Vein Graft Neointima Research Articles

O015 CD34+ vascular stem cells play a key role in vein graft remodelling

Abstract Introduction Venous conduits that are grafted into arterial circulation undergo neointima remodelling, causing excessive hyperplasia that contributes to early graft failure which a major drawback of surgical vein grafting. Stem cells expressing the CD34 surface protein have been postulated to have a key role in the process, but their involvement has not been studied. Methods A segment of the inferior vena cava of wild-type mice was interposition grafted into mice in which CD34-expressing cells were located through their genetically induced expression of tdTomato red marker protein (CD34-CreERT2xRosa26-tdTomato mice). This enabled us to determine whether CD34+ derived cells found in the vein after grafting originated from the donor mouse or from the host. Grafts were explanted 4wks after surgery and analysed by immunohistology and single cell RNA sequencing to resolve cell-level gene expression. Cells from vein grafts were also cultured in vitro and proliferation/differentiation assays were carried out on purified CD34+ cells. Results 70% of cells in the vein graft neointima were derived from CD34+ graft lineage whereas there was no significant contribution of recipient-derived stem cells or bone marrow cells to the neointima. Vein graft neointima smooth muscle cells (SMC) are not stem cells derived. CD34+ stem cells differentiated predominantly into fibroblasts which induced vein SMC phenotype switching and proliferation. Conclusion The majority of CD34+ stem cells found in the neointima of veins, grafted into the arterial circulation were derived from the resident cell population. These cells

Effects of the different-sized external stents on vein graft intimal hyperplasia and inflammation.

The poor long-term patency ratio of vein grafts prevents patients from benefiting from coronary artery bypass graft (CABG). It is reported that external venous stents have notably improved the patency ratio of stented vein grafts in animal models. The most crucial influence on stented grafts' fate is the size of the stents. This study aims to investigate the effects on intimal hyperplasia and inflammation of vein graft by using different sizes of stents and explore the potential mechanism. Two different sizes of external stents were fabricated through 3D printing technology. Male SD rats were divided into three groups. In the control group rat's autologous left jugular vein was grafted on the ipsilateral artery directly. In the stent groups, grafts were surrounded by two different-sized stents before anastomosing with arteries. The patency ratio and diameter of the grafts were examined by ultrasound. Masson staining was used to characterize intimal hyperplasia. The expression of inflammatory factors was detected by immunohistochemical staining. Moreover, TUNEL staining was used to label apoptotic cells. The two sizes of external stents were fabricated by 3D printing technology. In the control group, the intima area and wall thickness dramatically increased 8 weeks after implantation. While in the stent groups, these data only slightly increased, especially in the 1.5 mm-stent group. The expressions of inflammatory factors in TNF signaling were more remarkable than in the control group. On the contrary, the expressions were rarely detected in the stent groups. Similarly, the number of TUNEL positive cells dramatically decreased by using the appropriate-sized stent. In this study, we concluded that the appropriate sizes of external stents could effectively inhibit vein graft neointima formation, attenuate inflammatory reaction and reduce cell apoptosis, which might improve the long-term patency ratio of vein grafts.

The BD2 domain of BRD4 is a determinant in EndoMT and vein graft neointima formation

