Byoung H. Koh

Platelet-derived growth factor receptor-α cells in mouse urinary bladder: a new class of interstitial cells

Specific classes of interstitial cells exist in visceral organs and have been implicated in several physiological functions including pacemaking and mediators in neurotransmission. In the bladder, Kit+ interstitial cells have been reported to exist and have been suggested to be neuromodulators. More recently a second interstitial cell, which is identified using antibodies against platelet‐derived growth factor receptor‐α (PDGFR‐α) has been described in the gastrointestinal (GI) tract and has been implicated in enteric motor neurotransmission. In this study, we examined the distribution of PDGFR‐α+ cells in the murine urinary bladder and the relation that these cells may have with nerve fibres and smooth muscle cells. Platelet‐derived growth factor receptor‐α+ cells had a spindle shape or stellate morphology and often possessed multiple processes that contacted one another forming a loose network. These cells were distributed throughout the bladder wall, being present in the lamina propria as well as throughout the muscularis of the detrusor. These cells surrounded and were located between smooth muscle bundles and often came into close morphological association with intramural nerve fibres. These data describe a new class of interstitial cells that express a specific receptor within the bladder wall and provide morphological evidence for a possible neuromodulatory role in bladder function.

Functional expression of SK channels in murine detrusor PDGFRα+ cells

•  SK currents have been recorded from detrusor smooth muscle cells, but current density at physiological holding potentials is negligible. •  We discovered a new class of interstitial cell in the bladder that were identified using antibodies against platelet‐derived growth factor receptor‐α(PDGFRα+ cells). •  SK3 channel transcripts and protein are highly expressed in PDGFRα+ cells in comparison to smooth muscle cells. •  Current density attributable to SK‐like currents is much higher in PDGFRα+ cells than in smooth muscle cells. Single channel currents, consistent with the conductance and Ca2+ sensitivity of SK3 channels were measured in PDGFRα+ cells. •  The abundance of SK3 channels in PDGFRα+ cells in detrusor muscles suggests that PDGFRα+ cells, not SMCs, provide apamin‐sensitive regulation of detrusor excitability.

Purinergic inhibitory regulation of murine detrusor muscles mediated by PDGFRα+ interstitial cells

Platelet‐derived growth factor receptor‐α‐positive (PDGFRα+) interstitial cells in detrusor muscles may participate in post‐junctional responses to neurotransmitters. PDGFRα+ interstitial cells express purinergic receptors (P2Y) and small conductance Ca2+‐activated K+ channels (mainly SK3). ATP elicited large amplitude outward currents and hyperpolarization in PDGFRα+ cells. SK channel blockers and a P2Y1 receptor antagonist blocked responses to ATP. ATP elicited only minor responses in PDGFRα+ cells of P2ry1−/− mice. ATP elicited transient inward currents in smooth muscle cells and purinergic receptor (P2X) agonists had no effect on PDGFRα+ cells. A specific P2Y1 receptor blocker decreased electrical field stimulation‐induced relaxation. Our findings provide an explanation for the purinergic relaxation of detrusor muscles and describe a novel mechanism for inhibitory regulation of bladder muscles that may control detrusor excitability during the filling phase.

A Novel Class of Interstitial Cells in the Mouse and Monkey Female Reproductive Tracts

ABSTRACT Growing evidence suggests important roles for specialized platelet-derived growth factor receptor alpha-positive (PDGFRalpha+) cells in regulating the behaviors of visceral smooth muscle organs. Examination of the female reproductive tracts of mice and monkeys showed that PDGFRalpha+ cells form extensive networks in ovary, oviduct, and uterus. PDGFRalpha+ cells were located in discrete locations within these organs, and their distribution and density were similar in rodents and primates. PDGFRalpha+ cells were distinct from smooth muscle cells and interstitial cells of Cajal (ICC). This was demonstrated with immunohistochemical techniques and by performing molecular expression studies on PDGFRalpha+ cells from mice with enhanced green fluorescent protein driven off of the endogenous promoter for Pdgfralpha. Significant differences in gene expression were found in PDGFRalpha+ cells from ovary, oviduct, and uterus. Differences in gene expression were also detected in cells from different tissue regions within the same organ (e.g., uterine myometrium vs. endometrium). PDGFRalpha+ cells are unlikely to provide pacemaker activity because they lack significant expression of key pacemaker genes found in ICC (Kit and Ano1). Gja1 encoding connexin 43 was expressed at relatively high levels in PDGFRalpha+ cells (except in the ovary), suggesting these cells can form gap junctions to one another and neighboring smooth muscle cells. PDGFRalpha+ cells also expressed the early response transcription factor and proto-oncogene Fos, particularly in the ovary. These data demonstrate extensive distribution of PDGFRalpha+ cells throughout the female reproductive tract. These cells are a heterogeneous population of cells that are likely to contribute to different aspects of physiological regulation in the various anatomical niches they occupy.

UTP activates small-conductance Ca2+-activated K+ channels in murine detrusor PDGFRα+ cells.

