Age- Related Changes in Astrocytic and Ependymal Cells of the Subventricular Zone

Neurogenesis persists in the adult subventricular zone (SVZ) of the mammalian brain. During aging, the SVZ neurogenic capacity undergoes a progressive decline, which is attributed to a decrease in the population of neural stem cells (NSCs). However, the behavior of the NSCs that remain in the aged brain is not fully understood. Here we performed a comparative ultrastructural study of the SVZ niche of 2-month-old and 24-month-old male C57BL/6 mice, focusing on the NSC population. Using thymidine-labeling, we showed that residual NSCs in the aged SVZ divide less frequently than those in young mice. We also provided evidence that ependymal cells are not newly generated during senescence, as others studies suggest. Remarkably, both astrocytes and ependymal cells accumulated a high number of intermediate filaments and dense bodies during aging, resembling reactive cells. A better understanding of the changes occurring in the neurogenic niche during aging will allow us to develop new strategies for fighting neurological disorders linked to senescence. GLIA 2014;62:790-803 Main Points: (i) We investigate the proliferative activity of the NSCs during aging, showing that they divide less frequently than in the young mice; (ii) We explore the cell differentiation process of the NSCs, providing new evidence that they do not generate new ependymal cells during aging; (iii) Interestingly, we found that both astrocytes and ependymal cells acquire features of reactive cells in the aged SVZ. A better understanding of the changes occurring in the neurogenic niche during aging will allow us to develop new strategies to fight neurological disorders linked to senescence.