Objectives Understanding the mechanisms of fibrosis development in the heart during hypertension is pivotal to find new therapies to counteract heart failure. In this study, we aimed to define the role of Cathepsin S (Cat S) in the development of cardiac inflammation and fibrosis induced by angiotensin II (Ang II).
Methods Cat S-/- and age-matched wild-type (WT) C57BL/6J mice were infused continuously with Ang II or saline for 7 days. Immunohistochemical staining and real-time PCR were performed for cardiac fibrosis and inflammation detection. LC3 level either in Ang II-infused hearts or in cultured macrophages were determined by Western Blot and transmission electron microscopy. NF-kB transcriptional activity of macrophages was measured after adenovirus infection with NF-kB luciferase reporter.
Results Cat S-/- mice showed severe cardiac fibrosis, including elevated expression of collagen I and α-SMA as compared with WT mice. Moreover, macrophage infiltration and expression of inflammatory cytokines (TNF-α, TGF-β1 and IL-1β) were significantly higher in Cat S-/- than WT hearts. These Ang II-induced effects in Cat S-/- mouse hearts was associated with abnormal accumulation of autophagosomes and reduced clearance of damaged mitochondria, which led to increased levels of ROS and activation of NF-kB in macrophages.
Conclusions Cat S is a lysosomal protease expressed in human atherosclerotic and aneurysmal tissues that may contribute to inflammatory diseases. Clearance of damaged mitochondria prevents ROS production and inflammation. Ang II infusion increased Cat S expression in macrophages, and Cat S knockout led to significant accumulation of autophagosomes, increased macrophage production of mitochondrial ROS and activation of NF-kB, which led to macrophage infiltration and expression of pro-inflammatory cytokines and cardiac fibrosis. We provide novel insights into the roles of Cat S in regulating cardiac fibrosis and the inflammatory response to Ang II in mouse by modulating mitophagy degradation.