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Abstract: FR-OR13

Proteomic Analysis Reveals Proteins Associated Exclusively With Urinary Muddy Brown Granular Casts

Session Information

  • AKI Research: Mechanisms
    November 04, 2022 | Location: W230, Orange County Convention Center‚ West Building
    Abstract Time: 04:48 PM - 04:57 PM

Category: Acute Kidney Injury

  • 103 AKI: Mechanisms

Authors

  • Janech, Michael G., College of Charleston, Charleston, South Carolina, United States
  • Fongheiser, Elizabeth Ann, College of Charleston, Charleston, South Carolina, United States
  • Compton, Noah F., College of Charleston, Charleston, South Carolina, United States
  • Bland, Alison, College of Charleston, Charleston, South Carolina, United States
  • Neely, Benjamin A., National Institute of Standards and Technology Material Measurement Laboratory, Charleston, South Carolina, United States
  • Varghese, Vipin, Ochsner Medical Center, New Orleans, Louisiana, United States
  • Velez, Juan Carlos Q., Ochsner Medical Center, New Orleans, Louisiana, United States

Group or Team Name

  • Ochsner Nephrology
Background

The presence of “muddy” brown granular casts (MBGC) in the urinary sediment is pathognomonic for acute tubular injury (ATI), but the composition of MBGC remains understudied and no proteomic studies have been reported. Because MBGC are only visualized via manual inspection by microscopy, a diagnostic test to identify MBGC without microscopic inspection of the urine could be clinically useful. Unlike most acute kidney injury (AKI) biomarker discovery approaches, we hypothesized that MBGC-enriched urinary sediment (MBGC-sedi) contains unique proteins that could serve as biomarkers of ATI.

Methods

MBGC were enriched from 12 patients with AKI using a series of cell strainers (mesh size: 40 - 100µm). Enriched MBGC, matching urine supernatant samples, and urine sediments controls without MBGC (N=6) were proteolytically digested using S-traps and analyzed using tandem mass spectrometry. Proteins were identified by MASCOT and accepted at 1% false discovery. Identified proteins were quantified by weighted spectral count and ranked using exponentially modified protein abundance index (emPAI). ANOVA was utilized to filter proteins that were enriched in MBGC samples versus sediment lacking MBGC or urine supernatant.

Results

A total of 3367 proteins were identified across all MBGC samples (mean±SD = 1976±243 proteins/sample). The most abundant proteins in MBGC samples were Ig kappa constant region and retinol-binding protein 4. Although abundant, uromodulin had a mean rank of 15 across all MBGC samples. A total of 272 proteins were higher in MBGC compared to urine supernatant or control sediment without MBGC. Only one protein was exclusive to all MBGC samples, adrenodoxin, a small 19 kDa iron-binding mitochondrial protein known to be expressed in kidney tubules. A second protein, PDZ/LIM domain protein 1 was exclusive to 11 out of 12 MBGC samples and is involved in cytoskeletal stress fiber assembly in fibroblasts.

Conclusion

Mitochondrial adrenodoxin (ferrodoxin) and PDZ/LIM domain protein 1 may constitute a biomarker of MBGC presence and serve an alternative method to urine microscopy for identifying the presence of MBGC. We conclude that urinary adrenodoxin and PDZ/LIM domain protein 1 are potential target proteins for ATI diagnosis.

Funding

  • NIDDK Support