Original Article Optineurin immunoreactivity in neuronal and glial intranuclear inclusions in adult-onset neuronal intranuclear inclusion disease

Optineurin (OPTN) is a multifunctional protein involved in cellular morphogenesis, vesicle trafficking, maintenance of the Golgi complex, and transcription activation through its interactions with the Rab8, myosin 6 (MYO6), huntingtin. Recently, OPTN immunoreactivity has been reported in intranuclear inclusions in patients with neuronal intranuclear inclusions disease (NIID). Other studies have shown that the RNA-binding protein, fused in sarcoma (FUS), is a component of intranuclear inclusions in NIID. We aimed to investigate the relationship between OPTN, its binding protein MYO6 and FUS in this study. In control subjects, OPTN (C-terminal) (OPTN-C) and MYO6 im- munoreactivity was mainly demonstrated in the cytoplasm of neurons. In NIID patients, both neuronal intranuclear inclusions (NII) and glial intranuclear inclusions (GII) were immunopositive for MYO6 as well as OPTN-C. However, the intensity of OPTN-C immunostaining of the neuronal cytoplasm with and without NII was less than that of the control subjects. Double immunofluorescence staining for OPTN-C, ubiquitin (Ub), p62 and FUS revealed co-local - ization of these proteins within NII. Moreover, Ub positive inclusions were co-localized with MYO6. The percentage of co-localization of Ub with OPTN-C, FUS or MYO6 in NII was 100%, 52% and 92%, respectively. Ultrastructurally, the inclusions consisted of thin and thick filaments. Both filaments were immunopositive for Ub and OPTN-C. These findings suggest that OPTN plays a central role in the disease pathogenesis, and that OPTN may be a major com - ponent of NII.