Mesangial cell-derived transforming growth factor-β1 reduces macrophage adhesiveness with consequent deactivation

Abstract

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.

Evidence for TGF-β-Mediated ‘Defense’ of the Glomerulus: A Blackguard Molecule Rehabilitated?

“…It has been reported that TGF-β down-regulates expression of these adhesion receptors in macrophages [12, 13]. Consistent with these data, we recently reported that mesangial cell-derived TGF-β impairs adhesiveness of macrophages in vitro [11]. Furthermore, compared to adherent cells, detached macrophages showed blunted expression of cytokines in response to lipopolysaccharide.…”

“…data]. Cultured mesangial cells produce the active form of TGF-β [11, 14], and mesangial cells expressing a dominant negative mutant of TGF-β type II receptor are resistant to oxidant-initiated apoptotic death [Kitamura, unpubl. data].…”

Thrombospondin-1 is a major activator of TGF-β in fibrotic renal disease in the rat in vivo

“…While in vivo and in vitro studies have shown that TGF-b1 can be chemotactic for mononuclear cells as well as it can reduce macrophage adhesiveness potentially leading to deactivation and/or increased clearence from inflammatory sites [38], blocking peptide treatment in this study did not affect glomerular macrophage accumulation in the anti-Thy1 model.…”

TGF-beta signal transduction in chronic kidney disease

“…Conversely, knockout of the TGF-beta1 gene causes mice to succumb to wasting and overwhelming inflammatory infiltration of abdominal viscera (3). In vitro , TGF-beta downregulates beta2 integrin (CR3), a receptor required by macrophages to adhere to areas of injury (4). In cultured mesangial and tubular epithelial cells, TGF-beta prevents mitosis through cyclin kinase inhibition (5), suppressing macrophage-derived IL-1 secretion.…”