*Article* **Uromodulin and microRNAs in Kidney Transplantation—Association with Kidney Graft Function**

**Špela Borštnar 1,2, Željka Veˇceri´c-Haler 1,2, Emanuela Boštjanˇciˇc 3, Živa Pipan Tkalec 3, Damjan Kovaˇc 1,2, Jelka Lindiˇc 1,2 and Nika Kojc 3,\***


Received: 30 June 2020; Accepted: 30 July 2020; Published: 5 August 2020

**Abstract:** Uromodulin and microRNAs (miRNAs) have recently been investigated as potential biomarkers for kidney graft associated pathology and outcome, with a special focus on biomarkers indicating specific disease processes and kidney graft survival. The study's aim was to determine whether expression of serum uromodulin concentration and selected miRNAs might be related to renal function in kidney transplant recipients (KTRs). The uromodulin concentration and expression of six selected miRNAs (*miR-29c*, *miR-126*, *miR-146a*, *miR-150*, *miR-155*, and *miR-223*) were determined in the serum of 100 KTRs with stable graft function and chronic kidney disease of all five stages. Kidney graft function was estimated with routine parameters (creatinine, urea, cystatin C, and Chronic Kidney Disease Epidemiology Collaboration study equations) and precisely measured using chromium-51 labelled ethylenediaminetetraacetic-acid clearance. The selected miRNAs were shown to be independent of kidney graft function, indicating their potential as biomarkers of associated kidney graft disease processes. In contrast, the serum uromodulin level depended entirely on kidney graft function and thus reflected functioning tubules rather than any specific kidney graft injury. However, decreased concentrations of serum uromodulin can be observed in the early course of tubulointerstitial injury, thereby suggesting its useful role as an accurate, noninvasive biomarker of early (subclinical) kidney graft injury.

**Keywords:** microRNA; uromodulin; kidney graft function; biomarker; kidney transplantation
