Human TRH-degrading ectoenzyme cDNA cloning, functional expression, genomic structure and chromosomal assignment

A single nucleotide polymorphism of the thyrotropin releasing hormone degrading ectoenzyme (TRHDE) gene is associated with post-partum anestrus in Murrah buffalo

Thyrotropin releasing hormone degrading enzyme (TRHDE) gene is implicated in Thyrotropin releasing hormone (TRH) mediated prolactin secretion. It has been shown that the prolactin secretion alters the Gonadotropin-releasinghormone(GnRH) mediated estrous cycle. Therefore, TRHDE may also regulate postpartum anestrus. Earlier studies reported the role of non-synonymous single nucleotide polymorphism (SNPs) in various pathophysiological conditions by altering the structure and function of the proteins. Hence, in the present study, we identified SNPs in the putative promoter, first exon, middle exon and 3'-UTR containing the last exon of TRHDE gene and determined their association with postpartum anestrus (PPA) in Murrah buffaloes. We found one non synonymous SNP (G > C at 118095875 bp on chromosome 4) in the first exon of TRHDE and performed its association analysis in a population sample of 50 extreme PPA (residual PPAI: 123.06 ± 12.98 days) and 50 normal (residual PPAI: -80.46 ± 3.19 days) buffaloes. The residual PPAI value was the observed PPAI adjusted for the effect of 38 non-genetic factors. The analysis showed a significant (P < 0.004167) association of this SNP with PPA in buffaloes. Molecular dynamics simulations (MDS) also supported that the C allele altering Glutamine to Histidine at the amino acid 148 of TRHDE could enhance the stability and rigidity of TRHDE protein, which may lower its activity, increase TRH and prolactin, and reduce GnRH in PPA buffaloes. The MDS analysis further strengthens the association of the SNP (G > C) in the TRHDE gene with PPA condition in Murrah buffaloes. However, further investigation is needed to prove the MDS observations.

Evolution of thyrotropin-releasing factor extracellular communication units

Thyroid hormones (THs) are ancient signaling molecules that contribute to the regulation of metabolism, energy homeostasis and growth. In vertebrates, the hypothalamus-pituitary-thyroid (HPT) axis links the corresponding organs through hormonal signals, including thyrotropin releasing factor (TRF), and thyroid stimulating hormone (TSH) that ultimately activates the synthesis and secretion of THs from the thyroid gland. Although this axis is conserved among most vertebrates, the identity of the hypothalamic TRF that positively regulates TSH synthesis and secretion varies. We review the evolution of the hypothalamic factors that induce TSH secretion, including thyrotropin-releasing hormone (TRH), corticotrophin-releasing hormone (CRH), urotensin-1-3, and sauvagine, and non-mammalian glucagon-like peptide in metazoans. Each of these peptides is part of an extracellular communication unit likely composed of at least 3 elements: the peptide, G-protein coupled receptor and bioavailability regulator, set up on the central neuroendocrine articulation. The bioavailability regulators include a TRH-specific ecto-peptidase, pyroglutamyl peptidase II, and a CRH-binding protein, that together with peptide secretion/transport rate and transduction coupling and efficiency at receptor level shape TRF signal intensity and duration. These vertebrate TRF communication units were coopted from bilaterian ancestors. The bona fide elements appeared early in chordates, and are either used alternatively, in parallel, or sequentially, in different vertebrate classes to control centrally the activity of the HPT axis. Available data also suggest coincidence between apparition of ligand and bioavailability regulator.

Genome-wide association and transcriptome studies identify candidate genes and pathways for feed conversion ratio in pigs

Background

The feed conversion ratio (FCR) is an important productive trait that greatly affects profits in the pig industry. Elucidating the genetic mechanisms underpinning FCR may promote more efficient improvement of FCR through artificial selection. In this study, we integrated a genome-wide association study (GWAS) with transcriptome analyses of different tissues in Yorkshire pigs (YY) with the aim of identifying key genes and signalling pathways associated with FCR.

Results

A total of 61 significant single nucleotide polymorphisms (SNPs) were detected by GWAS in YY. All of these SNPs were located on porcine chromosome (SSC) 5, and the covered region was considered a quantitative trait locus (QTL) region for FCR. Some genes distributed around these significant SNPs were considered as candidates for regulating FCR, including TPH2, FAR2, IRAK3, YARS2, GRIP1, FRS2, CNOT2 and TRHDE. According to transcriptome analyses in the hypothalamus, TPH2 exhibits the potential to regulate intestinal motility through serotonergic synapse and oxytocin signalling pathways. In addition, GRIP1 may be involved in glutamatergic and GABAergic signalling pathways, which regulate FCR by affecting appetite in pigs. Moreover, GRIP1, FRS2, CNOT2, and TRHDE may regulate metabolism in various tissues through a thyroid hormone signalling pathway.

Conclusions

Based on the results from GWAS and transcriptome analyses, the TPH2, GRIP1, FRS2, TRHDE, and CNOT2 genes were considered candidate genes for regulating FCR in Yorkshire pigs. These findings improve the understanding of the genetic mechanisms of FCR and may help optimize the design of breeding schemes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07570-w.

The Thyrotropin-Releasing Hormone-Degrading Ectoenzyme, a Therapeutic Target?

