Biomarkers of Renal Diseases Printed Edition of the Special Issue Published in International Journal of Molecular Sciences www.mdpi.com/journal/ijms Joaquín García-Estañ and Felix Vargas Edited by Biomarkers of Renal Diseases Biomarkers of Renal Diseases Editors Joaqu ́ ın Garc ́ ıa-Esta ̃ n Felix Vargas MDPI • Basel • Beijing • Wuhan • Barcelona • Belgrade • Manchester • Tokyo • Cluj • Tianjin Editors Joaqu ́ ın Garc ́ ıa-Esta ̃ n Universidad de Murcia Spain Felix Vargas Universidad de Granada Spain Editorial Office MDPI St. Alban-Anlage 66 4052 Basel, Switzerland This is a reprint of articles from the Special Issue published online in the open access journal International Journal of Molecular Sciences (ISSN 1422-0067) (available at: https://www.mdpi.com/si/ ijms/Biomarkers Renal Diseases). For citation purposes, cite each article independently as indicated on the article page online and as indicated below: LastName, A.A.; LastName, B.B.; LastName, C.C. Article Title. Journal Name Year , Volume Number , Page Range. ISBN 978-3-03943-911-9 (Hbk) ISBN 978-3-03943-912-6 (PDF) c © 2020 by the authors. Articles in this book are Open Access and distributed under the Creative Commons Attribution (CC BY) license, which allows users to download, copy and build upon published articles, as long as the author and publisher are properly credited, which ensures maximum dissemination and a wider impact of our publications. The book as a whole is distributed by MDPI under the terms and conditions of the Creative Commons license CC BY-NC-ND. Contents About the Editors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii Preface to ”Biomarkers of Renal Diseases” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix Joaqu ́ ın Garc ́ ıa-Esta ̃ n and Felix Vargas Editorial for Special Issue—Biomarkers of Renal Disease Reprinted from: Int. J. Mol. Sci. 2020 , 21 , 8077, doi:10.3390/ijms21218077 . . . . . . . . . . . . . . 1 Koen E. Groeneweg, Jacques M.G.J. Duijs, Barend W. Florijn, Cees van Kooten, Johan W. de Fijter, Anton Jan van Zonneveld, Marlies E.J. Reinders and Roel Bijkerk Circulating Long Noncoding RNA LNC-EPHA6 Associates with Acute Rejection after Kidney Transplantation Reprinted from: Int. J. Mol. Sci. 2020 , 21 , 5616, doi:10.3390/ijms21165616 . . . . . . . . . . . . . . 5 ˇ Spela Borˇ stnar, ˇ Zeljka Veˇ ceri ́ c-Haler, Emanuela Boˇ stjanˇ ciˇ c, ˇ Ziva Pipan Tkalec, Damjan Kovaˇ c, Jelka Lindiˇ c and Nika Kojc Uromodulin and microRNAs in Kidney Transplantation—Association with Kidney | Graft Function Reprinted from: Int. J. Mol. Sci. 2020 , 21 , 5592, doi:10.3390/ijms21165592 . . . . . . . . . . . . . . 15 Francesco Guzzi, Luigi Cirillo, Elisa Buti, Francesca Becherucci, Carmela Errichiello, Rosa Maria Roperto, James P. Hunter and Paola Romagnani Urinary Biomarkers for Diagnosis and Prediction of Acute Kidney Allograft Rejection: A Systematic Review Reprinted from: Int. J. Mol. Sci. 2020 , 21 , 6889, doi:10.3390/ijms21186889 . . . . . . . . . . . . . . 27 Marco Quaglia, Guido Merlotti, Gabriele Guglielmetti, Giuseppe Castellano and Vincenzo Cantaluppi Recent Advances on Biomarkers of Early and Late Kidney Graft Dysfunction Reprinted from: Int. J. Mol. Sci. 2020 , 21 , 5404, doi:10.3390/ijms21155404 . . . . . . . . . . . . . . 49 Yury E. Glazyrin, Dmitry V. Veprintsev, Irina A. Ler, Maria L. Rossovskaya, Svetlana A. Varygina, Sofia L. Glizer, Tatiana N. Zamay, Marina M. Petrova, Zoran Minic, Maxim V. Berezovski and Anna S. Kichkailo Proteomics-Based Machine Learning Approach as an Alternative to Conventional Biomarkers for Differential Diagnosis of Chronic Kidney Diseases Reprinted from: Int. J. Mol. Sci. 2020 , 21 , 4802, doi:10.3390/ijms21134802 . . . . . . . . . . . . . . 85 Hee-Sung Ahn, Jong Ho Kim, Hwangkyo Jeong, Jiyoung Yu, Jeonghun Yeom, Sang Heon Song, Sang Soo Kim, In Joo Kim and Kyunggon Kim Differential Urinary Proteome Analysis for Predicting Prognosis in Type 2 Diabetes Patients with and without Renal Dysfunction Reprinted from: Int. J. Mol. Sci. 2020 , 21 , 4236, doi:10.3390/ijms21124236 . . . . . . . . . . . . . . 97 Wei-Cheng Tseng, Ming-Tsun Tsai, Nien-Jung Chen and Der-Cherng Tarng Trichostatin A Alleviates Renal Interstitial Fibrosis Through Modulation of the M2 Macrophage Subpopulation Reprinted from: Int. J. Mol. Sci. 2020 , 21 , 5966, doi:10.3390/ijms21175966 . . . . . . . . . . . . . . 117 v Michele Provenzano, Salvatore Rotundo, Paolo Chiodini, Ida Gagliardi, Ashour Michael, Elvira Angotti, Silvio Borrelli, Raffaele Serra, Daniela Foti, Giovambattista De Sarro and Michele Andreucci Contribution of Predictive and Prognostic Biomarkers to Clinical Research on Chronic Kidney Disease Reprinted from: Int. J. Mol. Sci. 2020 , 21 , 5846, doi:10.3390/ijms21165846 . . . . . . . . . . . . . . 