Effect of Metalloprotease Inhibition on Age-Associated Arterial Remodeling

National Institute On Aging

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Abstract

Age-associated arterial remodeling involves changes to the arterial wall including collagen deposition, elastin fragmentation, amyloidosis as well as an increase in arterial pressure. This adverse arterial remodeling is linked to an increase in proinflammatory signaling molecules, including milk fat globule EGF-8 (MFG-E8) and its fragment medin, transforming growth factor-beta1 (TGF-1), monocyte chemoattractant protein 1 (MCP-1), and proendothelin 1 (pro-ET1), activation of extracellular MMPs via the transcriptional factor, ETS-1, as well as a decreases in the anti-inflammatory molecule vasorin. We tested the hypothesis that inhibition of MMP activation can decelerate adverse age-associated arterial remodeling leading to an increase in arterial pressure. Indeed, chronic administration (8 months) of the broad-spectrum MMP inhibitor, PD166793, via a daily gavage, to 16-month-old FXBN rats markedly blunted the expected age-associated increases in arterial pressure. This was accompanied by the following: (1) inhibition of age-associated increases in aortic gelatinase and interstitial collagenase activity in situ; (2) inhibition of age-associated decrease aortic vasorin in situ; (3) preservation of the elastic fiber network integrity; (4) a reduction in collagen deposition; (5) a reduction of MCP-1 and TGF- 1 activity; (6) a diminution in the phosphorylation activity of the profibrogenic signaling molecule SMAD-2/3; (7) inhibition of pro-ET1 activation; and (8) a downregulation of the expression of ETS-1. In addition, our in vitro study shows that treating cultured vascular smooth muscle cells (VSMC) with pro-ET1 increased both the transcription and translation levels of ETS-1, and these effects were markedly reduced with MMP inhibition. Furthermore, infecting VSMCs with an adenovirus harboring full-length ETS-1 cDNA, increased the levels of activated forms of both TGF-1 and MCP-1 proteins. Collectively, our results indicate that MMP inhibition retards age-associated arterial proinflammatory signaling, and is accompanied by the preservation of intact elastin fibers, a reduction in collagen, and a blunting of age-associated increases in blood pressure. Aging exponentially increases the incidence of morbidity and mortality of quintessential inflammatory cardiovascular disease mainly due to arterial proinflammatory shifts at the molecular, cellular, and tissue levels within the arterial wall. Calorie restriction (CR) in rats improves arterial function and extends both healthspan and lifespan. How CR effects the proinflammatory landscape of molecular, cellular, and tissue phenotypic shifts within the arterial wall in rats, however, remains to be elucidated. Aortae were harvested from young (6-month-old) and old (24-month-old) Fisher 344 rats, fed ad libitum (AL) and a second group maintained on a 40% CR beginning at one month of age. Histopathologic and morphometric analysis of the arterial wall demonstrated that CR markedly reduced age-associated intimal medial thickening, collagen deposition, and increased elastin fraction within the arterial walls. Aortic wall immunostaining/blotting showed that CR effectively prevented an age-associated increase in the density of platelet derived growth factor (PDGF-BB), MMP2 activity, TGF-1 and its downstream signaling molecule, p-SMAD-2/3. In early passage cultured VSMCs isolated from both AL and CR rat aortae, CR alleviated the age-associated VSMC phenotypic shifts, pro-fibrogenic signaling, and proliferation in response to PDGF-BB. Collectively, CR reduces matrix and cellular proinflammation associated with aging that occurs within the aortic wall and is attributable to PDGF signaling. Thus, CR reduces PDGF-associated MMP activation signaling cascade and contributes to the postponement of biological aging, preserving a more youthful aortic wall phenotype. Recently, we report exquisitely distinct material properties of primary VSMC isolated from the thoracic aorta of adult (8 months) vs. aged (30 months) F344XBN rats. Individual VSMC showed a tense internal network of the actin cytoskeleton (CSK), exhibiting increased stiffness (elastic) and frictional (loss) moduli with aging. This discrete mechanical response was long-lived. Strikingly, the pro-fibrotic transforming growth factor 1 (TGF1) emerged as a specific modifier of age-associated VSM stiffening in vitro. TGF1 reinforced the mechanical phenotype of arterial aging in VSM cells 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 VSM stiffness and serve as a proof-of-concept that the broad-based inhibition of TGF1 expression, or TGF1 signal transduction in VSM, may be a useful therapeutic approach to mitigate the pathologic progression of central arterial wall stiffening associated with aging.