Biology subjects

Nicoli, S.

Publications and source records attributed to Nicoli, S..

11 recordsLinked to original sources

bioRxiv2026

A mitochondrial program encodes brain vascular reserve

Brain resilience depends on collateral vessels whose geometries preserve blood flow when primary arteries are perturbed. How these protective vascular architectures are developmentally established remains unknown. Using longitudinal in vivo imaging in zebrafish, we show that mitochondrial state in embryonic angiogenic tip cells encodes the topology of basal and surface brain collateral networks. Mechanistically, microRNA-125a establishes the bioenergetic and redox balance of endothelial tip-cell mitochondria through conserved repression of the metabolic regulator PGC1a. Disruption of the microRNA-125a-PGC1a axis uncouples mitochondrial capacity from redox buffering in developing brain tip cells, redirecting their migration toward sparse, incompletely connected collateral network topologies and increasing adult cerebrovascular vulnerability. Consistent with this mechanism, humans with subclinical cerebrovascular injury exhibit reduced circulating microRNA-125a levels associated with incomplete basal collateral configurations. Together, these findings identify mitochondrial state as an instructive and conserved developmental program that encodes brain vascular reserve.

developmental biology↗

bioRxiv2025

Epidermal Stem Cells Control Periderm Injury Repair via Matrix-Driven Specialization of Intercellular Junctions

Epidermal stem cells interact with the extracellular matrix (ECM) to regulate their differentiation and maintain skin architecture. Here, we demonstrate a novel role for basal epidermal stem cells (BECs)-ECM interaction in regulating adhesion molecules expressed by the periderm--the superficial epidermal cells (SECs) of the embryonic bilayered skin. Using the developing zebrafish fin fold, we identify BECs form distinct regions of collagen-versus laminin-enriched basement membranes through integrin-mediated adhesions. Mechanistically, collagen-associated BECs form desmosomes and adherens junctions (AJs) with SECs while laminin-associated BECs display reduced desmosomes but sustain AJs and actomyosin expression with SECs. Notably, we show both in vivo and in a bilayered human keratinocyte model, that laminin, compared to collagen, is sufficient to repress desmosome formation while sustaining AJs specifically at the interlayer cell contacts. In vivo, laminin deficiency enhances desmosome expression across layers and impairs the wound-healing capacity of SECs. This defect was partially rescued by genetic reduction of the desmosome protein Desmoplakin-1a, highlighting the role of ECM-dependent junctional specialization in mediating differences in SEC injury response. Overall, our findings identify that stem cells, through their matrix, establish specialized junctions in the overlying stratified epithelium, which contribute to skin healing properties.

developmental biology↗

bioRxiv2024

Latrophilin-2 mediates fluid shear stress mechanotransduction at endothelial junctions

Endothelial cell responses to fluid shear stress from blood flow are crucial for vascular development, function and disease. A complex of PECAM-1, VE-cadherin, VEGF receptors (VEGFRs) and PlexinD1 located at cell-cell junctions mediates many of these events. But available evidence suggests that another mechanosensor upstream of PECAM-1 initiates signaling. Hypothesizing that GPCR and G proteins may serve this role, we performed siRNA screening of G subunits and found that Gi2 and Gq/11 are required for activation of the junctional complex. We then developed a new activation assay, which showed that these G proteins are activated by flow. We next mapped the G residues required for activation and developed an affinity purification method that used this information to identify latrophilin-2 (Lphn-2/ADGRL2) as the upstream GPCR. Latrophilin-2 is required for all PECAM-1 downstream events tested. In both mice and zebrafish, latrophilin-2 is required for flow-dependent angiogenesis and artery remodeling. Furthermore, endothelial specific knockout demonstrates that latrophilin plays a role in flow-dependent artery remodeling. Human genetic data reveal a correlation between the latrophilin-2-encoding Adgrl2 gene and cardiovascular disease. Together, these results define a pathway that connects latrophilin-dependent G protein activation to subsequent endothelial signaling, vascular physiology and disease.

