Cell Biology and Physiology Division, CSIR-Indian Institute of Chemical Biology, 4 Raja S. C. Mullick Road, Kolkata 700 032, India.
Cell Biology and Physiology Division, CSIR-Indian Institute of Chemical Biology, 4 Raja S. C. Mullick Road, Kolkata 700 032, India.
Brain Behav Immun. 2020 Jul;87:804-819. doi: 10.1016/j.bbi.2020.03.014. Epub 2020 Mar 16.
Alzheimer's disease (AD) is characterized by two pathologic species, extracellular amyloid-β (Aβ) plaques and intracellular neurofibrillary tangles. Astrocytes that maintain normal homeostasis in the brain undergo a set of molecular, cellular and functional changes called reactive astrogliosis in various neurological diseases including AD. It is hypothesized that reactive astrocytes initially tend to protect neurons by reducing Aβ load and by secreting a plethora of cytokines, however, their functions have only been poorly investigated. Our studies on the kinetics of activation of cortical astrocytes following Aβ-exposure revealed significant level of activation as early as in 6 h. The astrocyte conditioned medium (ACM) from 6 h Aβ-treated astrocytes (Aβ-ACM) provided significant neuroprotection of cultured cortical neurons against Aβ insults. Analysis of the secreted proteins in Aβ-ACM revealed a marked increase of Tissue inhibitor of Metalloproteinase-1 (TIMP-1) within 6 h. Interestingly, we found that neutralization of TIMP-1 with antibody or knockdown with siRNA in astrocytes abolished most of the neuroprotective ability of the 6 h Aβ-ACM on Aβ-treated cultured neurons. Furthermore addition of exogenous rat recombinant TIMP-1 protein protects primary neurons from Aβ mediated toxicity. In a well characterized Aβ-infused rodent model of AD, intra-cerebroventricular administration of TIMP-1 revealed a reduction in Aβ load and apoptosis in hippocampal and cortical regions. Finally, we found that TIMP-1 can ameliorate Aβ-induced cognitive dysfunctions through restoration of Akt and its downstream pathway and maintenance of synaptic integrity. Thus, our results not only provide a functional clarity for TIMP-1, secreted by activated astrocytes, but also support it as a major candidate in cytokine-mediated therapy of AD especially at the early phase of disease progression.
阿尔茨海默病（AD）的特征是两种病理物种，细胞外淀粉样蛋白-β（Aβ）斑块和细胞内神经原纤维缠结。在包括 AD 在内的各种神经疾病中，维持大脑正常内稳态的星形胶质细胞会发生一系列称为反应性星形胶质细胞的分子、细胞和功能变化。据推测，反应性星形胶质细胞最初通过减少 Aβ 负荷和分泌大量细胞因子来保护神经元，但其功能仅得到了很差的研究。我们对 Aβ 暴露后皮质星形胶质细胞激活动力学的研究表明，早在 6 小时就出现了明显的激活水平。来自 6 小时 Aβ 处理星形胶质细胞（Aβ-ACM）的星形胶质细胞条件培养基（ACM）为培养的皮质神经元提供了针对 Aβ 损伤的显著神经保护作用。对 Aβ-ACM 中分泌蛋白的分析表明，TIMP-1（基质金属蛋白酶组织抑制剂-1）在 6 小时内明显增加。有趣的是，我们发现星形胶质细胞中 TIMP-1 的中和抗体或 siRNA 敲低可消除 6 小时 Aβ-ACM 对 Aβ 处理的培养神经元的大部分神经保护作用。此外，外源性大鼠重组 TIMP-1 蛋白可保护原代神经元免受 Aβ 介导的毒性。在一种经过充分特征描述的 AD 型 Aβ 输注啮齿动物模型中，脑室内给予 TIMP-1 可减少海马和皮质区域的 Aβ 负荷和细胞凋亡。最后，我们发现 TIMP-1 可以通过恢复 Akt 及其下游途径和维持突触完整性来改善 Aβ 引起的认知功能障碍。因此，我们的研究结果不仅为激活星形胶质细胞分泌的 TIMP-1 提供了功能上的明确性，还支持它作为 AD 细胞因子介导治疗的主要候选物，特别是在疾病进展的早期阶段。
