Clusterin promotes the aggregation and adhesion of renal porcine epithelial cells.

The function of clusterin, a heterodimeric glycoprotein markedly induced in renal and other organ injuries, is unclear. Since renal injury is accompanied by alterations in cell attachment, it is possible that clusterin functions to promote cell-cell and cell-substratum interactions. In this study, a single cell suspension of renal epithelial (LLC-PK1) cells was treated with purified human clusterin, resulting in time- and dose-dependent cell aggregation. Electron microscopy of the cell aggregates demonstrated cell junction and lumen formation. To determine the effect of clusterin on cell adhesion, tissue culture plates were coated with clusterin, fibronectin, PBS, or albumin. Clusterin and fibronectin promoted cell adhesion to the same extent. The adhesion to clusterin was dose dependent and specific, as a monoclonal antibody against clusterin inhibited cell adhesion to clusterin but not fibronectin. Perterbations of the cytoskeleton may underlie the alterations in cell attachment which occur in renal injury. Induction of clusterin mRNA was seen after disruption of both microtubules and microfilaments and after inhibition of cell-substratum interactions. In conclusion, clusterin is a potent renal epithelial cell aggregation and adhesion molecule. We speculate that clusterin functions to promote cell-cell and cell-substratum interactions which are perturbed in the setting of renal injury, thereby preserving the integrity of the renal epithelial barrier.

Induction of clusterin in acute and chronic oxidative renal disease in the rat and its dissociation from cell injury.

BACKGROUND: Clusterin is a glycoprotein incriminated in diverse biologic processes including complement regulation, cell death, and tissue remodelling. Induction of clusterin occurs in renal and other tissue injuries. EXPERIMENTAL DESIGN: The purpose of this study was to determine the effect of prooxidant states, one acute (glycerol-induced acute renal failure) and the other chronic (vitamin E and selenium deficiency) on renal clusterin expression, and to attempt to delineate the signals which in these in vivo models can elicit expression of clusterin in vitro. RESULTS: In glycerol-induced acute renal failure, a model of rhabdomyolysis, clusterin mRNA was markedly increased 24 hours after injection of glycerol (control 97 +/- 21 versus glycerol 3644 +/- 134 optical density units; p < 0.001). Immunohistochemical clusterin was also increased in glycerol-treated rats with tubules in both cortex and medulla staining for clusterin. In vitamin E and selenium deficiency, clusterin mRNA was increased 9 weeks after initiation of the deficient diet (control 97 +/- 13 versus deficient 1137 +/- 403 optical density units; p < 0.04) as were the number of tubules staining for clusterin. Since renal injury is instigated in the glycerol model by muscle damage, we tested the effect of muscle extract on clusterin expression in vitro. A homogenate of skeletal muscle induced clusterin mRNA and this induction was not associated with disruption of cell membranes and was not inhibited by cycloheximide treatment, but was blocked by actinomycin D. Since increased generation of hydrogen peroxide is a pivotal biochemical lesion in both in vivo models, we tested the effect of peroxide to induce clusterin in vitro; no such induction occurred. CONCLUSIONS: Renal tubular clusterin expression was increased in both acute glycerol-induced renal failure and chronic vitamin E and selenium deficiency, two in vivo models of oxidant injury to the kidney. In vitro induction of clusterin can occur and can be dissociated from cell injury.

Expression of clusterin in human renal diseases.

Clusterin, a glycoprotein with potent cohesive properties, is induced in a wide variety of acute and chronic experimental renal diseases. The purpose of this study was to examine clusterin expression in human renal diseases. Clusterin immunostaining was examined in nephrectomy specimens from patients with autosomal-dominant polycystic kidney disease (N = 5), autosomal-recessive polycystic kidney disease (N = 3), multilocular cyst of the kidney (N = 2), renal hypoplasia/dysplasia (N = 7), Wilms' tumor (nephroblastoma) (N = 6), renal cell carcinoma (N = 9), and acute and/or chronic renal transplant rejection (N = 15). No clusterin staining was detected in normal renal tissue distant from renal cell carcinomas. Increased expression of clusterin was found in epithelial cells lining cysts in all of the cystic disorders studied. Clusterin expression was found in some immature tubules in hypoplastic/dysplastic kidneys and in tubules of rejected renal allografts, but was not a prominent finding in renal neoplasms, although some renal cell carcinomas expressed clusterin in a focal manner. Common features of clusterin induction included exclusively epithelial production of clusterin in cysts, immature nephrons, and injured tubules, heterogeneity of clusterin expression, with only some tubules and/or cysts in a given area staining for clusterin, and uniform clusterin staining of epithelial cells in a given tubule or cyst in most cases. Based on its cohesive properties, we speculate clusterin functions to maintain cell-cell and cell-substratum interactions which become perturbed in the setting of renal injury and cystic diseases.