Targeting alphavbeta3 and alpha5beta1 for gene delivery to proliferating VSMCs: synergistic effect of TGF-beta1

Osteoprotegerin Prevents Intracranial Aneurysm Progression by Promoting Collagen Biosynthesis and Vascular Smooth Muscle Cell Proliferation

Background Decreased extracellular matrix formation and few vascular smooth muscle cells (VSMCs) in cerebral vascular walls are the main characteristics of intracranial aneurysm (IA) pathogenesis. Recently, osteoprotegerin was reported to activate collagen biosynthesis and VSMC proliferation via the TGF-β1 (transforming growth factor-β1) signaling. This study aimed to investigate whether osteoprotegerin can prevent IA progression in rats through enhanced collagen expression and VSMC proliferation. Methods and Results IAs were surgically induced in 7-week-old male Sprague-Dawley rats; at 1-week post-operation, recombinant mouse osteoprotegerin or vehicle control was continuously infused for 4 weeks into the lateral ventricle using an osmotic pump. In the osteoprotegerin-treatment group, the aneurysmal size was significantly smaller (37.5 μm versus 60.0 μm; P<0.01) and the media of IA walls was thicker (57.1% versus 36.0%; P<0.01) than in the vehicle-control group. Type-I and type-III collagen, TGF-β1, phosphorylated Smad2/3, and proliferating cell nuclear antigen were significantly upregulated in the IA walls of the osteoprotegerin group than that in the control group. No significant difference was found in the expression of proinflammatory genes between the groups. In mouse VSMC cultures, osteoprotegerin treatment upregulated the expression of collagen and TGF-β1 genes, and activated VSMC proliferation; the inhibition of TGF-β1 signaling nullified this effect. Conclusions Osteoprotegerin suppressed the IA progression by a unique mechanism whereby collagen biosynthesis and VSMC proliferation were activated via TGF-β1 without altering proinflammatory gene expression. Osteoprotegerin may represent a novel therapeutic target for IAs.

Vascular Smooth Muscle Cells and Arterial Stiffening: Relevance in Development, Aging, and Disease

The cushioning function of large arteries encompasses distension during systole and recoil during diastole which transforms pulsatile flow into a steady flow in the microcirculation. Arterial stiffness, the inverse of distensibility, has been implicated in various etiologies of chronic common and monogenic cardiovascular diseases and is a major cause of morbidity and mortality globally. The first components that contribute to arterial stiffening are extracellular matrix (ECM) proteins that support the mechanical load, while the second important components are vascular smooth muscle cells (VSMCs), which not only regulate actomyosin interactions for contraction but mediate also mechanotransduction in cell-ECM homeostasis. Eventually, VSMC plasticity and signaling in both conductance and resistance arteries are highly relevant to the physiology of normal and early vascular aging. This review summarizes current concepts of central pressure and tensile pulsatile circumferential stress as key mechanical determinants of arterial wall remodeling, cell-ECM interactions depending mainly on the architecture of cytoskeletal proteins and focal adhesion, the large/small arteries cross-talk that gives rise to target organ damage, and inflammatory pathways leading to calcification or atherosclerosis. We further speculate on the contribution of cellular stiffness along the arterial tree to vascular wall stiffness. In addition, this review provides the latest advances in the identification of gene variants affecting arterial stiffening. Now that important hemodynamic and molecular mechanisms of arterial stiffness have been elucidated, and the complex interplay between ECM, cells, and sensors identified, further research should study their potential to halt or to reverse the development of arterial stiffness.

P2Y2 nucleotide receptor mediates arteriogenesis in a murine model of hind limb ischemia

OBJECTIVE

Arteriogenesis represents the maturation of preformed vascular connections in response to flow changes and shear stress. These collateral vessels can restore up to 60% of the native blood flow. Shear stress and vascular injury can induce the release of nucleotides from vascular smooth muscle cells and platelets that can serve as signaling ligands, suggesting they may be involved in mediating arteriogenesis. The P2Y2 nucleotide receptor (P2Y2R) has also been shown to mediate smooth muscle migration and arterial remodeling. Thus, we hypothesize that P2Y2R mediates arteriogenesis in response to ischemia.

METHODS

Hind limb ischemia was induced by femoral artery ligation (FAL) in C57Bl/6NJ or P2Y2R negative mice (P2Y2(-/-)). Hind limb perfusion was measured with laser Doppler perfusion imaging and compared with the sham-operated contralateral limb immediately and at 3, 7, 14, 21, and 28 days after ligation. Collateral vessel size was measured by Microfil casting. Muscle specimens were harvested and analyzed with immunohistochemistry for Ki67, vascular cell adhesion molecule, macrophages, and muscle viability by hematoxylin and essoin stain.

RESULTS

Hind limb ischemia induced by FAL in C57Bl/6NJ mice resulted in significant ischemia as measured by laser Doppler perfusion imaging. There was rapid recovery to nearly normal levels of perfusion by 2 weeks. FAL in P2Y2(-/-) mice resulted in severe ischemia with greater tissue loss. Recovery of perfusion was impaired, achieving only 40% compared with wild-type mice by 28 days. Collateral vessels in the P2Y2(-/-) mice were underdeveloped, with reduced vascular cell proliferation and smaller vessel size. The collaterals were ∼65% the size of wild-type collateral vessels (P = .011). Angiogenesis at 28 days in the ischemic muscle, however, was greater in the P2Y2(-/-) mice (P < .001), possibly related to persistent ischemia leading and angiogenic drive. Early macrophage recruitment was reduced by nearly 70% in P2Y2(-/-) despite significantly more myocyte necrosis. However, inflammation was greater at 28 days in the P2Y2(-/-) mice.

