| Summary: | 碩士 === 國立陽明大學 === 解剖學及細胞生物學研究所 === 100 === Gap junctions are widely distributed in astrocytes, where they play an important role in regulating the homeostasis of the central nervous system. Changes in gap junction intercellular communication (GJIC) may cause abnormal development of the brain and trigger neurodegenerative diseases. In this study, we investigated the effects of the lysophosphatidic acid (LPA) on connexin43 (Cx43) gap junctions in rat primary astrocytes. Following LPA treatment, Cx43 protein expression was reduced in a dose-dependent manner. Short-term treatment (< 1 h) of astrocytes with LPA induced a significantly inhibition of GJIC without any change in Cx43 protein levels. Furthermore, LPA induced a significant increase in phospho-Src and extracellular signal-related kinase (pERK) levels at 15 minutes and maximum at 30 minutes. The LPA-induced GJIC inhibition was abolished by co-treatment of astrocytes with Src inhibitor PP2 or ERK inhibitor PD98059. The LPA-induced ERK activation could be prevented by PP2 co-treatment. Prolonged LPA treatment further reduced Cx43 protein expression and down-regulated Cx43 mRNA levels. Moreover, LPA induced a reduction in Cx43 immunoreactivity at cell-cell junctions and significantly inhibited the GJIC function. ERK activation was sustained at 6 hours and the LPA-induced Cx43 protein down-regulation was prevented by PD98059 co-treatment. Pretreatment of PD98059 could restore the LPA-reduced Cx43 immunoreactivity at cell-cell junctions. Our results exhibit that short-term treatment of the LPA reduces the GJIC through Src-ERK signaling cascade, whereas long-term LPA treatment not only sustains the inhibition of the GJIC, but also decreases Cx43 protein levels via ERK activation and eventually causes gap junction disassembly.
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