Activation of Smad2/3 signaling by low fluid shear stress mediates artery inward remodeling

Hemodynamics and Wall Mechanics of Vascular Graft Failure

Blood vessels are subjected to complex biomechanical loads, primarily from pressure-driven blood flow. Abnormal loading associated with vascular grafts, arising from altered hemodynamics or wall mechanics, can cause acute and progressive vascular failure and end-organ dysfunction. Perturbations to mechanobiological stimuli experienced by vascular cells contribute to remodeling of the vascular wall via activation of mechanosensitive signaling pathways and subsequent changes in gene expression and associated turnover of cells and extracellular matrix. In this review, we outline experimental and computational tools used to quantify metrics of biomechanical loading in vascular grafts and highlight those that show potential in predicting graft failure for diverse disease contexts. We include metrics derived from both fluid and solid mechanics that drive feedback loops between mechanobiological processes and changes in the biomechanical state that govern the natural history of vascular grafts. As illustrative examples, we consider application-specific coronary artery bypass grafts, peripheral vascular grafts, and tissue-engineered vascular grafts for congenital heart surgery as each of these involves unique circulatory environments, loading magnitudes, and graft materials.

Transient low shear-stress preconditioning influences long-term endothelial traction and alignment under high shear flow

Endothelial cells (ECs) within the vascular system encounter fluid shear stress (FSS). High, laminar FSS promotes vasodilation and anti-inflammatory responses, whereas low or disturbed FSS induces dysfunction and inflammation. However, the adaptation of endothelial cells (ECs) to dynamically changing FSS patterns remains underexplored. Here, by combining traction force microscopy with a custom flow chamber, we examined human umbilical vein endothelial cells adapting their traction during transitions from short-term low shear to long-term high shear stress. We discovered that the initial low FSS elevates the traction by only half of the amount in response to direct high FSS even after flow changes to high FSS. However, in the long term under high FSS, the flow started with low FSS triggers a substantial second rise in traction for over 10 h. In contrast, the flow started directly with high FSS results in a quick traction surge followed by a huge reduction below the baseline traction in <30 min. Importantly, we find that the orientation of traction vectors is steered by initial shear exposure. Using Granger causality analysis, we show that the traction that aligns in the flow direction under direct high FSS functionally causes cell alignment toward the flow direction. However, EC traction that orients perpendicular to the flow that starts with temporary low FSS functionally causes cell orientation perpendicular to the flow. Taken together, our findings elucidate the significant influence of initial short-term low FSS on lasting changes in endothelial traction that induces EC alignment.NEW & NOTEWORTHY In our study, we uncover that preconditioning with low shear stress yields enduring impacts on endothelial cell traction and orientation, persisting even after transitioning to high-shear conditions. Using Granger causality analysis, we demonstrate a functional link between the direction of cell traction and subsequent cellular alignment across varying shear environments.

Low Shear in Short-Term Impacts Endothelial Cell Traction and Alignment in Long-Term

Within the vascular system, endothelial cells (ECs) are exposed to fluid shear stress (FSS), a mechanical force exerted by blood flow that is critical for regulating cellular tension and maintaining vascular homeostasis. The way ECs react to FSS varies significantly; while high, laminar FSS supports vasodilation and suppresses inflammation, low or disturbed FSS can lead to endothelial dysfunction and increase the risk of cardiovascular diseases. Yet, the adaptation of ECs to dynamically varying FSS remains poorly understood. This study focuses on the dynamic responses of ECs to brief periods of low FSS, examining its impact on endothelial traction-a measure of cellular tension that plays a crucial role in how endothelial cells respond to mechanical stimuli. By integrating traction force microscopy (TFM) with a custom-built flow chamber, we analyzed how human umbilical vein endothelial cells (HUVECs) adjust their traction in response to shifts from low to high shear stress. We discovered that initial exposure to low FSS prompts a marked increase in traction force, which continues to rise over 10 hours before slowly decreasing. In contrast, immediate exposure to high FSS causes a quick spike in traction followed by a swift reduction, revealing distinct patterns of traction behavior under different shear conditions. Importantly, the direction of traction forces and the resulting cellular alignment under these conditions indicate that the initial shear experience dictates long-term endothelial behavior. Our findings shed light on the critical influence of short-lived low-shear stress experiences in shaping endothelial function, indicating that early exposure to low FSS results in enduring changes in endothelial contractility and alignment, with significant consequences for vascular health and the development of cardiovascular diseases.

