Abstract Body: Background: Glycogen synthase kinase-3 (GSK-3) is a family of ubiquitously expressed serine-threonine kinases consisting of the GSK-3α and GSK-3β isoforms. GSK-3α/β plays a critical role in regulating various biological processes vital to cardiac biology. Previously, our research identified cardiac fibroblast (FB) GSK-3β as a negative regulator of fibrotic remodeling in the ischemic heart. However, the role of cardiomyocytes GSK-3β (CM- GSK-3β) in the adult heart remains incompletely defined.
Methods: To examine the role of CM- GSK-3β, we employed an α-MHC promoter-driven, inducible CM-GSK-3β knockout (CM-GSK-3β-KO) model. At 12 weeks of age, mice were placed on a tamoxifen (TAM) diet for 2 weeks, followed by a regular chow for an additional 5 weeks. After the TAM protocol, echocardiography was performed to assess cardiac function.
Results: Echocardiographic analysis revealed that CM-GSK-3β KO mice developed severe spontaneous systolic dysfunction and dilative cardiac remodeling. An increased heart weight/tibia length ratio was also observed in the CM-GSK-3β KO mice, indicating cardiac hypertrophy. These structural remodelings were pathological as the KO heart demonstrated significantly increased fibrotic remodeling compared to control hearts. To further confirm the role of CM-GSK-3β in processes contributing to cardiac remodeling, flow cytometric analysis was performed with a single cell suspension of CM-GSK-3β and control hearts. Considering the CM-specific model, it was a great surprise to note dramatic changes in the FB-specific and immune cell parameters. Specifically, KO hearts demonstrated a higher frequency of FBs and profibrotic COL1A1⁺ FBs. This is entirely consistent with the increased fibrosis at the histology level. Regarding immune cells, an increased frequency of infiltrated CD45⁺ leukocytes and myeloid cells such as monocytes (CD45⁺CD11b⁺), macrophages (CD45⁺CD11b⁺F4/80⁺), neutrophils (CD45⁺CD11b⁺LY6G⁺) and dendritic cells (CD45⁺CD11C⁺) in KOs indicated myeloid cells, particularly macrophages, neutrophils and DCs have been shown to contribute to excessive inflammation in CM-GSK-3β KO hearts. Our extensive flow cytometry analysis further suggested that CM-GSK-3β regulates pro-inflammatory immune cell subsets in the heart.
Conclusion: Our findings reveal that CM-GSK-3β-mediated crosstalk of FBs and immune cells is vital to maintaining cardiac homeostasis.