The Role of Integrin-Mediated Cell Adhesion in Atherosclerosis: Pathophysiology and Clinical Opportunities

Deletion of Talin1 in Myeloid Cells Facilitates Atherosclerosis in Mice

BACKGROUND

Integrin-regulated monocyte recruitment and cellular responses of monocyte-derived macrophages are critical for the pathogenesis of atherosclerosis. In the canonical model, talin1 controls ligand binding to integrins, a prerequisite for integrins to mediate leukocyte recruitment and induce immune responses. However, the role of talin1 in the development of atherosclerosis has not been studied. Our study investigated how talin1 in myeloid cells regulates the progression of atherosclerosis.

METHODS

On an Apoe-/- background, myeloid talin1-deficient mice and the control mice were fed with a high-fat diet for 8 or 12 weeks to induce atherosclerosis. The atherosclerosis development in the aorta and monocyte recruitment into atherosclerotic lesions were analyzed.

RESULTS

Myeloid talin1 deletion facilitated the formation of atherosclerotic lesions and macrophage deposition in lesions. Talin1 deletion abolished integrin β2-mediated adhesion of monocytes but did not impair integrin α4β1-dependent cell adhesion in a flow adhesion assay. Strikingly, talin1 deletion did not prevent Mn2+- or chemokine-induced activation of integrin α4β1 to the high-affinity state for ligands. In an in vivo competitive homing assay, monocyte infiltration into inflamed tissues was prohibited by antibodies to integrin α4β1 but was not affected by talin1 deletion or antibodies to integrin β2. Furthermore, quantitative polymerase chain reaction and ELISA (enzyme-linked immunosorbent assay) analysis showed that macrophages produced cytokines to promote inflammation and the proliferation of smooth muscle cells. Ligand binding to integrin β3 inhibited cytokine generation in macrophages, although talin1 deletion abolished the negative effects of integrin β3.

CONCLUSIONS

Integrin α4β1 controls monocyte recruitment during atherosclerosis. Talin1 is dispensable for integrin α4β1 activation to the high-affinity state and integrin α4β1-mediated monocyte recruitment. Yet, talin1 is required for integrin β3 to inhibit the production of inflammatory cytokines in macrophages. Thus, intact monocyte recruitment and elevated inflammatory responses cause enhanced atherosclerosis in talin1-deficient mice. Our study provides novel insights into the roles of myeloid talin1 and integrins in the progression of atherosclerosis.

Adhesion Molecules and Vulnerable Plaques – Promoters of Acute Coronary Syndromes

Biological factors that characterize extrinsic plaque vulnerability include various pro- and anti-inflammatory cytokines that contribute to the development and progression of atherosclerosis. Adhesion molecules are among the initiators of the atherosclerotic process, by mediation of endothelial inflammation. The soluble forms of these adhesion molecules have been identified in the circulatory blood, with an increased level in case of subjects with atherosclerotic lesions and higher levels in patients with acute coronary syndromes or vulnerable plaques. In addition, several authors have found a significant predictive capacity of these molecules in case of patients presenting with acute coronary and cerebrovascular events. The aim of this manuscript is to provide a short description of the role of adhesion molecules in the development and progression of atherosclerotic lesions towards acute coronary syndromes, as well as their capacity for predicting major adverse cardiovascular events in vulnerable cardiovascular patients.

The Connection Between Rap1 and Talin1 in the Activation of Integrins in Blood Cells

Integrins regulate the adhesion and migration of blood cells to ensure the proper positioning of these cells in the environment. Integrins detect physical and chemical stimuli in the extracellular matrix and regulate signaling pathways in blood cells that mediate their functions. Integrins are usually in a resting state in blood cells until agonist stimulation results in a high-affinity conformation ("integrin activation"), which is central to integrins' contribution to blood cells' trafficking and functions. In this review, we summarize the mechanisms of integrin activation in blood cells with a focus on recent advances understanding of mechanisms whereby Rap1 regulates talin1-integrin interaction to trigger integrin activation in lymphocytes, platelets, and neutrophils.

