gms | German Medical Science

24. Jahrestagung der Deutschen Gesellschaft für Arterioskleroseforschung

Deutsche Gesellschaft für Arterioskleroseforschung

18.03. - 20.03.2010, Blaubeuren

CXCR3-mediated mTORC1 activation plays a crucial role in inflammatory cell recruitment during vascular remodeling

Meeting Contribution

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  • Johannes B.K. Schwarz - Medizinische Klinik II-Kardiologie und Pulmologie, Campus Benjamin Franklin, Charité, Berlin, Germany; Berlin-Brandenburg Center for Regenerative Therapies, Berlin, Germany; Comprehensive Pneumology Center, University Hospital Grosshadern, Ludwig-Maximilians-University, and Helmholtz Zentrum München, Munich, Germany
  • corresponding author Dietlind Zohlnhöfer-Momm - Medizinische Klinik II-Kardiologie und Pulmologie, Campus Benjamin Franklin, Charité, Berlin, Germany; Berlin-Brandenburg Center for Regenerative Therapies, Berlin, Germany

Deutsche Gesellschaft für Arterioskleroseforschung e.V.. 24. Jahrestagung der Deutschen Gesellschaft für Arterioskleroseforschung. Blaubeuren, 18.-20.03.2010. Düsseldorf: German Medical Science GMS Publishing House; 2011. Doc10dgaf01

DOI: 10.3205/10dgaf01, URN: urn:nbn:de:0183-10dgaf010

Published: March 23, 2011

© 2011 Schwarz et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by-nc-nd/3.0/deed.en). You are free: to Share – to copy, distribute and transmit the work, provided the original author and source are credited.


Abstract

Atherosclerosis, restenosis and post-transplant graft atherosclerosis are characterized by intimal hyperplasia as a result of endothelial damage, infiltration of leukocytes, recruitment of hematopoietic stem and progenitor cells (HSPCs) and accumulation of smooth muscle cells (SMCs). The CXCR3 chemokine IP10 has been implicated in vascular repair; however, the molecular mechanisms affected hereby remain elusive. Using a mouse model of arterial injury we showed that the IP10-CXCR3-axis is critical for injury-induced early inflammation and governed by activation of mTORC1. Wire-mediated vascular injury induced not only recruitment of CXCR3+ T cells, but also CXCR3+ endothelial cells (ECs) and CXCR3+ positive HSPCs to the intimal, medial and adventitial compartment of the vessel. Moreover, stimulation of T cells with the CXCR3 chemokine IP10 was followed by an activation of the mTORC1 pathway, shown by increased phosphorylation of its downstream target p70 S6 kinase. Inhibition of the CXCR3 axis by mTORC1 inhibitor sirolimus diminished phosphorylation of p70 S6 kinase in vitro and in vivo, decreased recruitment of CXCR3+ cells 14d after vascular injury and resulted in reduced neointima formation.

These findings establish the CXCR3-mediated mTORC1 activation as a major player in early recruitment of inflammatory T cells, ECs and HSPCs during vascular remodeling, a process which is essential for vascular repair.


Introduction

The impact of inflammation in atherosclerosis, the most important cause of morbidity in the Western world, has been well known for a longtime [1]. The defined recruitment of inflammatory cells such as T cells and monocytes is essential for remodeling and repair of injured vessels [2], [3], [4]. The chemokine receptor 3 (CXCR3) chemokine IFN-γ inducible protein 10 (IP10) critically regulates the recruitment of cells expressing CXCR3 in atheromas, such as T helper type 1 lymphocytes [5], [6]. Likewise, blockade or depletion of CXCR3 results in diminished recruitment of Th1 cells to the sites of inflammation and reduces the early steps of atherogenesis [7], [8], [9]. However, the intracellular signal transduction mechanisms of CXCR3, a transmembrane G protein coupled receptor, are not completely understood.

