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Podocyte injury is a vital factor, which induces massive proteinuria. Studies have shown that tacrolimus (TAC) protected podocyte via stabilizing cytoskeleton. Our latest study indicates that calcineurin binding protein 1 (Cabin1) undergoes nuclear translocation during podocytes injury. Whether TAC targets on Cabin1 during podocyte injury is still not clear. This study establishes non-immunological proteinuric model. To observe the effect of the treatment of TAC on Cabin1 expression in 5/6 nephrectomized rats. Sprague–Dawley rats were injected with TAC (0.2 mg/kg/day) for 4–8 weeks after 5/6 nephrectomy. Then, rats were sacrificed in the eighth week after operation, renal tissues were processed for morphological studies under light and electrical microscope. Cabin1 expression and distribution were detected by western blot and indirect immunofluorescence staining. In 5/6 nephrectomized rats, urinary protein excretion reached 90.2 ± 30.1 mg/24 h, glomerular sclerosis index and tubulointerstitial fibrosis score were significantly increased, and widespread of podocyte foot processes fusion was found. Moreover, Cabin1 protein expression was markedly increased, and its distribution became much more obviously in podocytes nuclei. In TAC treated rats, urinary protein excretion significantly decreased (44.9 ± 22.5 mg/24 h), glomerular sclerosis and tubulointerstitial fibrosis were alleviated, and podocyte foot processes fusion was inhibited. Furthermore, TAC alleviated the increased protein expression and abnormal distribution of Cabin1. In conclusion, TAC restores podocyte injury and stabilizes the expression of Cabin1. Cabin1 may become a new target to demonstrate the mechanism of TAC in podocyte injury. [ABSTRACT FROM AUTHOR]

Calcineurin binding protein 1 (Cabin1) is a natural inhibitor of calcineurin (CN). Moreover, Cabin1 retards tumor cell apoptosis by regulating p53. This study was designed to observe the expression of Cabin1 during podocyte injury, as well as its relationship with p53. Sprague-Dawley rats were used for the establishment of 5/6 nephrectomized rat model. Sham-operated rats underwent ventral laparotomy without nephrectomy. Then, rats were sacrificed at 8 and 12 weeks after nephrectomy. WT-1, a podocyte nuclear protein, was used for indicating the localization of Cabin1 in glomeruli. As tacrolimus protects podocyte via inhibiting AngiotensinII (AngII) induced CN activation. Cultured podocytes were injured by AngII or restored by tacrolimus. The protein expression and localization was detected by western blot or immunofluorescence staining. Cabin1 was knocked down by siRNA in cultured podocytes. In 5/6 nephrectomized rats, the colocalization of Cabin1 and WT-1 became more obviously in podocyte nuclei. Cabin1 protein was markedly increased in rats at 8 and 12 weeks after nephrectomy, as well as in AngII injured podocytes at 48 h (0.99 ± 0.12 in AngII group versus 0.80 ± 0.16 in control group). Cabin1 and p53 colocalized in cultured podocyte nuclei, p53 expression was significantly decreased (0.21 ± 0.05 in siRNA group versus 0.31 ± 0.05 in negative control group) after Cabin1 was being knocked down. In conclusion, Cabin1 expression significantly increases during podocyte injury. Knockdown of Cabin1 induces p53 expression decrease in cultured podocyte. Cabin1 may provide a new target to investigate podocyte injury. [ABSTRACT FROM PUBLISHER]

Context: Podocyte injury is related to increasing proteinuria and contributes to the progression of kidney disease. Calcineurin binding protein 1 (Cabin1) is a repressor of myocyte enhancer factor 2 (MEF2) and calcineurin-mediated transcription in the immune system. Moreover, Cabin1 interacts with p53 and negatively regulates p53 in tumor cells. However, its function in kidney is unknown.Objective: To explore the exact localization of Cabin1 in glomeruli, as well as the relationship between Cabin1 and podocyte injury.Methods: Sprague–Dawley rats were sacrificed to observe the localization and protein expression of Cabin1 in the kidney. Cabin1 localization and protein expression were detected by immunofluorescence staining and western blot, respectively. Mouse podocytes were cultivated at 33 °C to propagate, then cells were transferred to an incubator at 37 °C to allow differentiation. Differentiated podocytes were stimulated by angiotensin II (AngII) or AngII plus tacrolimus. Cells were harvested to detect the localization and protein expression of Cabin1. Cytoplasmic and nuclear protein were separated by protein extraction kit.Results: Cabin1 mainly localized in the nuclei of glomerular innate cells, it colocalized with WT-1 in podocytes nuclei. Western bolt showed Cabin1 protein remarkably expressed in renal cortex. AngII-induced Cabin1 nuclear protein significantly increased, accompanied by cytoskeleton disruption in cultured mouse podocytes.Conclusion: Cabin1 localizes in glomerular podocytes. AngII induces nuclear translocation of Cabin1 in cultured podocytes. [ABSTRACT FROM AUTHOR]