PolyU triggered viral myocarditis cardiac injury via TLR7/NF-κB activation and programmed cell death
C Su, T H Chao, C F Tsai, Y H KuanAbstract
Introduction
Single-stranded RNA (ssRNA) virus–associated myocarditis is driven by innate nucleic-acid sensing and can progress through inflammatory amplification and programmed cell death, resulting in virus myocardial injury. Polyuridylic acid (PolyU) is a synthetic ssRNA mimic and a canonical TLR7/8 agonist, providing a tractable model ssRNA-triggered cardiac inflammation.
Purpose
To establish a PolyU-induced murine model of ssRNA-driven myocarditis and to delineate a TLR7/NF-κB signaling that couples inflammatory amplification with apoptotic and pyroptotic cell-death programs in cardiac tissue.
Methods
Five-week-old male BALB/c mice were assigned to Control and PolyU-treated cohorts . At day 3 after PolyU administration, mice were euthanized for serum collection and cardiac tissue harvest. Myocardial pathology was evaluated using hematoxylin and eosin (H&E) staining to assess inflammatory infiltration and tissue injury. Circulating injury and inflammatory burden were quantified by serum lactate dehydrogenase (LDH) and C-reactive protein (CRP), together with pro-inflammatory cytokines (TNF-α, IL-1β, IL-6). Mechanistic profiling of heart tissue was performed by western blot to quantify TLR7 pathway components (TLR7, MyD88, TRAF6) and NF-κB activation (IκBα/p-IκBα, p65/p-p65). Programmed cell death signaling was assessed by western blot for apoptosis markers (Bad, Bax, Bcl-2, Bcl-xL) and pyroptosis markers (NLRP3, ASC, pro/cleaved caspase-1, GSDMD).
Results
H&E staining demonstrated myocarditis-like changes in PolyU-treated hearts, characterized by inflammatory cell infiltration and myocardial tissue injury. In parallel, systemic injury/inflammatory burden increased following PolyU exposure, reflected by elevated serum LDH and CRP, along with increased circulating pro-inflammatory cytokines. Mechanistically, western blot analyses of cardiac tissue showed activation of the TLR7 signaling axis with concomitant NF-κB activation which enhanced phosphorylation of IKK, IκBα, and p6. These inflammatory signals were accompanied by coordinated engagement of programmed cell-death pathways, evidenced by pro-apoptotic shifts and induction of pyroptosis-related components including NLRP3, ASC, caspase-1 activation, and GSDMD cleavage, supporting a TLR7-centered linkage between inflammatory amplification and coupled apoptosis/pyroptosis in PolyU-induced myocarditis.
Conclusion
PolyU induced a robust ssRNA-mimic murine myocarditis phenotype characterized by inflammatory myocardial infiltration and injury, systemic elevation of LDH/CRP and pro-inflammatory cytokines, and activation of the cardiac TLR7/NF-κB axis. This inflammatory cascade is tightly coupled to concurrent engagement of apoptotic and pyroptotic programs, supporting a mechanistic framework in which TLR7/NF-κB signaling links innate immune sensing to programmed cardiomyocyte death in ssRNA-driven viral myocarditis.