133 Nadezda Petejova, Arnost Martinek, Josef Zadrazil, Marcela Kanova, Viktor Klementa, Radka Sigutova, Ivana Kacirova, Vladimir Hrabovsky, Zdenek Svagera and David Stejskal Acute Kidney Injury in Septic Patients Treated by Selected Nephrotoxic Antibiotic Agents—Pathophysiology and Biomarkers—A Review Reprinted from: Int. J. Mol. Sci. 2020 , 21 , 7115, doi:10.3390/ijms21197115 . . . . . . . . . . . . . . 159 Satoshi Washino, Keiko Hosohata and Tomoaki Miyagawa Roles Played by Biomarkers of Kidney Injury in Patients with Upper Urinary Tract Obstruction Reprinted from: Int. J. Mol. Sci. 2020 , 21 , 5490, doi:10.3390/ijms21155490 . . . . . . . . . . . . . . 175 F ́ elix Vargas, Rosemary Wangesteen, Isabel Rodr ́ ıguez-G ́ omez and Joaqu ́ ın Garc ́ ıa-Esta ̃ n Role as Predictive Renal Aminopeptidases in Cardiovascular and Renal Function. Injury Biomarkers Reprinted from: Int. J. Mol. Sci. 2020 , 21 , 5615, doi:10.3390/ijms21165615 . . . . . . . . . . . . . . 193 Wojciech Wołyniec, Wojciech Ratkowski, Joanna Renke and Marcin Renke Changes in Novel AKI Biomarkers after Exercise. A Systematic Review Reprinted from: Int. J. Mol. Sci. 2020 , 21 , 5673, doi:10.3390/ijms21165673 . . . . . . . . . . . . . . 213 Laura Martinez Valenzuela, Juliana Draibe, Xavier Fulladosa and Juan Torras New Biomarkers in Acute Tubulointerstitial Nephritis: A Novel Approach to a Classic Condition Reprinted from: Int. J. Mol. Sci. 2020 , 21 , 4690, doi:10.3390/ijms21134690 . . . . . . . . . . . . . . 233 Armando Coca, Carmen Aller, Jimmy Reinaldo S ́ anchez, Ana Luc ́ ıa Valencia, Elena Bustamante-Munguira and Juan Bustamante-Munguira Role of the Furosemide Stress Test in Renal Injury Prognosis Reprinted from: Int. J. Mol. Sci. 2020 , 21 , 3086, doi:10.3390/ijms21093086 . . . . . . . . . . . . . . 243 Takahiro Uchida and Takashi Oda Glomerular Deposition of Nephritis-Associated Plasmin Receptor (NAPlr) and Related Plasmin Activity: Key Diagnostic Biomarkers of Bacterial Infection-related Glomerulonephritis Reprinted from: Int. J. Mol. Sci. 2020 , 21 , 2595, doi:10.3390/ijms21072595 . . . . . . . . . . . . . . 255 vi About the Editors Joaqu ́ ın Garc ́ ıa-Esta ̃ n studied medicine at the University of Murcia in 1974–1980 and began his academic activity in 1982 in the Department of Physiology of the Faculty of Medicine of the University of Murcia. He earned his medical degree in 1986 at the University of Murcia. He completed a postdoctoral stay at the Medical College of Wisconsin (Milwaukee, USA) in 1987 and 1988, under the guidance of Dr. Richard J. Roman. He became Associate Professor of Physiology at the University of Murcia in 1987 and became Full Professor in 2002. Since 1989, he has been Principal Investigator in the Research Group of Physiopathology of the Liver Cirrhosis and Arterial Hypertension. He has been Principal Investigator in 10 research projects funded by the National Plan of Biomedicine, Carlos III Health Institute, and Seneca Foundation since 1989. He has authored or co-authored almost 130 articles and book chapters, many of them in international journals with medium–high impact. He has been the director of nine doctoral theses, four of them receiving the Extraordinary Doctorate Award. He has held the positions of Vice-Dean of the Faculty of Medicine of the University of Murcia (1992–1995), Coordinator of International Relations for the Health Sciences (1992–1999), Coordinator of Curriculum Planning of the Vice-Rectorate of Studies and Postgraduate Studies of the University of Murcia (from July 2002 to March 2006), Dean of the Faculty of Medicine of the University of Murcia (2006–2014), and President of the National Conference of Deans of Spanish Medical Schools (2008–2012). He is the founder (2014) and current secretary of the Center of Studies on Medical Education. Felix Vargas studied medicine at the University of Granada in 1973–1979 and began his academic activity in 1980 in the Department of Physiology of the Faculty of Medicine of the University of Granada. He earned his doctoral degree in 1984 at the University of Granada. He completed a postdoctoral stay in the Blood Pressure Unit (Glasgow, UK) in 1986, under the guidance of Dr. A. F. Lever. He completed another scientific stay at Paris INSERM Unite 400, directed by Dr. R. P. Garay. He became Associate Professor of Physiology at the University of Granada in 1984 and became Full Professor in 2000. Since 1990, he has been Principal Investigator in the Research Group of Physiopathology of the Thyroid Disorders and Arterial Hypertension. He has completed studies and obtained a patent on the aminopeptidases as early renal biomarkers of renal diseases. He has been Principal Investigator in 10 research projects funded by the National Plan of Biomedicine, Carlos III Health Institute, and the Department of Innovation and Science since 1990. He is a member of the National Group of Investigation of Renal Diseases (REDinREN). He has authored or co-authored almost 135 articles and reviews, many of them in international journals with medium–high impact. He has been the director