Insect peptide hormones, an overview of the present literature

A comprehensive overview of the recent state of the art of insect peptide hormones with chemical structures is presented. An increased interest in insect neuropeptides and dynamic development of that research area has been influenced by a rapid improvement of instrumentation necessary for isolation and structural characterization. Several research teams have studied the relationships between biological properties of insect and vertebrate peptide hormones. Thus hormones from the AKH family can be considered glucagon counterparts, whereas the myotropic hormones such as proctolin and Lem-PK (LPK) are a substance P equivalent. Insect melanization hormones Bom-MRCH in their structural characteristics and properties resemble those of mammal MSH, and leucosulfakinins Lem-SK-I and -II show some similarities with gastrin II and cholecystokinin. Bombyxin-II (Bom-PTTH-II) reveals a structural homology with human insulin and similar biological properties to adenocorticotropic mammal hormone. Allatostatin (Dip-JHS-I) may be compared to somatostatin as it can be inferred from the observations that this peptide modulates JH secretion in cockroach, Blattella germanica. Determination of the primary structure of eclosion hormones Mas-EH and Bom-EH-II as well as the amino acid sequence of allatotropin and allatostatin is a significant contribution to the understanding of the molecular mechanisms of metamorphosis and insect development.

PAI-1 and kidney fibrosis

Substantial evidence demonstrates a link of increased plasminogen activator inhibitor-1 (PAI-1) and glomerulosclerosis and kidney fibrosis, providing a novel therapeutic option for prevention and treatment of chronic kidney diseases. Several mechanisms contributing to increased PAI-1 will be addressed, including classic key profibrotic factors such as the renin-angiotensin-system (RAS) and transforming growth factor-beta (TGF-b???and novel molecules identified by proteomic analysis, such as thymosin- b4. The fibrotic sequelae caused by increased PAI-1 in kidney depend not only on its classic inhibition of tissue-type and urokinase-type plasminogen activators (tPA and uPA), but also its influence on cell migration.

The communication factor EDF and the toxin-antitoxin module mazEF determine the mode of action of antibiotics

It was recently reported that the production of Reactive Oxygen Species (ROS) is a common mechanism of cell death induced by bactericidal antibiotics. Here we show that triggering the Escherichia coli chromosomal toxin-antitoxin system mazEF is an additional determinant in the mode of action of some antibiotics. We treated E. coli cultures by antibiotics belonging to one of two groups: (i) Inhibitors of transcription and/or translation, and (ii) DNA damaging. We found that antibiotics of both groups caused: (i) mazEF-mediated cell death, and (ii) the production of ROS through MazF action. However, only antibiotics of the first group caused mazEF-mediated cell death that is ROS-dependent, whereas those of the second group caused mazEF-mediated cell death by an ROS-independent pathway. Furthermore, our results showed that the mode of action of antibiotics was determined by the ability of E. coli cells to communicate through the signaling molecule Extracellular Death Factor (EDF) participating in mazEF induction.

The SV40 capsid is stabilized by a conserved pentapeptide hinge of the major capsid protein VP1

The simian virus 40 (SV40) outer shell is composed of 72 pentamers of VP1. The core of the VP1 monomer is a beta-barrel with jelly-roll topology and extending N- and C-terminal arms. A pentapeptide hinge, KNPYP, tethers the C-arm to the VP1 beta-barrel core. The five C-arms that extend from each pentamer insert into the neighbouring pentamers, tying them together through different types of interactions. In the mature virion, this element adopts either of six conformations according to their location in the capsid. We found that the hinge is conserved among 16 members of the Polyomaviridae, attesting to its importance in capsid assembly and/or structure. We have used site-directed mutagenesis to gain an understanding into the structural requirements of this element: Y299 was changed to A, F, and T, and P300 to A and G. The mutants showed reduction in viability to varying degrees. Unexpectedly, assembly was reduced only to a small extent. However, the data showed that the mutants were highly unstable. The largest effect was observed for mutations of P300, indicating a role of the proline in the virion structure. P300G was more unstable than P300A, indicating a requirement for rigidity of the pentapeptide hinge. Y299T and Y299A were more defective in viability than Y299F, highlighting the importance of an aromatic ring at this position. Structural inspection showed that this aromatic ring contacts C-arms of neighbouring pentamers. Computational modelling predicted loss of stability of the Y mutants in concordance with the experimental results. This study provides insights into the structural details of the pentapeptide hinge that are responsible for capsid stability.

