Nr4a1 Modulates Inflammation and Heart Regeneration in Zebrafish

Recent findings have highlighted the complex role of inflammation in zebrafish heart regeneration, demonstrating that while inflammation is essential for initiating transient fibrosis and tissue repair, chronic inflammation and unresolved fibrosis could impede full regenerative recovery. In this study, we identified the nuclear receptor Nr4a1 as a critical regulator of this regenerative process in zebrafish. Loss of Nr4a1 function led to a prolonged and excessive inflammatory response, disrupted neutrophil migration, delayed fibrin clearance, and ultimately impaired heart regeneration. Transcriptome-wide RNA-seq analysis at different injury stages revealed molecular disruptions associated with dysregulated inflammation and fibrosis in Nr4a1 mutants. Notably, partial inhibition of the pro-inflammatory cytokine Tnf-a rescued heart regeneration in the nr4a1 mutants, highlighting the therapeutic potential of modulating inflammation. Our findings suggest that Nr4a1 plays a crucial role in orchestrating the immune response during heart regeneration and may serve as a valuable target for enhancing cardiac repair following injury. Overall design: To elucidate the molecular basis of the phenotypes observed in the nr4a1 mutant, we performed transcriptome-wide bulk RNA sequencing on the ventricles from both control and mutant hearts at several key time points. Baseline transcriptomic profiles were established from uninjured hearts to compare the cardiac transcriptomics of the wildtype control and nr4a1 mutant. Given the critical involvement of inflammation in heart regeneration, samples were also collected at 2 and 7 dpci, corresponding to stages marked by an active inflammatory response. Moreover, to elucidate the prolonged fibrosis phenotype in the late injury stage, we performed transcriptomic analysis on hearts collected at 21 dpci.