Gremlin Promotes Peritoneal Membrane Injury in an Experimental Mouse Model and Is Associated with Increased Solute Transport in Peritoneal Dialysis Patients

Abstract

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 β (TGF-β) antibody. Neovascularization was not inhibited with a TGF-β antibody, suggesting a TGF-β-independent angiogenic mechanism. Swiss/Jackson Laboratory (SJL) mice, which are resistant to TGF-β-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-β expression in both SJL and C57BL/6 mice, but SJL mice demonstrated a defective TGF-β-induced GREM1 expression. In summary, GREM1 induces fibrosis and angiogenesis in mouse peritoneum and is associated with increased solute transport in these PD patients.

Genomic reprograming analysis of the Mesothelial to Mesenchymal Transition identifies biomarkers in peritoneal dialysis patients

“…5a–c). Surprisingly, effluent levels of GREM1 also showed statistical differences between low/low-average and high/high-average transporters, but in the opposite direction to what could be expected with respect to microarray and RT-PCR studies and according to previous reports31 (Fig. 5d).…”

“…Interestingly, peritoneal transport of the PD patients from whom the cells were harvested was associated with the ex vivo expression levels of molecules that were over-expressed during MMT in cultured effluent MC2427. As a proof of concept, levels of MMT-associated molecules in the PD effluent, including VEGF, CTGF/CCN2, Gremlin-1 (GREM1), and MMP9 were found to correlate with the peritoneal transport status2829303132. Herein, by using whole genome microarray analysis of MCs undergoing MMT in vitro and ex vivo , we aimed to identify novel molecular biomarkers that may facilitate diagnosis of the integrity and functionality of the patient’s peritoneum and hence allow early adaption of treatment to the patient’s needs.…”

Experimental systems to study the origin of the myofibroblast in peritoneal fibrosis

“…We have quantified the EMT response and find that very few cells express both mesenchymal and epithelial markers in the peritoneum after injury. In general, we find only 1–2 cells per high power field to be dual labeled [50] , [56] . This could indicate that EMT is a rare event in peritoneal fibrosis or that our “snapshot” of peritoneal membrane injury captures only those cells in the process of transition, not those cells fully transitioned to a myofibroblast phenotype.…”

Molecular Mechanisms Underlying Peritoneal EMT and Fibrosis

“…For example, CTGF is produced in response to TGF- β 1 and inhibits BMP7 effects [ 59 ]. Also, gremlin concentration in the peritoneal effluent correlated with measures of peritoneal membrane damage and may modulate BMP7-mediated effects [ 60 ]. HGF may stabilize the epithelial phenotype inhibiting EMT in MCs [ 43 ].…”