ラット海馬における虚血耐性の発現と熱ショック蛋白70の役割

Correlation between Induction of Ischemic Tolerance and Expression of Heat Shock Protein-70 in the Rat Hippocampus

　ラット脳において非致死的な短時間の脳虚血を前処置することによる虚血耐性の獲得，および，熱ショック蛋白70（HSP 70）の役割を検討した。4血管閉塞法で非致死的な3分間虚血を前処置した3日後に6，8，10分間虚血を負荷し，7日後に組織学的に海馬CA 1領域の神経細胞密度を測定した。また，虚血後2時間，1，3，7日後に免疫組織化学的にHSP 70を染色した。6，8，10分虚血ではCA 1神経細胞は高度に脱落したが，3分間虚血を前処置すると6および，8分虚血後のCA 1神経細胞数は有意に多く残存した。HSP 70染色は，3分間虚血の1，3，7日後，3分＋6分間虚血の2時間，1，3，7日後にCA 1領域に強く染色された。偽手術＋6分間虚血の1，3日後にもHSP 70は染色された。以上より，虚血耐性の獲得にはHSP 70が発現されることが必要であるが，虚血後遅れて発現されても脳保護作用は発揮されず，虚血中および直後にHSP 70が存在することが虚血耐性の発現に重要であると考えられた。

We investigated the correlation between protec-tion against ischemic neuronal damage by precon-ditioning with sublethal ischemia and the expression of heat shock protein-70 (HSP70). Three minutes of forebrain ischemia in the rat induced by four-vessel occlusion and 3 days of reperfusion was foll-owed by 6, 8, and 10 minutes of ischemia. Seven days after the second ischemia, the brains were used for histology. Two hours, 1, 3, and 7 days after 3 or6 minutes of ischemia, the brains were used for immunohistochemistry with an antibody raised against HSP70. Three minutes of ischemia prod-uced no neuronal damage in the hippocampus. Six, 8, and 10 minutes of ischemia produced severe neuronal damage to CA1. However, CA1 neurons were preserved in animals subjected to 6 and 8 minutes of ischemia following preconditioning with 3 minutes of ischemia. Immunostaining showed that HSP70 was induced in the CA1 subfield 3 days after 3 minutes of ischemia. HSP70 was stained in the CA1, CA3, and CA4 subfields 1 and 3 days after 6 minutes of ischemia with or without precondition-ing. However, HSP70 was also stained in CA1 2 hours and 7 days after 6 minutes of ischemia follow-ing preconditioning. These results strongly suggest that stress response induced by sublethal ischemia protects against ischemic neuronal damage. How-ever, the protection was not seen when HSP70synthesis was delayed. Presence of HSP70 during and immediately after ischemia may be critical for the protection against ischemic neuronal damage following preconditioning.