Inorganic arsenic exposure-induced premature senescence and senescence-associated secretory phenotype (SASP) in human hepatic stellate cells

Exposure to inorganic arsenic has been known to induce cancers in various organs, however, the underlying mechanisms remain unclear. Premature senescence refers to the irreversible growth arrest induced by stress stimuli. The senescence-associated secretory phenotype (SASP), particularly in fibroblasts, has been shown to promote cancer development. In this study, we examined whether arsenite exposure causes premature senescence and induction of SASP in liver fibroblasts using the human hepatic stellate cell line, LX-2. Exposure of LX-2 cells to 5 or 7.5 mu M of sodium arsenite for 144 h induced the features of senescence in the cells, including morphological changes, growth inhibition, increased senescence-associated beta-galactosidase activity, increased P21 gene expression, and decreased LAMINB1 gene expression. The mRNA expressions of SASP factors, such as MMP1, MMP3, IL-8, IL-1 beta, and CXCL1, were also highly upregulated. The wound healing assay revealed that the conditioned medium from LX-2 cells with arsenite-induced senescence increased the migration activity of cells of the human hepatoma cell line, Huh-7. Gene expression data of liver cancer samples from the Human Protein Atlas showed that high expression levels of the SASP factors that were upregulated in the cells with arsenite-induced senescence were strongly associated with a poor prognosis. In addition, the cellular levels of gamma-H2AX, a DNA double-strand break marker, were increased by arsenite exposure, suggesting that DNA damage could contribute to premature senescence induction. These results show that arsenite exposure induces premature senescence in hepatic stellate cells and suggest that the SASP factors from the senescent cells promote hepatic carcinogenesis.