Bladder hypersensitivity and transcriptional regulation of potassium channel subunit mRNA expression in mice with cystitis

Hyperexcitability in bladder primary afferents contributes to bladder overactivity and pain in pathological urological conditions. Target-derived growth factors can alter primary afferent expression of membrane-bound ion channels that regulate neuronal excitability, such as voltage-gated potassium (Kv) channels. Several Kv channels are expressed in primary afferent neurons and contain a binding site for repressor element-1-silencing transcription factor (REST). Growth factor-mediated, REST-induced, long-lasting downregulation of Kv channels may provide a mechanism through which persistent changes in bladder afferent sensitivity can occur. In the present study we used a model of cyclophosphamide (CYP)-induced cystitis to examine interactions between bladder-derived growth factors and REST-mediated regulation of Kv channel expression in lumbosacral (LS) bladder afferents. C57Bl/6 mice were administered CYP (100 mg/kg, i.p.) or vehicle every other day for five days. Visceromotor responses (VMR) to bladder distension, real-time PCR, and single cell PCR were used to examine nociception, bladder growth factor mRNA, and REST/Kv channel mRNA in LS bladder afferents, respectively. A significant increase in VMRs following CYP treatment was paralleled by increases in bladder growth factors (nerve growth factor (NGF), artemin (ARTN), and glial cell line-derived growth factor (GDNF)) and LS afferent expression of REST. These increases occurred in conjunction with a decrease in bladder afferent expression of Kv4.3 and Kv7.3. These results suggest that CYP-induced hypersensitivity may involve growth factor-mediated sensitization of primary afferents, at least in part via changes in Kv regulation of neuronal excitability as a result of transcriptional regulation by REST. Further preliminary data show that administration of the growth factor-sequestering antibody, anti-ARTN, can prevent behavioral sensitization following CYP. Ongoing studies will use additional sequestering antibodies to determine whether they also block changes in afferent expression of Kv4.3, Kv7.3, and REST and result in suppression of neuronal hyperexcitability, as well as examine similar changes in thoracolumbar bladder afferents.