Fig. 8: ISG15 in human SCA1 brains.

a Co-immunostaining of ISG15 and Calbindin. ISG15 signals were increased in the cytosol, neurites, and nucleus of Calbindin⁺ Purkinje cells of SCA1 patients in comparison with the control. Representative images of a SCA1 patient with 50 CAG repeats are shown. b Quantitative analysis of ISG15 signal intensities in Purkinje cells, granule cells, and molecular layers. Forty cells or twenty visual fields per person were observed in three controls and three SCA1 patients. The two-sided Student’s t-test was used for statistical comparisons. The box plot shows the median and 25–75th percentile, and whiskers represent data outside the 25–75th percentile range. c Super-resolution microscopy of human Purkinje cells in autopsy samples from SCA1 patients or non-neurological disease controls revealed colocalization of ISG15 and Atxn1 and of ISG15 and Ub. d An ELISA was developed to measure ISG15 or ISGylated proteins in plasma of human SCA1 patients and non-neurological disease controls. The two-sided Welch’s t-test was used for statistical comparison. Blood sampling was performed multiple times in eight of nine SCA1 patients, but only once in normal controls. The maximum value of ISG15 in each SCA1 patient is used in the left graph, and the value of ISG15 at the initial blood sampling is used in the right graph. e Relationships between the plasma ISG15 level and period from the first consultation or disease severity (SARA) and between the change of the plasma ISG15 level and the change of disease severity (SARA score) were examined. f Relationships between the CAG repeat number and the plasma ISG15 level were examined. Mean values of ISG15 in each patient are used in the upper graph, while the highest values in each patient are used in the lower graph.