Reduction of DNA Topoisomerase Top2 reprograms the epigenetic landscape and extends health and life span across species

Reviewer #1 (Public review):

Summary

This very interesting article describes extensive work by the authors connecting topoisomerase 2 to aging across multiple model systems. The authors began by analyzing published transcriptomes for genes previously reported to be connected to increased lifespan in S. cerevisiae, focusing on genes whose downregulation is highly correlated with increased lifespan. One of these candidates was topoisomerase 2, which had previously been shown to be connected to lifespan in yeast.

The authors here show that reduction in topoisomerase 2 levels can significantly extend lifespan in yeast (by damp), C. elegans (by RNAi), and mice (by CRISPR CasRx).

Next, the authors demonstrate in both C. elegans and mice that in addition to increased survival times, animals with decreased top2 levels also show increased healthspan, as measured by using rates of body bends and of pharyngeal pumping in C. elegans, and using the Frailty Index (FI) for mice. Further, they report that lowered top2 levels result in less aged tissue phenotypes in multiple tissues in mice as assayed by histology, and positively affect multiple hallmarks of aging in both mouse tissues and human IMR-90 cells.

The authors go on to perform thorough transcriptomic analysis of reduced top2 animals in both C. elegans and mice. Many interesting GO terms are highly overrepresented among both up- and down-regulated transcripts from these experiments, and the authors conclude that in the case of mice there is significant tissue specific biology based on differing results in the tissues they examined.

Given the previously known biological roles of top2, the authors looked at changes in the epigenetic landscape of reduced top2 organisms as evidenced by changes in H3K4me3, H3K9me3 and H3K27me3. Overall, the authors conclude from these data that reduction of top2 "differentially down-regulates genes with active promoters/high abundance".

Overall this well-written manuscript summarizes a great deal of new data that will be of great interest to aging researchers broadly.

The figures and tables are all very clear and well-designed, and all add greatly to the manuscript overall including the use of color which is in all cases justified.

Reviewer #2 (Public review):

Summary:

Previous studies have shown that Topoisomerase 2 (Top2) depletion in yeast can extend the lifespan of the organism, but no known mechanisms have been reported. In the current study, Zhu et al. reported that reduction of Top2 enhances longevity and mitigates aging phenotypes across multiple model organisms, including not yeast, but also C. elegans and mouse. The evidence of reduction of aging phenotypes is particularly strong, which include markers of cellular senescence, nutrient sensing, epigenetic markers, and lysosome biogenesis. They propose that Top2b reduction confers longevity through a conserved mechanism, and may be used a novel therapeutic strategy for countering aging. Overall, their findings should be of broad interest to the fields of Aging and Topoisomerase research. The technical quality of the work is in general solid but can be improved.

Strengths:

Top2 is an essential type II topoisomerase that resolves DNA topological stress generated during transcription, replication, chromosome segregation, and other DNA metabolic processes by introducing transient double-strand breaks (DSBs), passing the DNA strands, and re-ligating them. Top2 is a target for anticancer therapies, but its connection to aging and longevity remains largely unexplored. The authors' findings are notable, as Top2 has been deemed indispensable for normal development. Yet, this study suggests that its reduction confers benefits in the context of healthy aging. Their results convincingly show extended lifespan and improvements in physiological and molecular aging phenotypes, supported by behavioral assays and tissue morphology analyses.

Weaknesses:

Despite these strengths, the manuscript is weak on the proposed "conserved mechanism". The authors proposed in Discussion that Top2/Top2b knockdown may be similar to the classical insulin/IGF1 and the mTORC pathway, but did not provide any genetic evidence to support this.

The authors also mentioned in the Discussion that the potential mechanism could be selective down-regulation of transcription of genes of active promoter and high abundance, such as ribosomal genes, which could be relevant to yeast aging. But there is no evidence in worms or mouse that Top2b directly binds and promotes transcription of certain high abundance genes critical for aging.

I understand that this mechanism issue may be difficult to address, and I do not expect that the authors can fully address this issue. However, as both yeast and worms have been widely-used in aging studies with many tools available, I suggest that the authors can improve their studies by performing the following experiments.