TREM2 and amyotrophic lateral sclerosis: Indeed, it was previously shown that during disease progression, in addition to neurotoxic factors, ALS microglia concurrently show induction of neuroprotective factors such as insulin-like growth factor 1 (IGF1), progranulin (GRN) and triggering receptor expressed on myeloid cells 2 (TREM2) [87].