Thyrotropin releasing hormone (TRH: Glp-His-Pro-NH2) is a peptide mainly produced by brain neurons. In mammals, hypophysiotropic TRH neurons of the paraventricular nucleus of the hypothalamus integrate metabolic information and drive the secretion of thyrotropin from the anterior pituitary, and thus the activity of the thyroid axis. Other hypothalamic or extrahypothalamic TRH neurons have less understood functions although pharmacological studies have shown that TRH has multiple central effects, such as promoting arousal, anorexia and anxiolysis, as well as controlling gastric, cardiac and respiratory autonomic functions. Two G-protein-coupled TRH receptors (TRH-R1 and TRH-R2) transduce TRH effects in some mammals although humans lack TRH-R2. TRH effects are of short duration, in part because the peptide is hydrolyzed in blood and extracellular space by a M1 family metallopeptidase, the TRH-degrading ectoenzyme (TRH-DE), also called pyroglutamyl peptidase II. TRH-DE is enriched in various brain regions but is also expressed in peripheral tissues including the anterior pituitary and the liver, which secretes a soluble form into blood. Among the M1 metallopeptidases, TRH-DE is the only member with a very narrow specificity; its best characterized biological substrate is TRH, making it a target for the specific manipulation of TRH activity. Two other substrates of TRH-DE, Glp-Phe-Pro-NH2 and Glp-Tyr-Pro-NH2, are also present in many tissues. Analogs of TRH resistant to hydrolysis by TRH-DE have prolonged central efficiency. Structure-activity studies allowed the identification of residues critical for activity and specificity. Research with specific inhibitors has confirmed that TRH-DE controls TRH actions. TRH-DE expression by β2-tanycytes of the median eminence of the hypothalamus allows the control of TRH flux into the hypothalamus-pituitary portal vessels and may regulate serum thyrotropin secretion. In this review we describe the critical evidences that suggest that modification of TRH-DE activity in tanycytes, and/or in other brain regions, may generate beneficial consequences in some central and metabolic disorders and identify potential drawbacks and missing information needed to test these hypotheses.

Genetic Polymorphisms Associated with Spontaneous Intracerebral Hemorrhage

Differences in the incidence of spontaneous intracerebral hemorrhage (ICH) between ethnicities exist, with an estimated 42% of the variance explained by ethnicity itself. Caucasians have a higher proportion of lobar ICH (LICH, 15.4% of all ICH) than do Asians (3.4%). Alterations in the causal factor exposure between countries justify part of the ethnic variance in ICH incidence. One third of ICH risk can be explained by genetic variation; therefore, genetic differences between populations can partly explain the difference in ICH incidence. In this paper, we review the current knowledge of genetic variants associated with ICH in multiple ethnicities. Candidate gene variants reportedly associated with ICH were involved in the potential pathways of hypertension, vessel wall integrity, lipid metabolism, endothelial dysfunction, inflammation, platelet function, and coagulopathy. Furthermore, variations in APOE (in multiple ethnicities), PMF1/SLC25A44 (in European), ACE (in Asian), MTHFR (in multiple ethnicities), TRHDE (in European), and COL4A2 (in European) were the most convincingly associated with ICH. The majority of the associated genes provide small contributions to ICH risk, with few of them being replicated in multiple ethnicities.

Transcriptomic Changes in Broiler Chicken Hypothalamus during Growth and Development

The hypothalamus plays an overarching role that is reflected in the physiological processes observed in the entire organism. The hypothalamus regulates selected metabolic processes and activities of the autonomic nervous system. The avian hypothalamus due to the structural complexity is not well described and has a slightly different function than the mammalian hypothalamus that is the subject of numerous studies. The present study evaluated activities of hypothalamic genes in fast-growing chickens during development (at the 1^st day and 3^rd and 6^th weeks after hatching). The hypothalamic transcriptomes for 3- and 6-week-old cockerels were analysed using an RNA sequencing method in next-generation sequencing (NGS) technology. The differentially expressed gene analysis was conducted using DESeq2 software. In younger 22-day-old cockerels, 389 genes showed higher expression (fold change > 1.5) than that in 45-day-old birds. These genes played a role in several biological processes because they encoded proteins involved in integrin signalling, regulation of hormone levels, camera-type eye development, and blood vessel development. Moreover, surprisingly in the hypothalamus of 3-week-old cockerels, transcripts were identified for proteins involved in both anorexigenic (POMC, NMU) and orexigenic (PMCH, ALDH1A1, LPL, and GHRH) pathways. The RNA-seq results were confirmed by qPCR methods. In summary, the intensive growth of 3-week-old chickens was reflected in hypothalamic activities because the genes associated with the somatotropin axis and regulation of satiety centre showed increased expression.

Identification of MEF2B and TRHDE Gene Polymorphisms Related to Growth Traits in a New Ujumqin Sheep Population

2 SNPs were discovered in our previous genome-wide association study (GWAS): s58995.1 (rs420767326 A>G) in MEF2B gene and OAR3_115712045.1 (rs401775061 A>C) in TRHDE gene, which were significantly associated with post-weaning gain in sheep. Herein, we performed a replication experiment to investigate single nucleotide polymorphisms (SNPs) within the MEF2B and TRHDE gene exons, the 5′untranslated regions (within 1000bp), the 3′ untranslated regions (within 1000bp) and their associations with Ujumqin sheep growth traits in 4-month age and 6-month age, respectively. Finally,3 SNPs were selected to be investigated including 1 SNP in 3′untranslated regions in MEF2B gene (rs417014745 A>G) and 2 SNPs in TRHDE gene (rs426980328 T>C and rs430810656 G>A).The χ2 test showed all the 3 variations were in Hardy–Weinberg equilibrium (P>0.05) status. Association analysis suggested that rs426980328 T>C was significantly associated with body weight and chest girth in 4-month age (P<0.05). rs430810656 G>A exhibited extremely significant association with body weight and chest girth in 4-month age (P<0.01). rs417014745 A>G was extremely significantly associated with body weight and chest girth in 4-month age and chest girth in 6-month age (P<0.01), and it was also significantly associated with body weight in 6-month age (P<0.05). Combined effect analysis indicated significant associations between the combinations of rs426980328-rs417014745, rs430810656-rs417014745 and several growth traits (P<0.05). These results suggested MEF2B and TRHDE genes affected growth traits in Ujumqin sheep and the combination effect of the two genes also played a significant effective role. These SNPs might have potential value as genetic markers for growth traits and it could be used in Ujumqin sheep breeding in future. Further studies are necessary to confirm our findings.

Molecular analysis of cluster headache

OBJECTIVES

Cluster headache (CH) is characterized by severe, recurrent, unilateral attacks of extreme intensity and brief duration. Variants in a myriad of genes were studied in sporadic CH patients, often with conflicting results.

METHODS

We studied gene mutations in some candidate genes, hypocretin receptor 2, Clock, and alcohol dehydrogenase 4 (ADH4), in 54 unrelated sporadic CH patients and in 200 controls in 8 kindreds/families that included more affected and nonaffected cases. Furthermore, we performed the whole-genome scanning by comparative genomic hybridization, searching for rearrangements associated with DNA gain or loss in a subset of sporadic and familial CH and control participants.

