Cellular Expression Profile for Interstitial Cells of Cajal in Bladder - A Cell Often Misidentified as Myocyte or Myofibroblast

Abstract

BackgroundInterstitial cells of Cajal (ICC) have been identified in urinary bladder of several species, but their presence in mice remains uncertain. Meanwhile, dozens of reports indicate that dysregulation of connexin 43 plays an important role in bladder overactivity, but its localization has not been clearly defined, with reports of expression in either the smooth muscle or in myofibroblasts. We recently identified a population of ectonucleoside triphosphate diphosphohydrolase 2 (NTPDase2) positive cells that resemble ICC and are distinct from smooth muscle, fibroblasts, myofibroblasts and neurons. Thus we sought to define more clearly the molecular signature of ICC and in doing so resolve some of these uncertainties.Principle findingsImmunofluorescent localization revealed that NTPDase2-positive cells lie closely adjacent to smooth muscle but are separate from them. NTPDase2 positive cells exhibited co-localization with the widely accepted ICC marker - c-kit. They were further shown to co-localize with other ICC markers CD34 and Ano1, but not with mast cell marker tryptase. Significantly, they show convincing co-localization with connexin 43, which was not present in smooth muscle. The identity of these cells as ICC was further confirmed by the presence of three mesenchymal markers – vimentin, desmin, and PDGFβ receptor, which indicates their mesenchymal origin. Finally, we observed for the first time, the presence of merlin/neurofibromin 2 in ICC. Normally considered a neuronal protein, the presence of merlin suggests ICC in bladder may have a role in neurotransmission.ConclusionsNTPDase2 positive cells in mice bladder are ICC, which can be defined by the presence of c-Kit, CD34, Ano1, NTPDase2, connexin 43, vimentin, desmin, PDGFβ receptor and merlin/NF2. These data establish a definitive molecular expression profile, which can be used to assist in explorations of their functional roles, and the presence of NTPDase2 suggests that purinergic signaling plays a role in regulation of ICC function.

Control of Urinary Drainage and Voiding

“…In urinary bladder, much less is understood. We and others recently demonstrated that ICC markers are expressed in BICCs, including c-kit, anoctamin 1, gap junction protein connexin 43, and CD34 (88). These cells are closely associated with intramural nerves and BSM cells (89)(90)(91).…”

Purinergic signalling in the urinary tract in health and disease

“…A comparison of electrical and mechanical activity and ICCs in urinary bladders from WT and the mouse W/W v mutation phenotype, showed upregulation of the purinergic component of contraction for the W/W v mice, perhaps involving ICCs [477]. In a recent paper, it was claimed that ICCs in mouse bladder express NTPDase2 [752], indicating specific mechanisms for ATP disposition.…”

“…Interstitial cells of Cajal (ICCs) have been claimed to be present, not only in gut, where they express P2X and P2Y receptors [122,696], but also in the bladder of guinea-pigs [193,712], mice [476,752] and humans [476,608]. ICCs (also referred to as myofibroblasts; see [727]) are considered to be pacemaker cells, regulating smooth muscle activity.…”

The stem cell growth factor receptor KIT is not expressed on interstitial cells in bladder

“…The inspiration to look for the presence of KIT in the bladder came from functional gut research, where KIT + ICC are well known to play central roles in pacemaking and signal transduction [11]. KIT was first described in the bladder of guinea pig by the group of McCloskey et al [12] and has later also been detected in rat [13], mouse [14], guinea pig [15] and human bladder [16].…”