Intimal Smooth Muscle Cells

Injury to the tunica media initiates atherogenesis in the presence of hyperlipidemia

Background and aims

Fatty streaks initiating the formation of atheromatous plaque appear in the tunica intima. The tunica media is not known to be a nidus for lipid accumulation initiating atherogenesis. We assessed changes to the tunica media in response to a micro-injury produced in the pig aorta. In addition, we assessed human carotid endarterectomy plaques for indication of atheroma initiation in the tunica media.

Methods

Three healthy landrace female pigs underwent laparotomy to inject autologous blood and create micro-hematomas at 6 sites within the tunica media of the infrarenal abdominal aorta. These pigs were fed a high-fat diet (HFD) for 4-12 weeks. Post-mortem aortas from all pigs, including a control group of healthy pigs, were serially stained to detect lipid deposits, vasa vasora (VV), immune cell infiltration and inflammatory markers, as well as changes to the vascular smooth muscle cell (vSMC) compartment. Moreover, 25 human carotid endarterectomy (CEA) specimens were evaluated for their lipid composition in the tunica media and intima.

Results

High lipid clusters, VV density, and immune cell infiltrates were consistently observed at 5 out of 6 injection sites under prolonged hyperlipidemia. The hyperlipidemic diet also affected the vSMC compartment in the tunica media adjacent to the tunica adventitia, which correlated with VV invasion and immune cell infiltration. Analysis of human carotid specimens post-CEA indicated that 32% of patients had significantly greater atheroma in the tunica media than in the arterial intima.

Conclusion

The arterial intima is not the only site for atherosclerosis initiation. We show that injury to the media can trigger atherogenesis.

Human coronary microvascular contractile dysfunction associates with viable synthetic smooth muscle cells

AIMS

Coronary microvascular smooth muscle cells (SMCs) respond to luminal pressure by developing myogenic tone (MT), a process integral to the regulation of microvascular perfusion. The cellular mechanisms underlying poor myogenic reactivity in patients with heart valve disease are unknown and form the focus of this study.

METHODS AND RESULTS

Intramyocardial coronary micro-arteries (IMCAs) isolated from human and pig right atrial (RA) appendage and left ventricular (LV) biopsies were studied using pressure myography combined with confocal microscopy. All RA- and LV-IMCAs from organ donors and pigs developed circa 25% MT. In contrast, 44% of human RA-IMCAs from 88 patients with heart valve disease had poor (<10%) MT yet retained cell viability and an ability to raise cytoplasmic Ca2+ in response to vasoconstrictor agents. Comparing across human heart chambers and species, we found that based on patient medical history and six tests, the strongest predictor of poor MT in IMCAs was increased expression of the synthetic marker caldesmon relative to the contractile marker SM-myosin heavy chain. In addition, high resolution imaging revealed a distinct layer of longitudinally aligned SMCs between ECs and radial SMCs, and we show poor MT was associated with disruptions in these cellular alignments.

CONCLUSION

These data demonstrate the first use of atrial and ventricular biopsies from patients and pigs to reveal that impaired coronary MT reflects a switch of viable SMCs towards a synthetic phenotype, rather than a loss of SMC viability. These arteries represent a model for further studies of coronary microvascular contractile dysfunction.

Review: Tissue Engineering of Small-Diameter Vascular Grafts and Their In Vivo Evaluation in Large Animals and Humans

To date, a wide range of materials, from synthetic to natural or a mixture of these, has been explored, modified, and examined as small-diameter tissue-engineered vascular grafts (SD-TEVGs) for tissue regeneration either in vitro or in vivo. However, very limited success has been achieved due to mechanical failure, thrombogenicity or intimal hyperplasia, and improvements of the SD-TEVG design are thus required. Here, in vivo studies investigating novel and relative long (10 times of the inner diameter) SD-TEVGs in large animal models and humans are identified and discussed, with emphasis on graft outcome based on model- and graft-related conditions. Only a few types of synthetic polymer-based SD-TEVGs have been evaluated in large-animal models and reflect limited success. However, some polymers, such as polycaprolactone (PCL), show favorable biocompatibility and potential to be further modified and improved in the form of hybrid grafts. Natural polymer- and cell-secreted extracellular matrix (ECM)-based SD-TEVGs tested in large animals still fail due to a weak strength or thrombogenicity. Similarly, native ECM-based SD-TEVGs and in-vitro-developed hybrid SD-TEVGs that contain xenogeneic molecules or matrix seem related to a harmful graft outcome. In contrast, allogeneic native ECM-based SD-TEVGs, in-vitro-developed hybrid SD-TEVGs with allogeneic banked human cells or isolated autologous stem cells, and in-body tissue architecture (IBTA)-based SD-TEVGs seem to be promising for the future, since they are suitable in dimension, mechanical strength, biocompatibility, and availability.

