Activation of the RXR/PPARγ axis improves long-term outcomes after ischemic stroke in aged mice

RXR/PPARγ 轴的激活可改善老年小鼠缺血性中风后的长期结果

• 批准号: 10364171
• 负责人: Jun Chen
• 金额: --
• 依托单位: VETERANS HEALTH ADMINISTRATION
• 依托单位国家: 美国
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-01-01 至 2025-12-31
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/10364171
• 关键词: Acute; Acute Brain Injuries; Adopted; Aging; Agonist; Animals; Anti-Inflammatory Agents; Antineoplastic Agents; Arbitration; Attenuated; Bexarotene; Biological; Body Size; Brain; Brain Ischemia; Caring; Cause of Death; Cells; Cerebral Ischemia; Cerebral cortex; Cerebrum; Chronic; Clinical Treatment; Clinical Trials; Cognitive; Data; Decision Trees; Development; Diagnosis; Disease; Distal; Dose; Elderly; Electrophysiology (science); Equilibrium; Evolution; Exhibits; FDA approved; Foundations; Funding; Future; Gatekeeping; Genetic Transcription; Goals; Guidelines; Histologic; Hyperactivity; Immune; Immune response; Immune system; Immunosuppression; Impairment; In Vitro; Inflammation; Inflammatory; Inflammatory Response; Injury; Ischemic Brain Injury; Ischemic Stroke; Knock-out; Left; Measurement; Metabolism; Microglia; Middle Cerebral Artery Occlusion; Modeling; Molecular; Mus; Nature; Nerve Fibers; Nervous System Physiology; Neuroglia; Neurologic Deficit; Neurological outcome; Neurons; Outcome; Oxidation-Reduction; PPAR gamma; Phagocytes; Phagocytosis; Pharmaceutical Preparations; Phenotype; Pilot Projects; Positioning Attribute; Primary Cell Cultures; Production; Proteins; RXR; Recovery; Recovery of Function; Research; Resolution; Role; Safety; Solid; Stroke; Survivors; Tamoxifen; Testing; Therapeutic; Time; Tissues; Veterans; aged; angiogenesis; behavior test; brain repair; central nervous system injury; clinical translation; clinically relevant; conditional knockout; disability; functional disability; functional outcomes; gray matter; healing; immune function; improved; in vitro testing; in vivo; insight; intraperitoneal; macrophage; mature animal; military men; military women; monocyte; neuroinflammation; neurological recovery; neuroprotection; new therapeutic target; novel; post stroke; pre-clinical; primary outcome; receptor binding; repaired; response; sex; stroke model; stroke outcome; stroke recovery; stroke therapy; tool; transcriptome; transcriptome sequencing; white matter; young adult

Ischemic stroke is a leading cause of death and long-term disability in elderly veterans. It is well established that post-stroke immune responses have a substantial impact on the progression of ischemic brain injury and brain recovery, but there are no clinical treatments that successfully harness the restorative power of the immune system while also tempering inflammation-induced secondary injuries. The reasons for this gap are multifactorial, but include a preclinical overemphasis on young adult animals, which simply do not display the same pathophysiological mechanisms underlying brain ischemia as the aged, including the dynamic inflammatory dialogue between glia and neurons. We propose to fill the critical gap in elderly veteran care by focusing on aged animals and repurposing an FDA-approved drug at low doses to correct hyperactive immune responses and tip the balance in favor of sustained tissue healing and long-term recovery of neurological functions. To commence this goal, we have conducted pilot studies on proteins that are highly enriched in microglia and brain-infiltrating macrophages (Mi/MΦ)—including the retinoid X receptor (RXR). RXR binds to peroxisome proliferator-activated receptor γ (PPARγ) to govern the transcription of genes critically involved in redox status, inflammation resolution, trophic factor production, and metabolism. Thus, RXR/PPARγ activation lies at the apex of a decision tree for arbitrating between polymorphic, often-opposing immune responses in Mi and MΦ. To engage this important biological target, we have chosen a selective RXR agonist, bexarotene, an FDA-approved antineoplastic agent lacking in pan-immunosuppressive effects and with excellent safety profiles. The scientific premise underlying the engagement of the RXR/PPARγ axis as a superior biological target for stroke is its ability to titrate immune balance toward anti-inflammatory/pro-repair phenotypes, while avoiding indiscriminate suppression of immune function in the vulnerable elderly. The premise of this proposal is also strengthened by our new preliminary discoveries: 1) Mi/MΦ-specific conditional knockout (mKO) of RXR or PPARγ worsens long-term outcomes after permanent distal middle cerebral artery occlusion (dMCAO) in mice. 2) RXR or PPARγ mKO mice exhibit impairments in post-stroke efferocytosis (Mi/MΦ phagocytosis of dying neurons) and resolution of neuroinflammation. 3) PPARγ mKO alters the Mi/MΦ transcriptome, with heightened proinflammatory responses and impaired phagocytosis according to RNA sequencing data. 4) Excitingly, intraperitoneal administration of low-dose bexarotene (10-20 times lower than in clinical trials) improves long-term outcomes after dMCAO in aged mice (20 months old). Accordingly, our research group is now in an excellent position to test the following core hypothesis: Activation of RXR improves long-term outcomes after ischemic stroke by promoting efferocytosis and inflammation-resolving, pro- repair microglial/macrophage responses. If funded, we will tackle three aims in a timely and efficient manner: Aim 1: Systematically test if bexarotene improves long-term histological and functional outcomes in aged (20 months old) stroke mice of both sexes. Aim 2: Test the subhypothesis that bexarotene promotes efferocytosis in Mi/MΦ and attenuates acute ischemic brain injury via activation of RXR. Aim 3: Test the subhypothesis that enhanced inflammation-resolving, pro-repair actions of Mi/MΦ contribute to bexarotene-afforded, RXR-dependent long-term beneficial effects against stroke. We will use aged subjects of both sexes and deploy state-of-the-art tools, such as cell-specific, conditional RXR knockout, electrophysiological measurements, stereological counting, and a battery of established behavior tests to gain novel mechanistic insights into the role of Mi/MΦ in stroke evolution. A rigorously confirmed beneficial effect of bexarotene on aged mice would facilitate its clinical translation into a potential stroke therapy for military men and women as well as elderly civilians.

