Non-Proximal Renal Tubule-Derived Urinary Exosomal miR-200b as a Biomarker of Renal Fibrosis

Abstract

Background: Renal fibrosis is a common outcome of nearly all kinds of chronic kidney disease (CKD) and eventually progresses to end-stage renal disease. The identification of an optimal biomarker of renal fibrosis to replace the invasive renal biopsy will have important clinical implications. Methods: We isolated urinary exosomes from 50 participants and examined the exosomal protein content and particle number in 38 CKD patients with different degrees of renal fibrosis and in 12 normal individuals. We examined the levels of exosomal microRNAs (miRNAs), namely, miR-200a, miR-200b, miR-200c, miR-141, miR-429, miR-29a, miR-29b, miR-29c, miR-192, and miR-21, by sorting the exosomes and comparing the levels of proximal tubular, non-proximal tubular, and total exosomal miR-200b. Results: The exosome content was higher in the CKD group, but no differences were evident among the mild, moderate, and severe fibrosis groups. Among the 10 exosomal miRNAs, miR-200b was lower in the CKD group than in the normal group and decreased more significantly with fibrosis progression as well as in IgA nephropathy and diabetic kidney disease. CD13⁺ CD63⁺ exosomes constituted 18.6% of all urinary exosomes. Sorting the proximal tubular exosomes with the CD13 protein marker revealed that miR-200b in the CD13⁺ group was extremely low; however, the result was significantly different in the CD13^– group but not in the CD13⁺ group. The magnitude of the decline was greater in the CD13^– groups than in the non-sorted whole groups between the fibrosis and normal patients. Conclusions: Non-proximal renal tubule-derived urinary exosomal miR-200b is a biomarker of renal fibrosis. Exosomes can be used as a liquid biopsy and may replace the traditional invasive renal biopsy in the diagnosis of renal fibrosis.