Abstract A99: Endothelial cell activation in the conditional Vhlh knockout kidney through oncostatin M pathway

Clear-cell renal cell carcinoma (ccRCC) is the most prevalent histologic subtype of RCC. Interestingly, about 80% of the ccRCC cases are associated with early inactivation of the von Hippel Lindau (VHL) tumor suppressor gene. In our conditional Vhlh knockout mouse model (Hoxb7-Cre-GFP; VhlhloxP/loxP), kidney tissue exhibited a high penetrance of interstitial inflammation and fibrosis in addition to hyperplasia and the appearance of transformed clear cells as early as two months of age. These results support the notion that inflammation is a precursor of ccRCC. We also found that the expression of inflammatory marker p-Jnk was enriched in endothelial cells (ECs) in the inflamed Vhlh knockout kidney, even though the Vhlh knockout occurs in epithelial tubule cells, not in ECs. Therefore, we aim to investigate the contribution of ECs in Vhlh knockout microenvironment, and uncover the “dominant regulator” that regulates the response of ECs, which could be a novel target for treatment of kidney inflammation and fibrosis, and prevention of ccRCC tumorigenesis. ECs were isolated from kidneys of 3-month old mice by PECAM1-coupled Dynabeads. Total RNA was extracted immediately without further manipulation and subjected to mRNA sequencing. The gene expression (GE) analysis of ECs from Vhlh knockout mice (ECs-KO) indicates inflammatory response, including pathways shown to participate in atherosclerosis signaling, hepatic fibrosis, leukocyte extravasation signaling, etc. The ECs-KO GE suggests contribution of ECs to the development of Vhlh knockout phenotype in the following ways: (1) expression of typical kidney injury markers, (2) regulating inflammatory microenvironment by expressing proinflammatory cytokines, (3) recruiting and trafficking immune cells, and (4) contributing to fibrosis by undergoing EndoMT. IPA analysis predicts that the Osm pathway may be the dominant regulator of the above ECs-KO response profile. IHC staining shows the upregulation of Osm expression in Vhlh knockout tubule. In addition, qPCR validation of Osmr in isolated ECs-KO shows a nearly 3-fold increase. Treatment of EC with recombinant human OSM induces inflammatory profile similar to ECs-KO. The results indicate that the crosstalk between mutant epithelial cells and ECs may be mainly through the Osm pathway. Activated ECs by OSM increase recruitment and adhesion of monocytes. They also increase adhesion of kidney cancer cells and promote endothelial invasion of cancer cells in vitro. In