Objective: A mutant of apolipoproteinE (apoE), ApoE-Sendai (Arg145Pro), is one of the major causative factors of human lipoprotein glomerulopathy (LPG). An apoE-deficient mouse with introduced ApoE-Sendai gene (ApoE-Sendai mouse) developed a murine counterpart of LPG, whereas it was also reported that apoE-deficient mouse (apoE KO mouse) spontaneously developed LPG-like lesion regardless of introduction of ApoE-Sendai gene. In the present study, we differentiated renal lesions between these two models by detailed analyses of histology and lipoprotein profile, and clarified the role of apoE variants.
Method: ApoE-Sendai mice were induced by injection of adenovirus vectors. The kidneys showing LPG-like lesions in apoE-Sendai and apoE KO mice were histopathologically evaluated. Plasma lipids and lipoproteins of both mice were also examined.
Results: Histological alteration of the kidney in ApoE-Sendai mice was observed with light microscopy (in 40 out of 50 mice; mild 24, moderate 13, severe 3). Characteristic lesions were dilated vascular lumens mimicking lipoprotein thrombi in human LPG. Similar changes were found in hematoxylin-eosin stained sections of aged apoE KO mice. Meanwhile, periodic acid-Schiff, Azan Mallory, and Oil red O/Sudan III stained sections revealed that the dilated lumens of ApoE-Sendai mice mainly contained lipids and lipoproteins but those of aged apoE KO mice contained much other materials, e.g., proteins and fibrils. These findings were supported by electron micrographs, in which round-shaped droplets indicating lipoproteins were observed in ApoE-Sendai mice but not in aged apoE KO mice. In the kidney of apoE KO mice many anti-mouse CD68 Ab positive cells were detected. This contrasts with the result seen in ApoE-Sendai mice. The plasma lipoprotein compositions of the two types of mice were totally different.
Conclusion: It was certain that the kidneys of aged apoE KO mice showed morphological alteration, but the histological findings of glomerular lesions were different from those seen in the kidneys of ApoE-Sendai mice. According to the histological findings and plasma lipoprotein profile, ApoE-Sendai mice, not apoE KO mice, is a murine model for human LPG. This means that apoE variants are essential to LPG.