Repeated intracerebral teneurin C-terminal associated peptide (TCAP)-1 injections produce enduring changes in behavioral responses to corticotropin-releasing factor (CRF) in rat models of anxiety

A novel role for Teneurin C-terminal Associated Peptide (TCAP) in the regulation of cardiac activity in the Sydney rock oyster, Saccostrea glomerata

Teneurin C-terminal associated peptide (TCAP) is an ancient bioactive peptide that is highly conserved in metazoans. TCAP administration reduces cellular and behavioural stress in vertebrate and urochordate models, yet despite numerous studies in higher animals, there is limited knowledge of its role in invertebrates. In particular, there are no studies on TCAP's effects on the heart of any metazoan, which is a critical organ in the stress response. We used the Sydney rock oyster (SRO) as an invertebrate model to investigate a potential role for sroTCAP in regulating cardiac activity, including during stress. sroTCAP is localized to the neural innervation network of the SRO heart, and suggested binding with various heart proteins related to metabolism and stress, including SOD, GAPDH and metabotropic glutamate receptor. Intramuscular injection of sroTCAP (10 pmol) significantly altered the expression of heart genes that are known to regulate remodelling processes under different conditions, and modulated several gene families responsible for stress mitigation. sroTCAP (1 and 10 pmol) was shown to cause transient bradycardia (heart rate was reduced by up to 63% and for up to 40 min post-administration), indicative of an unstressed state. In summary, this study has established a role for a TCAP in the regulation of cardiac activity through modulation of physiological and molecular components associated with energy conservation, stress and adaptation. This represents a novel function for TCAP and may have implications for higher-order metazoans.

Skeletal muscle metabolism and contraction performance regulation by teneurin C-terminal-associated peptide-1

Skeletal muscle regulation is responsible for voluntary muscular movement in vertebrates. The genes of two essential proteins, teneurins and latrophilins (LPHN), evolving in ancestors of multicellular animals form a ligand-receptor pair, and are now shown to be required for skeletal muscle function. Teneurins possess a bioactive peptide, termed the teneurin C-terminal associated peptide (TCAP) that interacts with the LPHNs to regulate skeletal muscle contractility strength and fatigue by an insulin-independent glucose importation mechanism in rats. CRISPR-based knockouts and siRNA-associated knockdowns of LPHN-1 and-3 in the C2C12 mouse skeletal cell line shows that TCAP stimulates an LPHN-dependent cytosolic Ca2+ signal transduction cascade to increase energy metabolism and enhance skeletal muscle function via increases in type-1 oxidative fiber formation and reduce the fatigue response. Thus, the teneurin/TCAP-LPHN system is presented as a novel mechanism that regulates the energy requirements and performance of skeletal muscle.

Teneurin and TCAP Phylogeny and Physiology: Molecular Analysis, Immune Activity, and Transcriptomic Analysis of the Stress Response in the Sydney Rock Oyster (Saccostrea glomerata) Hemocytes

Teneurin C-terminal associated peptide (TCAP) is an ancient bioactive peptide that is highly conserved in metazoans. TCAP administration reduces cellular and behavioral stress in vertebrate and urochordate models. There is little information for invertebrates regarding the existence or function of a TCAP. This study used the Sydney rock oyster (SRO) as a molluscan model to characterize an invertebrate TCAP, from molecular gene analysis to its physiological effects associated with hemocyte phagocytosis. We report a single teneurin gene (and 4 teneurin splice variants), which encodes a precursor with TCAP that shares a vertebrate-like motif, and is similar to that of other molluscan classes (gastropod, cephalopod), arthropods and echinoderms. TCAP was identified in all SRO tissues using western blotting at 1-2 different molecular weights (~22 kDa and ~37kDa), supporting precursor cleavage variation. In SRO hemolymph, TCAP was spatially localized to the cytosol of hemocytes, and with particularly high density immunoreactivity in granules. Based on 'pull-down' assays, the SRO TCAP binds to GAPDH, suggesting that TCAP may protect cells from apoptosis under oxidative stress. Compared to sham injection, the intramuscular administration of TCAP (5 pmol) into oysters modulated their immune system by significantly reducing hemocyte phagocytosis under stress conditions (low salinity and high temperature). TCAP administration also significantly reduced hemocyte reactive oxygen species production at ambient conditions and after 48 h stress, compared to sham injection. Transcriptomic hemocyte analysis of stressed oysters administered with TCAP demonstrated significant changes in expression of genes associated with key metabolic, protective and immune functions. In summary, this study established a role for TCAP in oysters through modulation of physiological and molecular functions associated with energy conservation, stress and cellular defense.