[Research Progress in the Role of Liquid-Liquid Phase Separation in Human Cancer]

Liquid-liquid phase separation (LLPS) is a reversible process, during which biological macromolecules, including proteins and nucleic acids, condense into liquid membraneless organelles under the influence of weak multivalent interactions. Currently, fluorescence recovery after photobleaching is the primary method used to detect the phase separation of biological macromolecules. Recent studies have revealed the link between abnormal LLPS and the pathogenesis and development of various human cancers. Through phase separation or abnormal phase separation, tumor-related biological macromolecules, such as mRNA, long noncoding RNAs (lncRNAs), and tumor-related proteins, can affect transcriptional translation and DNA damage repair, regulate the autophagy and ferroptosis functions of cells, and thus regulate the development of various tumors. In this review, we summarized the latest research findings on the mechanism of LLPS in the pathogenesis and progression of tumors and elaborated on the promotion or inhibition of autophagy, tumor immunity, DNA damage repair, and cell ferroptosis after abnormal phase separation of biomolecules, including mRNA, lncRNA, and proteins, which subsequently affects the pathogenesis and progression of tumors. According to published findings, many biological macromolecules can regulate transcriptional translation, expression, post-transcriptional modification, cell signal transduction, and other biological processes through phase separation. Therefore, further expansion of the research field of phase separation and in-depth investigation of its molecular mechanisms and regulatory processes hold extensive research potential.

Cadherin-linked morphogen gradient actualizes robust tissue patterning

Morphogen gradients govern tissue patterning. These gradients provide positional information, instructing cells to adopt distinct fates. Over the past few decades, extensive studies have revealed the detailed mechanisms by which morphogens generate tissue patterns. However, the communication between morphogen-receiving cells is still poorly understood. Here, I describe how cadherin-mediated cell competition ensures robust morphogen-gradient formation. In normal zebrafish embryos, unfit cells with abnormal Wnt signaling activity spontaneously appear and produce a noisy morphogen gradient. These unfit cells communicate with neighboring cells through cadherins and are subsequently killed by cell competition. This process of killing unfit cells corrects noisy gradients to support reproducible patterning. I also discuss the significance of cell-competition-mediated morphogen-gradient correction from the perspectives of evolution and disease biology.

A computational growth and remodeling framework for adaptive and maladaptive pulmonary arterial hemodynamics

Hemodynamic loading is known to contribute to the development and progression of pulmonary arterial hypertension (PAH). This loading drives changes in mechanobiological stimuli that affect cellular phenotypes and lead to pulmonary vascular remodeling. Computational models have been used to simulate mechanobiological metrics of interest, such as wall shear stress, at single time points for PAH patients. However, there is a need for new approaches that simulate disease evolution to allow for prediction of long-term outcomes. In this work, we develop a framework that models the pulmonary arterial tree through adaptive and maladaptive responses to mechanical and biological perturbations. We coupled a constrained mixture theory-based growth and remodeling framework for the vessel wall with a morphometric tree representation of the pulmonary arterial vasculature. We show that non-uniform mechanical behavior is important to establish the homeostatic state of the pulmonary arterial tree, and that hemodynamic feedback is essential for simulating disease time courses. We also employed a series of maladaptive constitutive models, such as smooth muscle hyperproliferation and stiffening, to identify critical contributors to development of PAH phenotypes. Together, these simulations demonstrate an important step toward predicting changes in metrics of clinical interest for PAH patients and simulating potential treatment approaches.

Integration of Chemo-mechanical signaling in response to fluid shear stress by the endothelium

Physical forces exert profound effects on cells affecting fate, function, and response to stressors. In the case of the endothelium, the layer that resides in the inner surface of blood vessels, the collective effect of hemodynamic forces influences the onset and severity of vascular pathologies. Justifiably, much emphasis has been placed in understanding how endothelial cells sense and respond to mechanical challenges, particularly hemodynamic shear stress. In this review, we highlight recent developments that have expanded our understanding of the molecular mechanisms underlying mechanotransduction. We describe examples of protein compartmentalization in response to shear stress, consider the contribution of the glycocalyx, and discuss the specific role ion channels in response to flow. We also highlight the recently recognized contribution of the receptor ALK5 in sensing turbulent flow. Research in the last three years has enriched our understanding of the molecular landscape responsible for recognizing and transducing shear stress responses, including novel transcriptional-dependent and transcriptional-independent mechanisms.

