[The antagonistic effects of adrenomedullin on biological events governed by transforming growth factor beta in HK-2 cell line].

OBJECTIVE

To investigate the influence of adrenomedullin (AM) on the biological events governed by transforming growth factorbeta (TGF-beta) in human tubular epithelial cell line (HK-2).

METHODS

Cell proliferation was determined by (3)H-TdR incorporation; ELISA method was used to detect the level of secreted fibronectin (FN); total collagen synthesis and secretion were reflected by (3)H-proline incorporation and the radioactivity of (3)H-hydroproline in the culture medium; the expression of FN mRNA, collagen IV mRNA and TIMP-1mRNA was determined by RT-PCR; plasma AM was measured by radioimmunoassay.

RESULTS

(1) AM had no effect on cell growth inhibition of TGF-beta(1) (P > 0.05); (2) AM dose-dependently inhibited collagen synthesis and secretion stimulated by TGF-beta(1). As compared with those in TGF-beta group, collagen synthesis and secretion in AM (10(-8) mol/L group were inhibited by 8% (P > 0.05) and 30% (P < 0.05), respectively; and the collagen synthesis and secretion in AM (10(-7) mol/L) group were inhibited by 57% (P < 0.05) and 64% (P < 0.01), respectively in AM (10(-7) mol/L) group. Similarly, AM (10(-8) mol/L) inhibited the FN secretion (20 ng/microliter +/- 5 ng/microliter) stimulated by TGF-beta(1) (28 ng/microliter +/- 6 ng/microliter) (P < 0.05). RT-PCR showed that AM significantly down-regulated the expression of collagen IV, FN and TIMP-1 mRNA stimulated by TGF-beta(1). (3) The plasma AM in patients with mild tubulointerstitial lesion was 1. 2 times higher than that in normal controls. the plasma AM in patients with severe tubulointerstitial lesion was 2.2 times higher than that in normal controls. The plasma AM in patients with severe tubulointerstitial lesion was 50% higher than that in patients with mild tubulointerstitial lesion (P < 0.01).

CONCLUSIONS

AM antagonizes the biological action of TGF-beta(1) on extracellular matrix accumulation; plasma AM increases in glomerulonephritis patients and correlates with the degree of tubulointerstitial lesion.