Salmona M, Forloni G, Diomede L, Algeri M, De Gioia L, Angeretti N, Giaccone G, Tagliavini F, Bugiani O
Istituto di Ricerche Farmacologiche Mario Negri, Milan, Italy.
Neurobiol Dis. 1997;4(1):47-57. doi: 10.1006/nbdi.1997.0133.
Prion-related encephalopathies are characterized by astrogliosis and nerve cell degeneration and loss. These lesions might be the consequence of an interaction between the abnormal isoform of the cellular prion protein that accumulates in nervous tissue and the plasma membranes. Previously we found that a synthetic peptide, homologous to residues 106-126 of the human prion protein, is fibrillogenic and toxic to neurons and trophic to astrocytes in vitro. This study dealt with the ability of the peptide to interact with membranes. Accordingly, we compared PrP 106-126 with different synthetic PrP peptides (PrP 89-106, PrP 127-147, a peptide with a scrambled sequences of 106-126, and PrP 106-126 amidated at the C-terminus) as to the ability to increase the microviscosity of artificial and natural membranes. The first three had no effect on nerve and glial cells in vitro, whereas the amidated peptide caused neuronal death. Using a fluorescent probe that becomes incorporated into the hydrocarbon core of the lipid bilayer and records the lipid fluidity, we found PrP 106-126 able to increase significantly the membrane microviscosity of liposomes and of all cell lines investigated. This phenomenon was associated with the distribution of the peptide over the cell surface, but not with changes in the membrane lipid or protein content, or with membrane lipid phase transitions. Accordingly, we deduced that increased membrane microviscosity was unrelated to changes in the membrane native components and was the result of increased lipid density following PrP 106-126 embedding into the lipid bilayer. No control peptides had comparable effects on the membrane microviscosity, except PrP 106-126 amidated at the C-terminus. Since the latter was as neurotoxic, but not as fibrillogenic, as PrP 106-126, we argued that the ability of PrP 106-126 to increase membrane microviscosity was unrelated to the propensity of the peptide to raise fibrils. Rather, it could be connected with the primary structure of PrP 106-126, characterized by two opposing regions, one hydrophilic and the other hydrophobic, that enabled the peptide to interact with the lipid bilayer. Based on these findings, we speculated that the glial and nerve cell involvement occurring in prion-related encephalopathies might be caused by the interaction with the plasma membrane of a PrP 106-126-like fragment or of the sequence spanning residues 106-126 of the abnormal isoform of the prion protein.
朊病毒相关脑病的特征是星形胶质细胞增生以及神经细胞变性和丧失。这些病变可能是蓄积在神经组织中的细胞朊病毒蛋白异常异构体与质膜之间相互作用的结果。此前我们发现，一种与人朊病毒蛋白第106 - 126位残基同源的合成肽在体外具有纤维原性，对神经元有毒性，对星形胶质细胞有营养作用。本研究探讨了该肽与膜相互作用的能力。因此，我们将朊病毒蛋白106 - 126与不同的合成朊病毒蛋白肽（朊病毒蛋白89 - 106、朊病毒蛋白127 - 147、一种106 - 126序列打乱的肽以及C端酰胺化的朊病毒蛋白106 - 126）就增加人工膜和天然膜微粘度的能力进行了比较。前三种肽在体外对神经和胶质细胞没有影响，而酰胺化肽导致神经元死亡。使用一种能掺入脂质双层烃核并记录脂质流动性的荧光探针，我们发现朊病毒蛋白106 - 126能够显著增加脂质体以及所有所研究细胞系的膜微粘度。这一现象与该肽在细胞表面的分布有关，但与膜脂质或蛋白质含量的变化以及膜脂质相变无关。因此，我们推断膜微粘度增加与膜天然成分的变化无关，而是朊病毒蛋白106 - 126嵌入脂质双层后脂质密度增加的结果。除了C端酰胺化的朊病毒蛋白106 - 126外，没有对照肽对膜微粘度有类似影响。由于后者与朊病毒蛋白106 - 126一样具有神经毒性，但不具有纤维原性，我们认为朊病毒蛋白106 - 126增加膜微粘度的能力与该肽形成纤维的倾向无关。相反，它可能与朊病毒蛋白106 - 126的一级结构有关，其特征是有两个相对的区域，一个亲水，另一个疏水，这使得该肽能够与脂质双层相互作用。基于这些发现，我们推测朊病毒相关脑病中发生的胶质细胞和神经细胞受累可能是由与朊病毒蛋白异常异构体第106 - 126位残基类似片段或该序列的质膜相互作用引起的。
