ADORA2A and Alzheimer disease: Among them, α2-AR agonist regulates the production of pigment in melanocytes and erythrophores, includes the aggregation of melanin granules through mediating NE and affects the melanocyte apoptosis; β2-AR stimulates adenylate cyclase (cAMP), a key step comparable to the regulation of melanogenesis pathway, and will mediate AD to inhibit melanocyte aggregation [43].