*Purpose: Transplant glomerulopathy(TG) is a major cause of late allograft loss. Increase in urine podocin/creatinine ratio in TG signifies acceleration of podocyte detachment from glomerular basement membrane. We evaluated the mechanism by which antibodies lead to podocyte injury in transplant glomerulopathy. We focused on calcium calmodulin kinase IV(CAMKIV), a serine threonine kinase which we have shown to be upregulated in immune podocytopathies.

*Methods: Expression of CaMKIV in transplant biopsy kidney specimens was evaluated by immunofluorescence. Immortalized human podocytes were examined for actin cytoskeleton changes after exposure to IgG from patients with TG versus controls. We subjected IgG from TG patients to deglycosylation and silenced the podocyte expressed neonatal Fc receptor (FcRn) by CRISPR technology and siRNA.

*Results: CaMKIV was increased in podocytes of transplant kidney biopsies from patients with TG but not in samples without TG. Culture of podocytes in the presence of IgG from TG patients or patients who eventually developed TG, led to increased CAMKIV expression in a dose dependent manner along with reduction in expression of nephrin and alpha actinin 4, podocyte migration and significant actin cytoskeleton changes. This was not seen with IgG from normal transplant subjects. Silencing of FcRn reduced the entry of IgG into podocytes. IgG from patients with TG subjected to N-deglycosylation failed to increase the expression of CaMKIV. CAMKIV deficiency or pharmacologic inhibition preserved nephrin and alpha actinin 4 expression and prevented the disruption of actin cytoskeleton in podocytes. CAMKIV inhibited GSK3beta by phosphorylating it at serine 9 which led to stabilization of transcription factor SNAIL and subsequent repression of nephrin transcription.

*Conclusions: We conclude that targeting CaMKIV may represent a novel biomarker for the early detection of transplant glomerulopathy and a pathway for development of novel therapeutics in this disease. Furthermore, glycosylated IgG from patients with TG enters podocytes through the FcRn causing an increase in CaMK4 and transcriptional repression of nephrin. The ability of IgG in the sera of patients with TG vs controls to disrupt structure and function of podocytes can serve as a bioassay for impending TG. Targeting the glycosylation of IgG may prevent allograft failure.

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