Production and regulation of matrix metalloproteinases and their inhibitors by human peritoneal mesothelial cells.

OBJECTIVE: Human peritoneal mesothelial cells (HPMC) are likely to be involved in maintenance of the peritoneal membrane. We determined whether these cells were able to synthesize the matrix degrading enzymes, matrix metalloproteinases (MMPs), likely to be responsible for the breakdown of this membrane, and whether this secretion could be modulated by cytokines involved in the inflammatory response.

DESIGN: MMP activity in conditioned medium of growth-arrested HPMC was measured by zymography. Cultures were incubated in the presence and absence of the cytokines transforming growth factor-beta (TGFbeta) and interleukin (IL)-1beta in order to determine the effects of these cytokines on this process. The mRNA for these MMPs, together with that of their specific inhibitors, tissue inhibitors of metalloproteinases (TIMPs), was also examined by reverse transcriptase polymerase chain reaction

RESULTS: HPMC were shown to constitutively secrete the metalloproteinases MMP-2 and MMP-3 in vitro. In response to the proinflammatory cytokine IL-1beta , the protein and mRNA for MMP-9 was induced, while secretion of MMP-2 was unaltered. Similarly, the mRNA for MMP-3 was also increased relative to actin following the addition of IL-1beta. TGFbeta was shown to slightly induce the secretion of MMP-2 together with the mRNA for TIMP I, TIMP II, and, to a greater extent, TIMP III. Used peritoneal dialysate was also shown to induce MMP-9 secretion, and this effect was blocked by the co-incubation of IL-1 receptor antagonist. The secretion of enzyme activity was shown to be from the apical surface of the cells.

CONCLUSION: HPMC have the ability to control the accumulation of extracellular matrix by secreting the matrix degrading molecules MMP-2, MMP-3, and MMP-9. In addition, the secretion of these enzymes, together with that of their inhibitors (TIMPs) is regulated by the cytokines IL-1beta and TGFbeta. This process is likely to be important in both the normal maintenance of the integrity of the peritoneal membrane and in the changes that occur following prolonged peritoneal dialysis.