Synthetic Peptides as Therapeutic Agents: Lessons Learned From Evolutionary Ancient Peptides and Their Transit Across Blood-Brain Barriers

Peptides play a major role in the transmission of information to and from the central nervous system. However, because of their structural complexity, the development of pharmacological peptide-based therapeutics has been challenged by the lack of understanding of endogenous peptide evolution. The teneurin C-terminal associated peptides (TCAP) possess many of the required attributes of a practical peptide therapeutic. TCAPs, associated with the teneurin transmembrane proteins that bind to the latrophilins, members of the Adhesion family of G-protein-coupled receptors (GPCR). Together, this ligand-receptor unit plays an integral role in synaptogenesis, neurological development, and maintenance, and is present in most metazoans. TCAP has structural similarity to corticotropin-releasing factor (CRF), and related peptides, such as calcitonin and the secretin-based peptides and inhibits the (CRF)-associated stress response. Latrophilins are structurally related to the secretin family of GPCRs. TCAP is a soluble peptide that crosses the blood-brain barrier and regulates glucose transport into the brain. We posit that TCAP represents a phylogenetically older peptide system that evolved before the origin of the CRF-calcitonin-secretin clade of peptides and plays a fundamental role in the regulation of cell-to-cell energy homeostasis. Moreover, it may act as a phylogenetically older peptide system that evolved as a natural antagonist to the CRF-mediated stress response. Thus, TCAP's actions on the CNS may provide new insights into the development of peptide therapeutics for the treatment of CNS disorders.

Activity of the Carboxy-Terminal Peptide Region of the Teneurins and Its Role in Neuronal Function and Behavior in Mammals

Teneurin C-terminal associated peptides (TCAPs) are an evolutionarily ancient family of 40- to 41-residue bioactive peptides located on the extracellular end of each of the four teneurin transmembrane proteins. TCAP-1 may exist as a tethered peptide at the teneurin-1 carboxy end or as an independent peptide that is either released via post-transcriptional cleavage from its teneurin-1 pro-protein or independently expressed as its own mRNA. In neurons, soluble TCAP-1 acts as a paracrine factor to regulate cellular activity and neuroplastic interactions. In vitro studies indicate that, by itself, synthetic TCAP-1 promotes neuron growth and protects cells from chemical insult. In vivo, TCAP-1 increases hippocampal neuron spine density, reduces stress-induced behavior and ablates cocaine-seeking behaviors. Together, these studies suggest that the physiological effects of TCAP-1 are a result of an inhibition of corticotropin-releasing factor (CRF) activity leading to increased energy production. This hypothesis is supported by in vivo functional positron emissions tomography studies, which demonstrate that TCAP-1 significantly increases glucose uptake in rat brain. Complimentary in vitro studies show that enhanced glucose uptake is the result of TCAP-1-induced insertion of the glucose transporter into the neuronal plasma membrane, leading to increased glucose uptake and ATP production. Interestingly, TCAP-1-mediated glucose uptake occurs through a novel insulin-independent pathway. This review will focus on examining the role of TCAP on neuronal energy metabolism in the central nervous system.

Teneurin Structures Are Composed of Ancient Bacterial Protein Domains

Pioneering bioinformatic analysis using sequence data revealed that teneurins evolved from bacterial tyrosine-aspartate (YD)-repeat protein precursors. Here, we discuss how structures of the C-terminal domain of teneurins, determined using X-ray crystallography and electron microscopy, support the earlier findings on the proteins’ ancestry. This chapter describes the structure of the teneurin scaffold with reference to a large family of teneurin-like proteins that are widespread in modern prokaryotes. The central scaffold of modern eukaryotic teneurins is decorated by additional domains typically found in bacteria, which are re-purposed in eukaryotes to generate highly multifunctional receptors. We discuss how alternative splicing contributed to further diversifying teneurin structure and thereby function. This chapter traces the evolution of teneurins from a structural point of view and presents the state-of-the-art of how teneurin function is encoded by its specific structural features.

Teneurins and Teneurin C-Terminal Associated Peptide (TCAP) in Metabolism: What's Known in Fish?

