Changes in cell size occur across brain regions in the aging Drosophila brain

Aging is accompanied by complex cellular changes in the brain, yet the interplay between cell size dynamics and ploidy, or DNA content during physiological aging is not well understood. Here, we employed flow cytometry to quantitatively analyze changes in cell size and DNA content in the aging Drosophila brain across specific brain regions, comparing the optic lobes (OLs) and central brain (CB). Our results reveal a large heterogeneity in brain cell size that is maintained during aging, despite an overall shift towards smaller cell sizes. This shift was observed early in the aging process and occurs similarly in OLs and CBs, with the OLs consistently exhibiting significantly smaller soma sizes than the CB. Simultaneously, we detected a significant, age-dependent accumulation of polyploid cells (cells with >2C DNA content), which was mostly evident in the OLs. Notably, although the polyploid cells are larger than diploid cells, the increase in polyploid cells was insufficient to counterbalance the age-related decline in cell size. This is in part because the average size of the polyploid cells also exhibited a decrease in size in the CB with age. We suggest that polyploidization exhibits region-specific differences with age, but that the age-associated loss of larger cells and cellular atrophy occurs across the brain and in polyploid as well as diploid cells. This work provides a foundation for future investigations into the mechanisms and consequences of age-dependent cellular shifts in the brain.