Over the last two decennaries Urotensin II ( UII ) and Urotensin Related Peptide ( URP ) have been identified as endogenous peptides moving at the Urotensin II receptor ( UT ) . [ 1, 3, 4 ] All possess proposed activity and specificity in the kidney of mammalian species. [ ] and other craniate species. The function of URP in nephritic physiology is still to be confirmed, and specific functions in pathology yet to be eluded.
In vivo analysis of URP ‘s nephritic map, utilizing an anaesthetised rat theoretical account, will allow farther word picture of this peptide. Physiological elucidation of UII, URP, and UT on kidney map, will enable a greater grasp of disease map. Development of fresh curative marks requires cognition of receptors, ligands, and physiological effects. The context of the UII and UT system is already identified to be similar to other cardinal osmoregulatory ligands and receptors ; for which therapeutics are already available. To let for the optimal analysis of URP in an carnal theoretical account, old surveies should supply converting grounds back upingNormal kidney map in worlds is established via legion homeostatic mechanisms which allow all right control over urine end product, and hence elimination of metabolic waste merchandises. In a normal kidney there is a finely orchestrated hormone and exocrine secernments.
These serve legion intents, but chiefly function to regulated urine end product, with derivative effects on systemic blood force per unit area. Many biologically active peptides play of import functions in kidney map. With the aid of endocrines such as antidiuretic endocrine, aldosterone, and angiotonin II, the human organic structure can increase the permeableness of the roll uping canals in the kidney to resorb H2O and prevent it from being excreted. Four procedures occur in mammals:* filtration – unstable part of blood ( plasma ) is filtered from a uriniferous tubule ( functional unit of vertebrate kidney ) construction known as the glomerulus into Bowman ‘s capsule or glomerular capsule ( in the kidney ‘s cerebral mantle ) and flows down the proximal convoluted tubule to a “ u-turn ” called the Loop of Henle ( cringle of the uriniferous tubule ) in the myelin part of the kidney.
* resorption – most of the syrupy glomerular filtrate is returned to blood vass that surround the convoluted tubules.* secernment – the staying fluid becomes urine, which travels down roll uping canals to the medullary part of the kidney.* elimination – the piss ( in mammals ) is stored in the urinary vesica and exits via the urethra ; in other craniates, the urine mixes with other wastes in the cloaca before go forthing the organic structure ; ( toads besides have a urinary vesica ) .A cardinal illustration of such a regulative system is Renin-angiotensin.
Functions in osmoregulation
With the increasing incidence of chronic kidney disease, such as diabetic kidney disease, throughout the universe ; biologically active peptides with of import functions in the kidney homeostasis may turn out utile chances as drugable marks. With the classical illustration system ( RAS ) : Angiotensin II plays critical functions in the patterned advance of chronic kidney disease, via a stimulatory action on cell proliferation.
A renin inhibitor, aliskiren, has late been shown to be a clinically effectual drug to cut down albuminurias in patients with diabetic kidney disease. ( Pro ) renin receptor, a specific receptor forrenin and prorenin, was freshly identified as a member of the RAS. When edge to prorenin, ( pro ) reninreceptor activates the angiotensin I-generating activity of prorenin in the absence of cleavage of the prosegment, and straight stimulates the tract of mitogen-activated protein kinase independently from the RAS. The kidney peptides that antagonise the intrarenal RAS may hold renoprotective actions. Adrenomedullins, powerful vasodilative peptides, have been shown to hold renoprotective actions.UII, a powerful vasoconstrictive peptide, may advance the nephritic disfunction in chronic kidney disease together with the nephritic RAS. Thus, in add-on to the renin inhibitor and ( pro ) renin receptor, adrenomedullins and urotensin II may be fresh marks to develop curative schemes against chronic kidney disease.
GPCRs are one fo the prevailing research countries for the indentification of curative marks, therefore the word picture of this one time orphan receptor and its ligands could supply utile informations for future disease therapies. Current therapies aiming the renin-angiotensin system highlight the significance of UT and its ligands as valuable chancesThe maps of UT and UII will be examined to help in finding URP effects in vivo.The G-protein coupled receptor GPR14 was identified by legion groups around a decennary ago, and is confirmed to be the functional receptor for Urotensin II peptide ( which was originally isolated from teleost urophysis ) . GPR14 was allocated as the urotensin II receptor ( UT ) after… The human receptor has a 75 % homology with the rat receptor.
