Proteinuria in thrombotic microangiopathy is associated with partial podocytopathy

ABSTRACT

Background. Thrombotic microangiopathy (TMA) results in acute kidney injury, but the cause of heavy proteinuria in this disorder is puzzling. The goal of this study was to determine if there were significant effacement of foot processes and CD133-positive hyperplastic podocytes in TMA to explain the proteinuria. Methods. The study included 12 negative controls (renal parenchyma removed from renal cell carcinoma) and 28 thrombotic microangiopathy due to different etiologies. The percent of foot process effacement was estimated, and proteinuria level was obtained for each TMA case. Both groups of cases were stained for CD133 by immunohistochemical method, and the number of positive CD133 in hyperplastic podocytes was counted and analyzed. Results. Nineteen (19) of 28 (68%) TMA cases had nephrotic range proteinuria (urine protein/creatinine >3). Twenty-one (21) of 28 (75%) TMA cases showed positive CD133 staining in scattered hyperplastic podocytes within Bowman’s space but was absent in control cases. The percent of foot process effacement (56 ± 4%) correlated with proteinuria (protein/creatinine ratio 4.4 ± 0.6) (r = 0.46, p = .0237) in TMA group. Conclusion. Our data indicate that the proteinuria in TMA can be associated with significant effacement of foot processes. CD133-positive hyperplastic podocytes can be seen in the majority of TMA cases of this cohort, indicating a partial podocytopathy.

KEYWORDS:

• Acute kidney injury
• effacement of foot processes
• podocyte hyperplasia
• podocytopathy
• proteinuria
• thrombotic microangiopathy

Acknowledgments

The authors would like to thank the technologists in Beaumont’s electron microscopic laboratory, histology laboratory, and immuno-laboratory, Royal Oak, MI, for their excellent technical assistance.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The author(s) reported that there is no funding associated with the work featured in this article.