BMAL1/ARNTL plays a critical, non-circadian role in secondary tissue damage after contusive SCI

昼夜节律调节着对生物体至关重要的广泛的生物过程 健康。这些节律的紊乱是许多病理的基础，包括全身性炎症、抑郁、 和神经退化。从机制上讲，昼夜节律是由基因的内在振荡变化驱动的。 由几个基因转录和信使核糖核酸翻译调节器协调的表达，形成 核心振荡器电路。这些关键调控因子，最重要的是非冗余转录/翻译 BMAL1/ARNTL因子在全身大多数细胞中都是活跃的，并经历昼夜节律的携带 外部时间提示，如光线或进食。在生物体水平上，振荡器的促节奏作用是 被广泛认为是动态平衡的关键贡献者。独立于中枢的BMal1效应 节律包括大脑中的抗氧化保护，寿命调节，对动脉粥样硬化的贡献和 内质网(ER)对癌细胞的应激敏化。这些或类似的组织特异性功能 BMal1可能影响脊髓损伤后的转归。然而，在分子水平上的时钟功能从来没有 在SCI的背景下进行的调查。出乎意料的是，我们发现：(I)中度挫伤的胸部脊髓 上调半暗带少突胶质细胞BMAL1，与内质网应激反应的诱导相一致 ERSR激活的促凋亡转录因子CHOP和内质网应激介导的OL的凋亡，(Ii)在 脊髓损伤，BMal1-/-小鼠表现出更好的运动恢复和白质储备(WMS)，以及选择性 CHOP及其促凋亡靶基因死亡受体5(DR5)表达下调与血液减少 渗出和炎症，小胶质细胞/巨噬细胞(MM)和内皮细胞(EC)广泛改变- 特定的基因表达。此外，BMAL1负反馈抑制的药理作用增强 降低OPC培养中的内质网应激毒性。这些令人兴奋的发现表明，BMAL1在 脊髓损伤的发病机制可能包括细胞自主调节CHOP介导的OL细胞凋亡 和/或EC/MM-细胞自主调节脊髓损伤后出血/血管功能障碍/细胞毒神经- 发炎。因此，我们将检验BMAL1调节OL、EC和/或MM基因表达的假设 这会导致脊髓损伤相关的脑白质丢失和运动恢复受损。为了检验这一假设， 我们将：(I)确定OL-、MM-和EC-BMAL1在脊髓损伤相关白质中的细胞自主作用 损伤和运动恢复，(Ii)确定BMAL1介导的增强运动功能的机制(S) 脊髓损伤引起的脑白质丢失，以及(Iii)评估BMAL1负反馈抑制的中介因子AS 减少脊髓损伤相关脑白质丢失和运动干预的药理学靶点 减损。我们将在野生型或细胞类型选择性的BMal1-/-小鼠中使用中度T9脊髓挫伤模型 以及针对BMAL1反馈调节的无毒、中枢神经系统通透性药物。这项研究可能会揭示 BMAL1对脊髓损伤后继发性组织损伤的新的、以前未被认识到的作用。

Circadian rhythms regulate a wide spectrum of biological processes of critical importance for organismal health. Perturbations of those rhythms underlie many pathologies including systemic inflammation, depression, and neurodegeneration. Mechanistically, circadian rhythms are driven by intrinsic oscillatory changes in gene expression that are orchestrated by several regulators of gene transcription and mRNA translation forming the core oscillator circuitry. Those key regulators, most importantly the non-redundant transcription/translation factor BMAL1/ARNTL, are active in most cells throughout the body and undergo circadian entrainment by external time cues such as light or feeding. At the organismal level, the pro-rhythmic role of the oscillator is widely recognized as a critical contributor to homeostasis. BMAL1 effects that are independent of the central rhythm include anti-oxidant protection in the brain, life span regulation, contributions to atherosclerosis and endoplasmic reticulum (ER) stress-sensitization of cancer cells. Those, or similar, tissue-specific functions of BMAL1 may affect the outcome after SCI. However, clock function at the molecular level has never been investigated in the context of SCI. Unexpectedly, we found that: (i) moderate contusive thoracic SCI upregulates BMAL1 in penumbral oligodendrocytes (OLs), coinciding with induction of the ER stress response (ERSR)-activated pro-apoptotic transcription factor CHOP and ER stress-mediated apoptosis of OLs, (ii) after SCI, Bmal1-/- mice show improved locomotor recovery and white matter sparing (WMS), as well as selective downregulation of Chop and its pro-apoptotic target gene death receptor 5 (Dr5) and reduced blood extravasation and inflammation, with extensive changes in microglia/macrophage (MM) and endothelial (EC)- specific gene expression. Also, pharmacological enhancement of the negative feedback inhibition of BMAL1 reduces ER stress toxicity in OPC cultures. These exciting findings suggest a novel role of BMAL1 in the pathogenesis of SCI which may include OL-cell autonomous regulation of CHOP-mediated OL apoptosis and/or EC/MM-cell autonomous modulation of post-SCI hemorrhage/vascular dysfunction/cytotoxic neuro- inflammation. Therefore, we will test the hypothesis that BMAL1 regulates OL, EC, and/or MM gene expression that contributes to SCI-associated white matter loss and impaired locomotor recovery. To test this hypothesis, we will: (i) determine the cell autonomous roles of OL-, MM-, and EC-BMAL1 in SCI-associated white matter damage and locomotor recovery, (ii) identify mechanism(s) that underlie BMAL1-mediated enhancement of SCI-driven white matter loss, and (iii) evaluate mediators of the negative feedback inhibition of BMAL1 as pharmacological targets for interventions to reduce SCI-associated white matter loss and locomotor impairment. We will use a moderate T9 SCI contusion model in wild type or cell type-selective Bmal1-/- mice and non-toxic, CNS-permeable drugs targeting the feedback regulation of BMAL1. This research may uncover novel, previously unrecognized contributions of BMAL1 to `secondary tissue injury after SCI.