Integrin-Ligand Interactions in Inflammation, Cancer, and Metabolic Disease: Insights Into the Multifaceted Roles of an Emerging Ligand Irisin

Integrins are transmembrane proteins that mediate cellular adhesion and migration to neighboring cells or the extracellular matrix, which is essential for cells to undertake diverse physiological and pathological pathways. For integrin activation and ligand binding, bidirectional signaling across the cell membrane is needed. Integrins aberrantly activated under pathologic conditions facilitate cellular infiltration into tissues, thereby causing inflammatory or tumorigenic progressions. Thus, integrins have emerged to the forefront as promising targets for developing therapeutics to treat autoimmune and cancer diseases. In contrast, it remains a fact that integrin-ligand interactions are beneficial for improving the health status of different tissues. Among these ligands, irisin, a myokine produced mainly by skeletal muscles in an exercise-dependent manner, has been shown to bind to integrin αVβ5, alleviating symptoms under unfavorable conditions. These findings may provide insights into some of the underlying mechanisms by which exercise improves quality of life. This review will discuss the current understanding of integrin-ligand interactions in both health and disease. Likewise, we not only explain how diverse ligands play different roles in mediating cellular functions under both conditions via their interactions with integrins, but also specifically highlight the potential roles of the emerging ligand irisin in inflammation, cancer, and metabolic disease.

The integrin PSI domain has an endogenous thiol isomerase function and is a novel target for antiplatelet therapy

Integrins are a large family of heterodimeric transmembrane receptors differentially expressed on almost all metazoan cells. Integrin β subunits contain a highly conserved plexin-semaphorin-integrin (PSI) domain. The CXXC motif, the active site of the protein-disulfide-isomerase (PDI) family, is expressed twice in this domain of all integrins across species. However, the role of the PSI domain in integrins and whether it contains thiol-isomerase activity have not been explored. Here, recombinant PSI domains of murine β3, and human β1 and β2 integrins were generated and their PDI-like activity was demonstrated by refolding of reduced/denatured RNase. We identified that both CXXC motifs of β3 integrin PSI domain are required to maintain its optimal PDI-like activity. Cysteine substitutions (C13A and C26A) of the CXXC motifs also significantly decreased the PDI-like activity of full-length human recombinant β3 subunit. We further developed mouse anti-mouse β3 PSI domain monoclonal antibodies (mAbs) that cross-react with human and other species. These mAbs inhibited αIIbβ3 PDI-like activity and its fibrinogen binding. Using single-molecular Biomembrane-Force-Probe assays, we demonstrated that inhibition of αIIbβ3 endogenous PDI-like activity reduced αIIbβ3-fibrinogen interaction, and these anti-PSI mAbs inhibited fibrinogen binding via different levels of both PDI-like activity-dependent and -independent mechanisms. Importantly, these mAbs inhibited murine/human platelet aggregation in vitro and ex vivo, and murine thrombus formation in vivo, without significantly affecting bleeding time or platelet count. Thus, the PSI domain is a potential regulator of integrin activation and a novel target for antithrombotic therapies. These findings may have broad implications for all integrin functions, and cell-cell and cell-matrix interactions.

Functional analysis of four single (RGDWL, RGDWM, RGDWP, RGDMN) and two double (RGDNM, RGDMP) mutants: The importance of methionine (M) in the functional potency of recombinant mojastin (r-Moj)

