MiR‐21 is up‐regulated in urinary exosomes of chronic kidney disease patients and after glomerular injury

With 500 million people affected worldwide, chronic kidney disease (CKD) constitutes a major public health problem.1 Mostly arising from arterial hypertension and diabetes mellitus, it is a terminal disease without any causal therapy, leading to dialysis and/or kidney transplantation. Glomerulopathies are the main cause of end stage renal disease (ESRD), which are mainly caused by podocyte effacement or loss.2 A relevance of microRNAs (miRs) on podocyte function and the pathogenesis of glomerulopathies3 could have been clarified. Both, their molecular influence on translation and their potential role as biomarkers for kidney diseases, including CKD, became of major research interest. Especially miRs derived from urinary exosomes appear to have a promising potential as biomarkers, since they can be accessed non‐invasively and they are protected against degradation,4 making sample preparation more unsusceptible against environmental influences. Unfortunately, only little is known about exosomal miR expression in urine of CKD patients. Therefore, the present study aims at the investigation of the expression levels of the well‐investigated miRs miR‐21, miR‐30a‐5p and miR‐92a in urinary exosomes of CKD patients, representing a new promising, non‐invasive sample type and their functional roles in different injury models.