.The formal construction of UT clearly shows similarities with other GPCRs, and belongs to category A which are homologous with the visual purple receptor. ( which are ) ( ) shows a derived topology with seven transmembrane spheres. This construction, and ligand adhering pockets were identified utilizing mutational analysis
Activation & A ; Desensitisation
The chief transduction pathway associated with UT is the yoke and activation of the G?q/11 subtype of heterotrimeric G proteins [ 100 ] . Activation of G ?q/11 leads to an addition in inositol triphosphates [ 85 ] and mobilization of intracellular Ca2+ [ 4 ] .Greenwich mean time may besides match to G?i/o proteins which exhibit effects on Ca2+ mobilization and the phosphorylation provinces of ERK1/2 [ 20,33,109 ] . UT activation enables a RhoA-dependent addition in arterial smooth musculus contraction, cytoskeleton administration and aortal SMC proliferation [ 87 ] . On the one manus, Rho activation is normally associated with G?12/13 matching in GPCRs.
On the other manus, some contention exists as to the function of G?q/11 in Rho activation, as some surveies have clearly shown that G?q/11 is responsible for Rho activation [ 36,50,54,86,91 ] , whereas others have indicated that there is no such engagement [ 18,40,46,47 ] . UT may therefore match to G?12/13 in add-on to G?q/11 and G?i/o. However, the possibility that UT twosomes to G?12/13 remains to be investigated.As antecedently stated, activation of UT chiefly promotes intracellular Ca2+ mobilization [ 4 ] . Ca2+ channels, tyrosine kinases, p38MAPK, ERK1/2, RhoA/ROCK and the PKC/CPI-17 system are besides involved in vasoconstriction induced by UT activation [ 82,83,87,98 ] . The latter two tracts are besides involved in Ca sensitisation taking to myosin-light concatenation ( MLC ) phosphorylation [ 93 ]TMD motion may be restricted when the receptor is in an inactive conformation by intramolecular interactions [ ] .
Downstream effecter interactions would be promoted by agonist binding ; let go ofing restraints, and mutants within the receptor ; taking to constituent activation.Intracellular trafficking and internalization of UT has been specualted to follow mechanism similar to that of the angiotonin II type 1 receptor ( AT1 ) [ 57,106 ] , with [ et al ] show some of the mechanisms of UT receptor desensitisation utilizing an look system with Rat UT in COS-7 cells. They show “slow internalisation kinetics” initiated via a the clathrin-coated cavity tract. This is confirmed by the presence of “caveolins binding” sites on the carboxy-terminal of UT [ ] .
Inhibition of this tract, via the usage of saccharose, “does non wholly block internalisation of the UT receptor” . Therefore, beta-arrestin coupled internalization may be another account. There is grounds back uping both beta-arrestin dependant and independent internalization.
In conformity with observations for AT1 ; UT may follow an angonist-dependent ( UII/URP ) synergism of these tracts. What remains clear is the mechanism for UT internalization required farther probe [ ]As with the bulk of GPCRs agonist binding is required for the activation of UT. The bulk of adhering in category A GPCRs occurs within the ECLs of the receptor, with an extra aqueous “pocket” of “binding determinants” formed by the seven TMDs. However if the UT has conserved functional homology with AT1, so peptide adhering will happen in the TMDs ; evocative of GPCR activation by little aminoalkanes.The conserved cyclic C-terminus of UII has been confirmed by structure-activity relationship ( SAR ) as the chief determiner for binding and activation of UT. This part is extremely conserved over a broad scope of species, the N-terminal part shows species speficity. The disulphide span of UT is a cardinal determiner of ligand binding, and is proposed to interact with WKY residues of UII.