molecular biology↗

bioRxiv2023

Hemodynamics regulate spatiotemporal artery muscularization in the developing circle of Willis

Vascular smooth muscle cells (VSMCs) envelop vertebrate brain arteries, playing a crucial role in regulating cerebral blood flow and neurovascular coupling. The dedifferentiation of VSMCs is implicated in cerebrovascular diseases and neurodegeneration. Despite its importance, the process of VSMC differentiation on brain arteries during development remains inadequately characterized. Understanding this process could aid in reprogramming and regenerating differentiated VSMCs in cerebrovascular diseases. In this study, we investigated VSMC differentiation on the zebrafish circle of Willis (CoW), comprising major arteries that supply blood to the vertebrate brain. We observed that the arterial expression of CoW endothelial cells (ECs) occurs after their migration from the cranial venous plexus to form CoW arteries. Subsequently, acta2+ VSMCs differentiate from pdgfrb+ mural cell progenitors upon recruitment to CoW arteries. The progression of VSMC differentiation exhibits a spatiotemporal pattern, advancing from anterior to posterior CoW arteries. Analysis of blood flow suggests that earlier VSMC differentiation in anterior CoW arteries correlates with higher red blood cell velocity wall shear stress. Furthermore, pulsatile blood flow is required for differentiation of human brain pdgfrb+ mural cells into VSMCs as well as VSMC differentiation on zebrafish CoW arteries. Consistently, the flow-responsive transcription factor klf2a is activated in ECs of CoW arteries prior to VSMC differentiation, and klf2a knockdown delays VSMC differentiation on anterior CoW arteries. In summary, our findings highlight the role of blood flow activation of endothelial klf2a as a mechanism regulating the initial VSMC differentiation on vertebrate brain arteries.

developmental biology↗

bioRxiv2022

Hematopoietic stem and progenitor cell heterogeneity is inherited from the embryonic hemogenic endothelium

Multipotent hematopoietic stem/progenitor cells (HSPCs) generate all mature blood cells in the erythroid, lymphoid, and myeloid lineages. HSPCs are initially produced in the embryo, via transdifferentiation of hemogenic endothelial cells (hemECs) in the aorta-gonad mesonephros (AGM). HSPCs in the AGM are functionally heterogenous in differentiation and proliferative output, but how these intrinsic differences are acquired remains unanswered. This knowledge could inform approaches to overcome the dysregulation of HSPC heterogeneity associated with poor outcomes of autologous transplants. Here we discovered that loss of microRNA (miR)-128 (miR-128{Delta}/{Delta}) in zebrafish leads to an expansion of hemECs forming replicative HSPCs in the AGM, and a skew towards the erythroid and lymphoid lineages in larval and adult stages. Furthermore, we found that inhibiting miR-128 during the differentiation of human pluripotent stem cells into hemECs, but not during the endothelial-to-hematopoietic transition, recapitulated the lineage skewing. In vivo, expression of wild-type miR-128 in endothelium restored the blood lineage distribution in miR-128{Delta}/{Delta} zebrafish. We found that miR-128 represses the expression of the Wnt inhibitor csnk1a1 and the Notch ligand jag1b, and thus promotes Wnt and Notch signaling in hemECs. De-repression of cskn1a1 resulted in hemECs generating replicative and erythroid-biased HSPCs, whereas de-repression of jag1b resulted in hemECs forming lymphoid-biased HSPCs in the AGM and relative mature blood cells in adult. We propose that HSPC heterogeneity is established in hemogenic endothelium prior to transdifferentiation and is programmed in part by Wnt and Notch signaling modulation.

developmental biology↗

bioRxiv2021

Non-coding function for mRNAs in Focal Adhesion Architecture and Mechanotransduction

