EAGER: The molecular basis of aging: The role of allele-specific gene expression, protein folding, and protein stability on the progression of aging

衰老的分子机制仍不清楚。提出的理论将衰老归因于有害突变或受损大分子的积累，归因于生命早期某些基因的差异优势，这些基因后来是有害的，或者归因于生命早期用于繁殖的代谢能量与用于修复和维护的能量之间与年龄相关的权衡。这些模型并不是相互排斥的，每一个都可能在衰老过程中发挥作用。从模式生物的研究中，已知衰老与能量代谢的降低、蛋白质翻译速率的降低、蛋白质周转率的降低以及受损蛋白质的积累有关。这种蛋白质损伤被认为是新陈代谢的自然副产品，寿命可能与代谢率呈负相关。主要研究者（PI）提出了一个关于衰老分子基础的新想法。PI假设随着衰老积累的受损蛋白质越来越难以被细胞降解和消除。细胞通过增强编码参与蛋白质折叠的伴侣蛋白和参与蛋白质降解的酶的蛋白质代谢基因的表达来响应受损蛋白质的积累。提出增强的蛋白质折叠能力以减少使不稳定蛋白质的表达最小化的细胞蛋白质质量控制机制，从而产生正反馈回路，导致产生甚至更多受损或未折叠的蛋白质。该系统的调节可以是蛋白质及其mRNA的分解，或者是基因表达水平，假设表观遗传机制已经进化为下调编码不稳定蛋白质的mRNA。所提出的工作模型是不稳定或弱折叠蛋白质的受控表达（即，等位基因特异性基因表达）是年轻状态的关键质量控制成分，其在衰老个体中丢失，使得老年个体活力降低并且更易患病。该老化模型预测，等位基因特异性基因表达和蛋白质质量控制将在通过热量限制延长寿命期间以及在具有延长寿命的蠕虫和果蝇突变体中维持。该模型还预测，等位基因特异性基因表达的鉴定实验结合相对蛋白质稳定性的计算分析将作为一种有效的检测方法来监测和评估衰老的进展。这种分子模型可以很容易地测试相结合的计算和湿实验室的方法集中在小鼠，蠕虫和苍蝇。这一新理论的概念验证具有重要的更广泛的影响，导致开发新的计算方法来解决衰老过程，这可能提供诊断和计算方法来减轻人类遗传有害基因的影响。

The molecular mechanisms responsible for aging remain unclear. Proposed theories ascribe aging to a buildup of deleterious mutations or damaged macromolecules, to the differential advantage of some genes early in life that are later detrimental, or to an age-related trade-off between metabolic energy used early in life for reproduction versus energy used for repair and maintenance. These models are not mutually exclusive and each may play a role in the aging process. From studies of model organisms it is known that aging is associated with a decrease in energy metabolism, decreased rates of protein translation, lower protein turnover, and a buildup of damaged proteins. This protein damage is proposed to be a natural by-product of metabolism and lifespan may be inversely correlated with metabolic rate. The Principal Investigator (PI) proposes a novel idea about the molecular basis of aging. The PI hypothesizes that damaged proteins that accumulate with aging are increasingly difficult for cells to degrade and eliminate. Cells respond to the accumulation of damaged proteins by enhancing the expression of protein metabolism genes encoding chaperonins involved in protein folding and enzymes involved in protein degradation. The enhanced protein folding capability is proposed to decrease a cellular protein quality control mechanism that minimizes expression of unstable proteins, thus creating a positive feedback loop that causes even more damaged or unfolded proteins to be created. Regulation of the system could be at either the breakdown of the protein and its mRNA, or at the level of gene expression assuming epigenetic mechanisms have evolved to down-regulate mRNAs encoding unstable proteins. The proposed working model is that controlled expression of unstable or weakly folding proteins (i.e., allele-specific gene expression) is a critical quality-control component of the youthful state that is lost in aging individuals, making the aged individual less vigorous and more susceptible to disease. This aging model predicts that allele-specific gene expression and protein quality control will be maintained during lifespan extension by caloric restriction as well as in worm and fruit fly mutants with extended lifespan. The model also predicts that identification of allele-specific gene expression experimentally coupled with computational analysis of relative protein stability will serve as an efficient assay to monitor and assess the progression of aging. This molecular model can be readily tested by combined computational and wet-lab approaches focused on mice, worms, and flies. Proof-of-concept of this novel theory has important broader impacts, leading to the development of new computational approaches for addressing the aging process which may provide diagnostic and computational approaches to mitigate the impact of inherited deleterious genes in humans.