Defective autophagy triggered by arterial cyclic stretch promotes neointimal hyperplasia in vein grafts via the p62/nrf2/slc7a11 signaling pathway.

Autophagy is an adaptation mechanism to keep cellular homeostasis, and its deregulation is implicated in various cardiovascular diseases. After vein grafting, hemodynamic factors play crucial roles in neointimal hyperplasia, but the mechanisms are poorly understood. Here, we investigated the impacts of arterial cyclic stretch on autophagy of venous smooth muscle cells (SMCs) and its role in neointima formation after vein grafting. Rat jugular vein graft were generated via the 'cuff' technique. Autophagic flux in venous SMCs is impaired in 3-day, 1-week and 2-week grafted veins. 10%-1.25 Hz cyclic stretch (arterial stretch) loaded with FX5000 stretch system on venous SMCs blocks cellular autophagic flux in vitro and shows no significant impact on activity of mTORC1 and AMPK. Microtubule depolymerization but not lysosome dysfunction nor autophagosome/amphisome-lysosomal membrane fusion blockade is involved in the impairment of autophagic flux. Microtubule stabilization, induced by paclitaxel treatment and external stents intervention respectively, restores venous SMC autophagy and ameliorates neointimal hyperplasia in vivo. Moreover, autophagy impairment causes accumulation of the cargo receptor p62, which sequesters keap1 to p62 aggregates and results in the stabilization and nuclear translocation of nrf2 to modulate its target antioxidative gene SLC7A11. p62 silencing abrogates the increases of nrf2 and slc7a11 protein expression, glutathione level and venous SMC proliferation triggered by arterial cyclic stretch in vitro, and further hinders nrf2 nuclear translocation, reduces neointimal thickness after vein grafting in vivo. p62 (T349A) mutation also inhibited venous SMC proliferation and alleviated neointimal formation in vivo. These findings suggest that stabilization of microtubules to rescue autophagic flux or direct silencing of p62 are potential therapeutic strategies for neointimal hyperplasia.

Arterial cyclic stretch regulates Lamtor1 and promotes neointimal hyperplasia via circSlc8a1/miR-20a-5p axis in vein grafts.

Rationale: Neointimal hyperplasia caused by dedifferentiation and proliferation of venous smooth muscle cells (SMCs) is the major challenge for restenosis after coronary artery bypass graft. Herein, we investigated the role of Lamtor1 in neointimal formation and the regulatory mechanism of non-coding RNA underlying this process. Methods: Using a "cuff" model, veins were grafted into arterial system and Lamtor1 expression which was correlated with the activation of mTORC1 signaling and dedifferentiation of SMCs, were measured by Western blot. Whole transcriptome deep sequencing (RNA-seq) of the grafted veins combined with bioinformatic analysis identified highly conserved circSlc8a1 and its interaction with miR-20a-5p, which may target Lamtor1. CircSlc8a1 was biochemically characterized by Sanger sequencing and resistant to RNase R digestion. The cytoplasmic location of circSlc8a1 was shown by fluorescence in situ hybridization (FISH). RNA pull-down, luciferase assays and RNA immunoprecipitation (RIP) with Ago2 assays were used to identify the interaction circSlc8a1 with miR-20a-5p. Furthermore, arterial mechanical stretch (10% elongation) was applied in vitro. Results:In vivo, Lamtor1 was significantly enhanced in grafted vein and activated mTORC1 signaling to promote dedifferentiation of SMCs. Arterial mechanical stretch (10% elongation) induced circSlc8a1 expression and positively regulated Lamtor1, activated mTORC1 and promoted SMC dedifferentiation and proliferation. Local injection of circSlc8a1 siRNA or SMC-specific Lamtor1 knockout mice prevented neointimal hyperplasia in vein grafts in vivo. Conclusions: Our study reveals a novel mechanobiological mechanism underlying the dedifferentiation and proliferation of venous SMCs in neointimal hyperplasia. CircSlc81/miR-20a-5p/Lamtor1 axis induced by arterial cyclic stretch may be a potential clinical target that attenuates neointimal hyperplasia in grafted vessels.

Platelet-derived microvesicles regulate vascular smooth muscle cell energy metabolism via PRKAA after intimal injury.

