過量表現peripherin導致PC12神經細胞死亡

Abstract

Peripherin是一種出現在肌萎縮性脊髓側索硬化症(amyotrophic lateral sclerosis)患者運動神經元之病理性蛋白質堆積的神經元中間絲蛋白。在基因轉殖鼠體內，peripherin的過量表達也會導致神經元退化以及部份運動神經元的死亡。為了探討peripherin的過量表達，與神經元細胞死亡之間的關聯，本實驗先將大鼠的peripherin的核酸序列頭端接上綠色螢光蛋白質的核酸序列，然後轉殖到由大鼠腎上腺髓質嗜鉻酸細胞瘤(pheochromocytoma)選殖出的PC12 細胞株。經過神經生長因子(nerve growth factor)的誘導後，PC12細胞會分化為外觀類似交感神經元的細胞；而分化完成的細胞，在神經生長因子被撤除以後，則會進行細胞凋亡。我們發現，經過神經生長因子誘導以後，過量表達的peripherin與其他神經元中間絲蛋白，會堆積在經過pEGFP-Peripherin轉殖的細胞核旁，以及神經纖維裡。除此以外，在細胞質異常堆積的中間絲蛋白、腫脹的粒線體、自嗜體；及退化的神經纖維等超微結構，均出現在已分化為神經元的細胞中。而TUNEL反應以及activated caspase-3的陽性免疫反應，不只出現在對照組撤除神經生長因子後的PC12細胞，也出現在pEGFP-Peripherin轉殖的細胞中。另外，在接受神經生長因子的誘導以後，ubiquitin的陽性免疫反應亦出現在pEGFP-Peripherin轉殖的細胞中。經由這些觀察，我們可以推測，不論的蛋白質脢體的活性為何，過量表達peripherin與中間絲蛋白大量堆積的結果，可能會導致神經元細胞凋亡。

Peripherin is a neuronal intermediate filament (IF) protein detected in the pathological aggregates of motor neurons in amyotrophic lateral sclerosis (ALS) patients. Also in transgenic mice, overexpression of peripherin results in neurodegeneration and the selective cell death of motor neurons. To gain a better understanding of the relation between overexpression of peripherin and neuronal cell death, the cDNA of rat peripherin tagged with enhanced green fluorescent protein (EGFP) was transfected into a rat adrenal pheochromocytoma cell line PC12 in this study. PC12 cells differentiate into a sympathetic neuron-like phenotype in response to nerve growth factor (NGF) induction and terminally differentiated PC12 cells undergo apoptosis after NGF withdrawal. We found that overexpressed peripherin together with other neuronal IF proteins were accumulated in the perikaryon and cell processes of pEGFP-peripherin transfected cells after NGF induction. Moreover, ultrastructural patterns of abnormal IF accumulations in the cytoplasm, swelling mitochondria, autophagosomes and degenerating neurites were detected in the differentiated neurons. Both TUNEL activity and activated caspase-3 immunopositive reaction could be found not only in the positive control of NGF-deprived PC12 cells but also in the pEGFP-peripherin transfected cells. Besides, an immunopositive reactivity for ubiquitin could be also detected in pEGFP-peripherin transfected cells after NGF induction. From these observations, we suggest that overexpression of peripherin and massive accumulation of IF proteins may trigger the apoptotic-like neuronal cell death regardless of the proteasome activity.