Efeito do envelhecimento e do treinamento de força no remodelamento de fêmures de ratos

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Ceilândia, Programa de Pós-Graduação em Ciências da Reabilitação, 2017.O osso é um tecido dinâmico capaz de absorver impactos e, como outros tecidos, sofre os efeitos do envelhecimento. As propriedades da matriz extracelular ficam fragilizadas, levando a maior risco de fraturas em idosos. Exercícios físicos, como o treinamento de força, são bem estabelecidos como atenuadores desses efeitos deletérios, logo, nesse contexto, faz-se necessário estudos biomoleculares que expliquem tais benefícios no remodelamento ósseo. Objetivo: Avaliar os efeitos do envelhecimento, bem como o efeito do treinamento de força sobre as propriedades da MEC, relacionados ao remodelamento ósseo em ratos. Materiais e métodos: foram utilizados 20 ratos Wistar Novergicus Albinos, de 3 e 20 meses, divididos em quatro grupos experimentais com 5 animais cada Jovens Sedentários (JS), Velhos Sedentários (VS), Jovens Treinados (JT) e Velhos Treinados (IT). O treinamento de força (TF) de 12 semanas foi realizado uma vez a cada dois dias. Primeiramente, os ratos foram adaptados ao protocolo de TF para escalarem uma escada vertical, com pesos presos as suas caudas, realizando de 8 a 12 movimentos por escalada. As sessões de TF consistiram de quatro escaladas na escada, com 65%, 85%, 95% e 100% da capacidade máxima de carregamento do rato, determinada na sessão anterior. Posteriormente, os fêmures foram retirados e, a expressão gênica, atividade da MMP-2 e conteúdo proteico de COL-1 foram analisadas. Resultados: foi identificado menor expressão gênica da SOST e MEPE nos grupos VT. A expressão gênica do COL-1 apresentou redução significante nos grupos velhos, mas houve diferença no conteúdo proteico. A expressão das MMPs-2 e -13 bem como a atividade da MMP-2, apresentaram diminuição no envelhecimento, e não houve influência do treinamento. Conclusão: O TF demonstrou efeito protetor no osso envelhecido, sem alterar o conteúdo proteico estrutural e o remodelamento. Sugere-se que protocolos que adotem um tempo maior de treinamento podem gerar resultados mais favoráveis.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES).Bone is a dynamic tissue able to sustain impacts and, like other tissues, is affected negatively by aging. Its extracellular matrix properties become weakened, resulting in greater fracture risks. Exercises, as resistance training, are well established as attenuators of these deleterious effects, therefore, considering this context, biomolecular studies are crucial to explain such benefits in bone remodeling. Objectives: To identify aging effects on ECM, and resistance training as well, related to bone remodeling in rats. Materials and methods: 20 rats Wistar novergicus albinos were used, aged 3 and 20 months, and divided into four experimental groups (5 animais per group): young sedentary (YS), young trained (YT), old sedentary (OS), old trained (OT). A 12-week RT was conducted once every two days. Initially, the rats were adapted to the resistance training protocol, which required them to climb a vertical ladder with weights attached to their tails, making them perform from 8 to 12 movements per climb. The training sessions consisted of four ladder climbs with 65, 85, 95, and 100% of the rat’s maximal carrying capacity, as determined in the previous session. Afterwards, femurs were dissected and MMPs genic expression, MMP-2 activity and COL-1 protein tissue content were analyzed. Results: there was reduced genic expression of SOST and MEPE in OT group compared to sedentary. COL-1 showed reduced gene expression in old groups, however it was not reproduced on proteic tissue content. MMP-2 and -13 expression and activity of MMP-2 were reduced in aged animals, and RT had no influence on these results. Conclusion: Resistance training showed protective effect on aged bone, without showing any alterations on proteic structural content and remodeling activity. Different protocols with longer periods of training may have more favorable results

Resistance training modulates the matrix mtalloproteinase-2 activity in different trabecular bones in aged rats

Background: Aging decreases osteogenic ability, inducing harmful effects on the bone extracellular matrix (ECM), while exercise training has been indicated as a tool to counteract bone disorders related to advancing age. The modulation of bone ECM is regulated by several types of matrix metalloproteinase (MMP); however, MMP-2 activity in different trabecular bones in response to resistance training (RT) has been neglected. Remodeling differs in different bones under the application of the same mechanical loading. Thus, we investigated the effects of 12 weeks of RT on MMP-2 activity in the lumbar vertebra (L6), tibia, and femur of young (3 months) and older rats (21 months). Methods: Twenty Wistar rats were divided into four groups (five animals per group): young sedentary or trained and older sedentary or trained. The 12-week RT consisted of climbing a 1.1-m vertical ladder three times per week with progressive weights secured to the animals’ tails. The animals were killed 48 h after the end of the experimental period. The MMP-2 activity was assessed by the zymography method. Results: The aging process induced lower MMP-2 activity in the lumbar vertebrae and tibia (p=0.01). RT upregulated pro, intermediate, and active MMP-2 activity in the tibia of young rats (p=0.001). RT also upregulated pro and active MMP-2 activity in the lumbar vertebrae and tibia with advancing age (p=0.01). There was no significant difference (p> 0.05) between groups for MMP-2 of the femur, regardless of age and RT. Conclusion: The aging process impairs MMP-2 activity, but RT is a potential therapeutic approach to minimize the deleterious effects of ECM degeneration in different aged bones. Distinct MMP-2 responses to exercise training may result in specific remodeling processes

Remodeling process in bone of aged rats in response to resistance training

Aims We investigate the effects of RT on the mechanical function, gene, and protein expression of key factors involved in bone remodeling during aging. Main methods Male rats of 3 and 21 months of age were randomly allocated into four groups (8 per group): young sedentary (YS), young trained (YT), old sedentary (OS), and old trained (OT). RT was performed three times per week (12 weeks). Bone tenacity and stiffness were measured by biomechanical tests and mRNA levels of COL1A1, MEPE, SOST, OPG, BMP-2, PPAR-y, MMP-2-9-13, and TIMP-1 were evaluated by quantitative PCR. COL1A1 protein and MMP-2 activity were detected by western blotting and zymography assays. Key findings Aging increased stiffness, while BMP-2, OPG, COL1A1 and MMP-2 mRNA levels reduced (OS vs YS; p ≤ 0.05). RT increased the tenacity of the femur and reduced PPAR-γ regardless of age (YT vs. YS; OT vs. OS; p ≤ 0.05). RT downregulated SOST mRNA levels only in the OT group (vs. OS group, p ≤ 0.05). RT mitigated the age-associated increase in MMP-9 mRNA levels (p ≤ 0.05). In young animals, upregulation in MEPE, MMP-13, TIMP-1 were observed after RT, as well an increase in COL1A1 protein and MMP-2 activity (p ≤ 0.05). Significance RT improved bone tenacity independent of aging, which is relevant for mechanical function, while, at protein levels, RT upregulated MMP-2 activity and collagen 1 only in young rats. This study highlights the importance of exercise on bone health and identifies specific molecular changes in response to RT. Our findings provide insights into the mechanisms involved in age-related changes