In vivo multiplex quantitative analysis of 3 forms of alpha melanocyte stimulating hormone in pituitary of prolyl endopeptidase deficient mice

Treatment of hypothalamic obesity in people with hypothalamic injury: new drugs are on the horizon

Hypothalamic obesity (HO) is a complex and rare disorder affecting multiple regulatory pathways of energy intake and expenditure in the brain as well as the regulation of the autonomic nervous system and peripheral hormonal signaling. It can be related to monogenic obesity syndromes which often affect the central leptin-melanocortin pathways or due to injury of the hypothalamus from pituitary and hypothalamic tumors, such as craniopharyngioma, surgery, trauma, or radiation to the hypothalamus. Traditional treatments of obesity, such as lifestyle intervention and specific diets, are still a therapeutic cornerstone, but often fail to result in meaningful and sustained reduction of body mass index. This review will give an update on pharmacotherapies of HO related to hypothalamic injury. Recent obesity drug developments are promising for successful obesity intervention outcomes.

Prolyl Carboxypeptidase Mediates the C-Terminal Cleavage of (Pyr)-Apelin-13 in Human Umbilical Vein and Aortic Endothelial Cells

The aim of this study was to investigate the C-terminal cleavage of (pyr)-apelin-13 in human endothelial cells with respect to the role and subcellular location of prolyl carboxypeptidase (PRCP). Human umbilical vein and aortic endothelial cells, pre-treated with prolyl carboxypeptidase-inhibitor compound 8o and/or angiotensin converting enzyme 2 (ACE2)-inhibitor DX600, were incubated with (pyr)-apelin-13 for different time periods. Cleavage products of (pyr)-apelin-13 in the supernatant were identified by mass spectrometry. The subcellular location of PRCP was examined via immunocytochemistry. In addition, PRCP activity was measured in supernatants and cell lysates of LPS-, TNFα-, and IL-1β-stimulated cells. PRCP cleaved (pyr)-apelin-13 in human umbilical vein and aortic endothelial cells, while ACE2 only contributed to this cleavage in aortic endothelial cells. PRCP was found in endothelial cell lysosomes. Pro-inflammatory stimulation induced the secretion of PRCP in the extracellular environment of endothelial cells, while its intracellular level remained intact. In conclusion, PRCP, observed in endothelial lysosomes, is responsible for the C-terminal cleavage of (pyr)-apelin-13 in human umbilical vein endothelial cells, while in aortic endothelial cells ACE2 also contributes to this cleavage. These results pave the way to further elucidate the relevance of the C-terminal Phe of (pyr)-apelin-13.

POMC: The Physiological Power of Hormone Processing

Pro-opiomelanocortin (POMC) is the archetypal polypeptide precursor of hormones and neuropeptides. In this review, we examine the variability in the individual peptides produced in different tissues and the impact of the simultaneous presence of their precursors or fragments. We also discuss the problems inherent in accurately measuring which of the precursors and their derived peptides are present in biological samples. We address how not being able to measure all the combinations of precursors and fragments quantitatively has affected our understanding of the pathophysiology associated with POMC processing. To understand how different ratios of peptides arise, we describe the role of the pro-hormone convertases (PCs) and their tissue specificities and consider the cellular processing pathways which enable regulated secretion of different peptides that play crucial roles in integrating a range of vital physiological functions. In the pituitary, correct processing of POMC peptides is essential to maintain the hypothalamic-pituitary-adrenal axis, and this processing can be disrupted in POMC-expressing tumors. In hypothalamic neurons expressing POMC, abnormalities in processing critically impact on the regulation of appetite, energy homeostasis, and body composition. More work is needed to understand whether expression of the POMC gene in a tissue equates to release of bioactive peptides. We suggest that this comprehensive view of POMC processing, with a focus on gaining a better understanding of the combination of peptides produced and their relative bioactivity, is a necessity for all involved in studying this fascinating physiological regulatory phenomenon.

