Schlegel, N. | Search bioRxiv

bioRxiv2022

Soluble VE-cadherin disrupts endothelial barrier function via VE-PTP/RhoA signalling

AimIncreased levels of soluble Vascular endothelial (VE)-cadherin fragments (sVE-cadherin) have previously been linked with inflammation-induced loss of endothelial barrier function. We tested whether sVE-cadherin is critically involved in the onset of endothelial barrier dysfunction. Methods and ResultsApplication of recombinant human sVE-cadherin (extracellular domains EC1-5) on human microvascular endothelial cells in vitro and in a rat model in vivo induced loss of endothelial barrier function and reduced microcirculatory flow. sVE-cadherinEC1-5 led to decreased localization of VE-cadherin at cell borders. Additionally, sVE-cadherinEC1-5 perturbed VE-protein tyrosine phosphatase (VE-PTP)/VE-cadherin interaction. VE-PTP inhibitor AKB9778 blunted all sVE-cadherinEC1-5-induced effects in vitro and in vivo. Downstream effects involve VE-PTP-dependent RhoA activation which was attenuated by AKB9778. Rho-kinase inhibitor Y27632 blocked sVE-cadherinEC1-5-induced loss of endothelial barrier function. ConclusionsVE-cadherin disrupts endothelial barrier function by dismantling the VE-cadherin complex at cell borders via VE-PTP-dependent RhoA activation. This uncovers a novel pathophysiological role of sVE-cadherin in the context of endothelial barrier dysfunction in inflammation.

physiology↗

bioRxiv2021

G6b-B regulates an essential step in megakaryocyte maturation

G6b-B is a megakaryocyte lineage-specific immunoreceptor tyrosine-based inhibition motif (ITIM)-containing receptor, essential for platelet homeostasis. Mice with a genomic deletion of the entire Mpig6b locus develop severe macrothrombocytopenia and myelofibrosis, which is reflected in humans with null-mutations in MPIG6B. The current model proposes that megakaryocytes lacking G6b-B develop normally, while proplatelet release is hampered, but the underlying molecular mechanism remains unclear. Here, we report on a spontaneous recessive single nucleotide mutation in C57BL/6 mice, localized within the intronic region of the Mpig6b locus that abolishes G6b-B expression and reproduces macrothrombocytopenia, myelofibrosis and osteosclerosis. As the mutation is based on a single nucleotide exchange, Mpig6bmut mice represent an ideal model to study the role of G6b-B. Megakaryocytes from these mice were smaller in size, displayed a less developed demarcation membrane system and reduced expression of receptors. RNA sequencing revealed a striking global reduction in the level of megakaryocyte-specific transcripts, in conjunction with decreased protein levels of the transcription factor GATA-1, and impaired thrombopoietin signaling. The reduced number of mature MKs in the bone marrow was corroborated on a newly developed Mpig6b null mouse strain. Our findings highlight an unexpected essential role of G6b-B in the early differentiation within the megakaryocytic lineage.

cell biology↗