Modulation of transgene expression in mesothelial cells by activation of an inducible promoter.

Background. The eYcacy of peritoneal dialysis and its success as a long-term treatment depends on the preser- inducible promoter; intraperitoneal; mesothelial cells; mMT-1; peritoneal cavity; peritoneal dialysis; peritonvation of the integrity of the peritoneal membrane. With increasing time on dialysis, the membrane may eal mesothelium; systemic delivery become compromised resulting in decreased dialysing capacity. We have pursued an innovative strategy, i.e. genetic modification of the mesothelial cell to change Introduction the properties of the membrane to potentially improve its dialysing capacity and longevity, and have demon- In peritoneal dialysis (PD), the peritoneal membrane strated the feasibility of this approach in a rat model functions as a semi-permeable membrane that regulates of ex vivo gene transfer. The potential to regulate the selective transport of water and solutes between transgene expression in this model is examined here. the systemic circulation and the peritoneal cavity [1]. Methods. Rat peritoneal mesothelial cells (MCs) were The eYcacy of PD and its success as a long-term stably modified to express human growth hormone treatment depend, therefore, on the maintenance of (hGH ) under control of the heavy metal ion and the dialysing capacity and integrity of the peritoneal glucocorticoid-regulatable murine metallothionein-1 membrane. Ironically, PD solutions are considered to promoter. The eVect of zinc and the synthetic glucocor- be largely bioincompatible [2] and may have adverse ticoid dexamethasone on hGH expression was analysed eVects on the mesothelium [3‐7] and on host defence in MC clones maintained in continuous passage or mechanisms [8‐10] which in turn may contribute to stationary phase, and in our rat model of ex vivo eventual peritoneal membrane failure [11]. New and gene transfer. innovative strategies to improve or enhance the durabResults. Exposure of these clones to zinc and dexa- ility of the membrane in order to prevent injury during methasone, either singly or in combination, resulted in peritoneal dialysis must be investigated. To this end significant (i.e. 2‐200-fold ) increases in hGH produc- we have developed a molecular genetic approach, i.e. tion. Zinc-induced modulation of hGH production was to genetically modify peritoneal mesothelial cells demonstrated in cells in continuous passage and sta- (MCs) to express potentially therapeutic proteins, and tionary culture. Regulation was also demonstrated through this modification, change the properties of the after ex vivo gene transfer by both the intraperitoneal membrane. administration of zinc ions or the systemic administra- We have previously established a rat model of ex tion of dexamethasone. vivo MC-mediated gene therapy. Specifically, we have Conclusions. Our results demonstrate the modulation shown that MCs can be isolated from rat parietal of transgene expression in MCs in vitro and in vivo, peritoneum, genetically modified, and then implanted and suggest the potential for the regulation of gene onto the denuded parietal peritoneal surface of synexpression in a genetically modified mesothelium that geneic recipients [12]. We have demonstrated MC may ultimately be used for the delivery of therapeutic -mediated production of an intracellular marker proproteins to maintain peritoneal membrane viability in tein, b-galactosidase [12]; the delivery of a MC-secreted the peritoneal dialysis patient. protein, human growth hormone (hGH ), to the systemic circulation [13]; and the expression of a membrane-bound recombinant protein, thrombomodulin,