The Genetic Basis of Adaptation following Plastic Changes in Coloration in a Novel Environment

Phenotypic plasticity has been hypothesized to precede and facilitate adaptation to novel environments [1-8], but examples of plasticity preceding adaptation in wild populations are rare (but see [9, 10]). We studied a population of side-blotched lizards, Uta stansburiana, living on a lava flow that formed 22,500 years ago [11] to understand the origin of their novel melanic phenotype that makes them cryptic on the black lava. We found that lizards living on and off of the lava flow exhibited phenotypic plasticity in coloration but also appeared to have heritable differences in pigmentation. We sequenced the exomes of 104 individuals and identified two known regulators of melanin production, PREP and PRKAR1A, which had markedly increased levels of divergence between lizards living on and off the lava flow. The derived variants in PREP and PRKAR1A were only found in the lava population and were associated with increased pigmentation levels in an experimental cohort of hatchling lizards. Simulations suggest that the derived variants in the PREP and PRKAR1A genes arose recently and were under strong positive selection in the lava population. Overall, our results suggest that ancestral plasticity for coloration facilitated initial survival in the lava environment and was followed by genetic changes that modified the phenotype in the direction of the induced plastic response, possibly through de novo mutations. These observations provide a detailed example supporting the hypothesis that plasticity aids in the initial colonization of a novel habitat, with natural selection subsequently refining the phenotype with genetic adaptations to the new environment. VIDEO ABSTRACT.

Mouse prolyl oligopeptidase plays a role in trophoblast stem cell differentiation into trophoblast giant cell and spongiotrophoblast

INTRODUCTION

Prolyl oligopeptidase (prolyl endopeptidase, Prep), a multifunctional protease hydrolyzing -Pro-X- peptide bonds, is highly expressed in the mouse placenta, but the function during development is not known. We explored the possibility of Prep's involvement in placental differentiation.

METHODS

We cultured trophoblast stem cells (TSCs) derived from the E6.5 mouse embryo and investigated the detailed expression pattern of Prep during their differentiation. Prep-specific inhibitors were added to the TSC culture, and the effect on the differentiation was assessed by microscopic observation and the expression of marker gene for each placental cell.

RESULTS

During TSC differentiation for 6 days, Prep was constantly detected at mRNA, protein, and activity levels, and the protein was found mainly in the cytoplasm. The addition of 30 μM and 10 μM SUAM-14746, a Prep-specific inhibitor, effectively inhibited the differentiation into spongiotrophoblasts (SpTs) and trophoblast giant cells (TGCs), while the TSC viability was not affected. 5 μM SUAM-14746 impaired the differentiation into SpTs, and 1 μM SUAM-14746 exhibited no effects. Another Prep-specific inhibitor, KYP-2047, did not affect the differentiation. We confirmed efficient inhibition of Prep enzymatic activity in TSCs by both inhibitors.

CONCLUSION

The dose-dependent effect of SUAM-14746 on TSCs suggests that Prep plays an important role in the differentiation into SpTs and TGCs in the mouse placenta.

Differential peptidomics assessment of strain and age differences in mice in response to acute cocaine administration

Neurochemical differences in the hypothalamic-pituitary axis between individuals and between ages may contribute to differential susceptibility to cocaine abuse. This study measured peptide levels in the pituitary gland (Pit) and lateral hypothalamus (LH) in adolescent (age 30 days) and adult (age 65 days) mice from four standard inbred strains, FVB/NJ, DBA/2J, C57BL/6J, and BALB/cByJ, which have previously been characterized for acute locomotor responses to cocaine. Individual peptide profiles were analyzed using mass spectrometric profiling and principal component analysis. Sequences of assigned peptides were verified by tandem mass spectrometry. Principal component analysis classified all strains according to their distinct peptide profiles in Pit samples from adolescent mice, but not adults. Select pro-opiomelanocortin-derived peptides were significantly higher in adolescent BALB/cByJ and DBA/2J mice than in FVB/NJ or C57BL/6J mice. A subset of peptides in the LH, but not in the Pit, was altered by cocaine in adolescents. A 15 mg/kg dose of cocaine induced greater peptide alterations than a 30 mg/kg dose, particularly in FVB/NJ animals, with larger differences in adolescents than adults. Neuropeptides in the LH affected by acute cocaine administration included pro-opiomelanocortin-, myelin basic protein-, and glutamate transporter-derived peptides. The observed peptide differences could contribute to differential behavioral sensitivity to cocaine among strains and ages. Peptides were measured using mass spectrometry (MALDI-TOF) in individual lateral hypothalamus and pituitary samples from four strains and two ages of inbred mice in response to acute cocaine administration. Principal component analyses (PCA) classified the strains according to their peptide profiles from adolescent mice, and a subset of peptides in the lateral hypothalamus was altered by cocaine in adolescents.

