Phenotypic Aging and Sexual Dimorphism in C57BL/6J, SAMR1, and SAMP8 Mice: A Comparative Study

Aging research increasingly relies on animal models to study the multifactorial processes of senescence. This study aimed to compare the physiological and metabolic parameters of C57BL/6J mice, a reference strain for biomedical research, with two strains commonly used to assess senescence: senescence-accelerated resistant 1 (SAMR1) and senescence-accelerated prone 8 (SAMP8) mice, over a 1-year period, in order to enhance our understanding of their utility in aging research. We focused on reproductive performance, glucose metabolism, bone density, hematological profiles, and overall longevity. SAMR1 mice exhibited higher prolificacy compared to C57BL/6J and SAMP8, with no significant differences in other reproductive parameters. Both SAMR1 males and females were larger and heavier, while C57BL/6J mice consumed less food relative to their body weight. Bone density decreased in all male groups from the fourth to the tenth month, while SAMP8 females showed an unexpected increase. C57BL/6J mice presented higher glucose levels, with SAMP8 males showing similar glucose intolerance and insulin resistance. Hematological analyses revealed sexual dimorphism, with SAMP8 males showing a distinct immunosenescence profile. Longevity varied by strain and sex, with SAMP8 males and SAMR1 females exhibiting shorter lifespans. These findings suggest that SAMR1 animals, despite sharing a genetic background with SAMP8, display a phenotype more akin to normal aging, supporting their use as a control in aging studies. Moreover, SAMP8's accelerated senescence makes it a valuable model for immunosenescence research. The study highlights the importance of considering strain- and sex-specific differences when working on aging research.