Impact of paracrine effects of different clonal hematopoiesis-driver mutations in human macrophages on cardiac cells

Abstract Background Age-acquired, non-malignant somatic mutations in hematopoietic stem cells can lead to expansion of blood cells, known as clonal hematopoiesis of indeterminate potential (CHIP). CHIP-driving mutations in a spectrum of genes are correlated with an increased incidence of and poor prognosis in patients with cardiovascular disease. Recent reports suggest increased inflammation in carriers of frequent mutations in DNMT3A and TET2. Less frequent mutations in splicing factors, signaling molecules and epigenetic regulators were found to be associated with greater myeloid malignancy and cardiovascular mortality risks, but paracrine effects of these mutations on cardiac tissue is not known. Purpose We aim to assess the impact of less frequent CHIP-driver mutations on paracrine activities of macrophages on cardiac cells. Methods & Results In order to identify interesting CHIP-driver mutations, we analysed frequency and all-cause mortality of 56 potential CHIP driver genes in two cohorts of patients with heart failure and aortic stenosis (1168 patients). Besides the well-studied mutations in TET2 and DNMT3A, we identified nine mutations with a relative higher frequency and impact on prognosis, among them splicing factors SF3B1, SRSF2, ZRSR2, TP53-related genes PPM1D and PHF6, signaling mediators CALR and GNAS, and epigenetic regulators EZH2, KDM6A. To mimic CHIP-driving conditions, we assessed the effect of siRNA-mediated silencing of the so far understudied genes on the paracrine activity of primary human macrophages, which are differentiated from primary CD14+ sorted monocytes. We achieved >40% reductions in mRNA expression for each of the targeted genes (p<0.05). To gain first insights into a potential paracrine activity of individual mutations, we incubated cardiomyocytes with the conditioned medium collected from macrophages. Notably, supernatants from ZRSR2-, PPM1D- or CALR-silenced macrophages significantly reduced cardiomyocyte beating frequencies (53.1%, 64.9% and 63.7% of control, respectively; all p<0.05). Interestingly, only supernatants of ZRSR2-, CALR-silenced macrophages induced hypertrophy (all p<0.05). Next, we assessed the effects on primary human cardiac fibroblasts. Treatment with conditioned media did not affect collagen 1A1 expression and cell counts, but conditioned media of EZH2-, and CALR-silenced macrophages induced fibroblast senescence evaluated by senescence-associated β-galactosidase staining (158.3% and 154.1% of control, respectively; both p<0.05). The mechanisms driving the different effects are currently under investigation. Conclusion Loss of genes from a broad spectrum of clonal hematopoiesis drivers differentially affects the paracrine activity of human monocyte-derived macrophages. Silencing of ZRSR2 or CALR in macrophages had most profound effects on cardiomyocytes. Surprisingly, EZH2 and CALR-silenced macrophages augmented senescence of cardiac fibroblasts, a finding that further needs to be explored.