BackgroundVein-graft bypass is commonly performed to overcome atherosclerosis but is limited by high failure rates, principally due to neointimal wall thickening. Recent studies reveal that endothelial-mesenchymal transition (EndoMT) is critical for vein-graft neointima formation. BETs are a family of Bromo/ExtraTerminal domains-containing epigenetic reader proteins (BRD2, BRD3, BRD4). They bind acetylated histones through their unique tandem bromodomains (BD1, BD2), facilitating transcriptional complex formation and cell-state transitions. The role for BETs, including individual BRDs and their unique BDs, is not well understood in EndoMT and neointimal formation. Methods and resultsRepression of BRD4 expression abrogated TGFβ1-induced EndoMT, with greater effects than BRD2 or BRD3 knockdown. An inhibitor selective for BD2 in all BETs, but not that for BD1, blocked EndoMT. Moreover, expression of a dominant-negative BRD4-specific BD2 fully abolished EndoMT. Concordantly, BRD4 knockdown repressed TGFβ1-stimulated increase of ZEB1 protein – a transcription factor integral in EndoMT. In vivo, lentiviral gene transfer of either BRD4 shRNA or dominant negative BRD4-specific BD2 mitigated neointimal development in rat jugular veins grafted to carotid arteries. ConclusionsOur data reveal the BD2 domain of BRD4 as a determinant driving EndoMT in vitro and neointimal formation in vivo. These findings provide new insight into BET biology, while offering prospects of specific BET domain targeting as an approach to limiting neointima and extending vein graft patency.

Corrigendum: Role of Excessive Autophagy Induced by Mechanical Overload in Vein Graft Neointima Formation: Prediction and Prevention.

Scientific Reports 6: Article number: 22147; published online: 26 February 2016; updated: 14 November 2016 The original version of this Article contained errors in the affiliations. ‘Institute of Basic Medical Sciences, National Cheng Kung University, Tainan, Taiwan’ was incomplete, and now reads: ‘Institute of Basic Medical Sciences, College of Medicine, National Cheng Kung University, Tainan, Taiwan’

Role of Excessive Autophagy Induced by Mechanical Overload in Vein Graft Neointima Formation: Prediction and Prevention

Role of Excessive Autophagy Induced by Mechanical Overload in Vein Graft Neointima Formation: Prediction and Prevention

Role of Excessive Autophagy Induced by Mechanical Overload in Vein Graft Neointima Formation: Prediction and Prevention.

Little is known regarding the interplays between the mechanical and molecular bases for vein graft restenosis. We elucidated the stenosis initiation using a high-frequency ultrasonic (HFU) echogenicity platform and estimated the endothelium yield stress from von-Mises stress computation to predict the damage locations in living rats over time. The venous-arterial transition induced the molecular cascades for autophagy and apoptosis in venous endothelial cells (ECs) to cause neointimal hyperplasia, which correlated with the high echogenicity in HFU images and the large mechanical stress that exceeded the yield strength. The ex vivo perfusion of arterial laminar shear stress to isolated veins further confirmed the correlation. EC damage can be rescued by inhibiting autophagy formation using 3-methyladenine (3-MA). Pretreatment of veins with 3-MA prior to grafting reduced the pathological increases of echogenicity and neointima formation in rats. Therefore, this platform provides non-invasive temporal spatial measurement and prediction of restenosis after venous-arterial transition as well as monitoring the progression of the treatments.

Polymer-based delivering of shRNA to rabbit aortic smooth muscle cells suppressed the expression of IGF-1R <italic>in vitro</italic> and <italic>in vivo</italic>

Restenosis is one of clinical limitations for vein graft in coronary bypass graft. It has been proved that signal pathway IGF-1 and its receptor (IGF-1R) activated by hemodynamic mechanical stretch are responsible for the vascular smooth muscle cells proliferation in vein graft neointima formation. Unfortunately, there is no routinely successful method to resolve this problem. Gene delivering to vein graft possesses great therapeutic potential to prevent neointima formation. Polymer is one kind of nanoparticles, which can activate the process of endocytosis of cells. In this study, we evaluated the transfection efficiency and therapeutic potential of polymer-based transfection of plasmids expressing GFP and shRNAs targeting IGF-1R (pGFPshIGF-1Rs) to smooth muscle cells and rabbit external jugular vein graft. Results showed that polymer-based transfection provided high efficiency of transgene expression in smooth muscle cells in vitro. In vitro, IGF-1R-specific shRNA transfected by polymer inhibited IGF-1R protein expression by 52 ± 3.6%, when compared with mock transfected cells. In vivo delivering efficiency of pGFPshIGF-1R plasmid into the rabbit external jugular vein graft was significantly high in the polymer-based transfection group, when compared with negative control group. In vivo, polymer-based transfection IGF-1R-specific shRNA efficiently inhibited the expression of IGF-1R protein by 77 ± 3.6%, 65.6 ± 4.9%, and 76.7 ± 4.3% at 24, 48, and 72 h, respectively, when compared with negative control group. Our findings indicated that polymer-based transfection may be a promising technique that allows the targeting of gene therapy for vein graft restenosis.

