Chemokines in Vascular Dysfunction and Remodeling

Src-dependent STAT-3-mediated expression of monocyte chemoattractant protein-1 is required for 15(S)-hydroxyeicosatetraenoic acid-induced vascular smooth muscle cell migration

To understand the role of human 15-lipoxygenase 1 (15-LOX1) in vascular wall remodeling, we have studied the effect of the major 15-LOX1 metabolite of arachidonic acid, 15(S)-hydroxyeicosatetraenoic acid (15(S)-HETE), on vascular smooth muscle cell (VSMC) migration both in vitro and in vivo. Among 5(S)-HETE, 12(S)-HETE, and 15(S)-HETE, 15(S)-HETE potentially stimulated more vascular smooth muscle cell (VSMC) migration. In addition, 15(S)-HETE-induced VSMC migration was dependent on Src-mediated activation of signal transducer and activator of transcription-3 (STAT-3). 15(S)-HETE also induced monocyte chemoattractant protein-1 (MCP-1) expression via Src-STAT-3 signaling, and neutralizing anti-MCP-1 antibodies completely negated 15(S)-HETE-induced VSMC migration. Cloning and characterization of a 2.6-kb MCP-1 promoter revealed the presence of four putative STAT-binding sites, and the site that is proximal to the transcription start site was found to be essential for 15(S)-HETE-induced Src-STAT-3-mediated MCP-1 expression. Rat carotid arteries that were subjected to balloon injury and transduced with Ad-15-LOX1 upon exposure to [(3)H]arachidonic acid ex vivo produced 15-HETE as a major eicosanoid and enhanced balloon injury-induced expression of MCP-1 in smooth muscle cells in Src and STAT-3-dependent manner in vivo. Adenovirus-mediated delivery of 15-LOX1 into rat carotid artery also led to recruitment and homing of macrophages to medial region in response to injury. In addition, transduction of Ad-15-LOX1 into arteries enhanced balloon injury-induced smooth muscle cell migration from media to intima and neointima formation. These results show for the first time that 15-LOX1-15(S)-HETE axis plays a major role in vascular wall remodeling after balloon angioplasty.

Sustained hypoxia promotes the development of a pulmonary artery-specific chronic inflammatory microenvironment

Recent studies demonstrate that sustained hypoxia induces the robust accumulation of leukocytes and mesenchymal progenitor cells in pulmonary arteries (PAs). Since the factors orchestrating hypoxia-induced vascular inflammation are not well-defined, the goal of this study was to identify mediators potentially responsible for recruitment to and retention and differentiation of circulating cells within the hypoxic PA. We analyzed mRNA expression of 44 different chemokine/chemokine receptor, cytokine, adhesion, and growth and differentiation genes in PAs obtained via laser capture microdissection in adjacent lung parenchyma and in systemic arteries by RT-PCR at several time points of hypoxic exposure (1, 7, and 28 days) in Wistar-Kyoto rats. Analysis of inflammatory cell accumulation and protein expression of selected genes was concomitantly assessed by immunochemistry. We found that hypoxia induced progressive accumulation of monocytes and dendritic cells in the vessel wall with few T cells and no B cells or neutrophils. Upregulation of stromal cell-derived factor-1 (SDF-1), VEGF, growth-related oncogene protein-alpha (GRO-alpha), C5, ICAM-1, osteopontin (OPN), and transforming growth factor-beta (TGF-beta) preceded mononuclear cell influx. With time, a more complex pattern of gene expression developed with persistent upregulation of adhesion molecules (ICAM-1, VCAM-1, and OPN) and monocyte/fibrocyte growth and differentiation factors (TGF-beta, endothelin-1, and 5-lipoxygenase). On return to normoxia, expression of many genes (including SDF-1, monocyte chemoattractant protein-1, C5, ICAM-1, and TGF-beta) rapidly returned to control levels, changes that preceded the disappearance of monocytes and reversal of vascular remodeling. In conclusion, sustained hypoxia leads to the development of a complex, PA-specific, proinflammatory microenvironment capable of promoting recruitment, retention, and differentiation of circulating monocytic cell populations that contribute to vascular remodeling.