of 23 doctoral theses, 10 of them receiving the Extraordinary Doctorate Award. He is the coordinator of teaching activities at the Department of Physiology of the University of Granada (2008–2020). vii Preface to ”Biomarkers of Renal Diseases” The National Institutes of Health (NIH) Biomarkers Definitions Group has defined a biomarker as “A characteristic that is objectively measured and evaluated as an indicator of normal biologic processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention.” For acute or chronic kidney diseases, the ideal biomarker should, among others, show rapid and reliable changes with the progression of the disease and be highly sensitive and specific, be able to detect injury to the different segments of the nephron, and be rapidly and easily measurable. Creatinine, for instance, is not a good renal marker since acute injuries would not show changes in filtration rate until the progression of the disease allows its accumulation. Similarly, in chronic renal disease, the elevation in serum creatinine is a late indicator of the reduction in glomerular filtration. Other conventional biomarkers such as proteinuria, cell cylinders, and fractional excretion of sodium have shown a lack of sensitivity and specificity for the early recognition of acute kidney injury, leading to the need for and the enormous interest surrounding the possibility of using other biomarkers with the ability to perform early detection, differential diagnosis, prognostic assessment, response to treatment, and functional recovery. In this Special Issue, we have published reviews and experimental papers showing significant advances in the field of renal biomarkers. Joaqu ́ ın Garc ́ ıa-Esta ̃ n, Felix Vargas Editors ix International Journal of Molecular Sciences Editorial Editorial for Special Issue—Biomarkers of Renal Disease Joaqu í n Garc í a-Estañ 1, * and Felix Vargas 2, * 1 Departamento de Fisiologia, Facultad de Medicina, IMIB, Universidad de Murcia, 30120 Murcia, Spain 2 Departamento de Fisiologia, Facultad de Medicina, Universidad de Granada, 18071 Granada, Spain * Correspondence: jgestan@um.es (J.G.-E.); fvargas@ugr.es (F.V.) Received: 21 October 2020; Accepted: 27 October 2020; Published: 29 October 2020 The National Institutes of Health (NIH) Biomarkers Definitions Group has defined a biomarker as “A characteristic that is objectively measured and evaluated as an indicator of normal biologic processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention.” For acute or chronic kidney diseases, the ideal biomarker should, among others, show rapid and reliable changes with the progression of the disease and be highly sensitive and specific, be able to detect injury to the di ff erent segments of the nephron, and be rapidly and easily measurable. Creatinine, for instance, is not a good renal marker since acute injuries would not show changes in filtration rate until the progression of the disease allows its accumulation. Similarly, in chronic renal disease, the elevation in serum creatinine is a late indicator of the reduction in glomerular filtration. Other conventional biomarkers such as proteinuria, cell cylinders, and fractional excretion of sodium have shown lack of sensitivity and specificity for the early recognition of acute kidney injury; hence, leading to the need and the enormous interest surrounding the possibility of using other biomarkers with the ability to perform early detection, di ff erential diagnosis, assessment prognostic, response to treatment, and functional recovery. In this Special Issue [ 1 ], we have published reviews or experimental papers showing significant advances in the field of renal biomarkers. Regarding research articles, we have an interesting contribution by Groeneweg et al. [ 2 ] to the topic of rejection of a kidney graft. These authors demonstrate that the use of circulating long noncoding RNAs (lncRNAs) may be a suitable marker for vascular injury in that setting, specially LNC-EPHA6, a substance that has been found to relate to diabetic nephropathy. An additional paper [ 3 ] by Borštnar et al. , working with microRNAs (miRNAs), concluded that six selected miRNAs (miR-29c, miR-126, miR-146a, miR-150, miR-155, and miR-223) were shown to be independent of kidney graft function, indicating their potential as biomarkers of associated kidney graft disease processes, but using serum uromodulin levels, which were also analyzed, depended entirely on kidney graft function and thus reflected functioning tubules rather than any specific kidney graft injury. In line with these studies, a good review by Guzzi et al. [4] followed the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines to conclude that urinary C-X-C motif chemokine ligands were the most promising and frequently studied biomarkers for diagnosis and prediction of acute kidney allograft rejection. In the same field, the review by Quaglia and colleagues [ 5 ] explores new biomarkers of early and late graft dysfunction, which are very much needed in renal transplants to improve the management of complications and prolong graft survival. Thus, OMIC technology (all technologies aimed at detection of genes (genomics), mRNA (transriptomics), proteins (proteomics) and metabolites (metabolomics)) has allowed the identification of many candidate biomarkers, providing diagnostic and prognostic information at very early stages of pathological processes. Donor-derived cell-free DNA and extracellular vesicles are further promising tools. However, most of these biomarkers still need to be validated in multiple independent cohorts and standardized, and prospective studies are needed to assess whether introduction of these new sets of biomarkers into clinical practice could Int. J. Mol. Sci. 2020 , 21 , 8077; doi:10.3390 / ijms21218077 www.mdpi.com / journal / ijms 1 Int. J. Mol. Sci. 2020 , 21 , 8077 actually reduce the need for renal biopsy, integrate traditional tools, and ultimately improve graft survival compared to current management. In an interesting study [ 6 ], Glazyrin and coworkers examined several machine learning algorithms linked to a full-proteomic approach, which were examined for the di ff erential diagnosis of chronic kidney disease (CKD) of three origins, diabetic nephropathy, hypertension, and glomerulonephritis—three of the most common causes of CKD. While the group of hypertensive nephropathy could not be reliably separated according to plasma data, this group of hypertensive nephropathy was reliably separated from all other renal patients by urine proteome data. However, the analysis of the entire proteomics data of urine did not allow di ff erentiating between the three diseases. Thus, it seems that the urine proteome, compared with the plasma proteome, is of much less importance. Clearly, this is an area of interest that will benefit from the incorporation of data technicians and proteomic analysts to these hospital services. Additional information came with the results shown in the article by Ahn et al. [7] They used proteome analysis for the prediction of type 2 diabetic patients with or without renal dysfunction. In the results of these authors, it looks that several proteins (ACP2, CTSA, GM2A, MUC1, and SPARCL1) performed better than mucin-1 or albumin as predictors of direct kidney function in these diabetic patients with kidney impairment. Tseng et al. [ 8 ], in the field of renal fibrosis, showed that histone deacetylase inhibition by trichostatin A significantly attenuated renal fibrosis through promoting an M1(proinflammatory) to M2 (anti-inflammatory) macrophage transition in obstructed kidneys, therefore alleviating the renal fibrosis in obstructed kidneys. However, it is first necessary to establish the role of M2 macrophages regarding its profibrotic or antifibrotic roles. An important review by Provenzano and coworkers [ 9 ] has reported a framework for implementing biomarkers in observational and intervention studies. To that end, biomarkers are classified as either prognostic or predictive, the first type is used to identify the likelihood of a patient to develop an endpoint regardless of treatment, whereas the second type is used to determine whether the patient is likely to benefit from a specific treatment. Thus, the authors revise current biomarkers useful for chronic kidney patients, not only kidney biomarkers but also markers of oxidative stress, tissue remodeling, metabolism, and cardiac biomarkers, together with some important paragraphs on the role, either prognostic or predictive, of proteomics, metabolomics, and genomics. A final page on biomarkers in intervention studies should be of interest to clinical studies and those in the experimental phase of drug development. The contribution by Petejova et al. [ 10 ] covered the pathophysiology of vancomycin and gentamicin nephrotoxicity. In particular, septic acute kidney injury (AKI) and the microRNAs involved in the pathophysiology of both syndromes and also the pathophysiology and potential biomarkers of septic and toxic acute kidney injury in septic patients was studied. In addition, five miRNAs (miR-15a-5p, miR-192-5p, miR-155-5p, miR-486-5p and miR-423-5p) specific to septic and toxic acute kidney injury in septic patients, treated by nephrotoxic antibiotic agents (vancomycin and gentamicin), were identified. Partial or complete obstruction of the urinary tract is a common and challenging urological condition caused by a variety of conditions, eventually impairing renal function. Washino and coworkers [ 11 ] report that biomarkers of acute kidney injury are useful for the early detection and monitoring of kidney injury induced by upper urinary tract obstruction, including levels of neutrophil gelatinase-associated lipocalin (NGAL), monocyte chemotactic protein-1, kidney injury molecule 1, N-acetyl-b-D-glucosaminidase, and vanin-1 in the urine and serum NGAL and cystatin C concentrations. In a review by the group of Vargas et al. [ 12 ], they focused on the role of four aminopeptidases in the control of blood pressure (BP) and renal function and their association with di ff erent cardiovascular and renal diseases. Beyond their role as therapeutic tools for BP control and renal diseases, they also explored their role as urinary biomarkers of renal injury in both acute and chronic renal nephropathies, including those induced by nephrotoxic agents, obesity, hypertension, or diabetes. 