Substitution of residues organizing the disulphide span, or WKY residues ( of UII cyclic part ) drastically cut down the activity of UII. URP besides possesses the cyclic part of UII, and hence is able to adhere and trip UT, without an N-terminal part.Therefore far UT receptor messenger RNA look has been shown as greatest in CNS tissues ( ref ) . With the highest degrees in the encephalon messenger RNA was besides found to be present in “key osmoregulatory epithelial tissue, gill, kidney, vesica, and gut” . The receptor showed the highest localization of function of immunoreactivity in vascular parts of the kidney and gills [ ] . These parts are symphonic with mRNA look of the natural ligand U-II.Using a UT smasher mouse to determine ligands for the receptor, Behm et Al ( 2003 ) show UII to be the the lone vasoactive ligand moving at UT. [ ] They besides exclude the being of receptor subtypes.
– besides the defects of utilizing mouse theoretical account for reproduction of vasoactive neurohormones [ ]In drumhead, as with legion other peptidergic GPCRs, U-II binding determiners are located in the ECLs and the top part of the transmembrane domains. It is of involvement that those receptor determiners of import for adhering the cyclic part of U-II are located in the top part of the TMDs, as is the instance with little aminergic GPCRs.
The cyclic peptide UII was has a conserved terminal hexapeptide sequence between species allowing functional checks in murine theoretical accounts. Its effects vary significantly depending on species and location of UT. Its vasoconstrictive actions appear to be mediated by calcium-ion mobilisation, via the activation of signalling tracts including ; tyrosine kinase, p38 MAPK, ERK 1/2 and Ca channels. The vasodilative action of UII is thought to be Nitric Oxide and endothelium dependant. [ 2 ]
Indentification and History
Initially considered a neurologically active endocrine, preponderantly moving in the caudate neurosecretory system ( CNSS ) , the find that UII is besides expressed in the CNS, and encephalon of Amphibians ( and in the last decennary: worlds ) prompted more strict word picture, and isolation, of the peptide. This established the conserved cyclic hexapeptide described earlier ( -Cys-Phe-Trp-Lys-Tyr-Cys- ) , which is shared between all craniate UII sequences.
Analysis of flounder ( Platichthys flesus ) genomic and complementary DNA by Lu et Al ( 2006 ) showed the being of four UII coding DNAs. Further probe indicated a similar coding DNA ( four ) and noncoding DNA ( three ) agreement conserved between the human and Fugu Rubripes UII cistron. Located on chromosome 1p36, human UII has similar cistron neighbors ( upstream and downstream ) to those shown in fugu with the same predicted written text way. This is of evolutionary and functional relevancy as conserved cistrons, and boosters, suggest historical importance the UII cistron bunch.
( exposing cistrons in close propinquity? ? ? )Coinciding with initial surveies utilizing fish ; urotensin II acquired its name via: ability to excite smooth musculus, and “contract trout hindgut preparations” . In the 1980s work by assorted groups identified assorted functions of UII in murine species. The presence of receptor for the peptide ligand was besides indentified utilizing iodized UII derived from Gillichthys. These preliminary theoretical accounts provided strong grounds for the being of a UII system in mammals, nevertheless, decennary passed before mammalian UII look ; and affinity for GPR14, was confirmed
Vascular action in Mammals
Early surveies in non-human Primatess indicated a potent UII action on the vascular system ( Ames et al 1999 ) . [ ] Further to these initial observations a far more complex function for UII is developing.
The outgrowth of UII as a 100-fold more powerful arterial spasmogen ( in rats and worlds ) than endothelin I [ ] supports douglas et Al ‘s suggestion that the binding of UII to the UT receptor is “pseudo-irreversible” and the ordinance of vascular tone is via a chronic, ( instead than acute modulatory ) , mechanism. There is besides grounds back uping the vasodilatory action of UII [ ] .The evident contradictory vasodilator/vasoconstrictor actions of UII are shown to be instrumented by the distribution of the UT receptor. [ ] UT receptors located on endothelium trigger vasodilatory response ; UT receptors on smooth musculus mediate vasoconstrictive effects. Discrete receptor location supports possible paracrine and endocrinal actions of UII, and conceptual variableness of UII physiological actions [ ] .Adding farther complexness to the contrasting vasodilator/constrictor actions: Prosser et al guess the usage of non-native peptides ; bring oning misdirecting physiological responses in vivo. Their informations supports proposals that N terminal fluctuation of UII leads to change authority at the UT receptor in different species.
