Tarbox Haley E, Branch Audrey, Fried Stephen D
Department of Chemistry, Johns Hopkins University, Baltimore, MD 21218, USA.
Department of Psychological and Brain Sciences, Johns Hopkins University, Baltimore, MD 21218, USA.
bioRxiv. 2024 Sep 24:2024.09.20.614172. doi: 10.1101/2024.09.20.614172.
Cognitive decline during aging represents a major societal burden, causing both personal and economic hardship in an increasingly aging population. There are a few well-known proteins that can misfold and aggregate in an age-dependent manner, such as amyloid β and α-synuclein. However, many studies have found that the proteostasis network, which functions to keep proteins properly folded, is impaired with age, suggesting that there may be many more proteins that incur structural alterations with age. Here, we used limited-proteolysis mass spectrometry (LiP-MS), a structural proteomic method, to globally interrogate protein conformational changes in a rat model of cognitive aging. Specifically, we compared soluble hippocampal proteins from aged rats with preserved cognition to those from aged rats with impaired cognition. We identified several hundred proteins as having undergone cognition-associated structural changes (CASCs). We report that CASC proteins are substantially more likely to be nonrefoldable than non-CASC proteins, meaning they typically cannot spontaneously refold to their native conformations after being chemically denatured. The potentially cofounding variable of post-translational modifications is systematically addressed, and we find that oxidation and phosphorylation cannot significantly explain the limited proteolysis signal. These findings suggest that noncovalent, conformational alterations may be general features in cognitive decline, and more broadly, that proteins need not form amyloids for their misfolded states to be relevant to age-related deterioration in cognitive abilities.
衰老过程中的认知衰退是一项重大的社会负担，在人口老龄化日益严重的情况下，会导致个人和经济困难。有一些知名蛋白质会以年龄依赖的方式错误折叠并聚集，比如淀粉样β蛋白和α-突触核蛋白。然而，许多研究发现，负责保持蛋白质正确折叠的蛋白质稳态网络会随着年龄增长而受损，这表明可能还有更多蛋白质会随着年龄增长而发生结构改变。在这里，我们使用了一种结构蛋白质组学方法——有限蛋白水解质谱法（LiP-MS），来全面研究认知衰老大鼠模型中的蛋白质构象变化。具体而言，我们将认知功能保留的老年大鼠的可溶性海马体蛋白质与认知功能受损的老年大鼠的可溶性海马体蛋白质进行了比较。我们鉴定出数百种发生了与认知相关的结构变化（CASC）的蛋白质。我们报告称，与非CASC蛋白质相比，CASC蛋白质更有可能无法重新折叠，这意味着它们在化学变性后通常无法自发地重新折叠成其天然构象。我们系统地研究了翻译后修饰这一潜在的混杂变量，发现氧化和磷酸化并不能显著解释有限蛋白水解信号。这些发现表明，非共价的构象改变可能是认知衰退的普遍特征，更广泛地说，蛋白质在错误折叠状态下不一定非要形成淀粉样蛋白才会与年龄相关的认知能力衰退有关。