2 Int. J. Mol. Sci. 2020 , 21 , 8077 The review by Wołyniec et al. [ 13 ] has identified and analyzed several studies that have studied these markers after physical exercise, concluding that there is evidence that cystatin C is a better indicator of glomerular filtration rate (GFR) in athletes after exercise than creatinine. Additionally, serum and plasma NGAL are increased after prolonged exercise, but the level also depends on inflammation and hypoxia; therefore, it seems that in physical exercise, it is too sensitive for AKI diagnosis. It may, however, help to diagnose subclinical kidney injury, e.g., in rhabdomyolysis. Although urinary biomarkers are increased after many types of exercise, such as NGAL, KIM-1, cystatin-C, L-FABP and interleukin 18, their levels decrease rapidly after exercise; thus, the importance of this short-term increase in AKI biomarkers after exercise lacks a physiological explanation and it merits further studies that show their relation to kidney injury. In the search for biomarkers of acute tubulointerstitial nephritis, Martinez-Valenzuela and coworkers [ 14 ] have summarized the available evidence on this topic, with a special focus on urinary cytokines and chemokines that may reflect kidney local inflammation. However, they conclude that to date, there is a lack of reliable non-invasive diagnostic and follow-up markers and that the gold standard for diagnosis is still kidney biopsy, which shows a pattern of tubulointerstitial leukocyte infiltrate. Coca et al. have revised the [ 15 ] furosemide stress test as a low-cost, fast, safe, and easy-to-perform test to assess tubular integrity, to allow for risk stratification and accurate patient prognosis in the management of patients with kidney disease. However, the findings published so far regarding its clinical use provide insu ffi cient evidence to recommend the generalized application of the test in daily clinical routine, and they recommend the need for standardization in the application of the test in order to facilitate the comparison of results. Finally, Uchida et al. [ 16 ] write about the glomerulonephritis that often develops after the curing of an infection, such as the glomerulonephritis (GN) in children following streptococcal infections (poststreptococcal acute glomerulonephritis, PSAGN). Nephritis-associated plasmin receptor (NAPlr), isolated from the cytoplasmic fraction of group A streptococcus, has been shown to trap plasmin and maintain its activity and was originally considered as a nephritogenic protein for PSAGN. Indeed, NAPlr deposition and related plasmin activity have been observed to have an almost identical distribution in the glomeruli of early phase PSAGN patients at a high frequency. The authors conclude that the interactions among NAPlr, plasmin activity, and the streptococcal cysteine proteinase SpeB, and the association between these elements and complements or immune complexes, both in vitro and in vivo, should be investigated in future studies. Author Contributions: Both authors have contributed equally. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Conflicts of Interest: The authors declare no conflict of interest. References 1. Biomarkers of Renal Disease. Special Issue. Available online: https: // www.mdpi.com / journal / ijms / special_ issues / Biomarkers_Renal_Diseases#published (accessed on 15 October 2020). 2. Groeneweg, K.E.; Duijs, J.M.; Florijn, B.W.; van Kooten, C.; de Fijter, J.W.; van Zonneveld, A.J.; Reinders, M.E.; Bijkerk, R. Circulating Long Noncoding RNA LNC-EPHA6 Associates with Acute Rejection after Kidney Transplantation. Int. J. Mol. Sci. 2020 , 21 , 5616. [CrossRef] [PubMed] 3. Borštnar, Š.; Veˇ ceri ́ c-Haler, Ž.; Boštjanˇ ciˇ c, E.; Pipan Tkalec, Ž.; Kovaˇ c, D.; Lindiˇ c, J.; Kojc, N. Uromodulin and microRNAs in Kidney Transplantation—Association with Kidney Graft Function. Int. J. Mol. Sci. 2020 , 21 , 5592. [CrossRef] [PubMed] 4. Guzzi, F.; Cirillo, L.; Buti, E.; Becherucci, F.; Errichiello, C.; Roperto, R.M.; Hunter, J.P.; Romagnani, P. Urinary Biomarkers for Diagnosis and Prediction of Acute Kidney Allograft Rejection: A Systematic Review. Int. J. Mol. Sci. 2020 , 21 , 6889. [CrossRef] [PubMed] 5. Quaglia, M.; Merlotti, G.; Guglielmetti, G.; Castellano, G.; Cantaluppi, V. Recent Advances on Biomarkers of Early and Late Kidney Graft Dysfunction. Int. J. Mol. Sci. 2020 , 21 , 5404. [CrossRef] [PubMed] 3 Int. J. Mol. Sci. 2020 , 21 , 8077 6. Glazyrin, Y.E.; Veprintsev, D.V.; Ler, I.A.; Rossovskaya, M.L.; Varygina, S.A.; Glizer, S.L.; Zamay, T.N.; Petrova, M.M.; Minic, Z.; Berezovski, M.V.; et al. Proteomics-Based Machine Learning Approach as an Alternative to Conventional Biomarkers for Di ff erential Diagnosis of Chronic Kidney Diseases. Int. J. Mol. Sci. 2020 , 21 , 4802. [CrossRef] [PubMed] 7. Ahn, H.