A Molecular Marker for the Development of Interstitial Cystitis in a Rat Model: Isoactin Gene Expression

Abstract

Purpose To determine whether the differential expression of bladder smooth muscle isoactin can be used as a molecular marker for the development of interstitial cystitis (IC). Methods Three groups of five female Sprague-Dawley rats each underwent urethral catheterization and intravesical instillation of 0.5 ml. of 0.4N HCl. One group was sacrificed one, two, and four weeks after the application of HCl, and their bladders harvested for histologic examination and evaluation using northern blot analysis of bladder smooth muscle isoactins. Five control animals were sacrificed and their bladders harvested to establish isoactin gene expression of bladder smooth muscle in the normal state. The bladders of the rats in each group were excised, immediately frozen in liquid nitrogen, pooled, then stored at -70C until needed for RNA isolation. Isoactin cDNA probes have been developed, therefore isoactin specific cDNA insert fragments were isolated and insert DNA was purified by gel electrophoresis. Total cellular RNA was isolated from 1.0 gm. of bladder smooth muscle from each group. After spectrophotometric quantification, Northern Blot analysis was performed using 2% agarose-formaldehyde gels and Biotrans nylon membranes. Two complete Northern Blot series were run on a single gel and blotted to a single membrane to eliminate gel and blotting discrepancies. Results Microscopic histologic analysis revealed detrusor mastocystosis and eosinophilia as has been noted in humans with chronic interstitial cystitis. Two weeks after the intravesical application of hydrochloric acid, the relative expression of gamma-smooth muscle isoactin was noted to increase by 1.7-fold, while alpha-smooth muscle isoactin expression increased by a factor of 9. These effects were seen to stabilize four weeks after acid application. Conclusions The intravesical application of dilute HCl in rats results in a histologic appearance which mimics that seen in humans with interstitial cystitis. The appearance of detrusor mastocytosis and eosinophilia was accompanied by a relative decrease in the expression of gamma- and a relative increase in alpha-smooth muscle isoactin gene expression. This pattern of smooth muscle isoactin expression is consistent with a more immature and possibly synthetic smooth muscle phenotype, which may be responsible for the clinical presentation of those with IC. Northern blot analysis of bladder smooth muscle cells may serve as an effective marker for the development of interstitial cystitis in humans.