| Objectives: Increased peritoneal solute transport rate is one of major contributors which restrict long-term peritoneal dialysis(PD). The mechanism is still not fully understood. The present study aimed to explore the regulation of platelet-derived growth factor and its receptor(PDGF/PDGFR) signaling between endothelial cell and pericyte on peritoneal solute transport rate in uremic PD rats.Methods: Male SD rats(n = 36) were randomly grouped into sham group(n = 12), uremia group(n = 12) and uremic PD group(n = 12). 5/6 nephrectomy was used to construct uremia model, and 5/6 nephrectomy + intraperitoneal infusion of 4.25% glucose PD solution to build uremic PD model. Morphology of peritoneal membrane was observed by HE and Masson staining. CD31 immunohistochemical staining was applied to detect peritoneal vessel density, and CD31 /desmin double immunofluorescence staining was applied to detect pericyte coverage. Peritoneal equilibration test(PET) was used to measure peritoneal transport rates. And FITC-BSA(69 k Da)and FITC-dextran(4 k Da)were applied to estimate peritoneal vessel permeability. PDGF/PDGFR protein expression was evaluated by western blot. SPSS 13.0 and Image J were applied to analyze correlations between PDGF/PDGFR protein expression and peritoneal solute transport, pericyte coverage and vessel permeability. Ad-FLAG and Ad-PDGFR-Fc were constructed and tail injuected into uremic PD rats. The effects of PDGF inhibition on peritoneal membrane morphology, solute transport rate, pericyte coverage and peritoneal vessel permeability were investigated.Results: 1. Compared to the sham rats, morphological changes of peritoneal membrane were noted in the uremia rats, including thickened mesothelial cells loss, submesothelial extracellular matrix(136.4±39.9 ?m vs 36.5±3.9 ?m, P=0.048), increased peritoneal vessel [5.5(3.75, 6)vs 2(1.75, 3)/ HP, P=0.005]. After PD solution infusion for 4 weeks, these changes were more intensive, including more mesothelial cells loss, submesothelial extracellular matrix further thickened(654.2±142.1?m vs 136.4±39.9?m, P=0.004), and peritoneal vessel number further increased[9(7.75, 12)vs 5.5(3.75, 6)/ HP, P=0.004 ].Uremic PD rats had higher D/P cr than that in the sham group(0.92±0.06 vs 0.50±0.09, P=0.003)and uremia group(0.92±0.06 vs 0.65±0.13,P=0.03). Compared to sham rats, pericyte coverage of uremia rats was significantly reduced(0.59±0.02 vs 0.81±0.07, P=0.006), and further reduced in uremic PD rats(0.35±0.05 vs 0.59±0.02, P=0.001). Permeability of peritoneal microcirculation to FITC-BSA(197.01 vs 1.00, P<0.001)and FITC-dextran(105.91 vs 2.98,P < 0.001)in uremia rats were higher than that in sham rats. After 4-week's PD solution infusion, the permeability of peritoneal microcirculation to FITC-BSA(304.16 vs 197.01,P<0.001)and FITC-dextran(358.85 vs 105.91,P < 0.001)were further increased. 2. Peritoneal expression of PDGF protein in uremic group was decreased compared to sham rats(0.59±0.52 vs 0.76±0.08, P=0.035), and further down-regulated after 4-week's PD solution infusion(0.47±0.04 vs 0.59±0.52, P=0.037). Peritoneal PDGF protein level was significantly correlated with peritoneal solute transport(R2 = 0.7397, P=0.003), peritoneal microcirculation permeability to BSA(R2 = 0.8496, P < 0.001),and peritoneal microcirculation permeability to dextran(R2 = 0.7661, P =0.002), and pericyte coverage(R2 =0.7283, P=0.003). 3. Compared to Ad-FLAG group, Ad-PDGFR-Fc group had decreased PDGF expression, higher peritoneal solute transport(0.68±0.07 vs 0.50±0.05, P=0.014). Pericyte coverage in Ad-PDGFR group reduced when compared with the Ad-FLAG group(0.21±0.03 vs 0.38±0.02, P=0.01). Peritoneal microcirculation permeability to both FITC-BSA(518.99±92.90 vs 320.96±17.68, P=0.03)and FITC-dextran(360.19±12.80 vs 263.63±31.64, P=0.03)in Ad-PDGFR-Fc group was significantly higher than that in the Ad-FLAG group.Conclusion: 1. Uremia and PD solution could alter peritoneal morphology and function, including reduced pericyte coverage and enhanced permeability of peritoneal microcirculation. 2. Uremia and PD solution down-regulated PDGF protein expression in peritoneal membrane. PDGF expression was significantly correlated with pericyte coverage, permeability of peritoneal microcirculation and peritoneal solute transport. 3. Blockade PDGF/PDGFR pathway further reduced pericyte coverage, increased permeability of microcirculation and peritoneal solute transport rate, suggesting that PDGF/PDGFR pathway might regulate permeability of microcirculation by affecting pericyte coverage, thus participating in increasing peritoneal solute transport rate. PDGF/PDGFR pathway might be a new target to prevent increased peritoneal solute transport rate. |
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