CaMK4 compromises podocyte function in autoimmune and nonautoimmune kidney disease
Kayaho Maeda, Kotaro Otomo, Nobuya Yoshida, Mones S. Abu-Asab, Kunihiro Ichinose, Tomoya Nishino, Michihito Kono, Andrew Ferretti, Rhea Bhargava, Shoichi Maruyama, Sean Bickerton, Tarek M. Fahmy, Maria G. Tsokos, George C. Tsokos
Kayaho Maeda, Kotaro Otomo, Nobuya Yoshida, Mones S. Abu-Asab, Kunihiro Ichinose, Tomoya Nishino, Michihito Kono, Andrew Ferretti, Rhea Bhargava, Shoichi Maruyama, Sean Bickerton, Tarek M. Fahmy, Maria G. Tsokos, George C. Tsokos
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Research Article Autoimmunity Nephrology

CaMK4 compromises podocyte function in autoimmune and nonautoimmune kidney disease

Abstract

Podocyte malfunction occurs in autoimmune and nonautoimmune kidney disease. Calcium signaling is essential for podocyte injury, but the role of Ca2+/calmodulin–dependent kinase (CaMK) signaling in podocytes has not been fully explored. We report that podocytes from patients with lupus nephritis and focal segmental glomerulosclerosis and lupus-prone and lipopolysaccharide- or adriamycin-treated mice display increased expression of CaMK IV (CaMK4), but not CaMK2. Mechanistically, CaMK4 modulated podocyte motility by altering the expression of the GTPases Rac1 and RhoA and suppressed the expression of nephrin, synaptopodin, and actin fibers in podocytes. In addition, it phosphorylated the scaffold protein 14-3-3β, which resulted in the release and degradation of synaptopodin. Targeted delivery of a CaMK4 inhibitor to podocytes preserved their ultrastructure, averted immune complex deposition and crescent formation, and suppressed proteinuria in lupus-prone mice and proteinuria in mice exposed to lipopolysaccharide-induced podocyte injury by preserving nephrin/synaptopodin expression. In animals exposed to adriamycin, podocyte-specific delivery of a CaMK4 inhibitor prevented and reversed podocyte injury and renal disease. We conclude that CaMK4 is pivotal in immune and nonimmune podocyte injury and that its targeted cell-specific inhibition preserves podocyte structure and function and should have therapeutic value in lupus nephritis and podocytopathies, including focal segmental glomerulosclerosis.

Authors

Kayaho Maeda, Kotaro Otomo, Nobuya Yoshida, Mones S. Abu-Asab, Kunihiro Ichinose, Tomoya Nishino, Michihito Kono, Andrew Ferretti, Rhea Bhargava, Shoichi Maruyama, Sean Bickerton, Tarek M. Fahmy, Maria G. Tsokos, George C. Tsokos

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Figure 4

Inhibition or genetic deletion of CaMK4 protects mice from LPS-induced podocyte injury.

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Inhibition or genetic deletion of CaMK4 protects mice from LPS-induced p...
Mice treated with KN93-loaded nlg targeted to podocytes and CaMK4-deficient mice develop proteinuria after exposure to LPS. Each B6 or B6 Camk4–/– mouse was injected i.p. with LPS on day 0. (A) Urine albumin/creatinine ratio of mice treated with anti-nephrin antibody–coated nlg either empty or loaded with KN93. Nlg were injected i.p. on day –1 (n = 10 mice in each group). (B) Urine albumin/creatinine ratio of B6 or B6 Camk4–/– mice (n = 6 in each group). Error bars represent mean ± SEM. *P < 0.05; **P< 0.01, 2-way ANOVA with Bonferroni’s post test. (C) Representative immunofluorescent images of nephrin (upper panels) and synaptopodin (lower panels) in the kidneys of mice injected with LPS or PBS. Scale bar: 50 μm. (D) Nphs1 expression in human podocytes after stimulation with LPS with or without KN93. Cells were treated with KN93 1 hour before stimulation. Results were normalized by the expression of GAPDH. Four independent experiments were performed. *P < 0.05, 1-way ANOVA with Tukey’s post test. (E and F) Mean percentage of nephrin-positive human podocytes evaluated by flow cytometry after stimulation with LPS for 72 hours with KN93 (E) or CAMK4 siRNA (F). Four independent experiments were performed. *P < 0.05, 1-way ANOVA with Tukey’s post test.