Regulation of chemokine mRNA expression in a rat model of vanadium-inducedpulmonary inflammation

Environmental and occupational exposure to vanadium dusts results in toxic effects mainly confined to the respiratory system. Using a rat model of acu te lung inflammation induced by intratracheal instillation of sodium metava nadate (NaVO3) at the dose of 200 mug V/kg, we investigated the relationshi p between the cytologic characterization of pulmonary inflammation and the expression of chemokine mRNA. Significant polymorphonuclear leukocyte (PMN) influx (P < 0.01) into the lung was noted 4 h after NaVO3 instillation, wh ereas alveolar macrophages (Ah ls) in bronchoalveolar lavage (BAL) cells ap peared to decrease significantly. In contrast, neither PMNs nor AMs changed substantially 1 h after NaVO3 instillation. By Northern analysis, macropha ge inflammatory protein (MIP)-2 mRNA in BAL cells increased markedly I h af ter NaVO3 instillation and reduced a little bit at 4 h, whereas MIP-1<alpha > mRNA in BAL cells was expressed relatively high 1 h after NaVO3 instillat ion, although a basal expression was detected in control group, and returne d rapidly nearly to control level at 4 h. Since MIP-2 is a potent PMN chemo attractant and MIP-1 alpha is a potent macrophage/monocyte chemoattractant has been well known. The facts that PMN influx was preceded by increased MI P-2 mRNA expression, suggesting that MIP-2 is involved in the development o f NaVO3-induced pulmonary inflammation, whereas increased MIP-1 alpha mRNA expression was followed by decreased AMs in BAL cells, suggesting AMs might be activated by MIP-1 alpha, adherent to the lining surface of the airways and then resistant to be washed out. To delineate the mechanisms of transc riptional activation, we recently cloned the 5'-flanking region of the MIP- 2 gene. The promotor region contains consensus binding sites for transcript ion factor nuclear factor KB (NF-kappaB) and activator protein- 1 (AP-1). U sing electrophoretic mobility shift assay, increased nuclear NF-kappaB, not AP-1, binding activity was detected 1 h after NaVO3 instillation, which co rrelated with the induction of MIP-2 mRNA. p6.5 (Rel A) and p50 protein app ears to be involved in MIP-2 NF-kappaB binding. Taken together, our studies suggest that MIP-2 is an important mediator of NaVO3-induced pulmonary inf lammation in the rat model. In addition, elevated MIP-2 mRNA levels are acc ompanied by increased NF-kappaB binding activity in BAL cells, suggesting p ossible MIP-2 transcriptional regulation through NF-kappaB.