Ca(2+)/calmodulin-dependent protein kinase II is associated with pelvic pain of neurogenic cystitis

Mechanisms of oxidative stress in interstitial cystitis/bladder pain syndrome

Interstitial cystitis/bladder pain syndrome (IC/BPS) is characterized by bladder and/or pelvic pain, increased urinary urgency and frequency and nocturia. The pathophysiology of IC/BPS is poorly understood, and theories include chronic inflammation, autoimmune dysregulation, bacterial cystitis, urothelial dysfunction, deficiency of the glycosaminoglycan (GAG) barrier and urine cytotoxicity. Multiple treatment options exist, including behavioural interventions, oral medications, intravesical instillations and procedures such as hydrodistension; however, many clinical trials fail, and patients experience an unsatisfactory treatment response, likely owing to IC/BPS phenotype heterogeneity and the use of non-targeted interventions. Oxidative stress is implicated in the pathogenesis of IC/BPS as reactive oxygen species impair bladder function via their involvement in multiple molecular mechanisms. Kinase signalling pathways, nociceptive receptors, mast-cell activation, urothelial dysregulation and circadian rhythm disturbance have all been linked to reactive oxygen species and IC/BPS. However, further research is necessary to fully uncover the role of oxidative stress in the pathways driving IC/BPS pathogenesis. The development of new models in which these pathways can be manipulated will aid this research and enable further investigation of promising therapeutic targets.

The Unmet Needs for Studying Chronic Pelvic/Visceral Pain Using Animal Models

The different definitions of chronic pelvic/visceral pain used by international societies have changed over the years. These differences have a great impact on the way researchers study chronic pelvic/visceral pain. Recently, the role of systemic changes, including the role of the central nervous system, in the perpetuation and chronification of pelvic/visceral pain has gained weight. Consequently, researchers are using animal models that resemble those systemic changes rather than using models that are organ- or tissue-specific. In this review, we discuss the advantages and disadvantages of using bladder-centric and systemic models, enumerating some of the central nervous system changes and pain-related behaviors occurring in each model. We also present some drawbacks when using animal models and pain-related behavior tests and raise questions about possible, yet to be demonstrated, investigator-related bias. We also suggest new approaches to study chronic pelvic/visceral pain by refining existing animal models or using new ones.

AOAH remodels arachidonic acid-containing phospholipid pools in a model of interstitial cystitis pain: A MAPP Network study

Interstitial cystitis/bladder pain syndrome (IC) is a debilitating condition of chronic pelvic pain with unknown etiology. Recently, we used a genetic approach in a murine model of IC to identify the lipase acyloxyacyl hydrolase (AOAH) as a modulator of pelvic pain. We found that AOAH-deficient mice have elevated pelvic pain responses, and AOAH immunoreactivity was detected along the bladder-brain axis. Lipidomic analyses identified arachidonic acid (AA) and its metabolite PGE₂ as significantly elevated in the sacral spinal cord of AOAH-deficient mice, suggesting AA is a substrate for AOAH. Here, we quantified the effects of AOAH on phospholipids containing AA. Spinal cord lipidomics revealed increased AA-containing phosphatidylcholine in AOAH-deficient mice and concomitantly decreased AA-phosphatidylethanolamine, consistent with decreased CoA-independent transferase activity (CoIT). Overexpression of AOAH in cell cultures similarly altered distribution of AA in phospholipid pools, promoted AA incorporation, and resulted in decreased membrane fluidity. Finally, administration of a PGE₂ receptor antagonist reduced pelvic pain in AOAH-deficient mice. Together, these findings suggest that AOAH represents a potential CoA-independent AA transferase that modulates CNS pain pathways at the level of phospholipid metabolism.