New Insights into the Pathophysiology of Primary and Secondary Lymphedema: Histopathological Studies on Human Lymphatic Collecting Vessels

Background: Lymphedema is characterized by an accumulation of interstitial fluids due to inefficient lymphatic drainage. Primary lymphedema is a rare condition, including congenital and idiopathic forms. Secondary lymphedema is a common complication of lymph node ablation in cancer treatment. Previous studies on secondary lymphedema lymphatic vessels have shown that after an initial phase of ectasia, worsening of the disease is associated with wall thickening accompanied by a progressive loss of the endothelial marker podoplanin. Methods and Results: We enrolled 17 patients with primary and 29 patients with secondary lymphedema who underwent lymphaticovenous anastomoses surgery. Histological sections were stained with Masson's trichrome, and immunohistochemistry was performed with antibodies to podoplanin, smooth muscle α-actin (α-SMA), and myosin heavy chain 11 (MyH11). In secondary lymphedema, we found ectasis, contraction, and sclerosis vessel types. In primary lymphedema, the majority of vessels were of the sclerosis type, with no contraction vessels. In both primary and secondary lymphedema, not all α-SMA-positive cells were also positive for MyH11, suggesting transformation into myofibroblasts. The endothelial marker podoplanin had a variable expression unrelatedly with the morphological vessel type. Conclusions: Secondary lymphedema collecting vessels included all the three types described in literature, that is, ectasis, contraction, and sclerosis, whereas in primary lymphedema, we found the ectasis and the sclerosis but not the contraction type. Some cells in the media stained positively for α-SMA but not for MyH11. These cells, possibly myofibroblasts, may contribute to collagen deposition.

The Key Role of Phosphate on Vascular Calcification

Vascular calcification (VC) is common in dialysis and non-dialysis chronic kidney disease (CKD) patients, even in the early stage of the disease. For this reason, it can be considered a CKD hallmark. VC contributes to cardiovascular disease (CVD) and increased mortality among CKD patients, although it has not been proven. There are more than one type of VC and every form represents a marker of systemic vascular disease and is associated with a higher prevalence of CVD in CKD patients, as shown by several clinical studies. Major risk factors for VC in CKD include: Increasing age, dialysis vintage, hyperphosphatemia (particularly in the setting of intermittent or persistent hypercalcemia), and a positive net calcium and phosphate balance. Excessive oral calcium intake, including calcium-containing phosphate binders, increases the risk for VC. Moreover, it has been demonstrated that there is less VC progression with non-calcium-containing phosphate binders. Unfortunately, until now, a specific therapy to prevent progression or to facilitate regression of VC has been found, beyond careful attention to calcium and phosphate balance.

Lipid-Lowering Therapy With Ezetimibe Decreases Spontaneous Atherothrombotic Occlusions in a Rabbit Model of Plaque Erosion: A Role of Serum Oxysterols

OBJECTIVE

Plaque erosion is increasing its importance as one of the mechanisms of acute coronary syndromes in this statin era. However, the clinical efficacy of currently used lipid-lowering agents in the prevention of thrombotic complications associated with plaque erosion has not been clarified. Therefore, we examined the therapeutic effects of ezetimibe or rosuvastatin monotherapy on spontaneous atherothrombotic occlusion.

APPROACH AND RESULTS

Femoral arteries of Japanese white rabbits, fed a high-cholesterol diet, were injured by balloon catheter, and then angiotensin II was continuously administrated. In 94% of these arteries, spontaneous thrombotic occlusions were observed after 5 weeks (median) of balloon injury. Histochemical analyses indicated that the injured arteries had similar pathological features to human plaque erosions; (1) spontaneous thrombotic occlusion, (2) lack of endothelial cells, and (3) tissue factor expression in vascular smooth muscle cells. Ezetimibe (1.0 mg/kg per day), but not rosuvastatin (0.6 mg/kg per day), significantly decreased thrombotic occlusion of arteries accompanied with accelerated re-endothelialization and the decreases of serum oxysterols despite the comparable on-treatment serum cholesterol levels. The 7-ketocholesterol inhibited the migration of human umbilical vein endothelial cells. Both 7-ketocholesterol and 27-hydroxycholesterol increased tissue factor expression in cultured rat vascular smooth muscle cells. Tissue factor expression was also induced by serum from vehicle- or rosuvastatin-treated rabbits, but the induction was attenuated with serum from ezetimibe-treated rabbits.

