Abstract
The inflammatory pathways that drive the development of intimal hyperplasia (IH) following arterial injury are not fully understood. We hypothesized that the lysosomal cysteine protease cathepsin L activates processes leading to IH after arterial injury. Using a mouse model of wire-induced carotid artery injury we showed that cathepsin L activity peaks at day 7 and remains elevated to 28 days. The genetic deletion of cathepsin L prevented IH and monocyte recruitment in the carotid wall. The injury-induced increases in cathepsin L mRNA and activity were mitigated in mice with myeloid-specific deletion of toll like receptor 4 (TLR4) or myeloid differentiation primary response gene 88 (MyD88). We further discovered that a HIV-protease inhibitor saquinavir (SQV), which is known to block recombinant mouse cathepsin L activity in vitro, prevented IH after arterial injury. SQV also suppressed LPS (TLR4 agonist) induced monocyte adhesion to endothelial monolayers. These findings establish cathepsin L as a critical regulator of the inflammation that leads to IH and that the TLR4- MyD88 pathway in myeloid lineages regulates cathepsin L expression in the vessel wall following wire injury. The FDA approved drug, SQV blocks IH though mechanisms that may include the suppression of cathepsin L.