以果蠅為模式分析PP2A Bb調控次單元在粒線體重塑及細胞凋亡的功能

Abstract

第十二型脊髓小腦萎縮症致病原因歸因於ppp2r2b表現量的提高，為了探討釐清此退化性神經失調以及尋找藥理學的治療藥物，因此本研究建立一SCA12的果蠅動物模式藉由大量表現ppp2r2b在果蠅的同源基因,tws。藉由異位表現tws會導致許多病理特徵，包括神經退化、細胞凋亡以及縮短壽命。而更進一步的研究發現提高ppp2r2b或tws的表現會促使粒線體斷裂並伴隨著增加細胞中的氧化壓力(ROS)及細胞色素c(Cyt c)以及增加半胱氨酸蛋白酶3(caspase 3)的活性。藉由穿透式電子顯微鏡(TEM)的結果顯示在過度表現tws的果蠅感光神經細胞中發現斷裂的粒線體會伴隨著塉(cristae)的破壞並會被細胞自噬體(autophagosome)所吞沒。除此之外，轉殖果蠅對於巴拉刈所引起的氧化壓力更為敏感。相比之下，異位表現dSOD2及藉由餵食抗氧化劑可有效的降低氧化壓力(ROS)及半胱氨酸蛋白脢3(caspase 3)的活性，並延長SCA12果蠅模式的生存壽命。總而言之，我們的研究顯示粒線體的功能失調所引發的氧化壓力是造成SCA12的原因，以及降低氧化壓力為神經病理學更提供一可能的治療性方法。我們的結果也顯示Tws也參與在發育性的程式細胞死亡機制中。現在我們正在仔細研究Tws在細胞凋亡路徑上所扮演的上位性。除此之外，也正在探究中的是Tws可能參與調控的下游目標蛋白例如粒線體重塑蛋白PINK1以及Drp1。

Spinal cerebellar ataxia type 12 (SCA12) has been attributed to the elevated expression of ppp2r2b. To better elucidate the pathomechanism of the neuronal disorder and to search for a pharmacological treatment, Drosophila models of SCA12 were generated by overexpression of a human ppp2r2b and its Drosophila homolog, tws. Ectopic expression of ppp2r2b or tws caused various pathological features, including neurodegeneration, apoptosis and shortened lifespan. More detailed analysis revealed that elevated ppp2r2b and tws induced fission of mitochondria accompanied by increases in cytosolic reactive oxygen species (ROS), cytochrome c (Cyt c) and caspase 3 activity. TEM revealed that fragmented mitochondria with disrupted cristae were engulfed by autophagosomes in photoreceptor neurons of flies overexpressing tws. Additionally, transgenic flies were more susceptible to oxidative injury induced by paraquat. By contrast, ectopic dSod2 expression and antioxidant treatment reduced ROS and caspase 3 activity, and extended the lifespan of the SCA12 fly model. In summary, our study demonstrates that oxidative stress induced by mitochondrial dysfunction plays a causal role in SCA12, and reduction of ROS is a potential therapeutic intervention for this neuropathy. Other than these findings, I have also demonstrated that Tws is involved in developmental programmed cell death. Currently, we are dissecting the epistatic status of tws in apoptotic pathway. Addition, possible downstream targets of Tws, such as Pink1 and Drp1, in remodelling of mitochondria is under investigated.