D ROJAS-CANALES 1,3, E TUCKER 3, K MCNICHOLAS 3, A MEHDORN 2, J GLEADLE 1,3
1Department of Renal Medicine, Flinders Medical Centre, Southern Adelaide Local Health Network, Bedford Park, Australia, 2Flinders Centre for Innovation in Cancer, Department of Gastroenterology and Hepatology, Flinders Medical Centre, Bedford Park, Australia, 3College of Medicine and Public Health, Flinders University, Bedford Park, Australia
Aim: To examine genetic changes in the initiation of compensatory renal hypertrophy.
Background: The removal of a kidney for renal cancer or living kidney donation results in compensatory renal hypertrophy (CRH). This response is dominated by an increase in individual kidney cell size, that leads to increase in excretory function. We sought to investigate the initiating mechanisms driving renal growth, as a way of identifying novel pathways to preserve and improve renal function. Previous work has implicated a role for Insulin-like growth factor (IGF) but the mechanism is unknown
Method: C57BL6 mice underwent nephrectomy of the left kidney (unx) or sham operation. The remaining kidney was collected 24, 48 and 72 hours post-surgery (n=6 and RNA extracted for RNA-Seq analysis). We undertook differential gene expression (DEG) (log2 fold change <-1 or >1, p-adjusted <0.05) and pathway analysis using Ingenuity Pathway Analysis (IPA). Genes of interest were validated by Real-time qPCR.
Results: Four genes were differentially expressed at all time-points; 3 genes with roles in cell cycle and Papp-a2 which was induced 2.4-fold (p<0.0001). From 1975 DEGs (log2foldchange ≤-0.5 or ≥0.5; padj≤0.05) IPA identified cholesterol biosynthesis as the top pathway activated in the first 24h. We confirmed that gene expression of Papp-a2 was significantly upregulated at all time-points post nephrectomy. We also saw significant repression of Abca1, and upregulation of Lipg, Hmgcs2, and Pcsk9 (genes involved in cholesterol homeostasis).
Conclusions: Papp-a2 is crucial for the tight regulation of IGF bioavailability and its upregulation provides a candidate for the mechanism of IGF induction and growth control of CRH. Interestingly we also saw differential regulation of cholesterol genes suggesting it may play a novel role in CRH.
Dr Rojas-Canales is a Hospital Scientist that completed her PhD developing a targeted therapy for transplant rejection in 2011. She then completed an international post-doctoral fellowship at the Thomas E. Starzl Transplantation Institute at the University of Pittsburgh working on a skin transplantation model to assess the role of pro-inflammatory neuropeptides. Her appointment as hospital scientist led to the Flinders Renal Laboratory management and full academic status at Flinders University. Her research interests are now focused on developing novel therapies for chronic kidney disease, leading to the establishment of a research program with Prof Gleadle to investigate renal compensatory hypertrophy.