Loss of IDH1 and IDH2 in macrophages induces pathological phenotypes in cardiomyocytes

Abstract Introduction The clonal expansion of hematopoietic stem cells can be induced by a variety of age-related somatic mutations, a phenomenon known as "clonal hematopoiesis of indeterminate potential" (CHIP). CHIP is associated with an increased incidence and poor outcomes in patients with cardiovascular disease. The mechanisms underlying the crosstalk between CHIP cells and cardiac tissue are yet to be elucidated. Rare mutations in the metabolism-regulating isocitrate dehydrogenases encoding genes IDH1 and IDH2 have been identified as AML-like and cardiovascular high-risk CHIP-driving mutations in patient cohorts. However, the potential paracrine effects of these mutations in immune cells on cardiac tissue are unknown. Therefore, we assessed the impact of IDH1 and IDH2 mutations on the paracrine activities of macrophages. Methods and Results To gain first insights into the functional consequences of the IDH mutations, we used the AlphaMissense algorithm, which predicts the impact of mutations on protein function. IDH1 and IDH2 mutations identified in our patient cohorts were predicted to induce pathological alterations of protein function with a score >0.99. Therefore, we assessed the effects of silencing of the two genes in primary human CD14+ M0 macrophages on the paracrine activity on neonatal rat cardiomyocytes. Transfection with siRNA pools targeting IDH1 and IDH2 to mimic CHIP-driving conditions reduced mRNA abundance by 78% and 73%, respectively (both p<0.05). To assess the impact of IDH-silencing on cardiovascular cells, cardiomyocytes were treated with the supernatant of the macrophages. Interestingly, supernatants of IDH1 silenced macrophages significantly increased apoptosis of cardiomyocytes (8.6-fold increased expression of cleaved caspase-3; p<0.05) and reduced beating frequency. In addition, supernatants of IDH1 silenced macrophages induced a 1.5-fold increase in cardiomyocyte hypertrophy (p<0.01), whereas silencing of IDH2 showed no effect on cardiomyocyte hypertrophy and apoptosis. However, supernatants of both IDH1 and IDH2 silenced macrophages resulted in significantly increased numbers of bi- and multinucleated cardiomyocytes. Conclusion: Loss of isocitrate dehydrogenases in human macrophages affects cardiomyocyte functions in a paracrine fashion. Particularly silencing of IDH1 in macrophages introduced cardiomyocyte hypertrophy, apoptosis, and bi- and multinucleation, and reduced contractile function. Ongoing studies will address how IDH1 and IDH2 silencing-induced alterations in macrophages control their paracrine activity on cardiomyocytes.