Hi, I'm busy working on proving it is worth testing interstitial cystitis patients for XMRV. Much of what I'm finding which is pointing to IC being XMRV related is similar to the ideas Dr. Light has had on both fibromyaligia. The idea that Dr. Light has had on fibro is that the muscle fatigue of fibromyalgia stems from the purinergic receptor malfunction. Dr. Light said that there are purinergic receptors which monitor ATP consumption and that these purinergic receptors send pain signals based on ATP to save muscle wear.
I'm finding something similiar with IC:
Studies have shown that when bladder epithelial cells are stretched they release ATP. In the bladders of people with interstitial cystitis, more extracellular ATP is released than in control patients.
Quote: (BMJ August 8th, 2009: 339:337-342)
(IC bladder uroepithelial cells released significantly higher concentrations of ATP (adenosine triphosphate) than control biopsies suggesting that ATP plays an important role in this syndrome. An investigation of cultured bladder epithelial cells showed that such cells have an abnormal, much higher concentration of ATP. This higher concentration of ATP decreases the ability of the bladder wall to conduct (channel) potassium ions which again indicates impaired potassium ion conduction is part of the pathology of interstitial cystitis.
Studies on ME/CFS have shown deficient ion channelopathy to be part of the pathology of ME/CFS. Some studies about ME/CFS and potassium conduction attribute this flaw to abnormal mitochondrial gene expression.
The BMJ article cited says studies on IC showing ATP increase and changes in potassium conduction as also resulting from abnormal gene expression.
I suggest the issue of ATP, potassium ion channelopathy as being the result of XMRV. Idiosyncratic production of ATP and its components such as purinergic receptors, ATP- binding cassettes (ABCs) and or ABC transporters is well documented in many other autoimmune diseases and can be fully attributed to the source of most IC symptoms.
I hypothesize these abnormalities are the result the presence of XMRV in interstitial cystitis, and occur through many different mechanisms, including viral mimicry and others.
The hypothesis that XMRV likely cause of significantly high release of ATP in bladder urothelial cells is supported by observed defects in ATP-binding cassette transporters, where XMRV viral mimicry of proteins is likely to have occurred..
About ATP Binding Cassettes
ATP-binding cassette transporters are members of a protein superfamily that is one of the largest and oldest proteins.
ABC transporters are transmembrane proteins that utilize the energy of adenosine triphosphate (ATP) hydrolysis to carry out certain biological processes including the translocation of various substrates across membranes and non-transport related processes such as translation of RNA and DNA repair. ABCs transport a wide variety of substrates across extra and intracellular membranes, including metabolic products, lipids and sterols, and drugs. Proteins are classified as ABC transporters based on the sequence and organization of their ATP-binding cassette (ABC) domain(s). ABC transporters are involved in tumor resistance, cystic fibrosis, bacterial multi drug resistance and a range of other inherited human diseases.
One of these diseases is Pseudoxanthoma Elasticum (PXE), a hereditary connective tissue disease in which proteoglycans have altered properties. In pseudoxanthoma elasticum there are abnormalities which show some relevance to interstitial cystitis. Both diseases show a relationship with sulfated glycosaminoglycans. The only difference is that in PXE, an inherited genetic defect in an ATP-binding cassette transporter identified as ABCC6/MRP6
The idea that ABCC6/MRP6 is the cause of PXE was tested in 2003 in Italy.
Proteoglycan metabolism in PXE was studied by Francesca Maccari, Dealba Gheduzzi and Nicola Vopi at the University of Modena, in Modena, Italy.
In this study, the researchers measured sulfated glycosaminoglycans in the urine of people with PXE, people carrying the disease and healthy controls. Sulfated glycosaminoglycans are what compose the mucosal lining of the human bladder, known as the GAG layer. The GAG layer is deficient in IC patients because the bladder epithelial cells which secrete GAG become compromised and cease to serve their function.
The glycosaminoglycans this study on PXE tested for were chondriotin sulfate disaccharide and heparan sulfate disaccharide. Note also that to treat interstitial cystitis, heparin sulfate is instilled into the bladder to augment the defective GAG layer. In Canada and elsewhere outside the U.S., chondriotin sulfate has been used with even better results than heparin sulfate as a bladder instillation, to help IC patients in those places.
In PXE 34% less of the polysaccharides were detected in the urine of PXE individuals, than controls or unaffected carriers of the genetic defect.
It is worth noting that the commonality between IC and PXE patients may extend beyond glycosaminoglycans being abnormally low. On the revealing of the genome for XMRV, a comparison of what human proteins the XMRV retrovirus mimics finds a link between the virus and ABC transporters.
A retrovirus is different from normal viruses. Normal viruses only have their DNA transcribed into RNA in the host, and the RNA is then translated into a protein. A retrovirus functions in a different way, which more adeptly inserts its genome into human DNA. Retroviruses have their RNA reverse-transcribed into DNA, which is then integrated into the hosts genome and then undergoes the usual transcription and translation processes to express the genes carried by the virus.
How this relates to the issue of XMRV and autoimmune diseases, its speculated that XMRV creates proteins which mimic those in the human body. The idea is that the fake DNA created by the virus initiates a response from the human immune system. Some believe that the human immune system becomes confused from the retroviral proteins which mimic its own proteins. This leads to the unending attack from the body on its own tissue.
