Nuclear translocation of SMAD3 may enhance the TGF-β/SMADS pathway in high glucose circumstances

Objectives. Posttransplant diabetes mellitus is one of the most frequent complications after kidney transplantation. It is considered to be one cause of chronic allograft nephropathy. This study sought to investigate the effects of high glucose on the expression and nuclear translocation of Smad3, which is an important signal mediator involved in the fibrotic signal pathway. Methods. The established rat renal mesangial cell line HBZY-1 was cultured in medium with various concentrations of glucose (4.5 mg/mL, 9.0 mg/mL, or 13.5 mg/mL), which was collected at 7, 14, or 21 days. The total expression of Smad3, including both inner and outer nucleus proteins was examined by Western blot analysis. The nuclear translocated Smad3, representing only the inner nucleus protein, was detected by immunofluorescence staining observed under a laser confocal scanning microscope. Results. No significant difference in the total Smad3 expression was demonstrated by Western blot analysis among the three groups of HBZY-1 cells at various concentration of glucose after 7, 14, or 21 days. There was no fluorescence detected in the nucleus at day 7 by immunofluorescence, staining; however, robust positive expression of Smad3 was detected at days 14 and 21. Conclusion. As a restricted Smads member, Smad3 protein might not be upregulated in the presence of high glucose. However, with prolonged culture time, Smad3 translocates from cytoplasm to nucleus, which may be a pivotal step in the fibrotic signal pathway.