Induction and Direction of Angiogenesis for Bladder Wall Regeneration and Replacement

About This Grant

Project Summary/Abstract For patients with neuropathic bladder from spina bifida or spinal cord injury, the current surgery of using intestine for bladder augmentation causes high morbidity, as well as short- and long-term complications. A recent clinical trial using bioengineered bladder wall showed the feasibility and relative safety of bioengineering bladder wall but failed due to dehiscence and graft contraction from ischemia. While these grafts were engineered from synthetic matrices and autologous urothelium and muscle, they had no blood vessels. Angiogenesis from the patient’s bladder is not fast enough to prevent large graft necrosis since early imbibition and perfusion are limited to the outer perimeter of the graft. As shown in murine and porcine models, bladder vessels will connect (inosculate) with graft vessels within a few days after transplantation to the bladder and facilitate blood flow to the entire graft. Thus, engineering vessels in a large animal bladder graft and evaluating these grafts are the next and final steps before development of grafts for clinical testing. To vascularize matrix grafts, others are trying to “endothelize” grafts by soaking them with stem cells and growth factors in vitro, which creates capillary-like structures rather than organized vessels with lumens. This proposal employs a different strategy where grafts are cellularized and vascularized in vivo on the rectus muscle bed. This ensures optimum graft maturity and a healthy and functional vasculature prior to bladder transplantation. The current proposal is to build upon successes in the rodent and porcine models to design and test endothelial cell ligands to enhance endothelial adhesion and angiogenesis (Aim 1), to evaluate a novel strategy to create long, coronally-directed vessels in large grafts (Aim 2) and to then transplant these matured grafts to the bladder after partial cystectomy in pigs (Aim 3). Grafts will be analyzed grossly to determine size and histologically to determine vessel density, length, perfusion, endothelial/vascular maturity, and epithelial and stromal differentiation. Graft vessel function will be analyzed via perfusion of dyes into the blood stream. Graft function will be assessed by urodynamics to measure bladder capacity and compliance, and by standard biomechanical testing for material and viscoelastic properties. The long-term, translationally directed goals for this project are to produce and evaluate a vascularized graft in a large animal model and to develop vascularized grafts for patients with spinal anomalies or injury. Since bioengineering human bladder wall has proven feasible but not safe or efficacious due to insufficient blood supply, this project has the potential to make bioengineered bladder a realistic treatment option. The directed vascularization technologies developed in this project could be used to improve engineering of other organ tissue.