Peter A. Knight

Role of cAMP-Phosphodiesterase 1C Signaling in Regulating Growth Factor Receptor Stability, Vascular Smooth Muscle Cell Growth, Migration, and Neointimal Hyperplasia

RATIONALE Neointimal hyperplasia characterized by abnormal accumulation of vascular smooth muscle cells (SMCs) is a hallmark of occlusive disorders such as atherosclerosis, postangioplasty restenosis, vein graft stenosis, and allograft vasculopathy. Cyclic nucleotides are vital in SMC proliferation and migration, which are regulated by cyclic nucleotide phosphodiesterases (PDEs). OBJECTIVE Our goal is to understand the regulation and function of PDEs in SMC pathogenesis of vascular diseases. METHODS AND RESULTS We performed screening for genes differentially expressed in normal contractile versus proliferating synthetic SMCs. We observed that PDE1C expression was low in contractile SMCs but drastically elevated in synthetic SMCs in vitro and in various mouse vascular injury models in vivo. In addition, PDE1C was highly induced in neointimal SMCs of human coronary arteries. More importantly, injury-induced neointimal formation was significantly attenuated by PDE1C deficiency or PDE1 inhibition in vivo. PDE1 inhibition suppressed vascular remodeling of human saphenous vein explants ex vivo. In cultured SMCs, PDE1C deficiency or PDE1 inhibition attenuated SMC proliferation and migration. Mechanistic studies revealed that PDE1C plays a critical role in regulating the stability of growth factor receptors, such as PDGF receptor β (PDGFRβ) known to be important in pathological vascular remodeling. PDE1C interacts with low-density lipoprotein receptor-related protein-1 and PDGFRβ, thus regulating PDGFRβ endocytosis and lysosome-dependent degradation in an low-density lipoprotein receptor-related protein-1-dependent manner. A transmembrane adenylyl cyclase cAMP-dependent protein kinase cascade modulated by PDE1C is critical in regulating PDGFRβ degradation. CONCLUSIONS These findings demonstrated that PDE1C is an important regulator of SMC proliferation, migration, and neointimal hyperplasia, in part through modulating endosome/lysosome-dependent PDGFRβ protein degradation via low-density lipoprotein receptor-related protein-1.

Vinpocetine Suppresses Pathological Vascular Remodeling by Inhibiting Vascular Smooth Muscle Cell Proliferation and Migration

Abnormal vascular smooth muscle cell (SMC) activation is associated with various vascular disorders such as atherosclerosis, in-stent restenosis, vein graft disease, and transplantation-associated vasculopathy. Vinpocetine, a derivative of the alkaloid vincamine, has long been used as a cerebral blood flow enhancer for treating cognitive impairment. However, its role in pathological vascular remodeling remains unexplored. Herein, we show that systemic administration of vinpocetine significantly reduced neointimal formation in carotid arteries after ligation injury. Vinpocetine also markedly decreased spontaneous remodeling of human saphenous vein explants in ex vivo culture. In cultured SMCs, vinpocetine dose-dependently suppressed cell proliferation and caused G1-phase cell cycle arrest, which is associated with a decrease in cyclin D1 and an increase in p27Kip1 levels. In addition, vinpocetine dose-dependently inhibited platelet-derived growth factor (PDGF)-stimulated SMC migration as determined by the two-dimensional migration assays and three-dimensional aortic medial explant invasive assay. Moreover, vinpocetine significantly reduced PDGF-induced type I collagen and fibronectin expression. It is noteworthy that PDGF-stimulated phosphorylation of extracellular signal-regulated kinases 1/2 (ERK1/2), but not protein kinase B, was specifically inhibited by vinpocetine. Vinpocetine powerfully attenuated intracellular reactive oxidative species (ROS) production, which largely mediates the inhibitory effects of vinpocetine on ERK1/2 activation and SMC growth. Taken together, our results reveal a novel function of vinpocetine in attenuating neointimal hyperplasia and pathological vascular remodeling, at least partially through suppressing ROS production and ERK1/2 activation in SMCs. Given the safety profile of vinpocetine, this study provides insight into the therapeutic potential of vinpocetine in proliferative vascular disorders.