RESULTS

The analysis of candidate genes revealed that only allele and genotype frequency of the 2 ADH4 mutations resulted significantly between sporadic CH and controls; the same mutations were homozygous in CH patients from 2 families. The comparative genomic hybridization analysis revealed 2 novel rearrangements that involved the intron regions of thyrotropin-releasing hormone-degrading enzyme and neurexin 3 (NRXN3) genes, respectively. The first arrangement was present either in CH or in controls, whereas the second one was specifically found in some sporadic and familial CH cases.

CONCLUSIONS

Our data (although obtained on a small number of cases) confirm the genetic heterogeneity of CH, suggesting that mutations in the ADH4 gene and a novel rearrangement involving NRXN3 gene might be related to CH in a subset of cases.

Demographic, psychosocial, and genetic risk associated with smokeless tobacco use among Mexican heritage youth

BACKGROUND

Despite well-established negative health consequences of smokeless tobacco use (STU), the number and variety of alternative non-combustible tobacco products on the market have increased tremendously over the last 10 years, as has the market share of these products relative to cigarettes. While STU among non-Hispanic white youth has decreased over the last 10 years, the prevalence has remained constant among Hispanic youth. Here we examine demographic, psychosocial, and genetic risk associated with STU among Mexican heritage youth.

METHODS

Participants (50.5 % girls) reported on psychosocial risk factors in 2008-09 (n = 1,087, mean age = 14.3 years), and smokeless tobacco use in 2010-11 (mean age = 16.7 years). Participants provided a saliva sample that was genotyped for genes in the dopamine, serotonin and opioid pathways.

RESULTS

Overall 62 (5.7 %) participants reported lifetime STU. We identified five single nucleotide polymorphisms that increased the risk for lifetime use. Specifically, rs2023902 on SERGEF (OR = 1.93; 95 % CI: 1.05-3.53), rs16941667 on ALDH2 (OR = 3.14; 95 % CI: 1.65-5.94), and rs17721739 on TPH1 (OR = 1.71; 95 % CI: 1.00-2.91) in the dopamine pathway, rs514912 on TRH-DE (OR = 1.84; 95 % CI: 1.25-2.71) in the serotonin pathway, and rs42451417 on the serotonin transporter gene, SLC6A4 (OR = 3.53; 95 % CI: 1.56-7.97). After controlling for genetic risk, being male (OR = 1.86; 95 % CI: 1.02-3.41), obesity status (OR = 2.22; 95 % CI: 1.21-4.09), and both higher levels of anxiety (OR = 1.04; 95 % CI: 1.01-1.08) and social disinhibition (OR = 1.26; 95 % CI: 1.07-1.48) were associated with increased use. High subjective social status (OR = 0.78; 95 % CI: 0.64-0.93) was protective against use, while higher parental education (OR = 2.01; 95 % CI: 1.03-3.93) was associated with increased use.

CONCLUSIONS

These data suggest that use of genetic risk, along with psychosocial, demographic, and behavioral risk factors may increase our ability to identify youth at increased risk for STU, which in turn may improve our ability to effectively target prevention messages to Mexican heritage youth.

Genome-wide association studies for growth and meat production traits in sheep

BACKGROUND

Growth and meat production traits are significant economic traits in sheep. The aim of the study is to identify candidate genes affecting growth and meat production traits at genome level with high throughput single nucleotide polymorphisms (SNP) genotyping technologies.

METHODOLOGY AND RESULTS

Using Illumina OvineSNP50 BeadChip, we performed a GWA study in 329 purebred sheep for 11 growth and meat production traits (birth weight, weaning weight, 6-month weight, eye muscle area, fat thickness, pre-weaning gain, post-weaning gain, daily weight gain, height at withers, chest girth, and shin circumference). After quality control, 319 sheep and 48,198 SNPs were analyzed by TASSEL program in a mixed linear model (MLM). 36 significant SNPs were identified for 7 traits, and 10 of them reached genome-wise significance level for post-weaning gain. Gene annotation was implemented with the latest sheep genome Ovis_aries_v3.1 (released October 2012). More than one-third SNPs (14 out of 36) were located within ovine genes, others were located close to ovine genes (878bp-398,165bp apart). The strongest new finding is 5 genes were thought to be the most crucial candidate genes associated with post-weaning gain: s58995.1 was located within the ovine genes MEF2B and RFXANK, OAR3_84073899.1, OAR3_115712045.1 and OAR9_91721507.1 were located within CAMKMT, TRHDE, and RIPK2 respectively. GRM1, POL, MBD5, UBR2, RPL7 and SMC2 were thought to be the important candidate genes affecting post-weaning gain too. Additionally, 25 genes at chromosome-wise significance level were also forecasted to be the promising genes that influencing sheep growth and meat production traits.

CONCLUSIONS

The results will contribute to the similar studies and facilitate the potential utilization of genes involved in growth and meat production traits in sheep in future.

Emerging treatments for narcolepsy and its related disorders

IMPORTANCE OF THE FIELD

Narcolepsy is a chronic sleep disorder, characterized by excessive daytime sleepiness (EDS), cataplexy, hypnagogic hallucinations, sleep paralysis and nocturnal sleep disruption. Non-pharmacological treatments (i.e., behavioral modification) are often helpful for the clinical management of narcoleptic patients. As these symptoms are often disabling, most patients need life-long treatments. Over 90% of diagnosed narcoleptic patients are currently prescribed medications to control their symptoms; however, available treatments are merely symptomatic.

AREAS COVERED IN THIS REVIEW

This review presents a description of the clinical symptoms of narcolepsy, followed by a discussion of the state-of-the-art knowledge regarding the disorder and related emerging treatments. In preparing this review, an extensive literature search was conducted using Pubmed. Only selected references from 1970 to 2008 are cited.