缺血性中风是老年退伍军人死亡和长期残疾的主要原因。已充分证实 脑卒中后免疫应答对缺血性脑损伤和脑损伤的进展具有实质性影响， 恢复，但没有临床治疗，成功地利用免疫的恢复能力， 系统，同时也缓和炎症引起的继发性损伤。造成这种差距的原因是多方面的， 但包括对年轻成年动物的临床前过度注射， 老年脑缺血的病理生理机制，包括动态炎症反应， 神经胶质和神经元之间的对话。我们建议通过关注老年人， 动物和重新利用FDA批准的药物在低剂量，以纠正过度活跃的免疫反应和提示 有利于持续组织愈合和神经功能长期恢复的平衡。 为了实现这一目标，我们对小胶质细胞中高度富集的蛋白质进行了初步研究 和脑浸润巨噬细胞（Mi/MΦ）-包括类维生素A X受体（RXR）。RXR与过氧化物酶体结合 增殖物激活受体γ（PPARγ）控制关键参与氧化还原状态的基因的转录， 炎症消退、营养因子产生和代谢。因此，RXR/PPARγ的激活位于 用于在Mi和MΦ中多态且通常相反的免疫反应之间进行仲裁的决策树。到 我们选择了一种选择性RXR激动剂，贝沙罗汀，一种FDA批准的 缺乏泛免疫抑制作用且具有优异安全性的免疫抑制剂。科学 RXR/PPARγ轴作为卒中的上级生物学靶点的潜在前提是其能够 滴定抗炎/促修复表型的免疫平衡，同时避免不加选择地 抑制脆弱老年人的免疫功能。 我们的新的初步发现也加强了这一建议的前提：1）Mi/MΦ特异性 RXR或PPARγ基因的条件性敲除（mKO）在永久性远端中间 小鼠脑动脉闭塞（dMCAO）。2)RXR或PPARγ mKO小鼠在卒中后表现出损伤 细胞吞噬作用（死亡神经元的Mi/MΦ吞噬作用）和神经炎症消退。3)PPARγ mKO改变 Mi/MΦ转录组，具有增强的促炎反应和受损的吞噬作用， RNA测序数据。4)令人兴奋的是，腹腔注射低剂量贝沙罗汀（低10-20倍） 在老年小鼠（20个月大）中，dMCAO后的长期结果得到改善。因此，我们的 研究小组现在处于一个很好的位置来测试以下核心假设：RXR的激活提高了 缺血性卒中后的长期结果，通过促进红细胞增多和炎症消退， 修复小胶质细胞/巨噬细胞反应。如果获得资助，我们将及时有效地实现三个目标： 目的1：系统地测试贝沙罗汀是否改善老年人的长期组织学和功能结局 (20月龄）中风小鼠。 目的2：检验贝沙罗汀促进Mi/MΦ中的巨噬细胞增多并减弱急性 通过RXR激活的缺血性脑损伤。 目的3：验证Mi/MΦ的增强的炎症消退、促修复作用有助于 与贝沙罗汀提供的RXR依赖性抗卒中的长期有益作用有关。 我们将使用老年男女受试者，并部署最先进的工具，如细胞特异性，条件性 RXR敲除、电生理测量、体视学计数和一系列既定行为 测试以获得对Mi/MΦ在中风演变中的作用的新的机制见解。一个严格证实 贝沙罗汀对老年小鼠的有益作用将促进其临床转化为潜在的中风治疗 为军人男女和老年平民服务。