Background. We have previously shown that macrophages are able to promote p
rosclerotic responses in rat mesangial cells. Th2-type cytokines, including
interleukin-10(IL-10), IL-13, and IL-4 as well as transforming growth fact
or-beta (TGF-P), are known to have suppressive effects on various aspects o
f macrophage function. In the current study, we investigated the effect of
TGF-beta pretreatment on the ability of macrophages to induce fibronectin e
xpression.
Results. Conditioned medium from TGF-beta pretreated macrophages (MPCMTGF)
induced lower fibronectin levels in mesangial cells in both the secreted an
d cell-associated forms, compared with conditioned medium from standard mac
rophages (MPCM) (5.5 +/- 0.2 vs. 3.4 +/- 0.3 and 4.05 +/- 0.45 vs. 2.3 +/-
0.2 fold increase over medium alone for MPCM versus MPCMTGF in supernatants
and cell lysates, respectively), Northern blot analysis demonstrated that
fibronectin message was marginally reduced to 0.88 +/- 0.04 (P < 0.03 vs. M
PCM, N = 3) of MPCM induced levels. However, mesangial cell transin mRNA le
vels induced in response to MPCMTGF were 2.29 +/- 0.47-fold greater than th
ose induced by standard MPCM (P = 0.03 vs. MPCM, N = 4), TIMP-1 mRNA levels
were also increased in response to MPCMTGF, but only by 1.43 +/- 0.1-fold
(P = 0.02 vs. MPCM, N = 5). Casein-FITC digestion studies confirmed that MP
CM,GF stimulated more mesangial cell caseinolytic activity than did MPCM. I
n addition, MPCM-mediated up-regulation of mesangial cell TGF-beta mRNA and
protein expression was significantly reduced in response to conditioned me
dium from macrophages pretreated with TGF-beta.
Conclusion. This study suggests that TGF-beta is able to regulate negativel
y the profibrotic effects of macrophages on mesangial cells by both enhanci
ng matrix degradation and reducing synthesis.