Progression of Arterial Aging: the Local MCP-1/MMP-2/TGF-beta 1 Signaling Loop

本研究首次在体内和体外研究中发现，衰老大鼠增厚内膜中MCP-1和强效促纤维化细胞因子tgf - β 1在主动脉壁内显著增加并共表达。此外，我们发现MCP-1与tgf - β -1相互作用，位于中心并与炎症级联直接相关，而炎症级联与MMP-2激活密切相关。

In this study, the first in vivo and in vitro studies show that MCP-1 and TGF-beta1, a powerful profibrogenic cytokine, markedly increase and co-expression within the aortic wall in the thickened intima of aging rats. Furthermore, we document that MCP-1 interacts with TGF-beta1 and is centrally located and directly connected with the inflammation cascade, which is closely associated with MMP-2 activation. It is well known that age-associated arterial remodeling involves arterial wall collagen deposition and elastin fragmentation, as well as an increase in arterial pressure. We tested the hypothesis that inhibition of MMP activation can decelerate the age-associated arterial proinflammation and its attendant increase in arterial pressure. Indeed, chronic administration of a broad-spectrum MMP inhibitor, PD166739, via a daily gavage, to 16-month-old rats for 8 months markedly blunted the expected age-associated increases in arterial pressure. This was accompanied by the following: (1) inhibition of the age-associated increases in aortic gelatinase and interstitial collagenase activity in situ; (2) preservation of the elastic fiber network integrity; (3) a reduction of collagen deposition; (4) a reduction of monocyte chemoattractant protein 1 and transforming growth factor-beta1 activation; (5) a diminution in the activity of the profibrogenic signaling molecule SMAD-2/3 phosphorylation; (6) inhibition of proendothelin 1 activation; and (7) downregulation of expression of ets-1. Collectively, our results indicate that MMP inhibition retards age-associated arterial proinflammatory signaling, and this is accompanied by preservation of intact elastin fibers, a reduction in collagen, and blunting of an age-associated increase in blood pressure. In addition, there is no proven therapy or prevention for the vascular type Ehlers-Danlos syndrome (vEDS), a genetic disorder associated with increased metalloproteinase (MMP) activity, reduced collagen content in the arterial walls, and spontaneous development of lesions of varying severity in the aorta. We hypothesized that chronic treatment with MMP inhibitor would increase the collagen content and prevent the development of spontaneous aortic lesions. Indeed, heterozygous COL3A1-deficient mice (HT) were treated since weaning with broad spectrum MMP inhibitor, doxycycline, added to food. At the age of 9 months MMP-9 expression was twice as high in tunica media of aorta in untreated HT, while total collagen content was 30% lower and the cumulative score of aortic lesions was 8 times higher than in wild type mice WT. After 9 months of doxycycline treatment, MMP-9 activity, collagen content and lesions in aorta of HT were at the level of WT. In the aneurismal mouse model of collagen III haploinsufficiency, treatment with broad spectrum MMP inhibitor started early in life normalized increased MMP activity and reduced aortic collagen content in adult and prevented development of spontaneous aortic lesions. These findings provide experimental justification for clinical evaluation of the benefit of doxycycline at least in the haploinsufficient variety of vEDS patients. Recently, in vivo studies show that transcription and translation of vasorin, a glycosylated protein, are markedly decreased within the aortic walls in old (30 mo) vs. young (8 mo) FXBN rats. In vitro studies indicate that levels of vasorin protein in primary cultured early passage VSMC from old aortas are substantially reduced compared to those of young. Furthermore, co-immunoprecipitation reveals that interaction of vasorin and TGF-beta1 is significantly decreased within VSMC with aging. Importantly, exposure of Ang II to young VSMC mimicking old cells or young vasorin gene silenced cells, increases p-SMAD2/3 and collagen type I production. These effects are abolished by an AT1 antagonist, Losartan, or overexpression of vasorin. Exposure of an AT1 antagonist to old VSMC, like overexpression of the vasorin gene, markedly reduces p-SMAD2/3 and collagen production. In addition, overexpression of vasorin substantially inhibited the migration/invasion capacity of VSMC with aging or Ang II treatment, accompanied by an inactivation of MMP-2. Taken together, the TGF-beta1/vasorin-linked with Ang II signaling cascade plays a determinant role in age-associated VSMC pro-inflammatory shift. Thus, vasorin is a naive molecule to retard arterial aging. Taken together, this complex local signaling loop of MCP-1/MMP-2/TGF-beta1 plays a bedrock role in the initiation and progression of age-associated arterial intimal cellularity and fibrosis and relevant vascular diseases, including aneurysm. Interruption of this vicious cycle is a potential therapeutic approach to arterial health.