Vascular intimal injury initiates various cardiovascular disease processes. Exposure to subendothelial collagen can cause platelet activation, leading to collagen-activated platelet-derived microvesicles (aPMVs) secretion. In addition, vascular smooth muscle cells (VSMCs) exposed to large amounts of aPMVs undergo abnormal energy metabolism; they proliferate excessively and migrate after the loss of endothelium, eventually contributing to neointimal hyperplasia. However, the roles of aPMVs in VSMC energy metabolism are still unknown. Our carotid artery intimal injury model indicated that platelets adhered to injured blood vessels. In vitro, phosphorylated Pka (cAMP-dependent protein kinase) content was increased in aPMVs. We also found that aPMVs significantly reduced VSMC glycolysis and increased oxidative phosphorylation, and promoted VSMC migration and proliferation by upregulating phosphorylated PRKAA (α catalytic subunit of AMP-activated protein kinase) and phosphorylated FoxO1. Compound C, an inhibitor of PRKAA, effectively reversed the enhancement of cellular function and energy metabolism triggered by aPMVs in vitro and neointimal formation in vivo. We show that aPMVs can affect VSMC energy metabolism through the Pka-PRKAA-FoxO1 signaling pathway and this ultimately affects VSMC function, indicating that the shift in VSMC metabolic phenotype by aPMVs can be considered a potential target for the inhibition of hyperplasia. This provides a new perspective for regulating the abnormal activity of VSMCs after injury.

Extracellular matrix stiffness controls VEGF165 secretion and neuroblastoma angiogenesis via the YAP/RUNX2/SRSF1 axis.

Aberrant variations in angiogenesis have been observed in tumor tissues with abnormal stiffness of extracellular matrix (ECM). However, it remains largely unclear how ECM stiffness influences tumor angiogenesis. Numerous studies have reported that vascular endothelial growth factor-A (VEGF-A) released from tumor cells plays crucial roles in angiogenesis. Hence, we demonstrated the role of ECM stiffness in VEGF-A release from neuroblastoma (NB) cells and the underlying mechanisms. Based on 17 NB clinical samples, a negative correlation was observed between the length of blood vessels and stiffness of NB tissues. In vitro, an ECM stiffness of 30 kPa repressed the secretion of VEGF165 from NB cells which subsequently inhibited the tube formation of human umbilical vein endothelial cells (HUVECs). Knocked down VEGF165 in NB cells or blocked VEGF165 with neutralizing antibodies both repressed the tube formation of HUVECs. Specifically, 30 kPa ECM stiffness repressed the expression and nuclear accumulation of Yes-associated protein (YAP) to regulate the expression of Serine/Arginine Splicing Factor 1 (SRSF1) via Runt-related transcription factor 2 (RUNX2), which may then subsequently induce the expression and secretion of VEGF165 in NB tumor cells. Through implantation of 3D col-Tgels with different stiffness into nude mice, the inhibitory effect of 30 kPa on NB angiogenesis was confirmed in vivo. Furthermore, we found that the inhibitory effect of 30 kPa stiffness on NB angiogenesis was reversed by YAP overexpression, suggesting the important role of YAP in NB angiogenesis regulated by ECM stiffness. Overall, our work not only showed a regulatory effect of ECM stiffness on NB angiogenesis, but also revealed a new signaling axis, YAP-RUNX2-SRSF1, that mediates angiogenesis by regulating the expression and secretion of VEGF165 from NB cells. ECM stiffness and the potential molecules revealed in the present study may be new therapeutic targets for NB angiogenesis.

Platelet-Derived Microvesicles Promote VSMC Dedifferentiation After Intimal Injury via Src/Lamtor1/mTORC1 Signaling.

Phenotypic switch of vascular smooth muscle cells (VSMCs) is important in vascular remodeling which causes hyperplasia and restenosis after intimal injury. Platelets are activated at injured intima and secrete platelet-derived microvesicles (PMVs). Herein, we demonstrated the role of PMVs in VSMC phenotypic switch and the potential underlying mechanisms. In vivo, platelets were locally adhered and activated at intimal injury site, while Lamtor1 was promoted and VSMCs were dedifferentiated. PMVs, collected from collagen-activated platelets in vitro which mimicked collagen exposure during intimal injury, promoted VSMC dedifferentiation, induced Lamtor1 expression, and activated mTORC1 signaling, reflected by the phosphorylation of two downstream targets, i.e., S6K and 4E-BP1. Knockdown of Lamtor1 with small interfering RNA attenuated these processes induced by PMVs. Based on the previously published proteomic data, Ingenuity Pathway Analysis revealed that Src may participate in regulating effects of PMVs. Src inhibitor significantly reversed the effects of PMVs on VSMC dedifferentiation, Lamtor1 expression and mTORC1 activation. Furthermore, in SMC-specific Lamtor1 knockout mice, intimal hyperplasia was markedly attenuated after intimal injury compared with the wild type. Our data suggested that PMVs secreted by activated platelets promoted VSMC dedifferentiation via Src/Lamtor1/mTORC1 signaling pathway. Lamtor1 may be a potential therapeutic target for intimal hyperplasia after injury.

