[792] Distribution of Smoothelin Expression in the Musculature of the Genitourinary Tract

S Khayyata, M Dudas, SM Rohan, A Gopalan, SW Fine, VE Reuter, SK Tickoo. Memorial Sloan-Kettering Cancer Center, New York, NY

Background: Smoothelin is a novel smooth muscle (SM)-specific marker expressed strongly in terminally differentiated SM cells with absent to limited expression in non-contractile SM and myofibroblastic cells. It has been suggested that smoothelin expression may help distinguish bladder muscularis propria (MP) from muscularis mucosae (MM), with implications for cancer staging. However, smoothelin expression in various smooth muscle components of the GU tract has not been well studied.
Design: Normal bladder, ureter, bladder neck, prostate, urachal remnant, and bladder diverticulae tissues were identified and sections were stained with antibody to smoothelin (1:500; mAb, Abcam Inc, Cambridge, MA). Immunohistochemical staining was evaluated for staining intensity (0 to 3+) and % positive cells.
Results: Normal bladder [n=10]: all cases showed moderate (2+) to strong (3+) staining in 70 to 100% of cells of MP and no (0) to weak (1+), focal staining in MM. Ureter [n=5]: smoothelin staining did not identify a distinct MM. 2 to 3+ staining was observed throughout the MP, but with progressively weaker labeling from outer MP to MP closest to the lumen, corresponding to the thinning of the MP fibers on H&E. Bladder neck [n=5]: medium/large discrete SM bundles from the bladder base margin of radical prostatectomy specimens showed no labeling to 1 to 2+ staining in <25% of cells. Prostate [n=5]: although dispersed among glandular elements, the SM component of prostatic stroma consistently stained strongly (2 to 3+) and diffusely (nearly 100% of cells). Urachal remnant [n=3]: the entire musculature of the urachal remnant showed 0 to 1+ focal staining in contrast to the 3+ bladder MP, often seen in the same section. Bladder diverticulae [n=15]: two types of SM were observed in diverticular walls: thin wisps only [n=5], which were uniformly negative, and hypertrophic SM bundles accompanied by thin wisps [n=10], in which 1+ labeling was seen in 10-25% of cells in 5 cases.
Conclusions: Intensity and extent of smoothelin staining accurately distinguishes muscularis propria from muscularis mucosae in the intact urinary bladder. The immunostaining patern of the muscles in diverticular walls strongly supports their muscularis mucosae origin, even when appearing hypertrophic. Further investigation of patterns of smoothelin expression is warranted, as its variable positivity in GU tract smooth muscles may help define their functional status (ureter, bladder neck) and/or impact cancer staging (bladder, urachus).
Category: Genitourinary (including renal tumors)

Monday, March 9, 2009 1:00 PM

Poster Session II # 123, Monday Afternoon