Abstract
Mercury (Hg) and lead (Pb) are toxic to the development and function of the central nervous system (CNS). Interleukin-6 (IL 6) produced by astroglia protects neurons from damage in many progressive degenerative disorders. IL-6 secretion is chaperoned by a 78 kD glucose-regulated protein (GRP78), which is an ER-chaperone protein involved in protein folding, assembly, and trafficking. We hypothesized that Pb and Hg could target GRP78 and thereby block IL-6 secretion from astroglia. In this report, we constructed an IL-6-EGFP chimera and transiently transfected rat C6 glioma cells and rat primary astroglia. IL-6-EGFP signal in transfected cultures exposed to Pb, Hg, or anti-oligos against GRP78 was detected with a bio-image fluorescence microscope. Data of the bio-image analysis showed that the retention of IL-6-EGFP in both astroglia and C6 cells transfected with IL-6-EGFP was at an undetectable level. However, the IL-6-EGFP signal in these cultures, while exposed to Pb (0-10 ưM) or Hg (0-10 ưM) for 24 hours, apparently increased, suggesting that Pb or Hg could block IL-6 secretion from astroglia. Furthermore, when these transfected cultures were exposed to anti-oligos against GRP78, as expected, the retention of IL-6-EGFP within the cultures increased. In order to quantify the increase of IL-6-EGFP retention, we used ELISA to detect IL-6 levels in the medium of non-transfected astroglia exposed to Pb (0-100 ưM) and Hg (0-10 ưM). Data showed that IL-6 levels in the medium decreased when the primary astrocyte cultures were exposed to Pb or Hg, suggesting that the increased retention results in part from a decrease in IL-6 secretion. We used an immunocytochemistry assay as an additional approach for quantifying IL-6 amounts of cells treated or not treated with metals. The immunocytochemistry data concurred with the ELISA findings. These data, together with our previous studies, suggest that Pb and Hg may target GRP78, thereby reducing the amount of IL-6 secreted from astroglia. The decrease in IL-6 secretion prevents this cytokine from doing its job of protecting and restoring neighboring neural tissue.
Pourrajabi, Nima Matthew (2003). Blockage of IL-6 secretion in glia by lead and mercury. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -2003 -THESIS -P68.