Consequences of Age-Related Impairments in the Dynamic Regulation of Active Microglia by Astrocytes

 描述(申请人提供)：小胶质细胞和星形胶质细胞是识别、解释、繁殖和调节免疫反应的关键细胞。在老年人中，外周感染会引发精神错乱和行为障碍。此外，老年人正在进行的炎症过程与抑郁样并发症有关。这些并发症不是衰老的正常部分，对生活质量和寿命有负面影响。随着年龄的增长，免疫系统和大脑之间的通信发生变化的原因尚不清楚，但我们的数据表明，小胶质细胞的调节受损。我们已经报道了来自老年小鼠的小胶质细胞在用脂多糖(LPS)进行外周免疫攻击后被激活并变得过度活跃。衰老的小胶质细胞产生炎症(IL-1)和抗炎(IL-10)细胞因子的放大水平。尽管IL-10是一种有效的抗炎细胞因子，但内毒素诱导的老年脑内小胶质细胞激活时间延长，并与抑郁样行为的发展有关。我们的修订方案以一种创新的方式解决了这一关键问题，将星形胶质细胞确定为免疫挑战后未能解决老龄大脑中小胶质细胞激活的关键细胞。这里提供的新数据表明，老年大脑中激活的星形胶质细胞减少了IL-10受体-1的表达，并相应地降低了对IL-10的敏感性。老化的星形胶质细胞对IL-10的这种不敏感导致不能产生转化生长因子β并减弱小胶质细胞的激活。这些发现填补了该领域关于如何调节小胶质细胞以防止夸大的神经炎症的一个重大空白。因此，该项目的目标是检验这一假说，即老年大脑在外周炎症挑战后持续的神经炎症是由星形胶质细胞依赖的小胶质细胞调节受损引起的。为了解决这一假设，本文提出了三个具体目标。在AIM-1中，我们将确定衰老星形胶质细胞IL-10敏感性降低对其体内和体外调节活跃小胶质细胞能力的损害程度。免疫攻击后星形胶质细胞中IL-10/IL-10R1信号功能的年龄相关问题将被描绘出来，小胶质细胞中转化生长因子β/转化生长因子βR信号的相应缺陷将被确定。我们将使用几种独特的方法来确定免疫攻击后成年和老年小鼠小胶质细胞和星形胶质细胞的mRNA拷贝数、蛋白表达、形态和体外相互作用。在AIM-2中，我们将确定病毒基因治疗在多大程度上增强了星形胶质细胞上的IL-10R1特异性，恢复了小胶质细胞的调节，并防止了免疫攻击后老年小鼠的抑郁样行为。在AIM-3中，我们将确定在老年脑中恢复转化生长因子β是否可以绕过免疫攻击后星形胶质细胞对IL-10的不敏感，并减弱小胶质细胞的过度激活，防止抑郁样行为。了解受损的星形胶质细胞IL-10重新编程如何导致神经炎症和抑郁样行为，将导致针对星形胶质细胞的新干预措施，以减少与老年人炎症挑战相关的神经精神并发症。

 DESCRIPTION (provided by applicant): Microglia and astrocytes are key cells that recognize, interpret, propagate and regulate immune responses. In the elderly, peripheral infections can trigger delirium and behavioral disturbances. Moreover, ongoing inflammatory processes in the elderly are associated with depressive-like complications. These complications are not a normal part of aging and negatively affect quality of life and life-span. The cause of this altered communication between the immune system and the brain with age is unclear, but our data points to an impaired regulation of microglia. We have reported that microglia from aged mice are primed and become hyperactive following a peripheral immune challenge with lipopolysaccharide (LPS). Aged microglia produce amplified levels of both inflammatory (IL-1) and anti-inflammatory (IL-10) cytokines. Although IL-10 is a potent anti-inflammatory cytokine, LPS-induced microglial activation in the aged brain is prolonged and is associated with development of depressive-like behavior. Our revised proposal addresses this critical problem in an innovative manner by identifying astrocytes as the pivotal cell in the failure to resolve microglial activation in the aged brain following immune challenge. Novel data provided here indicate that activated astrocytes in the aged brain have decreased IL-10 receptor-1 expression with corresponding reduced sensitivity to IL-10. This IL-10 insensitivity of aged astrocytes results in failure to produce TGFβ and attenuate microglial activation. These findings fill a majo gap in the field about how microglia are regulated to prevent exaggerated neuroinflammation. Thus, the goal of this project is to test the hypothesis that prolonged neuroinflammation in the aged brain following a peripheral inflammatory challenge is caused by impaired astrocyte-dependent regulation of microglia. To address this hypothesis, three specific aims are proposed. In Aim-1, we will determine the degree to which reduced IL-10 sensitivity of aged astrocytes impairs their ability to regulate active microglia in vivo and ex vivo. Age-related issues in the functionality of IL-10/IL-10R1 signaling in astrocytes following immune challenge will be delineated and corresponding deficits in TGFβ/TGFβR signaling in microglia will be determined. We will use several unique approaches to determine microglia and astrocyte mRNA copy number, protein expression, morphology, and ex vivo interactions in adult and aged mice after immune challenge. In Aim-2, we will ascertain the extent to which viral gene therapy enhancement of IL-10R1 specifically on astrocytes restores microglial regulation and prevents depressive-like behavior in aged mice following immune challenge. In Aim-3, we will determine if restoration of TGFβ in the aged brain circumvents IL-10 insensitivity of astrocytes after immune challenge and attenuates microglia hyper-activation and prevents depressive-like behavior. Understanding how impaired IL-10 re-programming of astrocytes contributes to neuroinflammation and depressive-like behavior will lead to new interventions that target astrocytes in order to reduce neuropsychiatric complications associated with inflammatory challenge in the aged.