Circular RNA UVRAG Mediated by Alternative Splicing Factor NOVA1 Regulates Adhesion and Migration of Vascular Smooth Muscle Cells.

The movement of abnormal vascular smooth muscle cells (VSMCs) contributes to intimal hyperplasia in vein graft disease. Circular RNAs (circRNAs) are single stranded RNAs with 3' and 5' ends covalently joined together. They have been shown to regulate cell function in many diseases. NOVA1 is considered to be a brain-specific splicing factor that plays an important role in the nervous system and cancer. The role of NOVA1 in VSMCs remains unclear. In the present study, transcriptome sequencing was used to identify differentially expressed circRNAs in the rat vein graft model. A novel circRNA, circUVRAG, was decreased in the grafted vein and stably located in the cytoplasm. Knockdown of circUVRAG suppressed VSMC adhesion and migration. In addition, we demonstrated that the alternative splicing factor NOVA1 co-located with UVRAG pre-mRNA in the nucleus and modulated the production of circUVRAG. These new discoveries may serve as a potential means to treat intimal hyperplasia after vein grafts.

Platelet-Derived Extracellular Vesicles Increase Col8a1 Secretion and Vascular Stiffness in Intimal Injury.

The arterial mechanical microenvironment, including stiffness, is a crucial pathophysiological feature of vascular remodeling, such as neointimal hyperplasia after carotid endarterectomy and balloon dilatation surgeries. In this study, we examined changes in neointimal stiffness in a Sprague-Dawley rat carotid artery intimal injury model and revealed that extracellular matrix (ECM) secretion and vascular stiffness were increased. Once the endothelial layer is damaged in vivo, activated platelets adhere to the intima and may secrete platelet-derived extracellular vesicles (pEVs) and communicate with vascular smooth muscle cells (VSMCs). In vitro, pEVs stimulated VSMCs to promote collagen secretion and cell adhesion. MRNA sequencing analysis of a carotid artery intimal injury model showed that ECM factors, including col8a1, col8a2, col12a1, and elastin, were upregulated. Subsequently, ingenuity pathway analysis (IPA) was used to examine the possible signaling pathways involved in the formation of ECM, of which the Akt pathway played a central role. In vitro, pEVs activated Akt signaling through the PIP3 pathway and induced the production of Col8a1. MicroRNA (miR) sequencing of pEVs released from activated platelets revealed that 14 of the top 30 miRs in pEVs targeted PTEN, which could promote the activation of the Akt pathway. Further research showed that the most abundant miR targeting PTEN was miR-92a-3p, which promoted Col8a1 expression. Interestingly, knockdown of Col8a1 expression in vivo abrogated the increase in carotid artery stiffness and simultaneously increased the degree of neointimal hyperplasia. Our results revealed that pEVs may deliver miR-92a-3p to VSMCs to induce the production and secretion of Col8a1 via the PTEN/PIP3/Akt pathway, subsequently increasing vascular stiffness. Therefore, pEVs and key molecules may be potential therapeutic targets for treating neointimal hyperplasia.

Platelet-derived microvesicles induce calcium oscillations and promote VSMC migration via TRPV4.

Rationale: Abnormal migration of vascular smooth muscle cells (VSMCs) from the media to the interior is a critical process during the intimal restenosis caused by vascular injury. Here, we determined the role of platelet-derived microvesicles (PMVs) released by activated platelets in VSMC migration. Methods: A percutaneous transluminal angioplasty balloon dilatation catheter was used to establish vascular intimal injury. Collagen I was used to activate PMVs, mimicking collagen exposure during intimal injury. To determine the effects of PMVs on VSMC migration in vitro, scratch wound healing assays were performed. Fluorescence resonance energy transfer was used to detect variations of calcium dynamics in VSMCs. Results: Morphological results showed that neointimal hyperplasia was markedly increased after balloon injury of the carotid artery in rats, and the main component was VSMCs. PMVs significantly promoted single cell migration and wound closure in vitro. Fluorescence resonance energy transfer revealed that PMVs induced temporal and dynamic calcium oscillations in the cytoplasms of VSMCs. The influx of extracellular calcium, but not calcium from intracellular stores, was involved in the process described above. The channel antagonist GSK219 and specific siRNA revealed that a membrane calcium channel, transient receptor potential vanilloid 4 (TRPV4), participated in the calcium oscillations and VSMC migration induced by PMVs. Conclusions: TRPV4 participated in the calcium oscillations and VSMC migration induced by PMVs. PMVs and the related molecules might be novel therapeutic targets for vascular remodeling during vascular injury.

