Cathepsin G Controls Arterial But Not Venular Myeloid Cell Recruitment

Abstract

BACKGROUND Therapeutic targeting of arterial leukocyte recruitment in the context of atherosclerosis has been disappointing in clinical studies. Reasons for such failures include the lack of knowledge of arterial-specific recruitment patterns. Here we establish the importance of the cathepsin G (CatG) in the context of arterial myeloid cell recruitment. METHODS Intravital microscopy of the carotid artery, the jugular vein, and cremasteric arterioles and venules in Apoe−/− and CatG-deficient mice (Apoe−/−Ctsg−/−) was used to study site-specific myeloid cell behavior after high-fat diet feeding or tumor necrosis factor stimulation. Atherosclerosis development was assessed in aortic root sections after 4 weeks of high-fat diet, whereas lung inflammation was assessed after inhalation of lipopolysaccharide. Endothelial deposition of CatG and CCL5 was quantified in whole-mount preparations using 2-photon and confocal microscopy. RESULTS Our observations elucidated a crucial role for CatG during arterial leukocyte adhesion, an effect not found during venular adhesion. Consequently, CatG deficiency attenuates atherosclerosis but not acute lung inflammation. Mechanistically, CatG is immobilized on arterial endothelium where it activates leukocytes to firmly adhere engaging integrin clustering, a process of crucial importance to achieve effective adherence under high-shear flow. Therapeutic neutralization of CatG specifically abrogated arterial leukocyte adhesion without affecting myeloid cell adhesion in the microcirculation. Repetitive application of CatG-neutralizing antibodies permitted inhibition of atherogenesis in mice. CONCLUSIONS Taken together, these findings present evidence of an arterial-specific recruitment pattern centered on CatG-instructed adhesion strengthening. The inhibition of this process could provide a novel strategy for treatment of arterial inflammation with limited side effects.

The Ins and Outs of Myeloid Cells in Atherosclerosis

“…These chemokines, such as CCL5, CXCL1, and CCL2, can be produced either by endothelial cells or by subendothelial macrophages, neutrophils, and monocytes [20, 21]. In addition, activated leukocytes release granular proteins, such as CRAMP, MPO, and cathepsin G, which can bind to the endothelium and attract leukocytes [22, 23]. …”

“…In agreement with this, also other studies have highlighted the importance of the platelet-neutrophil interaction in monocyte recruitment during the initial phase of atherosclerosis. Besides heteromer formation of platelet-derived CCL5 with neutrophil HNP-1, CCL5 also activates neutrophils to release cathepsin G, which binds to endothelium and fosters monocyte adhesion [23]. Hypercholesterolemia-induced neutrophilia is positively correlated with the extent of early lesion development, while neutropenic mice have fewer lesional inflammatory monocytes and macrophages [20].…”

Decision shaping neutrophil‐platelet interplay in inflammation: From physiology to intervention

“…In this context, a recent study has identified the importance of cathepsin G during arterial myeloid cell recruitment, a mechanism of minor relevance during microvascular myeloid cell adhesion. Accordingly, neutralization of cathepsin G in mouse models did not affect neutrophil extravasation during acute lung inflammation but instead specifically limited atherogenic leucocyte recruitment . Secondly, disruption of protein heteromers formed by neutrophil and platelet secretory products efficiently reduces myeloid cell adhesion.…”

“…First, in a sequential cooperativity, platelets activated by high‐shear forces secrete CCL5 which is deposited on arterial endothelial cells. Interestingly, the deposition of CCL5 predominantly at sites of high‐shear forces initiates a recruitment mechanism restricted to large arteries . CCL5 promotes the release of cathepsin G from neutrophils which in turn is laid onto arterial endothelial cells.…”

“…Immobilized cathepsin G evokes an active response in rolling monocytes that induces shear‐resistant adhesion strengthening in a process involving integrin clustering but independent of integrin conformation changes. Ultimately, this cascade of events promotes arterial‐specific monocyte adhesion . In a second mechanism involving a simultaneous cooperativity, neutrophil and platelet secretory products form protein heteromers to stimulate monocyte adhesion.…”