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Different expression of modified low density lipoprotein receptors in rabbit peritoneal macrophages and Kupffer cells
1Department of Geriatric Medicine, Faculty of Medicine, Kyoto University, Japan.
Abstract:
We have previously reported that mouse peritoneal macrophages have three types of modified low density lipoprotein (LDL) receptors. One is specific for acetylated LDL (Ac-LDL), the second is for oxidized LDL (Ox-LDL), and the third recognizes both (Arai, H. et al. (1989) Biochem. Biophys. Res. Commun. 159, 1375-1382). In the current study, the characteristics of modified LDL receptors in rabbit peritoneal macrophages and Kupffer cells from rabbits were investigated. Cross-competition studies of the degradation assay between Ox-LDL and Ac-LDL in rabbit peritoneal macrophages showed that the degradation of 125I-labeled Ox-LDL was almost completely inhibited by an excess amount of unlabeled Ac-LDL. On the other hand, an excess amount of unlabeled Ox-LDL suppressed 125I-labeled Ac-LDL degradation only partially. In contrast, in Kupffer cells an excess amount of unlabeled Ox-LDL inhibited the degradation of 125I-labeled Ac-LDL almost completely, whereas the degradation of 125I-labeled Ox-LDL was inhibited only partially by Ac-LDL. Scatchard analysis of binding assay showed that rabbit peritoneal macrophages have a single class of receptor for Ox-LDL, which binds maximally 0.31 microgram/mg cellular protein (Bmax) with an apparent dissociation constant (Kd) of 19.3 micrograms/ml, and two classes of receptors for Ac-LDL; one with high affinity (Bmax 0.025 microgram/mg cellular protein, Kd 0.040 micrograms/ml) and the other with low affinity (Bmax 0.08 microgram/mg cellular protein, Kd 11.31 micrograms/ml). On the other hand, Kupffer cells have two classes for Ox-LDL; one is a high affinity receptor (Bmax 0.53 microgram/mg cellular protein, Kd 0.99 microgram/ml) and the other is a low affinity receptor (Bmax 3.71 micrograms/mg cellular protein, Kd 16.2 micrograms/ml) and a single class for Ac-LDL (Bmax 0.60 microgram/mg cellular protein, Kd 7.24 micrograms/ml). These results indicate that rabbit peritoneal macrophages have two kinds of modified LDL receptors; one is specific for Ac-LDL, and the other recognizes both Ox-LDL and Ac-LDL.
Insights
Rabbit macrophages exhibit distinct modified low-density lipoprotein (LDL) receptors. One receptor is specific for acetylated LDL (Ac-LDL), while another recognizes both Ac-LDL and oxidized LDL (Ox-LDL).
Area of Science:
- Cell Biology
- Biochemistry
- Immunology
Background:
- Previous studies identified three modified low-density lipoprotein (LDL) receptors in mouse peritoneal macrophages.
- These receptors include specific ones for acetylated LDL (Ac-LDL) and oxidized LDL (Ox-LDL), and one recognizing both.
- The current study investigates these modified LDL receptors in rabbit macrophages.
Purpose of the Study:
- To characterize the modified LDL receptors in rabbit peritoneal macrophages and Kupffer cells.
- To compare the binding and degradation characteristics of Ac-LDL and Ox-LDL in these cells.
- To elucidate the specific types and affinities of modified LDL receptors present.
Main Methods:
- Utilized cross-competition studies to assess the degradation of 125I-labeled Ox-LDL and Ac-LDL.
- Employed Scatchard analysis to determine the binding characteristics (affinity and capacity) of LDL receptors.
- Investigated both rabbit peritoneal macrophages and Kupffer cells.
Main Results:
- Rabbit peritoneal macrophages showed that Ac-LDL significantly inhibited Ox-LDL degradation, while Ox-LDL only partially inhibited Ac-LDL degradation.
- Kupffer cells demonstrated the opposite pattern, with Ox-LDL strongly inhibiting Ac-LDL degradation, and Ac-LDL only partially inhibiting Ox-LDL degradation.
- Scatchard analysis revealed specific receptor profiles for Ox-LDL and Ac-LDL in both cell types, indicating distinct receptor populations and affinities.
Conclusions:
- Rabbit peritoneal macrophages possess two types of modified LDL receptors: one specific for Ac-LDL and another that binds both Ac-LDL and Ox-LDL.
- Kupffer cells exhibit a different receptor profile, with distinct high- and low-affinity receptors for Ox-LDL and a single class for Ac-LDL.
- These findings highlight cell-specific differences in modified LDL receptor expression and function in rabbits.