Role of Girdin in intimal hyperplasia in vein grafts and efficacy of atelocollagen-mediated application of small interfering RNA for vein graft failure

Intimal hyperplasia is a major obstacle to patency in grafted veins. Although migration and proliferation of vascular smooth muscle cells (SMCs) pivotally affect the vascular remodeling process, no therapy has been established to prevent intimal hyperplasia of vein grafts. We previously reported that the actin-binding protein Girdin crucially affects arterial remodeling. In this study, we investigated the role of Girdin in venous SMCs and evaluated a therapeutic strategy for vein graft failure in vivo using small interfering RNA (siRNA) that targets Girdin. We investigated the relationship between Girdin expression and intimal hyperplasia using a rabbit vein graft model. Vein grafts under low-flow conditions were performed in Japanese White rabbits. For in vitro analyses, we isolated primary venous SMCs from vein graft neointima. siRNA that targets Girdin was mixed with atelocollagen, which stabilizes and releases nucleic acid reagents slowly and is applied perivascularly to the vein grafts at operation. Intimal hyperplasia was evaluated 4 weeks later. In the rabbit model, increased Girdin expression was seen in the neointima after the grafting operation. Using primary venous SMCs, we showed that Girdin is required for rearrangement of the actin cytoskeleton in venous SMCs and that siRNA-mediated Girdin knockdown significantly reduced venous SMC migration and proliferation. Girdin knockdown via perivascular application of siRNA using atelocollagen markedly reduced intimal thickening after the grafting operation. Depletion of Girdin attenuated venous SMCs migration and proliferation in vitro and intimal hyperplasia in vein grafts in vivo. Our findings suggest that Girdin affects migration and proliferation of vascular SMCs in vein grafts and that controlled release of Girdin siRNA using atelocollagen could be a novel therapeutic strategy for vein graft failure.

Abstract 18427: Dysregulation of the miR143/145 Cluster and Mir133a During Progression of Vein Graft Neointima Formation

Background: The late failure of autologus human saphenous vein bypass grafts due to neointimal formation carries a major clinical burden. Therefore, identifying novel strategies to prevent neointimal formation is desirable. The principal cell type responsible for the neointimal lesion are smooth muscle cells (SMC), which are activated in response to injury leading to accelerated rates of proliferation and migration. MicroRNAs (miRs) are small non-coding RNAs that play an important role in modulating vascular phenotypes through regulation of gene expression. Methods and results: We undertook a microarray profiling approach to identify miRs which may be modulated during the development of neointimal lesions in the setting of vein graft disease. Profiling experiments revealed several miRs (miR133a, miR143 and miR145) which have been previously implicated in SMC de-differentiation and activation. These results were validated by q-PCR which demonstrated that miR-133a and miR-143 were down-regulated 4-5 fold and miR-145 was down regulated between 7-11 fold in the human saphenous vein ex vivo culture model and the porcine interposition model of vein graft neoinitma formation (both models, n=6). Treatment of isolated SMC harvested from human saphenous veins with TGF-β 1 (10ng/ml), to induce differentiation to a more quiescent and contractile phenotype, up-regulated miR-145 by 2.2+0.2 fold (n=3) but miR-133a levels were unaffected . A wounding assay was utilised to determine whether miR levels were elevated during SMC migration. Following quiescence, SMC were subjected to multiple scratch wounds and placed in serum to induce migration for a period of 16 hours. Quantification of miR-145 levels in migrating SMC revealed a 5-fold reduction in miR-145 levels following induction of migration. Conclusion: These results suggest that the miR-143/145 cluster plays an important role in the dedifferentiation of SMCs during neointimal formation following vein grafting. We also demonstrate that TGF-β 1, an established modulator of SMC differentiation and proliferation, increased miR-143/145 levels suggesting that elevation of miR-143/145 in vein grafts may prevent SMC de-differentiation and elevated rates of SMC proliferation and migration.

