Estudo morfológico e morfométrico das fibras musculares e junções neuromusculares do músculo sóleo de ratos em diferentes idades submetidos à restrição proteica materna

Abstract

Inadequate maternal nutritional may predispose to neuromuscular disorders in the offspring, a phenomenon known as fetal programming. In this context, the present study aimed to evaluate the effects of maternal protein restriction (during pregnancy and lactation) on muscle fibers and neuromuscular junctions (NMJs) of the soleus muscle from pups at 21 and 365 days old. Male Wistar rats were divided in two experimental groups: Control (CG) - offspring of mothers fed a normal protein diet (17%) and restricted (RG) - offspring of mothers fed a low protein diet (6%). All pups were maintained with their mothers during the lactation period (21 days) and after weaning, one part of males from each group were euthanized to collect samples of the soleus muscle. The remaining rats received standard food ad libitum until 365 days, when they were also euthanatized. The samples of the soleus muscle from animals with 21 days old were collected for analysis of muscle fibers (by HE staining and ultrastructure) and NMJs (by Nonspecific Esterase technique). In animals with 365 days of age, soleus muscle samples were obtained for verification of muscle fibers (by HE staining, NADH-TR reaction and ultrastructure), quantification of intramuscular collagen (picrosirius red staining) and also for analysis of NMJs (Nonspecific Esterase technique). Regarding the results, at 21 days muscle fibers was immature and the presence of myotubes, central nuclei, fetal fibres and fibroblasts were observed in both experimental groups. An increase in the number of muscle fiber and nuclei in the RG compared to controls was observed. Muscle fibers with rarefied or loosely arranged myofibrils, Z-line disorganized and nuclei in central position were observed in CG and RG. Regarding the NMJs, the RG showed a decreased in area, larger and smaller diameter compared to the CG. At 365 days, the RG showed a decrease in the cross sectional area in type I and IIa fibers, associated with an increase in type IIb fibers. The percentage of intramuscular collagen was lower in RG. Myofibrils and Z line disorganization was also observed at ultrastructural level, with the presence of mitochondria clusters in both groups studied. A reduction in the area and smaller diameter of NMJs was observed in the GR, along with an increase in the larger diameter of these structures compared to CG. These results indicate that maternal protein restriction affects the morphology and morphometry of the neuromuscular junctions and muscle fibers. Such changes can be detected early and persist throughout adulthood and senescence, seeming irreversible