Expression of lipid storage droplet protein-1 may define the role of AKH as a lipid mobilizing hormone in Manduca sexta

Adipokinetic hormone (AKH) is the main hormone involved in the acute regulation of hemolymph lipid levels in several insects. In adult Manduca sexta AKH promotes a rapid phosphorylation of "Lipid storage protein-1", Lsd1, and a concomitant activation of the rate of hydrolysis of triglycerides by the main fat body lipase. In contrast, in the larval stage AKH modulates hemolymph trehalose levels. The present study describes the sequence of a full-length Lsd1 cDNA obtained from M. sexta fat body and investigates a possible link between Lsd1 expression and the distinct effects of AKH in larva and adult insects. The deduced protein sequence showed a high degree of conservation compared to other insect Lsd1s, particularly in the central region of the protein (amino acids 211-276) in which the predicted lipid binding helices are found. Lsd1 was absent in feeding larva and its abundance progressively increased as the insect develops from the non-feeding larva to adult. Contrasting with the levels of protein, Lsd1 transcripts were maximal during the feeding larval stages. The subcellular distribution of Lsd1 showed that the protein exclusively localizes in the lipid droplets. Lsd1 was found in the fat body but it was undetectable in lipid droplets isolated from oocytes or embryos. The present study suggests a link between AKH-stimulated lipolysis in the fat body and the expression of Lsd1.

Functions of flatworm neuropeptides NPF, GYIRF and FMRF in course of pharyngeal regeneration of anterior body fragments of planarian, Girardia tigrina

The development of the new pharynx in anterior body fragments of G. tigrina was followed for 7 days by immunocytochemical (ICC) study using antiserum to neuropeptide F (NPF) and muscle staining with phalloidin. ICC investigation revealed the presence of NPF in pharyngeal nervous system, peripheral nerve plexuses, in central nervous system of intact planarians. NPF-immunoreactive (IR) nerve fibres were found at the site of regeneration surrounding pharyngeal rudiment. Restoration of the pharynx function during regeneration was analysed by appearance of food response in anterior fragments. Stimulating effects of NPF and FMRF on the pharyngeal regeneration has been observed. The data indicates an important role of neuropeptides in morphogenetic processes.

Possible involvement of dynorphin A release via mu1-opioid receptor on supraspinal antinociception of endomorphin-2

It has been demonstrated that the antinociception induced by i.t. or i.c.v. administration of endomorphins is mediated through mu-opioid receptors. Moreover, though endomorphins do not have appreciable affinity for kappa-opioid receptors, pretreatment with the kappa-opioid receptor antagonist nor-binaltorphimine markedly blocks the antinociception induced by i.c.v.- or i.t.-injected endomorphin-2, but not endomorphin-1. These evidences propose the hypothesis that endomorphin-2 may initially stimulate the mu-opioid receptors, which subsequently induces the release of dynorphins acting on kappa-opioid receptors to produce antinociception. The present study was performed to determine whether the release of dynorphins by i.c.v.-administered endomorphin-2 is mediated through mu-opioid receptors for producing antinociception. Intracerebroventricular pretreatment with an antiserum against dynorphin A, but not dynorphin B or alpha-neo-endorphin, and s.c. pretreatment with kappa-opioid receptor antagonist nor-binaltorphimine dose-dependently attenuated the antinociception induced by i.c.v.-administered endomorphin-2, but not endomorphin-1 and DAMGO. The attenuation of endomorphin-2-induced antinociception by pretreatment with antiserum against dynorphin A or nor-binaltorphimine was dose-dependently eliminated by additional s.c. pretreatment with a selective mu-opioid receptor antagonist beta-funaltrexamine or a selective mu1-opioid receptor antagonist naloxonazine at ultra low doses, which are inactive against micro-opioid receptor agonists in antinociception, suggesting that endomorphin-2 stimulates distinct subclass of micro1-opioid receptor that induces the release of dynorphin A acting on kappa-opioid receptors in the brain. It concludes that the antinociception induced by supraspinally administered endomorphin-2 is in part mediated through the release of endogenous kappa-opioid peptide dynorphin A, which is caused by the stimulation of distinct subclass of micro1-opioid receptor.