We have demonstrated in previous studies that a single amino acid change can alter the activity of the recombinant disintegrin r-Moj. In this study, four r-Moj recombinants containing single mutations (r-Moj-WL, r-Moj-WM, r-Moj-WP, r-Moj-MN) and two containing double mutations (r-Moj-MP and r-Moj-NM) at the binding loop were produced, purified, and tested. All r-Moj-W_, r-Moj-M_, and r-Moj-NM mutant peptides inhibited platelet aggregation at higher potency than r-Moj-D_ mutants. Five of the seven r-Moj peptides inhibited angiogenesis at different levels. Two of the mutant peptides with a methionine at the second position carboxyl of the RGD (r-Moj-WM and r-Moj-NM) were the strongest angiogenesis inhibitors, with r-Moj-WM being the most potent. Recombinant r-Moj-MP and r-Moj-WN failed to inhibit angiogenesis. Only the r-Moj-MP mutant peptide induced apoptosis of SK-Mel-28 cells significantly (p = 0.001). This was confirmed by chromatin condensation. Proliferation of SK-Mel-28 cells was inhibited at high levels (>70%) by all r-Moj mutant peptides. Recombinant r-Moj-MN and r-Moj-WN failed to inhibit cell migration significantly (p > 0.5). Recombinant r-Moj-NM was the strongest cell migration inhibitor (98% ± 0.69), followed by r-Moj-MP (80% ± 2.87), and r-Moj-WM (61.8% ± 5.45). The lowest inhibitor was r-Moj-WL (50% ± 12.16). Our functional data suggest that the most potent r-Moj disintegrins contain a methionine in the first or the second position carboxyl to the RGD.

Under-expression of α8 integrin aggravates experimental atherosclerosis

Integrins play an important role in vascular biology. The α8 integrin chain attenuates smooth muscle cell migration but its functional role in the development of atherosclerosis is unclear. Therefore, we studied the contribution of α8 integrin to atherosclerosis and vascular remodelling. We hypothesized that α8 integrin expression is reduced in atherosclerotic lesions, and that its under-expression leads to a more severe course of atherosclerosis. α8 Integrin was detected by immunohistochemistry and qPCR and α8 integrin-deficient mice were used to induce two models of atherosclerotic lesions. First, ligation of the carotid artery led to medial thickening and neointima formation, which was quantified in carotid cross-sections. Second, after crossing into ApoE-deficient mice, the formation of advanced vascular lesions with atherosclerotic plaques was quantified in aortic en face preparations stained with Sudan IV. Parameters of renal physiology and histopathology were assessed: α8 integrin was detected in the media of human and murine vascular tissue and was down-regulated in arteries with advanced atherosclerotic lesions. In α8 integrin-deficient mice (α8(-/-) ) as well as α8(+/-) and α8(+/+) littermates, carotid artery ligation increased media:lumen ratios in all genotypes, with higher values in ligated α8(-/-) and α8(+/-) compared to ligated α8(+/+) animals. Carotid artery ligation increased smooth muscle cell number in the media of α8(+/+) mice and, more prominently, of α8(-/-) or α8(+/-) mice. On an ApoE(-/-) background, α8(+/-) and α8(-/-) mice developed more atherosclerotic plaques than α8(+/+) mice. α8 Integrin expression was reduced in α8(+/-) animals. Renal damage with increased serum creatinine and glomerulosclerosis was detected in α8(-/-) mice only. Thus, under-expression of α8 integrin aggravates vascular lesions, while a complete loss of α8 integrin results in reduced renal mass and additional renal disease in the presence of generalized atherosclerosis. Our data support the hypothesis that integrin α8β1 has a protective role in arterial remodelling and atherosclerosis.

Overexpression of integrin-β1 in leiomyoma promotes cell spreading and proliferation

CONTEXT

Uterine leiomyoma, the most common tumors found in the women of the reproductive age, may cause abnormal uterine bleeding and be life threatening. Compared with myometrium, leiomyoma contains excessive extracellular matrix (ECM). However, the pathological roles of ECM in the development of leiomyoma remain largely unknown. Integrins are the major adhesion molecules on cell surface to interact with ECM. The interactions of ECM with integrins regulate cell adhesion and initiate signals for cell growth, differentiation, and migration.