Teneurins have well established roles in function and maintenance of the central nervous systems of vertebrates. In addition, teneurin c-terminal associated peptide (TCAP), a bioactive peptide found on the c-terminal portion of teneurins, has been shown to regulate glucose metabolism. Although, the majority of research conducted on the actions of teneurins and TCAPs has strictly focused on neurological systems in rodents, TCAP was first identified in rainbow trout after screening trout hypothalamic cDNA. This suggests a conserved functional role of TCAP across vertebrates, however, the current depth of literature on teneurins and TCAPs in fish is limited. In addition, the overall function of TCAP in regulating metabolism is unclear. This review will highlight work that has been conducted specifically in fish species in relation to the teneurin system and metabolism in order to identify areas of research that are needed for future work.

Teneurin C-Terminal Associated Peptide (TCAP)-1 and Latrophilin Interaction in HEK293 Cells: Evidence for Modulation of Intercellular Adhesion

The teneurins are a family of four transmembrane proteins essential to intercellular adhesion processes, and are required for the development and maintenance of tissues. The Adhesion G protein-coupled receptor (GPCR) subclass latrophilins (ADGRL), or simply the latrophilins (LPHN), are putative receptors of the teneurins and act, in part, to mediate intercellular adhesion via binding with the teneurin extracellular region. At the distal tip of the extracellular region of each teneurin lies a peptide sequence termed the teneurin C-terminal associated peptide (TCAP). TCAP-1, associated with teneurin-1, is itself bioactive, suggesting that TCAP is a critical functional region of teneurin. However, the role of TCAP-1 has not been established with respect to its ability to interact with LPHN to induce downstream effects. To establish that TCAP-1 binds to LPHN1, a FLAG-tagged hormone binding domain (HBD) of LPHN1 and a GFP-tagged TCAP-1 peptide were co-expressed in HEK293 cells. Both immunoreactive epitopes were co-localized as a single band after immunoprecipitation, indicating an association between the two proteins. Moreover, fluorescent co-labeling occurred at the plasma membrane of LPHN1 over-expressing cells when treated with a FITC-tagged TCAP-1 variant. Expression of LPHN1 and treatment with TCAP-1 modulated the actin-based cytoskeleton in these cells in a manner consistent with previously reported actions of TCAP-1 and affected the overall morphology and aggregation of the cells. This study indicates that TCAP-1 may associate directly with LPHN1 and could play a role in the modulation of cytoskeletal organization and intercellular adhesion and aggregation via this interaction.

Teneurins: Domain Architecture, Evolutionary Origins, and Patterns of Expression

Disruption of teneurin expression results in abnormal neural networks, but just how teneurins support the development of the central nervous system remains an area of active research. This review summarizes some of what we know about the functions of the various domains of teneurins, the possible evolution of teneurins from a bacterial toxin, and the intriguing patterns of teneurin expression. Teneurins are a family of type-2 transmembrane proteins. The N-terminal intracellular domain can be processed and localized to the nucleus, but the significance of this nuclear localization is unknown. The extracellular domain of teneurins is largely composed of tyrosine-aspartic acid repeats that fold into a hollow barrel, and the C-terminal domains of teneurins are stuffed, and least partly, into the barrel. A 6-bladed beta-propeller is found at the other end of the barrel. The same arrangement-6-bladed beta-propeller, tyrosine-aspartic acid repeat barrel, and the C-terminal domain inside the barrel-is seen in toxic proteins from bacteria, and there is evidence that teneurins may have evolved from a gene encoding a prokaryotic toxin via horizontal gene transfer into an ancestral choanoflagellate. Patterns of teneurin expression are often, but not always, complementary. In the central nervous system, where teneurins are best studied, interconnected populations of neurons often express the same teneurin. For example, in the chicken embryo neurons forming the tectofugal pathway express teneurin-1, whereas neurons forming the thalamofugal pathway express teneurin-2. In Drosophila melanogaster, Caenorhabditis elegans, zebrafish and mice, misexpression or knocking out teneurin expression leads to abnormal connections in the neural networks that normally express the relevant teneurin. Teneurins are also expressed in non-neuronal tissue during development, and in at least some regions the patterns of non-neuronal expression are also complementary. The function of teneurins outside the nervous system remains unclear.