WHAT THE READER WILL GAIN

This review focuses on emerging treatments for human narcolepsy, and the reader will gain significant knowledge of current and future treatment for this and related disorders. Traditionally, amphetamine-like stimulants (i.e., dopaminergic release enhancers) have been used for clinical management to improve EDS, and tricyclic antidepressants have been used as anticataplectics. However, treatments have recently evolved which utilize better tolerated compounds, such as modafinil (for EDS) and adrenergic/serotonergic selective reuptake inhibitors (as anticataplectics). In addition, night time administration of a short-acting sedative, gamma-hydroxybutyrate, has been used for the treatment for EDS and cataplexy. As a large majority of human narcolepsy is hypocretin peptide deficient, hypocretin replacement therapy may also be a new therapeutic option; yet, this option is still unavailable. In addition to the hypocretin-based therapy, a series of new treatments are currently being tested in animal and/or humans models. These potential options include novel stimulant and anticataplectic drugs as well as immunotherapy, based on current knowledge of the pathophysiology of narcolepsy with cataplexy.

TAKE HOME MESSAGE

We expect that more pathophysiology-based treatments, capable of curing and/or preventing narcolepsy and related diseases, will be available in near future. As cases of EDS, associated with other neurological conditions (i.e., symptomatic narcolepsy or narcolepsy due to medical conditions), are often linked with hypocretin deficiency, these novel therapeutic options may also be applied to treatment of these disabling conditions.

Histidine 379 of human laeverin/aminopeptidase Q, a nonconserved residue within the exopeptidase motif, defines its distinctive enzymatic properties

Human laeverin/aminopeptidase Q (LVRN/APQ) is a novel member of the M1 family of zinc aminopeptidases and is specifically expressed on the cell surface of human extravillous trophoblasts. Multiple sequence alignment of human M1 aminopeptidase revealed that the first Gly residue within the conserved exopeptidase motif of the M1 family, GXMEN motif, is uniquely substituted for His in human LVRN/APQ. In this study, we evaluated the roles of nonconserved His(379), comprising the exopeptidase motif in the enzymatic properties of human LVRN/APQ. We revealed that the substitution of His(379) with Gly caused significant changes in substrate specificity both toward fluorogenic substrates and natural peptide hormones. In addition, the susceptibilities of bestatin, a sensitive inhibitor for human LVRN/APQ, and natural inhibitory peptides were decreased in the H379G mutant. A molecular model suggested a conformational difference between wild-type and H379G human LVRN/APQs. These results indicate that His(379) of the enzyme plays essential roles in its distinctive enzymatic properties and contributes to maintaining the appropriate structure of the catalytic cavity of the enzyme. Our data may bring new insight into the biological significance of the unique exopeptidase motif of LVRN/APQ obtained during the evolution of primates.

Tanycyte pyroglutamyl peptidase II contributes to regulation of the hypothalamic-pituitary-thyroid axis through glial-axonal associations in the median eminence

Pyroglutamyl peptidase II (PPII), a highly specific membrane-bound metallopeptidase that inactivates TRH in the extracellular space, is tightly regulated by thyroid hormone in cells of the anterior pituitary. Whether PPII has any role in the region where axons containing hypophysiotropic TRH terminate, the median eminence, is unknown. For this purpose, we analyzed the cellular localization and regulation of PPII mRNA in the mediobasal hypothalamus in adult, male rats. PPII mRNA was localized in cells lining the floor and infralateral walls of the third ventricle and coexpressed with vimentin, establishing these cells as tanycytes. PPII mRNA extended in a linear fashion from the tanycyte cell bodies in the base of the third ventricle to its cytoplasmic and end-feet processes in the external zone of the median eminence in close apposition to pro-TRH-containing axon terminals. Compared with vehicle-treated, euthyroid controls, animals made thyrotoxic by the i.p. administration of 10 microg L-T(4) daily for 1-3 d, showed dramatically increased accumulation of silver grains in the mediobasal hypothalamus and an approximately 80% increase in enzymatic activity. PPII inhibition in mediobasal hypothalamic explants increased TRH secretion, whereas i.p. injection of a specific PPII inhibitor increased cold stress- and TRH-induced TSH levels in plasma. We propose that an increase in circulating thyroid hormone up-regulates PPII activity in tanycytes and enhances degradation of extracellular TRH in the median eminence through glial-axonal associations, contributing to the feedback regulation of thyroid hormone on anterior pituitary TSH secretion.

Attenuation of kindled seizures by intranasal delivery of neuropeptide-loaded nanoparticles

Thyrotropin-releasing hormone (TRH; Protirelin), an endogenous neuropeptide, is known to have anticonvulsant effects in animal seizure models and certain intractable epileptic patients. Its duration of action, however, is limited by rapid tissue metabolism and the blood-brain barrier. Direct nose-to-brain delivery of neuropeptides in sustained-release biodegradable nanoparticles (NPs) is a promising mode of therapy for enhancing CNS neuropeptide bioavailability. To provide proof of principle for this delivery approach, we used the kindling model of temporal lobe epilepsy to show that 1) TRH-loaded copolymer microdisks implanted in a seizure focus can attenuate kindling development in terms of behavioral stage, afterdischarge duration (ADD), and clonus duration; 2) intranasal administration of an unprotected TRH analog can acutely suppress fully kindled seizures in a concentration-dependent manner in terms of ADD and seizure stage; and 3) intranasal administration of polylactide nanoparticles (PLA-NPs) containing TRH (TRH-NPs) can impede kindling development in terms of behavioral stage, ADD, and clonus duration. Additionally, we used intranasal delivery of fluorescent dye-loaded PLA-NPs in rats and application of dye-loaded or dye-attached NPs to cortical neurons in culture to demonstrate NP uptake and distribution over time in vivo and in vitro respectively. Also, a nanoparticle immunostaining method was developed as a procedure for directly visualizing the tissue level and distribution of neuropeptide-loaded nanoparticles. Collectively, the data provide proof of concept for intranasal delivery of TRH-NPs as a viable means to 1) suppress seizures and perhaps epileptogenesis and 2) become the lead compound for intranasal anticonvulsant nanoparticle therapeutics.