Altered expression of itch‑related mediators in the lower cervical spinal cord in mouse models of two types of chronic itch

In this study, we focused on several itch-related molecules and receptors in the spinal cord with the goal of clarifying the specific mediators that regulate itch sensation. We investigated the involvement of serotonin receptors, opioid receptors, glia cell markers and chemokines (ligands and receptors) in models of acetone/ether/water (AEW)- and diphenylcyclopropenone (DCP)-induced chronic itch. Using reverse transcription-quantitative polymerase chain reaction, we examined the expression profiles of these mediators in the lower cervical spinal cord (C5-8) of two models of chronic itch. We found that the gene expression levels of opioid receptor mu 1 (Oprm1), 5-hydroxytryptamine receptor 1A (Htr1a) and 5-hydroxytryptamine receptor 6 (Htr6) were upregulated. Among the chemokines, the expression levels of C-C motif chemokine ligand (Ccl)21, Cxcl3 and Cxcl16 and their receptors, Ccr7, Cxcr2 and Cxcr6, were simultaneously upregulated in the spinal cords of the mice in both models of chronic itch. By contrast, the expression levels of Ccl2, Ccl3, Ccl4 and Ccl22 were downregulated. These findings indicate that multiple mediators, such as chemokines in the spinal cord, are altered and may be central candidates in further research into the mechanisms involved in the development of chronic itch.

Neurochemical difference between somato- and viscero-projecting sensory neurons in the pig

The chemical coding of porcine somato (skin)- and viscero (urinary bladder)-projecting sensory neurons have been studied and compared using immunohistochemistry. Cell bodies of skin and bladder afferents were identified following Fast Blue injections into the skin of the hind leg as well as into wall of the urinary bladder, respectively. Immunohistochemistry revealed that small and medium-sized neurons projecting to both skin and bladder contained all of the studied substances i.e. substance P (SP), calcitonin gene-related pepide (CGRP), transient receptor potential vanilloid (TRPV1), lectin from Bandeiraea simplicifolia - Griffonia simplicifolia isolectin B4 (IB4) and galanin (GAL). Moreover, small-sized sensory neurons projecting to the bladder and skin of hind leg showed predominantly immunoreactivity to SP and TRPV1 and CGRP, as well as to CGRP and TRPV1 and IB4. It is worth stressing that the subset of sensory neurons innervating the skin exhibited these substances more often than bladder-projecting neurons. In addition, medium-sized skin-projecting neurons contained SP/GAL; SP/CGRP and CGRP/IB4 much more often than their bladder counterparts. On the other hand, small-sized perikarya that innervate the skin were less frequently expressed TRPV1, CGRP and GAL than the bladder-projecting neurons. In conclusion, the present report describes, for the first time, significant differences in the chemical coding between somato- and viscero-projecting sensory neurons in dorsal root ganglia. Moreover, these results provide morphological basis for further functional studies, which may explain the exact roles played by various subpopulations of somato- and viscero-projecting sensory neurons.

A MAPP Network study: overexpression of tumor necrosis factor-α in mouse urothelium mimics interstitial cystitis

Interstitial cystitis/bladder pain syndrome is a chronic bladder condition associated with pain and voiding dysfunction that is often regarded as a neurogenic cystitis. Patient symptoms are correlated with the presence of urothelial lesions. We previously characterized a murine neurogenic cystitis model that recapitulates mast cell accumulation and urothelial lesions, and these events were dependent on TNF. To further explore the role of TNF in bladder inflammation and function, we generated a transgenic mouse model with chronic TNF overexpression in urothelium under the control of the uroplakin II (UPII) promoter. Transgenic mouse lines were maintained by backcross onto wild-type C57BL/6J mice and evaluated for pelvic tactile allodynia as a measure of visceral pain, urinary function, and urothelial lesions. TNF mRNA and protein were expressed at greater levels in bladders of UPII-TNF mice than in those of wild-type mice. UPII-TNF mice showed significantly increased urinary frequency and decreased void volume. UPII-TNF mice had increased urothelial apoptosis and loss of urothelial integrity consistent with urothelial lesions. Overexpression of TNF was also associated with pelvic tactile allodynia. Consistent with these findings, UPII-TNF mice exhibited increased bladder afferent activity in response to stretch ex vivo. In summary, UPII-TNF mice display significant pelvic pain, voiding dysfunction, urothelial lesions, and sensory input. Thus UPII-TNF mice are a model for characterizing mechanisms of interstitial cystitis symptoms and evaluating therapies.

