Institute of Marine Biotechnology, National Dong Hwa University, Pingtung, Taiwan.
PLoS One. 2013 May 14;8(5):e63112. doi: 10.1371/journal.pone.0063112. Print 2013.
The protein quality control (PQC) mechanism is essential for cell function and viability. PQC with proper biological function depends on molecular chaperones and proteases. The hypertonicity-induced protein damage and responses of PQC mechanism in aquatic organisms, however, are poorly understood. In this study, we examine the short-term effects of different hypertonic shocks on the levels of heat shock proteins (HSPs, e.g., HSP70 and HSP90), ubiquitin-conjugated proteins and protein aggregation in gills of the Mozambique tilapia (Oreochromis mossambicus). Following transfer from fresh water (FW) to 20‰ hypertonicity, all examined individuals survived to the end of experiment. Moreover, the levels of branchial HSPs and ubiquitin-conjugated proteins significantly increased at 3 and 24 h post-transfer, respectively. Up-regulation of HSPs and ubiquitin-conjugated proteins was sufficient to prevent the accumulation of aggregated proteins. However, the survival rate of tilapia dramatically declined at 5 h and all fish died within 7 h after direct transfer to 30‰ hypertonicity. We presumed that this result was due to the failed activation of gill PQC system, which resulted in elevating the levels of aggregated proteins at 3 and 4 h. Furthermore, in aggregated protein fractions, the amounts of gill Na(+)/K(+)-ATPase (NKA) remained relatively low when fish were transferred to 20‰ hypertonicity, whereas abundant NKA was found at 4 h post-transfer to 30‰ hypertonicity. This study demonstrated that the response of PQC in gills is earlier than observable changes in localization of ion-secreting transport proteins upon hypertonic challenge. To our knowledge, this is the first study to investigate the regulation of PQC mechanism in fish and characterize its important role in euryhaline teleost survival in response to hypertonic stress.
蛋白质质量控制（PQC）机制对于细胞功能和存活至关重要。具有适当生物学功能的 PQC 依赖于分子伴侣和蛋白酶。然而，水生生物中 PQC 机制对高渗诱导的蛋白质损伤的反应仍知之甚少。在这项研究中，我们研究了不同高渗冲击对罗非鱼（Oreochromis mossambicus）鳃中热休克蛋白（HSPs，例如 HSP70 和 HSP90）、泛素化蛋白和蛋白质聚集水平的短期影响。从淡水（FW）转移到 20‰高渗后，所有被检查的个体都存活到实验结束。此外，鳃 HSPs 和泛素化蛋白的水平分别在转移后 3 和 24 小时显著增加。HSPs 和泛素化蛋白的上调足以防止聚集蛋白的积累。然而，罗非鱼的存活率在 5 小时时急剧下降，所有鱼在直接转移到 30‰高渗后 7 小时内死亡。我们推测这是由于鳃 PQC 系统的激活失败导致的，这导致在 3 和 4 小时时聚集蛋白水平升高。此外，在聚集蛋白部分中，当鱼转移到 20‰高渗时，鳃 Na(+)/K(+)-ATP 酶（NKA）的含量仍然相对较低，而在转移到 30‰高渗后 4 小时时发现大量 NKA。这项研究表明，PQC 在鳃中的反应早于高渗刺激时离子分泌转运蛋白定位的可见变化。据我们所知，这是第一项研究鱼类 PQC 机制的调节，并描述其在鱼类应对高渗应激时的重要作用。
