Meox1 is a Cell-cycle Oscillator Required for Mitotic Transition and Proliferation in Cardiac Fibroblasts

Background: Tissue fibrosis plays important roles in the pathogenesis of chronic diseases, including heart failure. The mechanism underlying interstitial fibroblast proliferation is a promising analytical target for therapeutic applications. Here we developed quantitative epigenome profiling to identify a critical regulator in interstitial cell populations that emerges during the progression of heart failure. Methods and Results: We subjected pressure-overloaded hearts of mice to trimethylated histone H3 lysine 4 (H3K4me3) ChIP-sequence and RNA-sequence. Expression analysis followed by quantitative H3K4me3 profiling identified 45 fibrosis-related genes with significant H3K4me3 enrichment in failing hearts, including Meox1 transcription factor. Meox1 emerged in the interstitial fibrotic region in failing heart, and intriguingly Meox1 was expressed in the limited population of cardiac fibroblasts both in vivo and in vitro. Meox1-positive fibroblasts were increased in response to a paracrine signal from cardiomyocytes, and knockdown of Meox1 completely inhibited the reactive proliferation of cardiac fibroblasts stimulated by conditioned medium from cardiomyocytes. Gene expression profiling combined with siRNAs clarified that Meox1 depletion resulted in down regulation in the mitosis-related genes including Aurora B kinase. Indeed, Meox1 depletion decreased the cells under mitosis, but conversely increased the proportion of DNA synthesizing cells, thereby inhibited mitotic transition. The cell-cycle synchronization analysis and promoter analysis using live-cell imaging clarified that Meox1 oscillated throughout the cell-cycle and specifically emerged in G2/M phase. Finally, we revealed that Meox1 heterogenously expressed in the interstitial fibrotic are of human ventricular heart tissues from patients with end-stage heart failure. Notably, Meox1 expression was significantly correlated with the fibrosis-related genes in diseased ventricular heart tissues (n=15), suggesting the pathological relevance in clinical settings. Conclusion: Our findings identify a novel cell-cycle regulator and propose that Meox1 is a potential target for therapies aimed at preventing tissue fibrosis.