Involvement of CD34+ progenitor cells in regeneration of the bladder acellular matrix graft (BAMG): time-dependent neovasculogenesis and regeneration of different bladder wall components

Abstract

Purpose To determine the involvement of progenitor hematopoietic stem cells in the regeneration of BAMG along with restoration of other compartments of bladder wall in rats. Material and methodsS Thirty-three rats underwent partial cystectomy and the acellular matrices were grafted to the remaining host bladder. At 4, 7, 14, 30, 60, 90, and 180 days after grafting, animals were sacrificed and their bladders were excised and paraffin-embedded. The inflammatory process was evaluated using anti-CD3 for labeling of T lymphocytes, anti-CD20 for determining B lymphocytes, and anti-CD68 for macrophages. The BAMG neovascularization was studied using anti-CD31 for staining of microvessels and anti-CD34 for identification of angioblasts and progenitor haematopoietic stem cells. Tissue sections were also stained for determination of smooth muscle cell α-actin and neurofilament protein. Results In acellular matrices, there was no expression of cellular markers. Polymorphonuclear cells and lymphocytes densely infiltrated BAMG during the first 2 weeks after grafting; however the inflammation resolved by the 1st post-surgical month. CD34+ endothelial progenitor cells were found in all grafts 4 days after surgery. The number of CD34+ cells increased continuously and peaked 2 months after grafting. The increment in number of CD31+ microvessels in grafted matrices followed that of CD34+ cells and reached 144.5% of control values at 3rd post-surgical month. The mean number of CD34+ and CD31+ cells returned to control ranges by 6 months after grafting. Expression of α-actin was first visualized on day 4 and α-actin intensity reached control values 6 months after grafting. Neural elements appeared 1 week after grafting and just 60% of normal intensity was achieved by 6th post-surgical month. Conclusions Our results demonstrate the effective cellular regeneration in BAMG and suggest a considerable role for the CD34+ endothelial progenitor cells in the neo-vasculogenesis of the grafts.