Deposition of immune complexes and activation of the complement system mediates glomerular injury and is involved in the inflammatory process in patients with lupus nephritis. Podocytes are highly specialized epithelial cells which are critical for the proper function of the glomerular filtration barrier and are injured in several proteinuric kidney diseases. Podocytes produce a number of complement factors and cathepsin proteases. Preliminary evidence suggests that podocytes exposed to IgG form patients with lupus nephritis produce increased amounts of complement which becomes activated intracellularly. We hypothesize that exposure of podocytes to IgG from patients with lupus nephritis or to hypoxia promotes the production and activation of complement intracellularly. We propose to identify complement components that are produced by podocytes after exposure to IgG from patients with lupus nephritis or hypoxia. Next, we will determine how cathepsin proteases activate complement intracellularly. For our studies we will use IgG from patients with lupus nephritis, a newly establish method to culture podocytes on surfaces coated with decellularized fibroblasts and podocytes from lupus-prone and cathepsin-deficient mice. CRISPR/Cas9 system will be utilized to knockdown C3 and cathepsins (B, L and S) in podocytes. The studies will produce a novel concept that intracellularly activated complement contributes to podocyte and glomerular damage independently of the deposited circulating complement. Our studies will point to the pursuit of avenues to limit increased production and activation of complement in podocytes in patients with lupus nephritis.
Podocytes are highly specialized epithelial cells and are critical in maintaining the glomerular filtration barrier and when injured they lead to kidney failure. The proposed studies will prove that injured podocytes produce complement which is activated intracellularly and will identify novel targets to prevent or reverse podocyte injury and kidney damage.