Estimation of shear stress heterogeneity along capillary segments in angiogenic rat mesenteric microvascular networks

OBJECTIVE

Fluid shear stress is thought to be a regulator of endothelial cell behavior during angiogenesis. The link, however, requires an understanding of stress values at the capillary level in angiogenic microvascular networks. Critical questions remain. What are the stresses? Do capillaries experience similar stress magnitudes? Can variations explain vessel-specific behavior? The objective of this study was to estimate segment-specific shear stresses in angiogenic networks.

METHODS

Images of angiogenic networks characterized by increased vascular density were obtained from rat mesenteric tissues stimulated by compound 48/80-induced mast cell degranulation. Vessels were identified by perfusion of a 40 kDa fixable dextran prior to harvesting and immunolabeling for PECAM. Using a network flow-based segment model with physiologically relevant parameters, stresses were computed per vessel for regions across multiple networks.

RESULTS

Stresses ranged from 0.003 to 2328.1 dyne/cm2 and varied dramatically at the capillary level. For all regions, the maximum segmental shear stresses were for capillary segments. Stresses along proximal capillaries branching from arteriole inlets were increased compared to stresses along capillaries in more distal regions.

CONCLUSIONS

The results highlight the variability of shear stresses along angiogenic capillaries and motivate new discussions on how endothelial cells may respond in vivo to segment-specific microenvironment during angiogenesis.

cSTAR analysis identifies endothelial cell cycle as a key regulator of flow-dependent artery remodeling

Fluid shear stress (FSS) from blood flow is sensed by vascular endothelial cells (ECs) to determine vessel stability, remodeling and susceptibility to atherosclerosis and other inflammatory diseases but the regulatory networks that govern these behaviors are only partially understood. We used cSTAR, a powerful new computational method, to define EC transcriptomic states under low shear stress (LSS) that triggers vessel inward remodeling, physiological shear stress (PSS) that stabilizes vessels, high shear stress (HSS) that triggers outward remodeling, and oscillatory shear stress (OSS) that confers disease susceptibility, all in comparison to cells under static conditions (STAT). We combined these results with the LINCS database where EC transcriptomic responses to drug treatments to define a preliminary regulatory network in which the cyclin-dependent kinases CDK1/2 play a central role in promoting vessel stability. Experimental analysis showed that PSS induced a strong late G1 cell cycle arrest in which CDK2 was activated. EC deletion of CDK2 in mice resulted in inward artery remodeling and both pulmonary and systemic hypertension. These results validate use of cSTAR to determine EC state and in vivo vessel behavior, reveal unexpected features of EC phenotype under different FSS conditions, and identify CDK2 as a key element within the EC regulatory network that governs artery remodeling.

CAPILLARY LEAK AND EDEMA AFTER RESUSCITATION: THE POTENTIAL CONTRIBUTION OF REDUCED ENDOTHELIAL SHEAR STRESS CAUSED BY HEMODILUTION

ABSTRACT

Normal shear stress is essential for the normal structure and functions of the microcirculation. Hemorrhagic shock leads to reduced shear stress due to reduced tissue perfusion. Although essential for the urgent restoration of cardiac output and systemic blood pressure, large volume resuscitation with currently available solutions causes hemodilution, further reducing endothelial shear stress. In this narrative review, we consider how the use of currently available resuscitation solutions results in persistent reduction in endothelial shear stress, despite successfully increasing cardiac output and systemic blood pressure. We consider how this reduced shear stress causes (1) a failure to restore normal vasomotor function and normal tissue perfusion thus leading to persistent tissue hypoxia and (2) increased microvascular endothelial permeability resulting in edema formation and impaired organ function. We discuss the need for clinical research into resuscitation strategies and solutions that aim to quickly restore endothelial shear stress in the microcirculation to normal.

