Quantitation of argyrophilic nucleolar organizer regions in regenerating muscle fibers in Duchenne and Becker muscular dystrophies and polymyositis

We have investigated the quantity of argyrophilic nucleolar organizer region (AgNOR) proteins in vastus lateralis muscle samples from 13 patients with Duchenne muscular dystrophy (DMD) (6 months-12 years), 9 with Becker muscular dystrophy (BMD) (13 months-36 years), 9 with polymyositis (PM) (8-77 years) and 10 normal subjects (5 months-32 years). AgNORs were visualized on 4-μm-thick cryostat sections and quantified according to the guidelines of the Committee on AgNOR Quantitation; statistical analysis was performed on the mean AgNOR area (NORA) values. The mean NORA values encountered in DMD (4.327 ± 0.791 μm²), BMD (3.534 ± 0.312 μm²) and PM (3.785 ± 0.424 μm²) samples were significantly (P <0.001) higher than these of normal muscle (1.682 ± 0.288 μm²); a value of P <0.001 was also obtained when NORA values found in DMD were compared with those of BMD or PM. In addition, when NORA values were exclusively calculated in regenerating myofibers in DMD, BMD and PM, no differences were appreciable. On the other hand, in non-regenerating myofibers, the NORA values showed a significant increase in DMD versus BMD and PM (P <0.001) as well as in each disease group versus controls. Our study documents that muscle diseases, such as DMD, BMD and PM in which regeneration is a constant finding, have a high rDNA transcriptional activity. In particular, our findings suggest that (1) regenerating nuclei behave in the same way in dystrophinopathies or PM; (2) virtually all nuclei, including quiescent-looking ones, are activated to realize an increased intracellular protein synthesis for proliferative and/or functional purposes; and (3) the quantity of AgNOR does not seem related to age of patients at the time of biopsy.