Project Summary Interleukin 6 (IL-6) trans-signaling is a non-canonical signaling paradigm that is greatly enhanced in humans by the IL-6R Ala358 isoform (rs2228145; Asp358Ala), a variant that occurs at a high frequency across multiple ethnicities. Emerging evidence suggests that IL-6 trans-signaling contributes to cardiovascular (CV) disease pathogenesis and that the IL6R Ala358 variant is a predictor of fatal CV outcomes in patients with heart failure (HF). Thus the IL6R Ala358 variant may be an essential stratification factor for disease risk and response to therapies targeting IL-6 trans-signaling in subjects with CV disease or HF. Given the high prevalence of IL6R Ala358 in the population, its link to adverse CV outcomes, evidence of IL-6 trans-signaling in the development of cardiac fibrosis, and the availability of pharmacological strategy, it is fundamental to confirm the role of IL6R Ala358 in cardiac inflammation and fibrosis and that IL-6 trans-signaling blockade is an effective treatment strategy. In this application, we will use trans-aortic constriction to cause cardiac pressure overload (PO) in our novel C57BL/6 Il6raE357A mouse model of IL-6 trans-signaling. We hypothesize that increased circulating IL-6 produced in response to pressure overload (PO) will exacerbate cardiac fibrosis and HF in the presence of enhanced IL-6 trans-signaling determined by C57BL/6 Il6raE357A genotype and treatment with sgp130Fc will prevent or attenuate cardiac fibrosis and HF. Using state of the art spatial transcriptomics, we will identify the specific type and location of cardiac cells responsive to IL-6 trans-signaling. The goals of this project are: Aim 1. Assess the impact of the C57BL/6 Il6raE357A mouse genotype of enhanced sIL-6R shedding and IL-6 trans-signaling on PO-induced cardiac fibrosis and left ventricular dysfunction. Aim 2. Determine if selective IL-6 trans-signaling blockade with sgp130FC blockade is an effective strategy to ameliorate PO-induced cardiac fibrosis. These experiments will establish the proof-of-concept whether enhanced IL-6 trans-signaling increases cardiac fibrosis and HF risk. We will also explore specific cellular mechanisms by employing advanced spatial transcriptomics, which allows the identification of cardiac cell type and location affected by IL-6 trans-signaling. Additionally, given that he sgp130Fc is currently in phase II clinical trials (trade name Olamkicept) we will have establish a validated biological model to study IL-6 trans-signaling with translational value.