Optineurin immunoreactivity in neuronal nuclear inclusions of polyglutamine diseases (Huntington’s, DRPLA, SCA2, SCA3) and intranuclear inclusion body disease

Abstract

Optineurin (OPTN) is a ubiquitous cytoplasmic protein with various functions including membrane trafficking and signal transduction [9]. OPTN mutations are associated with adult-onset glaucoma and familial and sporadic amyotrophic lateral sclerosis (ALS) [4]. OPTN immunoreactivity has been reported in a variety of ubiquitinated inclusions including ALS-associated neuronal cytoplasmic inclusions, neurofibrillary tangles in Alzheimer’s disease, Pick bodies in Pick disease, Lewy bodies in Parkinson’s disease and glial cytoplasmic inclusions in multiple system atrophy [3, 6]. With respect to polyglutamine diseases, neuronal nuclear inclusions (NNIs) in Huntington’s disease (HD) and spinocerebellar ataxia type 3 (SCA3) are reported to be immunonegative for OPTN [2]. However, Schwab et al. [7] have contended that NNIs in HD are immunopositive for OPTN. We report that OPTN immunoreactivity is present in NNIs in various polyglutamine diseases and intranuclear inclusion body disease (INIBD). A total of 30 post-mortem cases were utilized in the present study; these included cases of HD (n = 3), dentatorubral-pallidoluysian atrophy (DRPLA; n = 5), SCA2 (n = 1), SCA3 (n = 5), SCA6 (n = 2), SCA17 (n = 1), spinal and bulbar muscular atrophy (SBMA; n = 3), INIBD (n = 5) and normal control subjects (n = 5). The diagnoses of polyglutamine diseases were confirmed genetically and histopathologically. Immunohistochemical analysis was carried out using formalin-fixed, paraffinembedded sections from the basal ganglia in HD, SCA2 and SCA17, the pons in DRPLA and SCA3, the cerebellum in SCA6, the spinal cord in SBMA, the frontal lobe in INIBD, and the cortical and subcortical regions in control subjects. Anti-ubiquitin (1B3; MBL, Nagoya, Japan), antipolyglutamine (1C2; Chemicon, Temecula, CA, USA) and anti-human OPTN C terminus (#100000; Cayman CHEMICAL, Ann Arbor, MI, USA) [2, 7, 8] were used as primary antibodies. In controls, anti-OPTN antibody weakly immunolabeled the neuronal cytoplasm in a diffuse granular pattern, and neuronal nuclei were negative for OPTN (Fig. 1a). OPTN-immunoreactive NNIs were found in all the cases of HD, DRPLA, SCA2 and SCA3 (Fig. 1b–e). Intranuclear inclusions in neurons, but not in glial cells, in INIBD were also immunopositive for OPTN (Fig. 1f). Double immunofluorescence analyses revealed that OPTN immunoreactivity was found in 69% of NNIs in HD, 46% in DRPLA, 17% in SCA2, 55% in SCA3 and 50% in INIBD (Fig. 2). Although ubiquitinated NNIs were seen in SCA17 and SBMA, these inclusions were F. Mori (&) K. Tanji K. Wakabayashi Department of Neuropathology, Institute of Brain Science, Hirosaki University Graduate School of Medicine, 5 Zaifu-cho, Hirosaki 036-8562, Japan e-mail: neuropal@cc.hirosaki-u.ac.jp