Messenger RNA (mRNA) compartmentalization within the cytosol is well-recognized as a key mechanism of local translation-mediated regulation of protein levels, but whether such localization could be a means of exercising non-coding mRNA function is unknown. Here, we explore non-coding functions for mRNAs associated with focal adhesions (FAs), cellular structures responsible for mediating cell adhesion and response to changes in the extracellular matrix (ECM). Using high-throughput single molecule imaging and genomic profiling approaches, we find that mRNAs with distinct sequence characteristics localize to FAs in different human cell types. Notably, [~]85% of FA-mRNAs are not translationally active at steady state or under conditions of FA dissolution or activation. Untranslated mRNA sequences are anchored to FA based on their functional states by the RNA binding protein, G3BP1, forming biomolecular granules. Removing RNA or G3BP1, but not blocking new polypeptide synthesis, dramatically changes FA protein composition and organization, resulting in loss of cell contractility and cellular ability to adapt to changing ECM. We have therefor uncovered a novel, non-coding role for mRNAs as scaffolds to maintain FA structure and function, broadening our understating of noncanonical mRNA functions.

cell biology↗

bioRxiv2021

Distinct Hypoxia-induced Translational Profiles of Embryonic and Adult-derived Macrophages

Tissue homeostasis and repair are orchestrated by resident and newly recruited macrophages that alter their gene expression program in response to changes in tissue microenvironment. Embryonic macrophages, such as fetal liver derived macrophages (FLDM) seed the organs, including heart and lung during embryonic development and persist throughout the adult lifetime, while bone marrow-derived macrophages (BMDM) are recruited following an acute perturbation. Transcriptome analyses of FLDM and BMDM identified differences between them at the level of RNA expression, which correlates imperfectly with protein levels. Post-transcriptional regulation by microRNAs (miRNAs) and RNA-binding proteins determines mRNA stability and translation rate and may override transcriptional cues in response to environmental changes, such as hypoxia. To identify distinct features of FLDM and BMDM response to hypoxia at the level of translation, we employed translating ribosome affinity purification (TRAP) to isolate polysomal RNA. RNA-seq profiling of translated RNA identified distinct hypoxia-induced translational signature of BMDM (Ly6e, vimentin and glycolysis-associated enzymes Pgk1, Tpi1, Aldoa, Ldha) and FLDM (chemokines Ccl7 and Ccl2). By translational profiling of BMDM and FLDM with deletion of the RNA-binding protein HuR, we identified transcripts that were dependent on HuR. These findings highlight the importance of HuR and identify its distinct targets for post-transcriptional regulation of gene expression in embryonic vs. adult-derived macrophages.

cell biology↗

bioRxiv2020

Akt is required for artery formation during embryonic vascular development

One of the first events in the development of the cardiovascular system is morphogenesis of the main embryonic artery, the dorsal aorta (DA). The DA forms via a conserved genetic process mediated by the migration, specification, and organization of endothelial progenitor cells into a distinct arterial lineage and vessel type. Several angiogenic factors activate different signaling pathways to control DA formation, however the physiological relevance of distinct kinases in this complex process remains unclear. Here, we identify the role of Akt during early vascular development by generating mutant zebrafish lines that lack expression of akt isoforms. Live cell imaging coupled with single cell RNA sequencing of akt mutants reveal that Akt is required for proper development of the DA by sustaining arterial cell progenitor specification and segregation. Mechanistically, inhibition of active FOXO in akt mutants rescues impaired arterial development but not the expression of arterial markers, whereas Notch activation rescues arterial marker expression. Our work suggests that Akt activity is critical for early artery development, in part via FOXO and Notch-mediated regulation.

developmental biology↗

bioRxiv2020

Latrophilins are essential for endothelial junctional fluid shear stress mechanotransduction

