白皮杉醇透過保護粒線體損傷及抑制氧化壓力以降低麩胺酸誘導PC12神經細胞及秀麗隱桿線蟲之神經退化

Abstract

神經退化性疾病 (neurodegenerative disease, ND) 爲一種常見於老年族群的疾病，可由神經元和神經系統的進行性損傷引起，可導致記憶、認知和運動方面的功能障礙。粒線體功能失調 (mitochondrial dysfunction) 爲帕金森氏症 (Parkinson’s disease) 等 ND 的常見病理機制之一。當 大腦受到中風或腦損傷的刺激時，會釋放出過量的麩胺酸 (glutamate, GLU) 會導致粒線體功能失調，並造成不可逆的神經元細胞死亡。白藜蘆醇 (resveratrol) 在 ND 中的生物活性及預防功效已經得到了廣泛的研究成果，但由於其生物利用率較低的限制而無法在生物體中達到預期的效果。文獻指出，白皮杉醇 (piceatannol, PIC) 爲生物可利用率較高的白藜蘆醇羥基化類似物，其已知擁有與白藜蘆醇類似的神經保護作用。在前人研究中，PIC 已證實可透過誘導抗氧化酵素 heme oxygenase-1 (HO-1) 的表達，延緩 GLU 所誘導的神經元死亡。然而，其在探討與 ND 相關的粒線體功能失調中的作用及潛在的分子機制尚不明確。基於先前文獻的研究，本研究旨在探討 PIC 在體外實驗中對 GLU 誘導的粒線體功能失調的保護作用，及其在體內實驗中延緩帕金森氏症的潛力。結果顯示，PIC 可通過調節 Bcl-2-associated X protein (Bax)/ B-cell lymphoma 2 (Bcl-2) 比例、nuclear factor erythroid 2 (Nrf2) 及其下游抗氧化酵素的表現及活性，延緩 GLU 誘導的 PC12 細胞凋亡和粒線體 ROS 生成。GLU 誘導的 ATP 耗竭、mtDNA 拷貝數及粒線體質量的改變在 PIC介入後顯著恢復至趨向於控制組的現象。此外，PIC 亦可誘導 peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) 轉入細胞核，促進粒線體的生合成相關蛋白及 sirtuin-3 (SIRT3) 的表達。PIC 透過上調粒線體融合相關基因 Opa1、Mfn1 及抑制粒線體分裂相關基因 Fis1 的 mRNA 表現量以調節粒線體動態平衡及細胞自噬。另一方面，PIC的介入顯著抑制了 GLU 誘導秀麗隱桿線蟲的多巴胺神經元損傷及粒線體的片段化，使其維持粒線體網絡的形態。綜合上述結果，推測 PIC 可做爲有效的神經保護化合物，在延緩 ND 中的粒線體功能失調具有一定的潛力。

Neurodegenerative diseases (ND), the disorders that particularly occur in elderly population, normally caused by progressive damage to neurons and nervous system, result in a wide range of impairment in memory, cognitive, and movement. Mitochondrial dysfunction is one of the common etiologies of neurodegenerative disorders, such as Parkinson’s disease. Excessive glutamate (GLU) is released when the brain is stimulated by a stroke or brain injury which subsequently leads to mitochondrial dysfunction and results in irreversible neuronal cell death. Resveratrol has been well-studied with its bioactivity and preventive effect on ND but being limited by its low bioavailability. Therefore, piceatannol (PIC), a hydroxylated resveratrol analog with higher bioavailability than its original counterpart, is expected to exert neuroprotective effect similar to that of resveratrol. In previous study, PIC has been proven to improve GLU-induced toxicity in neurons via its expression of the antioxidative enzyme heme oxygenase-1 (HO-1). Whereas, its role in mitochondrial dysfunction related to ND has not been clarified, as well as the potential underlying molecular mechanisms. In combination with previous evidences, this study aims to investigate the protective effect of PIC against GLU-induced mitochondrial dysfunction in vitro and its potential in Parkinson’s disease alleviation in vivo. The results showed that PIC could attenuate GLU-induced apoptosis and mitochondrial ROS production by regulating Bcl-2-associated X protein (Bax)/ B-cell lymphoma 2 (Bcl-2) ratio, nuclear factor erythroid 2 (Nrf2) and its downstream antioxidant enzymes in PC12 cells. Moreover, GLU-induced ATP depletion, altered mtDNA copy numbers and mitochondrial mass were restored in PIC treatment. Besides, nuclear translocation of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) was also promoted by PIC, which elevated the expression of mitochondrial biogenesis-related protein along with regulation of sirtuins-3 (SIRT3). PIC regulated mitochondrial dynamic balance and autophagy by inducing mRNA expression level of fusion related gene, Opa1, Mfn1 and inhibiting fission-related gene, Fis1. In addition, PIC alleviated GLU-induced dopaminergic neurodegeneration in Caenorhabditis elegans, which also improved mitochondrial morphology by ameliorated mitochondrial fragmentation. In conclusion, our study suggests that piceatannol may exhibit as potential neuroprotective agent in GLU-induced mitochondrial dysfunction in neurodegenerative disease.