THSD7A-Associated Membranous Nephropathy Involves Both Complement-Mediated and Autonomous Podocyte Injury

Background: As a distinctive subtype in the serology-based classification of membranous nephropathy (MN), thrombospondin type 1 domain containing 7A (THSD7A)-associated MN has attracted increasing interest, because THSD7A is also expressed in preclinical species, facilitating the study of its role in MN. This study aimed to establish models of THSD7A-associated MN by using a commercial antibody. Potential pathomechanisms and therapeutic efficacy of repository corticotropin injection (RCI; Purified Cortrophin® Gel, ANI Pharmaceuticals, Inc.) were tested in this model. Methods: Primary mouse podocytes were cultured in complete medium supplemented with fetal bovine serum containing complements or preheated to inactivate heat-labile complements, followed by exposure to a commercial rabbit anti-THSD7A antibody. In vivo, mice were injected with the anti-THSD7A antibody and treated with RCI or vehicle. To deplete complement, some mice were treated with cobra venom factor (CVF). Results: Mice developed massive proteinuria upon anti-THSD7A antibody insult, concomitant with histologic lesions of glomerular injury, including epimembranous or intramembranous electron-dense deposits in glomeruli as well as variable podocyte foot process effacement on electron microscopy, reminiscent of glomerular ultrastructural changes in human MN. Complement depletion with CVF only partially attenuated proteinuria and glomerular injury in this model, suggesting that complement-independent pathomechanisms also contribute. Consistently, in cultured primary podocytes, exposure to the anti-THSD7A antibody caused evident podocytopathic changes, such as disruption of the actin cytoskeleton integrity, podocyte hypermobility, oxidative stress and apoptosis. These signs of podocyte injury were preserved, although to a lesser extent, after complement inactivation, denoting an autonomous podocytopathic activity of this antibody. As an FDA-approved treatment option for primary nephrotic glomerulopathies including MN, RCI appeared to be beneficial in this model and significantly attenuated proteinuria and glomerular injury. Conclusion: Both complement-dependent and autonomous podocytopathy are involved in the mouse model of THSD7A-associated MN, which could be attenuated by RCI. This model, based on the use of a commercial anti-THSD7A antibody, could be an important tool for MN research. Funding: Commercial Support - ANI Pharmaceuticals, Inc