Department of Medicine, LKS Faculty of Medicine, The University of Hong Kong, 8/F, 21 Sassoon Road, Pokfulam, Hong Kong, Special Administrative Region of China.
Neuroimmunology and Neuroinflammation Research Laboratory, LKS Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong, Special Administrative Region of China.
J Neuroinflammation. 2019 May 25;16(1):110. doi: 10.1186/s12974-019-1492-6.
Microglia-mediated neuroinflammation is important in Alzheimer's disease (AD) pathogenesis. Extracellular deposition of β-amyloid (Aβ), a major pathological hallmark of AD, can induce microglia activation. Adiponectin (APN), an adipocyte-derived adipokine, exerts anti-inflammatory effects in the periphery and brain. Chronic APN deficiency leads to cognitive impairment and AD-like pathologies in aged mice. Here, we aim to study the role of APN in regulating microglia-mediated neuroinflammation in AD.
Inflammatory response of cultured microglia (BV2 cells) to AβO and effects of APN were studied by measuring levels of proinflammatory cytokines (tumor necrosis factor α [TNFα] and interleukin-1β [IL-1β]) in cultured medium before and after exposure to AβO, with and without APN pretreatment. Adiponectin receptor 1 (AdipoR1) and receptor 2 (AdipoR2) were targeted by small interference RNA. To study the neuroprotective effect of APN, cultured HT-22 hippocampal cells were treated with conditioned medium of AβO-exposed BV2 cells or were co-cultured with BV2 cells in transwells. The cytotoxicity of HT-22 hippocampal cells was assessed by MTT reduction. We generated APN-deficient AD mice (APN5xFAD) by crossing APN-knockout mice with 5xFAD mice to determine the effects of APN deficiency on microglia-mediated neuroinflammation in AD.
AdipoR1 and AdipoR2 were expressed in BV2 cells and microglia of mice. Pretreatment with APN for 2 h suppressed TNFα and IL-1β release induced by AβO in BV2 cells. Additionally, APN rescued the decrease of AMPK phosphorylation and suppressed nuclear translocation of nuclear factor kappa B (NF-κB) induced by AβO. Compound C, an inhibitor of AMPK, abolished these effects of APN. Knockdown of AdipoR1, but not AdipoR2 in BV2 cells, inhibited the ability of APN to suppress proinflammatory cytokine release induced by AβO. Moreover, pretreatment with APN inhibited the cytotoxicity of HT-22 cells co-cultured with AβO-exposed BV2 cells. Lastly, APN deficiency exacerbated microglia activation in 9-month-old APN5xFAD mice associated with upregulation of TNFα and IL-1β in the cortex and hippocampus.
Our findings demonstrate that APN inhibits inflammatory response of microglia to AβO via AdipoR1-AMPK-NF-κB signaling, and APN deficiency aggravates microglia activation and neuroinflammation in AD mice. APN may be a novel therapeutic agent for inhibiting neuroinflammation in AD.
小胶质细胞介导的神经炎症在阿尔茨海默病（AD）发病机制中很重要。β-淀粉样蛋白（Aβ）的细胞外沉积是 AD 的主要病理标志之一，可诱导小胶质细胞活化。脂联素（APN）是一种脂肪细胞衍生的脂肪因子，在周围和大脑中具有抗炎作用。慢性 APN 缺乏会导致老年小鼠认知障碍和类似 AD 的病理。在这里，我们旨在研究 APN 在调节 AD 中小胶质细胞介导的神经炎症中的作用。
通过测量暴露于 AβO 前后培养的小胶质细胞（BV2 细胞）中促炎细胞因子（肿瘤坏死因子α[TNFα]和白细胞介素-1β[IL-1β]）在培养物中的水平，研究 AβO 对培养物中小胶质细胞炎症反应的影响，以及 APN 预处理对其的影响。用小干扰 RNA 靶向脂联素受体 1（AdipoR1）和受体 2（AdipoR2）。为了研究 APN 的神经保护作用，用 AβO 暴露的 BV2 细胞的条件培养基处理培养的 HT-22 海马细胞，或在 Transwell 中共培养 BV2 细胞。通过 MTT 还原评估 HT-22 海马细胞的细胞毒性。我们通过将 APN 敲除小鼠与 5xFAD 小鼠杂交，生成 APN 缺乏的 AD 小鼠（APN5xFAD），以确定 APN 缺乏对 AD 中小胶质细胞介导的神经炎症的影响。
AdipoR1 和 AdipoR2 在 BV2 细胞和小鼠小胶质细胞中表达。APN 预处理 2 小时可抑制 AβO 诱导的 BV2 细胞中 TNFα和 IL-1β的释放。此外，APN 挽救了 AβO 诱导的 AMPK 磷酸化减少，并抑制了核因子 kappa B（NF-κB）的核易位。AMPK 的抑制剂 Compound C 消除了 APN 的这些作用。在 BV2 细胞中敲低 AdipoR1，但不敲低 AdipoR2，可抑制 APN 抑制 AβO 诱导的促炎细胞因子释放的能力。此外，APN 预处理可抑制与 AβO 暴露的 BV2 细胞共培养的 HT-22 细胞的细胞毒性。最后，APN 缺乏症加剧了 9 月龄 APN5xFAD 小鼠的小胶质细胞活化，与皮质和海马中 TNFα和 IL-1β的上调有关。
我们的研究结果表明，APN 通过 AdipoR1-AMPK-NF-κB 信号通路抑制小胶质细胞对 AβO 的炎症反应，APN 缺乏症会加剧 AD 小鼠的小胶质细胞活化和神经炎症。APN 可能是一种抑制 AD 中神经炎症的新型治疗剂。
