Tuberoinfundibular peptide of 39 residues: a new mediator of cardiac function via nitric oxide production in the rat heart

Identification of vascular dementia and Alzheimer's disease hub genes expressed in the frontal lobe and temporal cortex by weighted co-expression network analysis and construction of a protein-protein interaction

Background: It is difficult to distinguish cognitive decline due to AD from that sustained by cerebrovascular disease in view of the great overlap. It is uncertain in the molecular biological pathway behind AD and VaD.Objective: Our study aimed to explore the hub molecules and their associations with each other to identify potential biomarkers and therapeutic targets for the AD and VaD.Methods: We screened the differentially expressed genes of AD and VaD, used weighted gene co-expression network analysis and then constructed a VaD-AD-specific protein-protein interaction network with functional annotation to their related metabolic pathways. Finally, we performed a ROC curve analysis of hub proteins to get an idea about their diagnostic value.Results: In the frontal lobe and temporal cortex, hub genes were identified. With regard to VaD, there were only three hub genes which encoded the neuropeptides, SST, NMU and TAC1. The AUC of these genes were 0.804, 0.768 and 0.779, respectively. One signature was established for these three hub genes with AUC of 0.990. For the identification of AD and VaD, all hub genes were receptors. These genes included SH3GL2, PROK2, TAC3, HTR2A, MET, TF, PTH2R CNR1, CHRM4, PTPN3 and CRH. The AUC of these genes were 0.853, 0.859, 0.796, 0.775, 0.706, 0.677, 0.696, 0.668 and 0.652, respectively. The other signature was built for eleven hub genes with AUC of 0.990.Conclusion: In the frontal lobe and temporal cortex regions, hub genes are used as diagnostic markers, which may provide insight into personalized potential biomarkers and therapeutic targets for patients with VaD and AD.

Relationship between seminal plasma tuberoinfundibular peptide of 39 residues and sperm functional attributes in buffalo (Bubalus bubalis)

The buffalo seminal plasma protein profile and its relationship with sperm quality have not been studied in detail. Thus, the aim of the present study was to profile buffalo seminal plasma proteins and to assess the relationship between differentially expressed proteins and sperm characteristics. Semen samples (n = 44) were collected from 11 Murrah buffalo bulls (four ejaculates from each animal) and seminal plasma protein profiling was performed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Matrix-assisted laser desorption ionisation time-of-flight analysis of one of the differentially expressed proteins, namely the 11-12 kDa protein, identified it as tuberoinfundibular peptide of 39 residues (TIP39). Western blot analysis confirmed the presence of TIP39, with TIP39 expression in seminal plasma varying among bulls. Based on TIP39 levels, bulls were classified into two groups, those with high and low protein. The percentages of spermatozoa positive for mitochondrial membrane potential test, chromatin distribution test, synthetic media sperm penetrability test and acrosomal integrity test were significantly (P < 0.05) high in the high protein group. The present study is the first to demonstrate the presence of TIP39 in buffalo seminal plasma and the positive effect of TIP39 on the functional parameters and fertilising ability of spermatozoa.

Model of the complex of Parathyroid hormone-2 receptor and Tuberoinfundibular peptide of 39 residues

BACKGROUND

We aim to propose interactions between the parathyroid hormone-2 receptor (PTH2R) and its ligand the tuberoinfundibular peptide of 39 residues (TIP39) by constructing a homology model of their complex. The two related peptides parathyroid hormone (PTH) and parathyroid hormone related protein (PTHrP) are compared with the complex to examine their interactions.

FINDINGS

In the model, the hydrophobic N-terminus of TIP39 is buried in a hydrophobic part of the central cavity between helices 3 and 7. Comparison of the peptide sequences indicates that the main discriminator between the agonistic peptides TIP39 and PTH and the inactive PTHrP is a tryptophan-phenylalanine replacement. The model indicates that the smaller phenylalanine in PTHrP does not completely occupy the binding site of the larger tryptophan residue in the other peptides. As only TIP39 causes internalisation of the receptor and the primary difference being an aspartic acid in position 7 of TIP39 that interacts with histidine 396 in the receptor, versus isoleucine/histidine residues in the related hormones, this might be a trigger interaction for the events that cause internalisation.

CONCLUSIONS

A model is constructed for the complex and a trigger interaction for full agonistic activation between aspartic acid 7 of TIP39 and histidine 396 in the receptor is proposed.

