Early Stages of In Situ Bladder Regeneration in a Rodent Model

Abstract

Surgical removal of approximately 70% of the bladder (subtotal cystectomy [STC]) was used as a model system to gain insight into the normal regenerative process in adult mammals in vivo. Female F344 rats underwent STC, and at 2, 4, and 8 weeks post-STC, bladder regeneration was monitored via microcomputed tomography scans, urodynamic (bladder function studies) pharmacologic studies, and immunohistochemistry. Computed tomography imaging revealed a time-dependent increase in bladder size at 2, 4, and 8 weeks post-STC, which positively correlated with restoration of bladder function. Bladders emptied completely at all time points studied. The maximal contractile response to pharmacological activation and electrical field stimulation increased over time in isolated tissue strips from regenerating bladders, but remained lower at all time points compared with strips from age-matched control bladders. Immunostaining of the bladder wall of STC rats suggested a role for progenitor cells and cellular proliferation in the regenerative response. Immunostaining and the presence of electrical field stimulation-induced contractile responses verified innervation of the regenerated bladder. These initial studies establish the utility of the present model system for studying de novo tissue regeneration in vivo and may provide guidance with respect to optimization of intrinsic regenerative capacity for clinical applications.

The Pharmacology of Regenerative Medicine

“…These studies clearly documented that the early stages of functional bladder regeneration are characterized by time-dependent changes in the location of the proliferating cell population in distinct bladder wall layers and, furthermore, demonstrated time-dependent expression of several evolutionarily conserved developmental signaling proteins during this same 1-week period. This report extends our previous observations (Burmeister et al, 2010) and provides further evidence for the rodent bladder as an excellent model for studying novel aspects of mammalian organ regeneration.…”

“…This is a very different phenomenon than the bladder augmentations that are commonly used to study the impact of various stem cells and biomaterials (i.e., tissue engineering) on bladder regrowth after implantation (see below for more details). In summary, within 8 weeks STC rodents have a regenerated bladder that is both structurally and functionally (with respect to micturition and continence) identical to the native bladder that it replaced (Burmeister et al, 2010). This is true with respect to bladder capacity and bladder wall thickness, as well as the presence of all three bladder wall layers: urothelium, muscularis propria, and lamina propria.…”

“…In pioneering studies by Atala et al (2006), bladder neo-organs were constructed by seeding synthetic scaffolds (collagen or collagen/polyglycolic acid composites) with urothelial cells on the inside and smooth muscle cells on the outside and subsequently implanted into subjects with myelomeningocele. Numerous reports suggested that both animal (Liang and Goss, 1963;Oberpenning et al, 1999;Frederiksen et al, 2004;Burmeister et al, 2010) and human (Sisk and Neu, 1939;Liang, 1962;Tucci and Haralambidis, 1963) bladders have significant regenerative potential after removal of a large portion of the organ (subtotal cystectomy; STC).…”

“…In this regard, animal models can be used to characterize this compelling regenerative phenomenon, opening up new approaches to regenerative pharmacology. In a multidisciplinary effort to characterize bladder regeneration morphologically, physiologically, and pharmacologically, Burmeister et al (2010) used a trigone-sparing cystectomy (STC) performed in 12-week-old female rats. By 8 weeks post-STC, the bladder had regrown to a normal size via both computed tomography imaging and in vivo cystometric analysis.…”

“…A more recent follow up study (Peyton et al, 2012) used fluorescent bromodeoxyuridine (BrdU) labeling to quantify the spatiotemporal characteristics of the proliferative response that mediates the functional regeneration observed by Burmeister et al (2010), as occurs during the critical first week post-STC. In this study, less than 1% of cells in the bladder wall were labeled with BrdU in control bladders under resting conditions (i.e., no damage), but this percentage increased significantly, by 5-to 8-fold, at all time points post-STC.…”