Asparatic acid 221 is critical in the calcium-induced modulation of the enzymatic activity of human aminopeptidase A

Aminopeptidase A (APA) plays an important role in the regulation of blood pressure by mediating angiotensin II degradation in the renin-angiotensin system. The Ca2+-induced modulation of enzymatic activity is the most characteristic feature of APA among the M1 family of aminopeptidases. In this study, we used site-directed mutagenesis for any residues responsible for the Ca2+ modulation of human APA. Alignment of sequences of the M1 family members led to the identification of Asp-221 as a significant residue of APA among the family members. Replacement of Asp-221 with Asn or Gln resulted in a loss of Ca2+ responsiveness toward synthetic substrates. These enzymes were also unresponsive to Ca2+ when peptide hormones, such as angiotensin II, cholecystokinin-8, neurokinin B, and kallidin, were employed as substrates. These results suggest that the negative charge of Asp-221 is essential for Ca2+ modulation of the enzymatic activity of APA and causes preferential cleavage of acidic amino acid at the N-terminal end of substrate peptides.

Laeverin/Aminopeptidase Q, a Novel Bestatin-sensitive Leucine Aminopeptidase Belonging to the M1 Family of Aminopeptidases

Laeverin/aminopeptidase Q (APQ) is a cell surface protein specifically expressed on human embryo-derived extravillous trophoblasts that invades the uterus during placentation. The cDNA cloning of Laeverin/APQ revealed that the sequence encodes a protein with 990 amino acid residues, and Laeverin/APQ contains the HEXXHX(18)E gluzincin motif, which is characteristic of the M1 family of aminopeptidases, although the exopeptidase motif of the family, GAMEN, is uniquely substituted for the HAMEN sequence. In this study, we expressed a recombinant human Laeverin/APQ using a baculovirus expression system, purified to homogeneity, and characterized its enzymatic properties. It was found that Laeverin/APQ had a broad substrate specificity toward synthetic substrate, although it showed a preference for Leu-4-methylcoumaryl-7-amide. Searching natural substrates, we found that Laeverin/APQ was able to cleave the N-terminal amino acid of several peptides such as angiotensin III, kisspeptin-10, and endokinin C, which are abundantly expressed in the placenta. In contrast to the case with other M1 aminopeptidases, bestatin inhibited the aminopeptidase activity of Laeverin/APQ much more effectively than other known aminopeptidase inhibitors. These results indicate that Laeverin/APQ is a novel bestatin-sensitive leucine aminopeptidase and suggest that the enzyme plays important roles in human placentation by regulating biological activity of key peptides at the embryo-maternal interface.

Pyroglutamyl peptidase type I from Trypanosoma brucei: a new virulence factor from African trypanosomes that de-blocks regulatory peptides in the plasma of infected hosts

Peptidases of parasitic protozoans are emerging as novel virulence factors and therapeutic targets in parasitic infections. A trypanosome-derived aminopeptidase that exclusively hydrolysed substrates with Glp (pyroglutamic acid) in P1 was purified 9248-fold from the plasma of rats infected with Trypanosoma brucei brucei. The enzyme responsible was cloned from a T. brucei brucei genomic DNA library and identified as type I PGP (pyroglutamyl peptidase), belonging to the C15 family of cysteine peptidases. We showed that PGP is expressed in all life cycle stages of T. brucei brucei and is expressed in four other blood-stream-form African trypanosomes. Trypanosome PGP was optimally active and stable at bloodstream pH, and was insensitive to host plasma cysteine peptidase inhibitors. Native purified and recombinant hyper-expressed trypanosome PGP removed the N-terminal Glp blocking groups from TRH (thyrotrophin-releasing hormone) and GnRH (gonadotropin-releasing hormone) with a k(cat)/K(m) value of 0.5 and 0.1 s(-1) x microM(-1) respectively. The half-life of TRH and GnRH was dramatically reduced in the plasma of trypanosome-infected rats, both in vitro and in vivo. Employing an activity-neutralizing anti-trypanosome PGP antibody, and pyroglutamyl diazomethyl ketone, a specific inhibitor of type I PGP, we demonstrated that trypanosome PGP is entirely responsible for the reduced plasma half-life of TRH, and partially responsible for the reduced plasma half-life of GnRH in a rodent model of African trypanosomiasis. The abnormal degradation of TRH and GnRH, and perhaps other neuropeptides N-terminally blocked with a pyroglutamyl moiety, by trypanosome PGP, may contribute to some of the endocrine lesions observed in African trypanosomiasis.

Homology modeling and site-directed mutagenesis of pyroglutamyl peptidase II. Insights into omega-versus aminopeptidase specificity in the M1 family

Pyroglutamyl peptidase II (PPII), a highly specific membrane-bound omegapeptidase, removes N-terminal pyroglutamyl from thyrotropin-releasing hormone (<Glu-His-Pro-NH(2)), inactivating the peptide in the extracellular space. PPII and enzymes with distinct specificities such as neutral aminopeptidase (APN), belong to the M1 metallopeptidase family. M1 aminopeptidases recognize the N-terminal amino group of substrates or inhibitors through hydrogen-bonding to two conserved residues (Gln-213 and exopeptidase motif Glu-355 in human APN), whereas interactions involved in recognition of pyroglutamyl residue by PPII are unknown. In rat PPII, the conserved exopeptidase residue is Glu-408, whereas the other one is Ser-269. Given that variations in M1 peptidase specificity are likely due to changes in the catalytic region, we constructed three-dimensional models for the catalytic domains of PPII and APN. The models showed a salt bridge interaction between PPII-Glu-408 and PPII-Lys-463, whereas the equivalent APN-Glu-355 did not participate in a salt bridge. Docking of thyrotropin-releasing hormone in PPII model suggested that the pyroglutamyl residue interacted with PPII-Ser-269. According to our models, PPII-S269Q and -K463N mutations should leave Glu-408 in a physicochemical context similar to that found in M1 aminopeptidases; alternatively, PPII-S269E replacement might be sufficient to transform PPII into an aminopeptidase. These hypotheses were supported by site-directed mutagenesis; the mutants lost omegapeptidase but displayed alanyl-aminopeptidase activity. In conclusion, recognition of a substrate without an N-terminal charge requires neutralization of the aminopeptidase anionic binding site; furthermore, shortening of side chain at PPII-269 position is required for adjustment to the pyroglutamyl residue.

