Apolipoproteins and lipoprotein receptors in glomeruli in human kidney diseases

Abstract

This study offers morphological evidence of the involvement of lipid abnormalities in human glomerular injury. Renal biopsy tissues from patients with several types of glomerular diseases were immunocytochemically examined using antibodies to apolipoproteins (apo) A-I, B-100, and E, and antibodies to low density lipoprotein (LDL) receptors and scavenger receptors. Immunofluorescent staining showed the predominant deposition of apo B and apo E in the mesangial area in mesangial proliferative types of glomerulonephritis; the distribution and staining intensity of these apolipoproteins correlated with the grade of mesangial proliferation and proteinuria, but were independent of plasma lipid levels. Immunoelectron microscopy revealed that apo B and apo E were distributed in droplets within glomerular epithelial and mesangial cells or in a granular pattern in the expanded mesangial matrix. Apo A-I was mainly localized in the visceral epithelial cells of normal human kidneys. Staining for apo A-I was increased in the glomerular epithelial cells of nephritic kidneys, compared to the pattern in normal human kidneys, and was decreased in the sclerosed areas of glomeruli. An immunogold technique revealed the expression of LDL receptors on the surface membranes of glomerular mesangial and epithelial cells. Dual immunofluorescent staining showed that apo B and LDL receptors were occasionally co-localized in nephritic glomeruli. Scavenger receptor was detected on the plasma membranes of mesangial and visceral epithelial cells. The glomerular expression of scavenger receptor was increased in glomeruli with marked mesangial proliferation. In addition, the expression of this receptor was intense in monocytes/macrophages occasionally infiltrating the glomeruli. Our present findings indicate that in human nephritic kidneys, glomerular epithelial and mesangial cells express both LDL receptors and scavenger receptors. The accumulation of apolipoproteins, whether receptor-mediated or mediated by other mechanisms, can occur independently of plasma lipid levels, and may be associated with mesangial expansion and proteinuria.