Identification of Ceruloplasmin as a Gene that Affects Susceptibility to Glomerulonephritis Through Macrophage Function.

Tai-Di Chen,Marta Bagnati,Maxime Rotival,Jacques Behmoaras,Charles D Pusey,Ling-Yin Chiu,Prashant K Srivastava,H Terence Cook,Timothy J Aitman,Jeong-Hun Ko,Ping-Chin Lai,Enrico Petretto

doi:10.1534/genetics.116.197376

Abstract

Crescentic glomerulonephritis (Crgn) is a complex disorder where macrophage activity and infiltration are significant effector causes. In previous linkage studies using the uniquely susceptible Wistar Kyoto (WKY) rat strain, we have identified multiple crescentic glomerulonephritis QTL (Crgn) and positionally cloned genes underlying Crgn1 and Crgn2, which accounted for 40% of total variance in glomerular inflammation. Here, we have generated a backcross (BC) population (n = 166) where Crgn1 and Crgn2 were genetically fixed and found significant linkage to glomerular crescents on chromosome 2 (Crgn8, LOD = 3.8). Fine mapping analysis by integration with genome-wide expression QTLs (eQTLs) from the same BC population identified ceruloplasmin (Cp) as a positional eQTL in macrophages but not in serum. Liquid chromatography-tandem mass spectrometry confirmed Cp as a protein QTL in rat macrophages. WKY macrophages overexpress Cp and its downregulation by RNA interference decreases markers of glomerular proinflammatory macrophage activation. Similarly, short incubation with Cp results in a strain-dependent macrophage polarization in the rat. These results suggest that genetically determined Cp levels can alter susceptibility to Crgn through macrophage function and propose a new role for Cp in early macrophage activation.

Highlights

As macrophages are the major drivers in crescentic glomerulonephritis (Nikolic-Paterson and Atkins 2001; Isome et al 2004; Wang and Harris 2011), macrophage expression QTLs (eQTLs) from the same BC population were mapped and used for fine mapping together with whole-genome sequencing data (Figure 1B) available for parental Wistar Kyoto (WKY) and LEW strains (Atanur et al 2013)
During the development of crescentic glomerulonephritis, the major pathogenic event that causes crescent formation is the rupture of glomerular capillaries, which allows a relatively early macrophage infiltration into the Bowman’s space
Activity and numbers are critical in the inflammatory phase of Crescentic glomerulonephritis (Crgn) (Duffield et al 2005; Wang et al 2007; Wang and Harris 2011) and our group has contributed to the identification of genetic and epigenetic determinants of macrophage function, which associate with susceptibility to Crgn in rats and humans (Aitman et al 2006; Behmoaras et al 2008, 2010; Page et al 2012; Deplano et al 2013; Hull et al 2013; Kang et al 2014; Rackham et al 2017)

Summary

Introduction

In previous linkage studies using the uniquely susceptible Wistar Kyoto (WKY) rat strain, we have identified multiple crescentic glomerulonephritis QTL (Crgn) and positionally cloned genes underlying Crgn and Crgn, which accounted for 40% of total variance in glomerular inflammation. Complementary to linkage studies, expression QTL (eQTL) approaches using macrophages from a segregating population from WKY and LEW rats identified genes that could be targeted and reduce the severity of NTN in the WKY rat (Kang et al 2014) Despite all these positional cloning and QTL studies, the remaining NTN susceptibility loci account for 60% of glomerular crescent formation, and the biological mechanisms through which they regulate Crgn remain to be elucidated

Methods

Results

Conclusion