P2RY12 and neurodegenerative disease: The expression of P2RY12 was dramatically reduced during the progression of neurodegenerative diseases such as Alzheimer’s disease and multiple sclerosis (189–192), suggesting that the expression level of P2RY12 might be used as an indicator of resident microglia and activated microglia (i.e. TMEM119-positive and P2RY12-negative) after CNS injuries.