研究背景

作为一种复杂的多基因神经系统疾病，重度抑郁症对患者的生活质量及全球公共健康产生严重威胁。然而，由于存在病理机制尚未完全了解，用于临床的抗抑郁药物存在不完全有效、起效速度慢等一系列问题，新的抑郁症发病机制及治疗手段和药物正亟待被研究。最初被认为是DNA突变修复蛋白的PARP家族成员现在已越来越多地被证明在包括神经系统疾病在内的多种疾病的发病机制中扮演着重要角色。生信数据同样表明该家族成员PARP14及有可能作为FTO重要的下游靶标在抑郁症发病过程中起到作用。PARP14在众多研究中被发现与免疫细胞功能及转录调控中起到重要作用，而这种分子是否通过在免疫系统中的作用影响抑郁症发病过程仍有待研究。

研究目的

探究抑郁症模型小鼠相关脑区中PARP14表达水平是否存在差异，以及PARP14是否可能通过影响小胶质细胞的炎性反应从而影响抑郁症的发病过程。

研究方法

构建慢性束缚模型、慢性不可预知应激模型和脂多糖模型三种抑郁症模型小鼠，利用实时定量PCR和Western bolt的方法对三种抑郁症模型小鼠抑郁症相关脑区中PARP14的表达水平进行分析。培养永生化的BV2小胶质细胞系，分析PARP14表达水平是否会随LPS处理而产生变化；同时，通过在BV2细胞系过表达、敲低PARP14或经抑制剂处理后，通过验证几种促炎和抑炎的细胞因子mRNA表达情况以验证其响应LPS的炎症反应性。

研究结果

在慢性束缚、慢性不可预知应激和脂多糖三种抑郁症模型小鼠海马区均观察到了PARP14表达水平的升高，且CRS模型海马区PARP14表达水平与促炎炎症因子的表达水平呈正相关。LPS刺激小鼠永生化小胶质细胞系（BV2）后PARP14表达水平也随之升高；过表达Parp14后的BV2细胞响应LPS刺激表达更多的促炎性细胞因子，而敲低或抑制剂处理的BV2细胞响应LPS刺激表达更低的促炎性细胞因子。

结论

本研究表明，抑郁症模型小鼠海马区PARP14表达水平升高，且小胶质细胞中PARP14的表达水平影响其炎性反应过程。这提示我们压力应激可能通过增加小胶质细胞PARP14表达水平，从而促使神经炎性反应水平升高。

Background

As a complex polygenic mental disease, major depressive disorder has destructive impact on both the patients’ quality of life and the global public health. However, due to a series of problems such as the pathological mechanism has not been fully understood and the current clinical antidepressant drugs is incompletely effective and slowly take effect for patients, the comprehensive pathogenesis and new treatment of depression need to be studied urgently. Initially thought to be mutated DNA damage repair protein , PARP family members have now been increasingly shown to play an important role in the pathogenesis of various diseases including neurological diseases. At the same time,the data of our previous research suggest that PARP14, a member of this protein family, may play a role in the pathogenesis of depression as an important downstream target gene of FTO.PARP14 has also been proved playing critical role in the pathophysiology of several disease and the function of immune cells, but whether PARP14 plays a role in depression through its effects on the immune system still need further research.

Objectives

The purpose of this study is to examine whether there are differences in PARP14 expression levels in depression-related brain regions in mice models of depression and whether PARP14 may affect the pathogenesis of depression by affecting the inflammatory response of microglia cells.

Methods

Three kinds of mice models of depression were established to test whether the expression level of PARP14 is changed in depression-related brain areas by using real-time quantitative PCR and Western-bolt, including chronic restraint model(CRS), chronic unpredictable mild stress model(CUMS), lipopolysaccharide(LPS) model. Immortalized microglia cell line BV2 were cultured and simulated by lipopolysaccharide to analyze the change of PARP14 expression. At the cellular level, the inflammatory response of BV2 to lipopolysaccharide treatment after PARP14 overexpression, knockdown and PARP14 inhibitor treatment by analyzes the expression of several pro-inflammatory cytokines and anti-inflammatory cytokines detected by real-time quantitative PCR.

Results

We found that both mRNA and protein expression of PARP14 was increased in the hippocampus of three kinds of mice models of depression. Meanwhile, PARP14 expression level was correlated with the expression level of inflammatory factors in the hippocampus of chronic restraint model. When we used LPS to stimulate mouse immortalized microglia cell line (BV2),and found the expression level of PARP14 also increased; BV2 cells overexpressing Parp14 expressed more pro-inflammatory cytokines in response to LPS stimulation, while knockdown PARP14 or PARP14 inhibitor treated BV2 cells expressed less pro-inflammatory cytokines in response to LPS stimulation.

Conclusion

The present study shows that the expression level of PARP14 in the hippocampus of mice models of depression has increased; At the same time, the expression levels of PARP14 in microglia cells affected the inflammatory response process. All this suggests that stress may let the expression level of PARP14 in microglia cells and then promoting the increase of neuroinflammatory response which finally promotes the pathogenesis of depression.