In contrast, miR-21 plays a pivotal act in neuroinflammation as it can exert protective roles in AD, which might be dependent on Programmed Cell Death 4/Phosphoinositide 3-kinases/Protein kinase B/Glycogen synthase kinase 3 (PDCD4/PI3K/AKT/GSK-3β) signaling pathway in vitro [121]. The gene discussed is GSK3B; the disease is Alzheimer disease.