Yen, F. T. | Search bioRxiv

bioRxiv2026

Role of the lipolysis stimulated lipoprotein receptor LSR in the regulation of macrophage lipid homeostasis and metabolic activity

In atherosclerosis, monocyte-derived macrophages in the subendothelial space of the arterial wall, become lipid-laden and pro-inflammatory. Macrophages depend on lipoprotein receptors to regulate lipid influx, thereby shaping macrophage metabolic state and potentially dictating their phenotype. The lipolysis stimulated lipoprotein receptor, LSR, contributes to lipid homeostasis and was detected by immunofluorescence in aortic atherosclerotic plaques from ApoE-/- mice and by immunoblot in macrophages. The aim was to determine the role of LSR in macrophage lipid handling by studying LSR expression and activity before (M0) or after polarization of Raw 264.7 cells using LPS/IFN{gamma} (M1) or IL-4/IL-13 (M2), respectively. LSR mRNA (0.48-fold, p < 0.001), protein levels (0.28-fold, p < 0.001) were significantly lower in M1 (iNOS+/MCP1+) as compared to M2 (CD206+/Arg1+) macrophages. LSR activity, measured as oleate-induced uptake of DiI-labelled LDL, was significantly lower in M1 as compared to M2 macrophages. siRNA-mediated LSR knockdown (87{+/-}4%, p < 0.01) in M0 cells led to significantly decreased expression of genes involved in lipid influx (LDL-R, LRP1) and transport (ABCA1), increased basal glycolysis and decreased glycolytic reserve, but without changes in inflammatory markers. Raw 264.7 macrophages transformation into foam cells by 24h incubation with oxidized LDL also led to reduced LSR activity and expression. We propose that the lower LSR expression and activity observed in M1 and foam cell macrophages contribute to reduced lipid influx and increased glycolytic state that is associated with pro-inflammatory M1 phenotype. This provides new insight towards understanding how these immune cells depend on lipoprotein receptors regulating their metabolic uptake.

cell biology↗

bioRxiv2024

CRE mice exhibit hyperactive and impulsive behavior affecting their learning and retention performances

CRE recombinase is a protein that recognizes and mediates site-specific recombination between loxP site sequences. The Cre/loxP recombination system has become a useful tool for genetic manipulation. Spatial regulation of recombination can be achieved by using cell type-specific promoters that drive expression of CRE in the tissue of interest. The temporal regulation can be obtained with CreER recombinase, which consists of Cre fused to mutated hormone-binding domain of the estrogen receptor (ER). In the more improved versions of the construct, the CRE-mediated gene regulation can be controlled both spatially and temporally, by combining tissue-specific expression of a CreER recombinase with its tamoxifen-dependent activity. We recently generated and characterized an astrocyte specific mutant of the lipolysis-stimulated lipoprotein receptor lsr gene by crossing Glast ERT2 mice with floxed lsr mice (El Hajj et al., 2022). During the behavioral analysis of generated mice, we identified specific hyperactive traits in the Glast ERT2 mice (CRE mice) that prevented them from being used as a control group. Here we further assessed the hyperactive trait of those CRE mice using a battery of behavioral tests. We showed that CRE mice exhibited hyperactive behavior combined with attention-deficit, sleep disturbance and impulsivity that affect their learning and memorization performances. These mice may therefore serve as a model to study attention deficit / hyperactivity disorder. Our work also pointed out the need for proper behavioral analysis of control groups in transgenic animal generation to avoid misinterpretation and misattribution of behavioral traits.

animal behavior and cognition↗