Glial fibrillary acidic protein splice variants in hepatic stellate cells--expression and regulation

The glial fibrillary acidic protein (GFAP) is traditionally used as a marker for astrocytes of the brain, and more recently for the hepatic stellate cells (HSCs) of the liver. Several GFAP splice variants have been previously reported in the astrocytes of the CNS and in the non-myelinating Schwann cells of the PNS. In this study, we investigate whether GFAP splice variants are present in the HSCs and their expression as a function of HSCs activation. Furthermore, the regulation of these transcripts upon treatment with interferon gamma (IFN-gamma) will be explored. Using semi-quantitative RT-PCR and real-time PCR, we examine the expression and regulation of GFAP splice variants in HSCs as well as their respective half-life. We discover that most of the GFAP splice variants (GFAPalpha, beta, delta, epsilon, and kappa) found in the neural system are also expressed in quiescent and culture-activated primary HSCs. Interestingly, GFAPalpha is the predominant form in quiescent and culture-activated primary HSCs, while GFAPbeta predominates in the SV40-immortalized activated HSC-T6. GFAP delta, epsilon, and kappa have similar half-lives of 10 hours, while GFAPbeta has a half-life of 17 hours. Treatment of HSC-T6 with IFN-gamma results in a significant 1.29-fold up-regulation of GFAPalpha; whereas the level of the other transcripts remains unchanged. In summary, GFAPalpha, beta, delta, epsilon, and kappa are present in HSCs. They are differentially regulated on the transcription level, implying a role of the 5' and 3' untranslated regions.