Utilizing logical relationships in genomic data to decipher cellular processes

The wealth of available genomic data has spawned a corresponding interest in computational methods that can impart biological meaning and context to these experiments. Traditional computational methods have drawn relationships between pairs of proteins or genes based on notions of equality or similarity between their patterns of occurrence or behavior. For example, two genes displaying similar variation in expression, over a number of experiments, may be predicted to be functionally related. We have introduced a natural extension of these approaches, instead identifying logical relationships involving triplets of proteins. Triplets provide for various discrete kinds of logic relationships, leading to detailed inferences about biological associations. For instance, a protein C might be encoded within an organism if, and only if, two other proteins A and B are also both encoded within the organism, thus suggesting that gene C is functionally related to genes A and B. The method has been applied fruitfully to both phylogenetic and microarray expression data, and has been used to associate logical combinations of protein activity with disease state phenotypes, revealing previously unknown ternary relationships among proteins, and illustrating the inherent complexities that arise in biological data.

Structure-activity studies with high-affinity inhibitors of pyroglutamyl-peptidase II

Inhibitors of PPII (pyroglutamyl-peptidase II) (EC 3.4.19.6) have potential applications as investigative and therapeutic agents. The rational design of inhibitors is hindered, however, by the lack of an experimental structure for PPII. Previous studies have demonstrated that replacement of histidine in TRH (thyrotropin-releasing hormone) with asparagine produces a competitive PPII inhibitor (Ki 17.5 microM). To gain further insight into which functional groups are significant for inhibitory activity, we investigated the effects on inhibition of structural modifications to Glp-Asn-ProNH2 (pyroglutamyl-asparaginyl-prolineamide). Synthesis and kinetic analysis of a diverse series of carboxamide and C-terminally extended Glp-Asn-ProNH2 analogues were undertaken. Extensive quantitative structure-activity relationships were generated, which indicated that key functionalities in the basic molecular structure of the inhibitors combine in a unique way to cause PPII inhibition. Data from kinetic and molecular modelling studies suggest that hydrogen bonding between the asparagine side chain and PPII may provide a basis for the inhibitory properties of the asparagine-containing peptides. Prolineamide appeared to be important for interaction with the S2' subsite, but some modifications were tolerated. Extension of Glp-Asn-ProNH2 with hydrophobic amino acids at the C-terminus led to a novel set of PPII inhibitors active in vitro at nanomolar concentrations. Such inhibitors were shown to enhance recovery of TRH released from rat brain slices. Glp-Asn-Pro-Tyr-Trp-Trp-7-amido-4-methylcoumarin displayed a Ki of 1 nM, making it the most potent competitive PPII inhibitor described to date. PPII inhibitors with this level of potency should find application in exploring the biological functions of TRH and PPII, and potentially provide a basis for development of novel therapeutics.

Identification of Human Aminopeptidase O, a Novel Metalloprotease with Structural Similarity to Aminopeptidase B and Leukotriene A4 Hydrolase

We have cloned and characterized a human brain cDNA encoding a new metalloprotease that has been called aminopeptidase O (AP-O). AP-O exhibits a series of structural features characteristic of aminopeptidases, including a conserved catalytic domain with a zinc-binding site (HEXXHX18E) that allows its classification in the M1 family of metallopeptidases or gluzincins. The structural complexity of AP-O is further increased by the presence of an additional C-terminal domain 170 residues long, which is predicted to have an ARM repeat fold originally identified in the Drosophila segment polarity gene product Armadillo. This ARM repeat domain is also present in aminopeptidase B, aminopeptidase B-like, and leukotriene A4 hydrolase and defines a novel subfamily of aminopeptidases that we have called ARM aminopeptidases. Northern blot analysis revealed that AP-O is mainly expressed in the pancreas, placenta, liver, testis, and heart. Human AP-O was produced in Escherichia coli, and the purified recombinant protein hydrolyzed synthetic substrates used for assaying aminopeptidase activity. This activity was abolished by general inhibitors of metalloproteases and specific inhibitors of aminopeptidases. Recombinant AP-O also cleaved angiotensin III to generate angiotensin IV, a bioactive peptide of the renin-angiotensin pathway with multiple actions on diverse tissues, including brain, testis, and heart. On the basis of these results we suggest that AP-O could play a role in the proteolytic processing of bioactive peptides in those tissues where it is expressed.

A truncated isoform of pyroglutamyl aminopeptidase II produced by exon extension has dominant-negative activity

Thyrotropin-releasing hormone is inactivated in the extracellular space by a membrane-bound peptidase, pyroglutamyl aminopeptidase II (PPII), a member of the M1 family of zinc metallopeptidases. The functional significance of multiple PPII RNA species expression is unknown. We detected, in rat tissues, a RNA species derived from an alternative processing at the exon 14-intron 14 boundary. The alternatively processed RNA encoded a shorter version of PPII (PPII*), lacking part of the C-terminal domain. PPII* was expressed in COS-7 (or C6 glioma) cells but it did not exhibit any PPII activity. Co-transfection of PPII and increasing amounts of PPII* expression vectors resulted in a dose-dependent reduction in PPII activity and the formation of covalent PPII-PPII* heterodimers. PPII* is therefore a powerful dominant-negative isoform of PPII, and heterodimerization may be its mechanism of action. Natural expression of shortened versions of M1 aminopeptidases may constitute a new mode of regulation of their activity.

Cell-surface peptidases

The cell surface has various functions: communicating with other cells, integrating into the tissue, and interacting with the extracellular matrix. Proteases play a key role in these processes. This review focuses on cell-surface peptidases (ectopeptidases, oligopeptidases) that are involved in the inactivation or activation of extracellular regulatory peptides, hormones, paracrine peptides, cytokines, and neuropeptides. The nomenclature of cell-surface peptidases is explained in relation to other proteases, and information is provided on membrane anchoring, catalytic sites, regulation, and, in particular, on their physiological and pharmacological importance. Furthermore, nonenzymatic (binding) functions and participation in intracellular signal transduction of cell surfaces peptidases are described. An overview on the different cell-surface peptidases is given, and their divergent functions are explained in detail. An example of actual pharmacological importance, dipeptidyl-peptidase IV (CD26), is discussed.

