Neuropathological staging of spinocerebellar ataxia type 2 by semiquantitative 1C2-positive neuron typing. Nuclear translocation of cytoplasmic 1C2 underlies disease progression of spinocerebellar ataxia type 2

Abstract

Spinocerebellar ataxia type 2 (SCA2) is a hereditary neurodegenerative disorder caused by the expansion of the trinucleotide CAG repeats encoding elongated polyglutamine tract in ataxin-2, the SCA2 gene product. Polyglutamine diseases comprise nine genetic entities, including seven different forms of spinocerebellar ataxias, Huntington's disease, and spinal and bulbar muscular atrophy. These are pathologically characterized by neuronal loss and intranuclear aggregates or inclusions of mutant proteins including expanded polyglutamine in selected neuronal groups. Previously, we examined immunolocalization of ubiquitin, expanded polyglutamine (probed by 1C2 antibody), and ataxin-2 in genetically confirmed SCA2 patients. In the present study, we expanded this approach by distinguishing different patterns of subcellular 1C2 immunoreactivity ("granular cytoplasmic," "cytoplasmic and nuclear" and "nuclear with inclusions.") and by quantifying their regional frequencies in three autopsied SCA2 brains at different stage of the disease. Comparison with neuronal loss and gliosis revealed that overall 1C2 immunoreactivity was paralleled with their severity. Furthermore, appearance of granular cytoplasmic pattern corresponded to early stage, cytoplasmic and nuclear pattern to active stage, and nuclear with inclusions pattern to final stage. We conclude that this 1C2-immunoreactive typing may be useful for evaluating the overall severity and extent of affected regions and estimating the neuropathological stage of SCA2.

Keywords: 1C2-immunoreactive typing; cytoplasmic and nuclear; granular cytoplasmic; nuclear with inclusions; spinocerebellar ataxia type 2.

Figure 1

Each extent of neuronal loss and gliosis of spinocerebellar ataxia type 2 ( SCA 2) in comparison with control. A. Dentate nucleus of control. B. No neuronal loss and gliosis of dentate nucleus in SCA2 (case 2). C. Oculomotor nucleus of control. D. Mild neuronal loss and gliosis of oculomotor nucleus in SCA2 (case 2). E. Hypoglossal nucleus of control. F. Mild neuronal loss and gliosis of hypoglossal nucleus in SCA2 (case 3). G. Substantia nigra of control. H. Moderate neuronal loss and gliosis of substantia nigra in SCA2 (case1). I. Anterior horn of control. J. Moderate neuronal loss and gliosis of anterior horn in SCA2 (case 1). K. Pontine nucleus of control. L. Severe neuronal loss and gliosis of pontine nucleus in SCA2 (case 1). (M) Purkinje cells of control. N. Severe neuronal loss and gliosis of Purkinje cells in SCA2 (case 3). O. Inferior olivary nucleus of control. P. Severe neuronal loss and gliosis of inferior olivary nucleus in SCA2 (case 1). (hematoxylin and eosin; scale bars 100 μm).

Figure 2

1 C2–IR ‐labeling patterns classified into three groups. 1 C2–IR ‐labeling occurred in three patterns in the pons. A. The first pattern is characterized by granular staining in only the cytoplasm of a neuron. B,C. The second pattern shows fine granular and/or diffuse staining in the nucleus and cytoplasm. D. Neuronal intranuclear inclusions occur in the third pattern. (scale bars 10 μm).

Figure 3

1 C2 ‐immunoreactive frequency (1 C2‐IF ) in three patients with  SCA 2. The 1C2‐IF of cases 1 and 2 was very similar, and that of case 3 was higher.

Figure 4

Mapping of the severity and extent of neuronal loss, gliosis and 1 C 2‐immunoreactive frequency (1 C2‐IF ) in three patients with  SCA 2. The severity and extent of neuronal loss and gliosis increased almost in parallel with the 1C2‐IF.

Figure 5

Regional frequencies of three 1 C2–IR ‐labeling patterns in three  SCA 2 cases. A. In case 1, regions having 50% (red dotted line) or more 1C2‐immunoreactive frequency (1C2‐IF) included the oculomotor nucleus, red nucleus, substantia nigra, pontine nuclei, locus ceruleus, anterior horn, Purkinje layer and Golgi complex cells. Regions with 1C2‐IF of less than 10% (blue dotted line) were numerous, and nuclear staining with NIs was rarely observed. B. In case 2, regions having 50% or more 1C2‐IF included the hippocampus, substantia nigra, pontine nuclei, inferior olivary nucleus, anterior horn, Purkinje cells and the differences by region were remarkable. C. In case 3, regions having 50% or more 1C2‐IF included the cerebral cortex, oculomotor nuclei, red nucleus, substantia nigra, pontine nuclei, inferior olivary nucleus, anterior horn, Purkinje layer, and dentate nuclei, and the total 1C2‐IF for all patterns was high in each region. CNS = cytoplasmic and nuclear staining; CS = granular cytoplasmic staining; NS = nuclear with inclusions staining.

Figure 6

Distribution according to neuronal loss, gliosis, and 1 C 2‐immunoreactive frequency (1 C2‐IF ) of three labeling patterns in three patients with spinocerebellar ataxia type 2 ( SCA 2). The first pattern (cytoplasmic granular staining) was seen in almost all diffuse lesions in all three SCA2 cases. The second pattern was seen mainly in degenerative lesions (those with neuronal loss and gliosis) except for in the cerebellum. The third pattern was found in severely and mildly degenerative lesions.