Student Research: Leah Tait
The paraoxonase (PON) gene family consists of three members (PON1, PON2, and PON3). PON1 and PON3 are mainly synthesized in the liver and are secreted in the plasma, where they associate with high density lipoproteins (HDL). PON2 is widely expressed in tissues. The first aim of this study was to characterize PONs in mouse striatal astrocytes and in human astrocytoma (132-1N1) and neuroblastoma (SH-SY5Y) cell lines. PON2 protein expression, activity, and mRNA levels were found to be higher in mouse striatal astrocytes than in mouse striatal neurons, with little to no PON1 or PON3 protein present. PON2 was present in primary astrocytes and neurons as two alloforms. In contrast, PON2 protein expression and activity was found to be higher in neuroblastoma than in astrocytoma cells, and only a higher MW alloform was present. Female mice had been previously shown to have higher levels on PON2 than male mice, suggesting that there is hormonal control of PON2 expression. In vitro, PON2 expression in striatal astrocytes was induced by exposure to estradiol. Basal expression of PON2 in cultured striatal astrocytes from females was higher than in males. Both male and female astrocytes showed an induction of PON2 expression following estradiol exposure, but in male-derived astrocytes, the increase of PON2 was only to the basal level found in female-derived astrocytes. We also examined modulation of PON2 expression by quercetin and rosiglitazone. Quercetin and rosiglitazone increased PON2 expression in vitro in striatal astrocytes and striatal neurons. Quercetin upregulation of PON2 expression was attenuated completely by SP600125, a JNK/AP-1 inhibitor, and rosiglitazone upregulation of PON2 was attenuated by GW9662, a PPARÎ³ inhibitor. Cells pre-treated with quercetin were protected when challenged by agents known to cause oxidative stress (H2O2 and DMNQ) as measured by MTT and ROS assays, reinforcing the possible role of PON2 as an antioxidant. However, in the astrocytoma 132-1N1 cell line, no effect on PON2 was seen following exposure to estradiol, quercetin, or rosiglitazone.