Integrating Genetic Fine‐mapping in Outbred Rats with a Novel Human Tubule Fibrosis Model Identifies Sept8 as a Gene Involved in Cellular Structure and Kidney Fibrosis

Abstract

Chronic kidney disease (CKD), which can ultimately progress to kidney failure, is influenced both genetics and the environment. Genes identified in human genome wide association studies (GWAS) explain only a small proportion of the heritable variance, suggesting the need for additional model systems to identify CKD genes. We performed GWAS for urinary protein and serum biochemistries in male heterogeneous stock (HS) rats. Quantitative trait loci (QTL) were identified using a linear mixed effect model of imputed genotypes which accounts for unequal relatedness between rats. RNAseq and bioinformatics tools were used to identify candidate genes. We then developed a novel human tubule hypoxia induced fibrosis model to test these candidates. We identified two QTL for urinary protein and five for serum biochemistries. Protein modeling identified a missense variant within Sept8 as a proteinuria candidate. We demonstrate increased expression of Sept8 in the in vitro fibrosis model. We further demonstrate that SEPT8 localizes to the cilia in tubule cells under normal conditions and relocalizes outside the cilia after fibrosis, suggesting a role of SEPT8 in cellular organization and structure in response to environmental stress. In human biopsies, we show that SEPT8 expression levels increase with fibrosis levels, providing additional support for this gene in kidney fibrosis. This work suggests that integration of a rat genetic model with an environmentally induced cell culture system of tubule fibrosis has the power to elucidate aspects of the complex gene by environmental interactions that contribute to CKD risk.Support or Funding InformationR01 DK088975 and R01 DK106386 (LSW) and NIH/NHLBI R01HL137673 (MRG)