Abstract Body: Background: The adult mammalian heart exhibits limited regenerative capability, primarily due to the postnatal arrest of the cardiomyocyte (CM) cell cycle.
Aim: To elucidate the role of checkpoint kinase 2 (CHK2), a master regulator of cell cycle in DNA damage response pathway, in post-infarct heart failure.
Methods: We injected AAV9-TnT-CHK2shRNA 1-day post-myocardial infarction (MI, by mid-LAD ligation) to elucidate the effect of cardiomyocyte CHK2 suppression on cardiac function, scar size, and CM proliferation in mTmG lineage tracing mice one week after MI. We use Visium spatial transcriptomics to analyze differentially expressed genes across different regions and identify crucial gene programs modulated in different regions and clusters of cardiomyocytes after injury.
Results: The CHK2 and its active form, p-CHK2, significantly increased during development and post-MI. Spatial transcriptomic analysis indicated that two clusters of normal cardiomyocytes (most abundant in sham) were significantly lost in MI, and the CHK2shRNA-treated post-MI hearts maintained healthy CM clusters. Within the same clusters of “normal cardiomyocytes”, differentially expressed gene analysis shows upregulation of transcripts involved in the mitochondrial function, Ca-handling (SERCA2, RyR2), and better preservation of myofilaments (Myl9, Myh7, transgelin, etc) in the treated group. Changes in the expression of upstream transcriptional regulators suggest a shift from repressed metabolic states to an active state favorable for repair and adaptation. In parallel with the amelioration of transcriptional remodeling of the remaining viable cardiomyocytes, we observed increased GFP+ cardiomyocytes with multiple co-localized markers of cell cycles (BrdU, Ki-67, phospho-histone-3), attenuation of cardiac fibrosis, improvement of LV ejection fraction and prevention of adverse remodeling (LV chamber dilation) 1 week after MI.
Conclusions: Myocardial CHK2 suppression enhanced post-MI cardiac function and adverse remodeling, by promoting endogenous CM proliferation and creating a healthy microenvironment.