Effects of low-dose rapamycin on lymphoid organs of mice prone and resistant to accelerated senescence.

Aging is a complex, natural, and irreversible phenomenon that subjects the body to numerous changes in the physiological process, characterized by a gradual decline in the organism's homeostatic mechanisms, closely related to immunosenescence. Here, we evaluated the regulation of immunosenescence in lymphoid organs of senescence-accelerated prone 8 (SAM-P8) and senescence-accelerated resistant 1 (SAM-R1) mice treated with a low dose of rapamycin (RAPA). Mice were treated with a dose of 7.1 µg/kg RAPA for 2 months and had body mass and hematological parameters analyzed prior and during treatment. Cellular and humoral parameters of serum, bone marrow, thymus, and spleen samples were evaluated by ELISA, histology, and flow cytometry. Changes in body mass, hematological parameters, cell number, and in the secretion of IL-1ß, IL-6, TNF-α, IL-7, and IL-15 cytokines were different between the 2 models used. In histological analyses, we observed that SAM-P8 mice showed faster thymic involution than SAM-R1 mice. Regarding the T lymphocyte subpopulations in the spleen, CD4+ and CD8+ T cell numbers were higher and lower, respectively, in SAM-P8 mice treated with RAPA, with the opposite observed in SAM-R1. Additionally, we found that the low dose of RAPA used did not trigger changes that could compromise the immune response of these mice and the administered dose may have contributed to changes in important lymphocyte populations in the adaptive immune response and the secretion of cytokines that directly collaborate with the maturation and proliferation of these cells.

O efeito do tratamento com rapamicina em órgãos linfoides de camundongos propensos à senescência acelerada / The effect of rapamycin treatment on lymphoid organs of senescence accelerated mice prone

Envelhecer compreende um fenômeno complexo, natural e irreversível, que submete o organismo a inúmeras alterações nos processos biológicos, fisiológicos, ambientais, psicológicos, comportamentais e sociais. Esse processo é caracterizado por um declínio gradual dos mecanismos homeostáticos do organismo, intimamente relacionados com o estado senescente. A senescência, quando diz respeito ao sistema imunológico, é denominada de imunossenescência, que pode ser definida como uma parada estável do ciclo celular associada a mudanças, com uma resposta que limita a proliferação de células envelhecidas ou danificadas. A autofagia está diretamente relacionada com a manutenção do fenótipo senescente, em que a atividade autofágica exerce um papel essencial e ativo na influência da biossíntese de proteínas e organelas. Essa via é regulada naturalmente pela proteína mTOR e quimicamente pelo fármaco rapamicina. Assim, pretendemos investigar: (1) as alterações no perfil corporal e hematimêtrico dos animais ao longo do tratamento com rapamicina; (2) avaliar o perfil de citocinas; (3) observar as modificações histológicas em órgãos linfoides primários e secundário; (4) analisar as populações de células linfoides e mieloides; e (5) avaliar a capacidade proliferativa de linfócitos in vitro. Camundongos SAMP-8 e SAMR-1 foram tratados com rapamicina durante dois meses. A mensuração da massa corporal e análises hematológicas foram realizadas antes e durante o tratamento. Amostras de soro, medula óssea, timo e baço foram analisados em ensaios de ELISA, histologia, população e subpopulações de células. Alterações na massa corporal, parâmetros hematológicos e celularidade de células foram nítidas entre os dois modelos utilizados. Diferenças também foram percebidas na detecção de citocinas IL-1ß. IL-6 e TNF-α, com resultados significantes nas amostras de baço, timo e medula óssea. As citocinas IL-7 e IL-15 apresentaram diferenças de secreção entre os grupos, sendo a primeira maior detectada em camundongos com senescência acelerada tratados com rapamicina. Em nossa análise histológica observamos que os camundongos SAM-P8 apresentaram involução tímica. E nas subpopulações de linfócitos T do baço, células TCD4+ e TCD8+ estavam, respectivamente, em maior e menor quantidade nos camundongos SAM-P8 tratados com rapamicina. Dessa forma, o camundongo da linhagem SAM-P8 é um excelente modelo para se estudar as alterações da senescência, em que o mesmo apresenta características fisiológicas distintas dos camundongos utilizados como controle (SAM-R1). Além disso, verificamos que a dose de rapamicina empregada não desencadeou alterações que pudessem comprometer a resposta imunológica desses camundongos, bem como na possibilidade de atuar na resposta contra os efeitos complexos do envelhecimento

Aging comprises a complex, natural, and irreversible phenomenon, which subjects the organism to countless alterations in biological, physiological, environmental, psychological, behavioral, and social processes. This process is characterized by a gradual decline in the organism's homeostatic mechanisms, closely related to senescence effects. Senescence, when it concerns the immune system, is called immunosenescence, which can be defined as a stable cell cycle arrest associated with changes and is a response that limits the proliferation of aged or damaged cells. Autophagy is a genetically regulated, conserved cellular process and a metabolic pathway essential for maintaining cellular homeostasis, which plays a constitutive and active role in controlling the biosynthesis of proteins and organelles. This pathway is regulated naturally by mTOR or chemically by the drug rapamycin, having a direct relationship with cellular homeostasis and maintenance of the senescent phenotype. Thus, we intend to investigate: (1) the changes in the body and hematimetic profile of the animals throughout the rapamycin treatment; (2) evaluate the cytokine profile; (3) observe histological changes in primary and secondary lymphoid organs; (4) analyze lymphoid and myeloid cell populations; and (5) evaluate the proliferative capacity of lymphocytes in vitro. SAMP-8 and SAMR-1 mice were treated with rapamycin for two months. Body mass measurement and hematological analyses were performed before and during treatment. Serum, bone marrow, thymus and spleen samples were analyzed in ELISA assays, histology, cell population and subpopulations. Changes in body mass, hematological parameters, and cellularity were clear between the two models used. Differences were also noticed in the detection of cytokines IL-1ß. IL-6 and TNF-α, with significant results in the spleen, thymus and bone marrow samples. The cytokines IL-7 and IL-15 showed differences in secretion between groups, the former being higher detected in mice with accelerated senescence treated with rapamycin. In our histological analysis we observed that SAM-P8 mice showed thymic involution. And in the spleen T-lymphocyte subpopulations, TCD4+ and TCD8+ cells were, respectively, in higher and lower quantities in SAM-P8 mice treated with rapamycin. Thus, the SAM-P8 mouse is an excellent model to study the changes of senescence, since it presents physiological characteristics different from the control mice (SAM-R1). Furthermore, we verified that the dose of rapamycin used did not trigger changes that could compromise the immune response of these mice, as well as the possibility of acting in the modulatory response against the complex effects of aging