The proteomic landscape of small urinary extracellular vesicles during kidney transplantation

Abstract

Kidney transplantation is the preferred renal replacement therapy available. Yet, long‐term transplant survival is unsatisfactory, partially due to insufficient possibilities of longitudinal monitoring and understanding of the biological processes after transplantation. Small urinary extracellular vesicles (suEVs) – as a non‐invasive source of information – were collected from 22 living donors and recipients. Unbiased proteomic analysis revealed temporal patterns of suEV protein signature and cellular processes involved in both early response and longer‐term graft adaptation. Complement activation was among the most dynamically regulated components. This unique atlas of the suEV proteome is provided through an online repository allowing dynamic interrogation by the user. Additionally, a correlative analysis identified putative prognostic markers of future allograft function. One of these markers – phosphoenol pyruvate carboxykinase (PCK2) – could be confirmed using targeted MS in an independent validation cohort of 22 additional patients. This study sheds light on the impact of kidney transplantation on urinary extracellular vesicle content and allows the first deduction of early molecular processes in transplant biology. Beyond that our data highlight the potential of suEVs as a source of biomarkers in this setting.

Urinary Extracellular Vesicles Are a Novel Tool to Monitor Allograft Function in Kidney Transplantation: A Systematic Review

“…In healthy conditions, kidney-specific proteins, e.g., aquaporin-1 (AQP1), aquaporin-2 (AQP2), Na-Cl cotransporter (NCC), Na-K-Cl cotransporter 2 (NKCC2), and PODXL, show high abundance in uEV [ 36 , 37 ]. During low kidney functionality, decreased release of uEV-AQP1 and uEV-AQP2 effectively detect GFR in G4 and G5 categories (KIDIGO guidelines) with a high area under the curve (AUC) value of 0.945 in the receiver operator characteristics curve analysis [ 38 ].…”

“…A recent uEV-proteomic study demonstrated that PODXL was one of the top 10 highly expressed proteins in small uEV of KTR with no early graft dysfunction [ 37 ]. Compared to KTR with stable allograft function, KTR with acute T cell-mediated rejection (TCMR) showed significantly decreased PODXL in uEV [ 26 ].…”

“…C3 also showed the second highest correlation with TCMR among 63 overexpressed proteins in the uEV from KTR [ 26 ]. In addition, the overexpression of C1q subcomponent subunit B and C1r in uEV was strongly correlated with decreased GFR in the first year after kidney transplantation [ 37 ]. During CNI nephrotoxicity, a condition of immunosuppression, the levels of complement factors C3, C5, C7, C9 in uEV of KTR were significantly lower compared to KTR with interstitial fibrosis and tubular atrophy (IFTA), although only 17 KTR were enrolled [ 27 ].…”

A Review of Current and Emerging Trends in Donor Graft-Quality Assessment Techniques

“…However, while Braun et al's study showed the potential of suEVs as biomarkers, the small number of patients in their sample did not allow for a conclusive statement on the predictive value of suEV PCK2. Therefore, the potential use of this biomarker will depend on larger trials in the future [80].…”

Extracellular Vesicles in Transplantation

“…Kidney rejection is associated with different pathological conditions that induce changes in the urinary compartment that may also contain EVs. In humans, urine EVs are thus increased after transplantation and in chronic kidney diseases (107) and are a potential source of biomarkers (108). Ultracentrifugation isolated-EVs from blood of kidney transplant recipients with glomerulopathy have higher levels (up to 2-fold) of fibronectin and type IV collagen than EVs from patients with a stable transplant (109).…”