-S.; Kim, J.H.; Jeong, H.; Yu, J.; Yeom, J.; Song, S.H.; Kim, S.S.; Kim, I.J.; Kim, K. Di ff erential Urinary Proteome Analysis for Predicting Prognosis in Type 2 Diabetes Patients with and without Renal Dysfunction. Int. J. Mol. Sci. 2020 , 21 , 4236. [CrossRef] [PubMed] 8. Tseng, W.-C.; Tsai, M.-T.; Chen, N.-J.; Tarng, D.-C. Trichostatin A Alleviates Renal Interstitial Fibrosis through Modulation of the M2 Macrophage Subpopulation. Int. J. Mol. Sci. 2020 , 21 , 5966. [CrossRef] [PubMed] 9. Provenzano, M.; Rotundo, S.; Chiodini, P.; Gagliardi, I.; Michael, A.; Angotti, E.; Borrelli, S.; Serra, R.; Foti, D.; De Sarro, G.; et al. Contribution of Predictive and Prognostic Biomarkers to Clinical Research on Chronic Kidney Disease. Int. J. Mol. Sci. 2020 , 21 , 5846. [CrossRef] [PubMed] 10. Petejova, N.; Martinek, A.; Zadrazil, J.; Kanova, M.; Klementa, V.; Sigutova, R.; Kacirova, I.; Hrabovsky, V.; Svagera, Z.; Stejskal, D. Acute Kidney Injury in Septic Patients Treated by Selected Nephrotoxic Antibiotic Agents—Pathophysiology and Biomarkers—A Review. Int. J. Mol. Sci. 2020 , 21 , 7115. [CrossRef] [PubMed] 11. Washino, S.; Hosohata, K.; Miyagawa, T. Roles Played by Biomarkers of Kidney Injury in Patients with Upper Urinary Tract Obstruction. Int. J. Mol. Sci. 2020 , 21 , 5490. [CrossRef] [PubMed] 12. Vargas, F.; Wangesteen, R.; Rodr í guez-G ó mez, I.; Garc í a-Estañ, J. Aminopeptidases in Cardiovascular and Renal Function. Role as Predictive Renal Injury Biomarkers. Int. J. Mol. Sci. 2020 , 21 , 5615. [CrossRef] [PubMed] 13. Wołyniec, W.; Ratkowski, W.; Renke, J.; Renke, M. Changes in Novel AKI Biomarkers after Exercise. A Systematic Review. Int. J. Mol. Sci. 2020 , 21 , 5673. 14. Martinez Valenzuela, L.; Draibe, J.; Fulladosa, X.; Torras, J. New Biomarkers in Acute Tubulointerstitial Nephritis: A Novel Approach to a Classic Condition. Int. J. Mol. Sci. 2020 , 21 , 4690. [CrossRef] [PubMed] 15. Coca, A.; Aller, C.; Reinaldo S á nchez, J.; Valencia, A.L.; Bustamante-Munguira, E.; Bustamante-Munguira, J. Role of the Furosemide Stress Test in Renal Injury Prognosis. Int. J. Mol. Sci. 2020 , 21 , 3086. [CrossRef] [PubMed] 16. Uchida, T.; Oda, T. Glomerular Deposition of Nephritis-Associated Plasmin Receptor (NAPlr) and Related Plasmin Activity: Key Diagnostic Biomarkers of Bacterial Infection-related Glomerulonephritis. Int. J. Mol. Sci. 2020 , 21 , 2595. [CrossRef] [PubMed] Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional a ffi liations. © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http: // creativecommons.org / licenses / by / 4.0 / ). 4 International Journal of Molecular Sciences Article Circulating Long Noncoding RNA LNC-EPHA6 Associates with Acute Rejection after Kidney Transplantation Koen E. Groeneweg, Jacques M.G.J. Duijs, Barend W. Florijn, Cees van Kooten, Johan W. de Fijter, Anton Jan van Zonneveld, Marlies E.J. Reinders and Roel Bijkerk * Department of Internal Medicine (Nephrology) and the Einthoven Laboratory for Vascular and Regenerative Medicine, Leiden University Medical Center, Albinusdreef 2, 2333 ZA Leiden, Zuid Holland, The Netherlands; k.e.groeneweg@lumc.nl (K.E.G.); J.M.G.J.Duijs@lumc.nl (J.M.G.J.D.); b.w.florijn@lumc.nl (B.W.F.); C.van_Kooten@lumc.nl (C.v.K.); J.W.de_Fijter@lumc.nl (J.W.d.F.); A.J.van_Zonneveld@lumc.nl (A.J.v.Z.); M.E.J.Reinders@lumc.nl (M.E.J.R.) * Correspondence: R.Bijkerk@lumc.nl Received: 29 June 2020; Accepted: 3 August 2020; Published: 5 August 2020 Abstract: Acute rejection (AR) of a kidney graft in renal transplant recipients is associated with microvascular injury in graft dysfunction and, ultimately, graft failure. Circulating long noncoding RNAs (lncRNAs) may be suitable markers for vascular injury in the context of AR. Here, we first investigated the e ff ect of AR after kidney transplantation on local vascular integrity and demonstrated that the capillary density markedly decreased in AR kidney biopsies compared to pre-transplant biopsies. Subsequently, we assessed the circulating levels of four lncRNAs (LNC-RPS24, LNC-EPHA6, MALAT1, and LIPCAR), that were previously demonstrated to associate with vascular injury in a cohort of kidney recipients with a stable kidney transplant function ( n = 32) and recipients with AR ( n = 15). The latter were followed longitudinally six and 12 months after rejection. We found higher levels of circulating LNC-EPHA6 during rejection, compared with renal recipients with a stable kidney function ( p = 