CONCLUSIONS

We have established a novel rabbit model of spontaneous atherothromobotic occlusion without plaque rupture that is feasible to test the therapeutic effects of various pharmacotherapies. Ezetimibe may decrease atherothrombotic complications after superficial plaque erosion by reducing serum oxysterols.

TGF-β Family Signaling in Connective Tissue and Skeletal Diseases

The transforming growth factor β (TGF-β) family of signaling molecules, which includes TGF-βs, activins, inhibins, and numerous bone morphogenetic proteins (BMPs) and growth and differentiation factors (GDFs), has important functions in all cells and tissues, including soft connective tissues and the skeleton. Specific TGF-β family members play different roles in these tissues, and their activities are often balanced with those of other TGF-β family members and by interactions with other signaling pathways. Perturbations in TGF-β family pathways are associated with numerous human diseases with prominent involvement of the skeletal and cardiovascular systems. This review focuses on the role of this family of signaling molecules in the pathologies of connective tissues that manifest in rare genetic syndromes (e.g., syndromic presentations of thoracic aortic aneurysm), as well as in more common disorders (e.g., osteoarthritis and osteoporosis). Many of these diseases are caused by or result in pathological alterations of the complex relationship between the TGF-β family of signaling mediators and the extracellular matrix in connective tissues.

Prognostic impact of circulating soluble LR11 on long-term clinical outcomes in patients with coronary artery disease

BACKGROUND

LR11, a member of LDL receptor family, is a novel marker of the proliferation of intimal smooth muscle cells (SMCs). LR11 is released in soluble form (sLR11) by proteolytic shedding and has biological activity toward SMC migration. We previously showed that circulating sLR11 positively correlates with carotid intima-medial thickness (IMT) independently of classical atherosclerotic risk factors and that it significantly associates with the severity of CAD. However, the association between sLR11 and long-term clinical outcomes remain uncertain.

METHODS AND RESULTS

This study included 438 consecutive patients (mean age, 65.8 ± 9.6 y; male, 82.4%) who underwent coronary intervention between March 2003 and December 2004 at our institution. The patients were assigned to quartiles according to pre-procedural sLR11 values. The primary endpoints were composite cardiovascular disease (CVD) endpoints including cardiovascular death, non-fatal acute coronary syndrome and non-fatal stroke. During median follow-up of 2876 days, composite CVD endpoints occurred 97 (22.1%) patients including 41 (9.4%) with cardiovascular disease (CVD)-related death, 36 (8.2%) non-fatal ACS and 20 (4.6%) non-fatal strokes. The hazard ratio (HR) for composite CVD endpoints significantly and dose-dependently increased with sLR11 levels (p for trend = 0.0077). A higher logarithm-transformed sLR11 value was associated with a greater risk of composite CVD endpoints, and the increased number of adverse long-term clinical outcomes persisted even after adjustment for other independent variables (HR 1.87 95%CI 1.02-3.31, p = 0.0435).

CONCLUSIONS

Elevated sLR11 levels were significantly associated with higher long-term adverse cardiac events in patients with CAD. Further extensive studies are expected to elucidate the mechanistic role of sLR11 and its clinical value as a prognostic marker in the development of atherosclerosis.

Expression of smooth muscle cell markers and co-activators in calcified aortic valves

AIMS

Similar risk factors and mediators are involved in calcific aortic stenosis (CAS) and atherosclerosis. Since normal valves harbour a low percentage of smooth muscle cells (SMCs), we hypothesize that the SMC phenotype participates in the pathogenesis of CAS.

