Characterization of Thymocytes and Splenocytes in Gdf8^Gdf11MD mice

Abstract

Immunosenescence refers to an age-related decline in immune function, primarily characterized by the gradual degeneration of the thymus, also known as thymic involution. Transforming growth factor-β (TGF-β) signaling is integral to the formation and normal function of the thymus. As a member of the TGF-β superfamily, Growth differentiation factor 11 (GDF11) and its receptors are expressed during thymocyte development. Moreover, GDF11 plays a critical role in the immune system by reducing inflammation through the regulation of specific pathways and immune cell functions. More importantly, GDF11 has been shown to have potential rejuvenating effects on various organs, including the heart and brain. However, its impact on thymic rejuvenation remains unknown. To study the effect of GDF11 on thymic involution, here we utilized the Gdf8^Gdf11MD mice, which have increased levels of circulating GDF11, and analyzed changes in their thymocyte and splenocyte populations. Our results showed that young adult female (4-month-old) and male (3-month-old) Gdf8^Gdf11MD mice exhibited a trend toward accelerated thymic involution compared to controls. Although this difference diminished with age, the reduction in thymic cellularity persisted into late adulthood (8-month-old) in male mutants. Notably, significant changes in the absolute number of multiple thymic subsets were observed in young (3-month-old) and pre-middle-aged (8-month-old) Gdf8^Gdf11MD males, indicating potential alterations in thymocyte development. Using flow cytometry, distinct immune cell subsets within the spleen were analyzed to further explore the effects of accelerated thymic involution on peripheral T cells in mutant mice. We found that, despite a significant increase in spleen weight in 12-month-old female and 8-month-old male mutants, there were no differences in the frequency or absolute number of splenocytes compared to controls. In addition, 4-month-old female Gdf8^Gdf11MD mutants exhibited an increased spleen-to-body weight ratio, accompanied by a decreased proportion but increased number of CD4⁺ central memory T cells (TCM). These findings demonstrate a possible correlation between GDF11 expression levels and thymic involution, highlighting the important role of GDF11 in immunosenescence.Graduate Educatio