Abstract 317: Mast Cells Do Not Contribute to a Reduction in Vein Graft Neointima in the C-kit Mutant KitW-sh/w-sh Mice

Background: Recent evidence suggests mast cells are involved in the development of vascular diseases such as atherosclerosis. The presence of mast cells in vein grafts led us to hypothesise that mast cells may regulate the extent of vein graft neointima hyperplasia. In this study, we employed the Kit W-sh/W-sh mouse strain, a widely accepted mast cell deficient mouse model induced by a spontaneous inversion mutation in the transcriptional regulatory elements of the c-kit gene. Methods: The vein graft surgery was performed by inserting the inferior thoracic vena cava from the donor mouse into the common carotid artery of the littermate recipient. Vein grafts were harvested at 4 weeks and fixed with 4% formaldehyde for histology. In some groups, Kit W-sh/W-sh mice were reconstituted with cultured mast cells either systemically or locally 9 weeks before vein graft surgery. For primary cell culture studies, aortic endothelial cells and smooth muscle cells were isolated by collagenase digestion method and cultured in standard conditions. Results: Kit w-sh/w-sh vein grafts had a significant reduction (33%; p<0.05) in neointima area, compared to the wild type controls. The cellular composition of the Kit w-sh/w-sh neointima was similar to the wild type controls, most cells being smooth muscle alpha-actin positive. Neither the systemic nor local reconstitution of mast cells restored the neointima area to the wild type level. In the primary cell culture, Kit w-sh/w-sh vascular cells showed less migrating activity in the scratch wound healing test, which may account for the decrease in neointima formation. Conlusion: This study suggests that it is not the deficiency of mast cells in the Kit W-sh/W-sh mice which accounts for the reduction in neointima formation in vein grafts. Other cell types affected by the c-kit mutation may be responsible for the altered neointima formation in Kit W-sh/W-sh mice.

Sustained Reduction of Vein Graft Neointima Formation by Ex Vivo TIMP-3 Gene Therapy

Coronary artery vein graft failure, resulting from thrombosis, intimal thickening, and atherosclerosis, is a significant clinical problem, with approximately 50% of vein grafts failing within 10 years. Intimal thickening is caused by migration of vascular smooth muscle cells from the media to the intima, where they proliferate. Interventions using gene transfer to inhibit vascular smooth muscle cells proliferation and migration are attractive because ex vivo access to the graft is possible. The involvement of matrix-degrading metalloproteinases in intimal thickening is well established, and we previously showed that adenoviral-delivered overexpression of an endogenous inhibitor, the tissue inhibitor of metalloproteinases-3 (TIMP-3), significantly retarded intimal thickening in short-term autologous porcine arteriovenous interposition grafts (28 days). However, it is essential to determine whether this approach will provide longer-term benefits. We assessed whether a recombinant adenovirus that overexpresses TIMP-3 (RAdTIMP-3) affects vein graft intimal thickening in the longer term (at 3 months). Porcine saphenous veins were subjected to luminal infection with 2.5×10(10) pfu/mL RAdTIMP-3 or RAd60 (control virus) or vehicle control, for 30 minutes before implantation into the carotid artery. Analysis of grafts harvested 3 months after delivery revealed that RAdTIMP-3-infected grafts had significantly reduced intimal areas compared with both controls (3.2 ± 0.4 mm(2) versus 5.6 ± 0.7 mm(2) and 5.9 ± 0.5 mm(2), RAdTIMP-3, RAd60, and vehicle, respectively). Medial areas were also significantly decreased by TIMP-3 (3.8 ± 0.3 mm(2) versus 6.7 ± 1.0 mm(2) and 5.2 ± 0.4 mm(2), RAdTIMP-3, RAd60, and vehicle, respectively). Overexpression of TIMP-3 provides a sustained retardation of vein graft intimal thickening and highlights the translational potential for ex vivo TIMP-3 gene therapy.