Structures of Teneurin adhesion receptors reveal an ancient fold for cell-cell interaction

Teneurins are ancient cell–cell adhesion receptors that are vital for brain development and synapse organisation. They originated in early metazoan evolution through a horizontal gene transfer event when a bacterial YD-repeat toxin fused to a eukaryotic receptor. We present X-ray crystallography and cryo-EM structures of two Teneurins, revealing a ~200 kDa extracellular super-fold in which eight sub-domains form an intricate structure centred on a spiralling YD-repeat shell. An alternatively spliced loop, which is implicated in homophilic Teneurin interaction and specificity, is exposed and thus poised for interaction. The N-terminal side of the shell is ‘plugged’ via a fibronectin-plug domain combination, which defines a new class of YD proteins. Unexpectedly, we find that these proteins are widespread amongst modern bacteria, suggesting early metazoan receptor evolution from a distinct class of proteins, which today includes both bacterial proteins and eukaryotic Teneurins.

Teneurins are cell-cell adhesion receptors that evolved through horizontal gene transfer in which a bacterial YD-repeat protein fused to a eukaryotic receptor. Here the authors present crystallographic and cryo-EM structures of two Teneurins, revealing an ancient YD-repeat protein super-fold.

Neuroanatomical pathways underlying the effects of hypothalamo-hypophysial-adrenal hormones on exploratory activity

When injected via the intracerebroventricular route, corticosterone-releasing hormone (CRH) reduced exploration in the elevated plus-maze, the center region of the open-field, and the large chamber in the defensive withdrawal test. The anxiogenic action of CRH in the elevated plus-maze also occurred when infused in the basolateral amygdala, ventral hippocampus, lateral septum, bed nucleus of the stria terminalis, nucleus accumbens, periaqueductal grey, and medial frontal cortex. The anxiogenic action of CRH in the defensive withdrawal test was reproduced when injected in the locus coeruleus, while the amygdala, hippocampus, lateral septum, nucleus accumbens, and lateral globus pallidus contribute to center zone exploration in the open-field. In addition to elevated plus-maze and open-field tests, the amygdala appears as a target region for CRH-mediated anxiety in the elevated T-maze. Thus, the amygdala is the principal brain region identified with these three tests, and further research must identify the neural circuits underlying this form of anxiety.

Expression and actions of corticotropin-releasing factor/diuretic hormone-like peptide (CDLP) and teneurin C-terminal associated peptide (TCAP) in the vase tunicate, Ciona intestinalis: Antagonism of the feeding response

Teneurin C-terminal associated peptide (TCAP) is a neuropeptide that bears some structural similarity to the corticotropin-releasing factor (CRF) family of peptides. TCAP and CRF are both implicated in the regulation of stress-related behaviors, as established in rodent models. However, in vertebrates, both TCAP and CRF possess three additional paralogous forms making vertebrate models difficult to assess with respect to TCAP-CRF interaction. As a urochordate, this species possesses single homologs of TCAP and of a CRF/Diuretic-like peptide (CDLP) in the genome, thereby establishing Ciona intestinalis as an excellent model organism to examine the interaction of these peptide systems. However, the lack of C. intestinalis synthetic peptides and specific antisera has complicated experimentation. We, therefore, prepared synthetic versions of CDLP and TCAP to prepare specific antisera and to investigate their bioactivity in this species. To analyze stress-related behaviors, a novel behavioral assay was used to characterize different types of contraction-based behaviors, using buccal opening contractions, cloacal opening contractions, lateral contractions, longitudinal contractions and expulsions. Protein and mRNA expression data indicate that the mature versions of both peptides are present in a number of tissues. With respect to behavioral activity, both TCAP- and CDLP-treated animals had distinct contraction profiles under ambient conditions. Moreover, food stimulation tests revealed that whereas CDLP-treated animals displayed a strong expulsion behavior in response to feeding, TCAP-treated animals did not show this effect. These actions are consistent with previous studies done in vertebrates.

Teneurins, TCAP, and latrophilins: roles in the etiology of mood disorders

Mood disorders, including anxiety and depression, are thought to be characterized by disrupted neuronal synapses and altered brain plasticity. The etiology is complex, involving numerous regions of the brain, comprising a multitude of neurotransmitter and neuromodulator systems. Recently, new studies on the teneurins, an evolutionary ancient family of type II transmembrane proteins have been shown to interact with latrophilins (LPHN), a similarly phylogenetically old family of adhesion G protein-coupled receptors (GPCR) forming a transsynaptic adhesion and ligand-receptor pair. Each of the four teneurin proteins contains bioactive sequences termed the teneurin C-terminal associated peptides (TCAP-1-4), which possess a number of neuromodulatory effects. The primary structures of the TCAP are most closely similar to the corticotropin-releasing factor (CRF) family of peptides. CRF has been implicated in a number of diverse mood disorders. Via an association with dystroglycans, synthetic TCAP-1 administration to both embryonic and primary hippocampal cultures induces long-term changes in neuronal structure, specifically increased neurite outgrowth, dendritic branching, and axon growth. Rodent models treated with TCAP-1 show reduced anxiety responses in the elevated plus-maze, openfield test, and acoustic startle test and inhibited CRF-mediated cocaine-seeking behaviour. Thus the teneurin/TCAP-latrophilin interaction may play a major role in the origin, development and treatment of mood disorders.

