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Published on: December 29, 2023
Elevated Levels of Urinary Extracellular Vesicle Fibroblast-Specific Protein 1 in Patients with Active Crescentic
Yukie Morikawa1, Naoki Takahashi2, Kazuko Kamiyama1
1Department of Nephrology, Faculty of Medical Sciences, University of Fukui, Fukui, Japan.
Background/Aims:
Extracellular vesicles (EVs), including exosomes, are present in various bodily fluids, including urine. We and others previously reported that cells expressing fibroblast-specific protein 1 (FSP1) accumulate within damaged glomeruli, and that urinary FSP1, as well as urinary soluble CD163, could potentially serve as a biomarker of ongoing glomerular injury.
Methods:
To test that idea, we collected urine samples from 37 patients with glomerular disease; purified the urinary EVs; characterized them using Nanosight, western blotting, and immunoelectron microscopy; and determined FSP1 and soluble CD163 levels using enzyme-linked immunosorbent assays.
Results:
Deemed to be mainly exosomes based on their size distribution, the EVs in urine contained FSP1, and a portion of the FSP1-positive vesicles was also positive for podocalyxin. FSP1 levels in urinary EVs were (1) positively correlated with rates of biopsy-proven cellular crescent formation (r = 0.562, p < 0.001) and total crescent formation (r = 0.448, p = 0.005) among total glomeruli; (2) significantly higher in patients with cellular crescents affecting 20% or more of their glomeruli than in those with fewer affected glomeruli (p = 0.003); and (3) significantly decreased after glucocorticoid and immunosuppressant therapy (p < 0.05). A positive correlation between FSP1 levels in urinary EVs and urinary soluble CD163 levels was confirmed (r = 0.367, p < 0.05).
Conclusion:
These data suggest that a portion of urinary FSP1 is secreted as EVs originating from podocytes, and that FSP1 levels reflect active and ongoing glomerular injury and disease activity, such as cellular crescent formation.
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