Inhibitory effect of polydioxanone suture external stent on the vein graft neointima thickening and the possible mechanism

Objective To evaluate the effect of a biodegradable external stent on intimal vein graft thickening in an arteriovenous bypass grafting model, and study its possible mechanism. Methods Twenty-four rabbits underwent carotid interposition bypass via ipsilateral jugular vein. Half received the polydioxanone stent ( PDS group) and half a simple vein graft (controls). Group subsets received external stent removal or sham-control exploration at 4th and 12th week. Each of the specimens was detected for pathological and molecular biological examination. Results At 4th and 12th week the PDS group had significantly less medial and intimal thickening than the control group ( P ＜ 0, 05 ), and there were fewer proliferating smooth muscle cells and extra cellular matrix formation than the control group at every interval. The proliferating cell nuclear antigen (PCNA) and angiotensin Ⅱ type 1 receptor (AT1R) were over-expressed in the tunica media and intima in control group. The transforming growth factor-β1 (TGF-β1) was expressed mostly in adventitia in PDS group. Conclusion An macro-porous nonrestrictive, PDS external stent can effectively inhibit the intimal hyperplasia in vein bypass grafts, which might be contributed to the re-distribution of TGF-β1 and AT1R. Key words: Vein graft; Intimal thickening; TGF-β1 ; AT1R

Simvastatin Exerts Favourable Effects on Neointimal Formation in a Mouse Model of Vein Graft

Background Simvastatin inhibits human saphenous vein neointima formation in human saphenous vein organ cultures. However, it is not known if simvastatin actually inhibits vein graft intima hyperplasia in vivo, and the underlying mechanisms behind that. In this study, we used a murine vein graft model to address these issues. Methods and results Vein grafting was performed among C57BL/6 J mice treated with low-dose (2 mg kg −1) or high-dose (20 mg kg −1) simvastatin or vehicle subcutaneously 72 h before and then daily after surgery. As compared to the vehicle, simvastatin dose-dependently significantly inhibited vein graft intima hyperplasia 4 weeks after surgeries. Immunohistochemistry studies suggested that vein graft neointima was mainly composed of vascular smooth muscle cells (VSMCs), and the rate of proliferating cell nuclear antigen (PCNA)-positive cells in the intima of vein grafts was significantly lower in simvastatin-treated groups than in control group. We isolated VSMC from mouse vena cava, simvastatin significantly reduced VSMC proliferation, and platelet-derived growth factor (PDGF)-induced VSMC migration in a dose-dependent manner. Conclusion Simvastatin inhibits neointima formation of mouse vein graft under normocholesterolaemic condition in vivo, the mechanisms might be associated with inhibitory effects of simvastatin on VSMC proliferation and migration.

