Secreted long non-coding RNAs Gadlor1 and Gadlor2 affect multiple cardiac cell types and aggravate cardiac remodeling during pressure overload

Background: Pathological cardiac overload triggers maladaptive myocardial remodeling that predisposes to the development of heart failure. The contribution of long non-coding RNAs (lncRNAs) to intercellular signaling during cardiac remodeling is largely unknown. Methods: We analyzed the expression of Gadlor 1 and Gadlor2 lncRNAs in mouse hearts, mouse cardiac cells, extracellular vesicles (EVs), human failing hearts as well as patient serum. Gadlor knock-out (KO) mice were generated and analyzed. The effect of Gadlor knock-out and Gadlor overexpression during cardiac pressure overload induced by transverse aortic constriction (TAC) was analyzed by echocardiography, histological analyses and RNA sequencing in isolated cardiac cells. Gadlor1/2 interaction partners were identified by RNA antisense purification coupled with mass-spectrometry (RAP-MS). Results: In the heart, the related lncRNAs Gadlor1 and 2 are mainly expressed in endothelial cells and to a lesser extent in fibroblasts. Gadlor1/2 are upregulated in failing mouse hearts as well as in the myocardium and in serum of heart failure patients. Interestingly, Gadlor1 and 2 are secreted from endothelial cells within EVs, which are taken up by cardiomyocytes. Gadlor-KO mice exerted reduced cardiomyocyte hypertrophy, diminished myocardial fibrosis and improved cardiac function, but paradoxically suffered from sudden death during prolonged overload. Gadlor overexpression, in turn, triggered hypertrophy, fibrosis and cardiac dysfunction. Mechanistically, Gadlor1 and Gadlor2 inhibit angiogenic gene expression in endothelial cells, while promoting the expression of pro-fibrotic genes in cardiac fibroblasts. In cardiomyocytes, Gadlor1/2 upregulate mitochondrial genes, but downregulate angiogenesis genes, while interacting with the transcriptional regulator Glyr1 and the calcium/calmodulin-dependent protein kinase type II (CaMKII), entailing cardiomyocyte hypertrophy and perturbed cardiomyocyte calcium dynamics. Conclusions: We describe that Gadlor1 and 2, two related, novel lncRNAs, are upregulated in cardiac pathological overload and are secreted from endothelial cells within EVs. Gadlor1/2 induce cardiac dysfunction, cardiomyocyte hypertrophy and myocardial fibrosis by exerting heterocellular effects on cardiac cellular gene-expression and by affecting calcium dynamics in cardiomyocytes, which take up the Gadlor1/2 by EV mediated transfer from endothelial cells. Targeted inhibition of Gadlor lncRNAs in endothelial cells or fibroblasts might serve as a therapeutic strategy in the future. ### Competing Interest Statement The authors have declared no competing interest.