Similar to previous reports, we found that a variety of proteasome components, including 20S core particles (PSMA1 and PSMB7), 19S regulatory particles (Rpt1 and Rpn1), and mutant UBQLN2 protein were enriched in nuclei of old mutant UBQLN2 rats compared to those from one-month-old rats, indicating that this ALS/FTD-linked UBQLN2 mutant caused their mislocalization and that these abnormal accumulations were likely responsible for the age-dependent proteasome impairment. Here, RPN1 is linked to amyotrophic lateral sclerosis.