Aging accelerates endotoxin-induced thrombosis : increased responses of plasminogen activator inhibitor-1 and lipopolysaccharide signaling with aging.

Although older subjects are susceptible to thrombosis under septic conditions, the underlying molecular mechanisms have not been fully elucidated. Since elevated plasminogen activator inhibitor-1 (PAI-1) primarily contributes to endotoxin-induced thrombosis, we first compared the induction of PAI-1 by lipopolysaccharide (LPS) between young and aged mice. The higher induction of PAI-1 antigen and mRNA with increased renal glomerular fibrin deposition was observed in LPS-treated aged mice compared to young mice. In situ hybridization analysis showed that the aging-associated induction of PAI-1 mRNA by LPS was pronounced in hepatocytes and in renal glomerular cells. The increased magnitude of the response of aged mice to lower doses of LPS was observed in terms of renal glomerular fibrin deposition and PAI-1 mRNA induction in the tissues. Furthermore, older PAI-1 deficient mice treated with LPS developed much less fibrin deposition in kidneys. Importantly, a larger induction of receptor molecules for LPS (eg, CD14 and Toll-like receptor 4) was demonstrated in LPS-treated aged mice as compared with young mice. The enhanced LPS signaling in aged mice was also demonstrated by the marked induction of nuclear factor-kappaB in the tissues after endotoxin treatment. As a consequence, increases in an inflammatory cytokine, tumor necrosis factor-alpha, were pronounced in plasma and tissues of LPS-treated aged mice. These results emphasize the key role played by PAI-1 in aging-associated deterioration in this thrombosis model, and suggest that the hyperresponse of PAI-1 gene to LPS results from the enhanced LPS signaling and the subsequent inflammatory response in aged mice.