Suppressed nuclear envelope proteins activate autophagy of vascular smooth muscle cells during cyclic stretch application.

Dysfunctions of vascular smooth muscle cells (VSMCs) play crucial roles in vascular remodeling in hypertension, which correlates with pathologically elevated cyclic stretch due to increased arterial pressure. Recent researches reported that autophagy, a life-sustaining process, was increased in hypertension. However, the mechanobiological mechanism of VSMC autophagy and its potential roles in vascular remodeling are still unclear. Using renal hypertensive rats in vivo and FX5000 stretch application Unit in vitro, the autophagy of VSMCs was detected. The results showed that LC3II remarkably enhanced in hypertensive rats and 15% cyclic stretch (mimic the pathologically increased mechanical stretch in hypertension), and the activity of mammalian target of rapamycin (mTOR) was suppressed in 15% cyclic stretch. Administration of autophagy inhibitors, bafilomycin A1 and chloroquine, repressed VSMC proliferation efficiently, but did not affect the degradation of two important nuclear envelope (NE) proteins, lamin A/C and emerin. Using RNA interference to decline the expression of lamin A/C and emerin, respectively, we discovered that autophagy was upregulated under both static and 5% cyclic stretch conditions, accompanying with the decreased mTOR activity. During 15% cyclic stretch application, mTOR inhibition was responsible for autophagy elevation. Chloroquine administration in vivo inhibited the expression of PCNA (marker of proliferation) of abdominal aorta in hypertensive rats. Altogether, these results demonstrated that pathological cyclic stretch suppresses the expression of lamin A/C and emerin which subsequently represses mTOR pathway so as to induce autophagy activation. Blocking autophagic flux may be a practicable way to relieve the pathological vascular remodeling in hypertensive.

Cyclic Stretch Induces Vascular Smooth Muscle Cells to Secrete Connective Tissue Growth Factor and Promote Endothelial Progenitor Cell Differentiation and Angiogenesis.

Endothelial progenitor cells (EPCs) play a vital role in endothelial repair following vascular injury by maintaining the integrity of endothelium. As EPCs home to endothelial injury sites, they may communicate with exposed vascular smooth muscle cells (VSMCs), which are subjected to cyclic stretch generated by blood flow. In this study, the synergistic effect of cyclic stretch and communication with neighboring VSMCs on EPC function during vascular repair was investigated. In vivo study revealed that EPCs adhered to the injury site and were contacted to VSMCs in the Sprague-Dawley (SD) rat carotid artery injury model. In vitro, EPCs were cocultured with VSMCs, which were exposed to cyclic stretch at a magnitude of 5% (which mimics physiological stretch) and a constant frequency of 1.25 Hz for 12 h. The results indicated that stretched VSMCs modulated EPC differentiation into mature endothelial cells (ECs) and promoted angiogenesis. Meanwhile, cyclic stretch upregulated the mRNA expression and secretion level of connective tissue growth factor (CTGF) in VSMCs. Recombinant CTGF (r-CTGF) treatment promoted endothelial differentiation of EPCs and angiogenesis, and increased their protein levels of FZD8 and ß-catenin. CTGF knockdown in VSMCs inhibited cyclic stretch-induced EPC differentiation into ECs and attenuated EPC tube formation via modulation of the FZD8/ß-catenin signaling pathway. FZD8 knockdown repressed endothelial differentiation of EPCs and their angiogenic activity. Wnt signaling inhibitor decreased the endothelial differentiation and angiogenetic ability of EPCs cocultured with stretched VSMCs. Consistently, an in vivo Matrigel plug assay demonstrated that r-CTGF-treated EPCs exhibited enhanced angiogenesis; similarly, stretched VSMCs also induced cocultured EPC differentiation toward ECs. In a rat vascular injury model, r-CTGF improved EPC reendothelialization capacity. The present results indicate that cyclic stretch induces VSMC-derived CTGF secretion, which, in turn, activates FZD8 and ß-catenin to promote both differentiation of cocultured EPCs into the EC lineage and angiogenesis, suggesting that CTGF acts as a key intercellular mediator and a potential therapeutic target for vascular repair.