0.017), that normalized one year after AR. In addition, LNC-RPS24, LNC-EPHA6, and LIPCAR levels correlated significantly with the vascular injury marker soluble thrombomodulin. We conclude that AR and microvascular injury are associated with higher levels of circulating LNC-EPHA6, which emphasizes the potential role of lncRNAs as biomarker in the context of AR. Keywords: long noncoding RNA; kidney transplantation; rejection; microvascular injury 1. Introduction Acute rejection (AR) is considered to be a prominent cause of graft failure in the first year after transplantation in kidney transplant recipients [ 1 , 2 ], although the long-term consequences of AR remain a subject of discussion. Despite better screening and improved immune suppressive therapies, rejection is still suspected to cause a significant proportion of death censored graft failure after kidney transplantation [ 3 , 4 ]. Previous research showed a prolonged e ff ect on kidney function deterioration as well as graft survival after a rejection episode [ 2 ]. Microvascular endothelial cells (ECs) are very susceptible to injury, that can result from episodes of AR. Following the alloimmune response, cytokines and growth factors are produced that can lead to EC activation and microvascular destabilization [ 5 – 10 ]. These rejection-associated events can result in perpetual EC damage and promotion of (aberrant) angiogenesis within the allograft [ 5 , 7 , 9 ]. Together, these insults can lead to the loss of the microvasculature, chronic ischemia and cell death [ 11 , 12 ], and ultimately, to the development of interstitial fibrosis / tubular atrophy and graft dysfunction [ 5 , 6 , 9 ]. Therefore, monitoring the course Int. J. Mol. Sci. 2020 , 21 , 5616; doi:10.3390 / ijms21165616 www.mdpi.com / journal / ijms 5 Int. J. Mol. Sci. 2020 , 21 , 5616 of microvascular injury after rejection could be beneficial in deciding on the best treatment strategies. Previously, we found the vascular injury markers soluble thrombomodulin (sTM) and Angiopoietin-2 (Ang-2) to increase upon AR. sTM normalized in the first year after AR, while Ang-2 remained elevated [ 13 ]. Noncoding RNA, such as micro RNAs (miRNA) and long noncoding RNAs (lncRNA)are increasingly recognized to play an important role in vascular injury [ 14 ]. The functions of lncRNAs appear to be very diverse as they can bind DNA, proteins, and other RNAs. E.g. lncRNAs have been demonstrated to serve as a sca ff old for transcription factors or can assist chromatin-modifying enzymes, thereby regulating gene expression [ 15 ]. LncRNAs were also found to be important for miRNA processing, (alternative) splicing, translation and post-transcriptional regulation, for instance via sponging miRNAs [ 16 , 17 ]. In addition, lncRNAs can be promising biomarkers in a variety of vascular diseases and kidney injury [ 14 , 16 ]. Furthermore, lncRNAs have previously been associated with AR [ 18 ], but their dynamics after rejection have not been studied before. Earlier, we described that specific lncRNAs (MALAT1, LNC-RPS24, LNC-EPHA6, and LIPCAR) associate with microvascular damage and angiogenic factors in patients with diabetic nephropathy that received simultaneous kidney-pancreas transplantation [ 19 ], but their relation with AR and associated vascular damage is unclear. As such, in this study we first explored the relation of AR with local microvascular injury. Then, in a cross-sectional study of patients with T cell mediated AR, we analyzed selected vascular injury related lncRNAs as potential biomarkers for vascular damage in the context of kidney transplant rejection and assess the dynamics in these lncRNAs after rejection. 2. Results 2.1. Decreased Capillary Density in Acute Rejection Biopsies To assess the impact of AR on the local capillary density in the kidney, we quantified the number of endothelial cells (EC) and pericytes in archival acute rejection biopsies by immunohistochemical staining of the EC for CD34 antigen and the pericytes for the CD73 marker (resp. n = 102 and n = 29 ). Subsequently, we compared these parameters to the available pre-transplant biopsies (resp. n = 78 and n = 66) of these patients [ 20 ]. Patient characteristics can be found in Supplementary Table S1. As shown in Figure 1, we observed a strong decrease in both the number of endothelial cells (~2.5-fold, mboxemphp < 0.0001) as well as pericytes (~6-fold, p < 0.0001) in AR, indicating loss of the peritubular capillary network in AR. 2.2. Patient Characteristics of Cross Sectional and Longitudinal AR Study Population Next, we sought to investigate the relation of circulating lncRNAs with AR. To that end, we included plasma samples of a di ff erent cross-sectional study cohort that included patients with acute T cell mediated rejection and a control group of patients with stable kidney transplant function after transplantation (hereafter mentioned as ‘stable’). In addition, AR