Leukocyte Cathepsin C Deficiency Attenuates Atherosclerosis in LDL Receptor Deficient Mice

Introduction: Cathepsin C (CatC) is a lysosomal cysteine protease important in intracellular protein degradation. Studies in CatC knock-out mice have revealed its central role in the activation of granule serine proteases in cytotoxic T lymphocytes, natural killer cells, mast cells, neutrophils and monocytes, all cell types relevant to atherosclerosis. Although such indirect data may point to an involvement of CatC in atherosclerosis, no functional studies have been reported to substantiate this notion. Methods: LDLr−/− mice transplanted with either wild type (WT) or CatC−/− bone marrow cells were after 6-week recovery, fed a high fat diet for 6 weeks and thereafter placed semiconstrictive collars bilaterally at the carotids to induce atherosclerotic lesions. Mice continued with fat diet for 7 more weeks. At sacrifice, mice were bled and organs, aortic arches and carotids were excised and analyzed. Results: Immunohistochemistry on staged human endarterectomy plaques showed higher expression of CatC in ruptured compared with early and stable lesions. LDLr−/− mice with leukocyte CatC deficiency had smaller carotid artery lesions (p=0.029) and reduced ORO stained lipid accumulation in the descending aorta (p=0.009). Immunohistochemical analysis of the lesions for CD3, CD45, macrophages (Mac3), elastin breaks and collagen did not reveal significant differences between the groups. Moreover unlike the WT controls, plaques of CatC−/− chimeras were almost completely devoid of necrotic core (p=0.002). FACS analysis revealed significantly increased CD4 + and more specifically CD4 + CD25 + FoxP3 + (Treg) counts in lymph nodes of CatC−/− chimeras. Of note, levels of CD8+ cells, B-cells (B220 + ) and those of CD11c low B220 high and B220 high Ly6C high plasmacytoid DC’s were significantly reduced in the CatC−/− chimeras, which may have positively contributed to its anti-atherogenic effect. Conclusions: Leukocyte CatC deficiency delays atherogenesis and blunts necrotic core formation. Combined with the strongly elevated expression of CatC in human ruptured plaques, this finding identifies CatC as proatherogenic effector protein in plaque progression and thus as a potential target for manifest atherosclerosis.