Characterization of the teneurin C-terminal associated peptide (TCAP) in the vase tunicate, Ciona intestinalis: A novel peptide system associated with energy metabolism and reproduction

The vase tunicate, Ciona intestinalis, is a protochordate and is considered a sister lineage to the chordates. The recent sequencing of its genome has made this species a particularly important model to understand the genetic basis of vertebrate evolution. However, C. intestinalis is also a highly invasive species along the Atlantic coast of North America and other regions of the world which have caused considerable economic stress due to its biofouling actions and, in particular, negative impacts on the mussel- and oyster-based aquaculture industry. Despite this background, little is known about C. intestinalis physiology. The teneurin C-terminal associated peptides (TCAP) are a family of highly conserved peptide hormones found in most metazoans. Moreover, these peptides have been implicated in the inhibition of stress and stimulation of feeding-based metabolism. We have, therefore, identified this peptide using an in silico approach and characterized its immunological expression in tissues using a mouse polyclonal antiserum. These data indicate that its primary structure is more similar to invertebrate TCAPs relative to vertebrate TCAPs. Immunological expression indicates that it is highly expressed in the digestive tract and gonads consistent with findings in vertebrates. Synthetic mouse TCAP-1 administered into the brachial basket significantly increases the incidence of non-stress contractile behaviors. These findings support the hypothesis that TCAP is a bioactive peptide in C. intestinalis. Thus, C. intestinalis and tunicates in general may offer a simple model to investigate peptide interaction while providing information on how to control this invasive species.

Ancient interaction between the teneurin C-terminal associated peptides (TCAP) and latrophilin ligand-receptor coupling: a role in behavior

Teneurins are multifunctional transmembrane proteins that are found in all multicellular animals and exist as four paralogous forms in vertebrates. They are highly expressed in the central nervous system, where they exert their effects, in part, by high-affinity binding to latrophilin (LPHN), a G-protein coupled receptor (GPCR) related to the adhesion and secretin GPCR families. The teneurin C-terminal associated peptides (TCAPs) are encoded by the terminal exon of all four teneurins, where TCAPs 1 and 3 are independently transcribed as soluble peptides, and TCAPs 2 and 4 remain tethered to their teneurin proprotein. Synthetic TCAP-1 interacts with LPHN, with an association with β-dystroglycan, to induce a tissue-dependent signal cascade to modulate cytoskeletal dynamics. TCAP-1 reduces stress-induced behaviors associated with anxiety, addiction and depression in a variety of models, in part, by regulating synaptic plasticity. Therefore, the TCAP-1-teneurin-LPHN interaction represents a novel receptor-ligand model and may represent a key mechanism underlying the association of behavior and neurological conditions.

Repeated intravenous administrations of teneurin-C terminal associated peptide (TCAP)-1 attenuates reinstatement of cocaine seeking by corticotropin-releasing factor (CRF) in rats

The teneurin c-terminal associated peptides (TCAP) have been implicated in the regulation of the stress response, possibly via a corticotropin-releasing factor (CRF)-related mechanism. We have previously shown that repeated intracerebroventricular (ICV) injections of TCAP-1 attenuate the reinstatement of cocaine seeking by CRF in rats. Here, we determined whether intravenous (IV) administrations of TCAP-1 would likewise attenuate CRF-induced reinstatement, and whether this effect would vary depending on the rat's history of cocaine self administration. Rats were trained to self-administer cocaine for 10 days, during once daily sessions that were either 3h ("short access"; ShA) or 6h ("long access"; LgA). Rats were then given five daily injections of TCAP-1 (0, 300, or 3,000 pmol, IV) in their home cage. Subsequently, they were returned to the self-administration chambers where extinction of cocaine seeking and testing for CRF-induced reinstatement of cocaine seeking was carried out. Repeated IV administrations of TCAP-1 were efficacious in attenuating CRF-induced reinstatement of cocaine seeking, but at different doses in ShA and LgA rats. Taken together, the findings extend previous work showing a consistent effect of repeated ICV TCAP-1 on CRF-induced reinstatement of cocaine seeking, and point to a potential therapeutic benefit of TCAP-1 in attenuating cocaine seeking behaviors.

