Abstract Body: Background: Macrophages are critical in inflammation resolution and tissue repair post-cardiac ischemic injury. They are also involved in cholesterol efflux at the subendothelial space to limit inflammation in atherosclerotic plaques. Augmented macrophage's inflammatory gene expression impairs healing and exacerbates cardiac dysfunction. Given the intricate involvement of macrophages in cardiac and vascular disorders, we became interested in investigating the understudied role of the Sigma-1 receptor (Sigmar1) in regulating macrophage phenotype and cholesterol metabolism.
Objective: The Objective of the study was to decipher Sigmar1’s role in macrophage phenotypes against inflammatory stimuli utilizing complementary biochemical and genetic approaches.
Methods and Results: We have utilized Sigmar1 overexpressed transgenic mice (Sigmar1 Tg) and littermate non-transgenic (Ntg) mice bone marrow-derived macrophages (BMDMs). We confirmed the overexpression of Sigmar1 in Tg mice BMDMs. Sigmar1 Tg BMDMs exhibited macrophage cell surface proteins CD11b and F4/80 expression similar to Ntg. Ntg and Sigmar1 Tg BMDMs were treated with LPS+IFN-γ and ox-LDL for 24 hours. Sigmar1 Tg BMDMs exhibited reduced activation of NF-κB p65 with a coinciding decrease in iNOS expression post-LPS+IFN-γ. Sigmar1 Tg BMDMs expressed significantly attenuated pro-inflammatory, i.e., IL-6, IL-1α, IL-1β, and leukocyte adhesion, i.e., LFA1, Cxcl10, CCR2, genes expression than Ntg BMDMs. Sigmar1 Tg macrophages exhibited significantly diminished neutral lipids than Ntg BMDMs post-ox-LDL. The reduced lipid accumulation in Sigmar1 Tg BMDMs coincided with reduced necroptotic, i.e., MLKL, gene expression than Ntg BMDMs. However, Sigmar1 Tg BMDMs exhibited no significant difference in Dil-ox-LDL uptake than Ntg BMDMs.
Conclusions: Our study reports on a Sigmar1-dependent novel effector mechanism to govern macrophage regulatory gene responses in inflammation and ox-LDL stress. Sustained Sigmar1 activation prevents augmentation in inflammatory transcriptomics, lipid overload, and cell death gene responses against atherogenic ox-LDL. Our findings pave the way for future preclinical and clinical studies to assess the role of macrophage Sigmar1 in cardiac injury models.