IL-33/ST2L Pathway Dysregulation Promotes Cardiac Fibrotic Remodeling in Rat Animal Model of Obesity

Introduction: The IL-33/ST2L pathway exerts a fundamental protective role in cardiac tissue. It modulates the release of cytokines and mediators, and the activation of mast cells in response to cellular stress or damage, protecting the heart from maladaptive remodeling. In the heart, IL-33 reduces fibrosis, inflammation, and infarct size, and increases cardiac function and survival. Interestingly, IL-33/ST2L signaling is also related to fat deposition. On the other hand, the soluble form of ST2 receptor (sST2) is a decoy receptor, which blocks IL-33 signaling. Serum sST2 levels correlate to cardiovascular disease severity and represent an important clinical biomarker of heart failure. Here we assessed the IL-33/ST2 molecular pathway in a rat animal model of obesity to evaluate the role of fat accumulation in cardiac steatosis and fibrotic remodeling driven by IL-33/ST2 dysregulation. Methods: Twenty obese nondiabetic male Zucker rats (fa/fa-) and 10 lean littermates (Fa/+) were sacrificed at 25 weeks of age according to Italian Ministry of Health Authorization (N°325/2015PR of 2015/04/05), and heart and serum were collected. Serum IL-33 and sST2 levels were assessed through ELISA (R&D system). Molecular and Western blot analysis of IL-33 and ST2 were performed. Profibrotic signaling was evaluated by fibro-panel assay (Qiagen) on heart biopsies. Fibrosis deposition was evaluated on cardiac biopsies through Sirious Red and Western blot analysis of TGFβ and collagen 3 protein levels. Results: We showed that obesity determined a dysregulation of IL- 33/ST2 signaling characterized by a reduction of serum (p <0.05) andcardiac IL-33 (p = 0.05, and an increase of serum ST2 (p <0.05) in fat animals compared to lean controls. We showed increased TGFβ (p <0.05) and collagen 3 (p = 0.05) protein levels in cardiac biopsies of fat animals, together with increased collagen fiber deposition (p <0.05 Sircol Red quantification). Fat animals presented an impaired remodeling profile with downregulation of Il1a (FC -2.39), Il4 (FC -2.04) mmp8 (FC2.93), and Pdgfb (FC -2.14), and an upregulation of genes Serpine 1 (FC 2.07), Smad4 (FC 5.78), and Thbs1 (FC 1.73), all involved on Tgfb signaling related to IL-33/ST2 impairment. Conclusions: We observed fibrotic remodeling of cardiac tissue and activation of pro-remodeling pathways in cardiac biopsies of fat animals, suggesting that obesity promotes cardiac remodeling through the loss of IL-33/ST2L cardioprotective pathway.