Hypothalamic prolyl endopeptidase (PREP) regulates pancreatic insulin and glucagon secretion in mice

Prolyl endopeptidase (PREP) has been implicated in neuronal functions. Here we report that hypothalamic PREP is predominantly expressed in the ventromedial nucleus (VMH), where it regulates glucose-induced neuronal activation. PREP knockdown mice (Prep(gt/gt)) exhibited glucose intolerance, decreased fasting insulin, increased fasting glucagon levels, and reduced glucose-induced insulin secretion compared with wild-type controls. Consistent with this, central infusion of a specific PREP inhibitor, S17092, impaired glucose tolerance and decreased insulin levels in wild-type mice. Arguing further for a central mode of action of PREP, isolated pancreatic islets showed no difference in glucose-induced insulin release between Prep(gt/gt) and wild-type mice. Furthermore, hyperinsulinemic euglycemic clamp studies showed no difference between Prep(gt/gt) and wild-type control mice. Central PREP regulation of insulin and glucagon secretion appears to be mediated by the autonomic nervous system because Prep(gt/gt) mice have elevated sympathetic outflow and norepinephrine levels in the pancreas, and propranolol treatment reversed glucose intolerance in these mice. Finally, re-expression of PREP by bilateral VMH injection of adeno-associated virus-PREP reversed the glucose-intolerant phenotype of the Prep(gt/gt) mice. Taken together, our results unmask a previously unknown player in central regulation of glucose metabolism and pancreatic function.

Quantitation of endogenous peptides using mass spectrometry based methods

The mass spectrometry-based 'omics' sub-discipline that focuses on comprehensive, often exploratory, analyses of endogenous peptides involved in cell-to-cell communication is oftentimes referred to as peptidomics. Although the progress in bioanalytical technology development for peptide discovery has been tremendous, perhaps the largest advances have involved robust quantitative mass spectrometric approaches and data mining algorithms. These efforts have accelerated the discovery and validation of biomarkers, functionally important posttranslational modifications, and unexpected molecular interactions, information that aids drug development. In this article we outline the current approaches used in quantitative peptidomics and the technical challenges that stimulate new advances in the field, while also reviewing the newest literature on functional characterizations of endogenous peptides using quantitative mass spectrometry.

Recent advances in quantitative neuroproteomics

The field of proteomics is undergoing rapid development in a number of different areas including improvements in mass spectrometric platforms, peptide identification algorithms and bioinformatics. In particular, new and/or improved approaches have established robust methods that not only allow for in-depth and accurate peptide and protein identification and modification, but also allow for sensitive measurement of relative or absolute quantitation. These methods are beginning to be applied to the area of neuroproteomics, but the central nervous system poses many specific challenges in terms of quantitative proteomics, given the large number of different neuronal cell types that are intermixed and that exhibit distinct patterns of gene and protein expression. This review highlights the recent advances that have been made in quantitative neuroproteomics, with a focus on work published over the last five years that applies emerging methods to normal brain function as well as to various neuropsychiatric disorders including schizophrenia and drug addiction as well as of neurodegenerative diseases including Parkinson's disease and Alzheimer's disease. While older methods such as two-dimensional polyacrylamide electrophoresis continued to be used, a variety of more in-depth MS-based approaches including both label (ICAT, iTRAQ, TMT, SILAC, SILAM), label-free (label-free, MRM, SWATH) and absolute quantification methods, are rapidly being applied to neurobiological investigations of normal and diseased brain tissue as well as of cerebrospinal fluid (CSF). While the biological implications of many of these studies remain to be clearly established, that there is a clear need for standardization of experimental design and data analysis, and that the analysis of protein changes in specific neuronal cell types in the central nervous system remains a serious challenge, it appears that the quality and depth of the more recent quantitative proteomics studies is beginning to shed light on a number of aspects of neuroscience that relates to normal brain function as well as of the changes in protein expression and regulation that occurs in neuropsychiatric and neurodegenerative disorders.

P2-substituted N-acylprolylpyrrolidine inhibitors of prolyl oligopeptidase: biochemical evaluation, binding mode determination, and assessment in a cellular model of synucleinopathy

We have investigated the effect of regiospecifically introducing substituents in the P2 part of the typical dipeptide derived basic structure of PREP inhibitors. This hitherto unexplored modification type can be used to improve target affinity, selectivity, and physicochemical parameters in drug discovery programs focusing on PREP inhibitors. Biochemical evaluation of the produced inhibitors identified several substituent types that significantly increase target affinity, thereby reducing the need for an electrophilic "warhead" functionality. Pronounced PREP specificity within the group of Clan SC proteases was generally observed. Omission of the P1 electrophilic function did not affect the overall binding mode of three representative compounds, as studied by X-ray crystallography, while the P2 substituents were demonstrated to be accommodated in a cavity of PREP that, to date, has not been probed by inhibitors. Finally, we report on results of selected inhibitors in a SH-SY5Y cellular model of synucleinopathy and demonstrate a significant antiaggregation effect on α-synuclein.

