Department of Geriatrics, The First Affiliated Hospital, Chongqing Medical University, No. 1 Friendship Road, YuZhong District, Chongqing 400016, China.
The First People's Hospital of Zunyi, Zunyi, China.
Exp Cell Res. 2018 Feb 15;363(2):171-178. doi: 10.1016/j.yexcr.2017.12.030. Epub 2017 Dec 30.
Diabetes, characterized by chronic hyperglycemia, is known to induce synaptic degeneration in the brain, thereby resulting in cognitive dysfunction. Thrombospondin-1(TSP-1), the secreted protein produced by astrocytes, plays a crucial role in promoting synapse formation. Toll-like receptor 9 (TLR9) has been widely known to initiate the innate immune response. We recently reported TLR9 activation in neurons results in tau hyperphosphorylation induced by HG in vitro. Its activation has been also considered to mediate oxidative stress and astrocytic dysfunction under pathological circumstance. However, whether astrocytic TSP-1 alteration plays a role in synaptic protein loss under high glucose condition and whether TLR9 activation is involved in this process have not been reported. In this study, we found that primary mouse astrocytes incubated in high glucose (30mM) induced a significant decreased TSP-1 secretion and increased intracellular contents of TSP-1 without affecting transcription level. Addition of conditioned medium from high glucose (30mM) treated astrocytes to the primary neurons exhibited reduced synaptic proteins expression, which was attenuated by treatment with exogenous rTSP-1. In addition, we demonstrated that TLR9 activation along with reactive oxygen species (ROS) generation in astrocytes was induced by high glucose (30mM). Furthermore, we explored the relationship between TLR9 activation and TSP-1 production. Both TLR9 deficiency and the antioxidant N-acetyl-L-cysteine treatment improved altered intra- and extracellular TSP-1 levels under high glucose condition. Together, our findings suggest that high glucose (30mM) impairs TSP-1 secretion from astrocytes, which depends on astrocytic dysfunction associated with TLR9 activation mediated ROS signaling, ultimately contributing to the synaptic proteins loss.
糖尿病以慢性高血糖为特征，已知可诱导大脑中的突触退化，从而导致认知功能障碍。 由星形胶质细胞产生的分泌蛋白血栓素-1（TSP-1）在促进突触形成中起着至关重要的作用。 Toll 样受体 9（TLR9）已被广泛认为能引发固有免疫反应。我们最近报道称，神经元中 TLR9 的激活会导致体外高糖诱导的 tau 过度磷酸化。在病理情况下，其激活也被认为介导氧化应激和星形胶质细胞功能障碍。然而，星形胶质细胞 TSP-1 的改变是否在高糖条件下发挥作用，以及 TLR9 的激活是否参与这一过程尚未得到报道。在这项研究中，我们发现，在高葡萄糖（30mM）孵育的原代小鼠星形胶质细胞中，TSP-1 的分泌显著减少，细胞内 TSP-1 含量增加，而不影响转录水平。将高葡萄糖（30mM）处理的星形胶质细胞条件培养基添加到原代神经元中，可观察到突触蛋白表达减少，而外源性 rTSP-1 可减轻这种减少。此外，我们证明了 TLR9 的激活以及星形胶质细胞中活性氧（ROS）的产生是由高葡萄糖（30mM）诱导的。此外，我们还探讨了 TLR9 激活与 TSP-1 产生之间的关系。TLR9 缺乏和抗氧化剂 N-乙酰-L-半胱氨酸处理均可改善高糖条件下星形胶质细胞内外 TSP-1 水平的改变。总之，我们的研究结果表明，高葡萄糖（30mM）可损害星形胶质细胞中 TSP-1 的分泌，这依赖于与 TLR9 激活介导的 ROS 信号相关的星形胶质细胞功能障碍，最终导致突触蛋白丢失。
