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 regio n (AgNOR) proteins in vastus lateralis muscle samples from 13 patients with Duchenne muscular dystrophy (DMD) (6 months-12 years), 9 with Becker muscu lar dystrophy (BMD) (13 months-36 years), 9 with polymyositis (PM) (8-77 ye ars) and 10 normal subjects (5 months-32 years). AgNORs were visualized on 4-mu m-thick cryostat sections and quantified according to the guidelines o f the Committee on AgNOR Quantitation; statistical analysis was performed o n the mean AgNOR area (NORA) values. The mean NORA values encountered in DM D (4.327 +/- 0.791 mu m(2)), BMD (3.534 +/- 0.312 mu m(2)) and PM (3.785 +/ - 0.424 mu m(2)) samples were significantly (P < 0.001) higher than those o f normal muscle (1.682 +/- 0.288 mu m(2)); a value of P < 0.001 was also ob tained 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 gr oup 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 t ranscriptional activity. In particular, our findings suggest that (1) regen erating nuclei behave in the same way in dystrophinopathies or PM; (2) virt ually all nuclei, including quiescent-looking ones, are activated to realiz e an increased intracellular protein synthesis for proliferative and/or fun ctional purposes; and (3) the quantity of AgNOR does not seem related to ag e of patients at the time of biopsy.