Translational research on prolyl oligopeptidase inhibitors: the long road ahead

Despite the fact that some have passed early phases of clinical trials, no prolyl oligopeptidase inhibitors are currently on the market. Yet, since 2003, there has been a boost in patent applications claiming prolyl oligopeptidase inhibitors for the treatment of Alzheimer's and Parkinson's diseases, and other neurodegenerative and psychiatric disorders. While experts in the field call for innovative scaffolds to develop more potent inhibitors with more favorable properties, they also relate a lack of knowledge of the toxicology, bioavailability, pharmacokinetics and pharmacodynamics of existing compounds that hinders their assessment. Yet, with the current insights, it is difficult to correlate specific inhibitor effects with the postulated functions of prolyl oligopeptidase in the brain.

Epigenetic patterns at the mouse prolyl oligopeptidase gene locus suggest the CpG island in the gene body to be a novel regulator for gene expression

Prolyl oligopeptidase (POP) is a widely distributed serine peptidase which hydrolyzes small peptides on the carboxyl side of an internal proline residue. While its physiological role has been intensely studied, the regulatory mechanism of the gene expression is poorly understood. This time we assessed the POP mRNA expression in mouse embryos and tissues related to reproduction and development and found that POP mRNA was highly expressed in the ovarian granulosa cell, placental spongiotrophoblast, and blastocyst embryo. To elucidate the mechanism by which POP expression is regulated, we investigated DNA methylation and histone modification patterns of the two CpG islands (CGIs) found at the mouse POP locus. Whereas the CGI including the POP promoter (CGI-1) was completely hypomethylated in all the tissues examined, DNA methylation level of the CGI in the gene body (CGI-2) was lower in the granulosa cell, placenta, and blastocyst than in the liver. Some specific CpGs in CGI-2 were significantly demethylated in the three tissues. An in vitro reporter analysis indicated that CGI-2 enhanced POP promoter activity and its effect was significantly reduced by DNA methylation. Moreover, histone H3 acetylation and H3K4 methylation levels of CGI-2 were higher in the granulosa cell than liver. The results suggest that the CGI-2 region is a cis-element for the POP gene expression.

Maternal influence of prolyl endopeptidase on fat mass of adult progeny

Background

Maternal genotype has lifetime effects on progeny, but few specific genes, and no proteases, are known to underlie maternal effects. Prolyl endopeptidase (PREP) is a serine protease with putative substrates that regulate appetite or milk production.

Objective

To test effects of PREP on obesity phenotypes in mice.

Design

Mice with a gene-trap of PREP (PREP^gt/gt) on the C57BL/6J (B6) background were generated. Minimal PREP protein was detected by Western blot. In experiment 1, direct effects of PREP were measured in littermate mice derived from intercrosses of heterozygotes (PREP^WT/gt). In experiment 2, maternal effects of PREP were measured in reciprocal crosses of heterozygous (PREP^WT/gt) and wild-type (PREP^WT/WT) males and females.

Diets

Mice were fed either low-fat (LF, Experiments 1 and 2) or high-fat (HF, Experiment 1) defined diets.

Measurements

Adiposity index (AI) was calculated from body weight and weights of four fat depots measured in 120 day old mice. Fasting plasma glucose, insulin and leptin were measured. In vivo plasma α-MSH levels were measured by targeted quantitative peptidomics.

Results

Experiment 1. In intercross mice there were significant diet effects, but few genotype effects. Body weight and AI in females on the LF diet were marginally affected by pup genotype. There were no genotype effects in males on either diet or in females on the HF diet.

Experiment 2. In contrast, reciprocal crosses of heterozygous males or females with wild-type B6 revealed highly significant parent of origin effects on all traits except body length. Progeny (wild-type and heterozygous genotypes and both sexes) born to female PREP^WT/gt heterozygotes had fat pads that weighed as much as 2-fold more at 120 days old than progeny born to male heterozygotes.