Abstract Body: Background: Myocardial fibrosis is a key driver of heart failure (HF) progression, yet effective therapies directly targeting cardiac fibrosis remain elusive. Our lab identified Hipk2, a kinase, through unbiased screening and observed its significant downregulation in human ischemic cardiomyopathy. Notably, both global and cardiomyocyte-specific Hipk2 deletion in mice resulted in cardiac dysfunction and fibrotic remodeling. However, the specific role of Hipk2 in cardiac fibroblasts (CF), the primary mediators of fibrosis, remains unexplored. In the present study, we elucidate the fibroblast-specific contribution of Hipk2 to cardiac pathophysiology.
Methods and Results: To investigate the role of Hipk2 in cardiac fibroblasts, we generated CF-specific (FB-KO) and cardiac myofibroblast-specific (MF-KO) Hipk2 knockout mice using the Tcf21 and Postn promoter-driven MerCreMer transgenes, respectively. At 10 weeks of age, mice were subjected to a TAM diet protocol. Both control and KO mice were subjected to left anterior descending (LAD) artery ligation following a tamoxifen diet protocol. Cardiac function was assessed in control and MF- Hipk2-KO mice. Prior to MI, ventricular function was comparable between control and MF- Hipk2-KO mice. However, at 4 weeks post-MI, MF- Hipk2-KO mice displayed significant cardiac dysfunction and excessive fibrosis compared to controls. RT-PCR analysis revealed increased expression of hypertrophy marker ANP and extracellular matrix gene Col1a1 in FB- Hipk2-KO mice compared to controls. Cardiac fibroblasts were isolated from FB- Hipk2-KO and control mice four weeks post-MI for flow cytometry analysis of fibrosis and inflammatory cytokines. FB- Hipk2-KO hearts exhibited elevated levels of key pro-fibrotic cytokine TGF-β and pro-inflammatory cytokines TNF-α and IL-1β post-MI as compared to control mice. Notably, despite the fibroblast-specific deletion, FB- Hipk2-KO hearts showed increased leukocyte infiltration and heightened cytokine production by leukocytes, suggesting a fibroblast-leukocyte crosstalk mechanism. Interestingly, in an isolated fibroblast culture model, adenovirus-mediated Hipk2 expression markedly reduced p-Smad2/3 levels, highlighting a potential mechanistic link between Hipk2 and pro-fibrotic TGF- β 1-SMAD3 signaling.
Conclusion: Fibroblast-specific Hipk2 deletion exacerbates myocardial fibrosis and inflammation, identifying Hipk2 as a potential therapeutic target for fibrosis-associated HF.