OBJECTIVE

The aim of this study was to investigate the expression and functional role of integrin-β1 in leiomyoma pathogenesis.

DESIGN

Levels of integrin-β1 protein were determined by Western blotting in paired normal and leiomyomal tissues (n = 15). Knockdown of integrin-β1 and inhibition of ECM-integrin interaction by disintegrin were used to evaluate the impact of integrin-β1 in cell adhesion, spreading, and proliferation.

RESULTS

Levels of integrin-β1 were significantly up-regulated in leiomyomal cells compared with their normal counterparts. Knockdown of integrin-β1 did not affect cell adhesion on fibronectin or laminin matrix but significantly inhibits cell spreading ability. Consistent with this notion, the phosphorylation of focal adhesion kinase and the recruitment of paxillin to the focal contact were decreased in integrin-β1 knockdown cells, which attenuates contraction force. The inability of cell spreading leads to inhibition of cyclin D1 expression and impedes cell cycle progression. More importantly, disruption of ECM-integrin interaction by the small protein, disintegrin inhibited cyclin D1 expression and cell proliferation.

CONCLUSION

These data demonstrate that integrin-β1 is a critical ligand to enhance cell-ECM contact force and thus promotes cell proliferation. Disruption of ECM-integrin-β1 signaling may serve as an option to inhibit the progression of leiomyoma.

The role of ROS in ionizing radiation-induced VLA-4 mediated adhesion of RAW264.7 cells to VCAM-1 under flow conditions

Alteration of adhesion molecule expression on endothelial cells has a direct connection with ionizing radiation-induced atherosclerosis, which is an adverse effect observed after radiotherapy. However, minimal attention has been given to monocytes/macrophages role in atherosclerosis development, which are exposed to the radiation at the same time. Under flow conditions using a parallel plate flow chamber to mimic physiological shear stress, we demonstrate here that the avidity between very late antigen-4 (VLA-4) of RAW264.7 cells and its ligand vascular cell adhesion molecule-1 (VCAM-1), was increased after low dose (0.5 Gy) irradiation, but was reduced after higher dose (5 Gy) treatment of ionizing radiation despite the fact that the surface expression of VLA-4 was up-regulated at 5 Gy of ionizing radiation. Treating the cells with free radical scavenger N-acetylcysteine had no effect on VLA-4 expression, but did reduce the avidity between RAW264.7 cells and VCAM-1 to a similar level, independent of ionizing radiation dose. The effect of H(2)O(2) treatment (from 1-100 μM) on RAW264.7 cell adhesion to VCAM-1 generated a similar bell-shaped graph as ionizing radiation. These results suggest that ionizing radiation regulates adhesive interactions between VLA-4 and VCAM-1, and that reactive oxygen species might function as a regulator, for this increased adhesiveness but with altered expression of integrin not play a major role.

Panax notoginseng saponins inhibit Zymosan A induced atherosclerosis by suppressing integrin expression, FAK activation and NF-κB translocation

ETHNOPHARMACOLOGICAL SIGNIFICANCE

Panax notoginseng saponins (PNS) are ingredients extracted from traditional Chinese medicinal herb Panax notoginseng. It has been demonstrated that PNS have extensive effects on the cardiovascular system, including inhibition of platelet aggregation, increasing blood flow, improving left ventricular diastolic function in hypertensive patients and anti-inflammatory effect.

AIM OF STUDY

Recent researches indicated that PNS administration inhibited foam cells' formation. The present study was designed to study the effects of PNS on atherogenesis and to explore the relevant molecular mechanisms.

MATERIALS AND METHODS

The Zymosan A induced atherosclerosis models were used to investigate the anti-atherosclerosis effects of PNS. The integrin express array was used to check the changes of integrins. The foam cell formation was observed with transmission electron microscope. The effect of PNS on phosphorylation of FAK on threonine 397 and protein level of NF-κB was also evaluated in vitro.