Human iPSCs as Model Systems for BMP-Related Rare Diseases

Disturbances in bone morphogenetic protein (BMP) signalling contribute to onset and development of a number of rare genetic diseases, including Fibrodysplasia ossificans progressiva (FOP), Pulmonary arterial hypertension (PAH), and Hereditary haemorrhagic telangiectasia (HHT). After decades of animal research to build a solid foundation in understanding the underlying molecular mechanisms, the progressive implementation of iPSC-based patient-derived models will improve drug development by addressing drug efficacy, specificity, and toxicity in a complex humanized environment. We will review the current state of literature on iPSC-derived model systems in this field, with special emphasis on the access to patient source material and the complications that may come with it. Given the essential role of BMPs during embryonic development and stem cell differentiation, gain- or loss-of-function mutations in the BMP signalling pathway may compromise iPSC generation, maintenance, and differentiation procedures. This review highlights the need for careful optimization of the protocols used. Finally, we will discuss recent developments towards complex in vitro culture models aiming to resemble specific tissue microenvironments with multi-faceted cellular inputs, such as cell mechanics and ECM together with organoids, organ-on-chip, and microfluidic technologies.

Comparison of Ophthalmic Artery Morphological Characteristics and Retinal Vessel Diameter for Identifying Ocular Ischemic Syndrome

Purpose

To investigate the morphological characteristics of the ophthalmic artery (OA) and retinal vessels in ocular ischemic syndrome (OIS) and to compare their ability to identify OIS.

Methods

This cross-sectional observational study included 21 patients with unilateral OIS and 17 controls matched for age, sex, degree of internal carotid artery (ICA) stenosis, and cerebral collateral patency. This study used a three-dimensional reconstruction based on computed tomographic angiography to measure the morphological characteristics of the OA and the ICA. Quantitative measurements of retinal vessel diameter were performed using the Integrative Vessel Analysis software. Receiver operating characteristic (ROC) curve analysis was performed to assess the ability of the OA diameter and the central retinal artery equivalent (CRAE) to identify OIS.

Results

The diameter of the OA (odds ratio = 0.001; P = 0.001) and the CRAE (odds ratio = 0.951; P = 0.028) were significantly associated with the presence of OIS after adjusting for age, sex, and the degree of the ICA stenosis. The areas under the curve for the OA diameter and the CRAE were, respectively, 0.871 (P < 0.001) and 0.744 (P = 0.017) according to the ROC curves analysis.

Conclusions

The OA diameter measurement identified OIS better than CRAE measurement. The OA may reflect the changes in ocular blood supply in patients with OIS earlier than retinal vessels. The OA of eyes with OIS may undergo arterial wall remodeling, leading to a decrease in OA diameter and further reduction in blood flow.

Endothelial-to-mesenchymal transition: advances and controversies

Endothelial-to-mesenchymal transition (EndMT) is a physiological process that is equally important during development and under certain pathological conditions in adult tissues. The last decade has witnessed a remarkable explosion of information about EndMT from molecular mechanisms responsible for its development to its role in various disease processes. The emerging picture is that of a complex set of interactions that underly pathophysiological basis of some of the most deadly and intractable diseases. This mini review brings together recent advances and attempts to present a unified view of this complex field.

Shear stress induces autophagy in Schlemm's canal cells via primary cilia-mediated SMAD2/3 signaling pathway

The Schlemm's canal (SC) is a circular, lymphatic-like vessel located at the limbus of the eye that participates in the regulation of aqueous humor drainage to control intraocular pressure (IOP). Circumferential flow of aqueous humor within the SC lumen generates shear stress, which regulates SC cell behaviour. Using biochemical analysis and real-time live cell imaging techniques, we have investigated the activation of autophagy in SC cells by shear stress. We report, for the first time, the primary cilium (PC)-dependent activation of autophagy in SC cells in response to shear stress. Moreover, we identified PC-dependent shear stress-induced autophagy to be positively regulated by phosphorylation of SMAD2 in its linker and C-terminal regions. Additionally, SMAD2/3 signaling was found to transcriptionally activate LC3B, ATG5 and ATG7 in SC cells. Intriguingly, concomitant to SMAD2-dependent activation of autophagy, we also report here the activation of mTOR pathway, a classical autophagy inhibitor, in SC cells by shear stress. mTOR activation was found to also be dependent on the PC. Moreover, pharmacological inhibition of class I PI3K increased phosphorylation of SMAD2 at the linker and activated autophagy. Together, our data indicates an interplay between PI3K and SMAD2/3 signaling pathways in the regulation of PC-dependent shear stress-induced autophagy in SC cells.