Anatomy, function and regulation of neuropeptide EI (NEI)

This review is focused on the anatomy, role and behavior of neuropeptide-glutamic acid-isoleucine (NEI), providing a general report on the neuropeptide. In addition to hormone release, this peptide also takes part in the regulation of grooming behavior and locomotor activity. NEI is produced by cleavage of prepro-MCH that probably takes place at the Lys(129)-Arg(130) and Arg(145)-Arg(146) sites (the glycine residue on the C-terminus of NEI strongly suggests that this peptide is amidated). This same prohormone is also the precursor of MCH, widely studied in relation to food and water intake, and NGE, of which little is known. NEI and MCH are extensively colocalized throughout the central nervous system (CNS), and NEI is also present in peripheral tissues. The latter is also effective in stimulating luteinizing hormone (LH) release and, to a lesser extent, FSH from primary pituitary cell cultures. In addition to releasing LH from the medial eminence, NEI also acts directly on gonadotropes. Lastly, this neuropeptide also acts at the CNS level on gonadotropin-releasing hormone (GnRH) neurons.

Repression of RNA polymerase II transcription by a Drosophila oligopeptide

Background

Germline progenitors resist signals that promote differentiation into somatic cells. This occurs through the transient repression in primordial germ cells of RNA polymerase II, specifically by disrupting Ser2 phosphorylation on its C-terminal domain.

Methodology/Principal Findings

Here we show that contrary to expectation the Drosophila polar granule component (pgc) gene functions as a protein rather than a non-coding RNA. Surprisingly, pgc encodes a 71-residue, dimeric, alpha-helical oligopeptide repressor. In vivo data show that Pgc ablates Ser2 phosphorylation of the RNA polymerase II C-terminal domain and completely suppresses early zygotic transcription in the soma.

Conclusions/Significance

We thus identify pgc as a novel oligopeptide that readily inhibits gene expression. Germ cell repression of transcription in Drosophila is thus catalyzed by a small inhibitor protein.

Differentiation stage alters matrix control of stem cells

Cues from the material to which a cell is adherent (e.g., adhesion ligand presentation, substrate elastic modulus) clearly influence the phenotype of differentiated cells. However, it is currently unclear if stem cells respond similarly to these cues. This study examined how the overall density and nanoscale organization of a model cell adhesion ligand (arginine-glycine-aspartic acid [RGD] containing peptide) presented from hydrogels of varying stiffness regulated the proliferation of a clonally derived stem cell line (D1 cells) and preosteoblasts (MC3T3-E1). While the growth rate of MC3T3-E1 preosteoblasts was responsive to nanoscale RGD ligand organization and substrate stiffness, the D1 stem cells were less sensitive to these cues in their uncommitted state. However, once the D1 cells were differentiated towards the osteoblast lineage, they became more responsive to these signals. These results demonstrate that the cell response to material cues is dependent on the stage of cell commitment or differentiation, and these findings will likely impact the design of biomaterials for tissue regeneration.

Effects of kisspeptin-10 on the electrophysiological manifestation of gonadotropin-releasing hormone pulse generator activity in the female rat

