Biology subjects

Lagendijk, A.

Publications and source records attributed to Lagendijk, A..

5 recordsLinked to original sources

bioRxiv2024

Vascular mural cells protect the adult brain from haemorrhage but do not control the blood-brain barrier in developing zebrafish

The blood-brain barrier (BBB) protects the brain from circulating metabolites and plays central roles in neurological diseases. Endothelial cells (ECs) of the BBB are enwrapped by mural cells including pericytes and vascular smooth muscle cells (vSMCs) that regulate angiogenesis, vessel stability and barrier function. To explore mural cell control of the BBB, we investigated neurovascular phenotypes in zebrafish pdgfrb mutants that lack brain pericytes and vSMCs. As expected, mutants showed an altered cerebrovascular network with mispatterned capillaries. Unexpectedly, mutants displayed no BBB leakage at larval stages of development. This demonstrates that pericytes and vSMCs do not control BBB function in developing zebrafish. Instead, we observed juvenile and adult BBB disruption occurring at "hotspot" focal hemorrhages at large vessel aneurysms. ECs at leakage hotspots showed induction of caveolae on abluminal surfaces and structural defects including basement membrane thickening and disruption. Our work suggests that capillary pericytes regulate cerebrovascular patterning in development and vSMCs of major arteries protect from hemorrhage and BBB breakdown in older zebrafish. The fact that young zebrafish have a functional BBB in the absence of mural cells calls for renewed interrogation of mural cell control of the BBB throughout vertebrate evolution.

developmental biology↗

bioRxiv2023

c-Src induced vascular malformations require localised matrix degradation at focal adhesions

Endothelial cells lining the blood vessel wall communicate intricately with the surrounding extracellular matrix, translating mechanical cues into biochemical signals. Moreover, vessels require the capability to enzymatically degrade the matrix surrounding them, to facilitate vascular expansion. c-Src plays a key role in blood vessel growth, with its loss in the endothelium reducing vessel sprouting and focal adhesion signalling. Here, we show that constitutive activation of c-Src in endothelial cells results in rapid vascular expansion, operating independently of growth factor stimulation or fluid shear stress forces. This is driven by an increase in focal adhesion signalling and size, with enhancement of localised secretion of matrix metalloproteinases responsible for extracellular matrix remodelling. Inhibition of matrix metalloproteinase activity results in a robust rescue of the vascular expansion elicited by heightened c-Src activity. This supports the premise that moderating focal adhesion-related events and matrix degradation can counteract abnormal vascular expansion, with implications for pathologies driven by unusual vascular morphologies.

cell biology↗

bioRxiv2022

Prox1 dynamically regulates downstream targets and chromatin accessibility during venous to lymphatic endothelial cell transdifferentiation in the embryo

During development, the lymphatic vasculature forms as a second, new vascular network derived from blood vessels. The transdifferentiation of embryonic venous endothelial cells (VECs) into lymphatic endothelial cells (LECs) is the first step in this process. Specification, differentiation and maintenance of LEC fate are all driven by the transcription factor Prox1, yet downstream mechanisms remain to be elucidated. We present a single cell transcriptomic atlas of lymphangiogenesis in zebrafish revealing new markers and hallmarks of LEC differentiation over four developmental stages. We further profile single cell transcriptomic and chromatin accessibility changes in zygotic prox1a mutants that are undergoing a VEC-LEC fate reversion during differentiation. Using maternal and zygotic prox1a/prox1b mutants, we determine the earliest transcriptomic changes directed by Prox1 during LEC specification. This work altogether reveals new transcriptional targets and regulatory regions of the genome downstream of Prox1 in LEC maintenance, as well as showing that Prox1 specifies LEC fate primarily by limiting blood vascular and hematopoietic fate. This extensive single cell resource provides new mechanistic insights into the enigmatic role of Prox1 and the control of LEC differentiation in development.

developmental biology↗

bioRxiv2020

A unified view of neighbour cell engagement during apoptotic cell extrusion.

Epithelia must eliminate apoptotic cells to preserve tissue barriers and prevent inflammation [1]. Several different mechanisms exist for apoptotic clearance, including efferocytosis [2, 3] and apical extrusion [4, 5]. We found that extrusion was the first-line response to apoptosis in cultured monolayers and in zebrafish epidermis. During extrusion, the apoptotic cell elicited active lamellipodial protrusions and assembly of a contractile extrusion ring in its neighbours. Depleting E-cadherin compromised both the contractile ring and extrusion, implying that a cadherin-dependent pathway allows apoptotic cells to engage their neighbours for extrusion. We identify RhoA as the cadherin-dependent signal in the neighbour cells and show that it is activated in response to contractile tension from the apoptotic cell. This mechanical stimulus is conveyed by a Myosin VI-dependent mechanotransduction pathway that is necessary both for extrusion and to preserve the epithelial barrier when apoptosis was stimulated. Earlier studies suggested that release of sphingosine-1-phosphate (S1P) from apoptotic cells might define where RhoA was activated. However, we found that although S1P is necessary for extrusion, its contribution does not require a localized source of S1P in the epithelium. We therefore propose a unified view of how RhoA is stimulated to engage neighbour cells for apoptotic extrusion. Here, tension-sensitive mechanotransduction is the proximate mechanism that activates RhoA specifically in the immediate neighbours of apoptotic cells, but this also must be primed by S1P in the tissue environment. Together, these elements provide a coincidence detection system that confers robustness on the extrusion response.

cell biology↗

bioRxiv2017

Dissemination of Cryptococcus neoformans via localised proliferation and blockage of blood vessels

Cryptococcus neoformans is an opportunistic fungal pathogen that can cause life-threatening cryptoccocal meningitis, predominantly within immunocompromised individuals. Cortical infarcts are observed in as many as 30% of cryptococcal meningitis cases, being particularly common in severe infection. Limited clinical case studies suggest infarcts are secondary to vasculitis and blood vessel damage caused by cryptococcal infection. However, the cause of infarcts in cryptococcal infection has not been determined. To examine potential causes of vascular damage and cryptococcal dissemination in cryptococcal infection, the zebrafish C. neoformans infection model was used. We demonstrate that spread of cryptococci from the vasculature occurs at sites where cryptococci grow within the blood vessels, originating from a single or small number of cryptococci. We find that cryptococcal cells become trapped within the vasculature and can proliferate there resulting in vasodilation. Localised cryptococcal growth in the vasculature is also associated with sites of dissemination - in some cases simultaneously with a loss of blood vessel integrity. Using a cell-cell junction protein reporter (VE-cadherin) we identified sites dissemination associated with both intact blood vessels and where vessel rupture occurred. Thus, we have identified a mechanism for blood vessel damage during cryptococcal infection that may represent a cause of the vascular damage and cortical infarction observed in cryptococcal meningitis.\n\nAuthor summaryHuman infection by the fungal pathogen, Cryptococcus neoformans, can lead to life-threatening cryptococcal meningitis. In severe cases of cryptococcal meningitis, a lack of blood supply can cause tissue death and a resulting area of dead tissue (infarct) in the brain. Although vasculature inflammation in known to occur in cryptococcal meningitis, the cause of infarcts in unknown. Using a zebrafish model of cryptococcal infection, the growth and dissemination of fungal cells was observed over time. We show that cryptococcal cells become trapped and proliferate in the vasculature, resulting in cryptococcoma that damage the blood vessels. We propose that vessel damage results from increased blood pressure caused by cryptococci blocking blood vessels suggesting that the vascular damage that ensues on cryptococcoma formation may in turn be a cause of infarct formation seen in cryptococcal meningitis.

microbiology↗