GFAP and amyotrophic lateral sclerosis: Interestingly, sciatic nerves from ALS rats also showed upregulated endoneurial expression of colony-stimulating factor 1 (CSF1) and IL-34: CSF1 was expressed by a subset of phagocytic S100+ p75NTR+ SCs engulfing myelin debris, while IL-34 was expressed by a subset of denervated GFAP+ SCs with the morphology of repair SCs, which also expressed c-Kit (stem cell factor, SCF, receptor).