The coexistence of vascular smooth muscle cell (VSMC) infiltration and collagen deposition within a diffusely thickened intima is a salient feature of central arterial wall inflammation that accompanies advancing age. However, the molecular and cellular mechanisms involved remain undefined. Immunostaining and immunoblotting of rat aortae demonstrate that a triad of proinflammatory molecules MCP-1, TGF-1, and MMP-2 increase within the aortic wall with aging. Treating VSMCs, isolated from 8-mo-old rats (young), to MCP-1, via the CC-chemokine receptor 2 (CCR-2), produces both an increase in TGF-1 activity, up to levels of untreated VSMC from 30-mo-old (old) FXBN rats, and a concurrent increase in MMP-2 activation. Furthermore, treating young VSMCs with TGF-1 increases the levels of MCP-1 and MMP-2 activation, to levels of untreated VSMC from old rats. This autocatalytic signaling loop that enhances collagen production and invasiveness of VSMsC is effectively suppressed by silencing the MCP-1 gene, or treating with a CCR2 antagonist, or through MMP-2 inhibition. Certain levels of MCP-1, MMP-2, or TGF-1 activity trigger a feed-forward signaling mechanism that is implicated in the initiation and progression of adverse age-associated arterial wall senescent remodeling. Interventions that suppress this signaling loop may potentially retard age-associated adverse arterial remodeling. The MMP-associated activation of TGF-1 plays an important role in the stiffening of aging VSMCs. Distinct material properties of primary VSMC cells isolated from the thoracic aorta of adult (8 months) vs. aged (30 months) F344XBN rats were seen. Individual VSMCs derived from aged animals showed a tense internal network of the actin cytoskeleton, exhibiting increased stiffness and frictional (loss) moduli than those derived from the adult animals. This discrete mechanical response was long-lived in culture and was persistent across a physiological range of matrix rigidity. Strikingly, TGF-1 emerged as a specific modifier of age-associated VSMC stiffening in vitro. TGF-1 reinforced the mechanical phenotype of arterial aging in VSMCs on multiple time and length scales through clustering of mechanosensitive 51 and v3 integrins. Taken together, these studies identify a novel nodal point for the long-range regulation of VSMC stiffness and serve as a proof-of-concept that the broad-based inhibition of TGF-1 expression, or TGF-1 signal transduction in VSMC, may be a useful therapeutic approach to mitigate the pathologic progression of central arterial wall stiffening associated with aging. Indeed, we proved that the inhibition of MMP activation decelerates the age-associated arterial proinflammation and its attendant increase in arterial pressure. Chronic administration (8 months) of a broad-spectrum MMP inhibitor, PD166793, via a daily gavage, to 16-month-old rats 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 MCP-1 and TGF-1 activation; (5) a diminution in the activity of the profibrogenic signaling molecule SMAD 2/3 (Sma and Mad (Mothers against decapentaplegic)-2/3) phosphorylation; (6) inhibition of proendothelin 1 activation; and (7) downregulation of expression of V-Ets Avian Erythroblastosis Virus E26 Oncogene Homolog 1 ( Ets-1). Collectively, our results indicate that MMP inhibition retards age-associated arterial proinflammatory signaling, and this is accompanied by the preservation of intact elastin fibers, a reduction in collagen, and a blunting of age-associated increases in blood pressure. Our recent study has shown that a signaling relationship exists between angiotensin II (Ang II), TGF-1 and vasorin within aging VSMCs. In vivo studies in old (30-month-old) versus young (8-month-old) FXBN rats show that the aortic transcription and translation levels of vasorin markedly decreases with aging. In vitro studies of early passage VSMCs from old versus young rat aortae indicate that the abundance of vasorin protein is substantially reduced with aging. Ang II-associated reduction of vasorin protein abundance in young VSMC and age-associated changes in vasorin protein levels are reversed when treated with Losartan (Los), an Ang II receptor (AT1) antagonist, in both in in vitro and in vivo conditions, suggesting constitutive activation of AT1 signaling within the aged arterial wall. Dual immunolabeling and co-immunoprecipitation demonstrate that the co-incidence and physical interaction of vasorin and TGF-1 within VSMC are significantly decreased with aging. Importantly, treating young VSMC and young animals with Ang II increases p-SMAD2/3 and collagen type I production, mimicking old cells. and are abolished or substantially mitigated by treating with Los, or through the overexpression of vasorin or exogenous recombinant human-vasorin protein. In contrast, when old VSMCs are treated with Los, decreases in the production of p-SMAD2/3 and collagen type I are seen. An imbalance in the Ang II/TGF-1/vasorin signaling cascade is created, a feature of the aged arterial wall, that enhances collagen production in VSMCs. In addition, age-associated arterial vasorin is closely associated with enhanced capacity of MMP activation. Activated MMP-2/9 can cleave the full-length of vasorin, and is blocked by MMP Inhibitor, GM6001, in vitro and PD166793, in vivo. Thus, maintaining the balance of the full-length vasorin/TGF-1 signaling is a novel approach to retard adverse age-associated extracellular matrix remodeling, a determinant of arterial stiffening. Taken together, this complex local signaling loop of MCP-1/MMP-2/TGF-1 plays a vital role in the initiation and progression of age-associated arterial intimal cellularity, fibrosis and relevant vascular diseases. Blocking this vicious cycle is a potential therapeutic approach to preserving arterial health with advancing age
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