Subchronic cadmium treatment affects the abundance and arrangement of cytoskeletal proteins in rat renal proximal tubule cells

Disfunction of proximal tubules (PT) in cadmium (Cd) nephrotoxicity in mamm als results from the diminished functional capacity of brush-border membran e (BBM) caused by (a) direct inhibition of BBM transporters by Cd, (b) shor tening and loss of microvilli, and (c) loss of specific BBM transporters. T he loss of transporters may partially result from impaired intracellular ve sicle recycling due to loss or/and inhibition of vacuolar H+-ATPase in the PT cell organelles. Cytoskeleton plays an important role in vesicle-mediate d recycling and processing of BBM transporters in PT cells. Experiments in vitro have indicated that Cd may affect the state of polymerization of some cytoskeletal proteins. In this work we studied the in vivo effect of CdCl2 -treatment in rats (2 mg Cd/kg b. m., s.c., daily for 14 days) upon abundan ce and arrangement of actin filaments, actin-bundling protein villin, and m icrotubules (MT) in PT cells. Cd-treatment elicited a dramatic accumulation of Cd in the kidney cortex (200 mug/g tissue wet mass after 14 days) and a strongly increased abundance of metallothionein in PT cells. As revealed b y immunocytochemistry in tissue cryosections, the staining intensity of act in and villin in PT cells of Cd-treated rats was generally decreased, witho ut a marked change in their intracellular distribution, whereas MT became l argely irregular, diminished in most cells, and lost in many cells. However , the immunoblots revealed an increased content of villin and alpha -tubuli n in cortical tissue homogenates from Cd-treated rats, thus indicating an i mpaired bundling of actin and greatly depolymerized MT in cells intoxicated with Cd. The partial loss of apical actin and villin in PT cells of Cd-tre ated rats may reflect (or cause) shortening and loss of microvilli, whereas derangement and depolymerization of MT may contribute to the impairment of intracellular recycling of BBM proteins, and lead to the loss of BBM trans porters. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.