OPN has gained attention in the context of the neurobiology of depression in part due to the presence of OPN receptors on microglial cells; activation of these receptors can lead to either NF-κB activation and thereby expression of proinflammatory cytokines or integrin-related pathways generating actin remodeling and cell migration or phagocytosis (163). The gene discussed is SPP1; the disease is major depressive disorder.