脂联素调控成体海马可塑性与抗抑郁机制的研究

Reduction of hippocampal neurogenesis and synaptic plasticity after exposure to external stressors has been considered critical in the pathogenesis of depression. As an effective non-medicinal anti-depressive strategy, physical exercise is able to reverse the above-mentioned neurobiological changes with an unknown mechanism. Our previous study has shown that physical exercise-elicited increase of the adipokine adiponectin in the hippocampal region could enhance proliferation of neural progenitor cells, and concurrently decrease depression-like behaviors in non-stressed mice, which, for the first time, raised the possibility that adiponectin might be the key molecule mediating the anti-depressive effects of physical exercise. To verify this notion, we shall introduce external stress insult by repeated corticosterone injections, and employ both the transgenic mice as well as the cell culture platform to in depth investigate: 1) whether adiponectin exerts the therapeutic anti-depressive effects; 2) whether the antagonism towards corticosterone-triggered aversive influences by adiponectin involves its effects on proliferation and neuronal differentiation of hippocampal neural progenitor cells, as well as on synaptic plasticity; 3) what downstream signal transductions that enable adiponectin and corticosterone to affect neurogenesis have been activated, and whether the brain levels of neurotrophic factors are influenced in this process. The results are expected to shed light on the development of new drugs for the anti-depressive therapy; meanwhile, they may also assist in searching for objective biomarkers to better apply and evaluate the physical exercise intervention during anti-depressive medication.

外界应激刺激造成的海马神经发生与突触可塑性下降被认为是抑郁产生的重要成因。运动作为有效的非药物治疗手段可以逆转上述神经生物学改变，然而机制一直未明。我们在前期研究中发现运动后海马区脂肪细胞因子脂联素升高能促进小鼠神经前体细胞增殖并且减少非应激刺激下的抑郁行为，因而提出脂联素是介导运动抗抑郁的关键分子。为了证实该假说，本课题将利用持续皮质酮注射模拟外界应激刺激，同时借助转基因小鼠和细胞培养平台来深入探讨：1)脂联素有无治疗性的抗抑郁的能力；2)脂联素是否通过影响海马前体细胞的增殖与神经分化，以及改变突触可塑性来拮抗皮质酮升高所带来的不良影响；3)脂联素和皮质酮分别通过激活何种信号传导通路来调控神经发生，且是否影响脑内神经营养因子的水平。本研究旨在为治疗性的抗抑郁药物开发提供新思路，同时也有助于寻找客观的生物标记物来对抑郁治疗中的运动干预进行更有效地实施和评估。

应激造成海马神经发生与突触可塑性异常被认为是抑郁症的重要成因，运动作为其有效治疗手段起效机制未明。我们前期发现运动后海马脂联素（ADN）升高能促小鼠神经前体细胞（NPC）增殖，同时减少非应激下抑郁样行为；但若想证实ADN是介导运动抗抑郁的关键分子，则还须明确其有无治疗性的抗抑郁效果，如何拮抗皮质酮（COR）的影响，以及是否串扰经典神经营养因子。首先我们通过脑室病毒注射增加了海马ADN含量。对于未运动野生型（WT）小鼠，过表达ADN减轻了COR引起的抑郁样行为及海马新生细胞减少，且两者成负相关，提示ADN通过促海马NPC增殖发挥治疗性抗抑郁效果。ADN过表达的同时脑源性神经生长因子未增加，显示两者间无串扰。转基因小鼠实验证明在基础状态下，ADN敲除（KO）不影响运动能力、海马神经发生、焦虑或抑郁状态。COR注射相似地抑制了未运动WT和KO小鼠海马神经发生，增加了抑郁样行为，但运动对上述指标的逆转仅在WT小鼠中存在，且伴有血清和海马ADN增加以及促神经生长AMPK通路激活。在所设实验参数下，齿状回突触蛋白含量、突触数量、经典神经营养因子各组间均无差别。WT和KO小鼠处理前后神经元分化比例相似，同时ADN信号通路下游组分表达水平各组间亦相仿，仅WT运动小鼠的衔接蛋白APPL2和糖皮质激素受体下降，提示ADN对运动治疗性抗抑郁效果必不可少。体外原代海马NPC和神经元实验显示单纯敲除ADN不干扰下游通路分子表达或基础状态下NPC增殖、分化。外源性ADN通过脂联素受体1(ADNR1)激活AMPK可促NPC增殖，但不影响神经分化，亦不改变成熟神经元突触蛋白表达。ADN可通过AMPK通路拮抗COR造成的NPC增殖抑制。综上所述，ADN被证实是介导运动抗抑郁的关键分子。其通过激活ADNR1/AMPK通路提高海马新生神经元数量，从而对抗COR所致NPC增殖抑制，且起效不依赖于经典神经营养因子参与。本研究的成果为治疗性抗抑郁药物开发提供了新思路，同时检测ADN水平也有助于抑郁症运动治疗的临床开展和评估。