Gene expression profile in monocyte during in vitro mineral fiber degradation

A human monocytes cell line, U-937, incubated in the presence of filtered medium from Escherichia coli culture (FS) has been previously reported to degrade man made mineral fiber and it has been indicated as a good paradigm of in vivo fiber biopersistence evaluation (manuscript accepted for publication). In the present paper, a study is reported aimed to define the molecular modification occurring in the U-937 monocytes during in vitro fiber degradation. The induction of gene expression was investigated in U-937 exposed to rock wool fibers (HDN) in the presence of FS by transcriptome analysis using 20 K DNA microarrays and quantitative RT-PCR. The over-expression of genes related to mobility and cellular adhesion, oxidative stress, immune system stimulation, enzymes, and ions transport protein systems were identified. Among them NCF1 gene, the gene encoding a subunit of NADPH oxidase, over-expression was detected. As the product of this gene allows the formation of superoxide anion that could lead to oxidative stress, HDN fibers were exposed to hydrogen peroxide. Fiber degradation similar to those observed upon incubation with U-937 in the presence of FS was obtained thus suggesting that reactive oxygen species production may be responsible for fiber degradation by U-937 monocytes.