features with human AVM ECs, including angiogenic tip cell markers and a strong glycolytic signature. Among its defining markers, Kit emerged as a direct downstream target of BMP9-ALK1 signaling. Pharmacological KIT inhibition using Masitinib, Imatinib, or KIT-blocking antibodies prevented bAVM formation in Alk1iECKO mice. ConclusionOur study uncovers a previously unrecognized EC population, the angiogenic-2 cluster, as a key contributor to bAVM development. We identify Kit as a central regulator of this cluster, establishing it as a promising therapeutic target for preventing bAVMs in HHT2. Clinical PerspectiveO_ST_ABSWhat is new?C_ST_ABSO_LIUsing endothelial-specific Alk1 knockout mouse models and single-cell transcriptomics, we identified a novel angiogenic endothelial cell population as a key driver of brain AVM formation. C_LIO_LIThis angiogenic EC cluster shares molecular features with human bAVM cells, including high expression of KIT, which we identified as a new direct transcriptional target of BMP9-ALK1 signaling. C_LIO_LIPharmacological inhibition of KIT using small molecules or blocking antibodies effectively prevents AVM formation in vivo, establishing KIT as a promising therapeutic target. C_LI What are the clinical implications?O_LIOur findings support the therapeutic potential of targeting KIT with FDA-approved drugs such as Imatinib to treat HHT2-associated brain AVMs, offering a non-invasive alternative to surgical intervention. C_LIO_LICharacterizing AVM-specific endothelial subtypes may enable the development of targeted and personalized therapies, improving patient outcomes and minimizing treatment-associated risks in HHT. C_LI

cell biology↗

bioRxiv2023

Bmp9 regulates Notch signaling and the temporal dynamics of angiogenesis via Lunatic Fringe

In briefThe mechanisms regulating the signaling pathways involved in angiogenesis are not fully known. Ristori et al. show that Lunatic Fringe (LFng) mediates the crosstalk between Bone Morphogenic Protein 9 (Bmp9) and Notch signaling, thereby regulating the endothelial cell behavior and temporal dynamics of their identity during sprouting angiogenesis. HighlightsO_LIBmp9 upregulates the expression of LFng in endothelial cells. C_LIO_LILFng regulates the temporal dynamics of tip/stalk selection and rearrangement. C_LIO_LILFng indicated to play a role in hereditary hemorrhagic telangiectasia. C_LIO_LIBmp9 and LFng mediate the endothelial cell-pericyte crosstalk. C_LI Bone Morphogenic Protein 9 (Bmp9), whose signaling through Activin receptor-like kinase 1 (Alk1) is involved in several diseases, has been shown to independently activate Notch target genes in an additive fashion with canonical Notch signaling. Here, by integrating predictive computational modeling validated with experiments, we uncover that Bmp9 upregulates Lunatic Fringe (LFng) in endothelial cells (ECs), and thereby also regulates Notch activity in an inter-dependent, multiplicative fashion. Specifically, the Bmp9-upregulated LFng enhances Notch receptor activity creating a much stronger effect when Dll4 ligands are also present. During sprouting, this LFng regulation alters vessel branching by modulating the timing of EC phenotype selection and rearrangement. Our results further indicate that LFng can play a role in Bmp9-related diseases and in pericyte-driven vessel stabilization, since we find LFng contributes to Jag1 upregulation in Bmp9-stimulated ECs; thus, Bmp9-upregulated LFng results in not only enhanced EC Dll4-Notch1 activation, but also Jag1-Notch3 activation in pericytes.

developmental biology↗