Role of endothelial PDGFB in arterio-venous malformations pathogenesis.

Arterial-venous malformations (AVMs) are direct connections between arteries and veins without an intervening capillary bed. Either familial inherited or sporadically occurring, localized pericytes (PCs) drop is among the AVMs' hallmarks. Whether impaired PC coverage triggers AVMs or it is a secondary event is unclear. Here we evaluated the role of the master regulator of PC recruitment, Platelet derived growth factor B (PDGFB) in AVM pathogenesis. Using tamoxifen-inducible deletion of Pdgfb in endothelial cells (ECs), we show that disruption of EC Pdgfb-mediated PC recruitment and maintenance leads to capillary enlargement and organotypic AVM-like structures. These vascular lesions contain non-proliferative hyperplastic, hypertrophic and miss-oriented capillary ECs with an altered capillary EC fate identity. Mechanistically, we propose that PDGFB maintains capillary EC size and caliber to limit hemodynamic changes, thus restricting expression of Krüppel like factor 4 and activation of Bone morphogenic protein, Transforming growth factor ß and NOTCH signaling in ECs. Furthermore, our study emphasizes that inducing or activating PDGFB signaling may be a viable therapeutic approach for treating vascular malformations.

Tissue factor binds to and inhibits interferon-α receptor 1 signaling.

Tissue factor (TF), which is a member of the cytokine receptor family, promotes coagulation and coagulation-dependent inflammation. TF also exerts protective effects through unknown mechanisms. Here, we showed that TF bound to interferon-α receptor 1 (IFNAR1) and antagonized its signaling, preventing spontaneous sterile inflammation and maintaining immune homeostasis. Structural modeling and direct binding studies revealed binding of the TF C-terminal fibronectin III domain to IFNAR1, which restricted the expression of interferon-stimulated genes (ISGs). Podocyte-specific loss of TF in mice (PodΔF3) resulted in sterile renal inflammation, characterized by JAK/STAT signaling, proinflammatory cytokine expression, disrupted immune homeostasis, and glomerulopathy. Inhibiting IFNAR1 signaling or loss of Ifnar1 expression in podocytes attenuated these effects in PodΔF3 mice. As a heteromer, TF and IFNAR1 were both inactive, while dissociation of the TF-IFNAR1 heteromer promoted TF activity and IFNAR1 signaling. These data suggest that the TF-IFNAR1 heteromer is a molecular switch that controls thrombo-inflammation.

SMAD4 maintains the fluid shear stress set point to protect against arterial-venous malformations.

Vascular networks form, remodel, and mature under the influence of both fluid shear stress (FSS) and soluble factors. Physiological FSS promotes and maintains vascular stability via synergy with bone morphogenic proteins 9 and 10 (BMP9 and BMP10). Conversely, mutation of the BMP receptors activin-like kinase 1 (ALK1), endoglin (ENG), or the downstream effector, SMAD family member 4 (SMAD4) leads to hereditary hemorrhagic telangiectasia (HHT), characterized by fragile and leaky arterial-venous malformations (AVMs). How endothelial cells (ECs) integrate FSS and BMP signals in vascular development and homeostasis and how mutations give rise to vascular malformations is not well understood. Here, we aimed to elucidate the mechanism of synergy between FSS and SMAD signaling in vascular stability and how disruption of this synergy leads to AVMs. We found that loss of Smad4 increased the sensitivity of ECs to flow by lowering the FSS set point, with resulting AVMs exhibiting features of excessive flow-mediated morphological responses. Mechanistically, loss of SMAD4 disinhibits flow-mediated KLF4-TIE2-PI3K/Akt signaling, leading to cell cycle progression-mediated loss of arterial identity due to KLF4-mediated repression of cyclin dependent Kinase (CDK) inhibitors CDKN2A and CDKN2B. Thus, AVMs caused by Smad4 deletion are characterized by chronic high flow remodeling with excessive EC proliferation and loss of arterial identity as triggering events.

Studies of protein-protein interactions in Fanconi anemia pathway to unravel the DNA interstrand crosslink repair mechanism.

Fanconi anemia (FA), a cancer predisposition syndrome exhibits hallmark feature of radial chromosome formation, and hypersensitivity to DNA crosslinking agents. A set of FA pathway proteins mainly FANCI, FANCD2 and BRCA2 are expressed to repair the covalent crosslink between the dsDNA. However, FA, BRCA pathways play an important role in DNA ICL repair as well as in homologous recombination repair, but the presumptive role of FA-BRCA proteins has not clearly explored particularly in context to function associated protein-protein interactions (PPIs). Here, in-vivo, in-vitro and in-silico studies have been performed for functionally relevant domains of FANCI, FANCD2 and BRCA2. To our conclusion, FANCI ARM repeat interacts with FANCD2 CUE domain and BRCA2 C-terminal region. Interestingly, FANCD2 CUE domain also interacts strongly with BRCA2 C-terminal region. Interactions between BRCA2 CTR and functionally relevant mutations Ser222Ala (cell cycle checkpoint mutant) and Leu231Arg (DNA ICL repair mutant) present in FANCD2 CUE domain have been analysed. To our finding, these mutations abrogate the binding between FANCD2 CUE domain and BRCA2 CTR. Furthermore, (1) different domain of FANCI, FANCD2 and BRCA2 are playing important role in PPIs, (2) mutations cause the impairment in the PPIs which in turn may disrupt the DNA ICL repair mechanism.