Bone mesenchymal stem cells contributed to the neointimal formation after arterial injury

Impact of the transforming growth factor-β pathway on vascular restenosis and its mechanism

As a crucial regulatory molecule in the context of vascular stenosis, transforming growth factor-β (TGF-β), plays a pivotal role in its initiation and progression. TGF-β, a member of the TGF-β superfamily, can bind to the TGF-β receptor and transduce extracellular to intracellular signals through canonical Smad dependent or noncanonical signaling pathways to regulate cell growth, proliferation, differentiation, and apoptosis. Restenosis remains one of the most challenging problems in cardiac, cerebral, and peripheral vascular disease worldwide. The mechanisms for occurrence and development of restenosis are diverse and complex. The TGF-β pathway exhibits diversity across various cell types. Hence, clarifying the specific roles of TGF-β within different cell types and its precise impact on vascular stenosis provides strategies for future research in the field of stenosis.

Intra-arterial injection of mesenchymal stem cells to accelerate neointima formation after endovascular stenting in a rabbit model

OBJECTIVE

Delayed neointima formation over a neurovascular stent is associated with thrombotic complications that can lead to stroke. The purpose of this study was to evaluate whether an intra-arterial injection of mesenchymal stem cells (MSCs) after stent placement leads to improved neointima and reduced thrombus formation over the device.

METHODS

Solitaire stents were placed into the aortas of rabbits that were divided into MSC and control groups. The MSC group received an intra-arterial injection of MSCs through the same microcatheter used for stent deployment. Optical coherence tomography (OCT) was used to evaluate and compare neointima and thrombus formation in a blinded fashion. Explanted specimens were also imaged with scanning electron microscopy (SEM) and evaluated by observers blinded to group allocation using an endothelialization scoring system.

RESULTS

The 3-day MSC group was similar to the 7-day controls in terms of stent strut coverage ratio and maximum neointimal thickness, but these values were significantly higher than the 3-day control group based on a hierarchical mixed-effects linear regression analysis. SEM revealed a significantly higher endothelialization score for the MSC group compared with controls at the same time point. There was no difference in thrombus formation between any of the groups.

CONCLUSIONS

The intra-arterial injection of MSCs after endovascular stenting accelerated early neointima formation but had no effect on thrombus formation in this study. Larger studies are required to verify these findings and determine the durability and mechanism of this effect.

Bone marrow-derived mesenchymal stem cells inhibit vascular smooth muscle cell proliferation and neointimal hyperplasia after arterial injury in rats

We investigated whether mesenchymal stem cell (MSC)-based treatment could inhibit neointimal hyperplasia in a rat model of carotid arterial injury and explored potential mechanisms underlying the positive effects of MSC therapy on vascular remodeling/repair. Sprague-Dawley rats underwent balloon injury to their right carotid arteries. After 2 days, we administered cultured MSCs from bone marrow of GFP-transgenic rats (0.8 × 106 cells, n = 10) or vehicle (controls, n = 10) to adventitial sites of the injured arteries. As an additional control, some rats received a higher dose of MSCs by systemic infusion (3 × 106 cells, tail vein; n = 4). Local vascular MSC administration significantly prevented neointimal hyperplasia (intima/media ratio) and reduced the percentage of Ki67 + proliferating cells in arterial walls by 14 days after treatment, despite little evidence of long-term MSC engraftment. Notably, systemic MSC infusion did not alter neointimal formation. By immunohistochemistry, compared with neointimal cells of controls, cells in MSC-treated arteries expressed reduced levels of embryonic myosin heavy chain and RM-4, an inflammatory cell marker. In the presence of platelet-derived growth factor (PDGF-BB), conditioned medium from MSCs increased p27 protein levels and significantly attenuated VSMC proliferation in culture. Furthermore, MSC-conditioned medium suppressed the expression of inflammatory cytokines and RM-4 in PDGF-BB-treated VSMCs. Thus, perivascular administration of MSCs may improve restenosis after vascular injury through paracrine effects that modulate VSMC inflammatory phenotype.

Acute and chronic effects of treatment with mesenchymal stromal cells on LPS-induced pulmonary inflammation, emphysema and atherosclerosis development

BACKGROUND

COPD is a pulmonary disorder often accompanied by cardiovascular disease (CVD), and current treatment of this comorbidity is suboptimal. Systemic inflammation in COPD triggered by smoke and microbial exposure is suggested to link COPD and CVD. Mesenchymal stromal cells (MSC) possess anti-inflammatory capacities and MSC treatment is considered an attractive treatment option for various chronic inflammatory diseases. Therefore, we investigated the immunomodulatory properties of MSC in an acute and chronic model of lipopolysaccharide (LPS)-induced inflammation, emphysema and atherosclerosis development in APOE*3-Leiden (E3L) mice.