Distribution and neurochemistry of porcine urinary bladder-projecting sensory neurons in subdomains of the dorsal root ganglia: A quantitative analysis

The aim of the present study has been to verify the inter- and intraganglionic distribution pattern of porcine urinary bladder-projecting (UBP) neurons localized in the sacral dorsal root ganglia (DRGs). The morphology and chemical phenotype of these cells have also been investigated. These neurons were visualized using the fluorescent tracer Fast Blue (FB) which was injected bilaterally into the urinary bladder wall of five juvenile female pigs. The intraganglionic distribution showed that small- and medium-sized FB+ perikarya were mainly located in the central (S₃-S₄) and periphero-central (S₂) region of the ganglia, while large cells were heterogeneously distributed. Immunohistochemistry revealed that the most frequently observed markers in small and medium-sized UBP perikarya were: neurofilament 200, lectin from Bandeiraea simplicifolia (Griffonia simplicifolia) isolectin B4, substance P, calcitonin gene-related peptide, pituitary adenylate cyclase-activating polypeptide and transient receptor potential vanilloid 1. Moreover, UBP neurons containing these substances were also mainly observed in the central and periphero-central region of the ganglion. Differences in the percentage of traced cells and their neuropeptide content were observed between the S₂, S₃ and S₄ DRGs. In conclusion, the present study, for the first time, describes the arrangement of UBP DRGs neurons within particular subdomains of sacral ganglia, taking into account their size and chemical phenotype.

Acyloxyacyl hydrolase modulates pelvic pain severity

Chronic pelvic pain causes significant patient morbidity and is a challenge to clinicians. Using a murine neurogenic cystitis model that recapitulates key aspects of interstitial cystitis/bladder pain syndrome (IC), we recently showed that pseudorabies virus (PRV) induces severe pelvic allodynia in BALB/c mice relative to C57BL/6 mice. Here, we report that a quantitative trait locus (QTL) analysis of PRV-induced allodynia in F2_CxB progeny identified a polymorphism on chromosome 13, rs6314295 , significantly associated with allodynia (logarithm of odds = 3.11). The nearby gene encoding acyloxyacyl hydrolase ( Aoah) was induced in the sacral spinal cord of PRV-infected mice. AOAH-deficient mice exhibited increased vesicomotor reflex in response to bladder distension, consistent with spontaneous bladder hypersensitivity, and increased pelvic allodynia in neurogenic cystitis and postbacterial chronic pain models. AOAH deficiency resulted in greater bladder pathology and tumor necrosis factor production in PRV neurogenic cystitis, markers of increased bladder mast cell activation. AOAH immunoreactivity was detectable along the bladder-brain axis, including in brain sites previously correlated with human chronic pelvic pain. Finally, AOAH-deficient mice had significantly higher levels of bladder vascular endothelial growth factor, an emerging marker of chronic pelvic pain in humans. These findings indicate that AOAH modulates pelvic pain severity, suggesting that allelic variation in Aoah influences pelvic pain in IC.

Altered expression of target genes of spinal cord in different itch models compared with capsaicin assessed by RT-qPCR validation