Endothelial mechanobiology in atherosclerosis

Cardiovascular disease (CVD) is a serious health challenge, causing more deaths worldwide than cancer. The vascular endothelium, which forms the inner lining of blood vessels, plays a central role in maintaining vascular integrity and homeostasis and is in direct contact with the blood flow. Research over the past century has shown that mechanical perturbations of the vascular wall contribute to the formation and progression of atherosclerosis. While the straight part of the artery is exposed to sustained laminar flow and physiological high shear stress, flow near branch points or in curved vessels can exhibit 'disturbed' flow. Clinical studies as well as carefully controlled in vitro analyses have confirmed that these regions of disturbed flow, which can include low shear stress, recirculation, oscillation, or lateral flow, are preferential sites of atherosclerotic lesion formation. Because of their critical role in blood flow homeostasis, vascular endothelial cells (ECs) have mechanosensory mechanisms that allow them to react rapidly to changes in mechanical forces, and to execute context-specific adaptive responses to modulate EC functions. This review summarizes the current understanding of endothelial mechanobiology, which can guide the identification of new therapeutic targets to slow or reverse the progression of atherosclerosis.

High-resolution visualization of pial surface vessels by flattened whole mount staining

Understanding development of the cerebral vasculature is essential for the central nervous system (CNS) research and therapeutic developments. Here, we developed a simple, convenient, and fast method-the flattened cortex whole mount (FCWM) technique-for imaging of pial cerebral vessels. FCWM involves dissection of the whole cerebral cortex followed by flattening, sectioning and application of CLARITY technology. Compared to conventional methods, FCWM offers several advantages including (1) high-resolution visualization of the whole cortex pial surface vessel structures and distributions; (2) precise localization of a particular blood vessel, allowing observations of a desired blood vessel during normal development or in disease settings; (3) compatibility with confocal imaging. Application of FCWM for examination of cerebral vasculature during postnatal development or in stroke settings allowed us to demonstrate that cerebral blood vessels manifest type-specific maturation and remodeling which are linked to the rate of endothelial proliferation.

Epigenome-Wide Changes in the Cell Layers of the Vein Wall When Exposing the Venous Endothelium to Oscillatory Shear Stress

Epigenomic changes in the venous cells exerted by oscillatory shear stress towards the endothelium may result in consolidation of gene expression alterations upon vein wall remodeling during varicose transformation. We aimed to reveal such epigenome-wide methylation changes. Primary culture cells were obtained from non-varicose vein segments left after surgery of 3 patients by growing the cells in selective media after magnetic immunosorting. Endothelial cells were either exposed to oscillatory shear stress or left at the static condition. Then, other cell types were treated with preconditioned media from the adjacent layer's cells. DNA isolated from the harvested cells was subjected to epigenome-wide study using Illumina microarrays followed by data analysis with GenomeStudio (Illumina), Excel (Microsoft), and Genome Enhancer (geneXplain) software packages. Differential (hypo-/hyper-) methylation was revealed for each cell layer's DNA. The most targetable master regulators controlling the activity of certain transcription factors regulating the genes near the differentially methylated sites appeared to be the following: (1) HGS, PDGFB, and AR for endothelial cells; (2) HGS, CDH2, SPRY2, SMAD2, ZFYVE9, and P2RY1 for smooth muscle cells; and (3) WWOX, F8, IGF2R, NFKB1, RELA, SOCS1, and FXN for fibroblasts. Some of the identified master regulators may serve as promising druggable targets for treating varicose veins in the future.