Cyclic Nucleotide Phosphodiesterase 1 Regulates Lysosome-Dependent Type I Collagen Protein Degradation in Vascular Smooth Muscle Cells

Objective—The phenotypic modulation of vascular smooth muscle cells (VSMCs) to a synthetic phenotype is vital during pathological vascular remodeling and the development of various vascular diseases. An increase in type I collagen (collagen I) has been implicated in synthetic VSMCs, and cyclic nucleotide signaling is critical in collagen I regulation. Herein, we investigate the role and underlying mechanism of cyclic nucleotide phosphodiesterase 1 (PDE1) in regulating collagen I in synthetic VSMCs. Methods and Results—The PDE1 inhibitor IC86340 significantly reduced collagen I in human saphenous vein explants undergoing spontaneous remodeling via ex vivo culture. In synthetic VSMCs, high basal levels of intracellular and extracellular collagen I protein were markedly decreased by IC86340. This attenuation was due to diminished protein but not mRNA. Inhibition of lysosome function abolished the effect of IC86340 on collagen I protein expression. PDE1C but not PDE1A is the major isoform responsible for mediating the effects of IC86340. Bicarbonate-sensitive soluble adenylyl cyclase/cAMP signaling was modulated by PDE1C, which is critical in collagen I degradation in VSMCs. Conclusion—These data demonstrate that PDE1C regulates soluble adenylyl cyclase/cAMP signaling and lysosome-mediated collagen I protein degradation, and they suggest that PDE1C plays a critical role in regulating collagen homeostasis during pathological vascular remodeling.

Six-year integrated cardiothoracic surgery residency applicants: Characteristics, expectations, and concerns

OBJECTIVE During the past 5 years, 6-year integrated cardiothoracic surgery residency programs have increased in number and popularity. METHODS To understand the background and motivation of the applicants for 6-year integrated programs, we surveyed 80 candidates interviewing for Accreditation Council for Graduate Medical Education-accredited 6-year integrated cardiothoracic surgery residency programs for the 2012 match season, with 36 respondents completing the survey. RESULTS The applicants interviewed for 6-year integrated programs had peer-reviewed publications (91.7%) and were interested in academic careers (91.4%), dedicated research time (58.3%), and cardiac surgery (66.7%). The time saved in training was considered an advantage of the 6-year integrated cardiothoracic surgery residency programs, although concern was present about the development of the mature, well-rounded cardiothoracic surgeon. CONCLUSIONS We found that most of the candidates for 6-year integrated cardiothoracic surgery residency were young, high-achieving individuals oriented toward academic careers with a significant interest in dedicated research time and cardiac surgery.

Cannulation‐Related Complications on Veno‐Arterial Extracorporeal Membrane Oxygenation: Prevalence and Effect on Mortality

Cannulation-related complications are a known source of morbidity in patients supported on veno-arterial extracorporeal membrane oxygenation (VA-ECMO). Despite its prevalence, little is known regarding the outcomes of patients who suffer such complications. This is a single institution review of cannulation-related complications and its effect on mortality in patients supported on VA-ECMO from January 2010-2015 using three cannulation strategies: axillary, femoral, and central. Complications were defined as advanced if they required major interventions (fasciotomy, amputation, site conversion). Patients were divided into two groups (complication present vs. not present) and Kaplan-Meier analysis was performed to determine any differences in their survival distributions. There were 103 patients supported on VA-ECMO: 41 (40%), 36 (35%), and 26 (25%) were cannulated via axillary, femoral, and central access, respectively. Cannulation-related complications occurred in 33 (32%) patients and this did not differ significantly between either axillary (34%), femoral (36%), or central (23%) strategies (P = 0.52). The most common complications encountered were hemorrhage and limb ischemia in 19 (18%) and 11 (11%) patients. Hemorrhagic complications did not differ between groups (P = 0.37), while limb ischemia and hyperperfusion were significantly associated with femoral and axillary cannulation, at a rate of 25% (P < 0.01) and 15% (P = 0.01), respectively. There was no difference in the incidence of advanced complications between cannulation groups: axillary (12%) vs. femoral (14%) vs. central (8%; P = 0.75). In addition, no increase in mortality was noted in patients who developed a cannulation-related complication by Kaplan-Meier estimates (P = 0.37). Cannulation-related complications affect a significant proportion of patients supported on VA-ECMO but do not differ in incidence between different cannulation strategies and do not affect patient mortality. Improved efforts at preventing these complications need to be developed to avoid the additional morbidity in an already critical patient population.