Purines induce transient contraction and prolonged relaxation of detrusor muscles. Transient contraction is likely due to activation of inward currents in smooth muscle cells, and prolonged relaxation may be due to activation of small-conductance Ca(2+)-activated K(+) (SK) channels via P2Y1 receptors expressed by detrusor PDGF receptor (PDGFR)α(+) cells. We investigated whether other subtypes of P2Y receptors are involved in the activation of SK channels in PDGFRα(+) cells of detrusor muscles. Quantitative analysis of transcripts revealed that P2ry2, P2ry4, and P2ry14 are expressed in PDGFRα(+) cells of P2ry1-deficient/enhanced green fluorescent protein (P2ry1(-/-)/eGFP) mice at similar levels as in wild-type mice. UTP, a P2Y2/P2Y4 agonist, activated large outward currents in detrusor PDGFRα(+) cells. SK channel blockers and an inhibitor of phospholipase C completely abolished currents activated by UTP. In contrast, UTP activated nonselective cation currents in smooth muscle cells. Under current-clamp (current = 0), UTP induced significant hyperpolarization of PDGFRα(+) cells. MRS2500, a selective P2Y1 antagonist, did not affect UTP-activated outward currents in PDGFRα(+) cells from wild-type mice, and activation of outward currents by UTP was retained in P2ry1(-/-)/eGFP mice. As a negative control, we tested the effect of MRS2693, a selective P2Y6 agonist. This compound did not activate outward currents in PDGFRα(+) cells, and currents activated by UTP were unaffected by MRS2578, a selective P2Y6 antagonist. The nonselective P2Y receptor blocker suramin inhibited UTP-activated outward currents in PDGFRα(+) cells. Our data demonstrate that P2Y2 and/or P2Y4 receptors function, in addition to P2Y1 receptors, in activating SK currents in PDGFRα(+) cells and possibly in mediating purinergic relaxation responses in detrusor muscles.

Phospholipase C-independent effects of 3M3FBS in murine colon

The muscarinic receptor subtype M(3) is coupled to Gq/11 proteins. Muscarinic receptor agonists such as carbachol stimulate these receptors that result in activation of phospholipase C (PLC) which hydrolyzes phosphatidylinositol 4,5-bisphosphate into diacylglycerol and Ins(1,4,5)P(3). This pathway leads to excitation and smooth muscle contraction. In this study the PLC agonist, 2, 4, 6-trimethyl-N-(meta-3-trifluoromethyl-phenyl)-benezenesulfonamide (m-3M3FBS), was used to investigate whether direct PLC activation mimics carbachol-induced excitation. We examined the effects of m-3M3FBS and 2, 4, 6-trimethyl-N-(ortho-3-trifluoromethyl-phenyl)-benzenesulfonamide (o-3M3FBS), on murine colonic smooth muscle tissue and cells by performing conventional microelectrode recordings, isometric force measurements and patch clamp experiments. Application of m-3M3FBS decreased spontaneous contractility in murine colonic smooth muscle without affecting the resting membrane potential. Patch clamp studies revealed that delayed rectifier K(+) channels were reversibly inhibited by m-3M3FBS and o-3M3FBS. The PLC inhibitor, 1-(6-((17b-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione (U73122), did not prevent this inhibition by m-3M3FBS. Both m-3M3FBS and o-3M3FBS decreased two components of delayed rectifier K(+) currents in the presence of tetraethylammonium chloride or 4-aminopyridine. Ca(2+) currents were significantly suppressed by m-3M3FBS and o-3M3FBS with a simultaneous increase in intracellular Ca(2+). Pretreatment with U73122 did not prevent the decrease in Ca(2+) currents upon m-3M3FBS application. In conclusion, both m-3M3FBS and o-3M3FBS inhibit inward and outward currents via mechanisms independent of PLC acting in an antagonistic manner. In contrast, both compounds also caused an increase in [Ca(2+)](i) in an agonistic manner. Therefore caution must be employed when interpreting their effects at the tissue and cellular level.

Premature contractions of the bladder are suppressed by interactions between TRPV4 and SK3 channels in murine detrusor PDGFRα cells.

During filling, urinary bladder volume increases dramatically with little change in pressure. This is accomplished by suppressing contractions of the detrusor muscle that lines the bladder wall. Mechanisms responsible for regulating detrusor contraction during filling are poorly understood. Here we describe a novel pathway to stabilize detrusor excitability involving platelet-derived growth factor receptor-α positive (PDGFRα+) interstitial cells. PDGFRα+ cells express small conductance Ca2+-activated K+ (SK) and TRPV4 channels. We found that Ca2+ entry through mechanosensitive TRPV4 channels during bladder filling stabilizes detrusor excitability. GSK1016790A (GSK), a TRPV4 channel agonist, activated a non-selective cation conductance that coupled to activation of SK channels. GSK induced hyperpolarization of PDGFRα+ cells and decreased detrusor contractions. Contractions were also inhibited by activation of SK channels. Blockers of TRPV4 or SK channels inhibited currents activated by GSK and increased detrusor contractions. TRPV4 and SK channel blockers also increased contractions of intact bladders during filling. Similar enhancement of contractions occurred in bladders of Trpv4−/− mice during filling. An SK channel activator (SKA-31) decreased contractions during filling, and rescued the overactivity of Trpv4−/− bladders. Our findings demonstrate how Ca2+ influx through TRPV4 channels can activate SK channels in PDGFRα+ cells and prevent bladder overactivity during filling.

