Circulating YRNAs and Their Fragments Associate with Diabetic Kidney Disease and Endothelial Cell Function

Background: Diabetic kidney disease (DKD) occur commonly in patients with diabetes. Early detection of DKD may guide therapeutic strategies, so it is important to discover new biomarkers and therapeutic targets. Non-coding RNAs have been recognized as potential biomarkers or therapeutic targets in many diseases. yRNAs (RNYs), a class of non-coding RNAs, are highly conserved and can be processed into small fragments. Interestingly, yRNAs and their fragments are highly abundant in circulation. Here, we aim to investigate whether yRNAs and their fragments may serve as biomarkers for DKD and investigate their potential causal role. Methods: RNA was extracted from serum of patients with diabetes (DM, n=12), DKD (n=18) and healthy controls (HC, n=12), as well as from extracellular vesicles (EVs) isolated from these sera. qRT-PCR was used to measure expression levels of yRNAs and their fragments. Also yRNA subtypes ratios were determined, as it was previously shown that unique quantitative ratios of yRNA subtypes may reflect injury status. Human umbilical vein endothelial cells (HUVEC) and Human Dermal Microvascular Endothelial Cells (HDMEC) were used for in vitro studies. siRNA-mediated knockdown was performed to inhibit RNY1 expression. Barrier formation and function of endothelial cells were measured via the Electric Cell-substrate Impedance Sensing (ECIS) method. Results: The ratios of full length RNY4/RNY3 and RNY4/RNY1 increased in serum of patients with DKD, while the ratio of circulating RNY3/RNY1 and RNY4/RNY1 fragments decreased in DKD as compared to HC. We observed that circulating yRNAs are mostly present in EVs. Interestingly, for each type of yRNA, the ratio of fragment to full length yRNA expression increased in the serum of patients with DM but decreased in the DKD group suggesting a general effect on fragmentation. In addition, in vitro studies demonstrate that, upon stimulation with TGF-β and TNF-α, yRNA expression decreased in endothelial cells. Furthermore, RNY1 inhibition impeded the barrier function of endothelial cells that could be mainly attributed to the loss of cell-cell contacts and membrane capacitance. Conclusion: Our findings suggest that yRNAs are potential biomarkers for DKD, while yRNAs may also be directly involved in vascular injury through regulating EC barrier function. Funding: Government Support – Non-U.S.