G protein‐coupled receptor 26 immunoreactivity in intranuclear inclusions associated with polyglutamine and intranuclear inclusion body diseases

G protein‐coupled receptor 26 (GPR26) is one of the G‐protein‐coupled receptors (GPCRs), which comprise the largest family of membrane proteins and mediate most of the physiological responses to hormones, neurotransmitters and environmental stimulants. Although GPCRs are considered to play an important role in the pathophysiology of neurodegenerative disorders, it is uncertain whether GPR26 is involved in the pathogenesis of polyglutamine and intranuclear inclusion body diseases. We immunohistochemically examined the brain tissues of patients with four polyglutamine diseases (Huntington's disease, dentatorubral‐pallidoluysian atrophy, and spinocerebellar ataxia types 1 and 3) and intranuclear inclusion body disease, and normal control subjects. In controls, anti‐GPR26 antibody immunolabeled the neuronal cytoplasm in a diffuse granular pattern. Neuronal nuclear inclusions in polyglutamine diseases were immunopositive for GPR26. In intranuclear inclusion body disease, GPR26‐positive nuclear inclusions were found in both neurons and glial cells. Marinesco bodies in aged control subjects were also positive for GPR26. Double immunofluorescence analysis revealed co‐localization of GPR26 with polyglutamine or ubiquitin in these nuclear inclusions. These findings suggest that GPR26 may have a common role in the formation or degradation of intranuclear inclusions in several neurodegenerative diseases.