Alterations in Wnt pathway activity in mouse serum and kidneys during lupus development

Objective The canonical Wnt/β‐catenin pathway was recently identified as a factor in the pathogenesis of several renal diseases. The aim of this study was to evaluate Wnt signaling activity during disease development in a murine model of lupus nephritis. Methods Wnt activity and Dkk‐1 expression were serially assayed in the serum and kidneys of (NZB × NZW)F1 mice during progression of lupus nephritis. The effects of serum obtained from mice with lupus and serum‐equivalent concentrations of Dkk‐1 on mesangial cells were assessed in vitro. Results Gene expression analyses revealed increased canonical Wnt pathway activity in kidneys during development of lupus nephritis, paralleled by an increase in renal and serum levels of the Wnt inhibitor Dkk‐1. Sera obtained from proteinuric‐stage (NZB × NZW)F1 mice showed strong Wnt‐inhibitory effects in vitro. Dkk‐1 concentrations comparable to those observed in lupus‐prone mice induced apoptosis in tubular and mesangial cells in vitro, whereas no such effect was seen for the range of concentrations observed in young prediseased mice and control BALB/c mice. Conclusion These data demonstrate that renal Wnt signaling activity is increased in lupus and is accompanied by an increase in renal and serum levels of Dkk‐1. The Wnt pathway is involved in the turnover of extracellular matrix constituents and represents a potential mediator of the morphologic changes that occur within the glomerulus during the development of nephritis. Furthermore, increased levels of Dkk‐1 serve as a potential proapoptotic stimulus in vitro and possibly in vivo and could be an important element in the initiation and progression of systemic and end‐organ disease manifestations in systemic lupus erythematosus.