Gremlin promotes peritoneal membrane injury in an experimental mouse model and is associated with increased solute transport in peritoneal dialysis patients.

The peritoneal membrane becomes damaged in patients on peritoneal dialysis (PD). Gremlin 1 (GREM1) inhibits bone morphogenic proteins (BMPs) and plays a role in kidney development and fibrosis. We evaluated the role of gremlin in peritoneal fibrosis and angiogenesis. In a cohort of 32 stable PD patients, GREM1 concentration in the peritoneal effluent correlated with measures of peritoneal membrane damage. AdGrem1, an adenovirus to overexpress gremlin in the mouse peritoneum, induced submesothelial thickening, fibrosis, and angiogenesis in C57BL/6 mice, which was associated with decreased expression of BMP4 and BMP7. There was evidence of mesothelial cell transition to a mesenchymal phenotype with increased α smooth muscle actin expression and suppression of E-cadherin. Some of the GREM1 effects may be reversed with recombinant BMP7 or a pan-specific transforming growth factor ß (TGF-ß) antibody. Neovascularization was not inhibited with a TGF-ß antibody, suggesting a TGF-ß-independent angiogenic mechanism. Swiss/Jackson Laboratory (SJL) mice, which are resistant to TGF-ß-induced peritoneal fibrosis, responded in a similar fashion to AdGrem1 as did C57BL/6 mice with fibrosis, angiogenesis, and mesothelial-to-mesenchymal transition. GREM1 was associated with up-regulated TGF-ß expression in both SJL and C57BL/6 mice, but SJL mice demonstrated a defective TGF-ß-induced GREM1 expression. In summary, GREM1 induces fibrosis and angiogenesis in mouse peritoneum and is associated with increased solute transport in these PD patients.

Adenovirus-mediated gene transfer of TGF-ß1 to the renal glomeruli leads to proteinuria.

The mechanism of proteinuria in many common kidney diseases involves glomerular hemodynamic effects and local expression of angiogenic, fibrogenic, and vasoactive factors. Transforming growth factor (TGF)-ß has been associated with many diseases involving proteinuria and renal fibrosis. TGF-ß has been shown to induce podocyte dedifferentiation in vitro, but its in vivo effects on the glomerular filtration barrier are not well described. In this study, we used an adenovirus vector to transfer active TGF-ß1 to the glomeruli of rat kidneys. Transient TGF-ß1 overexpression induced significant proteinuria, podocyte foot process effacement, nephrin down-regulation, and nephrinuria. The expression of synaptopodin was also significantly down-regulated by TGF-ß1. Increased glomerular expression of Snail, suggestive of an in vivo dedifferentiation process, was associated with a loss of podocyte epithelial markers. The expression of angiopoietin-1 and angiopoietin-2 was significantly increased in TGF-ß1-transfected glomeruli, and TGF-ß1 increased the expression of the angiopoietin receptor, Tie2, in podocyte cell culture. TGF-ß1 down-regulated nephrin and synaptopodin expression in podocytes in cell culture; this effect was reversed by the blockade of both angiopoietin and Tie2 activities. These findings suggest that locally produced TGF-ß1 can cause podocyte dedifferentiation marked by a loss of synaptopodin, nephrin, and foot process effacement, partly regulated by angiopoietins. This process represents a novel pathway that may explain proteinuria in a variety of common renal diseases.

Prolonged peritoneal gene expression using a helper-dependent adenovirus.

BACKGROUND: Encapsulating peritoneal sclerosis (EPS) is a rare complication of peritoneal dialysis. The causes of EPS are not well defined and are likely multifactorial. A suitable animal model would facilitate research into the pathophysiology and treatment of EPS. METHODS: We developed a helper-dependent adenovirus that expresses both green fluorescent protein (GFP) and active transforming growth factor-beta (TGF-beta1; HDAdTGF-beta1). Mice were administered HDAdTGF-beta1 via intraperitoneal injection and the response was compared with mice administered either first-generation adenovirus expressing TGF-beta1 (AdTGF-beta1) or control adenovirus (AdGFP). RESULTS: HDAdTGF-beta1-treated mice continued to express the GFP reporter transgene to day 74, the end of the observation period. Transgene expression lasted less than 28 days in the animals treated with first-generation adenoviruses. Animals treated with first-generation AdTGF-beta1 demonstrated submesothelial thickening and angiogenesis at day 7, with almost complete resolution by day 28. The HDAdTGF-beta1-treated mice demonstrated progressive peritoneal fibrosis with adhesion formation and encapsulation of bowels. Weight gain was significantly reduced in animals treated with HDAdTGF-beta1 compared to both the control-treated animals and the AdTGF-beta1-treated animals. Inflammation was not a major component of the fibroproliferative response. CONCLUSIONS: Peritoneal administration of a first-generation AdTGF-beta1 leads to transient gene expression, resulting in a resolving fibrotic response and histology similar to that seen in simple peritoneal sclerosis. Prolonged TGF-beta1 expression induced by the helper-dependent HDAdTGF-beta1 led to changes in peritoneal morphology resembling EPS. This suggests that TGF-beta1 may be a contributing factor in both simple peritoneal sclerosis and EPS. This model will be useful for elucidation of the mechanism of EPS and evaluation of potential treatment.