Neuronal differentiation of embryonic midbrain cells by upregulation of peroxisome proliferator-activated receptor-gamma via the JNK-dependent pathway.

Our previous study showed that the peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonist 15-deoxy-PGJ(2) has the promoting ability to differentiate neuronal PC12 cells. To expand our study, the effect of 15-deoxy-PGJ(2) on the differentiation of embryonic midbrain cells into dopaminergic neuronal cells was investigated in this study. The relationship between cell differentiation with activation of PPAR-gamma and the possible signal pathway were also investigated. 15-Deoxy-PGJ(2) increased neurite extension, a typical characteristic of the differentiation of embryonic midbrain cells isolated from 12-day rat embryos in a dose-dependent manner. The expression of differentiation markers, neurofilament, tyrosine hydroxylase, and nestin, was also increased by the treatment of 15-deoxy-PGJ(2). Consistent with the increasing effect on cell differentiation, 15-deoxy-PGJ(2) increased the expression and transcriptional activity of PPAR-gamma in cultured embryonic midbrain cells. In addition, the expression of PPAR-gamma and NeuN in the differentiated neuron of fetus (17 days) and adult rat brain was co-localized. Furthermore, treatment of PPAR-gamma antagonist bisphenol A diglycidyl ether blocked 15-deoxy-PGJ(2)-induced neuronal differentiation of embryonic midbrain cells and expression of PPAR-gamma. To elucidate the possible signal pathway, the activation of mitogenic-activated protein (MAP) kinase family was determined. 15-Deoxy-PGJ(2) (0.5 microM) increased activation of Jun N-terminal kinase (JNK) and p38 kinase but not extra-signal response kinase (ERK). In addition, NGF (50 ng/ml) further increased the 15-deoxy-PGJ(2)-induced JNK activation. Moreover, pretreatment of specific inhibitor of JNK SP600125 blocked the 15-deoxy-PGJ(2)-induced JNK activation. This inhibition correlated well with the inhibition of neurite extension and expression of PPAR-gamma induced by 15-deoxy-PGJ(2). The present results therefore indicate that 15-deoxy-PGJ(2) stimulates differentiation of embryonic midbrain cells into dopaminergic neuronal cells, and its effect may be PPAR-gamma and JNK signal pathway dependent.

Ras transgene expression in TG-AC mice treated with benzo[a]pyrene.

Transgene expression and skin tumorigenicity were investigated in transgenic TG-AC mice carrying the v-Ha-ras after treatment with benzo[a]pyrene (BP). Animals treated with 40 microg BP (x2/week/mouse) showed 100% tumor response after 25 weeks, as did 40% of the mice treated with 20 microg BP but 10 microg BP did not produce a tumor response. In the case of animals treated with 40 microg BP for 25 weeks, most of the tumors were proven to be carcinomas (80%, 4 out of 5 mice), and all tumors were shown to be positive in terms of transgene expression detected by in situ hybridization. These data suggest that BP was tumorigenic in a dose-dependent manner in TG-AC mice and that TG-AC mice were dependent on transgene expression during BP carcinogenesis.

Inhibitory effect of peroxisome proliferator-activated receptor gamma agonist on ochratoxin A-induced cytotoxicity and activation of transcription factors in cultured rat embryonic midbrain cells.

The effects of 15-deoxy-delta12,14-prostaglandin J2 (15-deoxy PGJ2) on ochratoxin A (OTA)-induced neurotoxicity and on the activation of transcription factors activator protein-1 (AP-1) and nuclear factor-kappa B (NF-kappaB) were investigated in cultured rat embryonic midbrain cells. Twelve-day rat embryo midbrain cells were cultured for 48 h. OTA (0.5 or 1 microg/ml) and/or 1.5-deoxy PGJ2 (0.5 microM) were then added for 48 h. Cell number and neurite outgrowth were determined to assess the neurotoxicity of OTA. AP-1 and NF-kappaB activation was determined by gel mobility shift assay after 3 h of exposure to OTA and/or 15-deoxy PGI2. OTA caused concentration-dependent reductions in neurite outgrowth and cell number, and induced AP-1 and NF-kappaB activation. Cotreatment with 15-deoxy PGJ2 (0..5 microM) blocked OTA-induced decrease in neurite outgrowth and cell number and inhibited AP-1 and NF-kappaB activation. 15-Deoxy PGJ2 (0.5 microM) caused the expression of peroxisome proliferator-activated receptor-gamma (PPAR-gamma) in the cells. Results show that 1.5-deoxy PGJ2 blocked OTA-induced neurotoxicity by inhibiting AP-1 and NF-kappaB activation in cultured rat embryonic midbrain cells.