Differential expression of Hedgehog/Notch and transforming growth factor-β in human abdominal aortic aneurysms

OBJECTIVE The molecular mechanisms leading to the development of abdominal aortic aneurysms (AAAs) remain poorly understood. The aim of this study was to determine the expression of Sonic Hedgehog (SHh), transforming growth factor β (TGF-β), and Notch signaling components in human aneurysmal and nonaneurysmal aorta in vivo. METHODS Paired tissue samples were obtained from aneurysmal and nonaneurysmal (control) segments of the aortic wall of eight patients with suitable anatomy undergoing open repair of infrarenal AAAs. Protein and messenger RNA (mRNA) expression levels were determined by Western blot and quantitative real-time polymerase chain reaction analysis. RESULTS Aneurysm development resulted in a significant reduction in vascular smooth muscle (vSMC) differentiation genes α-actin and SMC22α at both mRNA and protein levels. In parallel experiments, an 80.0% ± 15% reduction in SHh protein expression was observed in aneurysmal tissue compared with control. SHh and Ptc-1 mRNA levels were also significantly decreased, by 82.0% ± 10% and 75.0% ± 5%, respectively, in aneurysmal tissue compared with nonaneurysmal control tissue. Similarly, there was a 50.0% ± 9% and 60.0% ± 4% reduction in Notch receptor 1 intracellular domain and Hrt-2 protein expression, respectively, in addition to significant reductions in Notch 1, Notch ligand Delta like 4, and Hrt-2 mRNA expression in aneurysmal tissue compared with nonaneurysmal tissue. There was no change in Hrt-1 expression observed in aneurysmal tissue compared with control. In parallel experiments, we found a 2.2 ± 0.2-fold and a 5.6 ± 2.2-fold increase in TGF-β mRNA and protein expression, respectively, in aneurysmal tissue compared with nonaneurysmal tissue. In vitro, Hedgehog signaling inhibition with cyclopamine in human aortic SMCs resulted in decreased Hedgehog/Notch signaling component and vSMC differentiation gene expression. Moreover, cyclopamine significantly increased TGF-β1 mRNA expression by 2.6 ± 0.9-fold. CONCLUSIONS These results suggest that SHh/Notch and TGF-β signaling are differentially regulated in aneurysmal tissue compared with nonaneurysmal tissue. Changes in these signaling pathways and the resulting changes in vSMC content may play a causative role in the development of AAAs.

Heterologous expression of Streptococcus mutans Cnm in Lactococcus lactis promotes intracellular invasion, adhesion to human cardiac tissues and virulence

ABSTRACT In S. mutans, the expression of the surface glycoprotein Cnm mediates binding to extracellular matrix proteins, endothelial cell invasion and virulence in the Galleria mellonella invertebrate model. To further characterize Cnm as a virulence factor, the cnm gene from S. mutans strain OMZ175 was expressed in the non-pathogenic Lactococcus lactis NZ9800 using a nisin-inducible system. Despite the absence of the machinery necessary for Cnm glycosylation, Western blot and immunofluorescence microscopy analyses demonstrated that Cnm was effectively expressed and translocated to the cell wall of L. lactis. Similar to S. mutans, expression of Cnm in L. lactis enabled robust binding to collagen and laminin, invasion of human coronary artery endothelial cells and increased virulence in G. mellonella. Using an ex vivo human heart tissue colonization model, we showed that Cnm-positive strains of either S. mutans or L. lactis outcompete their Cnm-negative counterparts for tissue colonization. Finally, Cnm expression facilitated L. lactis adhesion and colonization in a rabbit model of infective endocarditis. Collectively, our results provide unequivocal evidence that binding to extracellular matrices mediated by Cnm is an important virulence attribute of S. mutans and confirm the usefulness of the L. lactis heterologous system for further characterization of bacterial virulence factors.

