Abstract Body: Background: Dilated cardiomyopathy (DCM) is defined as the loss of cardiac function due to excessive dilation of the ventricle(s). There is a higher likelihood of cardiac death in DCM cases with detected fibrosis in their cardiac tissue. This highlights a critical need for an intervention that targets the excessive fibrosis in DCM. After injury, cardiac fibroblasts (CFs) convert to myofibroblasts to promote repair through fibrosis. We observe loss of IL-33 has an impact on severity of fibrosis in DCM. IL-33 is an alarmin cytokine; its function in cardiomyocytes has been well-documented but not in CFs. IL-33 signaling to cells can change based on its intracellular or extracellular localization. Yet none have considered how the localization of IL-33 impacts CFs to modulate DCM.
Hypothesis: We hypothesize that loss of intracellular IL-33 signaling in CFs promotes differentiation into myofibroblasts, which drives worsened fibrosis during DCM.
Methods: We induced DCM in IL-33 KO or WT mice and assessed fibrosis severity by histological analysis and hydroxyproline assay. Next, we characterized CFs in naïve IL-33 KO hearts and compared to ST2 KO heart along with WT mice. Finally, primary murine CF cultures were used to phenotype the CF conversion into myofibroblasts in-vitro for IL-33 KO cells.
Results: During DCM, we observe IL-33 KO hearts have significantly worsened fibrosis compared to WT controls, detected by Masson’s trichrome tissue staining. Furthermore, hydroxyproline assay reveals IL-33 KO mice have increased collagen production than WT mice by 121.8 ug/uL ± 54.15 (p=0.0365) in DCM. In naïve mice, IL-33 KO CFs greatly elevated the number and proportion of alpha-smooth muscle actin+ myofibroblasts compared to both ST2 KO and WT mice. For in-vitro culture, IL-33 KO CFs had increased expression of Col1a1 mRNA (p=0.0069).
Conclusions: Loss of IL-33 signaling to CFs during DCM had increased fibrosis and collagen production resulting in worsened disease. In naïve mice, loss of both extracellular and intracellular IL-33 (IL-33 KOs) promoted myofibroblast conversion in CFs compared to controls. This phenotype was not observed in ST2 KO mice, which only have loss of extracellular IL-33. This implicates that only the loss of intracellular IL-33 has an impact on CFs that could modulate fibrosis through myofibroblast conversion. Therefore, we posit intracellular IL-33 prevents the differentiation of CFs into myofibroblasts to protect the heart from severe DCM.