Abstract Body (Do not enter title and authors here): Objective: As one of the classic cell cycle checkpoint proteins, Checkpoint kinase 1 (CHK1) extensively participates in various biological processes primarily through mediating a cascade of reactions. Although previous studies have identified CHK1 as a critical factor in myocardial regeneration repair, its role in the natural senescence process of heart in mice remains unclear.

Methods: Firstly, the expression of CHK1 was detected in models of cardiomyocyte senescence by doxorubicin (DOX) and in natural senescence mice. Secondly, cardiomyocyte-specific CHK1 overexpression and knockdown were constructed to
explore the effect on natural cardiac senescence. Subsequently, the role of CHK1 was investaged in DOX-induced AC16. Finally, the molecular mechanism by which CHK1 attenuates cardiac senescence in aged mice was elucidated by combining transcriptomic sequencing (RNA-seq) and Co-immunoprecipitation coupled with mass spectrometry (IP/MS).

Results: CHK1 expression was significantly downregulated in both in vivo and in vitro senescence models. CHK1 overexpression attenuated cardiac senescence in aged mice, while CHK1 knockout had opposite impact. Overexpression of CHK1 markedly improved senescence of DOX-induced AC16 in vivo. RNA-seq reveled that CHK1 overexpression activates heat shock protein 90 (HSP90)-mediated mitophagy. IP/MS demonstrated that CHK1 specifically binds to the activator of 90kDa heat shock protein ATPase homolog 1 (AHSA1). Mechanistically, CHK1 activates HSP90-mediated mitophagy by binding to AHSA1 and inhibiting its ubiquitination-mediated degradation.

Conclusion: CHK1 activates mitophagy to attenuate cardiac senescence through binding to AHSA1 and inhibiting its ubiquitination-mediated degradation in aged mice. Our study reveals the significant role of CHK1 in the natural senescence process of heart and provides a potential therapeutic target for the treatment of age-related cardiac diseases in the future.