Effect of glucocorticoid receptor beta on glucocorticoid action in glomerular mesangial cells

To construct mesangial cell lines over- or under- expressing glucocorticoid receptor beta (GRbeta), to investigate the effect of GRbeta on glucocorticoid biological function, and to determine whether the overexpression of GRbeta explains the glucocorticoid-resistant in glomerular mesangial cells (GMCs).

The recombinant human sense or anti-sense gene of GRbeta was transferred into the rat GMCs by retrovirus-mediated stable transfection technique. Expression of hGRbeta mRNA in GMCs was determined by reverse transcription of total RNA followed by quantitative reverse transcription-polymerase chain reaction (RT-PCR), and the product of RT-PCR was then analyzed by gene sequencing. The expression of hGRbeta protein in GMCs was tested by Western blot. The inhibitory rate of dexamethasone-mediated cells on lipopolysaccharide (LPS)-stimulated GMC proliferation was detected to assess the effect of GRbeta at different expression levels on the glucocorticoid action. The cell proliferative activity in different cells with different levels of GRbeta was tested by MTT chromatometry. The change of cell cycle was analyzed by flow cytometry.

RT-PCR and gene sequencing showed that the recombinant sense and anti-sense genes were correctly integrated into genomic DNA of mesangial cells. The protein expression tested by Western blot showed that GRbeta in cells inserted with the sense hGRbeta gene was higher than those cells inserted with the anti-sense hGRbeta gene (109.74+/-10.63 vs. 19.08+/-1.01, P<0.05). The inhibitory rate of cell proliferation induced by dexamethasone was lower in GMCs transfected with sense hGRbeta gene than those transfected with anti-sense hGRbeta gene (18.47%+/-2.12% vs. 60.33%+/- 5.29%,P<0.05). Under the inhibition of dexamethasone, the decreased cell number of S-stage cells was significantly lower, and the increased cell number of G1- stage cells was significantly higher in GMCs transfected with sense hGRbeta gene than those of non-transfected cells.

The overexpression of GRbeta may inhibit the glucocorticoid action in GMCs. The GRbeta level in mesangial cells may be an important factor in determining whether they are sensitive or resistant to glucocorticoid.