Radiation-Induced Alteration of Rat Mesangial Cell Transforming Growth Factor-β and Expression of the Genes Associated with the Extracellular Matrix

We hypothesized that the altered mesangial cell phenotype observed in radiation nephropathy reflects, at least partly, radiation-induced changes in expression of the genes associated with transforming growth factor-β (TGF-β) and extracellular matrix (ECM). To test this hypothesis, rat mesangial cells were used between passages 7 and 11 after primary isolation from glomeruli. Cells were placed in serum-free medium 24 h prior to irradiation and irradiated with single doses of 5-20 Gy¹³⁷ Cs γ rays; control cells received sham irradiation. After irradiation, the cells were maintained in serum-free medium for up to 48 h postirradiation. Total RNA was isolated, and Northern analysis was performed using cDNA probes for <tex-math>${\rm TGF}\text{-}\beta _{1},\beta _{2}$</tex-math> and β₃ and several ECM genes. Irradiation resulted in isoform-specific alterations in TGF-β mRNA; TGF-β₁ levels showed a dose-independent increase 24-48 h postirradiation; <tex-math>${\rm TGF}\text{-}\beta _{3}$</tex-math> mRNA levels showed a progressive dose-independent decrease over the same period, decreasing to levels approximately 25% of those seen in controls. These changes were associated with a concomitant increase in levels of mRNA expressed by genes for the components of the ECM; no changes were observed in TGF-β₂, collagen I, collagen III or decorin. Thus radiation can alter mesangial cell TGF-β and the expression of the genes involved in ECM, although the nature of this alteration varies for the TGF-β isoforms and specific ECM genes.