BACKGROUND AND PURPOSE The cysteine residue 674 (C674) of sarcoplasmic/endoplasmic reticulum Ca2+ ATPase 2 (SERCA2) is pivotal in maintaining SERCA2 activity. Substitution of C674 with serine leads to SERCA2 dysfunction and exacerbates atherosclerosis by inducing endoplasmic reticulum stress and inflammation in bone marrow-derived macrophages (BMDMs) and endothelial cells. This study aimed to explore whether SERCA2 dysfunction aggravates atherosclerosis by disrupting fatty acid metabolism and promoting the formation of macrophage foam cells. EXPERIMENTAL APPROACH Heterozygous SERCA2 C674S gene mutation knock-in (SKI) mice were utilized to simulate SERCA2 dysfunction under pathological conditions. Serum from SKI and their littermate wild-type mice were employed for metabolomic testing. The whole aorta and aortic root were isolated for histological analysis. BMDMs were used for protein expression, lipid uptake and accumulation analysis. KEY RESULTS In SKI BMDMs, SERCA2 dysfunction induced the expression of calcineurin (CaN), which promoted nuclear translocation of forkhead box O1 (FoxO1) and transcription of its downstream target fatty acid-binding protein 4 (FABP4), leading to increased fatty acid synthesis and foam cell formation. Inhibition of CaN/FoxO1/FABP4 pathway can correct aberrant lipid metabolism and inhibit the formation of foam cell in SKI BMDMs. Pharmacological interventions targeting FoxO1 or FABP4, or FABP4 partial deficiency significantly ameliorated atherosclerosis progression. CONCLUSIONS AND IMPLICATIONS SERCA2 dysfunction accelerates the progression of atherosclerotic lesions by stimulating CaN/FoxO1/FABP4 pathway, and thus promotes the formation of foam cell. Our finding highlights the importance of SERCA2 function in the context of atherosclerosis and open up a novel therapeutic strategy to combat lipid accumulation and atherosclerosis.

BACKGROUND AND PURPOSE The cysteine674 (C674) thiol of Sarcoplasmic/endoplasmic reticulum Ca2+ ATPase 2 (SERCA2) is easily and irreversibly oxidized under atherosclerotic conditions. However, contribution of the C674 thiol redox status in the development of atherosclerosis remains unclear. Our goal was to elucidate the possible mechanism involved. EXPERIMENTAL APPROACH Heterozygous SERCA2 C674S knock-in (SKI) mice in which half of the C674 was substituted by serine674 were used to mimic removal of the reactive C674 thiol which occurs under patholog-ical conditions. The whole aorta and aortic root were isolated for histological analysis. Bone marrow derived macrophages (BMDMs) and a cardiac endothelial cell line were used for intra-cellular Ca2+, macrophage adhesion and protein expression analysis. KEY RESULTS SKI mice developed more severe atherosclerotic plaque and macrophage accumulation. Cell cul-ture studies suggest the partial substitution of SERCA2 C674 increased intracellular calcium lev-els and ER stress in both BMDMs and ECs. The release of pro-inflammatory factors and macro-phage adhesion increased in SKI BMDMs. In normal ECs, the overexpression of C674S mutant induced endothelial inflammation and promoted macrophage recruitment. Additionally, 4-phenyl butyric acid (4-PBA), an ER stress inhibitor, prevented the increased atherosclerosis observed in SKI mice, and alleviated ER stress and inflammatory responses in BMDMs and ECs exposed to 4-PBA. CONCLUSIONS AND IMPLICATIONS The substitution of SERCA2 C674 thiol accelerates the development of atherosclerosis by in-ducing ER stress and inflammation. Our findings highlight the importance of SERCA2 C674 redox status in the context of atherosclerosis, and open up a novel therapeutic strategy to combat atherosclerosis.

Background and Purpose Inactivation of Cys674 (C674) in the sarcoplasmic/endoplasmic reticulum Ca2+ ATPase 2 (SERCA2) by causing the accumulation of intracellular Ca2+ to activate calcineurin-mediated nuclear factor of activated T-lymphocytes (NFAT)/NF-κB pathways, resulted in the phenotypic modulation of smooth muscle cells (SMCs) to accelerate angiotensin II-induced aortic aneurysm. Our goal was to investigate the mechanism involved. Experimental Approach We used heterozygous SERCA2 C674S knock-in (SKI) mice, where half of C674 was substituted by serine, to represent partial irreversible oxidation of C674. The aortas of SKI mice and their littermate wild-type mice were collected for RNA sequencing, cell culture, protein expression, luciferase activity and aortic aneurysm analysis. KEY RESULTS Inactivation of C674 inhibited the promoter activity and protein expression of PPARγ, which could be reversed by inhibitors of calcineurin or NF-κB. Overexpression of PPARγ2 inhibited the phenotypic modulation of SKI SMCs. Pioglitazone, the activator of PPARγ, blocked the activation of NFAT/NF-κB, inhibited SMC phenotypic modulation, and ameliorated angiotensin II-induced aortic aneurysms in SKI mice. CONCLUSIONS AND IMPLICATIONS The inactivation of SERCA2 C674 promotes the development of aortic aneurysm by disrupting the balance between PPARγ and NFAT/NF-κB. Our study highlights the importance of C674 redox status in regulating PPARγ to maintain aortic homeostasis.