Sphingosine 1-phosphate induces the production of glial cell line-derived neurotrophic factor and cellular proliferation in astrocytes

Sphingosine 1-phosphate (S1P) is a platelet-derived bioactive sphingolipid that evokes a variety of biological responses. To understand the role of S1P in the central nervous system, we have examined the effect of S1P on the production of glial cell line-derived neurotrophic factor (GDNF) and growth regulation of cortical astrocytes from rat embryo. Moreover, we examined the possibility that the expression of GDNF is regulated differently in cultured astrocytes from the stroke-prone spontaneously hypertensive rat (SHRSP) than in those from Wistar kyoto rats (WKY). The mRNA expression was quantitated by RT-PCR based on the fluorescent TaqMan methodology. A new instrument capable of measuring fluorescence in real time was used to quantify gene amplification in astrocytes. GDNF protein was investigated by enzyme-linked immunosorbent assay. SIP induced the expression of GDNF mRNA and the production of GDNF protein in a dose-dependent manner in WKY astrocytes. Moreover, S1P increased cell numbers and induced the proliferation of astrocytes. In addition, the level of mRNA expression and protein production of GDNF was significantly lower in SHRSP than WKY astrocytes following exposure to S1P. These findings revealed that S1P augments GDNF protein production and cellular growth in astrocytes. Also, our results indicate that production in SHRSP astrocytes was attenuated in response to S1P compared with that observed in WKY. We conclude that S1P specifically triggers a cascade of events that regulate the production of GDNF and cell growth in astrocytes. Our results also suggest that the reduced expression of GDNF caused by S1P is a factor in the stroke proneness of SHRSP.