Hitoshi Ichimiya

The Actin-Binding Protein Girdin and Its Akt-Mediated Phosphorylation Regulate Neointima Formation After Vascular Injury

Rationale: It is well established that the migration and proliferation of vascular smooth muscle cells (VSMCs) have major roles in the vascular remodeling process. Our previous study showed that the Akt substrate Girdin, which is expressed in VSMCs and endothelial cells, is essential for postnatal angiogenesis. However, the function of Girdin and its Akt-mediated phosphorylation in VSMCs and their in vivo roles in vascular remodeling remain to be elucidated. Objective: We investigated the function of Girdin and its Akt-mediated phosphorylation using cultured VSMCs and animal models of vascular remodeling. Methods and Results: The depletion of Girdin by RNA interference disrupted the rearrangement of the actin cytoskeleton in VSMCs, resulting in impaired cell migration. The depletion of Girdin also inhibited VSMC proliferation. Girdin expression was highly upregulated and its serine at position 1416 was phosphorylated in the neointima of carotid arteries after balloon injury in a rat model. The introduction of an adenovirus harboring short hairpin RNA against Girdin attenuated the proliferation of VSMCs and neointima formation without affecting reendothelialization. Furthermore, we found that neointima formation after femoral wire injury was significantly attenuated in Girdin S1416A knock-in mice, in which the Akt phosphorylation site of Girdin was mutated, thus indicating a major role for Girdin phosphorylation in vascular remodeling. Conclusions: These findings indicate that Girdin and its Akt-mediated phosphorylation have major roles in the migration and proliferation of VSMCs and vascular remodeling, making the Akt/Girdin signaling pathway a potential target for the development of new therapeutics for vascular diseases.

Girdin/GIV regulates transendothelial permeability by controlling VE-cadherin trafficking through the small GTPase, R-Ras.

Vascular permeability is regulated by intercellular junction organization of endothelial cells, the dysfunction of which is implicated in numerous pathological conditions. Molecular mechanisms of how endothelial cells regulate intercellular junction in response to extracellular signals, however, have so far remained elusive. This study identified that Girdin (also termed GIV), an Akt substrate functioning in post natal angiogenesis, was expressed in a mature endothelial monolayer, where it regulated VE-cadherin trafficking to maintain vascular integrity. Girdin depletion abrogated VEGF-induced VE-cadherin endocytosis and the disassembly of adherens junctions in a monolayer of endothelial cells, thus leading to a significant decrease in the permeability. We also showed that activated R-Ras, a member of the Ras family GTPase, known to be a master regulator of transendothelial permeability, interacts with Girdin, and facilitates the complex formation between Girdin and VE-cadherin in endothelial cells. However, the increased permeability mediated by the loss of R-Ras was rescued by Girdin depletion, thus suggesting that the interaction of Girdin with R-Ras functions in VE-cadherin trafficking pathways distinct from endocytosis. The recycling of VE-cadherin was promoted by the exogenous expression of the active mutant of R-Ras, which was attenuated in the Girdin-depleted endothelial cells. These results show that Girdin regulates transendothelial permeability in synergy with R-Ras and VE-cadherin in an endothelial monolayer.

Akt-dependent Girdin phosphorylation regulates repair processes after acute myocardial infarction

Myocardial infarction is a leading cause of death, and cardiac rupture following myocardial infarction leads to extremely poor prognostic feature. A large body of evidence suggests that Akt is involved in several cardiac diseases. We previously reported that Akt-mediated Girdin phosphorylation is essential for angiogenesis and neointima formation. The role of Girdin expression and phosphorylation in myocardial infarction, however, is not understood. Therefore, we employed Girdin-deficient mice and Girdin S1416A knock-in (Girdin(SA/SA)) mice, replacing the Akt phosphorylation site with alanine, to address this question. We found that Girdin was expressed and phosphorylated in cardiac fibroblasts in vitro and that its phosphorylation was crucial for the proliferation and migration of cardiac fibroblasts. In vivo, Girdin was localized in non-cardiomyocyte interstitial cells and phosphorylated in α-smooth muscle actin-positive cells, which are likely to be cardiac myofibroblasts. In an acute myocardial infarction model, Girdin(SA/SA) suppressed the accumulation and proliferation of cardiac myofibroblasts in the infarcted area. Furthermore, lower collagen deposition in Girdin(SA/SA) mice impaired cardiac repair and resulted in increased mortality attributed to cardiac rupture. These findings suggest an important role of Girdin phosphorylation at serine 1416 in cardiac repair after acute myocardial infarction and provide insights into the complex mechanism of cardiac rupture through the Akt/Girdin-mediated regulation of cardiac myofibroblasts.

Optical coherence tomography images of a coronary artery aneurysm in an infarct-related artery 6 months after bare-metal stent implantation.

A 62-year-old man with hypertension and dyslipidemia underwent successful primary percutaneous coronary intervention with thrombus aspiration and bare-metal stent (3.5 × 13 mm) (Liberte, Boston Scientific, Natick, Massachusetts) implantation (12 atm) at proximal left anterior descending coronary

Impact of Coronary Stent Fracture on Restenotic Neointimal Tissue Characterization After Drug-Eluting Stent Implantation: An Integrated Backscatter Intravascular Ultrasound Study

Although drug-eluting stents (DESs) reduce the rates of in-stent restenosis (ISR) and subsequent target lesion revascularization, stent fracture (SF) after DES implantation has become an important concern because of its potential association with restenosis and stent thrombosis. We aimed to assess the pathogenic impact of SF on in-stent restenotic neointimal tissue components after DES implantation. We analyzed 43 consecutive patients (14 with SF and 29 without SF) with ISR requiring revascularization after DES implantation between January 2008 and March 2014. For evaluation of in-stent tissue components, integrated backscatter intravascular ultrasound (IB-IVUS) was performed. SF was defined as complete or partial separation of stent segments observed using plain fluoroscopy or intravascular ultrasound. On volumetric IB-IVUS analyses, patients with SF had a significantly higher percentage of lipid tissue volume within the neointima and a significantly lower percentage of fibrous tissue volume than those without (37.3 ± 18.9% versus 24.9 ± 12.4%, P = 0.02, and 61.2 ± 18.3 versus 72.6 ± 12.1%, P = 0.04, respectively). Moreover, SF was positively correlated with the percentage of lipid volume on multiple linear regression analysis after adjustment for confounding factors (β = 0.36, P = 0.03). The interval from stent implantation was similar in both groups (47.0 ± 28.7 versus 37.7 ± 33.3 months; P = 0.39). In conclusion, SF is associated with larger lipid tissue volume within the neointima after DES placement, suggesting a contribution to the development of neoatherosclerosis and vulnerable neointima. Thus SF might lead to future adverse coronary events.

Characteristics of in vivo images from an in-stent restenosis lesion of a saphenous vein graft after bare-metal stent implantation: Assessment using optical coherence tomography

Restenosis of saphenous vein grafts (SVG) after bare-metal stent (BMS) implantation remains a clinical problem. Recently, intravascular optical coherence tomography (OCT) has been proposed as a high resolution intravascular imaging modality, and is able to distinguish several components of intracoronary structures. In vivo images of in-stent restenosis (ISR) lesions in an SVG using OCT have not been reported. In this case report, we present the characteristics of in vivo OCT images from an ISR lesion of an SVG after BMS implantation.