Spinal cord plays a central role in the development and progression of pathogenesis of obstinate pruritus. In the current study, four groups of adult male C57Bl/6 mice were investigated; one group treated with saline, while the other groups intradermally injected with compound 48/80, histamine, α-Me-5-HT and capsaicin (algogenic substance), respectively. The intradermal microinjection of pruritic and algogenic compound resulted in a dramatic increase in the itch/algogenic behavior. Analysis of the microarray data showed that 15 genes in spinal cord (C5-C8) were differentially expressed between control group and 48/80 group, in which 9 genes were up-regulated and 6 genes were down-regulated. Furthermore, the results of RT-qPCR validation studies in C5-C8 spinal cord revealed that the 9 mRNA (Sgk1, Bag4, Fos, Ehd2, Edn3, Wdfy, Corin, 4921511E18Rik and 4930423020Rik) showed very different patterns for these different drugs, especially when comparing α-Me-5-HT and capsaicin. In three itch models, Fos and Ehd2 were up-regulated whereas Corin, 4921511E18Rik and 4930423020Rik were down-regulated. Furthermore, Corin and 4930423020Rik were down-regulated in itch model group compared to capsaicin group. Thus the application of microarray technique, coupled with RT-qPCR validation, further explain the mechanism behind itching evoked by pruritic compounds. It can contribute to our understanding of pharmacological methods for prevention or treatment of obstinate pruritus.

Host Responses to Urinary Tract Infections and Emerging Therapeutics: Sensation and Pain within the Urinary Tract

Urinary tract infection (UTI) pathogenesis is understood increasingly at the level of the uropathogens and the cellular and molecular mediators of host inflammatory responses. However, little is known about the mediators of symptoms during UTI and what distinguishes symptomatic events from asymptomatic bacteriuria. Here, we review bladder physiology and sensory pathways in the context of an emerging literature from murine models dissecting the host and pathogen factors mediating pain responses during UTI. The bladder urothelium is considered a mediator of sensory responses and appears to play a role in UTI pain responses. Virulence factors of uropathogens induce urothelial damage that could trigger pain due to compromised bladder-barrier function. Instead, bacterial glycolipids are the major determinants of UTI pain independent of urothelial damage, and the O-antigen of lipopolysaccharide modulates pain responses. The extent of pain modulation by O-antigen can have profound effects, from abolishing pain responses to inducing chronic pain that results in central nervous system features reminiscent of neuropathic pain. Although these effects are largely dependent upon Toll-like receptors, pain is independent of inflammation. Surprisingly, some bacteria even possess analgesic properties, suggesting that bacteria exhibit a wide range of pain phenotypes in the bladder. In summary, UTI pain is a complex form of visceral pain that has significant potential to inform our understanding of bacterial pathogenesis and raises the specter of chronic pain resulting from transient infection, as well as novel approaches to treating pain.

Mast Cell-Mediated Mechanisms of Nociception

Mast cells are tissue-resident immune cells that release immuno-modulators, chemo-attractants, vasoactive compounds, neuropeptides and growth factors in response to allergens and pathogens constituting a first line of host defense. The neuroimmune interface of immune cells modulating synaptic responses has been of increasing interest, and mast cells have been proposed as key players in orchestrating inflammation-associated pain pathobiology due to their proximity to both vasculature and nerve fibers. Molecular underpinnings of mast cell-mediated pain can be disease-specific. Understanding such mechanisms is critical for developing disease-specific targeted therapeutics to improve analgesic outcomes. We review molecular mechanisms that may contribute to nociception in a disease-specific manner.

Cdk5: An Emerging Kinase in Pain Signaling

Pain is an important survival mechanism for an organism. It can turn into severe mental and physical disorder however, if the molecular and/or cellular pathways involved in pain signaling are altered. Chronic pain is characterized by an altered pain perception that includes allodynia (a response to a normally non-noxious stimulus) and hyperalgesia (an exaggerated response to a normally noxious stimulus). Past few years of pain research has been mainly focused on precise understanding of the molecular and cellular nociceptive signatures altered during chronic pain, so that more effective pain relievers can be developed. The importance of protein kinases in normal cellular homeostasis and disease pathogenesis has evolved rapidly in the past few decades. The recent advancement defining the role of multiple protein kinases in regulating neuronal plasticity and pain sensitization has gained enough attention of pharmaceutical industry to develop specific and selective kinase inhibitors as analgesics. Cyclin-dependent kinase 5 (Cdk5) is one such emerging kinase in pain biology. We will discuss here the recent advancement and therapeutic potential of Cdk5 in pain signaling.