CONCLUSIONS

P2Y2R deficiency does not alter baseline collateral vessel formation but does significantly impair collateral maturation, with resultant persistent limb ischemia despite enhanced angiogenesis. These findings reinforce the importance of arteriogenesis in the recovery of perfusion in ischemic tissues compared with angiogenesis. They also support the role of P2Y2R in mediating this process. The mechanism by which P2Y2R mediates arteriogenesis may involve the recruitment of inflammatory cells to the ischemic tissues, which is essential to arteriogenesis. Approaches to target P2Y2R may yield new therapeutic strategies for the treatment of arterial occlusive disease.

The role of Src homology 2 containing protein tyrosine phosphatase 2 in vascular smooth muscle cell migration and proliferation

Vascular smooth muscle cells (VSMCs) perform essential smooth muscle contractile and synthetic functions including migration, differentiation and proliferation under physiological and pathological conditions. In response to pathological stimuli, VMSCs undergo phenotypic change resulting in abnormal migration and proliferation, which may contribute to a "pathogenesis-like" atherosclerosis. Intracellular signaling mechanisms governing this phenotypic switch are of great significance not only for better understanding of atherosclerotic plaque formation but also for strategy for pertinent therapeutic remedies. Src Homology 2 Containing Protein Tyrosine Phosphatase 2 (SHP2) is a ubiquitous tyrosine phosphatase containing Src Homology 2 domains which plays major biological functions in response to various growth factors, hormones or cytokines. In particular, SHP2 is implicated in cell signaling pathways controlling cell cycle progression, growth and migration. In this review we will mainly discuss the recent literature demonstrating the role of SHP2 in VSMC migration and proliferation.

Anti-angiogenic effects of non-peptide integrin alphavbeta3 specific antagonist on laser-induced choroidal neovascularization in mice

BACKGROUND

To evaluate the anti-angiogenic effects of integrin alphavbeta3 specific antagonist BS-1417 on laser-induced choroidal neovascularization (CNV) in mice.

METHODS

Male C57BL/6 mice were treated with daily intraperitoneal injections of BS-1417 or saline starting at the onset (day 0) of experiments. CNV was induced by laser photocoagulation the next day. Fluorescein angiograms (FA) and choroidal flatmount FITC-dextran perfusion were performed on experimental day 8. Histological and immunohistochemical examinations were performed with consecutive cryosections. Sub-confluent human vascular endothelial cells (HUVEC) were grown in vitro under various concentrations (0-10 microg/ml) of BS-1417 and the numbers of cell were measured at 48 hours of incubation. After fixation, immunocytochemistry was performed.

RESULTS

BS-1417 significantly decreased the area of dye leakage determined by FA (40% of control, p = 0.0008) and reduced the CNV size found on choroidal flatmount (18% of control, p = 0.007). In histological findings, BS-1417 apparently suppressed the size of laser-induced CNV. Immunoreactivities for VEGF and integrin alphav were remarkably attenuated with BS-1417 compared to control. BS-1417 inhibited the growth and VEGF expression of HUVEC in vitro.

CONCLUSIONS

The integrin alphavbeta3 may play a key role in the induction of laser-induced CNV. The antagonists for integrin alphavbeta3 may have therapeutic effects in CNV associated diseases such as age-related macular degenerations.

Molecular determinants of P2Y2 nucleotide receptor function: implications for proliferative and inflammatory pathways in astrocytes

In the mammalian nervous system, P2 nucleotide receptors mediate neurotransmission, release of proinflammatory cytokines, and reactive astrogliosis. Extracellular nucleotides activate multiple P2 receptors in neurons and glial cells, including G protein-coupled P2Y receptors and P2X receptors, which are ligand-gated ion channels. In glial cells, the P2Y2 receptor subtype, distinguished by its ability to be equipotently activated by ATP and UTP, is coupled to pro-inflammatory signaling pathways. In situ hybridization studies with rodent brain slices indicate that P2Y2 receptors are expressed primarily in the hippocampus and cerebellum. Astrocytes express several P2 receptor subtypes, including P2Y2 receptors whose activation stimulates cell proliferation and migration. P2Y2 receptors, via an RGD (Arg-Gly-Asp) motif in their first extracellular loop, bind to alphavbeta3/beta5 integrins, whereupon P2Y2 receptor activation stimulates integrin signaling pathways that regulate cytoskeletal reorganization and cell motility. The C-terminus of the P2Y2 receptor contains two Src-homology-3 (SH3)-binding domains that upon receptor activation, promote association with Src and transactivation of growth factor receptors. Together, our results indicate that P2Y2 receptors complex with both integrins and growth factor receptors to activate multiple signaling pathways. Thus, P2Y2 receptors present novel targets to control reactive astrogliosis in neurodegenerative diseases.

Altered primordial germ cell migration in the absence of transforming growth factor beta signaling via ALK5

Transforming growth factor beta (TGFbeta) inhibits proliferation and promotes the migration of primordial germ cells (PGCs) towards explants of gonadal ridges in vitro. However, its effects in vivo are still unclear. Here, we analyzed the behavior of PGCs in embryos lacking TGFbeta signaling via the type I receptor ALK5. TGFbeta in vivo was neither a chemoattractant for PGCs, nor did it affect their proliferation during migration towards the gonadal ridges up to embryonic day (E)10. Unexpectedly, the absence of TGFbeta signaling in fact resulted in significant facilitation of PGC migration out of the hindgut, due to the reduced deposition of collagen type I surrounding the gut of Alk5-deficient mutant embryos. Migratory PGCs adhere strongly to collagen; therefore, reduced collagen type I along the gut may result in reduced adhesion, facilitating migration into the dorsal mesenterium and gonadal ridges. Our results provide new evidence for the role of TGFbeta signaling in migration of PGCs in vivo distinct from that described previously.