The advent of highly effective immunosuppressants in the last 30 years has significantly reduced the incidence of acute rejection 1. Timely detection of acute rejections in patients after kidney transplantation is imperative to immediately intervene with immunosuppressive anti-rejection therapy. Rejection detection by a kidney biopsy and subsequent histological examination represents the gold standard of diagnosis, however, a kidney biopsy is invasive and associated with potentially severe side effects. A non-invasive biomarker of rejection is highly desired to circumvent this predicament. Kidney function may be assessed non-invasively by the use of creatinine in blood samples 2. Unfortunately, creatinine assessment is unreliable in precisely identifying a patient’s kidney function due to its dependency upon muscle mass and therefore is not sufficient to detect early rejection. Due to this unreliability, novel biomarkers with high sensitivity and specificity are constantly under investigation.
Circular RNAs (circRNAs) are a class of noncoding RNA that were previously thought to be insignificant byproducts of splicing errors. However, recent advances in RNA sequencing confirmed the presence of circRNAs in multiple cell lines and across different species suggesting a functional role of this RNA species. CircRNAs arise from back-splicing events resulting in a circular RNA that is stable, specific and conserved. They can be generated from exons, exon-introns, or introns. CircRNAs have multifaceted functions. They are likely part of the competing endogenous RNA class. They can regulate gene expression by sponging microRNAs, binding proteins, or they can be translated into a protein themselves. CircRNAs have been associated with health and disease, some with disease protective effects, some with disease promoting functions. The widespread expression and disease regulatory mechanisms allow circRNAs to be used as functional biomarkers and therapeutic targets for a variety of different disorders. CircRNA show a remarkable stability in body fluids due to resistance to exonucleases through circularization. This qualifies them as ideal biomarkers of disease.
We recently forwarded the first clinical evaluation of urinary circRNAs in patients with transplant-associated kidney disease 3. We were able to demonstrate that detection of circRNAs in urine is feasible and that a variety of circRNAs are dysregulated in the urine of transplant patients. Specifically, levels of hsa_circ_0001334 were up-regulated in patients with acute rejection compared to controls, normalized in patients with acute rejection following successful anti-rejection therapy, and were associated with subsequent decline in kidney function.
Johan Lorenzen is interested in the mechanisms of kidney injury mediated by non-coding RNAs. Merely 1 - 2% of the human genome is transcribed into RNA transcripts, which are subsequently translated into protein. The remainder (>98%) are so called non-coding RNAs (ncRNAs), which are arbitrarily separated into long ncRNAs (lncRNAs, ≥ 200 nucleotides) and small ncRNAs (≤200 nucleotides). He aims to identify novel non-coding RNAs in different mouse models of kidney injury and elucidate involved signaling pathways in vivo and in vitro. He is interested in modulating pathological non-coding RNA expression by RNA therapeutics, which enable specific targeting and cleavage of non-coding RNAs and thus modulation of pathological signaling pathways in vivo. In addition, non-coding RNAs are released into the extracellular compartment (blood and urine) in patients. Thus, circulating non-coding RNAs may serve as a non-invasive tool to detect and monitor disease activity. In several clinical projects he aims to investigate the release pattern of circulating non-coding RNAs.
- Hardinger KL and Brennan DC. Novel immunosuppressive agents in kindey transplantation. World J Transplant 2013; 3(4):68-77.
- Nankivell BJ, Borrows RJ’ Fung CL, O'Connell PJ, Allen RD, Chapman JR. Natural history, risk factors, and impact of subclinical rejection in kidney transplantation. Transplantation 2004; 78(2):242-9.
- Kölling M, Haddad G, Wegmann U, Kistler A, Bosakova A, Seeger H, Hübel K, Haller H, Mueller T, Wüthrich RP, Lorenzen JM. Circular RNAs in Urine of Kidney Transplant Patients with Acute T Cell-Mediated Allograft Rejection. Clin Chem. 2019; 65(10):1287-1294.