Alterations in immune cell heterogeneities in the brain of aged zebrafish using single-cell resolution

Immunocytes,including the microglia,are crucial in the neurodegenerative process in old people.However,the understanding regarding microglia heterogeneity and other involved immunocytes remains elusive.We analyzed 26,456 immunocytes from 12-and 26-month-old zebrafish brains at single-cell resolution.Microglia and T lymphocytes were detected in the brain at both time points.Two types of microglia were annotated,namely,ac+microglia and xr+microglia,which were clustered into subsets 1,2,3,4,5,and subsets 6,7,8,9,respectively.Diversified microglia predominated the adult brains and cooperated with T cells to perform the functions of immune response and neuronal nutrition.We validated the specific microglia markers.The novel transgenic lines,Tg(lgals3bpb:e GFP)and Tg(apoc1:e GFP),were created,which faithfully labeled ac+microglia and served as valuable labeling tools.However,the microglia population reduced while T cells of six subtypes intriguingly increased to serve as the primary immune cells in aged brains.Unlike in 12-month-old brains,T cells,together with microglia,exhibited a coordinated signature of inflammation in the 26-month-old brains.Our findings revealed the immunocytes atlas in aged zebrafish brains.It implied the involvement of microglia and T cells in the progression of neurodegeneration in aging.