👤 Mika Sasamoto

Although the regenerative capacity of the mammalian brain is quite weak, internal neural stem/progenitor cells (NSPCs) in the brain can provide new neurons into the brain lesions. Leukocytes, particularly T cells, infiltrate injured brain tissue and participate in immune reactions and have a large impact on the progress of the lesion. However, the effect of T cells on the regeneration of brain tissue remains unclear. Trimethyltin (TMT) is an organotin that has selective neurotoxicity on granule neurons in the hippocampal dentate gyrus. TMT-induced hippocampal lesion is mostly regenerated because adjacent NSPCs can provide new granule neurons. In this study, using TMT-injected mice as a model of brain tissue regeneration, the influence of T cells on hippocampal tissue regeneration was investigated. When TMT was injected into nude mice lacking T cells, they exhibited shortened immobility time in the tail suspension test, indicating improved functional outcomes. Immunohistochemical analysis revealed improved granule neuron replenishment and enhanced survival and differentiation of new neurons in nude mice. Microglial reaction characterized by phagocytosis and astrocytic reaction with brain-derived neurotrophic factor (BDNF) expression were enhanced in nude mice. Hippocampal tissue regeneration was impaired when nude mice were repopulated with total lymphocytes or with CD4- or CD8-positive cells. Repopulations of T cells altered microglial reactions; however, changes in astrocytes were not reproduced. These results suggest that both helper and cytotoxic T cells inhibit hippocampal tissue regeneration by preventing neuronal replenishment. T cells also affect lesion clearance by microglia and astrocytic BDNF expression; however, their effect is stronger on microglia. These findings provide novel insights into the immune regulation of brain tissue regeneration. Show less

Building on the identification of ABCB5 as a marker of limbal stem cells (LSCs), this study examines CD63, a newly identified molecule co-expressed with ABCB5 in limbal epithelial cells, to define its role in maintaining corneal epithelial cell identity. RNA sequencing (RNA-seq) was performed on flow cytometry-sorted Abcb5-positive and Abcb5-negative murine corneal epithelial cells. CD63 expression in human corneal tissue was assessed by immunostaining. CD63 was silenced in cultured human limbal epithelial cells using siRNA-mediated knockdown and resulting molecular and cellular changes were analyzed by qRT-PCR, flow cytometry, RNA-seq, Western blotting, and cell proliferation assays. RNA-seq analysis revealed increased expression of LSC markers, including Krt15, Krt6b, Fgfr1, Gpha2, Ifitm3, Ifitm1, and Cd63, and decreased expression of differentiation-associated markers, such as Krt12, Gja1, and Ovol1 in Abcb5-positive cells. Immunostaining of human corneal tissue demonstrated strong CD63 expression localized to the limbal region. Knockdown of CD63 in cultured human limbal epithelial cells resulted in reduced cell proliferation and significantly decreased expression of corneal epithelium-enriched genes, including KRT12, CLU, ALDH1A1, ALDH3A1, TGFBI, and MYEOV. Notably, CD63 knockdown led to an approximately 50% reduction in expression of PAX6, a key transcriptional regulator of corneal epithelial identity. CD63 is highly expressed in the human limbus and is required for maintaining cell proliferation and the expression of corneal epithelium-specific proteins, likely through regulation of PAX6. These findings establish CD63 as a functionally important component of limbal stem cell biology and a key contributor to corneal epithelial homeostasis. Show less