EFFECTS OF LEAD ON ACTIVITIES OF CATECHOLAMINE BIOSYNTHETIC ENZYMES AND ON TYROSINE HYDROXYLASE PROTEIN AND mRNA LEVELS

• Published in: Toxic substance mechanisms Vol. 16; no. 4; pp. 337 - 355
• Main Author: R. Renee Reams, Anthony M. Ndifor
• Format: Journal Article
• Language: English
• Published: Informa UK Ltd 01.10.1997
• ISSN: 1076-9188; 1091-7659
• DOI: 10.1080/107691897229522

Numerous clinical studies have documented a close association between lead (Pb) exposure and behavioral disorders, cognitive development, and impairment of learning processes. Although the neurotoxicity of Pb is well documented, the cellular and molecular mechanisms underlying Pb neurotoxicity remain unknown. The purpose of this study was twofold:Using pheochromocytoma cells (PC12) as a model cell line, we determined the effects of Pb on the activity of the three enzymes involved in catecholamine biosynthesis, tyrosine hydroxylase (TH), aromatic L-amino acid decarboxylase (AAAD), and dopamine-hydroxylase (D H), and then determined the effect of Pb on TH gene expression, the rate-limiting enzyme in catecholamine biosynthesis. PC12 cells were exposed to concentrations of Pb that ranged from 0.005 to 100 uM and we monitored the subsequent changes in the activities of TH, AAAD, and D H. Our results showed that Pb had no effect on the activity of AAAD nor on the activity of D H at Pb concentrations that ranged from 0.005 to 10 uM as compared to control conditions, but TH activity increased significantly at Pb concentrations ranging from 0.005 to 5 uM compared to controls. We then analyzed the effects of Pb on the induction of TH mRNA and on the TH protein levels using Northern and Western blot analysis, respectively. Western blot analysis revealed that 24-h treatment of PC12 cells with 50 uM Pb decreased both the water-soluble and the detergent-soluble TH protein fractions by 18% and 13%, respectively. Northern blot analysis of total RNA isolated from cells treated with 50 uM Pb for 24 h showed a 1.6-fold decrease in TH mRNA as compared with control conditions. The study demonstrates that Pb induces alterations in TH expression and optimal activity.