Tuberoinfundibular peptide of 39 residues (TIP39) signaling modulates acute and tonic nociception

Tuberoinfundibular peptide of 39 residues (TIP39) synthesizing neurons at the caudal border of the thalamus and in the lateral pons project to areas rich in its receptor, the parathyroid hormone 2 receptor (PTH2R). These areas include many involved in processing nociceptive information. Here we examined the potential role of TIP39 signaling in nociception using a PTH2R antagonist (HYWH) and mice with deletion of TIP39's coding sequence or PTH2R null mutation. Intracerebroventricular (icv) infusion of HYWH significantly inhibited nociceptive responses in tail-flick and hot-plate tests and attenuated the nociceptive response to hindpaw formalin injection. TIP39-KO and PTH2R-KO had increased response latency in the 55°C hot-plate test and reduced responses in the hindpaw formalin test. The tail-flick test was not affected in either KO line. Thermal hypoalgesia in KO mice was dose-dependently reversed by systemic administration of the cannabinoid receptor 1 (CB1) antagonist rimonabant, which did not affect nociception in wild-type (WT). Systemic administration of the cannabinoid agonist CP 55,940 did not affect nociception in KO mice at a dose effective in WT. WT mice administered HYWH icv, and both KOs, had significantly increased stress-induced analgesia (SIA). Rimonabant blocked the increased SIA in TIP39-KO, PTH2R-KO or after HYWH infusion. CB1 and FAAH mRNA were decreased and increased, respectively, in the basolateral amygdala of TIP39-KO mice. These data suggest that TIP39 signaling modulates nociception, very likely by inhibiting endocannabinoid circuitry at a supraspinal level. We infer a new central mechanism for endocannabinoid regulation, via TIP39 acting on the PTH2R in discrete brain regions.

The TIP39-PTH2 receptor system: unique peptidergic cell groups in the brainstem and their interactions with central regulatory mechanisms

Tuberoinfundibular peptide of 39 residues (TIP39) is the recently purified endogenous ligand of the previously orphan G-protein coupled parathyroid hormone 2 receptor (PTH2R). The TIP39-PTH2R system is a unique neuropeptide-receptor system whose localization and functions in the central nervous system are different from any other neuropeptides. TIP39 is expressed in two brain regions, the subparafascicular area in the posterior thalamus, and the medial paralemniscal nucleus in the lateral pons. Subparafascicular TIP39 neurons seem to divide into a medial and a lateral cell population in the periventricular gray of the thalamus, and in the posterior intralaminar complex of the thalamus, respectively. Periventricular thalamic TIP39 neurons project mostly to limbic brain regions, the posterior intralaminar thalamic TIP39 neurons to neuroendocrine brain areas, and the medial paralemniscal TIP39 neurons to auditory and other brainstem regions, and the spinal cord. The widely distributed axon terminals of TIP39 neurons have a similar distribution as the PTH2R-containing neurons, and their fibers, providing the anatomical basis of a neuromodulatory action of TIP39. Initial functional studies implicated the TIP39-PTH2R system in nociceptive information processing in the spinal cord, in the regulation of different hypophysiotropic neurons in the hypothalamus, and in the modulation of affective behaviors. Recently developed novel experimental tools including mice with targeted mutations of the TIP39-PTH2R system and specific antagonists of the PTH2R will further facilitate the identification of the specific roles of TIP39 and the PTH2R.

Vasodilatory effect of tuberoinfundibular peptide (TIP39): requirement of receptor desensitization and its beneficial effect in the post-ischemic heart

Tuberoinfundibular peptide of 39 residues (TIP39) is a member of the parathyroid hormone (PTH) family and a highly specific ligand of the PTH-receptor type 2 (PTH-2r). Recent studies have shown vasoactive properties of TIP39 in the kidney. This effect was stronger after desensitization of the parathyroid hormone-receptor type 1 (PTH-1r). The aims of our study were three-fold: (1) to investigate the influence of TIP39 on coronary resistance (CR), (2) to investigate a possible cross-talk between vascular PTH-receptors in the cardiovascular system, and (3) to investigate whether the endogenously released PTHrP during ischemia induces such a desensitizing effect. Experiments were performed on isolated rat hearts that were perfused with a constant pressure (Langendorff mode) and the coronary flow was determined. Under basal conditions, TIP39 showed no influences on CR. However, TIP39 reduced the CR by approximately 22% after pre-treatment of the hearts with a PTH-1r agonist. This TIP39 effect was abolished either by co-administration of a PTH-2r antagonist or by inhibition of nitric oxide (NO) formation. In an ischemia-reperfusion model endogenously released PTHrP desensitized the PTH-1r and pre-ischemic addition of TIP39 reduced post-ischemic CR by about 28%. Again, this effect was completely abolished in the presence of the PTH-2r antagonist or the PTH-1r-antagonist or by inhibition of NO formation. However, no effect was observed when TIP39 was washed-out prior to ischemia or if the treatment with TIP39 was restricted to the reperfusion. Furthermore, a pre-ischemic application of the NO-dependent vasorelaxant bradykinin provoked a similar effect on the post-ischemic CR than TIP39. In conclusion, a NO-dependent vasodilatory effect of TIP39 was demonstrated if the PTH-1r is desensitized by either exogenously applicated PTHrP peptides or endogenously released PTHrP.

