Inflammation and oxidative stress are pathogenic mediators of many diseases, but therapeutic targets remain elusive. In the vasculature, abdominal aortic aneurysm (AAA) formation critically involves inflammaton and matrix degradation. Cyclophilin A (CyPA, encoded by Ppia) is highly expressed in vascular smooth muscle cells (VSMC), is secreted in response to reactive oxygen species (ROS), and promotes inflammation. Using the angiotensin II (AngII)-induced AAA model in Apoe−/− mice, we show that Apoe−/−Ppia−/− mice were completely protected from AngII–induced AAA formation, in contrast to Apoe−/−Ppia+/+ mice. Apoe−/−Ppia−/− mice showed decreased inflammatory cytokine expression, elastic lamina degradation, and aortic expansion. These features were not altered by reconstitution of bone marrow cells from Ppia+/+ mice. Mechanistic studies demonstrated that VSMC-derived intracellular and extracellular CyPA were required for ROS generation and matrix metalloproteinase-2 activation. These data define a novel role for CyPA in AAA formation and suggest CyPA is a new target for cardiovascular therapies.

Cyclophilin A promotes atherosclerosis in part by inducing reactive oxygen species and promoting endothelial cell apoptosis and macrophage recruitment into lesions.

Background— Oxidative stress, generated by excessive reactive oxygen species, promotes cardiovascular disease. Cyclophilin A (CyPA) is a 20-kDa chaperone protein secreted from vascular smooth muscle cells (VSMCs) in response to reactive oxygen species that stimulates VSMC proliferation and inflammatory cell migration in vitro; however, the role CyPA plays in vascular function in vivo remains unknown. Methods and Results— We tested the hypothesis that CyPA contributes to vascular remodeling by analyzing the response to complete carotid ligation in CyPA knockout mice, wild-type mice, and mice that overexpress CyPA in VSMC (VSMC-Tg). After carotid ligation, CyPA expression in vessels of wild-type mice increased dramatically and was significantly greater in VSMC-Tg mice. Reactive oxygen species–induced secretion of CyPA from mouse VSMCs correlated significantly with intracellular CyPA expression. Intimal and medial hyperplasia correlated significantly with CyPA expression after 2 weeks of carotid ligation, with marked decreases in CyPA knockout mice and increases in VSMC-Tg mice. Inflammatory cell migration into the intima was significantly reduced in CyPA knockout mice and increased in VSMC-Tg mice. Additionally, VSMC proliferation assessed by Ki67 + cells was significantly less in CyPA knockout mice and was increased in VSMC-Tg mice. The importance of CyPA for intimal and medial thickening was shown by strong correlations between CyPA expression and the number of both inflammatory cells and proliferating VSMCs in vivo and in vitro. Conclusions— In response to low flow, CyPA plays a crucial role in VSMC migration and proliferation, as well as inflammatory cell accumulation, thereby regulating flow-mediated vascular remodeling and intima formation.

Mitochondrial injury and dysfunction, a significant feature in metabolic syndrome, triggers endothelial cell dysfunction and cell death. Increasing evidence suggests that mitophagy, a process of autophagic turnover of damaged mitochondria, maintains mitochondrial integrity. PINK1 (phosphatase and tensin homolog (PTEN)-induced putative kinase 1) and Parkin signaling is a key pathway in mitophagy control. In this study, we examined whether this pathway could protect mitochondria under metabolic stress. We found that palmitic acid (PA) induced significant mitophagy and activated PINK1 and Parkin in endothelial cells. Knocking down PINK1 or Parkin reduced mitophagy, leading to impaired clearance of damaged mitochondria and intracellular accumulation of mitochondrial fragments. Furthermore, PINK1 and Parkin prevented PA-induced mitochondrial dysfunction, ROS production and apoptosis. Finally, we show that PINK1 and Parkin were up-regulated in vascular wall of obese mice and diabetic mice. Our study demonstrates that PINK1-Parkin pathway is activated in response to metabolic stress. Through induction of mitophagy, this pathway protects mitochondrial integrity and prevents metabolic stress-induced endothelial injury.

Rationale: Excessive myocardial fibrosis is the main pathological process in the development of cardiac remodeling and heart failure; therefore, it is important to prevent excessive myocardial fibrosis. We determined that microRNA-378 (miR-378) is cardiac-enriched and highly repressed during cardiac remodeling. We therefore proposed that miR-378 has a critical role in regulation of cardiac fibrosis, and examined the effects of miR-378 on cardiac fibrosis after mechanical stress.Methods: Mechanical stress was respectively imposed on mice through a transverse aortic constriction (TAC) procedure and on cardiac fibroblasts by stretching silicon dishes. A chemically modified miR-378 mimic (Agomir) or an inhibitor (Antagomir) was administrated to mice by intravenous injection and to cells by direct addition to the culture medium. MiR-378 knockout mouse was constructed. Cardiac fibroblasts were cultured in the conditioned media from the cardiomyocytes with either miR-378 depletion or treatment with sphingomyelinase inhibitor GW4869. Quantitative real-time polymerase chain reaction analysis of gene and miRNA expression, Western blot analysis, immunochemistry and electron microscopy were performed to elucidate the mechanisms.Results: Mechanical stress induced significant increases in fibrotic responses, including myocardial fibrosis, fibroblast hyperplasia, and protein and gene expression of collagen and matrix metalloproteinases (MMPs) both in vivo and in vitro. All these fibrotic responses were attenuated by treatment with a chemically modified miR-378 mimic (Agomir) but were exaggerated by treatment with an inhibitor (Antagomir). MiR-378 knockout mouse models exhibited aggravated cardiac fibrosis after TAC. Media from the cardiomyocytes with either miR-378 depletion or treatment with sphingomyelinase inhibitor GW4869 enhanced the fibrotic responses of stimulated cardiac fibroblasts, confirming that miR-378 inhibits fibrosis in an extracellular vesicles-dependent secretory manner. Mechanistically, the miR-378-induced anti-fibrotic effects manifested partially through the suppression of p38 MAP kinase phosphorylation by targeting MKK6 in cardiac fibroblasts.Conclusions: miR-378 is secreted from cardiomyocytes following mechanical stress and acts as an inhibitor of excessive cardiac fibrosis through a paracrine mechanism.