Teneurin C-terminal associated peptides (TCAP): modulators of corticotropin-releasing factor (CRF) physiology and behavior

The existence of the teneurin C-terminal associated peptides (TCAP) was reported in 2004 after screening a rainbow trout hypothalamic cDNA for corticotropin-releasing factor (CRF)-related homologs. In vertebrates, there are four TCAP paralogs, where each peptide is associated with a teneurin transmembrane protein. The TCAPs are 40 or 41 amino acids in length and possess less than 20% residue identity with the CRF family of paralogs. Orthologs of TCAP are found in all metazoans with the possible exception of poriferans and cnidarians. Recent evidence indicates that TCAP and the teneurins may have been introduced into the Metazoa via horizontal gene transfer from prokaryotes into a basal protistan. Thus, the origin of the TCAPs likely predated that of the CRF family. In the mammalian brain, TCAP-1 is transcribed independently from teneurin-1. Moreover, TCAP-1 acts on neurons by a CRF-receptor independent signal transduction pathway to regulate cellular cytoskeletal function to stimulate cell activity. Administration of synthetic TCAP-1 to rodents inhibits a number of CRF- and stress-associated behaviors via a hypothalamic–pituitary–adrenal (HPA) axis-independent mechanism.

Origin of chordate peptides by horizontal protozoan gene transfer in early metazoans and protists: evolution of the teneurin C-terminal associated peptides (TCAP)

The teneurin C-terminal associated peptides (TCAP) are found at the extracellular face in C-terminal region of the teneurin transmembrane proteins. One of these peptides, TCAP-1 is independently transcribed as a smaller bioactive peptide that possesses a number of stress response-attenuating activities. The teneurin-TCAP system appears to be the result of a horizontal gene transfer from a prokaryotic proteinaceous polymorphic toxin to a choanoflagellate. In a basal metazoan, the TCAP region has been modified from a toxin to a soluble intercellular signaling system. New studies indicate that the teneurin-TCAP system form a complex signaling system associated with adhesion, cytoskeletal regulation and intracellular signaling. TCAP-1 is highly conserved in all vertebrates and in mammals, inhibits corticotropin-releasing factor (CRF)-associated stress. Using the TCAP-teneurin system as a model, it is likely that numerous peptide systems in the Chordata began as a result of horizontal gene transfer from prokaryotes early in metazoan ancestry.

C-terminal processing of the teneurin proteins: independent actions of a teneurin C-terminal associated peptide in hippocampal cells

Many neuropsychiatric conditions have a common set of neurological substrates associated with the integration of sensorimotor processing. The teneurins are a recently described family of proteins that play a significant role in visual and auditory development. Encoded on the terminal exon of the teneurin genes is a family of bioactive peptides, termed teneurin C-terminal associated peptides (TCAP), which regulate mood-disorder associated behaviors. Thus, the teneurin-TCAP system could represent a novel neurological system underlying the origins of a number of complex neuropsychiatric conditions. However, it is not known if TCAP-1 exerts its effects as part of a direct teneurin function, whereby TCAP represents a functional region of the larger teneurin protein, or if it has an independent role, either as a splice variant or post-translational proteolytic cleavage product of teneurin. In this study, we show that TCAP-1 can be transcribed as a smaller mRNA transcript. After translation, further processing yields a smaller 15 kDa protein containing the TCAP-1 region. In the mouse hippocampus, immunoreactive (ir) TCAP-1 is exclusively localized to the pyramidal layers of the CA1, CA2 and CA3 regions. Although the localization of TCAP and teneurin in hippocampal regions is similar, they are distinct within the cell as most ir-teneurin is found at the plasma membrane, whereas ir-TCAP-1 is predominantly found in the cytosol. Moreover, in mouse embryonic hippocampal cell culture, FITC-labeled TCAP-1 binds to the plasma membrane and is taken up into the cytosol via dynamin-dependent caveolae-mediated endocytosis. Our data provides novel evidence that TCAP-1 is structurally and functionally distinct from the larger teneurins.

