Efficacy of GFAP as a biomarker for Alexander disease and estrogenic regulation of GFAP

Alexander disease (AxD) is a rare and fatal neurodegenerative disorder caused by mutations in glial fibrillary acidic protein (GFAP), which leads to GFAP accumulation above an unknown toxic threshold. There is no cure for AxD, but reduction of GFAP may alleviate AxD patient symptoms. In anticipation of future drug therapies, we explored the potential of GFAP as a biomarker for analysis of drug efficacy in mouse models of AxD and AxD patients. In chapter 2, we investigated two independent measures of GFAP expression in AxD mouse models: a genetic reporter of promoter activity and quantification of GFAP protein directly in a manner that could also be employed in human studies. Using a reporter mouse line which expresses firefly luciferase under the control of the murine Gfap promoter, we found that luciferase activity reflected the regional CNS variability of Gfap mRNA in Gfap+/+ mice, and increased in a mouse model of AxD. We also quantified GFAP protein in CSF from three different AxD mouse models and found GFAP levels increased in all models. In chapter 3, we analyzed GFAP protein in CSF and plasma from AxD patients, finding GFAP was significantly elevated in both CSF and plasma of AxD patients compared with controls. The results from Chapters 2 and 3 suggest we have good biomarkers in mouse models of AxD (Gfap promoter activity and GFAP in CSF) and AxD patients (GFAP in both CSF and plasma). In chapter 4, we analyzed the potential GFAP regulatory effects of estradiol (E2). A previous drug screen revealed E2 decreased Gfap promoter activity by 26% (Cho et al. 2010). In a mouse model of AxD, we found minimal changes in GFAP expression resulting from either surgical or pharmacological manipulation of estradiol levels. In addition, no fluctuation in GFAP expression was evident during the natural variations in endogenous estrogens occurring during the estrous cycle. These studies suggest caution in the implementation of estrogen-based treatments for AxD. Overall, the conclusions of the work described in this report support GFAP as a biomarker for AxD that can be utilized in future clinical trials to determine drug efficacy.