Abstract: SA-PO857
Endothelial Tie2 Deficiency Increases Capillary Rarefaction and Tubulointerstitial Fibrosis
Session Information
- Molecular Mechanisms of CKD - III
October 27, 2018 | Location: Exhibit Hall, San Diego Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: CKD (Non-Dialysis)
- 1903 CKD (Non-Dialysis): Mechanisms
Author
- Jeansson, Marie, Uppsala University, Uppsala, Sweden
Background
Renal tubulointerstitial fibrosis is predictive of progressive decline in kidney function, independent of underlying disease. It is characterized by an increase in aSMA+ fibroblasts, myofibroblasts, that produce collagen. We previously showed that loss of Angiopoietin-1 (Angpt1) in adult mice predisposes to fibrosis in wound healing, diabetic nephropathy, and the unilateral ureter obstruction (UUO) model. The tyrosine kinase receptor, Tie2, is expressed on endothelial cells and Angpt1 binding results in Tie2 signaling that is pro-survival and anti-inflammatory. Here, we test the hypothesis that loss of Tie2 signaling in endothelial cells results in capillary defects leading to an increased fibrotic response in kidney fibrosis.
Methods
Tie2 floxed mice were crossed with tamoxifen inducible endothelial specific Cadh5-Cre and a reporter line expressing TdTomato upon Cre-activation. This line enables both an endothelial specific KO of Tie2 and an endothelial lineage tracer. To study the role of Tie2 signaling in renal fibrosis we utilized the unilateral ureter obstruction (UUO) model of kidney fibrosis. An additional line (Pdgfra-H2b-GFP) was crossed into the above line, resulting in a reporter of myofibroblasts.
Results
Endothelial specific KO of Tie2 resulted in an increase in fibrosis as seen by increased expression of aSMA and vimentin compared to WT mice 3 days after UUO. At the same time, there was significant increase in Kim1 and tubular ferroptosis, suggesting a more severe injury in ecTie2KO. Electron micrographs of peritubular capillaries 3 days after UUO showed significantly more loss of fenestrations in ecTie2KO mice. Investigation of blood vessels before fibrotic onset 1 day after UUO, revealed less perfused capillary area and increased hypoxia in Tie2 KO mice.
Ongoing work is designed to investigate blood vessel function in the early fibrotic process and to estimate the endothelial-mesenchymal contribution after UUO in controls and Tie2 knockout mice, utilizing the lineage tag of endothelial cells and myofibroblast reporter.
Conclusion
Our results suggest that loss of Tie2 signaling destabilizes the endothelial cell and increases tubulointerstitial fibrosis. The mechanisms we are investigating are an early loss of endothelial cells due to endothelial-mesenchymal transition and/or apoptosis, resulting in less functional peritubular capillaries and more fibrosis.
Funding
- Private Foundation Support