Ursolic acid inhibits human dermal fibroblasts hyperproliferation, migration, and collagen deposition induced by TGF-β via regulating the Smad2/3 pathway

Hypertrophic scar (HS) is a skin condition characterized by excessive fibrosis with disordered collagens from skin fibroblasts, which causes abnormal esthetic and even functional symptoms, thereby affecting millions of people. Ursolic acid (UA) is widely used in skincare and exerts anti-fibrotic effects. The present study aimed to delve into the impact of UA on HS and the mechanism. Fibroblasts (FBs) were incubated with TGF-β to investigate physiological characteristics compared with FBs isolated from normal skin (NSFBs) and hyperplastic scars (HSFBs). TGF-β-incubated FBs were subjected to treatment with UA (0-20 μM). The expressions of Vimentin, α-SMA, Collagen I, and Collagen III were examined using immunofluorescence, RT-qPCR, and western blot. Cell viability, proliferation, apoptosis, migration, and contractility were examined by CCK-8, EdU, Annexin V-FITC/PI, Transwell, and collagen gel contraction assays, respectively. The activation of Smad2/3 signaling was also determined by western blot. The binding sites for UA of TGF-βR1 (ALK5) were predicted by the Autodock tool. Compared with NSFBs, the cell proliferation, migration, and contractility of both HSFBs and TGF-β-incubated FBs were all significantly up-regulated. UA markedly impaired the TGF-β-induced increase in cell proliferation, migration, and contractility, α-SMA, collagen I, and Collagen III expression of FBs. UA significantly inhibited the phosphorylation levels of Smad2/3 in TGF-β-incubated FBs with no influence on TGF-βR1 and TGF-βR2 expressions, which might be because of the binding of UA to the catalytic domain of ALK5 protein. UA attenuated TGF-β1-induced hyperproliferation, migration, and collagen deposition in FBs via regulating the Smad2/3 pathway.

Vascular endothelial cell development and diversity

Vascular endothelial cells form the inner layer of blood vessels where they have a key role in the development and maintenance of the functional circulatory system and provide paracrine support to surrounding non-vascular cells. Technical advances in the past 5 years in single-cell genomics and in in vivo genetic labelling have facilitated greater insights into endothelial cell development, plasticity and heterogeneity. These advances have also contributed to a new understanding of the timing of endothelial cell subtype differentiation and its relationship to the cell cycle. Identification of novel tissue-specific gene expression patterns in endothelial cells has led to the discovery of crucial signalling pathways and new interactions with other cell types that have key roles in both tissue maintenance and disease pathology. In this Review, we describe the latest findings in vascular endothelial cell development and diversity, which are often supported by large-scale, single-cell studies, and discuss the implications of these findings for vascular medicine. In addition, we highlight how techniques such as single-cell multimodal omics, which have become increasingly sophisticated over the past 2 years, are being utilized to study normal vascular physiology as well as functional perturbations in disease.

Shear-mediated ALK5 expression regulates endothelial activation

Calcific aortic valve disease affects the aortic side of the valve, exposed to low magnitude multidirectional ("disturbed) blood flow, more than it affects the ventricular side, exposed to high magnitude uniaxial flow. Overt disease is preceded by endothelial dysfunction and inflammation. Here we investigate the potential role of the transforming growth factor-β (TGF-β) receptor ALK5 in this process. Although ECs are always subject to shear stress due to blood flow, and their responses to shear stress are important in healthy valve development and homeostasis, low magnitude multidirectional flow can induce pathophysiological changes. Previous work has shown ALK5 to be an important mechanosensor. ALK5 transduces mechanically sensed signals via the activation of the SMAD2/3 transcriptional modulators. However, it is currently unclear precisely how ALK5-mediated shear stress responses translate into pathological changes under conditions of chronically disturbed flow. Here, we demonstrate that ALK5 mechanosensory signalling influences flow-induced endothelial leukocyte adhesion and paracellular permeability. Low magnitude multidirectional flow resulted in downregulation of the receptor, accompanied by increased SMAD2 phosphorylation, in human umbilical vein endothelial cell (HUVEC) monolayers. These changes correlated with elevated monocyte adhesion and significantly increased transendothelial transport of an albumin-sized tracer. These effects were abolished by inhibition of ALK5 kinase activity. Analysis of ALK5 expression patterns in porcine aortic valve tissue corroborated the findings from cell-based experiments. Together, these results suggest that ALK5 has a role in shear stress-associated cardiovascular disease pathology, emphasising the importance of further mechanistic investigations and supporting it as a potential therapeutic target.

m6A Modification Mediates Endothelial Cell Responses to Oxidative Stress in Vascular Aging Induced by Low Fluid Shear Stress