Development of a rat parathyroid hormone 2 receptor antagonist

The parathyroid hormone 2 (PTH2) receptor is a Family B G-protein coupled receptor most highly expressed within the brain. Current evidence suggests that tuberoinfundibular peptide of 39 residues (TIP39) is the PTH2 receptor's endogenous ligand. To facilitate investigation of the physiological function of the PTH2 receptor/TIP39 system, we have developed a novel PTH2 receptor antagonist, by changing several residues within the amino terminal domain of TIP39. Histidine(4), tyrosine(5), tryptophan(6), histidine(7)-TIP39 binds the PTH2 receptor with high affinity, has over 30-fold selectivity for the rat PTH2 receptor over the rat PTH1 receptor and displays no detectable agonist activity. This ligand should be useful for in vivo investigation of PTH2 receptor function.

N-terminal parathyroid hormone-related peptide hyperpolarizes endothelial cells and causes a reduction of the coronary resistance of the rat heart via endothelial hyperpolarization

Parathyroid hormone-related peptide (PTHrP) is known to be a strong vasorelaxant peptide. The mechanisms by which PTHrP reduces the coronary resistance of the rat heart have not been worked out but seem to be independent of the classical PTH/PTHrP receptor-mediated, cAMP-dependent effect. In this study we hypothesized that PTHrP reduces the coronary resistance of the rat heart via endothelial cell hyperpolarization. Isolated microvascular endothelial cells from rat heart were incubated with PTHrP(1-36), and changes in the membrane potential were recorded via DiBAC fluorescence. Cells exposed to PTHrP showed a hyperpolarization of approximately 7mV. In the isolated Langendorff preparation, PTHrP-dependent vasodilatation of l-nitro-arginine-exposed hearts was abolished under depolarizing conditions (high potassium). Denudation of the endothelial cell layer significantly impaired the vasodilatory effect of PTHrP. In the presence of H89 (a cAMP/protein kinase A pathway antagonist) and indomethacin (a cyclooxygenase inhibitor), PTHrP dilated the vessels. In conclusion, PTHrP exerted a nitric oxide-independent vasodilatory effect that depends on endothelial cell hyperpolarization.

Recent advances in physiological calcium homeostasis

A constant extracellular Ca2+ concentration is required for numerous physiological functions at tissue and cellular levels. This suggests that minor changes in Ca2+ will be corrected by appropriate homeostatic systems. The system regulating Ca2+ homeostasis involves several organs and hormones. The former are mainly the kidneys, skeleton, intestine and the parathyroid glands. The latter comprise, amongst others, the parathyroid hormone, vitamin D and calcitonin. Progress has recently been made in the identification and characterisation of Ca2+ transport proteins CaT1 and ECaC and this has provided new insights into the molecular mechanisms of Ca2+ transport in cells. The G-protein coupled calcium-sensing receptor, responsible for the exquisite ability of the parathyroid gland to respond to small changes in serum Ca2+ concentration was discovered about a decade ago. Research has focussed on the molecular mechanisms determining the serum levels of 1,25(OH)2D3, and on the transcriptional activity of the vitamin D receptor. The aim of recent work has been to elucidate the mechanisms and the intracellular signalling pathways by which parathyroid hormone, vitamin D and calcitonin affect Ca2+ homeostasis. This article summarises recent advances in the understanding and the molecular basis of physiological Ca2+ homeostasis.

Differential expression of tuberoinfundibular peptide 38 and glucose-6-phosphatase in tilapia

A new parathyroid hormone (PTH)-like endocrine system has been identified in mammals and fishes consisting of the PTH type-2 receptor (PTH2R) and tuberoinfundibular peptide 39 (TIP39). Although the mammalian PTH2R-TIP39 system is involved in nociception and pituitary regulation, the function(s) of this system in fishes is undetermined. Using degenerate primers based on conserved zebrafish and fugu TIP39 nucleotide sequences, 3'-RACE reactions isolated the coding region of a putative TIP38 cDNA in the Nile tilapia (Oreochromis niloticus). Tilapia-specific primers were subsequently used in 5'-RACE reactions to isolate the remaining portion of the transcript. The cDNA encoding O. niloticus TIP (OnTIP38) was determined to yield a 38 amino acid secreted hormone. A second tilapia TIP38 cDNA was isolated from the euryhaline Mozambique tilapia (OmTIP38). Except for the 39th residue, both tilapia cDNA sequences showed significant identity to human, bovine, murine, fugu, and zebrafish TIP39. To determine the tissue-specific expression of OnTIP38 and OmTIP38, real-time quantitative RT-PCR (rQRT-PCR) was performed on skin, gill, kidney, testis, heart, and brain. In freshwater (FW)-acclimated Nile tilapia, OnTIP38 showed highest levels of expression in kidney and lowest levels in skin and gill. In Mozambique tilapia tissues, expression of OmTIP38 and G6Pase (glucose-6 phosphatase) were higher in salt water (SW)-acclimated fish than in FW-acclimated fish. G6Pase expression, and not OmTIP38, showed significant differences among various tissues in FW- and SW-acclimated fish. Results of the present study clearly indicate that the TIP38/39-PTH2R system shows considerable conservation in sequence identity and tissue-specific expression in mammals and fishes.