In vivo transfer of engineered macrophages into the glomerulus: endogenous TGF-beta-mediated defense against macrophage-induced glomerular cell activation.

Communication between resident glomerular cells and infiltrating macrophages plays a crucial role in the pathogenesis of glomerular disease. Using matrix metalloproteinase-9 (MMP-9) as an indicator molecule, we examined the interaction between mesangial cells and macrophages. Mesangial cells cocultured with activated macrophages or exposed to macrophage-conditioned media produced abundant MMP-9. We identified the stimulator secreted by macrophages as IL-1 because mesangial cells overexpressing IL-1 receptor antagonist protein showed a blunted expression of MMP-9 in response to the macrophage-conditioned medium. In contrast, culture supernatants of mesangial cells inhibited MMP-9 production by macrophages in a dose-dependent fashion. This inhibitor was identified to be TGF-beta1, since neutralization of TGF-beta1 abrogated the inhibitory effect of the mesangial cell-conditioned medium. To investigate whether activated macrophages induce glomerular MMP-9 expression, and if so, how endogenous TGF-beta1 modulates the induction, stimulated reporter macrophages were transferred into normal rat glomeruli or glomeruli in the regeneration phase of acute anti-Thy-1 glomerulonephritis. In the normal glomeruli, MMP-9 expression was up-regulated in resident cells after the transfer of activated macrophages. This induction was substantially repressed in the regenerating glomeruli that produced active TGF-beta1. These results point to potential mechanisms involved in glomerular control of MMP-9. Based upon the in vitro evidence, TGF-beta1 was identified as an endogenous "defender" that attenuates certain actions of infiltrating macrophages in the glomerulus.

TGF-beta and glomerulonephritis: anti-inflammatory versus prosclerotic actions.

TGF-beta has been considered as the key regulator in the generation of glomerulosclerosis. Despite abundant descriptive data, it still remains undetermined whether sustained, local expression of TGF-beta leads to irreversible glomerulosclerosis. There is no doubt that TGF-beta stimulates ECM production in the glomerulus, but this molecule has several anti-inflammatory properties as well. Towards a better understanding of the pathogenesis of glomerulonephritis and for the development of novel and efficient therapeutic interventions, extensive efforts should be made to clarify the 'bright side' of TGF-beta as well as its 'dark side' in individual experimental and human diseases, focusing especially on the concentration and the time-point at which its anti-inflammatory properties spill over into its prosclerotic actions.

Mesangial cell-derived transforming growth factor-beta 1 reduces macrophage adhesiveness with consequent deactivation.

Adhesion of macrophages is a crucial event that determines the number and function of macrophages at inflammatory sites. The aim of this study was to elucidate the role of mesangial cells in the regulation of macrophage adhesiveness. J774.2 macrophages were suspended in serial dilutions of mesangial cell conditioned medium (MC medium) and seeded on plastic tissue culture plates. MC medium did not affect the initial adhesion of macrophages but induced subsequent detachment in a concentration-dependent manner. A similar effect was observed when macrophages were plated on plastic coated with laminin, collagen type IV or Matrigel. The reduced adhesiveness was reversible, and cell viability was unaffected by MC medium, indicating that the effect is not due to cytotoxicity. Conditioned media from fibroblastic, epithelial and endothelial cell lines did not induce macrophage detachment. To identify the active component in MC medium, we examined the involvement of transforming growth factor-beta 1 (TGF-beta 1) in the process. Mesangial cells constitutively expressed TGF-beta 1 mRNA, and MC medium contained the active form of TGF-beta 1. Exogenously added TGF-beta 1 induced macrophage detachment in a dose-dependent manner, and an anti-TGF-beta 1 neutralizing antibody partially abolished the activity of MC medium, indicating the involvement of TGF-beta 1 as an active component. Compared to adherent cells, detached macrophages showed reduced mitogenic activity and blunted induction of IL-1 beta and IL-6 in response to lipopolysaccharide. These data demonstrate that TGF-beta 1 is a mesangial cell-derived factor that impairs adhesiveness of macrophages and confers blunted responses to a specific stimulus. These findings suggest one potential mechanism for macrophage clearance from inflamed glomeruli.