Kisspeptins are extraordinarily potent in stimulating gonadotropic hormone secretion via an action on the hypothalamic GnRH neural system. Because the physiological frequency of the GnRH pulse generator is a critical component of the control system that governs reproductive processes, the aim of this study was to examine the effect of kisspeptin-10 on pulsatile LH secretion and on the electrophysiological manifestation of GnRH pulse generator activity to determine frequency modulatory effects. Adult Sprague Dawley rats were ovariectomized and chronically implanted with electrodes in the arcuate nucleus to record the characteristic increases in hypothalamic multiunit electrical activity volleys coincident with the initiation of each LH pulse measured in peripheral blood and/or indwelling cardiac catheters for the collection of blood samples (25 microl) every 5 min for 6-7 h for the measurement of LH. Intravenous infusion of kisspeptin-10 (7.5, 35, and 100 nmol) induced a dose-dependent increase in LH secretion. The stimulatory effect of kisspeptin-10 (100 nmol) on LH secretion was blocked by the GnRH antagonist cetrorelix, precluding a singular action on gonadotropes. Unexpectedly, however, the marked increase in LH release in response to kisspeptin-10 (100 nmol) administration was not accompanied by any change in multiunit electrical activity volley frequency. It seem unlikely, therefore, that kisspeptin-10 has an appreciable frequency modulatory effect on GnRH pulse generator activity in the female rat.

Early development of forebrain gonadotrophin-releasing hormone (GnRH) neurones and the role of GnRH as an autocrine migration factor

Normal migration of the gonadotrophin-releasing hormone (GnRH) neurones during early development, from the olfactory region to the hypothalamus, is crucial for reproductive development in all vertebrates. The establishment of the GnRH system includes tangential migration of GnRH perikarya as well as extension of GnRH fibres to various areas of the central nervous system (CNS). The exact spatio-temporal nature of this process, as well as the factors governing it, are not fully understood. We studied the development of the GnRH system and the effects of GnRH knockdown using a newly developed GnRH3:EGFP transgenic zebrafish line. We found that enhanced green fluorescent protein is specifically and robustly expressed in GnRH3 neurones and fibres. GnRH3 fibres in zebrafish began to extend as early as 26 h post-fertilisation and by 4-5 days post-fertilisation had developed into an extensive network reaching the optic tract, telencephalon, hypothalamus, midbrain tegmentum and hindbrain. GnRH3 fibres also innervated the retina and projected into the trunk via the spinal cord. GnRH3 perikarya were observed migrating along their own fibres from the olfactory region to the preoptic area (POA) via the terminal nerve ganglion and the ventral telencephalon. GnRH3 cells were also observed in the trigeminal ganglion. The establishment of the GnRH3 fibre network was disrupted by morpholino-modified antisense oligonucleotides directed against GnRH3 causing abnormal fibre development and pathfinding, as well as anomalous GnRH3 perikarya localisation. These findings support the hypothesis that GnRH3 neurones migrate from the olfactory region to the POA and caudal hypothalamus. Novel data regarding the early development of the GnRH3 fibre network in the CNS and beyond are described. Moreover we show, in vivo, that GnRH3 is an important factor regulating GnRH3 fibre pathfinding and neurone localisation in an autocrine fashion.

Modulatory role of neuropeptide FF system in nociception and opiate analgesia

The tetra-peptide FMRF-NH(2) is a cardioexcitatory peptide in the clam. Using the antibody against this peptide, FMRF-NH(2)-like immunoreactive material was detected in mammalian CNS. Subsequently, mammalian FMRF-NH(2) immunoreactive peptides were isolated from bovine brain and characterized to be FLFQPQRF-NH(2) (NPFF) and AGEGLSSPFWSLAAPQRF-NH(2) (NPAF). The genes encoding NPFF precursor proteins and NPFF receptors 1 and 2 are expressed in all vertebrate species examined to date and are highly conserved. Among many biological roles suggested for the NPFF system, the possible modulatory role of NPFF in nocicetion and opiate analgesia has been most widely investigated. Pharmacologically, NPFF-related peptides were found to exhibit analgesia and also potentiate the analgesic activity of opiates when administered intrathecally but attenuate the opiate induced analgesia when administered intracerebroventricularly. RF-NH(2) peptides including NPFF-related peptides were found to delay the rate of acid sensing ion channels (ASIC) desensitization resulting in enhancing acid gated currents, raising the possibility that NPFF also may have a pain modulatory role through ASIC. The genes for NPFF as well as NPFF-R2, preferred receptor for NPFF, are highly unevenly expressed in the rat CNS with the highest levels localized to the superficial layers of the dorsal spinal cord. These two genes are also present in the dorsal root ganglia (DRG), though at low levels in normal rats. NPFF and NPFF-R2 mRNAs were found to be coordinately up-regulated in spinal cord and DRG of rats with peripheral inflammation. In addition, NPFF-R2 immunoreactivity in the primary afferents was increased by peripheral inflammation. The findings from the early studies on the analgesic and morphine modulating activities suggested a role for NPFF in pain modulation and this possibility is further supported by the distribution of NPFF and its receptor and the regulation of the NPFF system in vivo.