patients were studied longitudinally at 6 and 12 months after rejection to determine the dynamics after AR. The baseline characteristics of the transplant recipients in this cohort are described in Table 1. Most common causes of initial kidney failure before transplantation were autosomal dominant polycystic kidney disease (23%), focal segmental glomerulosclerosis (17%) and IgA nephropathy (13%). The mean time after transplantation (12 months) was comparable. Immunosuppressive regimen did not di ff er significantly. eGFR was lower and proteinuria higher in patients with AR, compared with stable patients (resp. p < 0.001 and p = 0.003 ). Factors that can influence the amount of vascular injury next to rejection, such as donor age, dialysis before transplantation, and months since transplantation, did not di ff er significantly. Incidence of active smokers was 7% in AR patients and 13% in stable patients. Panel reactive antibodies (PRA), mismatch, immunosuppressive regimen and the presence of previous transplantations did not di ff er between stable patients and patients with AR. Patients with AR had interstitial rejection, with or without involvement of the vasculature, and were treated with methylprednisolone (67%), ATG alone (13%), or a combination of methylprednisolone and ATG (13%) or alemtuzumab (13%). 6 Int. J. Mol. Sci. 2020 , 21 , 5616 Figure 1. Decreased capillary density after acute rejection. ( A ) Representative images of CD34 staining for pre-transplantation and acute rejection (AR) biopsies. ( B ) Quantification of CD34 staining (PreTx, n = 78 ; AR, n = 102). ( C ) Representative images of CD73 staining for pre-transplantation and acute rejection (AR) biopsies. ( D ) Quantification of CD73 staining (PreTx, n = 66, AR, n = 29). *** p -value < 0.001. Table 1. Cross-sectional study patient characteristics of patients with a stable kidney transplant function (stable) and patients with acute rejection (AR). Stable ( n = 32) AR ( n = 15) p -Value Sex, Male, n ( % ) 21 (66%) 10 (67%) 1.00 1 Age, Years ± SD 51 ± 14 54 ± 12 0.35 2 BMI ( kg / m 2 ) 26.4 ± 4.6 24.4 ± 3.5 0.15 1 Preemptive, n ( % ) 16 (50%) 5 (33%) 0.36 1 Months Since KTx, Median ( IQR ) 12 ± 1 12 ± 15 0.97 2 PRA > 5%, n ( % ) 6 (19%) 1 (7%) 0.40 1 Previous Transplantations, n ( % ) 2 (6%) 3 (20%) 0.31 1 Mismatch A / B / DR, Mean 1.0 / 1.2 / 0.8 0.9 / 1.3 / 1.0 0.76 / 0.81 / 0.63 1 Donor Characteristics Sex, male, n (%) 11 (34%) 7 (47%) 0.52 1 Age, years ± SD 50 ± 17 47 ± 12 0.64 2 Induction Therapy, n ( % ) 0.54 1 Alemtuzumab 3 (9%) 0 IL-2 receptor inhibitor 29 (91%) 15 (100%) Immunosuppressive Drugs, n ( % ) Tacrolimus 22 (69%) 8 (53%) 0.20 1 Cyclosporine 5 (16%) 3 (20%) 1.00 1 Prednisone 32 (100%) 14 (93%) 0.32 1 Mycophenolate mofetil 25 (78%) 8 (53%) 0.07 1 Everolimus 6 (19%) 1 (7%) 0.40 1 7 Int. J. Mol. Sci. 2020 , 21 , 5616 Table 1. Cont. Stable ( n = 32) AR ( n = 15) p -Value Acute Rejection Therapy, n ( % ) ATG 2 (13%) methylprednisolone - 10 (67%) methylprednisolone + ATG - 2 (13%) methylprednisolone + alemtuzumab - 1 (7%) eGFR (mL / min / 1.73 m 2 ) 54 ± 12 34 ± 14 < 0.001 2 Proteinuria (g / 24 h), Median ( IQR ) 0.17 (0.13–0.25) 0.36 (0.23–1.19) 0.003 3 1 Fisher’s exact test, 2 unpaired t-test, 3 Mann-Whitney U test, KTx = kidney transplantation, PRA = panel reactive antibody. 2.3. Circulating LNC-EPHA6 Levels Directly Correlate with Acute Rejection In order to assess the relationship between AR and vascular injury related lncRNAs LNC-RPS24, MALAT1, LNC-EPHA6, and LIPCAR, circulating levels of these lncRNAs were measured in stable patients and AR patients. In this cohort, MALAT1 levels were only detectable in less than 30% of patients and therefore not included in further analyses. Relative expression of circulating LNC-EPHA6 was significantly higher in patients with AR, compared with stable patients ( p = 0.017; Figure 2). LNC-RPS24 and LIPCAR showed a similar trend, although these di ff erences did not reach statistical significance (resp. p = 0.11 and p = 0.16). Figure 2. Circulating lncRNA levels are e ff ected by acute rejection. Relative expression of LNC-RPS24 ( A ), LNC-EPHA6 ( B ), and LIPCAR ( C ) in the cross-sectional cohort; kidney recipients with a stable kidney function (Stable; n = 32), kidney recipients with acute rejection at the time of rejection (R0), and 6 and 12 months after rejection (R6 and R12). Data are presented as mean ± SD, * p -value < 0.05 , ** p -value < 0.01, *** p -value < 0.001. 2.4. Circulating LNC-EPHA6 Decreases in the First Year After Acute Rejection Since vascular damage persists after a rejection episode, patients with AR were followed longitudinally to study the dynamics of lncRNAs in the first year after AR. Elevated levels of circulating LNC-EPHA6 persisted until six months after AR ( p < 0.001) and decreased significantly one year after rejection, although LNC-EPHA6 levels at one year after rejection remained slightly higher levels than in