Marginal Involvement of Pyroglutamyl Aminopeptidase I in Metabolism of Thyrotropin-Releasing Hormone in Rat Brain

On thyrotropin-releasing hormone (TRH) metabolism, pyroglutamyl aminopeptidase II (PAP-II), a zinc-dependent ectoenzyme primarily located in the central nervous system, is believed to play a predominant role. Recently we cloned pyroglutamyl aminopeptidase I (PAP-I) which is known for specifically removing a L-pyroglutamate (L-pGlu) residue from the amino terminus of proteins and peptides including TRH. To investigate possible contribution of PAP-I toward TRH metabolism, we conducted biochemical and immunohistochemical characterization using recombinant rat, mouse and human PAP-Is and an antibody raised against rat PAP-I. The Km values toward TRH by the recombinant PAP-Is were about 0.05 mM, being similar value to the reported value of recombinant PAP-II. The L-pGlu-cleaving activities toward TRH in rat brain homogenate were inhibited by a PAP-II specific inhibitor 1,10-phenanthroline, but not inhibited by the antibody against rat PAP-I. Immunohistochemical study in rats revealed heterogeneous distribution of PAP-I in the pituitary, the target tissue of TRH, but the distribution was cytosolic. Taken together, these results suggested that PAP-I might not be dominantly involved in the degradation of TRH in rats. Additionally, we found that PAP-I was localized in the renal proximal tubules. Further investigations are needed for elucidating the function of PAP-I in these restricted sites.

Extracellular cysteines define ectopeptidase (APN, CD13) expression and function

Alanyl aminopeptidase (APN) is a surface-bound metallopeptidase that processes the N-terminals of biologically active peptides such as enkephalins, angiotensins, neurokinins, and cytokines. It exerts profound activity on vital processes such as immune response, cellular growth, and blood pressure control. Inhibition of either APN gene expression or its enzymatic activity severely affects leukocyte growth and function. We show here that oxidoreductase-mediated modulations of the cell surface thiol status affect the enzymatic activity of APN. Additional evidence for the pivotal role of extracellular cysteines in the APN molecule was obtained when substitution of any of these six cysteines caused complete loss of surface expression and enzymatic activity. In contrast, the transmembrane Cys24 appears to have no similar function. Enzymatically inactive cysteine mutants were retained in the endoplasmic reticulum as shown by high-resolution imaging and Endoglycosidase H digestion. In the absence of any crystal-structure data, the demonstration that individual extracellular cysteines contribute to APN expression and function appears to be of particular importance. The data are the first to show thiol-dependent modulation of the activity of a typical surface-bound peptidase at the cell surface, probably reflecting a general regulating mechanism. This may relate to various disease processes such as inflammation or malignant transformation.

Purification and characterization of the thyrotropin-releasing hormone (TRH)-degrading serum enzyme and its identification as a product of liver origin

Previous biochemical studies have indicated that the membrane-bound thyrotropin-releasing hormone (TRH)-degrading enzyme (TRH-DE) from brain and liver and the serum TRH-DE are derived from the same gene. These studies also suggested that the serum enzyme is of liver origin. The present study was undertaken to verify these hypotheses. In different species, a close relationship between the activities of the serum enzyme and the particulate liver enzyme was noticed. The activity of the serum enzyme decreased when rats were treated with thioacetamide, a known hepatotoxin. With hepatocytes cultured in a sandwich configuration, release of the TRH-DE into the culture medium could also be demonstrated. The trypsin-solubilized particulate liver TRH-DE and the serum TRH-DE were purified to electrophoretic homogeneity. Both enzymes and the brain TRH-DE were recognized by a monoclonal antibody generated with the purified brain enzyme as antigen. Lectin blot analysis indicated that the serum enzyme and the liver enzyme are glycoproteins containing a sugar structure of the complex type, whereas the brain enzyme exhibits an oligomannose/hybrid glycostructure. A molecular mass of 97 000 Da could be estimated for all three enzymes after deglycosylation and SDS/PAGE followed by Western blotting. Fragment analysis of the serum TRH-DE revealed that the peptide sequences correspond to the cDNA deduced amino-acid sequences of the membrane-bound brain TRH-DE, whereby two peptides were identified that are encoded by exon 1. These data strongly support the hypothesis that the TRH-DEs are all derived from the same gene, whereby the serum enzyme is generated by proteolytic cleavage of the particulate liver enzyme.

The genetics of enuresis: a review

PURPOSE

Formal studies of the genetics of enuresis have been performed since the 1930s and molecular genetics since 1995, both highlighting the importance of hereditary factors in the etiology of nocturnal enuresis. We summarize the current state of knowledge with respect to the genetics of nocturnal enuresis and its genotype-phenotype interactions.

MATERIALS AND METHODS

A comprehensive review of the published data available on the genetic basis of enuresis was performed.

RESULTS

Genetic factors are the most important in the etiology of nocturnal enuresis but somatic and psychosocial environmental factors have a major modulatory effect. Most commonly, nocturnal enuresis is inherited via an autosomal dominant mode of transmission with high penetrance (90%). However, a third of all cases are sporadic, and the difference between sporadic and familial forms is not known. Four gene loci associated with nocturnal enuresis have been identified but the existence of others is presumed (locus heterogeneity). All likely candidate genes have been excluded so far. There is no specific association among the different loci, type of wetting and other aspects of the phenotype. All subtypes of nocturnal enuresis (primary, secondary, combined day/night wetting) are susceptible to comparable genetic influences. Certain syndromes of day wetting follow their own genetic mechanisms but this association with the genetics of nocturnal enuresis is not known.

CONCLUSIONS

Nocturnal enuresis is a common, genetic and heterogeneous disorder. The associations between genotype and phenotype are complex and are susceptible to environmental influences. Therefore, exact assessment of the clinical phenotype and identification of intermediary phenotypes or traits are needed. Future research will focus on the identification of genes, gene products and their interaction with environmental factors.