C-Terminal region of teneurin-1 co-localizes with dystroglycan and modulates cytoskeletal organization through an extracellular signal-regulated kinase-dependent stathmin- and filamin A-mediated mechanism in hippocampal cells

The pyramidal neurons in the hippocampus are extremely neuroplastic, and the complexity of dendritic branches can be dynamically altered in response to a variety of stimuli, including learning and stress. Recently, the teneurin family of proteins has emerged as an interneuronal and extracellular matrix signaling system that plays a significant role in brain development and neuronal communication. Encoded on the last exon of the teneurin genes is a new family of bioactive peptides termed the teneurin C-terminal-associated peptides (TCAPs). Previous studies indicate that TCAP-1 regulates axon fasciculation and dendritic morphology in the hippocampus. This study was aimed at understanding the molecular mechanisms by which TCAP-1 regulates these changes in the mouse hippocampus. Fluoresceinisothiocyanate (FITC)-labeled TCAP-1 binds to the pyramidal neurons of the CA2 and CA3, and dentate gyrus in the hippocampus of the mouse brain. Moreover, FITC-TCAP-1 co-localizes with β-dystroglycan upon binding to the plasma membrane of cultured immortalized mouse E14 hippocampal cells. In culture, TCAP-1 stimulates ERK1/2-dependent phosphorylation of the cytoskeletal regulatory proteins, stathmin at serine-25 and filamin A at serine-2152. In addition, TCAP-1 induces actin polymerization, increases immunoreactivity of tubulin-based cytoskeletal elements and causes a corresponding increase in filopodia formation and mean filopodia length in cultured hippocampal cells. We postulate that the TCAP-1 region of teneurin-1 has a direct action on the cytoskeletal reorganization that precedes neurite and process development in hippocampal neurons. Our data provides novel evidence that functionally links the teneurin and dystroglycan systems and provides new insight into the molecular mechanisms by which TCAP-1 regulates cytoskeletal dynamics in hippocampal neurons. The TCAP-dystroglycan system may represent a novel mechanism associated with the regulation of hippocampal-function.

Modulation of neuroplastic changes and corticotropin-releasing factor-associated behavior by a phylogenetically ancient and conserved peptide family

The co-evolution of peptides and early cells some 3.7 billion years ago provided bioactive peptides with a long history for the proliferation and refinement of peptide hormones. Central to the adaptation and evolution of cell types in metazoans is the development of peptide signaling systems that regulate stress mechanisms. The corticotropin-releasing factor (CRF) family of peptides represents the canonical family of peptides that are pivotal to the regulation of stress in vertebrates. However, these peptides appear to have evolved at least 2 billion years after the formation of the first postulated bioactive peptides, suggesting that before this, other peptide systems played a role in stress and energy metabolism. The teneurin C-terminal associated peptides (TCAPs) are a recently discovered family of highly conserved peptides that are processed from the teneurin transmembrane proteins. This peptide/protein system is ubiquitous in multicellular organisms and evolved before the CRF family. TCAP-1 is a potent regulator of CRF-associated physiology and behavior and may play a significant role in the regulation of cell-to-cell communication and neuroplasticity in neurons.

Teneurin C-terminal associated peptide-1 blocks the effects of corticotropin-releasing factor on reinstatement of cocaine seeking and on cocaine-induced behavioural sensitization

BACKGROUND AND PURPOSE

The stress-related neuropeptide, corticotropin-releasing factor (CRF), has become an important focus of studies of cocaine addiction, and in particular, the effects of stress on cocaine-related behaviours. A recently discovered peptide system, the teneurin C-terminal associated peptides (TCAP), has been implicated in the regulation of the stress response, via a CRF-related mechanism. Here we have determined whether treatment with TCAP-1, a synthetic analogue of TCAP, modulated two cocaine-related behaviours induced by CRF: reinstatement of cocaine seeking, and expression of cocaine-induced behavioural sensitization.

EXPERIMENTAL APPROACH

In Experiment 1, rats trained to self-administer cocaine were given acute or repeated (once daily for 5 days) i.c.v. injections of TCAP-1 before tests for reinstatement in response to CRF (105 pmol, i.c.v.), intermittent footshock stress (0.9 mA), or cocaine (15 mg·kg⁻¹, i.p.). In Experiment 2, rats pre-exposed to cocaine (15-30 mg·kg⁻¹, i.p.) or saline for 7 days were treated with TCAP-1 (once daily for 5 days; i.c.v.) and subsequently tested for locomotor responses to CRF (105 pmol, i.c.v.) or cocaine (15 mg·kg⁻¹, i.p.).