N6-methyladenosine (m6A) is one of the most prevalent, abundant, and internal transcriptional modification and plays essential roles in diverse cellular and physiological processes. Low fluid shear stress (FSS) is a key pathological factor for many cardiovascular diseases, which directly forces on the endothelial cells of vessel walls. So far, the alterations and functions of m6A modifications in vascular endothelial cells at the low FSS are still unknown. Herein, we performed the transcriptome-wide m6A modification profiling of HUVECs at different FSS. We found that the m6A modifications were altered earlier and more sensitive than mRNA expressions in response to FSS. The low FSS increased the m6A modifications at CDS region but decreased the m6A modifications at 3' UTR region and regulated both the mRNA expressions and m6A modifications of the m6A regulators, such as the RBM15 and EIF3A. Functional annotations enriched by the hypermethylated and hypomethylated genes at low FSS revealed that the m6A modifications were clustered in the aging-related signaling pathways of mTOR, PI3K-AKT, insulin, and ERRB and in the oxidative stress-related transcriptional factors, such as HIF1A, NFAT5, and NFE2L2. Our study provided a pilot view of m6A modifications in vascular endothelial cells at low FSS and revealed that the m6A modifications driven by low FSS mediated the cellular responses to oxidative stress and cell aging, which suggested that the m6A modifications could be the potential targets for inhibiting vascular aging at pathological low FSS.

Mechanosignals in abdominal aortic aneurysms

Cumulative evidence has shown that mechanical and frictional forces exert distinct effects in the multi-cellular aortic layers and play a significant role in the development of abdominal aortic aneurysms (AAA). These mechanical cues collectively trigger signaling cascades relying on mechanosensory cellular hubs that regulate vascular remodeling programs leading to the exaggerated degradation of the extracellular matrix (ECM), culminating in lethal aortic rupture. In this review, we provide an update and summarize the current understanding of the mechanotransduction networks in different cell types during AAA development. We focus on different mechanosensors and stressors that accumulate in the AAA sac and the mechanotransduction cascades that contribute to inflammation, oxidative stress, remodeling, and ECM degradation. We provide perspectives on manipulating this mechano-machinery as a new direction for future research in AAA.

MicroRNAs in Mechanical Homeostasis

Mechanical variables such as stiffness, stress, strain, and fluid shear stress are central to tissue functions, thus, must be maintained within the proper range. Mechanics are especially important in the cardiovascular system and lung, the functions of which are essentially mechanical. Mechanical homeostasis is characterized by negative feedback in which deviations from the optimal value or set point activates mechanisms to return the system to the correct range. In chronic diseases, homeostatic mechanisms are generally overcome or replaced with positive feedback loops that promote disease progression. Recent work has shown that microRNAs (miRNAs) are essential to mechanical homeostasis in a number of biological systems and that perturbations to miRNA biogenesis play key roles in cardiovascular and pulmonary diseases. In this review, we integrate current knowledge of miRNAs in mechanical homeostasis and how these mechanisms are altered in disease.

High Fluid Shear Stress Inhibits Cytokine‐Driven Smad2/3 Activation in Vascular Endothelial Cells

Background

Atherosclerosis occurs preferentially in regions of low and disturbed fluid shear stress (FSS) but is limited in regions of high laminar FSS as a result of inhibition of endothelial inflammatory pathways. Recent work has identified endothelial to mesenchymal transition (EndMT) driven by TGFβ2 (transforming growth factor beta 2)–Smad2/3 (mothers against decapentaplegic) signaling as a critical component of atherogenesis. However, interactions between FSS and EndMT in this context have not been investigated.

Methods and Results

Endothelial cells were treated with TGFβ2 and inflammatory cytokines (interleukin 1β and tumor necrosis factor alpha) with or without high FSS in a parallel plate flow chamber. Smad2/3 nuclear translocation and target gene expression, assayed by immunofluorescence and quantitative polymerase chain reaction, revealed that high FSS blocked the Smad2/3‐EndMT pathway. In vivo, mice were injected with TGFβ2 and inflammatory cytokines, then regions of the aorta under low versus high FSS were examined. TGFβ2 and inflammatory cytokine treatment stimulated Smad2/3 nuclear translocation and target gene expression predominantly in regions of low FSS with little effect in regions of high FSS.

