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SMAD4 maintains the Fluid Shear Stress set point to protect against Arterial-Venous Malformations

ABSTRACT: 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 Protein 9 (BMP9) and BMP10. Conversely, mutation of the BMP receptors ALK1, Endoglin or the downstream effector SMAD4 leads to Hereditary Hemorrhagic Telangiectasia (HHT), characterized by fragile and leaky arterial-venous malformations (AVMs). But how endothelial cells (EC) 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 fluid shear stress and SMAD signaling in vascular stability and its failure in HHT. We have now found that loss of Smad4 increases ECs’ sensitivity 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 increased EC proliferation and 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.

ORGANISM(S): Homo sapiens

PROVIDER: GSE232443 | GEO | 2023/07/03

REPOSITORIES: GEO

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Project description:Purpose: Hereditary Hemorrhagic Telangiectasia (HHT) is an autosomal dominant vascular disorder characterized by arteriovenous malformations (AVMs). Over 90% of HHT patients carry heterozygous loss-of-function mutations in Transforming Growth Factor-beta (TGFb) signaling components activin receptor-like kinase 1 (ACVRL1/ALK1), endoglin (ENG), or mothers against decapentaplegic homolog 4 (SMAD4). Brain AVMs can be lethal for HHT patients. Here, we use an inducible endothelial (EC)-specific mouse line to investigate brain AVMs characteristics in Alk1-, Eng-, and Smad4-HHT mouse models. Angiopientin-2 (Ang2) inhibition diminishes HHT associated cerebral vascular defects. We aim to identify the shared transcriptional changes in brain ECs between these three HHT types, and provide insights for transcriptional changes upon Ang2 inhibition. Methods: ECs were isolated from brains of both WT and HHT mutant mice at postnatal day 7 (P7) for Smad4 and Eng models, P6 for Alk1 model. Total RNA was extracted from isolated brain ECs and quantified using Qubit RNA High Sensitivity Assay Kit. RNA integrity was determined using the Bioanalyzer RNA 6000 Nano assay kit. RNA library construction was performed with the TruSeq RNA Library Prep Kit v2 from Illumina. The resulting mRNA library was quantified using Qubit dsDNA High Sensitivity Assay Kit and verified using the Bioanalyzer DNA1000 assay kit. Verified samples were sequenced using the NextSeq 500/550 High Output Kit v2.5 (150 Cycles) on a Nextseq 550 system. Sequenced reads were aligned to the mouse (mm10) reference genome with RNA-seq alignment tool (version 2.0.1). The aligned reads were used to quantify mRNA expression and determine differentially expressed genes using the RNA-seq Differential Expression tool (version 1.0.1). Both alignment and differential expression analysis were performed using the tools in the BaseSpace Sequence Hub. Results: We identified 5509, 5381, and 2663 differentially expressed genes in Smad4, Alk1, and Eng HHT models respectively. Also, Ang2 inhibition mainly funcioned through angiogenesis and cell migration processes to normalize cerebrovascular defects in Smad4-HHT model. Conclusions: A common but unique pro-angiogenic program among all HHT models included 14 consistent upregulated and 5 consistent downregulated angiogic genes. Also, Ang2 inhibition mainly funcioned through angiogenesis and cell migration processes to normalize cerebrovascular defects in Smad4-HHT model.

Project description:Hereditary Hemorrhagic Telangiectasia (HHT) is a rare congenital disease in which fragile vascular malformations focally develop in multiple organs. These can be small (telangiectasias) or large (arteriovenous malformations, AVMs) and can compromise tissue perfusion. Critically, they are prone to rupture leading to frequent and uncontrolled bleeding. As a result, HHT patients experience several debilitating clinical manifestations that reduce patient quality-of-life. Most HHT patients are heterozygous for loss-of-function mutations affecting signaling through the Alk1 pathway; yet, the pathogenesis of vascular malformation (VM) in HHT patients remains unclear and there are still few treatment options and no cure. Due to the complex, three-dimensional, and multicellular nature of vascular lesions in HHT, they are traditionally studied in intact genetically-modified mouse and zebrafish models, and studies in these animals have yielded important insights into HHT disease progression. However, intact animal studies can be time-consuming and expensive, and may be difficult to translate to human patients. In this study, we take advantage of our recently developed Vascularized Micro-Organ platform to develop an in vitro fully-humanized HHT-on-a-chip microphysiological model (HHT-VMO) that recapitulates vascular lesions of HHT patients. Using a tunable IPTG-inducible ACVRL1 (Alk1)-knockdown approach, we control the timing and extent of endogenous Alk1 expression in primary human endothelial cells seeded into the HHT-VMO device. We report that Alk1-deficient EC reliably form networks with aberrant morphology that includes lesions reminiscent of both patient telangiectasias and AVMs. HHT-VMO lesions are dependent upon the timing of Alk1 knockdown and their formation is blocked by the Vascular Endothelial Growth Factor Receptor (VEGFR) inhibitor pazopanib. Lastly, we find that AVM-like lesions that form in the HHT-VMO are comprised of mixed Alk1-intact and Alk1-deficient EC suggesting cell non-autonomous effects. Taken together, we report development of a novel HHT-on-a-chip model that appears to faithfully reproduce HHT patient lesions. In the future, we hope to use this model to better understand HHT disease biology and to perform drug screening studies to identify a cure for HHT.

Project description:Tissue Factor Pathway Inhibitor-2 is Induced by Fluid Shear Stress in Vascular Smooth Muscle Cells and Affects Cell Proliferation and Survival Introduction: Vascular smooth muscle cells (SMCs) are exposed to fluid shear stress (FSS) after interventional procedures such as balloon-angioplasty. Whereas the effects of hemodynamic forces on endothelial cells are explored in detail, the influence of FSS on smooth muscle cell function is poorly characterized. Here, we investigated the effect of FSS on SMC gene expression and function. Methods: Laminar FSS of arterial level (14 dynes/cm2) was applied to SMC cultures for 24 h in a parallel-plate flow chamber. The effect of FSS on gene expression was first screened with microarray technology and the results further verified by real time (RT) PCR and immunoblotting. Protein expression was also studied in the rat carotid artery after balloon-injury and DNA synthesis and apoptosis was examined in SMCs in vitro. Results: Microarrays identified tissue-pathway inhibitor-2 (TFPI-2) as the most differentially expressed gene by FSS in cultured SMCs. The regulatory effect of FSS on the expression of TFPI-2 was confirmed by RT-PCR and immunobloting demonstrating a more than 400-fold increase in TFPI-2 expression in SMCs exposed to FSS compared to static controls and a consistent upregulation at the protein level. Functionally, SMC proliferation was decreased by FSS and recombinant TFPI-2 was found to inhibit SMC proliferation and induce SMC apoptosis as indicated by activation of caspase-3. In vivo, TFPI-2 expression was found to be up-regulated 5, 10 and 20 h after rat carotid balloon-injury and immunohistochemistry demonstrated TFPI-2 protein in luminal SMCs exposed to FSS in rat carotid intimal hyperplasia 10 days after balloon-injury. Conclusion: FSS strongly influence gene expression in cultured SMCs and induce TFPI-2 expression, which is also expressed after rat carotid balloon injury in luminal SMCs exposed to FSS. Functionally, TFPI-2 may play an important role in vessel wall repair by regulating SMC proliferation and survival. Further studies are needed to elucidate the mechanisms by which TFPI-2 control SMC function. 3 x 2 samples from a paired fluid shear stress experiment on smooth muscle cells.

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SMAD4 maintains the Fluid Shear Stress set point to protect against Arterial-Venous Malformations

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