[Influence of integrin-binding motif (RGD) on attachment and internalization of avian adenovirus CELO in mammalian cells]

Recombinant avian adenovirus CELO bearing sequence RGD in the structure of a HI-loop of long fiber was designed. Experiments in vitro revealed that introduction of RGD-motif into fiber of CELO increased the ability of the virus to be attached to a surface of CAR-negative cells, and raised efficiency of the process of internalization of the virus both in CAR-positive, and in CAR-negative cells.

The role of osteoactivin-derived peptides in osteoblast differentiation

BACKGROUND

In our previous studies, we found that osteoactivin (OA) plays an important role in the regulation of osteoblast differentiation in vitro. Our studies also suggested that the region of OA protein that contains an RGD motif might play a vital role in the function of OA in osteoblast differentiation. In this study, we examined the functional role of OA-derived peptide containing the RGD motif (OA-D) in osteoblast differentiation.

MATERIAL/METHODS

For this purpose, we designed another peptide, termed OA-E, that has sequence similar to OA-D but with glutamic acid (E) instead of aspartic acid (D). The effect of OA-E peptide on osteoblast differentiation was examined. Interestingly, OA-E peptide induced osteoblast differentiation in a manner similar to OA-D peptide. These data suggested that the effect of OA-derived peptides is RGD independent and it could be dependent on other features in the amino acid sequence of these peptides.

RESULTS

OA-D peptide treatment markedly induced osteoblast differentiation markers in vitro compared to cultures treated with negative control peptide (NCP). Interestingly, OA-E peptide induced osteoblast differentiation in a manner similar to OA-D peptide. These data suggested that the effect of OA-derived peptides is RGD independent and it could be dependent on other features in the amino acid sequence of these peptides. Since phosphorylation of amino acid residues in proteins and peptides plays a major role in biological systems, the phosphorylation pattern of amino acid sequences of OA-derived peptides and OA protein family members were examined using bioinformatic analysis tools. We found that OA-derived peptides and OA protein family members have serine residue, close to c-terminus and might be phosphorylated with casein kinase II. Casein kinase II is known to phosphorylate many osteoblast-related proteins that regulate osteoblast development and differentiation such as osteopontin and vitronectin.

CONCLUSIONS

Collectively, these data showed that both OA-D and OA-E peptides significantly induced osteoblast differentiation in vitro and that effect is RGD independent.

From MIF-1 to endomorphin: the Tyr-MIF-1 family of peptides

The Tyr-MIF-1 family of small peptides has served a prototypic role in the introduction of several novel concepts into the peptide field of research. MIF-1 (Pro-Leu-Gly-NH(2)) was the first hypothalamic peptide shown to act "up" on the brain, not just "down" on the pituitary. In several situations, including clinical depression, MIF-1 exhibits an inverted U-shaped dose-response relationship in which increasing doses can result in decreasing effects. This tripeptide also can antagonize opiate actions, and the first report of such activity also correctly predicted the discovery of other endogenous antiopiate peptides. The tetrapeptide Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH(2)) not only shows antiopiate activity, but also considerable selectivity for the mu-opiate binding site. Tyr-W-MIF-1 (Tyr-Pro-Trp-Gly-NH(2)) is an even more selective ligand for the mu receptor, leading to the discovery of two more Tyr-Pro tetrapeptides that have the highest specificity and affinity for this site. These are the endomorphins: endomorphin-1 is Tyr-Pro-Trp-Phe-NH(2) and endomorphin-2 is Tyr-Pro-Phe-Phe-NH(2). Tyr-MIF-1 proved, contrary to the then prevailing dogma, that peptides can be saturably transported across the blood-brain barrier by a quantifiable transport system. Unexpectedly, the Tyr-MIF-1 transporter is shared with Met-enkephalin. In the era in which it was doubtful whether a peripheral peptide could exert CNS effects, the Tyr-MIF-1 family of peptides also explicitly showed that they can exert more than one central action that persists longer than their half-lives in blood. These peptides clearly illustrate that the name of a peptide restricts neither its actions nor its conceptual implications.

