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Transforming growth factor-beta suppresses macrophage-induced mesangial cell fibronectin expression
1Department of Nephrology, University of Leicester and Leicester General Hospital, Leicester, England, United Kingdom. izap1@le.ac.uk
Background:
We have previously shown that macrophages are able to promote prosclerotic responses in rat mesangial cells. Th2-type cytokines, including interleukin-10 (IL-10), IL-13, and IL-4 as well as transforming growth factor-beta (TGF-beta), are known to have suppressive effects on various aspects of macrophage function. In the current study, we investigated the effect of TGF-beta pretreatment on the ability of macrophages to induce fibronectin expression.
Results:
Conditioned medium from TGF-beta pretreated macrophages (MPCM(TGF)) induced lower fibronectin levels in mesangial cells in both the secreted and cell-associated forms, compared with conditioned medium from standard macrophages (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 MPCM(TGF) 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. MPCM, N = 3) of MPCM-induced levels. However, mesangial cell transin mRNA levels induced in response to MPCM(TGF) were 2.29 +/- 0.47-fold greater than those induced by standard MPCM (P = 0.03 vs. MPCM, N = 4). TIMP-1 mRNA levels were also increased in response to MPCM(TGF), but only by 1.43 +/- 0.1-fold (P = 0.02 vs. MPCM, N = 5). Casein-FITC digestion studies confirmed that MPCM(TGF) stimulated more mesangial cell caseinolytic activity than did MPCM. In addition, MPCM-mediated up-regulation of mesangial cell TGF-beta mRNA and protein expression was significantly reduced in response to conditioned medium from macrophages pretreated with TGF-beta.
Conclusion:
This study suggests that TGF-beta is able to regulate negatively the profibrotic effects of macrophages on mesangial cells by both enhancing matrix degradation and reducing synthesis.
Insights
Transforming growth factor-beta (TGF-beta) pretreatment of macrophages reduces their profibrotic effects on mesangial cells. This involves enhancing matrix degradation and decreasing fibronectin synthesis, suggesting a protective role for TGF-beta.
Area of Science:
- Cell Biology
- Immunology
- Renal Physiology
Background:
- Macrophages promote prosclerotic responses in rat mesangial cells.
- Th2-type cytokines like IL-10, IL-13, IL-4, and TGF-beta can suppress macrophage function.
- The study investigates TGF-beta's effect on macrophages' induction of fibronectin expression.
Purpose of the Study:
- To determine if TGF-beta pretreatment alters the ability of macrophages to induce fibronectin expression in mesangial cells.
- To investigate the impact of TGF-beta-primed macrophages on matrix degradation and synthesis markers in mesangial cells.
Main Methods:
- Macrophages were pretreated with TGF-beta.
- Conditioned medium from pretreated (MPCM(TGF)) and standard (MPCM) macrophages was used to treat mesangial cells.
- Fibronectin, transin, and TIMP-1 mRNA levels were analyzed using Northern blot.
- Mesangial cell caseinolytic activity was assessed.
- TGF-beta mRNA and protein expression in mesangial cells were measured.
Main Results:
- MPCM(TGF) significantly reduced fibronectin levels (secreted and cell-associated) in mesangial cells compared to MPCM.
- Transin mRNA levels were significantly increased by MPCM(TGF), while TIMP-1 mRNA showed a modest increase.
- MPCM(TGF) enhanced mesangial cell caseinolytic activity, indicating increased matrix degradation.
- The upregulation of mesangial cell TGF-beta by MPCM was significantly reduced by MPCM(TGF).
Conclusions:
- TGF-beta pretreatment negatively regulates the profibrotic effects of macrophages on mesangial cells.
- This regulation is achieved by enhancing matrix degradation and reducing fibronectin synthesis.
- TGF-beta plays a role in modulating macrophage-driven fibrotic responses in the kidney.