Uridine-Cytidine Kinase 2 (UCK2)/Uridine-Cytidine Kinase Like 1 (UCKL1) complex exacerbates the differentiation of myocardial fibroblasts via TRIM21/Smurf2/Smad3 pathway after myocardial infarction.

Cardiac fibrosis following myocardial infarction (MI) is a pivotal driver of ventricular dysfunction and heart failure, yet the molecular checkpoints orchestrating the persistent activation of cardiac fibroblasts remain incompletely defined. Here, we uncover a non-canonical, metabolism-independent function of Uridine-Cytidine Kinase 2 (UCK2) and Uridine-Cytidine Kinase Like-1 (UCKL1) as synergistic regulators of pathological remodeling. We demonstrate that both proteins are robustly upregulated in the border zone of ischemic murine hearts and transforming growth factor-β (TGF-β)-activated human cardiac fibroblasts (HCFs). Mechanistically, UCK2 and UCKL1 physically assemble into an obligate functional complex that acts as a molecular scaffold rather than a metabolic enzyme. This complex recruits the E3 ubiquitin ligase Tripartite Motif Containing 21 (TRIM21) to orchestrate the specific ubiquitination and degradation of the negative regulator SMAD Specific E3 Ubiquitin Protein Ligase 2 (Smurf2), thereby sustaining SMAD Family Member 3 (Smad3) phosphorylation and amplifying fibrogenic TGF-β signaling. Disruption of this axis via combined genetic silencing exerts a synergistic protective effect by abrogating myofibroblast differentiation and extracellular matrix production. Furthermore, therapeutic intervention using adeno-associated virus (AAV)-mediated knockdown of UCK2/UCKL1 significantly attenuates adverse ventricular remodeling, limits scar expansion, and preserves cardiac function in a murine MI model. Collectively, these findings identify the UCK2/UCKL1-TRIM21-Smurf2-Smad3 axis as a novel, druggable signalosome linking kinase "moonlighting" functions to transcriptional reprogramming, offering a transformative therapeutic strategy to arrest the progression of post-ischemic heart failure.