Endomorphins restored the endothelium-dependent relaxation of the rabbit aorta rings exposed to high D-glucose condition via NO-cGMP pathway

Rings of rabbit aorta that were both incubated in a high concentration of D-glucose and contracted submaximally by phenylephrine showed significantly decreased endothelium-dependent relaxations induced by acetylcholine. The cGMP production of aorta rings was also reduced. Treatment with endomorphins (1-1000 nmol/L) restored acetylcholine-induced relaxations of aorta rings incubated in high glucose concentrations and increased the cGMP synthesis. Moreover, this effect of endomorphins on endothelium was antagonized by naloxone, and the increase in the production of cGMP was also blocked.

Bax-inhibiting peptides derived from Ku70 and cell-penetrating pentapeptides

We found that Ku70, a known DNA repair factor, has a novel function to bind and inhibit Bax (Bcl-2-associated X protein), a key mediator of apoptosis. Pentapeptides derived from the Bax-binding domain of Ku70 were cell-permeable and protected cells from Bax-mediated apoptosis. These pentapeptides were called BIPs (Bax-inhibiting peptides). BIPs may become a useful therapeutic tool to reduce cellular damage. We also generated BIP mutant pentapeptides that do not inhibit Bax, but retain their cell-penetrating activity. Since both BIPs and BIP mutants are cell-permeable, these peptides were designated CPP5s (cell-penetrating pentapeptides). Among the CPP5s discovered, VPTLK (BIP) and KLPVM (BIP mutant) were confirmed to possess protein transduction activity by examination of the delivery of GFP (green fluorescent protein) into cells by these peptides. The mechanism of cell penetration by CPP5s is not known. CPP5s enter the cell at 0 and 4 degrees C. In preliminary studies, various inhibitors of endocytosis and pinocytosis did not show any significant suppression of CPP5 cell entry. CPP5s have very low toxicity in vitro and in vivo and so may be useful tools in order to develop non-toxic drug-delivery technologies.

αvβ5 Integrin Sustains Growth of Human Pre-B Cells through an RGD-independent Interaction with a Basic Domain of the CD23 Protein

CD23 is a type II transmembrane glycoprotein synthesized by hematopoietic cells that has biological activity in both membrane-bound and freely soluble forms, acting via a number of receptors, including integrins. We demonstrate here that soluble CD23 (sCD23) sustains growth of human B cell precursors via an RGD-independent interaction with the alphavbeta5 integrin. The integrin recognizes a tripeptide motif in a small disulfide-bonded loop at the N terminus of the lectin head region of CD23, centered around Arg(172), Lys(173), and Cys(174) (RKC). This RKC motif is present in all forms of sCD23 with cytokine-like activity, and cytokine activity is independent of the lectin head, an "inverse RGD" motif, and the CD21 and IgE binding sites. RKC-containing peptides derived from this region of CD23 bind alphavbeta5 and are biologically active. The binding and activity of these peptides is unaffected by inclusion of a short peptide containing the classic RGD sequence recognized by integrins, and, in far-Western analyses, RKC-containing peptides bind to the beta subunit of the alphavbeta5 integrin. The interaction between alphavbeta5 and sCD23 indicates that integrins deliver to cells important signals initiated by soluble ligands without the requirement for interactions with RGD motifs in their common ligands. This mode of integrin signaling may not be restricted to alphavbeta5.