METHODS

Hyperlipidemic E3L mice were intranasally instilled with 10 μg LPS or vehicle twice in an acute 4-day study, or twice weekly during 20 weeks Western-type diet feeding in a chronic study. Mice received 0.5x106 MSC or vehicle intravenously twice after the first LPS instillation (acute study) or in week 14, 16, 18 and 20 (chronic study). Inflammatory parameters were measured in bronchoalveolar lavage (BAL) and lung tissue. Emphysema, pulmonary inflammation and atherosclerosis were assessed in the chronic study.

RESULTS

In the acute study, intranasal LPS administration induced a marked systemic IL-6 response on day 3, which was inhibited after MSC treatment. Furthermore, MSC treatment reduced LPS-induced total cell count in BAL due to reduced neutrophil numbers. In the chronic study, LPS increased emphysema but did not aggravate atherosclerosis. Emphysema and atherosclerosis development were unaffected after MSC treatment.

CONCLUSION

These data show that MSC inhibit LPS-induced pulmonary and systemic inflammation in the acute study, whereas MSC treatment had no effect on inflammation, emphysema and atherosclerosis development in the chronic study.

Endothelial‑like cells differentiated from mesenchymal stem cells attenuate neointimal hyperplasia after vascular injury

The present study investigated the contribution of bone marrow-derived mesenchymal stem cells (BM-MSCs) to neointimal formation, and whether endothelial-like cells (ELCs) differentiated from BM-MSCs could attenuate intimal hyperplasia following vascular injury. BM-MSCs were isolated from rat femurs and tibias and expanded ex vivo. Differentiation into ELCs was induced by cultivation in the presence of 50 ng/ml vascular endothelial growth factor (VEGF). MSCs and ELCs were labeled with BrdU and injected via the femoral vein on the day of a balloon-induced carotid artery injury. Carotid artery morphology and histology were examined using ultrasound biomicroscopy and immunohistochemistry. Flow cytometry analysis measured CD31 and CD34 expression, and immunofluorescence analysis measured von Willebrand factor and VEGF receptor 2 expression in ELCs. Ultrasound biomicroscopy observed a significantly increased intima-media thickness in the phosphate-buffered saline (PBS) and BM-MSCs groups compared with the ELCs group. Intima/media ratios were significantly reduced in the ELCs group compared with the PBS and BM-MSCs groups. At 4 weeks of administration, the cells labeled with BrdU were abundantly located in the adventitial region and neointima. MSCs were able to differentiate into ELCs in vitro. Cell therapy with BM-MSCs was not able to attenuate neointima thickness, however transplantation with ELCs significantly suppressed intimal hyperplasia following vascular injury.

Effect of TGF-β1 on the Migration and Recruitment of Mesenchymal Stem Cells after Vascular Balloon Injury: Involvement of Matrix Metalloproteinase-14

Restenosis or occlusion after vascular procedures is ascribed to intimal hyperplasia. Transforming growth factor (TGF)-β1 is involved in recruitment of mesenchymal stem cells (MSCs) following arterial injury, and its release from latent TGF-binding protein by matrix metalloproteinase (MMP)-14-induced proteolysis contributes to neointima formation. However, the relationship between MMP-14 and TGF-β1 activation in restenosis is unknown. This study investigated the relationship using a rat model of balloon-induced injury. Rats were assigned to vehicle-, SB431542 (SB)-, or recombinant human (rh)TGF-β1-treated groups and examined at various time points after balloon-induced injury for expression of TGF-β1/Smad signalling pathway components, MMP-14 and MSCs markers including Nestin, CD29, and Sca1⁺CD29⁺CD11b/c⁻CD45⁻. Intimal hyperplasia was reduced in SB- and rhTGF-β1-treated rats. The expression of TGF-β1, TGF-β1RI, and Smad2/3 was decreased, but the levels of phosphorylated Smad2/3 were higher in SB-treated rats than vehicle-treated after 7 days to 14 days. rhTGF-β1 administration decreased the expression of TGF-β1/Smad pathway proteins, except for TGF-β1RI. Nestin and CD29 expression and the number of Sca1⁺CD29⁺CD11b⁻CD45⁻ cells were reduced, whereas MMP-14 expression was increased after SB431542 and rhTGF-β1 administration. These results suggest that TGF-β1/Smad signalling and MMP-14 act to recruit MSCs which differentiate to vascular smooth muscle cells and mesenchymal-like cells that participate in arterial repair/remodelling.

Mesenchymal stromal cells derived from various tissues: Biological, clinical and cryopreservation aspects

Originally isolated from bone marrow, mesenchymal stromal cells (MSCs) have since been obtained from various fetal and post-natal tissues and are the focus of an increasing number of clinical trials. Because of their tremendous potential for cellular therapy, regenerative medicine and tissue engineering, it is desirable to cryopreserve and bank MSCs to increase their access and availability. A remarkable amount of research and resources have been expended towards optimizing the protocols, freezing media composition, cooling devices and storage containers, as well as developing good manufacturing practices in order to ensure that MSCs retain their therapeutic characteristics following cryopreservation and that they are safe for clinical use. Here, we first present an overview of the identification of MSCs, their tissue sources and the properties that render them suitable as a cellular therapeutic. Next, we discuss the responses of cells during freezing and focus on the traditional and novel approaches used to cryopreserve MSCs. We conclude that viable MSCs from diverse tissues can be recovered after cryopreservation using a variety of freezing protocols, cryoprotectants, storage periods and temperatures. However, alterations in certain functions of MSCs following cryopreservation warrant future investigations on the recovery of cells post-thaw followed by expansion of functional cells in order to achieve their full therapeutic potential.

