轴索损伤后热休克蛋白70的变化对Tau蛋白表达的影响

Protective role of HSP70 in rats after axonal injury by down-regulating Tau expression

目的观察大鼠轴索损伤后相应神经元内热休克蛋白(heat shock protein70,HSP70)和Tau蛋白表达的变化及热应激对其表达的影响,探讨HSP70神经保护作用的机制。方法将57只雄性Wistar大鼠分为正常对照组(A组,3只)、单纯视神经牵拉伤组(B组,18只)、单纯热应激处理组(C组,18只)和热应激预处理牵拉伤组(D组,18只)。对B组大鼠右侧视神经施予牵拉,对C组大鼠施予热应激处理,D组大鼠经热应激预处理24h后再对右侧视神经施予牵拉。B、C、D组分别在伤后4、8、16h,1、3、5d各处死3只动物。光镜下观察视神经、视网膜神经节细胞(retinal ganglion cells,RGCs)的形态学变化,免疫组化染色检测各组动物RGCs中HSP70、Tau蛋白的表达情况。结果牵拉伤后视神经轴索、RGCs的形态发生明显的病理变化,热应激预处理再致伤后上述病理改变有显著改善。单纯牵拉伤可使RGCs中HSP70、Tau蛋白的表达增强,单纯热应激处理后HSP70的表达增强、Tau蛋白的表达不受影响,热应激预处理后再致伤使HSP70的表达明显增强、高峰表达时间提前、维持时间延长,而Tau蛋白的表达明显减弱。结论Tau蛋白表达增强可能参与了迟发性轴索断裂及迟发性神经元凋亡;HSP70可能通过减轻Tau蛋白的异常聚集而发挥神经保护作用;增强内源性神经保护作用可能是弥漫性轴索损伤治疗的新途径。

Objective To observe the expressions of heat shock protein 70 （HSP70） and Tau in retinal ganglion ceils （RGCs） after stretch injury to right optic nerve in rats and the effect of heat stress on HSP 70 and Tau expressions in order to explore the mechanism of neuroprotective role of HSP70. Methods Fifty-seven male Wistar rats were randomly divided into 4 groups, that is, control group （ Group A, 3 rats）, stretch-only group （Group B, 18 rats）, heat stress group （Group C, 18 rats） and heat stress pretreatment plus stretch group （Group D, 18 rats）. Stretch injury was induced in the right optic nerves of rats according to Gennarelli＇ s model stimulating diffuse axonal injury. Heat stress was applied to animals by keeping their rectal temperature up to 42 ℃ in water bath. Animals in Group D inflicted the stretch injury 24 h after heat stress. Three rats respectively from Group B, Group C and Group D were killed at 4, 8 and 16 h, 1,3 and 5 d after injury respectively. Morphological changes of optic nerves and RGCs after stretch injury were examined under light microscope. The expressions of HSP70 and Tau in RGCs were observed using immunohistochemistry. Results Obvious pathological changes of axons and RGCs after stretch injury were identified morphologically or quantitatively, and significantly amehorated through pretreatment with heat stress before stretch injury. The increased expressions of HSP70 and Tau in RGCs occurred Group B. The increased expression of HSP70 and no change of expression of Tau were observed in Group C. A much more enhanced expression of HSP 70 with an earlier peak and longer maintenance period and a significantly decreased expression of Tau were found in Group D. Conclusion The increased expression of Tau is associated to delayed axotomy and neuron apoptosis. The neuroprotection of HSP70 is likely based its effect on reducing aggregation of Tau. A new approach to treatment of diffuse axonal injury（DAI） may be developed through the enhancement of intrinsic neuroprotective functions.