AB297. SPR-24 Spinal cord injury and detrusor PDGFRα+ cells

Objective Neurogenic bladder dysfunction due to spinal cord injury (SCI) poses a significant threat to the well-being of patients. The complications of this condition include but not are limited to incontinence, renal impairment, urinary tract infection, stones, and poor quality of life. Clinical manifestations of SCI involve combination of storage and voiding bladder problems. Although a number of clinical studies have reported overactive bladder (OAB) after SCI, the pathophysiological mechanisms remain unclear. SCI is widely used to induce neurogenic bladder in rodent models. These animals exhibited dysfunctional condition results in different symptoms, ranging from acute urinary retention to an OAB or a combination of both. There is an abundance of PDGFRα+ cells in detrusor muscles. This cell involves the membrane stabilization via activation of SK channels in detrusor PDGFRα+ cells during filling. Thus we investigate the molecular and protein expression of PDGFRα+ cells from SCI mice to characterize the role of these cells that contributes to development of OAB in SCI. Methods SCI was induced by complete compression of T12-L1 spinal cord. Experiments were performed on 24, 48 and 72 hr after surgery. We employed molecular approaches and ex vivo cystometry. Pdgfrα and Kccn1−3 transcripts were analyzed for molecular expression. Ex vivo compliance was used for testing SK channel sensitivity in control and SCI mice. Results In quantitative analysis of transcripts, Pdgfrα and Kcnn3 transcripts in SCI detrusor were significantly decreased in a time-dependent manner after SCI surgery compared with control detrusor. In ex vivo cystometry, SCI bladder revealed an increase in the amplitude and frequency of non−voiding pressure responses during filling. Effects of a SK blocker (apamin) and a SK channel activator (SKA-31) were reduced in non-voiding contractions in SCI mice compared to control. Conclusions These findings support that downregulation of PDGFRα+ cells and SK channels in SCI detrusors might involve the development of OAB in SCI. Funding Source(s) NIDDK, RO1 DK098388

AB315. SPR-42 Cyclophosphamide-induced overactive bladder via downregulation of relaxation factors in detrusor PDGFRα+ cells

Objective Morphology and functional role of PDGFRα+ cells have been recently characterized in the detrusor muscle layer. Detrusor relaxation is caused by activation of small conductance Ca2+ activated-K+ (SK) channels and purinergic inhibitory responses in detrusor PDGFRα+ cells. Loss of PDGFRα+ cells or alteration of P2Y receptors and SK channels will affect detrusor excitability. Cyclophosphamide (CYP)-treated animals exhibited overactive bladder (OAB). We hypothesized that the downregulation of P2Y receptors and/or SK channels in PDGFRα+ cells will display the phenotype of CYP-induced OAB. Methods CYP was injected intraperitoneally in PDGFRα+/eGFP and SMC/eGFP mice. We harvested the detrusor muscle without urothelium and disperse the cells for the fluorescence activated cell sorting (FACS). Sorted PDGFRα+ cells and smooth muscle cells (SMCs) were used for molecular study to compare the changes in transcripts between CYP-injected and control group. Transcripts were examined included; Pdgfrα, P2ry1, P2ry2, P2ry4, Kcnn1, Kcnn2, Kcnn3 and inflammation marker (Il-6). Immunohistochemistry, mechanical contractility and ex vivo cystometry were also performed. Results Quantitative analysis of PCR revealed that CYP-injected detrusor muscle increased transcriptional expression of Il-6, but decreased the expression of Pdgfrα. Transcriptional changes in CYP-injected sorted PDGFRα+ cells from PDGFRα+/eGFP mice showed Pdgfα, Kccn3 (SK3), P2ry1, P2ry2 and P2ry4 genes were decreased compared with saline-injected control. Sorted SMCs from SMC/eGFP mice did not show significant expression of those genes and no detectable changes. Immunohistochemistry showed SK3 in PDGFRα immunoreactivity was downregulated in CYP-injected detrusor muscle. Apamin (a SK blocker) sensitivity on spontaneous contractile activity was decreased in CYP-injected mice compared to saline-injected mice. In ex vivo cystometry, increased spontaneous non-voiding contractions and less apamin sensitivity were observed in CYP-injected mice. Conclusions These findings are the first report to investigate the role of PDGFRα+ cells in relation to OAB mechanisms. In conclusion, we found that CYP-induced OAB is resulted from down regulation of PDGFRα, P2Y receptors and SK channels in CYP-injected bladder. These results provide novel mechanisms of functional role of PDGFRα+ cells on OAB. Funding Source(s) NIDDK, RO1 DK098388 and Urology Care Foundation Research Scholar Award (Interstitial Cystitis Association)