Human miR-221/222 in Physiological and Atherosclerotic Vascular Remodeling

A cluster of miR-221/222 is a key player in vascular biology through exhibiting its effects on vascular smooth muscle cells (VSMCs) and endothelial cells (ECs). These miRNAs contribute to vascular remodeling, an adaptive process involving phenotypic and behavioral changes in vascular cells in response to vascular injury. In proliferative vascular diseases such as atherosclerosis, pathological vascular remodeling plays a prominent role. The miR-221/222 cluster controls development and differentiation of ECs but inhibits their proangiogenic activation, proliferation, and migration. miR-221/222 are primarily implicated in maintaining endothelial integrity and supporting quiescent EC phenotype. Vascular expression of miR-221/222 is upregulated in initial atherogenic stages causing inhibition of angiogenic recruitment of ECs and increasing endothelial dysfunction and EC apoptosis. In contrast, these miRNAs stimulate VSMCs and switching from the VSMC "contractile" phenotype to the "synthetic" phenotype associated with induction of proliferation and motility. In atherosclerotic vessels, miR-221/222 drive neointima formation. Both miRNAs contribute to atherogenic calcification of VSMCs. In advanced plaques, chronic inflammation downregulates miR-221/222 expression in ECs that in turn could activate intralesion neoangiogenesis. In addition, both miRNAs could contribute to cardiovascular pathology through their effects on fat and glucose metabolism in nonvascular tissues such as adipose tissue, liver, and skeletal muscles.

TGF-β1/Smad signaling, MMP-14, and MSC markers in arterial injury: discovery of the molecular basis of restenosis

Transforming growth factor (TGF)-β1 has been suggested to be involved in the recruitment of mesenchymal stem cells (MSCs) following arterial injury, but the role of downstream signaling and the contribution of the recruited MSCs are still unknown. The release of latent TGF-β1 from latent TGF-binding protein (LTBP) by matrix metallopeptidase-14 (MMP-14) proteolysis was demonstrated, which contributed to neointima formation, but the relationship between MMP-14 and activated TGF-β1 in the process of restenosis has yet to be explored. In this study, we observed the change in expression and distribution of TGF-β1/Smad signaling pathway proteins, MMP-14, and MSC markers in the process of neointima formation using a rat model for balloon-induced carotid artery injury. We found that the increase in downstream Smad signaling was consistent with the elevation of TGF-β1 levels and MSCs accumulated at the lumen side of neointima. Furthermore, the activation of MMP-14 in the injured artery was preceded by the increase in TGF-β1 levels. Herein, we conclude that MMP-14 induces an elevation in the levels of TGF-β1/Smad signaling proteins in injured arteries, and that MSCs are recruited by TGF-β1/Smad signaling and MMP-14, possibly differentiating into vascular smooth muscle cell (VSMC)-like cells and VSMC via modulation of TGF-β1/Smads signaling and MMP-14.

Differential characteristics and in vitro angiogenesis of bone marrow- and peripheral blood-derived endothelial progenitor cells: evidence from avian species

OBJECTIVES

This study was conducted to compare phenotypes and in vitro angiogenic capacity of putative endothelial progenitor cells (EPCs) derived from bone marrow (BM) and peripheral blood (PB), from an avian species.

MATERIALS AND METHODS

Mononuclear cells were isolated from chicken BM and PB (BMMNCs and PBMNCs) and cultured in EGM-2 medium. Cells at days 7-14 were used for the experiments. Expression of progenitor and endothelial markers, number of Dil-ac-LDL/lectin dual-positive cells and adipogenic and osteogenic differentiation were determined. Migration and in vitro angiogenic ability between BMMNC- and PBMNC-derived cells were compared.

RESULTS

PBMNCs developed typical EPC appearance, with initial spindle shape followed by a cobblestone form, whereas BMMNC-derived cells retained their constitutive spindle-like morphology throughout the study. Cells derived from both sources expressed CD133, CD31 and VEGFR-2, although PBMNCs-derived cells had lower CD133 expression. Nevertheless, number of Dil-ac-LDL/lectin dual-positive cells did not differ between groups. Adipogenic and osteogenic lineages were verified in BMMNC- but not in PBMNC-derived cells. PBMNC-derived cells formed tubular networks on Matrigel. However, BMMNC-derived cells formed few tube-like structures, which were not morphologically comparable to those developed by their counterparts.

CONCLUSION

Our results suggest that so called EPCs derived from BMMNCs are not 'true' EPCs, supporting previous findings on mammals that BM may not serve as an optimal isolation source of EPCs.