亨廷頓舞蹈症(Huntington's disease)為一顯性遺傳神經退化疾病，造成亨廷頓舞蹈症的原因是在huntingtin (Htt)基因exon1中的CAG三核苷酸重複序列異常擴增，促使錯誤摺疊的亨廷頓蛋白形成聚集體並堆積於神經細胞中。細胞中主要有兩種清除錯誤摺疊蛋白的機制，分別是泛素-蛋白酶體降解系統(Ubiquitin-Proteasome System, UPS)及細胞自噬(Autophagy)。已有研究指出突變型亨廷頓蛋白會造成泛素-蛋白酶體降解系統功能失常致使聚集體數目增加，而泛素-蛋白酶體降解系統的正常運作需要靠許多蛋白質來共同調控。因此我們想探討在野生型STHdh Q7/Q7及突變型STHdh Q111/Q111細胞中與泛素-蛋白酶體降解系統相關的調控蛋白表現量是否有不同，結果發現UCHL1、ZNRF1的表現量在STHdh Q111/Q111細胞中都有明顯下降。UCHL1與ZNRF1分別為去泛素酶及E3泛素連接酶，所以我們進一步研究它們對UPS功能的影響，結果顯示UCHL1並不會影響泛素-蛋白酶體降解系統的功能。但在STHdh Q7/Q7細胞ZNRF1 knockdown後，泛素-蛋白酶體降解系統的降解功能有顯著提升。因為ZNRF1本身為E3泛素連接酶，可把蛋白質送至泛素-蛋白酶體降解系統進行降解，證明ZNRF1的下降可能會使某些可提高泛素-蛋白酶體降解系統降解功能的蛋白表現量上升。UCHL1與ZNRF1雖為去泛素酶及E3泛素連接酶，但先前有研究指出：細胞中UCHL1表現量降低時會使麩胱甘肽(Glutathione, GSH)在細胞中的含量也減少，進而導致氧化壓力使粒線體功能異常；此外也已知與ZNRF1同為E3泛素連接酶的Parkin會調控粒線體自噬(Mitophagy)，Parkin表現異常時會導致粒線體功能受損。因此我們想更進一步探討UCHL1與ZNRF1是否對粒線體功能有所影響。結果發現當ZNRF1在STHdh Q7/Q7細胞中的表現量降低時，會使粒線體的型態發生改變，進一步以西方墨點法觀察發現ZNRF1可能是經由增加DRP1的表現量及降低Mfn1的表現量所導致的。DRP1為粒線體外膜上的趨分裂蛋白，可使粒線體型態趨向分裂；Mfn1為粒線體外膜上的趨融合蛋白，可使粒線體型態趨向融合。已知造成過多麩醯胺酸疾病的主要原因為突變的多麩醯胺酸蛋白會使泛素-蛋白酶體降解系統功能失常導致聚集體不斷的堆積在細胞中。前人研究指出：Oleuropein可以增強蛋白酶體的活性，我們在實驗中也證實Oleuropein確實可提高細胞內泛素-蛋白酶體降解系統降解功能的效率，但並不是藉由增加三磷酸線苷(ATP)在細胞中的濃度以便供給更多的能量給泛素-蛋白酶體降解系統這一條路徑，所以未來我們還可以進一步探討Oleuropein究竟是藉由哪一條機制來調控蛋白酶體的活性。

UPS is highly regulated process usually involving many proteins. The presence of mutant huntingtin impairs UPS and leads to aggregates formation. This study attempted to study the UPS-related regulatory proteins in wild-type STHdhQ7/Q7and mutant STHdhQ111/Q111 striatal cells. Western blot assays showed that there is a significant decrease in levels of UCHL1 and ZNRF1 in STHdhQ111/Q111 cells. UCHL1 and ZNRF1 are deubiquitinating enzyme and E3 ubiquitin-protein ligase, respectively. Our results indicated that UCHL1 did not affect UPS functions. On the other hand, depletion of ZNRF1 in STHdhQ7/Q7 cells showed an increase in the UPS degradation activity. Earlier study found that reduced UCHL1 level in cells lowers the level of glutathione (GSH), which leads to increased oxidative stress followed by mitochondria dysfunction. Moreover, it is discovered that an abnormal expression of parkin, an E3 ubiquitin-protein ligase similar to ZNRF1, results in mitochondria dysfunction. Therefore, our study also examined the effects of UCHL1 and ZNRF1 on mitochondrial function. It is found that mitochondria morphology changes when ZNRF1 is down-regulated in STHdhQ7/Q7 cells. DRP1 is a pro-fission protein inducing mitochondrial fragmentation whereas Mfn1 is a mitochondrial fusion-promoting protein. Western blot assays showed that there is an increase in DRP1 level and a decrease in Mfn1 level after depletion of ZNRF1. Evidences indicated that poly-Q diseases are due to the mutated poly-Q chains impairs UPS and leads to aggregates accumulation. As previous study has shown that Oleuropein is able to enhance proteasomal activities, we also found that Oleuropein has improves on the UPS function. Increment of cellular ATP concentration however, is not the factor that provides more energy for proteasome pathway to take place.

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