Sonic Hedgehog Signaling Induces Vascular Smooth Muscle Cell Proliferation via Induction of the G 1 Cyclin-Retinoblastoma Axis

Proliferation of vascular smooth muscle cells (VSMCs) is a crucial event in the pathogenesis of intimal hyperplasia, the main cause of restenosis following vascular reconstruction. Here, the impact of sonic hedgehog (Shh)/Gli family zinc finger 2 (Gli2) signaling on VSMC proliferation was assessed. Increased Shh signaling was detected in VSMCs in the neointima of vein grafts obtained from mice undergoing restenosis. Comparable results were found in primary cultured human VSMCs (hVSMCs) obtained from patients undergoing coronary bypass surgery, which were used to further assess the impacts of Shh signaling on VSMC proliferation. Inhibition of Shh signaling in hVSMCs through treatment with cyclopamine or knockdown of Gli2 results in G(1) arrest and reduced cyclin D1, cyclin E, and phosphorylated retinoblastoma (pRB) levels. In contrast, activation of Shh/Gli2 signaling in hVSMCs results in increased levels of G(1) cyclins and promotes G(1)-S transition. Stimulation of hVSMC proliferation by Shh is abolished by cyclin D1 knockdown. Combined, these results demonstrate that Shh/Gli2 signaling stimulates VSMC proliferation via regulation of the G(1) cyclin-retinoblastoma axis and suggest that antagonists that target the Shh pathway may be therapeutically beneficial in the prevention of intimal hyperplasia.

Mechanisms of Vein Graft Adaptation to the Arterial Circulation

For patients with coronary artery disease or limb ischemia, placement of a vein graft as a conduit for a bypass is an important and generally durable strategy among the options for arterial reconstructive surgery. Vein grafts adapt to the arterial environment, and the limited formation of intimal hyperplasia in the vein graft wall is thought to be an important component of successful vein graft adaptation. However, it is also known that abnormal, or uncontrolled, adaptation may lead to abnormal vessel wall remodeling with excessive neointimal hyperplasia, and ultimately vein graft failure and clinical complications. Therefore, understanding the venous-specific pathophysiological and molecular mechanisms of vein graft adaptation are important for clinical vein graft management. Of particular importance, it is currently unknown whether there exist several specific distinct molecular differences in the venous mechanisms of adaptation that are distinct from arterial post-injury responses; in particular, the participation of the venous determinant Eph-B4 and the vascular protective molecule Nogo-B may be involved in mechanisms of vessel remodeling specific to the vein. This review describes (1) venous biology from embryonic development to the mature quiescent state, (2) sequential pathologies of vein graft neointima formation, and (3) novel candidates for strategies of vein graft management. Scientific inquiry into venous-specific adaptation mechanisms will ultimately provide improvements in vein graft clinical outcomes.

Local Delivery of Imatinib Mesylate (STI571)-Incorporated Nanoparticle Ex Vivo Suppresses Vein Graft Neointima Formation

Clinical outcome of surgical revascularization using autologous vein graft is limited by vein graft failure attributable to neointima formation. Platelet-derived growth factor (PDGF) plays a central role in the pathogenesis of vein graft failure. Therefore, we hypothesized that nanoparticle (NP)-mediated drug delivery system of PDGF-receptor (PDGF-R) tyrosine kinase inhibitor (imatinib mesylate: STI571) could be an innovative therapeutic strategy. Uptake of STI571-NP normalized PDGF-induced cell proliferation and migration. Excised rabbit jugular vein was treated ex vivo with PBS, STI571 only, FITC-NP, or STI571-NP, then interposed back into the carotid artery position. NP was detected in many cells in the neointima and media at 7 and 28 days after grafting. Significant neointima was formed 28 days after grafting in the PBS group; this neointima formation was suppressed in the STI571-NP group. STI571-NP treatment inhibited cell proliferation and phosphorylation of the PDGF-R-beta but did not affect inflammation and endothelial regeneration. STI571-NP-induced suppression of vein graft neointima formation holds promise as a strategy for preventing vein graft failure.

