Adipocyte differentiation is a very complex process in which whole-cell changes are accompanied. Among them, type I procollagen gene has been shown to specifically decrease during adipocyte differentiation; however, little is known about the molecular mechanism. To examine how type I procollagen gene expression is regulated at the level of transcription during adipocyte differentiation, 3T3-L1 preadipocyte cell line was used as an in vitro model. Northern blot analysis demonstrated that mRNA expression of type I procollagen gene was dramatically reduced during adipocyte differentiation. Time-course analysis indicated that decrease in mRNA expression occurred at early stage of differentiation. Studies on several stable cell lines showed that transcriptional activities of both alpha1 and alpha2 promoters decreased significantly during adipocyte differentiation. Despite extensive deletion-promoter analyses, however, we could not identify the cis-element responsible for the switch-off of type I procollagen gene during adipocyte differentiation, suggesting that the transcriptional repression of this gene occur through general transcription machinery rather than a specific cis-element. In conclusion, down-regulation of type I procollagen mRNA expression during adipocyte differentiation is due to repression of its promoter activity through general transcription machinery.
3T3 Cells ; Adipocytes/cytology/*metabolism ; Animal ; Cell Differentiation/*genetics ; Cell Line ; Collagen Type I/*genetics/metabolism ; Down-Regulation/genetics ; Gene Expression Regulation ; Genes, Reporter ; Kinetics ; Mice ; Mutation ; Procollagen/*genetics/metabolism ; Promoter Regions (Genetics) ; RNA, Messenger/metabolism ; Repressor Proteins/genetics/metabolism ; Transcription, Genetic

Adipocyte differentiation is a very complex process in which whole-cell changes are accompanied. Among them, type I procollagen gene has been shown to specifically decrease during adipocyte differentiation; however, little is known about the molecular mechanism. To examine how type I procollagen gene expression is regulated at the level of transcription during adipocyte differentiation, 3T3-L1 preadipocyte cell line was used as an in vitro model. Northern blot analysis demonstrated that mRNA expression of type I procollagen gene was dramatically reduced during adipocyte differentiation. Time-course analysis indicated that decrease in mRNA expression occurred at early stage of differentiation. Studies on several stable cell lines showed that transcriptional activities of both alpha1 and alpha2 promoters decreased significantly during adipocyte differentiation. Despite extensive deletion-promoter analyses, however, we could not identify the cis-element responsible for the switch-off of type I procollagen gene during adipocyte differentiation, suggesting that the transcriptional repression of this gene occur through general transcription machinery rather than a specific cis-element. In conclusion, down-regulation of type I procollagen mRNA expression during adipocyte differentiation is due to repression of its promoter activity through general transcription machinery.
3T3 Cells ; Adipocytes/cytology/*metabolism ; Animal ; Cell Differentiation/*genetics ; Cell Line ; Collagen Type I/*genetics/metabolism ; Down-Regulation/genetics ; Gene Expression Regulation ; Genes, Reporter ; Kinetics ; Mice ; Mutation ; Procollagen/*genetics/metabolism ; Promoter Regions (Genetics) ; RNA, Messenger/metabolism ; Repressor Proteins/genetics/metabolism ; Transcription, Genetic

BACKGROUND AND OBJECTIVES: Mesenchymal stem cells (MSCs) are used to treat autoimmune or inflammatory diseases. Our aim was to determine the immunomodulatory mechanisms elicited by MSCs during inflammation. METHODS AND RESULTS: We cocultured MSCs with peripheral blood mononuclear cells for a mixed lymphocyte reaction or stimulated them by phytohemagglutinin. Morphological changes of MSCs and secretion of acetylcholine (ACh) from MSCs were measured. The effects of an ACh antagonist and ACh agonist on lymphocyte proliferation and proinflammatory-cytokine production were determined. The inflammatory milieu created by immune-cell activation caused MSCs to adopt a neuronlike phenotype and induced them to release ACh. Additionally, nicotinic acetylcholine receptors (nAChRs) were upregulated in activated peripheral blood mononuclear cells. We observed that ACh bound to nAChR on activated immune cells and led to the inhibition of lymphocyte proliferation and of proinflammatory-cytokine production. MSC-mediated immunosuppression through ACh activity was reversed by an ACh antagonist called α-bungarotoxin, and lymphocyte proliferation was inhibited by an ACh agonist, ACh chloride. CONCLUSIONS: Our findings point to a novel immunomodulatory mechanism in which ACh secreted by MSCs under inflammatory conditions might modulate immune cells. This study may provide a novel method for the treatment of autoimmune diseases by means of MSCs.
Acetylcholine ; Autoimmune Diseases ; Humans ; Immunosuppression ; Inflammation ; Lymphocyte Culture Test, Mixed ; Lymphocytes ; Mesenchymal Stromal Cells ; Methods ; Phenotype ; Receptors, Nicotinic