Urine miRNA panel as accurate biomarkers for monitoring kidney graft function


Background. Improvement in short term outcomes in kidney transplantation (Tx) had been achieved. However, long-term outcomes have not changed. MicroRNAs (miRNAs), a recently discovered class of noncoding RNAs, have the potential of being biomarkers of allograft status. Methods. Gene expression (mRNA) and miRNA signatures were evaluated using microarray platforms in kidney allograft biopsies that were histological defi ned as IF/TA (N=13) and normal allograft (NA, N= 5). Total RNA was isolated from urine samples collected at the biopsy time. Five miRNAs (miR142-3p, miR-32, miR-204, miR-107, miR-211) were chosen for being evaluated in urine samples from the total miRNA signature identified in the same kidney biopsies. Selection was based on in silico predicted miRNA targeting of gene products identified as differentially expressed in the mRNA signature of the same biopsies. An independent set of 20 prospectively studied kidney transplant patients, urine samples were collected and evaluated for miRNA expression at 3, 9, and 12 months post-KTx. MiRNA expression was analyzed by QPCR analysis. Expression of individual miRNAs was measured through Ct value with relative expression assessed using two endogenous controls (RNU44, RNU48) for each sample. Results. Spearman’s rank correlation indicated a good correlation between the miRNAs in IF/TA tissues and urine samples (r=0.912, p=0.0012). The prospective evaluation of the miRNA panel expression in urine samples from the independent set of patients (classified according graft function (eGFR >45 mL/min (n=11) or ≤ 45 mL/min (n=9) at 12 month post-KTx), resulted in 3 miRNAs (miR142-3p, miR-32, miR-204), being able to differentiate patients according with their graft function at every point of the analysis. Interesting, miR-107 and miR-211 were able to differentiate patients according their graft function at 3-9 months but not at 12 months post-KTx. Furthermore, these two miRNAs were differentially expressed also between patients with and without delayed graft function and they might be good markers of recovery of graft function. Conclusions. miRNAs can be detected in urine samples and have the potential for being non-invasive biomarkers of kidney graft function. There was a correlation between tissues and urine samples at the diagnosis time (NA vs. IF/TA). Prospective evaluation of a limited panel of miRNAs was associated with graft function at 12 months post-KTx.