Flow-mediated vascular remodeling in hypertension: relation to hemodyamics

Repetitive remote occlusion (RRO) stimulates eNOS-dependent blood flow and collateral expansion in hindlimb ischemia

OBJECTIVE

Collateral expansion is an important compensatory mechanism to alleviate tissue ischemia after arterial occlusion. We investigated the efficacy and mechanisms of temporary remote hindlimb occlusion to stimulate contralateral blood flow and collateral expansion after hindlimb ischemia in mice and evaluated translation to peripheral artery disease in humans.

METHODS AND RESULTS

We induced unilateral hindlimb ischemia via femoral artery excision in mice. We studied central hemodynamics, blood flow, and perfusion of the ischemic hindlimb during single and repetitive remote occlusion (RRO) of the contralateral non-ischemic hindlimb with a pressurized cuff. Similar experiments were performed in patients with unilateral peripheral artery disease (PAD). Contralateral occlusion of the non-ischemic hindlimb led to an acute increase in blood flow to the ischemic hindlimb without affecting central blood pressure and cardiac output. The increase in blood flow was sustained even after deflation of the pressure cuff. RRO over 12 days (8/day, each 5 min) led to significantly increased arterial inflow, lumen expansion of collateral arteries, and increased perfusion of the chronically ischemic hindlimb as compared to control. In NOS3^-/- and after inhibition of NOS (L-NAME), and NO (ODQ), the acute and chronic effects of contralateral occlusion were abrogated and stimulation of guanylyl cyclase with cinaciguate exhibited a similar response as RRO and was not additive. Pilot studies in PAD patients demonstrated that contralateral occlusion increased arterial inflow to ischemic limbs and improved walking distance.

CONCLUSIONS

Repetitive remote contralateral occlusion stimulates arterial inflow, perfusion, and functional collateral expansion in chronic hindlimb ischemia via an eNOS-dependent mechanism underscoring the potential of remote occlusion as a novel treatment option in peripheral artery disease.

High shear stress induces atherosclerotic vulnerable plaque formation through angiogenesis

Rupture of atherosclerotic plaques causing thrombosis is the main cause of acute coronary syndrome and ischemic strokes. Inhibition of thrombosis is one of the important tasks developing biomedical materials such as intravascular stents and vascular grafts. Shear stress (SS) influences the formation and development of atherosclerosis. The current review focuses on the vulnerable plaques observed in the high shear stress (HSS) regions, which localizes at the proximal region of the plaque intruding into the lumen. The vascular outward remodelling occurs in the HSS region for vascular compensation and that angiogenesis is a critical factor for HSS which induces atherosclerotic vulnerable plaque formation. These results greatly challenge the established belief that low shear stress is important for expansive remodelling, which provides a new perspective for preventing the transition of stable plaques to high-risk atherosclerotic lesions.

Effects of cell grafting on coronary remodeling after myocardial infarction

BACKGROUND

With recent advances in therapeutic applications of stem cells, cell engraftment has become a promising therapy for replacing injured myocardium after infarction. The survival and function of injected cells, however, will depend on the efficient vascularization of the new tissue. Here we describe the arteriogenic remodeling of the coronary vessels that supports vascularization of engrafted tissue postmyocardial infarction (post-MI).

METHODS AND RESULTS

Following MI, murine hearts were injected with a skeletal myoblast cell line previously shown to develop into large grafts. Microcomputed tomography at 28 days postengraftment revealed the 3-dimensional structure of the newly formed conducting vessels. The grafts elicited both an angiogenic response and arteriogenic remodeling of the coronary arteries to perfuse the graft. The coronaries upstream of the graft also remodeled, showing an increase in branching, and a decrease in vascular density. Histological analysis revealed the presence of capillaries as well as larger vascular lumens within the graft. Some graft vessels were encoated by smooth muscle α-actin positive cells, implying that vascular remodeling occurs at both the conducting arterial and microvascular levels.

CONCLUSIONS

Following MI and skeletal myoblast engraftment, the murine coronary vessels exhibit plasticity that enables both arteriogenic remodeling of the preexisting small branches of the coronary arteries and development of large and small smooth muscle encoated vessels within the graft. Understanding the molecular mechanisms underlying these 2 processes suggests mechanisms to enhance the therapeutic vascularization in patients with myocardial ischemia.

