Supplementary Material for: Interleukin-11 Is Elevated in Patients with Atrial Fibrillation, Correlates with Serum Fibrosis Markers, and Represents a Therapeutic Target for Atrial Fibrosis

<b><i>Introduction:</i></b> Inflammatory cytokines are closely associated with developing cardiac fibrosis. This research aimed to explore the significant role of IL-11 in atrial fibrosis progression and potential therapeutic targets. <b><i>Methods:</i></b> 207 AF patients and 160 healthy subjects were included in the case-control study. Blood samples were analyzed for the level of IL-11 by enzyme-linked immunosorbent assay (ELISA). Angiotensin II (Ang II)-treated fibrosis mouse models were generated, and expression of IL-11 mRNA and protein was detected by RT-qPCR and Western blot. IL-11 antagonist was used to evaluating atrial fibrosis-related markers. <b><i>Results:</i></b> The persistent atrial fibrillation patients (<i>n</i> = 76) had significantly larger left atrial size, higher serum levels of hypertrophic protein BNP, proinflammatory cytokine high-sensitivity C-reactive protein (hs-CRP), and interleukin-6 (IL-6) compared to paroxysmal atrial fibrillation patients (<i>n</i> = 131), and healthy subjects (all <i>p</i> &lt; 0.05). Pearson correlation analysis revealed significant positive correlation between serum IL-11 and cardiac fibrosis markers BNP (<i>r</i> = 0.394, <i>p</i> &lt; 0.001), CTX-I (<i>r</i> = 0.418, <i>p</i> &lt; 0.001), PICP (<i>r</i> = 0.306, <i>p</i> &lt; 0.001), PIIINP (<i>r</i> = 0.335, <i>p</i> &lt; 0.001), and TGF-β1 (<i>r</i> = 0.273, <i>p</i> &lt; 0.001). In the fibrosis mouse model, Ang II infusion significantly upregulated IL-11 mRNA and protein expression in the left atrium of mice (<i>p</i> &lt; 0.05), as well as staining intensity of Masson trichrome, the intensity of α-SMA, and it increased mRNA expression of collagen I and III in atrial tissue. IL-11 antagonist treatment significantly attenuated Masson trichrome, number of α-SMA-positive myofibroblasts in atrial tissue. Also, it significantly reduced the p-ERK1/2 in atrial tissue of mice infused with Ang II (<i>p</i> &lt; 0.05). <b><i>Conclusions:</i></b> IL-11 is upregulated in the serum of AF patients, and IL-11 inhibitor significantly inhibited Ang II-induced atrial fibrosis, a key pathological feature of AF. Therefore, IL-11 could be a potential therapeutic target for AF.