Lead Exposure Promotes Translocation of Protein Kinase C Activities in Rat Choroid Plexusin Vitro,but Notin Vivo

Abstract

Lead (Pb) exposure reportedly modulates PKC activity in brain endothelial preparations, which may underlie Pb-induced damage at the blood-brain barrier. Our previous work indicates that Pb accumulates in the choroid plexus and causes dysfunction of this blood-cerebrospinal fluid (CSF) barrier. The present studies were undertaken to test the hypothesis that Pb in the choroid plexus may alter PKC activity and thus affect the functions of the blood-CSF barrier. When choroidal epithelial cells in a primary culture were exposed to Pb (10 μM in culture medium), the membrane-bound PKC activity increased by 5.2-fold, while the cytosolic PKC activities decreased, an indication of the induction of PKC translocation by Pb. The effect of Pb on cellular PKC was concentration dependent in the range of 0.1-10 μM. We further evaluated PKC activity of the choroid plexus in rats chronically exposed to Pb in the drinking water (control, 50 or 250 μg Pb/ml) for 30, 60, or 90 days. Two-way analysis of variance revealed a significant age-related decline of PKC activities in both cytosol and membrane of the choroid plexus. However, Pb treatment did not alter plexus PKC activities. In addition, we found that short-term, acute Pb exposure in rats did not significantly change PKC activities nor did it affect the expression of PKC isoenzymes in the choroid plexus. Our results suggest that Pb exposure may promote the translocation of PKC from cytosol to membrane in rat blood-CSF barrier in vitro, but not in vivo.The mammalian blood-cerebrospinal fluid (CSF) barrier resides primarily in the choroid plexus and plays a pivotal role in regulating the chemical stability of the central nervous system (Johanson, 1995;Davson and Segal, 1996). Toxic metals, especially lead (Pb), have been known to accumulate in the choroid plexus (Friedheim et al., 1983;Manton et al., 1984;O'Tuama et al., 1976;Zheng et al., 1991;Zheng, 1996). Our recent work revealed that accumulation of Pb in the choroid plexus is associated with a significant reduction in CSF concentrations of transthyretin (TTR), a major thyroxine-carrying protein in brain (Zheng et al., 1996). We postulated that Pb accumulation in the choroid plexus might also alter key enzymes that are apparently targeted by cellular Pb toxicity, such as the protein kinase C (PKC).

Early lead exposure increases the leakage of the blood-cerebrospinal fluid barrier, in vitro

“…Possible mechanisms include the activation of protein kinase C (PKC) by Pb, which subsequently increases the transcription of immediate early response genes (c-fos and c-jun), leading to an overexpression of vascular endothelial growth factor (VEGF) and dysfunction of the BBB. 38,39,45,46 Activation of PKC by Pb has also been demonstrated in the choroidal epithelial cells, 47 although the relationship between PKC activation and tightness of the BCB has not been established. Our data clearly demonstrate a selective inhibition by Pb of the expression of claudin-1 in choroidal epithelial cells, as supported by both RT-PCR on claudin-1 mRNA expression and Western blot on the protein level.…”

Cdc42 Regulates Arsenic-induced NADPH Oxidase Activation and Cell Migration through Actin Filament Reorganization

“…Superoxide (20). Briefly, the cells were sonicated for 4 s and then centrifuged at 100,000 ϫ g for 1 h to pellet membrane fraction in the homogenization buffer (20 mM Tris-HCl, 10 mM EGTA, 2 mM EDTA, 2 mM dithiothreitol, and protease inhibitors).…”

Distribution of Lead and Transthyretin in Human Eyes

“…Our earlier studies on the choroid plexus, which produces and secretes TTR to the CNS, indicate that sequestration of Pb in this blood-CSF barrier activates protein kinase C and reduces TTR levels in the CSF. 4,5,14 Because the RPE is a unique site of TTR synthesis in the eye, 3,6 it appears plausible that a high accumulation of Pb may influence TTR production by the retina. A disturbance in TTR homeostasis in the eyes could then contribute to the Pb-induced optical dysfunction, because TTR has been suggested as having a role in the intraocular cycling of the retinol as well as thyroxin.…”