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Abstract: PO2384

Glomerular Changes in Transplant Glomerulopathy

Session Information

Category: Transplantation

  • 1901 Transplantation: Basic

Authors

  • Husami, Samir, Washington University in Saint Louis Department of Medicine, Saint Louis, Missouri, United States
  • Hammad, Dina, Washington University in Saint Louis Department of Medicine, Saint Louis, Missouri, United States
  • Miner, Jeffrey H., Washington University in Saint Louis Department of Medicine, Saint Louis, Missouri, United States
  • Alhamad, Tarek, Washington University in Saint Louis Department of Medicine, Saint Louis, Missouri, United States
  • Suleiman, Hani, Washington University in Saint Louis Department of Medicine, Saint Louis, Missouri, United States
Background

Transplant glomerulopathy (TG) affects 20% of transplanted kidneys 5 years post transplantation. It carries an important significance due to its correlation with decreased graft survival. Repeated endothelial cell injury by chronic active antibody mediated rejection (cAMR) leads to glomerular basement membrane (GBM) reduplication and thickening, the hallmark finding of TG. Based on our previous molecular mapping of the GBM, we aim to define the composition of the thickened GBM in TG using super-resolution microscopy.

Methods

Two super-resolution microscopy techniques, STORM (Stochastic optical reconstruction microscopy) and Airyscan, were used to image confirmed TG and control biopsies. For STORM, fresh frozen, 200 nm sections were imaged. While for Airyscan, 1-3 microns, formalin fixed paraffin embedded (FFPE) sections were used. Samples were labeled with antibodies for Laminin a5, Integrin a8, Myosin IIA, Vimentin, Synaptopodin, Integrin b1, Fibronectin, and several Collagen IV chains.

Results

STORM TG samples showed increased distance between Integrin b1 labeled membranes, indicating thickening of the GBM. Collagen a3a4a5(IV) did not change, while Collagen a1a1a2(IV) was increased at the GBM’s endothelial aspect. There was an increase in Fibronectin, suggesting a role for the TGFb pathway. Airyscan TG images showed Vimentin- and Integrin a8-positive areas inside the GBM, indicating cellular protrusions extending into the GBM. Since these markers stain mesangial as well as endothelial cells, this suggests dedifferentiation of endothelial cells and transition to mesenchymal cells. We detected alternating Myosin IIA and Synaptopodin labeling in the form of “Sarcomere-like structures”.

Conclusion

Our data revealed increased Collagen a1a1a2(IV) secreted from the endothelial side, while Collagen a3a4a5(IV) was unchanged. The increase in Fibronectin, cellular protrusions positive for mesenchymal markers, and sarcomere-like structures inside the diseased GBM suggest an endothelial to mesenchymal transition as culprit for increased Collagen IV rather than injury signals from podocytes.