Renal microthrombosis and thrombomodulin deficiency in COVID-19–associated acute kidney injury

Figures

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  Fig. 1. Abundant tubular necrosis in critically ill COVID-19 patients. (A) Nuclear staining with Hoechst of renal cortex samples from normal human kidneys (NHK) obtained from nephrectomy specimens (n = 6, grey), postmortem controls (n = 7, blue), and kidneys from COVID-19 patients (C19, n = 7, red). (B) The area of nuclear staining was quantified and used as a measure of tubular cell integrity. (C) Fluorescence immunohistochemistry of ACE2 (green) and vimentin (VIM, red) expression in renal cortex from postmortem normal human kidney (NHK) and COVID-19. Vimentin is a marker of podocytes and mesenchymal cells. Original magnification x400, scale bars = 50 μm. (D) SARS-CoV-2 staining (brown dots) in renal cortex from postmortem normal human kidney (NHK) and two COVID-19 patients. Data are presented as median (IQR). Statistical analysis was performed using the Mann Whitney test

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  Fig. 2. Significant renal thrombosis in critically ill COVID-19 patients. (A) Martius Scarlet Blue (MSB) staining of kidney tissue from critically ill COVID-19 patients (C19) and normal human kidney (NHK). MSB stains fibrin (red), fresh fibrin (yellow), erythrocytes (yellow), and connective tissue (blue). Original magnification x200, scale bars = 50 μm. (B) Quantification of thrombi from MSB stained tissue expressed as thrombi/mm2, in normal human kidney (NHK) from nephrectomies (n = 6, grey), postmortem controls (n = 7, blue) and COVID-19 patients (C19, n = 7, red). Original magnification x400, scale bars = 50 μm. Data are presented as median (IQR). Statistical analysis was performed using the Mann Whitney test

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  Fig. 3. Renal thrombomodulin and angiopoietin-2 expression in critically ill COVID-19 patients. Representative images of immunohistochemistry and quantification of thrombomodulin (THBD) and angiopoietin-2 (ANGPT2) protein expression in (A-C) glomeruli and (D-F) cortex of normal human kidneys (NHK) from nephrectomies (n = 6, grey), postmortem controls (n = 7, blue) and kidneys from COVID-19 patients (C19, n = 7, red). (G, H) Correlation between THBD protein expression and thrombi. (I) Proximity ligation assay showing binding of THBD and ANGPT2 in NHK and COVID-19 kidneys. Original magnification x400, scale bars = 50 μm. Data are presented as median (IQR). Statistical analysis was performed using the Mann Whitney test

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  Fig. 4. Glomerulosclerosis, glomerular size, and fibrosis in critically ill COVID-19 patients. (A) Representative images of Masson trichrome staining of kidneys from normal human kidney (NHK) and COVID-19 patients (C19). Original magnification x200, scale bars = 400 μm (left images) and 100 μm (right images). Quantification of (B) glomerulosclerosis and (C) glomerular size from MSB-stained sections and (D) tubulointerstitial fibrosis from Masson trichrome stained sections from normal human kidney (NHK) from nephrectomies (n = 6, grey), postmortem controls (n = 7, blue) and kidneys from COVID-19 patients (C19, n = 7, red). (E, F) Correlation between glomerular sclerosis and tubulointerstitial fibrosis with age, respectively. Data are presented as median (IQR). Statistical analysis was performed using the Mann Whitney test

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  Fig. 5. A schematic illustration of several pathways leading to AKI. As the summary of the current study, healthy blood vessels have anticoagulant activity mediated by THBD. In COVID-19, elevated circulating inflammatory cytokines including ANGPT2, promote cleavage of THBD from the endothelial surface. Loss of endothelial THBD diminishes the local anticoagulant capacity resulting in a markedly increased risk of microthrombosis and subsequent loss of kidney function