酮体代谢对急性脊髓损伤神经保护作用机制的研究

Ketogenic diet (KD) with high fat and low carbohydrate, and calorie restriction in the form of every-other-day fasting (EODF) result in ketone body metabolism and increase the β-hydroxybutyrate (βOHB) level. We discovered that KD or EODF improved outcomes after an incomplete cervical spinal cord contusion injury. Exciting new data show that βOHB is an endogenous histone deacetylase inhibitor, resulting in an incrase of gene expression of oxidative stress resistance in kidney. We recently found that ketone body metabolisms enhanced acetylation and regulated gene expression in normal spinal cord, paving the way for neuroprotective mechanism of acute spinal cord injury under ketone body metabolism. Our overall hypothesis is that βOHB induced by ketone body metabolisms is an endogenous and specific inhibitor of histone deacetylase, increases histon acetylation in the spinal cord tissue and suppresses the oxidative stress after SCI. Changes in transcription of the genes encoding oxidative stress factors, and SCI oxidative stress is dose-dependent to the βOHB level. This study aims to: 1) explore effects of βOHB induced by ketone body metabolisms on expression of genes related to suppression of oxidative stress, and histone deacetylation in the spine cord tissues after acute cervical spinal cord contusion; 2) evaluate the effect of inhibition of monocarboxylate transporter on prevention of SCI neuroprotection, gene expression, HDACs and oxidative stress; 3) determine the suppression of oxidative stress and changes of histone acetylation after SCI treatments using ketone body metabolism; 4) evalute effects of every-other-day-ketone-diet on neuroprotection, acetylation and suppression of oxidative stress. This study will provide a solid preclinical basis in support of SCI treatment, and pave an innovative nutritional regimen for SCI.

生酮饮食或隔日禁食均使机体出现酮体代谢，提高β羟丁酸水平。我们前期研究证实大鼠急性脊髓损伤（SCI）后给予生酮饮食或隔日禁食都有明显的神经保护作用。近来发现β羟丁酸是组蛋白去乙酰化酶（HDACs）的内源性抑制剂，在肾脏组织中调节抗氧化应激因子的基因水平。我们继而发现酮体代谢导致正常脊髓组织的乙酰化水平上升和基因上调，为阐明其对SCI的神经保护机制提供了依据。由此，我们提出新理论假设：β羟丁酸特异性阻滞损伤脊髓的HDACs，抑制急性SCI的氧化应激；抗氧化应激因子的基因转录水平的调节和氧化应激的抑制程度与β羟丁酸有剂量相关性。本项目研究：1)酮体代谢对大鼠颈脊髓挫伤后脊髓HDACs的抑制和抗氧化应激因子的基因转录水平调节；2)阻断酮体转运的影响；3)酮体代谢治疗SCI远期的脊髓组织乙酰化和氧化应激程度；4）隔日生酮饮食对急性SCI的神经保护作用。这将为SCI治疗提出新理论，发展新的干预途径。

脊髓损伤（SCI）从病理角度可分为原发性和继发性损伤两个阶段。原发性损伤主要由机械刺激直接损伤，导致轴突、血管和神经细胞等的破坏，难以干预治疗。继发性损伤包括电解质紊乱、活性氧自由基(ROS)形成、缺血、水肿、炎症和凋亡等，是可施加治疗的关键因素。生酮饮食（KD）最早被用于治疗难治性癫痫，近年研究表明其在多种神经系统退行性病变及神经损伤的治疗中有一定作用。酮体主要成分β羟基丁酸（βOHB）在肾脏组织中被证实是一种内源性I型组蛋白去乙酰化酶（HDAC）抑制剂，在骨髓源性巨噬细胞中，βOHB也被证实可抑制NLRP3炎症小体的激活，从而调节炎症反应。在脊髓组织中βOHB对I型HDACs和NLRP3炎症小体的影响尚缺乏研究，有望进一步阐明KD治疗SCI的分子机制。本研究发现KD后大鼠血液及脑脊液中βOHB显著升高，为βOHB治疗脊髓损伤提供了依据。同时，我们发现KD干预后，大鼠SCI后其肢体运动功能及神经电生理指标得到明显恢复。其潜在的机制可能是βOHB在脊髓组织中通过抑制I型HDACs调节氧化应激，并且通过抑制NLRP3调节炎症反应来改善大鼠SCI后神经功能。这将为 SCI 治疗提出新理论基础，发展新的干预途径。最后，我们发现KD对啮齿类动物骨质产生的不利影响也不能小觑。KD能够导致啮齿类动物骨量丢失及生物力学性能减弱，其潜在的机制可能是KD抑制成骨细胞活性并增加破骨细胞活性。