Antidepressant effects of thyrotropin-releasing hormone analogues using a rodent model of depression

The antidepressant potential of two naturally occurring analogues of thyrotropin-releasing hormone (TRH), pGLU-GLU-PRO-NH2 (EEP) and pGLU-PHE-PRO-NH2 (EFP), were examined using a rodent model of antidepressant efficacy. The Porsolt Swim Test was used to assay the antidepressant properties of these two peptides. Both analogues of TRH produced significant antidepressant effects, with EEP producing the stronger response. No effect of EEP upon triiodothyronine (T3) was observed at the dosage used. EFP, which has previously been demonstrated to crossreact with the TRH receptor, significantly increased serum T3. Since an effect upon T3 was only observed in the weaker of the two compounds, these data suggest that the behavioral effect of EEP was not secondary to stimulation of thyroid hormone. Additionally, the differential behavioral response to the two compounds suggests a degree of sequence specificity in the ability of TRH-like tripeptides to produce an antidepressant effect.

Mutational analysis of the thyrotropin-releasing hormone-degrading ectoenzyme. similarities and differences with other members of the M1 family of aminopeptidases and thermolysin

Thyrotropin-releasing hormone-degrading ectoenzyme (TRH-DE) is a TRH-specific peptidase which catalyzes the inactivation of the peptidergic signal substance TRH. As indicated by sequence alignment, TRH-DE and the other members of the M1 family of aminopeptidases have a distinct set of conserved amino acid residues in common. By replacing amino acid residues that are putatively involved in catalysis, we could demonstrate that the enzymatic activities of the mutants E408D, E442D, E464Q, E464D, Y528F, H507R, and H507F are dramatically decreased, essentially due to the changes of V(max). The mutant enzymes E408Q and E442Q are inactive, whereas the specific enzymatic activity of the mutants R488Q, R488A, and Y554F are similar to that of the wild-type enzyme. These data strongly suggest that E408, E442, Y528, and H507 are involved in the catalytic process of TRH-DE while E464 presumably represents the third zinc-coordinating residue and may be equivalent to E166 in thermolysin. In contrast, amino acid residues R488 and Y554 seem not to be involved in the catalytic mechanism of TRH-DE.

Mutational analysis of the active site of human insulin-regulated aminopeptidase

Insulin-regulated aminopeptidase (IRAP) is a type II integral membrane protein belonging to the gluzincin family of metallopeptidases identified by the characteristic Zn(2+)-coordination sequence element, HEXXH-(18-64X)-E. A second conserved sequence element, the GXMEN motif, positioned 22-32 amino acids N-terminal to the Zn(2+)-coordination sequence element distinguishes the gluzincin aminopeptidases from other gluzincins. To investigate the importance of the G428AMEN and H464ELAH-(18X)-E487 motifs for the activity of IRAP, mutational analysis was carried out. cDNA encoding the full-length transmembrane form of human IRAP was expressed in HEK293 cells and recombinant wild-type IRAP was shown to have biochemical and enzymatic properties similar to those reported for native IRAP and the soluble serum form of IRAP. Mutational analysis using single amino-acid substitutions in the GAMEN motif (G428A, A429G, M430K, M430E, M430I, E431D and E431A) and in the Zn(2+)-binding motif (H464Y, E465D, E465Q, H468Y, E487D and E487Q) resulted in decreased or abolished aminopeptidase activity towards the leucine-para-nitroanilide substrate. The results show that conservation of residues within the GAMEN and Zn(2+)-binding motifs is important for IRAP enzyme activity.

Molecular characterization of a puromycin-insensitive leucyl-specific aminopeptidase, PILS-AP

The family M1 of Zn-dependent aminopeptidases comprises members of closely related enzymes which are known to be involved in a variety of physiologically important processes. On the basis of two highly conserved peptide motifs, we have identified a new member of this family by PCR amplification and cDNA-library screening. The longest ORF encodes a protein of 930 residues. It contains the HEXXH(X)18E Zn-binding motif and displays high homology to the other M1 family members except for its N-terminus for which a signal sequence of 20 residues can be predicted. This interpretation was supported by expressing fusion proteins formed with green fluorescent protein which localized to intracellular vesicles in COS-7 and BHK cells. Northern-blot analysis revealed ubiquitous expression of a major 3. 1-kb transcript. For enzymatic studies, the complete protein was expressed in Sf 9 insect cells. When aminoacyl beta-naphthylamides were used as substrates, efficient hydrolysis was only observed for Leu (and to a lesser extent Met). The activity was inhibited by chelators of bivalent cations and by other known aminopeptidase inhibitors, but surprisingly puromycin was without effect. This newly identified puromycin-insensitive leucyl-specific aminopeptidase is a signal-sequence-bearing member of family M1 and may be another example of the small subset of substrate-specific peptidases.

Analysis of the thyrotropin-releasing hormone-degrading ectoenzyme by site-directed mutagenesis of cysteine residues. Cys68 is involved in disulfide-linked dimerization

Thyrotropin-releasing hormone-degrading ectoenzyme is a member of the M1 family of Zn-dependent aminopeptidases and catalyzes the degradation of thyrotropin-releasing hormone (TRH; Glp-His-Pro-NH2). Cloning of the cDNA of this enzyme and biochemical studies revealed that the large extracellular domain of the enzyme with the catalytically active site contains nine cysteine residues that are highly conserved among species. To investigate the functional role of these cysteines in TRH-DE we used a site-directed mutagenesis approach and replaced individually each cysteine by a serine residue. The results revealed that the proteolytically truncated and enzymatically fully active enzyme consists of two identical subunits that are associated noncovalently by protein-protein interactions but not via interchain S-S bridges. The eight cysteines contained within this region are all important for the structure of the individual subunit and the enzymatic activity, which is dramatically reduced in all mutant enzymes. This is even true for the four cysteines that are clustered within the C-terminal domain remote from the Zn-binding consensus sequence HEICH. In contrast, Cys68, which resides within the stalk region seven residues from the end of the hydrophobic membrane-spanning domain, can be replaced by serine without a significant change in the enzymatic activity. Interestingly, this residue is involved in the formation of an interchain disulfide bridge. Covalent dimerization of the subunits, however, does not seem to be essential for efficient biosynthesis, enzymatic activity and trafficking to the cell surface.