Wednesday, April 2, 2025
4/2/2025
Mitochondrial R-loop in sepsis-induced cardiomyopathy - Abstract Sepsis is a life-threatening organ dysfunction that induces a multitude of defects in immunity for sustained periods of time after clinical recovery that is closely correlated with long-term mortality associated with septic cardiomyopathy. Although immune-based therapies have been designed to suppress inflammatory responses, this strategy alone has marginal benefits for sepsis patients, as the dominant molecular drivers of septic cardiomyopathy-associated inflammation remain unclear. As our knowledge of mitochondria advances, we first investigated a previously underappreciated activator in inflammation and disease progression, mitochondrial R- loop (RNA:DNA hybrid) termed mtR-loop, and discovered aberrant accumulation in cardiomyocytes after sepsis. The contributory role of mtR-loop toward cardiomyopathy post sepsis was documented in a pilot study showing that unresolved mtR-loop is pathological, which is linked to not only mitochondrial genome instability, but also unresolved chronic inflammation through activating both non-immune cells (cardiomyocytes) and immune cells (macrophages). Most importantly, these cardiomyocyte-derived mtR-loop could translocate to extracellular compartments and were sensed by macrophages in the heart to fuel a fata response to sepsis. This proposal will test the hypothesis that septic cardiomyocyte derived mtR-loop are the central hub that connect various pathways of the immune response in the inflammatory network. If identified, mtR-loop inhibition will be explored as a potential novel cardio-protector against stress. To this, we will employ genetic tools combined with reporter mice to monitor mtR-loop translocation within cells, track mtR-loop uptake by immune cells, define the mechanism underlying mtR-loop intercellular communication and initiated inflammation, and characterize the infiltrating cells. Mechanistically, our pilot data first showed that the SUMOlyation-dependent packaging of lncRNA (lncRP11) into mitochondria, which hybrids with mtDNA to form mtR-loop (lncRNA:mtDNA structure). Those lncRNA-associated mtR-loop acts an upstream trigger of inflammatory network in septic hearts. Based on these initial findings, we hypothesize that suppression of lncRP11 transcription can reduce or prevent cardiac dysfunction in post-sepsis by directly reversing or ameliorating inflammation associated with cardiomyocyte failure. Specifically, by 3D genome mapping, the physical contact of enhancer and promoter, but not their activities, was identified to regulate lncRP11 transcription in septic hearts. Interestingly, this is largely due to loss of CTCF-mediated insulator between lncRP11 promoter and enhancer. In addition, the CTCF binding on the insulator is sensitive to DNA methylation. Thus, we propose that gain of CTCF-mediated insulator by epigenetic editing tool could block enhancer/promoter interaction and thus silence lncRP11 transcription. Results of these studies will be used to develop a viable therapeutic approach using targeted epigenetic editing, which can efficiently resolve lncRP11-associated pathological mtR-loop and thereby ameliorate stress-induced cardiac damage and reduce the mortality and morbidity of patients with septic cardiomyopathy.
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