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Is Smad3 a major player in signal transduction pathways leading to fibrogenesis?
A B Roberts1, E Piek, E P Böttinger
1Laboratory of Cell Regulation and Carcinogenesis, National Cancer Institute, Bethesda, MD 20892-5055, USA. Robertsa@dce41.nci.nih.gov
Abstract:
Transforming growth factor (TGF)-beta plays a central role in fibrosis, contributing both to the influx and activation of inflammatory cells, as well as to activation of fibroblasts to elaborate extracellular matrix. In the past few years, new insight has been gained into signal transduction pathways downstream of the TGF-beta receptor serine-threonine kinases with the identification of a family of evolutionarily conserved Smad proteins. Two receptor-activated Smad proteins, Smad2 and Smad3, are phosphorylated by the activated TGF-beta type I receptor kinase, after which they partner with the common mediator, Smad4, and are translocated to the nucleus to where they participate in transcriptional complexes to control expression of target genes. We have shown in wound healing studies of mice null for Smad3, that loss of this key signaling intermediate interferes with the chemotaxis of inflammatory cells to TGF-beta as well as with their ability to autoinduce TGF-beta. Moreover, studies with mouse embryo fibroblasts null for Smad3 show that TGF-beta-dependent induction of c-Jun and c-Fos, important in induction of collagen as well as in autoinduction of TGF-beta, is mediated by Smad3. Based on these observations, we hypothesize that loss of Smad3 will confer resistance to fibrosis and result in reduced inflammatory cell infiltrates, reduced autoinduction of TGF-beta, important to sustain the process, and reduced elaboration of collagen. Preliminary observations in a model of radiation-induced fibrosis confirm this hypothesis and suggest that inhibitors of Smad3 might have clinical application both to improve wound healing and to reduce fibrosis.
Insights
Smad3 is crucial for transforming growth factor-beta (TGF-β)-induced fibrosis. Loss of Smad3 reduces inflammation and collagen production, suggesting Smad3 inhibitors could treat fibrosis and improve wound healing.
Area of Science:
- Cell Biology
- Molecular Biology
- Immunology
Background:
- Transforming growth factor-beta (TGF-β) is central to fibrosis.
- Smad proteins are key signal transducers downstream of TGF-β receptors.
- Smad3 mediates TGF-β-induced inflammatory cell chemotaxis and fibroblast activation.
Purpose of the Study:
- To investigate the role of Smad3 in fibrosis.
- To determine if Smad3 deficiency confers resistance to fibrosis.
- To explore the therapeutic potential of Smad3 inhibition.
Main Methods:
- Studies using Smad3-null mice and mouse embryo fibroblasts.
- Analysis of inflammatory cell infiltration, TGF-β autoinduction, and collagen elaboration.
- Preliminary observations in a radiation-induced fibrosis model.
Main Results:
- Smad3 deficiency impaired inflammatory cell chemotaxis and TGF-β autoinduction.
- Smad3 mediated TGF-β-dependent induction of c-Jun, c-Fos, and collagen.
- Preliminary data confirmed Smad3 loss confers resistance to radiation-induced fibrosis.
Conclusions:
- Smad3 is a critical mediator of TGF-β-driven fibrosis.
- Targeting Smad3 may offer a therapeutic strategy for fibrosis and wound healing.
- Inhibitors of Smad3 could have clinical applications in managing fibrotic diseases.