RESULTS

PNS treated rats had less plaque spots on the aortas compared with Zym induced group. The formation of foam cell was inhibited by PNS. Compared with Zym treated group, the expression of most integrin families decreased except Itgav and Itgb2 after PNS treatment. PNS inhibited phosphorylation of FAK on threonine 397 and translocation of NF-κB.

CONCLUSION

High fat diet together with Zym induces atherogenesis of rat. PNS inhibits zymosan A induced atherogenesis by suppressing FAK phosphorylation, integrins expression and NF-κB translocation.

WISP-1 increases MMP-2 expression and cell motility in human chondrosarcoma cells

Chondrosarcoma is a type of highly malignant tumor with a potent capacity to invade locally and cause distant metastasis. Chondrosarcoma shows a predilection for metastasis to the lungs. WISP-1 is a cysteine-rich protein that belongs to the CCN (Cyr61, CTGF, Nov) family of matricellular proteins. However, the effect of WISP-1 on migration activity in human chondrosarcoma cells is mostly unknown. Here we found that WISP-1 increased the migration and expression of matrix metalloproteinase (MMP)-2 in human chondrosarcoma cells (JJ012 cells). We also found that human chondrosarcoma tissues had significant expression of the WISP-1 which was higher than that in normal cartilage. α5β1 monoclonal antibody and MAPK kinase (MEK) inhibitors (PD98059 and U0126) inhibited the WISP-1-induced increase of the migration and MMP-2 up-regulation of chondrosarcoma cells. WISP-1 stimulation increased the phosphorylation of focal adhesion kinase (FAK), MEK and extracellular signal-regulated kinase (ERK). In addition, NF-κB inhibitors also suppressed the cell migration and MMP-2 expression enhanced by WISP-1. Moreover, WISP-1 increased NF-κB luciferase activity and binding of p65 to the NF-κB element on the MMP-2 promoter. Taken together, our results indicated that WISP-1 enhances the migration of chondrosarcoma cells by increasing MMP-2 expression through the α5β1 integrin receptor, FAK, MEK, ERK, p65 and NF-κB signal transduction pathway.

The mojastin mutant Moj-DM induces apoptosis of the human melanoma SK-Mel-28, but not the mutant Moj-NN nor the non-mutated recombinant Moj-WN

In this study, three recombinant mojastin peptides (Moj-WN, Moj-NN, and Moj-DM) were produced and compared functionally. Recombinant Moj peptides were purified as GST-fusions. GST-Moj-WN and GST-Moj-NN inhibited ADP-induced platelet aggregation in platelet rich plasma. The GST-Moj-WN had an IC(50) of 160nM, while the GST-Moj-NN had an IC(50) of 493nM. The GST-Moj-DM did not inhibit platelet aggregation. All three GST-Moj peptides inhibited SK-Mel-28 cell adhesion to fibronectin. The GST-Moj-WN inhibited the binding of SK-Mel-28 cells to fibronectin with an IC(50) of 11nM, followed by the GST-Moj-NN (IC(50) of 28nM), and the GST-Moj-DM (IC(50) of 46nM). The GST-Moj peptides' ability to induce apoptosis on SK-Mel-28 cells was determined using Annexin-V-FITC and nuclear fragmentation assays. Cells were incubated with 5muM GST-Moj peptides for 24h. At 5microM GST-Moj-DM peptide, 13.56%+/-2.08 of treated SK-Mel-28 cells were in early apoptosis. The GST-Moj-DM peptide also caused nuclear fragmentation as determined by fluorescent microscopy and Hoechst staining. The GST-Moj-WN and GST-Moj-NN peptides failed to induce apoptosis. We characterized the SK-Mel-28 integrin expression, as the first step in determining r-Moj binding specificity. Our results indicate that SK-Mel-28 cells express alphavbeta3, alphav, alpha6, beta1, and beta3 integrin receptors.