Clusterin protects against oxidative stress in vitro through aggregative and nonaggregative properties.

Perturbations of cell interactions, an early event in acute renal injury, have important pathophysiologic consequences. We hypothesized that promotion of cell interactions protects cells from injury. To test this hypothesis, a single cell suspension of LLC-PK1 cells (porcine proximal tubular cell line) treated with albumin (control) was compared to cells aggregated with fibrinogen or purified human clusterin (aggregation graded 0 to 4). Following aggregation, the cells were injured with 1.5 mM hydrogen peroxide (H2O2) for three hours. Cell aggregation induced by clusterin but not fibrinogen protected against oxidant injury by H2O2. Complete abrogation of cytotoxicity occurred at a clusterin concentration of 2.5 micrograms/ml, which resulted in an aggregation score of 1. In the absence of aggregation, clusterin at concentrations of 20 and 50 micrograms/ml, but not lower doses, partially protected against injury induced by H2O2. Cell aggregation induced by both clusterin and fibrinogen partially protected against endogenously generated oxidant stress induced by incubating LLC-PK1 cells with aminotriazole and 1-chloro-2,4-dinitrobenzene (CDNB). In conclusion, clusterin protects against models of oxidant stress in vitro, whether generated by exogenously administered hydrogen peroxide, or from endogenously produced peroxide, and such protective effects can accrue from aggregative and nonaggregative properties of clusterin.

Induction of clusterin in tubules of nephrotic rats.

Clusterin is a glycoprotein induced after renal tubular cell injury. The purpose of this study was to examine the expression of clusterin in a disease model characterized early in its course by predominant glomerular injury. Male Wistar rats (weighing 251 +/- 16 g) were treated with puromycin aminonucleoside (PAN: 15 mg/100 g body wt, subcutaneously; n = 7) or vehicle (control; n = 8). The kidneys were harvested 6 d after treatment, when rats were nephrotic. Clusterin mRNA was markedly induced in the kidneys of nephrotic rats (8.5-fold versus control). Immunohistochemistry studies demonstrated clusterin primarily in tubules in the cortex and medulla. Many of the tubules staining for clusterin were dilated but had no other differentiating morphologic features. Increased numbers of proliferating tubular cells were seen at 6 d, but there was no correlation between these cells and clusterin staining. In contrast to the extent and pattern of clusterin staining, vimentin was seen in only sporadic, dilated tubules, in addition to its expected glomerular localization. An increase in clusterin mRNA was not seen 1, 2, or 4 d after PAN injection. In conclusion, tubular epithelial cell induction of clusterin occurs in the kidneys of nephrotic rats. The appearance of clusterin precedes the development of tubulointerstitial disease and may be a response to the proteinuria.

Morphological studies on the origin of adult-type Leydig cells in rat testis.

The differentiation of adult-type Leydig cells (ATLC) in rat testis was studied with the help of electron microscopy and a combined technique of autoradiography and enzymehistochemistry. Male Wistar rats on each alternative day from postnatal day (pnd) 9 to 25 were perfused in situ, and the testicular sections were observed by electron microscopy. The cytoplasm of the ATLC contained smooth endoplasmic reticulum, mitochondria, a few small lipid droplets and a large well developed Golgi apparatus. In addition to typical fibroblasts/fibrocytes, a group of fibroblast-like cells was observed in the peritubular and perivascular spaces of the interstitial tissue. These cells, containing smooth endoplasmic reticulum and a large number of mitochondria with tubular-type cristae, were named as intermediate-type cells. In the autoradiographic experiments the 3-H-thymidine and 14-C-thymidine uptake behaviour of fetal-type Leydig cells, ATLC, intermediate-type cells and myoid cells was studied from 1 till 25 pnd. The intermediate-type cell, observed predominantly between pnd 9 to 21, showed the highest labelling index. The absolute number of fibroblasts/fibrocytes showed a peak on pnd 13 and decreased gradually with age. The duration of DNA synthesis phase ranged for interstitial fibroblasts: 7.9 h, for intermediate-type cell 10.4 h, for ATLC 17.4 h. The results lead to the conclusion that ATLC most probably originate to a large extent from the peritubular and to a lesser extent from perivascular fibroblast-like cells of the interstitial tissue.

The role of clusterin in tissue injury.

Clusterin is a widely distributed glycoprotein with a wide range of biologic properties. A prominent and defining feature of clusterin is its marked induction in such disease states as glomerulonephritis, cystic renal disease, renal tubular injury, neurodegenerative conditions, atherosclerosis, and myocardial infarction. The expression of clusterin in these states is intriguing given the apparent incongruity of the conditions listed, the variety of stimuli eliciting such expression, and the multiple proposed roles once induced. This review will outline the conditions associated with clusterin induction and speculate on its role in disease.