Background: ACAT1 catalyzes esterification of cellular free cholesterol, thereby converting macrophages to lipid-laden foam cells in atherosclerotic lesions and xanthoma. We reported that ACAT1 deficient hyperlipidemic mice developed extensive cutaneous xanthoma. It has been reported that cholesterol crystals triggered inflammasome activation, thereby contributing to the development of atherosclerosis. To test the hypothesis that NLRP3 inflammasome mediates the formation of xanthoma and/or atherosclerosis in mice lacking ACAT1, we compared the lesions in mice whose bone marrow-derived cells lack ACAT1, NLRP3 or both.
Methods:LDLR knockout (KO) mice were lethally radiated, and transplanted with bone marrow cells isolated from wild-type (W), ACAT1KO (A), NLRP3KO (N), or mice lacking both ACAT1 and NLRP3 (D), and were fed a high-cholesterol diet. Thickness of skins reflecting cutaneous xanthoma was evaluated by CT scan at the ankle joints of anterior paws. Aortic atherosclerotic lesions were evaluated by measuring the areas stained by Oil Red O of cross-sections at the aortic roots. Skin tissues were examined by HE staining. RNA was isolated from the tissues and used for qPCR.
Results: Thickness of skins was as follows: W,4.4±0.2; N,4.6±0.6; A,11.2±2.9*; D,5.4±0.5mm2, *p<0.05 vs W(n=5-9), indicating that aggravation of cutaneous xanthoma of mice lacking ACAT1 was reverted by NLRP3 deficiency. The skin lesions of A mice were characterized by accumulation of foam cells with cholesterol clefts. The expression of inflammatory genes, such as IL1β, TNFα, IL-6 and MCP-1, was 5-24 times higher in skin tissues of A mice compared with those of other mice. The atherosclerotic lesions were significantly larger in A mice, while they were smaller in N mice (W,25.0±8.2; N,15.6±8.6*; A,36.7±4.9*; D,27.4±10.2х104μm2, *p<0.05 vs W(n=11-13)). Staining with Oil Red O of the lesions of A and D mice were less intense, indicating that their lesions contained smaller amounts of cholesterol ester.
Conclusion: Elimination of ACAT1 in bone marrow-derived cells induced extensive cutaneous xanthoma mainly via NLRP3 inflammasome pathway, whereas involvement of NLRP3 inflammasome in the development of atherosclerosis was only limited compared with the cutaneous xanthoma.