[ ] This may assist to avoid confusing literature [ ] , utilizing merely the conserved cyclic part of UII as the quintessential constituent for biological activity. [ ] .
Renal action & A ; Osmoregulation
The functions of UII in osmoregulatory physiology in lower craniates is good established [ ] , taking to more recent scrutiny in mammals. ( In fish ) , the actions of UII are preponderantly involved with Na and chloride ion homeostatic balance. Transferral of flounder between fresh H2O and sea H2O induced rapid alterations in UII plasma concentrations.
Saltwater fish showed higher basal degrees of urophysial peptide, foregrounding its importance in keeping unstable balance. [ ] Further to surveies in fish, the kidney presented an obvious gap for probe of UII engagement in mammalian osmoregulation.The designation of high UII degrees in both rat and human piss [ ] ( comparative to plasma ) , suggests that the UII is preponderantly a nephritic peptide in these species. Ashton ( 2006 ) province that the kidney appears to be a major beginning of UII synthesis in mammals [ ] . Localization of function to the promixmal tubules and both interior and outer myelin via immunostaining corroborates with higher UII mRNA look in the myelin. [ ] and lower UII messenger RNA in the cerebral mantle observed in both worlds [ ] and rats [ ]
Whilst there are legion conflicting surveies with respect to UII influence on nephritic map [ ] , Song et Al ( 2006 ) administer urantide ( a potent UT receptor adversary [ ] ) , demoing an “increase in GFR alongside an addition in Na and chloride excretion” . This supports converting informations from [ ] [ ] connoting that endogenous UII activity lowers GFR and ion elimination in the kidney. Clearance of UII is either exceeds creatinine in normal human subjects.
Supporting this information [ ] [ ] show the actions of exogenic UII to hold comparable activity in anaesthetised rats.There are a few accounts of the discretion of GFR informations, one of which is the bringing and dose of UII to the studied animate being. Bolus dosage of UII appear to act upon nephritic vasculature, cut downing GFR ind a dose dependent manor. Continuous extract of UII consequences in a more modest decrease in GFR, but with a addition in filtered chloride. [ ] This action of UII reflects the earlier surveies in fish, and may be due to activation of UT receptors in the distal tubule or cringle of henle. Another account for disagreements in informations suggested by Douglass et Al is that UT receptors are preponderantly occupied by endogenous UII.
As stated antecedently the “pseudo irreversible” binding of UII, and usage of non-native peptides, may foretell the variable responses displayed in several instances.More late Abdel-Razik et Al show converting grounds back uping the theory that non merely does UII hold effects on nephritic vasculature, but besides to suppress conveyance of Na+ and K+ ions across epithelial tissue in the nephritic tubules. [ ] Importantly the information represents extract of UII within a determined physiological scope ( pmol ) . It becomes clear that the effects of higher doses of administered UII cut down urine flow and solute elimination rates ; but overall decreased GFR seems to account for these alterations.
Lower dose UII evoked an evident lessening in resorption of K and Na ions. This offers a far better account for the disagreements in informations produced by legion other groups ; whose concentrations of UII ( bolus or changeless extract ) tend to be in the nanomolar range.Song et al support this thought, happening that “sodium elimination was still reduced 1hr after UII injection, despite GFR holding returned to command levels” .
Surveies performed by Abdel-Razik et Al ( 2008 ) show a possible nexus between UII and the angiotonin II. A changeless extract of UII induced a dose-related decrease of AngII concentration in the piss of rats. [ ] [ ] antecedently reported by Wang/Lama. Any specific interaction was non confirmed, so it appears the decreased concentration in piss was preponderantly due to a decrease in filtered Ang II.
Activity of the UII system has been associated with a figure of human diseases, with go arounding degrees of UII elevated in congestive bosom disease, coronary arteria disease, and diabetes.[ It has been established that Urotensin II has of import physiological maps, with peculiar note in ordinance of blood force per unit area.
