[Structural and functional basis for accelerated thymic involution in OXYS rats]

Thymus involution is one of the most pronounced manifestations of aging immune system, associated with increase susceptibility to infections, autoimmune diseases and cancer. Its nature in normal aging is actively under investigation. Much less attention is paid to the study of mechanisms of accelerated thymic involution. Previously, we showed the connection of accelerated senescence in OXYS rats with accelerated thymic involution, the mechanisms of which remain unclear. The aim of the present work was to study multifunctional condition of thymic epithelial cells in aging OXYS rats. Immunohistochemical analysis showed the reduction of thymic epithelial cell net in OXYS rats, significant decrease in volume and surface area of epithelial cells in cortical substance as compared to control Wistar rats. Electron microscopic study revealed the marked changes of epithelial cell ultrastructure, namely the reduction of cytoplasm volume, sharp decrease in size and quantity of secretory vacuoles, the presence of multiple autophagosomes and phagolysomes. The results indicate that one of the possible mechanisms of epithelial cell net reduction in thymus of senescence-accelerated OXYS rats can be the aggravation of autophagy, probably associated with mitochondrial dysfunction typical for OXYS rats. Despite the known fact of slowing autophagy with aging in some tissues, the example of OXYS rats allows to suggest that chronic deviation of intensity of this process from physiological level, either to decrease or activation, can lead to degenerative changes in organs and finally form the progeric phenotype of the whole organism.