Expression of smoothelin in the normal and the overactive human bladder

We established the expression pattern of smoothelin, a marker protein for contractile smooth muscle cells, in the human detrusor and investigated its possible impact on bladder overactivity.

Detrusor samples of 13 overactive bladders (sensory urge and detrusor instability) were obtained before botulinum toxin injection and compared to those of 8 normally contractile, nonobstructed bladders obtained during radical cystectomy. Smoothelin mRNA expression patterns were investigated by Northern blot and variant specific reverse transcriptase-polymerase chain reaction as well as by quantitative reverse transcriptase-polymerase chain reaction on laser capture, microdissected smooth muscle. At the protein level smoothelin was investigated by standard and quantitative immunohistochemistry.

The bladder muscularis expressed vascular and visceral smoothelin isoforms, and 2 of the known splice variants. In the smooth muscle of patients with detrusor instability and sensory urge a significant 2.4 and 2.2-fold increase, respectively, in smoothelin variant 1 mRNA was observed in comparison to that of normal controls. Analyses at the smoothelin protein level confirmed significant up-regulation in these bladder dysfunctions by a factor of 2.3 and 1.8, respectively. No significant difference in smoothelin expression was observed between detrusor instability and sensory urge.

Increased expression of smoothelin in patients with detrusor instability and sensory urge implies that the etiology of these dysfunctions includes changes in myogenic parameters. In addition, our data support the new classification of the International Continence Society for overactive bladder proposing that sensory urge and detrusor instability represent a single clinical entity.