There is an ATP-binding cassette associated with the viral mimicry of XMRV infection. It is called ABCC9:
It is known as EAW96452.1. This is an ATP-binding cassette of the subfamily C (CFTR/MRP), member 9, isoform ABCC9. XMRV GAG- PRO-POL was found to mimic the natural properties of this ABC.
Note that ABCC6 in PXE where altered levels of glycosaminoglycans is very closely related to ABCC9. Both of these ATP-binding cassettes are of the subfamily MRP.
However, a link between this possibly compromised ATP binding cassette know as ABCC9 and interstitial cystitis goes further than its proximity in nature to ABCC6.
Here is what the genome mapping project says about ABCC9
ABC proteins transport various molecules across extra and intra cellular membranes. ABC genes are divided into seven distinct subfamilies (ABC1, MDR/TAP, MRP, ALD, OABP, GCN20, White). This protein is a member of the MRP subfamily which is involved in multi-drug resistance. This protein is thought to form ATP sensitive potassium channels in cardiac, skeletal and vascular and non-vascular smooth muscle. Protein structure suggests a role as the drug-binding channel modulating subunit of the extra pancreatic ATP-sensitive potassium channels. Mutations in this gene are associated in cardiomyopathy dilated type 10. Alternative splicing results in multiple transcript variants.
Now we go back to the idea the BMJ article expressed; the idea that come IC pain comes from inability for the bladder epithelial cells in IC patients to channel potassium ions. Also issues involving dysfunctional bladder smooth muscle activity parallel a possible defect in ABCC9 as a causative agent in IC symptoms. Bladder spasms and pelvic floor muscle issues become clearer when the idea of viral mimicry of ABCC9, or other ABCs.
Potassium channeling function by ABCC9 also alludes to the co-morbidity of mitral valve prolapse in interstitial cystitis patients. This too is another trait common to both IC and CFS/ME. Furthermore, defective cassette binders have been linked to the lack of energy proliferation in the bodies of CFS patients. Potassium channeling has also been linked to the pain of fibromyalgia.
The studies of Dr. Light bind the idea that a defect in receptors in the muscle fiber of fibromyalgia patientsreceptors which detect levels of ATP used or not used by the body which is part of the role which ABCs and or ATP sensors like purinergic receptors play in the pathology of that disease.
This makes good enough sense to me. Looking at the many studies which show the prevalence of extracellular ATP in both human and feline IC patients, and furthermore, studies which demonstrate a clear link between extracellular ATP and pain in the human bladders, I have a good feeling about the stability of my hypothesis.
Studies regarding extracellular ATP causing pain in human bladders go far beyond IC research. There was a study performed in Sweden demonstrating that extracellular ATP and the purinergic receptors P2Y are responsible for the inflammatory response in human bladders exposed to the E coli bacteria. Or to put in simple terms, ATP and purinergic receptors which bind to ATP are responsible for the pain and inflammation in the common urinary tract infection.
Bladder stretching itself also causes the bladder epithelial cells to excrete ATP. Studies have ranged from hypothesizing that extracellular ATP serves a role as a signaling mechanism in the human body, where its release upon stretching the human bladder generates the feeling and urge to go. I blame the inability of ABC transporters to serve their role in transporting substrates through intra and extracellular membranes as being part of why some substances irritate IC bladders and cause no sensation of pain in people with normal bladder tissue.
I attribute the experience of interstitial cystitis as being largely dependent upon defective ATP-binding cassette behavior.
I suggest exercise works as an IC therapy because it uses up the extracellular ATP.
I will show proof for my argument in referring to a study which show that extracellular ATP is responsible for other IC anomalies, including the defect where tryptophan in IC patients is broken down into kynurenine over serotonin and melatonin. The indoleamine 2,3, dioxygenase pathway is the formal name for the modification of tryptophan into various other chemicals.
There is a study proving that extracellular ATP effects the maturation of human dendritic cells (immune cells), affecting the indoleamine pathway.
Extracellular adenosine triphosphate affects the maturation of human dendritic cells, mainly by inhibiting T-helper (Th 1) cytokines, promoting Th2 cytokines and modulating the expression of costimulatory molecules. In this study we report that adenosine triphosphate can induce immunosuppression through its own action on DCs, defining a new role for extracellular nucleotides. Microarray analysis of ATP-stimulated human DCs revealed an inter alia a drastic up-regulation of 2 genes encoding mediators involved in immunosuppression: thrombospondin-1 and indoleamine 2,3 dioxygenase.
Hypothesis 2
It is possible that bladder stretching in interstitial cystitis is the result of when the bladder is distended, abnormal ATP release and possibly more abnormalities enable the glycosaminoglycans heparin sulfate to allow viruses, bacteria or mycoplasma to penetrate the blood brain barrier.
It is known that bladder stretching causes cells to release ATP. This is one way physical changes alone can alter bladder surface biochemistry.
Furthermore, the amounts of extracellular ATP becomes more prevalent upon mechanical stretch can be reduced by chemicals already present in the bladder. In a study by Sun Y and Chai TC at the Division of Urology at the University of Maryland School of Medicine, both heparin sulfate and dimethyl sulphoxide (DMSO) reduce the higher levels of stretch activated ATP release in the bladders of people with interstitial cystitis.
The idea supported by the results of this study is that bladder epithelial cells (bladder urothelial cells or BUCs) are able to detect levels of ATP and rely upon ATP as a chemical messenger of sorts.
Here are links to ATP and IC correlations:
http://ajpcell.physiology.org/content/290/1/C27.full
http://www.plosone.org/article/info%...l.pone.0018704