Abstract
Adipose tissue plays an important role in energy regulation able to influence metabolic activity. Hormones are major regulators of adipose tissue and are critical for adipocyte development and function. Estrogen can have direct effects on cellular constituents of adipose tissue. Bisphenol A (BPA) and nonylphenol (NP) are considered to be endocrine-disrupting chemicals. BPA and NP act as hormone mimics via estrogen receptor mechanisms. In this study, we examined whether BPA and NP influence the differentiation of adipogenesis resulted in genotoxicity and DNA damage. The preadipocyte 3T3-L1 cells were differentiated into adipocytes and treated with BPA or NP, individually, at 1 and 100 uM for 8 days. Estradiol (E2), a natural estrogen, was used as a positive control at 0.001 uM. We used quantitative real-time PCR method to characterize the gene expression profiles after 3T3-L1 cells differentiated into adipocytes. We determined adipocyte protein 2 (aP2), an adipocyte specific fatty acid�binding protein, to investigate the differentiation of 3T3-L1 cells to adipocytes. The results showed the 11.8-fold higher expression of aP2 in non-treated differentiated 3T3-L1 cells than preadipocyte cells. We also found there was 20.3-fold expression of aP2 in E2-treated differentiated 3T3-L1 cells. After 1 uM and 100 uM NP, and 100 uM BPA treatment, the aP2 gene was suppressed in the differentiated 3T3-L1 cells. Vitamin D receptor (VDR) is the earlier expression gene of adipogenesis. With the treatment of 1 uM and 100 uM NP, and 1 uM BPA, the differentiated 3T3-L1 cells had the similar expression of VDR compared to the non-treated differentiated cells. However, 100uM BPA suppressed the expression of VDR. Peroxisome proliferator-activated receptor Gamma (PPAR Gamma), a later expression marker of adipogenesis, expressed at 1 and 100 uM NP, and 100 uM BPA, but decreased at 1 uM BPA in differentiated 3T3-L1 cells. DNA damage recognition proteins were also observed in this study. After NP and BPA treatment, the differentiated 3T3-L1 cells had the higher expression of tumor suppressor gene, p53. The growth arrest DNA damage-inducible 45 (Gadd45a) was high expression at 1 and 100 uM NP, and 100 uM BPA, but suppressed at 1 uM BPA in differentiated 3T3-L1 cells. Proliferating cell nuclear antigen (PCNA) can stimulate the activity of DNA polymerase delta/epsilon to synthesize a new DNA strand. In this study, PCNA had the opposite expression pattern to Gadd45a. PCNA was high expression at 1 uM BPA, but relative lower expression at 1 and 100 uM NP, and 100 uM BPA in differentiated 3T3-L1 cells. NP and BPA caused genotoxicity and DNA damage of adipogenesis in differentiated 3T3-L1 cells. PCNA expression could repair the DNA damage resulted from the lower level of BPA at 1 uM. This study suggested the high level of NP and BPA influence the expression of adipogenesis-relevant genes and inhibited the DNA repair capacity.