CXCR4 gene transfer enhances the distribution of dermal multipotent stem cells to bone marrow in sublethally irradiated rats

Our previous study indicated that systemically transplanted dermal multipotent cells (DMCs) were recruited more frequently to bone morrow (BM) of rats with sublethal irradiation than that of normal rats, and the interactions between stromal-derived factor (SDF-1) and its receptor (CXC chemokine receptor 4, CXCR4) played an important role in this process. In the present study, we aimed to investigate whether CXCR4 gene transfer could promote the distribution of DMCs into irradiated BM and accelerate its function recovery. Firstly, adenovirus vector of CXCR4 (Adv-CXCR4) and green fluorescent protein (Adv-GFP) were constructed. Then male DMCs infected by Adv-CXCR4 (group A), or infected by Adv-GFP (group B), and non-infected DMCs (group C) were transplanted into irradiated female rats, and real-time polymerase chain reaction for the sex-determining region of Y chromosome was employed to determined the amount of DMCs in BM. The functional recovery of BM was examined by hematopoietic progenitor colonies assay. The results showed that the amount of DMCs in BM of group A was greater than that in group B and group C from day 5 after injury (P < 0.05), and the amount of CFU-F, CFU-E and CFU-GM were greater than that in group B and group C from day 14 after injury (P < 0.05). These findings suggest that DMCs infected by Adv-CXCR4 distributed more frequently to the bone marrow of sublethally irradiated rats and could accelerate hematopoiesis function recovery.

Astrocyte- and endothelial-targeted CCL2 conditional knockout mice: critical tools for studying the pathogenesis of neuroinflammation

While the expression of the C-C chemokine ligand 2 (CCL2) in the central nervous system (CNS) is associated with numerous neuroinflammatory conditions, the critical cellular sources of this chemokine, which is responsible for disease processes-as well as associated pathogenic mechanisms, remain unresolved. As the potential for anti-CCL2 therapeutics in treating neuroinflammatory disease is likely to be contingent upon effective drug delivery to the source(s) and/or target(s) of CCL2 action in the CNS, tools to highlight the course of CCL2 action during neuroinflammation are imperative. In response to this need, we used the Cre/loxP and FLP-FRT recombination system to develop the first two, cell-conditional CCL2 knockout mice-separately targeting CCL2 gene elimination to astrocytes and endothelial cells, both of which have been considered to play crucial though undefined roles in neuroinflammatory disease. Specifically, mice containing a floxed CCL2 allele were intercrossed with GFAP-Cre or Tie2-Cre transgenic mice to generate mice with CCL2-deficient astrocytes (astrocyte KO) or endothelial cells (endothelial KO), respectively. Polymerase chain reaction, reverse transcription polymerase chain reaction/quantitative reverse transcriptase polymerase chain reaction, and enzyme-linked immunosorbent assay of CCL2 gene, RNA, and protein, respectively, from cultured astrocytes and brain microvascular endothelial cells (BMEC) established the efficiency and specificity of the CCL2 gene deletions and a CCL2 null phenotype in these CNS cells. Effective cell-conditional knockout of CCL2 was also confirmed in an in vivo setting, wherein astrocytes and BMEC were retrieved by immune-guided laser capture microdissection from their in situ positions in the brains of mice experiencing acute, lipopolysaccharide-mediated endotoxemia to induce CCL2 gene expression. In vivo analysis further revealed apparent cross-talk between BMEC and astrocytes regarding the regulation of astrocyte CCL2 expression. Use of astrocyte KO and endothelial KO mice should prove critical in elaborating the pathogenic mechanisms of and optimizing the treatments for neuroinflammatory disease.

mTOR regulates vascular smooth muscle cell differentiation from human bone marrow-derived mesenchymal progenitors

OBJECTIVE

Vascular smooth muscle cells (VSMCs) and circulating mesenchymal progenitor cells (MSCs) with a VSMC phenotype contribute to neointima formation and lumen loss after angioplasty and during allograft arteriosclerosis. We hypothesized that phosphoinositol-Akt-mammalian target of rapamycin-p70S6 kinase (PI3K/Akt/mTOR/p70S6K) pathway activation regulates VSMC differentiation from MSCs.

METHODS AND RESULTS

We studied effects of PI3K/Akt/mTOR signaling on phenotypic modulation of MSC and VSMC marker expression, including L-type Ca(2+) channels. Phosphorylation of Akt and p70S6K featured downregulation of VSMC markers in dedifferentiated MSCs. mTOR inhibition with rapamycin at below pharmacological concentrations blocked p70S6K phosphorylation and induced a differentiated contractile phenotype with smooth muscle (sm)-calponin, sm-alpha-actin, and SM protein 22-alpha (SM22alpha) expression. The PI3K inhibitor Ly294002 abolished Akt and p70S6K phosphorylation and reversed the dedifferentiated phenotype via induction of sm-calponin, sm-alpha-actin, SM22alpha, and myosin light chain kinase. Rapamycin acted antiproliferative without impairing MSC viability. In VSMCs, rapamycin increased a homing chemokine for MSCs, stromal cell-derived factor-1-alpha, at mRNA and protein levels. The CXCR4-mediated MSC migration toward conditioned medium of rapamycin-treated VSMCs was enhanced.

CONCLUSIONS

We describe novel pleiotropic effects of rapamycin at very low concentrations that stabilized differentiated contractile VSMCs from MSCs in addition to exerting antiproliferative and enhanced homing effects.