Endothelial cell (EC) responses to fluid shear stress (FSS) are crucial for vascular development, adult physiology and disease. PECAM1 is an important transducer but earlier events remain poorly understood. We therefore investigated heterotrimeric G proteins in FSS sensing. Knockdown (KD) in ECs of single G proteins had little effect but combined depletion of Gi and Gq/11 blocked all known PECAM1-dependent responses. Re-expression of Gi2 and Gq but not Gi1 and Gi3 rescued these effects. Sequence alignment and mutational studies identified that K307 in Gi2 and Gq/11 (Q306 in Gi1/3), determines participation in flow signaling. We developed pull-down assays for measuring G activation and found that this residue, localized to the GPCR interface, determines activation by FSS. We developed a protocol for affinity purification of GPCRs on activated Gs, which identified latrophilins (ADGRLs) as specific upstream interactors for Gi2 and Gq/11. Depletion of latrophilin-2 blocked EC activation of Gi2 and Gq, downstream events in vitro, and flow-dependent vascular morphogenesis in zebrafish embryos. Surprisingly, latrophilin-2 depletion also blocked flow activation of two additional pathways activated at cell-cell junctions, Smad1/5 and Notch1, independently of G proteins. Latrophilins are thus central mediators of junctional shear stress mechanotransduction via G protein-dependent and -independent mechanisms.

molecular biology↗

bioRxiv2019

N-Glycome regulation limits the transdifferentiation of endothelial cells into hematopoietic stem cells

Hematopoietic stem and progenitor cells (HSPCs) that establish and maintain the blood system in adult vertebrates arise from the transdifferentiation of hemogenic endothelial cells (hemECs) during embryogenesis. This endothelial-to-hematopoietic transition (EHT) is tightly regulated, but the mechanisms are poorly understood. Here, we show that microRNA (miR)-223-mediated regulation of N-glycan biosynthesis in endothelial cells (ECs) regulates EHT. Single cell RNA-sequencing revealed that miR-223 is enriched in hemECs and in oligopotent nascent HSPCs. miR-223 restricts the EHT of lymphoid/myeloid lineages by suppressing the expression of mannosyltransferase alg2 and sialyltransferase st3gal2, two enzymes involved in N-linked protein glycosylation. High-throughput glycomics of ECs lacking miR-223 showed a decrease of high mannose versus sialylated complex/hybrid sugars on N-glycoproteins involved in EHT such as the metalloprotease Adam10. Endothelial-specific expression of an N-glycan Adam10 mutant or of the N-glycoenzymes phenocopied the aberrant HSPC production of miR-223 mutants. Thus, the N-glycome plays a previously unappreciated role as an intrinsic regulator of EHT, with specific mannose and sialic acid modifications serving as key endothelial determinants of their hematopoietic fate. One Sentence SummaryThe N-glycan "sugar code" governs the hematopoietic fate of endothelial cells and regulates blood stem cell production in vivo.

developmental biology↗

bioRxiv2018

microRNA-dependent regulation of biomechanical genes establishes tissue stiffness homeostasis

The mechanical properties of tissues, which are determined primarily by their extracellular matrix (ECM), are largely stable over time despite continual turnover of ECM constituents 1,2. These observations imply active homeostasis, where cells sense and adjust rates of matrix synthesis, assembly and degradation to keep matrix and tissue properties within the optimal range. However, the regulatory pathways that mediate this process are essentially unknown3. Genome-wide analyses of endothelial cells revealed abundant microRNA-mediated regulation of cytoskeletal, adhesive and extracellular matrix (CAM) mRNAs. High-throughput assays showed co-transcriptional regulation of microRNA and CAM genes on stiff substrates, which buffers CAM expression. Disruption of global or individual microRNA-dependent suppression of CAM genes induced hyper-adhesive, hyper-contractile phenotypes in multiple systems in vitro, and increased tissue stiffness in the zebrafish fin-fold during homeostasis and regeneration in vivo. Thus, a network of microRNAs and CAM mRNAs mediate tissue mechanical homeostasis.

cell biology↗