Different responses to DNA damage determine ageing differences between organs

Organs age differently, causing wide heterogeneity in multimorbidity, but underlying mechanisms are largely elusive. To investigate the basis of organ-specific ageing, we utilized progeroid repair-deficient Ercc1^{Δ /-} mouse mutants and systematically compared at the tissue, stem cell and organoid level two organs representing ageing extremes. Ercc1^{Δ /-} intestine shows hardly any accelerated ageing. Nevertheless, we found apoptosis and reduced numbers of intestinal stem cells (ISCs), but cell loss appears compensated by over-proliferation. ISCs retain their organoid-forming capacity, but organoids perform poorly in culture, compared with WT. Conversely, liver ages dramatically, even causing early death in Ercc1-KO mice. Apoptosis, p21, polyploidization and proliferation of various (stem) cells were prominently elevated in Ercc1^{Δ /-} liver and stem cell populations were either largely unaffected (Sox9+), or expanding (Lgr5+), but were functionally exhausted in organoid formation and development in vitro. Paradoxically, while intestine displays less ageing, repair in WT ISCs appears inferior to liver as shown by enhanced sensitivity to various DNA-damaging agents, and lower lesion removal. Our findings reveal organ-specific anti-ageing strategies. Intestine, with short lifespan limiting time for damage accumulation and repair, favours apoptosis of damaged cells relying on ISC plasticity. Liver with low renewal rates depends more on repair pathways specifically protecting the transcribed compartment of the genome to promote sustained functionality and cell preservation. As shown before, the hematopoietic system with intermediate self-renewal mainly invokes replication-linked mechanisms, apoptosis and senescence. Hence, organs employ different genome maintenance strategies, explaining heterogeneity in organ ageing and the segmental nature of DNA-repair-deficient progerias.

Abstract P1-19-02: Repurposing the FOXO4 senolytic against triple-negative breast cancer

Metastatic breast cancer is the second most common cause of cancer-related death in women. Triple Negative Breast Cancer (TNBC) has tan especially poor prognosis partly due to these tumors lacking relevant molecular targets. The most commonly mutated gene in TNBC is the tumor suppressor TP53. Mostly, p53 mutations give rise to stably expressed proteins with tumor promoting functions. Therefore, there is an urgent need for therapeutics that can target p53-mutated TNBCs. Here we show that an anti-senescence compound can target metastatic cancers. We found that, in TNBCs, mutant p53 attained a distinctive conformation that has novel oncogenic roles through binding to the transcription factor Forkhead box O (FOXO) 4 sequestered within promyelocytic leukemia (PML) foci. Since these nuclear structures are specific to senescent cells, we tested the senolytic FOXO4 peptide. In cytotoxicity experiments, we found this compound to target TNBCs specifically over other breast cancer subtypes. Most importantly, these compounds decrease metastatic burden in the most commonly-used mouse model for human breast cancer metastasis. In summary, our results demonstrate that mutant p53-driven cancers presented senescent cell-specific characteristics that makes them a great candidate for the FOXO4-directed anti-senescence therapy. We expect that creative repurposing of senolytics to translate to other types of cancer that are driven by mutant p53.

Citation Format: Diana Putavet, Marjolein Baar, Tao Shi, Johannes Lehmann, Tim Leyten, Esmee Bouma, Antoine Khalil, Harm-Jan Vos, Boudewijn Burgering, Tobias Dansen, Patrick Derksen, Peter de Keizer. Repurposing the FOXO4 senolytic against triple-negative breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-19-02.