Background: Thoracic radiotherapy remains a key treatment modality for various oncological diseases. Despite advancements in irradiation techniques and personalized treatment planning, patients undergoing thoracic radiation are at significantly higher risk for cardiac events and the development of myocardial fibrosis compared to non-irradiated controls. While the damaging effects of photon radiation are well-recognized, the underlying molecular mechanisms and the role of cardiomyocytes in radiation-induced cardiac fibrosis remain poorly understood.
In preliminary experiments, we identified Guanylate Binding Protein 5 (GBP5) as a radiation-inducible gene both in vitro and in vivo. GBP5 plays a central role in the assembly of the NLRP3 inflammasome, which mediates the release of pro-inflammatory cytokines (IL-1β, IL-18). However, the specific role of GBP5 in radiation-induced cardiac inflammation and fibrosis has not yet been elucidated.
Methods: We generated an inducible, conditional, cardiomyocyte-specific knock-in mouse model (GBP5-cKI), expressing a dysfunctional GBP5 protein lacking the C-terminal domain which is essential for NLRP3 inflammasome assembly. To investigate the role of GBP5 in radiation-induced cardiac fibrosis, mice were exposed to 16 Gray thoracic photon irradiation. Organs were harvested either 2 weeks (short-term) or 5 months (long-term) post-irradiation to assess acute and chronic inflammatory changes in the myocardium.
Results:
Mice expressing the dysfunctional GBP5 protein in cardiomyocytes exhibited significantly reduced radiation-induced mortality and prolonged survival compared to wild-type controls (p = 0.0276). Cardiac function remained largely preserved in treated knock-in mice even five months after irradiation (FS 26.9% ± 1.11 vs. 23.0% ± 1.55; p = 0.0001; EF 53.1% ± 1.69 vs. 46.9% ± 2.61; p < 0.0001; GLS –17.75% ± 0.43 vs. –12.60% ± 0.77; p < 0.0001; echocardiographically assessed under anesthesia). Five months post-irradiation, GBP5-cKI mice showed lower activation of caspase-1 and IL-1β, along with reduced expression of fibrosis-associated genes. Histologically, Sirius Red staining in long-term experiments revealed markedly reduced myocardial fibrosis in the GBP5-cKI mice compared to the wild-type controls. As early as two weeks post-irradiation, wild-type animals displayed signs of early diastolic dysfunction (shortened relaxation time, elevated E/e’ ratio), whereas these alterations were not observed in GBP5-cKI mice.
Conclusion: These findings suggest that inhibition of NLRP3 activity through GBP5 modification leads to significantly reduced cardiac fibrosis and prevents the early development of diastolic dysfunction.
