A MOLECULAR MARKER FOR THE DEVELOPMENT OF INTERSTITIAL CYSTITIS IN A RAT MODEL - ISOACTIN GENE-EXPRESSION

Purpose: To determine whether the differential expression of bladder s mooth muscle isoactin can be used as a molecular marker for the develo pment of interstitial cystitis (IC). Methods: Three groups of five fem ale Sprague-Dawley rats each underwent urethral catheterization and in travesical instillation of 0.5 ml. of 0.4N HCl. One group was sacrific ed one, two, and four weeks after the application of HCl, and their bl adders harvested for histologic examination and evaluation using north ern blot analysis of bladder smooth muscle isoactins. Five control ani mals were sacrificed and their bladders harvested to establish isoacti n gene expression of bladder smooth muscle in the normal state. The bl adders of the rats in each group were excised, immediately frozen in l iquid nitrogen, pooled, then stored at -70C until needed for RNA isola tion. Isoactin cDNA probes have been developed, therefore isoactin spe cific cDNA insert fragments were isolated and insert DNA was purified by gel electrophoresis. Total cellular RNA was isolated from 1.0 gm. o f bladder smooth muscle from each group. After spectrophotometric quan tification, Northern Blot analysis was performed using 2% agarose-form aldehyde gels and Biotrans nylon membranes. Two complete Northern Blot series were run on a single gel and blotted to a single membrane to e liminate gel and blotting discrepancies. Results: Microscopic histolog ic analysis revealed detrusor mastocystosis and eosinophilia as has be en noted in humans with chronic interstitial cystitis. Two weeks after the intravesical application of hydrochloric acid, the relative expre ssion of gamma-smooth muscle isoactin was noted to increase by 1.7-fol d, while alpha-smooth muscle isoactin expression increased by a factor of 9. These effects were seen to stabilize four weeks after acid appl ication. Conclusions: The intravesical application of dilute HCl in ra ts results in a histologic appearance which mimics that seen in humans with interstitial cystitis. The appearance of detrusor mastocytosis a nd eosinophilia was accompanied by a relative decrease in the expressi on of gamma- and a relative increase in alpha-smooth muscle isoactin g ene expression. This pattern of smooth muscle isoactin expression is c onsistent with a more immature and possibly synthetic smooth muscle ph enotype, which may be responsible for the clinical presentation of tho se with IC. Northern blot analysis of bladder smooth muscle cells may serve as an effective marker for the development of interstitial cysti tis in humans.