Evidence for gut factor in K+ homeostasis

We tested the hypothesis that K+ intake is sensed by putative K+ sensors in the splanchnic areas, and renal K+ handling is regulated by this signal. K+ was infused for 2 h into overnight-fasted rats via the jugular vein (systemic infusion), hepatic portal vein (intraportal infusion), or stomach (intragastric infusion) ( n = 5 each), and plasma K+ concentration ([K+]) and renal K+ excretion were measured during the 2-h preinfusion, 2-h K+ infusion, and 3-h washout periods. During systemic K+ infusion, plasma [K+] increased by ∼1.3 mM ( P < 0.05), and, on cessation of the K+ infusion, plasma [K+] fell to the preinfusion level within 1–2 h. Renal K+ excretion changed in proportion to the changes in plasma [K+]. During intraportal or intragastric K+ infusion, plasma [K+] and renal K+ excretion profiles were similar to those with systemic infusion. The effects of K+ infusions via the different routes ( n = 5 or 6 each) were also studied during simultaneous feeding of overnight-fasted rats with a K+-deficient diet. During the meal, intraportal infusion resulted in increases in plasma [K+] similar to those with the systemic K+ infusion, while intragastric K+ infusion did not significantly increase plasma [K+]. Thus, when the intragastric K+ infusion was combined with a meal, there was marked enhancement of clearance of the K+ infused, which was associated with an apparent increase in renal efficiency of K+ excretion. These data suggest that there may be a gut factor that enhances renal efficiency of K+ excretion during meal (or dietary K+) intake.

Engineering RGD nanopatterned hydrogels to control preosteoblast behavior: a combined computational and experimental approach

The adhesion ligand arginine-glycine-aspartic acid (RGD) has been coupled to various materials to be used as tissue culture matrices or cell transplantation vehicles, and recent studies indicate that nanopatterning RGD into high-density islands alters key cell behaviors. Previous studies have failed, however, to conclusively decouple the effects of RGD bulk density and individual pattern parameters (i.e. RGDs/island and island distribution) on these altered cell responses. Using a nanopatterned RGD-coupled alginate hydrogel matrix, this work combines computational, statistical and experimental approaches to elucidate the effects of RGD patterns on four key cell responses. This study shows that in MC3T3 preosteoblasts focal adhesion kinase (FAK) Y397 phosphorylation, cell spreading, and osteogenic differentiation can be controlled by RGD nanopatterning, with the distribution of islands throughout the hydrogel (i.e. how closely spaced the islands are) being the most significant pattern parameter. More closely spaced islands favor FAK Y397 phosphorylation and cell spreading, while more widely spaced islands favor differentiation. Proliferation, in contrast, is primarily a function of RGD bulk density. Nanopatterning of cell adhesion ligands has tremendous potential as a simple tool to gain significant control over multiple cell behaviors in engineered extracellular matrix (ECM).

Molecular changes in the vasculature of injured tissues

We have explored molecular specialization of the vasculature of regenerating wound tissue in the skin and tendons to identify a different repertoire of markers from that obtained by studying tumor vasculature. We screened a phage-displayed peptide library for peptides that home to wounds in mice and identified two peptides that selectively target phage to skin and tendon wounds: CARSKNKDC (CAR) and CRKDKC (CRK). CAR is homologous to heparin-binding sites in various proteins and binds to cell surface heparan sulfate and heparin. CRK is similar to a segment in thrombospondin type 1 repeat. Intravenously injected CAR and CRK phage, as well as fluorescein-labeled CAR and CRK peptides, selectively accumulated at wound sites, where they partially co-localized with blood vessels. The CAR peptide showed a preference for early stages of wound healing, whereas the CRK favored wounds at later stages of healing. The CAR peptide was internalized into the target cells and delivered the fluorescent label into the cell nuclei. These results identify new molecular markers in wound tissues and show that the expression of these markers in wound vasculature changes as healing progresses. The peptides recognizing these markers may be useful in delivering treatments into regenerating tissues.

Properties of Enterococcus faecalis plasmid pAD1, a member of a widely disseminated family of pheromone-responding, conjugative, virulence elements encoding cytolysin

The 60-kb pAD1 represents a large and widely disseminated family of conjugative, pheromone-responding, virulence plasmids commonly found in clinical isolates of Enterococcus faecalis. It encodes a hemolysin/bacteriocin (cytolysin) shown to contribute to virulence in animal models, and the related bacteriocin is active against a wide variety of Gram-positive bacteria. This review summarizes what is currently known about the molecular biology of pAD1, including aspects of its cytolytic, UV-resistance, replication, maintenance, and conjugative properties.