Evaluation of skeletal muscle regeneration in experimental model after malnutrition / Avaliação da regeneração do músculo esquelético em modelo experimental após desnutrição

Abstract The aim of this study was to analyze muscle regeneration after cryoinjury in the tibialis anterior muscle of young rats that were malnourished and then recovered. Forty Wistar rats were divided into a nourished group that received a normal protein diet (14% casein) for 90 days and a malnourished and recovered rats group (MR) that was submitted to 45 days of malnutrition with a hypoproteic diet (6% casein) followed by 45 days of a normal protein diet (14% casein). After the recovery period, all of the animals underwent cryoinjury in the right tibialis anterior muscle and euthanasia after 7, 14 and 21 days. The amount of connective tissue and the inflammation area was higher in the malnutrition recovered injury MR group (MRI) at 14 days post-injury (p < 0.05). Additionally, the cross-sectional area (CSA) of the regenerated fibers was decreased in the MRI (p < 0.05). The MyoD and myogenin protein levels were higher in the nourished injury group. Similar levels of TGF-β1 were found between groups. The proposed malnutrition protocol was effective in showing delayed changes in the regeneration process of the tibialis anterior muscle of young rats. Furthermore, we observed a delay in muscle repair even after nutritional recovery.

Resumo O objetivo do presente estudo foi analisar a regeneração muscular após criolesão no músculo tibial anterior de ratos jovens desnutridos e recuperados. Foram utilizados 40 ratos da linhagem Wistar, divididos em 2 grupos: ratos nutridos receberam dieta normoproteica (14% de caseína) por 90 dias; e ratos desnutridos e recuperado submetidos a duas fases nutricionais pós-desmame, correspondendo a 45 dias de desnutrição com dieta hipoproteica (6% caseína), seguida por 45 dias de dieta normoproteica (14% caseína). Ao completar a fase de recuperação, todos os animais foram submetidos à criolesão no músculo tibial anterior direito e a eutanasia ocorreu 7, 14 e 21 dias após a lesão. A quantidade de tecido conjuntivo e a área de inflamação 14 dias pós-lesão foi maior no grupo desnutrido, recuperado e lesado (MRI – malnourished, recovered and injured group) (p < 0,05). A área de secção transversa (AST) das fibras regeneradas do grupo MRI foi menor (p < 0,05). O conteúdo das proteínas MyoD e Miogenina foi maior no grupo nutridos e lesados. A citocina TGF-β1 não apresentou diferença entre os grupos. O protocolo proposto foi eficaz para demonstrar alterações no processo de regeneração do músculo tibial anterior de ratos jovens, atrasando o reparo muscular mesmo após a recuperação nutricional.

Implantation of muscle satellite cells overexpressing myogenin improves denervated muscle atrophy in rats

This study evaluated the effect of muscle satellite cells (MSCs) overexpressing myogenin (MyoG) on denervated muscle atrophy. Rat MSCs were isolated and transfected with the MyoG-EGFP plasmid vector GV143. MyoG-transfected MSCs (MTMs) were transplanted into rat gastrocnemius muscles at 1 week after surgical denervation. Controls included injections of untransfected MSCs or the vehicle only. Muscles were harvested and analyzed at 2, 4, and 24 weeks post-transplantation. Immunofluorescence confirmed MyoG overexpression in MTMs. The muscle wet weight ratio was significantly reduced at 2 weeks after MTM injection (67.17±6.79) compared with muscles injected with MSCs (58.83±5.31) or the vehicle (53.00±7.67; t=2.37, P=0.04 and t=3.39, P=0.007, respectively). The muscle fiber cross-sectional area was also larger at 2 weeks after MTM injection (2.63×103±0.39×103) compared with MSC injection (1.99×103±0.58×103) or the vehicle only (1.57×103±0.47×103; t=2.24, P=0.049 and t=4.22, P=0.002, respectively). At 4 and 24 weeks post-injection, the muscle mass and fiber cross-sectional area were similar across all three experimental groups. Immunohistochemistry showed that the MTM group had larger MyoG-positive fibers. The MTM group (3.18±1.13) also had higher expression of MyoG mRNA than other groups (1.41±0.65 and 1.03±0.19) at 2 weeks after injection (t=2.72, P=0.04). Transplanted MTMs delayed short-term atrophy of denervated muscles. This approach can be optimized as a novel stand-alone therapy or as a bridge to surgical re-innervation of damaged muscles.