Pharmacological Tie2 activation in kidney transplantation

To investigate the therapeutic potential of vasculotide (VT) - a Tie2 activating therapeutic - in kidney transplantation.

We performed a murine MHC-mismatched renal transplant model (C57Bl/6 male into Balb/c female) with 60 min cold and 30 min warm ischemia time. 500 ng VT was administered i.p. to donor mice 1 h before organ removal. In addition, recipients received 500 ng VT i.p. directly and 3 d after surgery. Survival was monitored and remaining animals were sacrificed 28 d after transplantation. In this model, we analyzed: (1) organ function; (2) Kaplan-Meier survival; (3) organ damage (periodic acid Schiff staining) via semi-quantitative scoring [0-4 (0 = no injury/inflammation to 4 = very severe injury/inflammation)]; (4) expression of renal endothelial adhesion molecules (ICAM-1) via immunofluorescence (IF) staining, immunoblotting and qPCR; (5) infiltration of inflammatory cells (IF Gr-1, F4/80); and (6) fibrosis via staining of α-smooth muscle actin (αSMA), Sirius red staining and immunoblotting of SMAD3 activation.

Exogenous activation of Tie2 with VT resulted in diminished expression of peritubular and glomerular endothelial adhesion molecules. Consequently, infiltration of inflammatory cells (analyzed as ICAM-1, Gr-1 and F4/80 positive cells) was reduced in VT-treated mice compared to controls. Additionally, VT was protective against fibrogenesis after kidney transplantation. Trends towards lower serum creatinine (vehicle: 142 ± 17 μmol/L vs VT: 94 ± 23 μmol/L), urea (vehicle: 76 ± 5 mmol/L vs VT: 60 ± 8 mmol/L) and lactate dehydrogenase (vehicle: 1288 ± 383 iU vs VT: 870 ± 275 iU) were observed on day 6 after transplantation. Kaplan-Meier survival analysis showed improved survival rates in the VT-treated mice that did not reach statistical significance (27% vs 54%, P = 0.24, n = 11 per group). Exogenous activation of Tie2 via VT might reduce infiltration of inflammatory cells into renal tissue thereby protecting the transplant from early graft dysfunction potentially affecting long-term function.

Protection of the endothelial microvasculature via the Tie2 axis in the early transplant setting might hold promise as a therapeutic target.