Time-dependent neovasculogenesis and regeneration of different bladder wall components in the bladder acellular matrix graft in rats

OBJECTIVES: To determine the time-dependent regeneration of different cellular components in the bladder acellular matrix graft (BAMG) and the involvement of hematopoietic stem cells in BAMG vascular regeneration. METHODS AND MATERIALS: Thirty-three male Sprague Dawley rats underwent partial cystectomy and the acellular matrices were grafted to the remaining host bladder. At 4, 7, 14, 30, 60, 90, and 180 d after grafting, animals were sacrificed and their bladders were excised and paraffin-embedded. Tissue sections were stained for determination of CD3, CD20, CD34, CD31, CD68, smooth muscle cell (SMC) alpha-actin, and neurofilament protein as well as elastin fibers and collagen typing. Cystometric evaluation of grafted bladders was also performed 3 mo after procedure. RESULTS: In acellular matrices, there was no expression of cellular markers and type-1 collagen fibers were predominant. One month after surgery, all grafted matrices were completely lined with urothelium. Polymorphonuclear cells and lymphocytes densely infiltrated BAMG during the first 2 wk after grafting; however the inflammation resolved by the first post-surgical mo. CD34+ endothelial progenitor cells (EPCs) were found in all grafts 4 d after surgery. The number of CD34+ cells increased continuously and peaked 2 mo 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 third post-surgical mo. The mean number of CD34+ and CD31+ cells returned to control ranges by 6 mo after grafting. Expression of SMC alpha-actin was first visualized on day 4 and alpha-actin intensity reached to control values 6 mo after grafting. Neural elements appeared 1 wk after grafting and just 60% of normal intensity was achieved by the sixth post-surgical mo; however complete nerve bundles were found in all grafted matrices after 1 mo. Cystometric studies revealed higher bladder capacity and compliance but lower maximum intravesical pressure in grafted bladders in comparison with controls, 3 mo after surgery. CONCLUSIONS: Our results demonstrate the effective cellular regeneration in BAMG and propose a considerable role for the CD34+ EPCs in the neo-vasculogenesis of the grafts.