METHOD AND RESULTS

We analysed 12 normal and 22 calcified aortic valves for SMC markers and the expression of co-activators of SMC gene expression, myocardin and myocardin-related transcription factors (MRTF-A/B). Transforming growth factor β (TGFβ1) was used to upregulate SMC markers and co-activators in valve interstitial cells (VICs) and transmission electron microscopy (TEM) was used to detect the presence of SMC in atypical regions of the valve leaflets. Smooth muscle cell markers and co-activators, myocardin, MRTF-A, and MRTF-B, demonstrated an increased incidence and aberrant expression around calcified nodules in all 22 calcified valves as well as in surface and microvessel endothelial cells. Smooth muscle cell markers and MRTF-A were significantly increased in calcified valves. Transforming growth factor β1 (TGFβ1) (10 ng/mL) was able to significantly upregulate the expression of some SMC markers and MRTF-A in VICs. Transmission electron microscopy of the fibrosa layer of calcified valves demonstrated the presence of bundles of SMCs and smooth muscle-derived foam cells.

CONCLUSION

Smooth muscle cell markers and co-activators, myocardin and MRTFs, were aberrantly expressed in calcified valves. Transforming growth factor β1 was able to significantly upregulate SMC markers and MRTF-A in VICs. Transmission electron microscopy unequivocally identified the presence of SMCs in calcified regions of valve leaflets. These findings provide evidence that the SMC phenotype plays a role in the development of CAS.

Circulating soluble LR11, a novel marker of smooth muscle cell proliferation, is enhanced after coronary stenting in response to vascular injury

OBJECTIVE

Restenosis after vascular intervention remains a major clinical problem. Circulating LR11 has been shown a novel marker of intimal smooth muscle cell (SMC) proliferation in human and animal studies. The present study was performed to clarify the clinical significance of circulating LR11 in patients with stable angina pectoris after coronary stenting.

METHODS AND RESULTS

We firstly investigated the circulating sLR11 levels for 28 days after arterial injury in mice, and then assessed time-dependent change in circulating sLR11 level after coronary stenting in a clinical study. Mouse sLR11 levels rapidly increased to 4.0-fold of the control value without cuff placement at postoperative day (POD) 14, and the levels gradually declined to 3.1-fold of the control value until POD 28 in mice. The circulating soluble LR11 levels were measured (before and at 14, 60 and 240 days after coronary stenting in a clinical study of 102 consecutive patients with stable angina pectoris who were treated with percutaneous coronary intervention. Circulating sLR11 levels were significantly increased on days 14 and 60 after the procedure and positively associated with the angiographic late loss index.

CONCLUSIONS

Our study suggested that circulating sLR11 levels may be a potential marker for angiographic late loss in patients after coronary stenting. Further mechanistic studies are expected to know the clinical significance of sLR11 as a novel marker for intimal SMC.

Development and pathologies of the arterial wall

Arteries consist of an inner single layer of endothelial cells surrounded by layers of smooth muscle and an outer adventitia. The majority of vascular developmental studies focus on the construction of endothelial networks through the process of angiogenesis. Although many devastating vascular diseases involve abnormalities in components of the smooth muscle and adventitia (i.e., the vascular wall), the morphogenesis of these layers has received relatively less attention. Here, we briefly review key elements underlying endothelial layer formation and then focus on vascular wall development, specifically on smooth muscle cell origins and differentiation, patterning of the vascular wall, and the role of extracellular matrix and adventitial progenitor cells. Finally, we discuss select human diseases characterized by marked vascular wall abnormalities. We propose that continuing to apply approaches from developmental biology to the study of vascular disease will stimulate important advancements in elucidating disease mechanism and devising novel therapeutic strategies.

Vascular histomolecular analysis by sequential endoarterial biopsy in a shunt model of pulmonary hypertension

The molecular mechanisms of pulmonary arterial hypertension (PAH) remain ill-defined. The aims of this study were to obtain sequential endoarterial biopsy samples in a surgical porcine model of PAH and assess changes in histology and mRNA expression during the disease progression. Differentially expressed genes were then analyzed as potential pharmacological targets. Four Yucatan micro-pigs underwent surgical anastomosis of the left pulmonary artery to the descending aorta. Endovascular samples were obtained with a biopsy catheter at baseline (before surgery) and from the left lung 7, 60, and 180 days after surgery. RNA was isolated from biopsy samples, amplified and analyzed. Dysregulated genes were linked to drugs with potential to treat or prevent PAH. With the development of PAH in our model, we identified changes in histology and in the expression of several genes with known or investigational inhibitors and several novel genes for PAH. Gene dysregulation displayed time-related variations during disease progression. Endoarterial biopsy provides a new method of assessing pulmonary vascular histology and gene expression in PAH. This analysis could identify novel applications for existing and new PAH drugs. The detection of stage- and disease-specific variation in gene expression could lead to individualized therapies.