The effects of angiotensin-converting enzyme-inhibitory peptide LAP on the left common carotid artery remodeling in spontaneously hypertensive rats

OBJECTIVE

To investigate the protective effect of angiotensin-converting enzyme (ACE)-inhibitory peptide LAP on the left common carotid artery remodeling in spontaneously hypertensive rats (SHRs).

METHODS

A cohort of male SHRs were randomly divided into three groups (n = 10 for each group): pseudo-experimental group, enalapril-treated group as a positive control group, ACE-inhibitory peptide LAP-treated group. After the experiment, the left common carotid artery from each rat was removed for morphological evaluation.

RESULTS

It was observed that the vascular medial thickness, media thickness/lumen diameter, medial cross-sectional area and mean nuclear area of smooth muscle cells of the left common carotid artery in the LAP group or enalapril group were significantly lower than those in the pseudo-experimental group, while there was no significant difference in these parameters observed between the LAP group and enalapril group. Additionally, the vascular area percentage of collagen fibers of the left common carotid artery in the LAP group and enalapril group was significantly lower than that of the pseudo-experimental group.

CONCLUSIONS

The protective vessel remodeling effect in SHRs was observed with ACE-inhibitory peptide LAP in SHRs by decreasing blood pressure, inhibiting smooth muscle cell hypertrophy and reducing the proliferation of collagen fibers.

Biomechanical factors as triggers of vascular growth

Haemodynamic factors influence all forms of vascular growth (vasculogenesis, angiogenesis, arteriogenesis). Because of its prominent role in atherosclerosis, shear stress has gained particular attention, but other factors such as circumferential stretch are equally important to maintain the integrity and to (re)model the vascular network. While these haemodynamic forces are crucial determinants of the appearance and the structure of the vasculature, they are in turn subjected to structural changes in the blood vessels, such as an increased arterial stiffness in chronic arterial hypertension and ageing. This results in an interplay between the various forces (biomechanical forces) and the involved vascular elements. Although many molecular mediators of biomechanical forces still need to be identified, there is plenty of evidence for the causal role of these forces in vascular growth processes, which will be summarized in this review. In addition, we will discuss the effects of concomitant diseases and disorders on these processes by altering either the biomechanics or their transduction into biological signals. Particularly endothelial dysfunction, diabetes, hypercholesterolaemia, and age affect mechanosensing and -transduction of flow signals, thereby underpinning their influence on cardiovascular health. Finally, current approaches to modify biomechanical forces to therapeutically modulate vascular growth in humans will be described.

A simplified murine intimal hyperplasia model founded on a focal carotid stenosis

Murine models offer a powerful tool for unraveling the mechanisms of intimal hyperplasia and vascular remodeling, although their technical complexity increases experimental variability and limits widespread application. We describe a simple and clinically relevant mouse model of arterial intimal hyperplasia and remodeling. Focal left carotid artery (LCA) stenosis was created by placing 9-0 nylon suture around the artery using an external 35-gauge mandrel needle (middle or distal location), which was then removed. The effect of adjunctive diet-induced obesity was defined. Flowmetry, wall strain analyses, biomicroscopy, and histology were completed. LCA blood flow sharply decreased by ∼85%, followed by a responsive right carotid artery increase of ∼71%. Circumferential strain decreased by ∼2.1% proximal to the stenosis in both dietary groups. At 28 days, morphologic adaptations included proximal LCA intimal hyperplasia, which was exacerbated by diet-induced obesity. The proximal and distal LCA underwent outward and negative inward remodeling, respectively, in the mid-focal stenosis (remodeling indexes, 1.10 and 0.53). A simple, defined common carotid focal stenosis yields reproducible murine intimal hyperplasia and substantial differentials in arterial wall adaptations. This model offers a tool for investigating mechanisms of hemodynamically driven intimal hyperplasia and arterial wall remodeling.