Selective isolation of vein graft endothelium and neointima by laser capture microdissection for temporal gene expression analysis

Selective isolation of vein graft endothelium and neointima by laser capture microdissection for temporal gene expression analysis

Abstract 2056: Blockade of PDGF Receptor Tyrosine Kinase by Ex Vivo Nano-DDS of Imatinib Mesylate into the Vein Suppresses Vein Graft Neointima Formation

Background: Clinical outcome of surgical revascularization using autologous vein graft is limited by vein graft failure due to neointima formation. Platelet-derived growth factor (PDGF), expressed by vascular smooth muscle cells (VSMCs), plays a central role in the pathogenesis of vein graft failure. Therefore, optimal nanotechnology-based drug delivery system (Nano-DDS) of PDGF receptor tyrosine kinase (TK) inhibitor, imatinib mesylate (STI571), can be an innovative therapeutic strategy for clinical application. We have developed such Nano-DDS using bioabsorbable PLGA nanoparticles (NP) for local ex vivo delivery. Hypothesis: Blockade of PDGF receptor TK by Nano-DDS of imatinib suppresses vein graft neointima formation. Methods and Results: [studies in human VSMCs in vitro] Addition of fluorescence (FITC)-encapsulated NP resulted in rapid and stable uptake by 99 % of cells. The Nano-DDS of imatinib prevented PDGF-induced phosphorylation of PDGF receptor TK, and thus normalized the PDGF-induced proliferation. [ ex vivo studies] Incubation of excised rabbit jugular vein and human saphenous vein ex vivo in FITC-encapsulated NP for 30 min resulted in highly efficient intracellular delivery rate (> 90 % cells) into cells of the venous wall. [ in vivo studies in rabbits] The excised jugular vein was treated ex vivo with PBS, imatinib only (100 mM), FITC NP only, or imatinib NP (100 mM) (n=5– 6, each) for 30 min, and then interposed into the carotid artery position of hypercholesterolemic rabbits. Seven and 28 days after ex vivo FITC NP treatment, FITC-positive cells were detected in many cells in the neointima and media (cellular uptake rate: 60 –70 %). Significant neointima was formed 28 days after grafting in PBS group, which was suppressed in imatinib NP group, but not in FITC NP only or imatinib only groups. Imatinib NP also inhibited the appearance of proliferating PCNA-positive cells and increased phosphorylation of PDGF receptor TK, but did not affect monocyte infiltration or endothelial regeneration process. Conclusions: Nano-DDS of imatinib into the excised vein ex vivo was feasible and suppressed vein graft neointima formation in rabbits. Nano-DDS of imatinib may be a clinically promising therapeutic strategy for prevention of vein graft failure.

A randomized trial of an external Dacron sheath for the prevention of vein graft disease: The Extent study

A randomized trial of an external Dacron sheath for the prevention of vein graft disease: The Extent study

Mechanical Stretch Simulates Proliferation of Venous Smooth Muscle Cells Through Activation of the Insulin-Like Growth Factor-1 Receptor

Activation and proliferation of vascular smooth muscle cells (VSMCs) occur in the venous neointima of vein grafts. VSMCs in a grafted vein are subjected to mechanical stretch; our goal is to understand the essential mechanical stretch-regulated signals that influence VSMCs during neointimal formation in vein grafts. In cultured vein VSMCs, mechanical stretch induces proliferation and upregulation of both IGF-1 and IGF-1R. Stretch of VSMCs sustained tyrosine phosphorylation of both IGF-1R and its substrate, IRS-1; these responses were related to mechanical stretch-induced activation of Src and autocrine IGF-1 production. Mechanical stretch-activated IGF-1R is functional because there is a prolonged activation of IRS-1-associated phosphatidylinositol-3 kinase (PI3K). When we knocked out IGF-1R, the mechanical stretch-induced increase in VSMC proliferation was blocked. To link mechanical stretch-activated IGF-1R cell signaling to venous VSMC proliferation in vivo, we also studied a vein graft model. Tamoxifen-inducible null deletion of IGF-1R in mice reduced the formation of neointima in the vein graft. Our results demonstrate for the first time that mechanical stretch activates IGF-1/IGF-1R signals in venous VSMCs, and we have uncovered a signaling pathway that leads to neointima formation in vivo.