Disrupting LXRα phosphorylation promotes FoxM1 expression and modulates atherosclerosis by inducing macrophage proliferation

Abstract

Macrophages are key immune cells for the initiation and development of atherosclerotic lesions. However, the macrophage regulatory nodes that determine how lesions progress in response to dietary challenges are not fully understood. Liver X receptors (LXRs) are sterol-regulated transcription factors that play a central role in atherosclerosis by integrating cholesterol homeostasis and immunity. LXR pharmacological activation elicits a robust antiatherosclerotic transcriptional program in macrophages that can be affected by LXRα S196 phosphorylation in vitro. To investigate the impact of these transcriptional changes in atherosclerosis development, we have generated mice carrying a Ser-to-Ala mutation in myeloid cells in the LDL receptor (LDLR)-deficient atherosclerotic background (M-S196A). M-S196A mice fed a high-fat diet exhibit increased atherosclerotic plaque burden and lesions with smaller necrotic cores and thinner fibrous caps. These diet-induced phenotypic changes are consistent with a reprogramed macrophage transcriptome promoted by LXRα-S196A during atherosclerosis development. Remarkably, expression of several proliferation-promoting factors, including the protooncogene FoxM1 and its targets, is induced by LXRα-S196A. This is consistent with increased proliferation of plaque-resident cells in M-S196A mice. Moreover, disrupted LXRα phosphorylation increases expression of phagocytic molecules, resulting in increased apoptotic cell removal by macrophages, explaining the reduced necrotic cores. Finally, the macrophage transcriptome promoted by LXRα-S196A under dietary perturbation is markedly distinct from that revealed by LXR ligand activation, highlighting the singularity of this posttranslational modification. Overall, our findings demonstrate that LXRα phosphorylation at S196 is an important determinant of atherosclerotic plaque development through selective changes in gene transcription that affect multiple pathways.

Inhibiting LXRαPhosphorylation in Hematopoietic Cells Reduces Inflammation and Attenuates Atherosclerosis and Obesity

“…Our findings complement a recent elegant study by Gage et al that demonstrated a myeloid-specific knock-in of LXRa S196A resulted in greater macrophage proliferation via the LXRa S196A dependent upregulation of FOXM1, and increased atherosclerosis (17). The difference in the phenotypes between the myeloid-specific expression of S196A versus our bone marrow transplant model, in which the entire complement of hematopoietic cells express LXRa S196A suggest that LXRa S196A expression within additional bone marrow-derived cells restrain In summary, we showed that reducing LXRa pS196 in bone marrow cells of Ldlr -/mice reduced VAT weight and attenuated atherosclerosis.…”

“…C57BL/6 LXRa S196A mice were generated by Ozgene, and have been described (17,19 sucrose/saline. Organs weight was measured.…”

“…We and others have shown that LXRa's ability to activate transcription is modulated by phosphorylation at serine 196 (S196 in mouse LXRa and S198 in human LXRa), which significantly modifies its target gene repertoire (14)(15)(16)(17). Whereas LXRa pS196 promotes an inflammatory gene signature, unphosphorylated LXRa stimulates an anti-inflammatory gene expression profile.…”

LXR alters CD4+ T cell function through direct regulation of glycosphingolipid synthesis

“…These differences likely lead to cell-type specific responses to LXR activation. To identify potential T cell specific LXR targets we cross-referenced our list of DEGs with two publically available RNA-sequencing datasets from murine macrophages (mMφ) treated with GW 21,22 . Of the DEGs identified in T cells, 52% were similarly regulated in mMφ, and remarkably, 29% were uniquely regulated in the T cell dataset (Fig.…”

Aged insulin resistant macrophages reveal dysregulated cholesterol biosynthesis, a pro-inflammatory profile and reduced foam cell formation capacity

“…Macrophages are phagocytic leukocytes of the innate immune system 21 that play significant direct and indirect roles in the progression of diabetes and atherosclerosis through their ability to secrete a wide array of potent inflammatory cytokines, proliferate in situ 22 and take up modified LDL in the arterial wall 23 . While the effects of insulin resistance in metabolic tissues in atherosclerosis are well defined [4][5][6] , the effects of insulin resistance in macrophages are less clear and often conflicting [10][11][12][18][19][20] , which may be due to a lack of consistency with the models used and end points measured.…”