Apolipoprotein J/clusterin prevents a progressive glomerulopathy of aging

Abstract

Apoliprotein J (apoJ)/clusterin has attracted considerable interest based on its inducibility in multiple injury processes and accumulation at sites of remodeling, regression, and degeneration. We therefore sought to investigate apoJ/clusterin's role in kidney aging, as this may reveal the accumulated effects of diminished protection. Aging mice deficient in apoJ/clusterin developed a progressive glomerulopathy characterized by the deposition of immune complexes in the mesangium. Up to 75% of glomeruli in apoJ/clusterin-deficient mice exhibited moderate to severe mesangial lesions by 21 months of age. Wild-type and hemizygous mice exhibited little or no glomerular pathology. In the apoJ/clusterin-deficient mice, immune complexes of immunoglobulin G (IgG), IgM, IgA, and in some cases C1q, C3, and C9 were detectable as early as 4 weeks of age. Electron microscopy revealed the accumulation of electron-dense material in the mesangial matrix and age-dependent formation of intramesangial tubulo-fibrillary structures. Even the most extensively damaged glomeruli showed no evidence of inflammation or necrosis. In young apoJ/clusterin-deficient animals, the development of immune complex lesions was accelerated by unilateral nephrectomy-induced hyperfiltration. Injected immune complexes localized to the mesangium of apoJ/clusterin-deficient but not wild-type mice. These results establish a protective role of apoJ/clusterin against chronic glomerular kidney disease and support the hypothesis that apoJ/clusterin modifies immune complex metabolism and disposal.

Figures

FIG. 1.

apoJ/clusterin-deficient mice develop glomerulopathy. Representative glomeruli are shown from a single kidney of a 21-month-old mouse to illustrate the range of affected structures and the basis of a glomerular lesion scoring system. The different panels represent scores of 0 to 4, based on the extent of expansion of the mesangium by hypocellular material, where 0 = normal, 1 = change affecting less than 25% of the glomerulus, 2 = change affecting 25 to 50%, 3 = change affecting 50 to 75%, and 4 = changes affecting greater than 75%. Magnification, ×400.

FIG. 2.

Accumulation of damaged glomeruli in apoJ/clusterin-deficient mice. (A) Summary of average glomerular scores of wild-type and apoJ/clusterin-deficient animals. (B) Distribution of scores for 100 scored glomeruli in each wild-type and apoJ/clusterin-deficient mouse. Although all mutant mice developed glomerular lesions, there was significant heterogeneity in the extent of mesangial deposition across each kidney.

FIG. 3.

Immune complexes are deposited in glomeruli of 21-month-old apoJ/clusterin-deficient mice but not hemizygous mice. Tissue sections from hemizygous (A to C, G to I) and apoJ/clusterin-deficient mice (D to F, J to L) were analyzed with antibodies specific for IgG (A and D), IgM (B and E), IgA (C and F), C1q (G and J), C3 (H and K), and C9 (I and L). Positive staining in a mesangial pattern was seen for the apoJ/clusterin-deficient mice for all markers, with particularly strong accumulation of IgM, IgA, and C9. Magnification, ×360.

FIG. 4.

Glomerular lesions contain deposits of collagen and immune complexes. The composition of the lesions in the glomeruli of wild-type (A) and apoJ/clusterin-deficient (B and C) mice was examined by using the Masson-Trichrome stain. Blue staining (wide arrows) suggests the accumulation of collagen deposits in the glomeruli, whereas fuchsin staining (narrow arrows) indicates the deposition of immune complexes. Magnification, ×360.

FIG. 5.

Electron-dense tubulo-fibrillar aggregates in the mesangium of apoJ/clusterin-deficient glomeruli. Sections from wild-type (A) and mutant (B) mice were silver stained. Mutant mice exhibited mesangial expansion and deposits of electron-dense material. Magnification, × 2,828. (C) High-power view of the mesangial deposits from mutant mice, demonstrating the tubulo-fibrillary structures. Magnification, ×18,800. The box indicates a region where the tubulo-fibrillary structures are evident.

FIG. 6.

apoJ/clusterin protects glomeruli from unilateral nephrectomy-accelerated accumulation of immune complex components in the mesangium. Tissue sections from 6-month-old unilaterally nephrectomized wild-type (A to C, G to I) and apoJ/clusterin-deficient mice (D to F, J to L) were analyzed with specific antibodies to IgG (A and D), IgM (B and E), IgA (C and F), C1q (G and J), C3 (H and K), and C9 (I and L). Mesangial pattern staining was detected only in the uninephrectomized apoJ/clusterin-deficient mice. Note also that C9 did not accumulate with either genotype. Magnification, ×400.

FIG. 7.

Glomeruli of uninephrectomized apoJ/clusterin-deficient mice developed two types of mesangial deposits. (A) Large lucent deposits, as indicated by the arrow, are associated with mesangial cells. (B) Electron-dense deposits (arrows) accumulated in the mesangial matrix or beneath the perimesangial basement membrane. Magnification, ×2,850. (C) The inset shows that the deposits had minimal fibrillar organization. Magnification, ×19,000.

FIG. 8.

apoJ/clusterin protects the kidney from deposition of preassembled immunoglobulin complexes in the glomerulus. Phase contrast microscopy (A and C) shows comparable glomerular fields, which upon indirect fluorescence (B and D) exhibit strongly different distributions of Texas Red-labeled sheep anti-goat IgG complexes. Wild-type animals do not show any glomerular accumulation, whereas apoJ/clusterin-deficient mice do, in a patchy mesangial distribution.