アルツハイマー型認知症におけるミクログリア制御—免疫チェックポイント分子Tim-3の役割

Immune Checkpoint Tim-3 Regulates Microglial Function in Alzheimer's Disease

免疫チェックポイント分子Tim-3はミクログリアに高発現し，TGF-β-Smad2シグナル経路を促進してその恒常性維持に寄与する。Tim-3欠損によりミクログリアのアミロイドβ貪食能が亢進し，5xFADマウスにおいてアミロイドβ蓄積の減少，神経毒性の軽減，さらに認知機能の改善が認められた。これらの知見は，ミクログリア機能の精密制御を基盤とするアルツハイマー病の新たな治療戦略の可能性を示唆する。

Abstract

Microglia are resident immune cells of the central nervous system and play a central role in the pathogenesis of Alzheimer's disease (AD). Emerging evidence indicates that their functional state critically influences amyloid-β (Aβ) clearance, neuroinflammation, and disease progression. Tim-3, an immune checkpoint molecule, is highly expressed in microglia and functions as a key regulator of microglial homeostasis through the transforming growth factor-β (TGF-β)-Smad2 signaling pathway. Microglia-specific deletion of Tim-3 enhances phagocytic activity. Moreover, microglia-specific Tim-3 deficiency results in reduced Aβ deposition, decreased neurotoxicity, and improved cognitive performance in the 5xFAD mouse model of AD. These effects are not mediated by changes in Aβ production but rather by enhanced microglial clearance and remodeling of Aβ plaques into less toxic forms. Furthermore, single-cell analyses reveal that Tim-3 deficiency promotes a microglial state characterized by increased phagocytic capacity and reduced pro-inflammatory signaling. These findings suggest that Tim-3 acts as a functional checkpoint that limits beneficial microglial responses in AD and that targeting Tim-3 may therefore represent a promising therapeutic strategy for reprogramming microglia and improving disease outcomes.