Conclusions

High FSS inhibits endothelial Smad2/3 activation and EndMT in response to inflammatory mediators, resulting in selective EndMT at athero‐susceptible, low FSS regions of arteries.

Sotatercept analog suppresses inflammation to reverse experimental pulmonary arterial hypertension

Sotatercept is an activin receptor type IIA-Fc (ActRIIA-Fc) fusion protein that improves cardiopulmonary function in patients with pulmonary arterial hypertension (PAH) by selectively trapping activins and growth differentiation factors. However, the cellular and molecular mechanisms of ActRIIA-Fc action are incompletely understood. Here, we determined through genome-wide expression profiling that inflammatory and immune responses are prominently upregulated in the lungs of a Sugen-hypoxia rat model of severe angio-obliterative PAH, concordant with profiles observed in PAH patients. Therapeutic treatment with ActRIIA-Fc—but not with a vasodilator—strikingly reversed proinflammatory and proliferative gene expression profiles and normalized macrophage infiltration in diseased rodent lungs. Furthermore, ActRIIA-Fc normalized pulmonary macrophage infiltration and corrected cardiopulmonary structure and function in Bmpr2 haploinsufficient mice subjected to hypoxia, a model of heritable PAH. Three high-affinity ligands of ActRIIA-Fc each induced macrophage activation in vitro, and their combined immunoneutralization in PAH rats produced cardiopulmonary benefits comparable to those elicited by ActRIIA-Fc. Our results in complementary experimental and genetic models of PAH reveal therapeutic anti-inflammatory activities of ActRIIA-Fc that, together with its known anti-proliferative effects on vascular cell types, could underlie clinical activity of sotatercept as either monotherapy or add-on to current PAH therapies.

Therapeutic Approaches for Treating Pulmonary Arterial Hypertension by Correcting Imbalanced TGF-β Superfamily Signaling

Pulmonary arterial hypertension (PAH) is a rare disease characterized by high blood pressure in the pulmonary circulation driven by pathological remodeling of distal pulmonary arteries, leading typically to death by right ventricular failure. Available treatments improve physical activity and slow disease progression, but they act primarily as vasodilators and have limited effects on the biological cause of the disease—the uncontrolled proliferation of vascular endothelial and smooth muscle cells. Imbalanced signaling by the transforming growth factor-β (TGF-β) superfamily contributes extensively to dysregulated vascular cell proliferation in PAH, with overactive pro-proliferative SMAD2/3 signaling occurring alongside deficient anti-proliferative SMAD1/5/8 signaling. We review the TGF-β superfamily mechanisms underlying PAH pathogenesis, superfamily interactions with inflammation and mechanobiological forces, and therapeutic strategies under development that aim to restore SMAD signaling balance in the diseased pulmonary arterial vessels. These strategies could potentially reverse pulmonary arterial remodeling in PAH by targeting causative mechanisms and therefore hold significant promise for the PAH patient population.

MEKK3-TGFβ crosstalk regulates inward arterial remodeling

Arterial remodeling is an important adaptive mechanism that maintains normal fluid shear stress in a variety of physiologic and pathologic conditions. Inward remodeling, a process that leads to reduction in arterial diameter, plays a critical role in progression of such common diseases as hypertension and atherosclerosis. Yet, despite its pathogenic importance, molecular mechanisms controlling inward remodeling remain undefined. Mitogen-activated protein kinases (MAPKs) perform a number of functions ranging from control of proliferation to migration and cell-fate transitions. While the MAPK ERK1/2 signaling pathway has been extensively examined in the endothelium, less is known about the role of the MEKK3/ERK5 pathway in vascular remodeling. To better define the role played by this signaling cascade, we studied the effect of endothelial-specific deletion of its key upstream MAP3K, MEKK3, in adult mice. The gene's deletion resulted in a gradual inward remodeling of both pulmonary and systematic arteries, leading to spontaneous hypertension in both vascular circuits and accelerated progression of atherosclerosis in hyperlipidemic mice. Molecular analysis revealed activation of TGFβ-signaling both in vitro and in vivo. Endothelial-specific TGFβR1 knockout prevented inward arterial remodeling in MEKK3 endothelial knockout mice. These data point to the unexpected participation of endothelial MEKK3 in regulation of TGFβR1-Smad2/3 signaling and inward arterial remodeling in artery diseases.