Endogenous rat UII appears to lend to glomerular filtration rate, urine flow, and sodium elimination rates in anaesthetised rat theoretical accounts ( WKY & A ; SHR rats ) . ]The presented ‘housekeeping ‘ function of UII. mRNA look of UII and its receptor have been reported as elevated spontaneously hypertensive rats. [ ] The importance of UII inWithIn most instances the true function of UII ( antiphonal or contributory, protective or causal ) is yet to be ascertained, backing continued research and investingand engagement in diabetesThe function of UII and UT in nephritic diseaseUrotensin-II Related Peptide
Structure cistron homology
“URP is an octapeptide with a high grade of homology with the cyclic part of the UII molecule, which is critical for the biological activity of UII.
” This part is illustrated in ”” The mature signifier of UII peptides in carp, toad, hog, and human species can easy be predicted from their precursors due to the being of ( Arg-Lys-Arg or Lys-Lys-Arg ) processing sites. ] , prepro URP.Human and rat UII make non possess these proteolytic cleavage sites,
Song et Al show the distribution of URP in rat kidney as “comparable with that for UII” .Following the more extended surveies with UII, URP is besides considered a rule ligand for UT, and the lone bing ligand in the rat encephalon.
mRNA look of URP is of a similar distribution to that of UII, therefore it would look sensible for URP to hold similar action at the same receptors. Mori et al indicate that URP “exists in the rat encephalon as the exclusive UII-immunoreactive substance” . [ ]Sugo et al demonstrate that URP besides binds to the UII receptor with high affinity, and in vivo, URP induces a similar hypotensive consequence in anaesthetised rats.Antagonism.
.This does non, nevertheless, separate the effects of UII from any effects URP may hold at the same receptors.The high authority of URP for intracellular Ca2+ mobilisation shown by Mori… can be compared to those shown for human UII in a similar look system.
Takahashi et al show a important addition in the mRNA look degrees of URP in the aorta and kidney of spontaneously hypertensive rats.
Previous surveies have indicated UII to be a… active peptide, widely expressed in a assortment of tissues, in a assortment of different species. UII has variable, and conflicting, effects on vascular beds, and therefore these should non supply the footing for farther probe of URP. Data is far more conclusive with respects to osmoregulation in the kidneys, irrespective of the species involved. With the effects of UII dosage in a physiological scope, the statement for analysis of URP nephritic map entirely is peculiarly clear.
The overall effects of UT receptor activation are still yet to be established, as there is huge volume of informations regarding.. the distribution of the receptor, and the signalling Cascadess downstream of the GPCR.URP in rats as a prognostic theoretical account for human URP in footings of physiology, and possible pathology, can be confidently utilized due to its strong similarities to human URP. These similarities are non sole URP itself, but besides to the UT receptor, and other endogenous ligand, UII. The importance of characterizing the actions of URP is non merely restricted to the kidney, but other tissues, including encephalon and nervous tissues.
However the kidney will be the focal point of in vivo work, where the functions of UII are more clearly defined. At present it is ill-defined what part URP has on nephritic map, but it would be assumed that the effects will be similar to UII. This seems a just premise to do provided with current informations, which suggests URP holding similar affinity and authority at UT to the initial ligand UII.Several groups have identified adversaries for both UII and URP, In the hereafter it would be good to determine antibodies capable of observing both signifiers of the peptide, to visually corroborate distribution of mRNA look.
It has can be speculated that URP will exercise similar effects to UII when administered as a uninterrupted extract in an anaesthetised rat theoretical account. URP should either exercise the same physiological profile on nephritic homeostasis as UII or illicit an wholly unexpected response. Concentrations of UII at degrees outside of physiological bounds has been shown to hold variable effects on vasculature, and filtration. The same rules should be applied to the probe of URP on nephritic map.
Using continous extract of URP at degrees within a physiological scope should determine the functions of this peptide, excepting influences causative to vascular alterations. For illustration “pseudo-irreversible adversary where dissociation from its blood relation receptor is so slow that re-equilibration is non achieved at the clip the response is measured.”1. Ames, R.S.
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