GFAP and amyotrophic lateral sclerosis: As GLT-1 is predominantly expressed on astrocytes, we next investigated whether sALS CSF-induced GLT-1 upregulation was also accompanied by reactive astrogliosis, another pathological hallmark observed in ALS.22 GFAP immunostaining intensity in the cervical spinal cord revealed higher GFAP expression in mice injected with sALS, C9orf72 and TARDBP CSF, indicating induction of reactive astrogliosis (Fig. 4A and B).