Late erosion of Amplatzer septal occluder device resulting in cardiac tamponade

Transcatheter device closure of atrial septal defects (ASDs) is a minimally invasive technique that offers an alternative to conventional surgical repair. There are risks imposed by this technique; however, they compare favourably with risks of surgical closure. Here, we present a case of a 59-year old male with late erosion of an Amplatzer septal occluder device resulting in cardiac tamponade 5 years after device placement. To the best of our knowledge, cardiac tamponade this late after device placement has not yet been reported. Septal occlusion device erosion remains a major issue among the risks imposed by device closure of an ASD. More data are needed to better understand its true causes and possible solutions.

Automated Remote Transapical Wound Closure System Study

PURPOSE A readily applied and reliable means to create and close transapical wound access sites through a small intercostal opening could benefit many cardiac patients. Using relevant surgical tissue models, this research evaluated a new approach to enable single-port transapical wound site closure toward the eventual development of safe percutaneous access to the left ventricle. DESCRIPTION Novel techniques and technologies were developed and successfully tested for remote automated placement of 2 pledgeted horizontal mattress sutures delivered concentrically around a transmural apical guidewire, which provided a tract to enable therapeutic intervention. Mechanical pledgeted knots secured these sutures after cannula removal. EVALUATION Automated transapical closures were created in 47 ex vivo porcine hearts and in 10 human cadavers, 8 through a thoracotomy and 2 thoracoscopically. Automated apical closures achieved hemostasis in an acute beating heart thoracotomy model in 3 anesthetized pigs. An ex vivo porcine heart pressurized infusate model demonstrated the intraventricular pressure tolerated by automated closures (mean, 327 mm Hg) compared with hand-sutured closures (mean, 303 mm Hg). CONCLUSIONS All automated apical closures were effective. Early results encourage further evaluation.

Anticoagulation Reversal Strategies for Left Ventricular Assist Device Patients Presenting with Acute Intracranial Hemorrhage

The safety of alternative vitamin K antagonist (VKA) reversal strategies in patients with left ventricular assist devices (LVAD’s) who present with intracranial hemorrhage (ICH) are not well known. A review of LVAD patients with ICH from May 2008 to 2015 was conducted, comparing the safety and efficacy of 4-factor prothrombin complex concentrate-assisted VKA reversal (4F-PCC group, n = 10) to reversal with traditional agents alone (no-PCC group, n = 10). An analysis of a no-reversal strategy in selected patients (n = 11) with ICH was additionally performed. Thirty-one cases of ICH on LVAD support were reviewed. The rate of post reversal thromboembolic events was not significantly different between 4F-PCC and no-PCC patients (0% vs. 10%, p = 1.0); however, the time to VKA reversal was shorter (474 vs. 945 minutes, p = 0.02) and fresh frozen plasma (FFP) requirements lower (1.9 vs. 3.6 units, p = 0.05) in 4F-PCC patients, with no difference in mortality between groups (p = 1.0). Eleven patients (mean ICH volume: 0.4 cm3) were successfully managed without active VKA reversal, with no increased hemorrhage noted on neuroimaging. These results suggest that 4F-PCC-assisted reversal in LVAD patients is safe and may improve the efficacy of VKA reversal. Our findings also indicate that carefully selected patients with small ICH volumes may be safely managed by discontinuing anticoagulation and allowing the international normalized ratio (INR) to normalize physiologically.