Inhibition of extracellular signal-regulated kinases ameliorates hypertension-induced renal vascular remodeling in rat models

The aim of this study is to investigate the effect of the extracellular signal-regulated kinases 1/2 (ERK1/2) inhibitor, PD98059, on high blood pressure and related vascular changes. Blood pressure was recorded, thicknesses of renal small artery walls were measured and ERK1/2 immunoreactivity and erk2 mRNA in renal vascular smooth muscle cells (VSMCs) and endothelial cells were detected by immunohistochemistry and in situ hybridization in normotensive wistar kyoto (WKY) rats, spontaneously hypertensive rats (SHR) and PD98059-treated SHR. Compared with normo-tensive WKY rats, SHR developed hypertension at 8 weeks of age, thickened renal small artery wall and asymmetric arrangement of VSMCs at 16 and 24 weeks of age. Phospho-ERK1/2 immunoreactivity and erk2 mRNA expression levels were increased in VSMCs and endothelial cells of the renal small arteries in the SHR. Treating SHR with PD98059 reduced the spontaneous hypertension-induced vascular wall thickening. This effect was associated with suppressions of erk2 mRNA expression and ERK1/2 phosphorylation in VSMCs and endothelial cells of the renal small arteries. It is concluded that inhibition of ERK1/2 ameliorates hypertension induced vascular remodeling in renal small arteries.

In-vivo assessment of the natural history of coronary atherosclerosis: vascular remodeling and endothelial shear stress determine the complexity of atherosclerotic disease progression

PURPOSE OF REVIEW

Atherosclerotic disease progression is determined by localized plaque growth, which is induced by systemic and local hemodynamic factors, and the nature of the wall remodeling response. The purpose of this review is to summarize the processes underlying the heterogeneity of coronary atherosclerosis progression in relation to the local hemodynamic and arterial remodeling environment.

RECENT FINDINGS

Multiple competing biological processes in the extracellular matrix define the extent of vascular remodeling and disease progression. The remodeling phenomenon is not consistent but is characterized by great phenotypical heterogeneity which reflects the complex effect of systemic, genetic and hemodynamic factors on the arterial wall response to plaque formation and progression. The exaggeration of expansive remodeling (i.e., excessive expansive remodeling) likely contributes to the transformation of an initially favorable action into an excessive course of vessel expansion, continued disease progression and plaque instability. Extremely low endothelial shear stress and excessive expansive remodeling establish a vicious cycle which leads to the formation of severe plaques with high-risk characteristics.

SUMMARY

The dynamic interplay between the local hemodynamic environment and the wall remodeling behavior determines the complexity of the natural history of atherosclerosis and explains the development of localized plaque vulnerability.

Glycogen synthase kinase 3 beta positively regulates Notch signaling in vascular smooth muscle cells: role in cell proliferation and survival

The role of glycogen synthase kinase 3 beta (GSK-3β) in modulating Notch control of vascular smooth muscle cell (vSMC) growth (proliferation and apoptosis) was examined in vitro under varying conditions of cyclic strain and validated in vivo following changes in medial tension and stress. Modulation of GSK-3β in vSMC following ectopic expression of constitutively active GSK-3β, siRNA knockdown and pharmacological inhibition with SB-216763 demonstrated that GSK-3β positively regulates Notch intracellular domain expression, CBF-1/RBP-Jκ transactivation and downstream target gene mRNA levels, while concomitantly promoting vSMC proliferation and inhibiting apoptosis. In contrast, inhibition of GSK-3β attenuated Notch signaling and decreased vSMC proliferation and survival. Exposure of vSMC to cyclic strain environments in vitro using both a Flexercell™ Tension system and a novel Sylgard™ phantom vessel following bare metal stent implantation revealed that cyclic strain inhibits GSK-3β activity independent of p42/p44 MAPK and p38 activation concomitant with reduced Notch signaling and decreased vSMC proliferation and survival. Exposure of vSMC to changes in medial strain microenvironments in vivo following carotid artery ligation revealed that enhanced GSK-3β activity was predominantly localized to medial and neointimal vSMC concomitant with increased Notch signaling, proliferating nuclear antigen and decreased Bax expression, respectively, as vascular remodeling progressed. GSK-3β is an important modulator of Notch signaling leading to altered vSMC cell growth where low strain/tension microenvironments prevail.