The mammalian target of rapamycin complex 1 (mTORC1) kinase, which regulates cell viability, translation initiation and cell cycle progression by altering the phosphorylation state of downstream targets such as p70 S6 kinase [10], [11], plays a fundamental role in cardiovascular disease. Pharmacological inhibition of mTORC1 by sirolimus or its analogues, such as everolimus, is able to prevent the development of atherosclerosis and intimal hyperplasia in patients and animal models [12], [13], [14], [15], [16]. So far, the underlying molecular mechanism linking the Th1 immune response to mTORC1 activation after vascular injury is still unknown.


Methods

Wire-mediated vascular injury was performed according to Schwarz et al. in WT and CXCR3 knockout mice [17]. To analyze the effect of IP10 on mTORC1 activation in vivo, mouse femoral arteries were injured as described and mTOR expression was investigated by immunoflurescences.


Results

CXCR3+ vascular cells correspond to T cells, ECs and HPCs

To characterize the CXCR3+ cells, which were recruited to the vascular lesion, we performed co-immunostaining of CXCR3 with the cell type markers for T cells (CD3), for ECs (CD31), for HSPCs (c-kit) and for SMCs (α-actin) 14 days after vascular injury. As shown in Figure 1 [Fig. 1] large portion of intimal CXCR3+ cells corresponded to CD3+ T cells (34.0%) and c-kit+ HSPCs (27.6%). However, CXCR3+ cells represented to a somewhat lower extent CD31+ ECs (25.7%). In contrast, α-actin+ SMCs did not express CXCR3 [17]. As shown in Figure 1 [Fig. 1], nearly all CD3+-T cells and most of c-kit+ cells co-expressed CXCR3, whereas CD31+-cells co-express the CXCR3 antigen to a lower extent. As expected, there was no co-expression of the CXCR3 antigen and the SMC marker α-actin. Unexpectedly, the latter results imply that CXCR3+ cells correspond not only to T cells, but also to a similar extent to recruited HSPCs, and to a smaller extent to ECs suggesting that the impact of the CXCR3 axis is not restricted to immune-mediated effects during vascular remodeling.

mTORC1 kinase is activated in vascular cells at the site of vessel injury through the CXCR3 axis

To further validate our hypothesis, that IP10 signaling involves activation of the mTORC1 kinase after vascular injury in vivo, we investigated expression of mTOR in our mouse model of arterial injury. As shown in Figure 2 [Fig. 2], vascular injury caused a profound activation of the mTORC1 kinase pathway measured by upregulation of the mTOR protein. Deletion of the CXCR3 axis caused a significant inhibition of the mTOR expression (p<0.05 vs WT mice, Figure 2 [Fig. 2]).

Most interestingly, the amount of T cell recruitment after vascular injury correlated positively with the amount of vascular cells expressing mTOR (Figure 3 [Fig. 3]) providing strong evidence for a central role of Th1 immune response in the activation of the mTORC1 kinase.

Therefore, these results demonstrate that engagement of the CXCR3 chemokine IP10 not only governs recruitment of CXCR3+ cells to the site of vascular injury, but also represents the critical step for activation of the highly conserved and essential protein kinase mTORC1 in vascular cells during vascular repair and remodeling.


Discussion

The CXCR3 chemokine IP10 is crucial for chemotaxis of T cells and regulation of Th1 immune responses during inflammation and after injury. We demonstrated that CXCR3 governs also early recruitment of ECs and HSPCs to the site of vascular injury [17]. Additionally, we have identified a novel and unexpected role of these chemokine in activation of the mTORC1 kinase after vascular injury. We demonstrate that the CXCR3-chemokine-system is critical in vascular inflammation after vascular injury in vivo. Further we provide evidence that the CXCR3 chemokine IP10 mediates mTORC1 activation after vascular injury in vivo.

These data strongly argue for a direct involvement of the mTORC1 complex in CXCR3 immune-mediated vascular repair and pathological remodeling after vascular injury. In conclusion, we provided strong evidence that the CXCR3 axis acts as an interface between the Th1 immune response, mTORC1 activation and intimal hyperplasia in cardiovascular disease. Therefore, therapies aiming at a selective blockade of the CXCR3 axis may be a promising approach to prevent cardiovascular disease in patients.


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