KEY RESULTS

Five day pre-exposure with TCAP-1 blocked CRF-, but not footshock- or cocaine-induced reinstatement of cocaine seeking; acute pretreatment with TCAP-1 was without effect in all test conditions. Similarly, repeated TCAP-1 pre-exposure blocked the cocaine-sensitized locomotor response to CRF, but not to cocaine.

CONCLUSIONS AND IMPLICATIONS

Repeated TCAP-1 exposure induced robust and selective inhibition of cocaine-related behavioural responses to CRF, suggesting that TCAP-1 may normalize signalling within CRF systems dysregulated by cocaine exposure.

Teneurin C-terminal associated peptide (TCAP)-1 modulates dendritic morphology in hippocampal neurons and decreases anxiety-like behaviors in rats

Teneurin C-terminal associated peptide (TCAP)-1 is a member of a novel family of neuropeptides that has been highly conserved throughout evolution. TCAP-1 is expressed in the limbic system in areas such as the hippocampus and amygdala. In vitro, TCAP-1 increases cytoskeletal proteins in immortalized neurons and modulates neurite outgrowth in cultured primary hippocampal neurons. In vivo, TCAP-1 blocks stress-induced c-Fos in the hippocampus and amygdala, and modulates stress-induced anxiety-like behaviors. This suggests that TCAP-1 plays a role in the remodeling of limbic system networks to alter stress behaviors. Dendritic spines on the apical and basilar shafts of hippocampal neurons are sensitive to stress and many receive incoming excitatory synaptic connections. In this study, repeated daily injection of TCAP-1 for 10 days increased spine density in the CA1 and CA3 regions of the hippocampus without affecting spine density in the amygdala. Further investigation of the CA3 region indicated that TCAP-1 did not affect the morphology of apical dendrites, but decreased branching in the basilar dendrites 90-130 μm away from the soma. Moreover, TCAP-1 treatment increased open arm time and decreased closed arm entries on the elevated plus maze, a test of anxiety-like behavior. These results suggest that TCAP-1 may be associated with anxiety-like behavior via regulation of dendritic morphology in the hippocampus, independent of amygdalar modification.

Behavioral effects of neuropeptides in rodent models of depression and anxiety

In recent years, studies have advocated neuropeptide systems as modulators for the behavioral states found in mood disorders such as depression and anxiety disorders. Neuropeptides have been tested in traditional animal models and screening procedures that have been validated by known antidepressants and anxiolytics. However, it has become clear that although these tests are very useful, neuropeptides have distinct behavioral effects and dose-dependent characteristics, and therefore, use of these tests with neuropeptides must be done with an understanding of their unique characteristics. This review will focus on the behavioral actions of neuropeptides and their synthetic analogs, particularly in studies utilizing various preclinical tests of depression and anxiety. Specifically, the following neuropeptide systems will be reviewed: corticotropin-releasing factor (CRF), urocortin (Ucn), teneurin C-terminal associated peptide (TCAP), neuropeptide Y (NPY), arginine vasopressin (AVP), oxytocin, the Tyr-MIF-1 family, cholecystokinin (CCK), galanin, and substance P. These neuropeptide systems each have a unique role in the regulation of stress-like behavior, and therefore provide intriguing therapeutic targets for mood disorder treatment.

Structural evolution of urotensin-I: reflections of life before corticotropin releasing factor

Peptides have a long evolutionary history that predates the appearance of metazoans. The corticotropin releasing factor (CRF) family of peptides is among the most ancient peptide lineages. The identification and characterization of urotensin-I and related orthologues led the way for the elucidation of the entire CRF peptide family. A comparative analysis of the CRF paralogue sequences suggest that CRF is the most derived of these peptides and has lost many of its ancestral characteristics after it became associated with the hypothalamic-pituitary-adrenal/interrenal (HPA/I axis). In vertebrates, the urotensin-I group of orthologues, which includes sauvagine and urocortin, possess a number of shared characteristics that may be indicative of the ancestral peptide. Given the early origin of the CRF family peptides, it is likely that other peptide lineages are distantly related to the CRF family. In silico or cDNA library screening using probes based on urotensin-I/urocortin characteristics have been used to identify novel CRF family and related sequences that provide clues the evolutionary origin of the CRF family.

Evolution of complementary peptide systems: teneurin C-terminal-associated peptides and corticotropin-releasing factor superfamilies

In chordates, the corticotropin-releasing factor (CRF) family of peptides consists of four paralogous lineages that include CRF, urocortin/urotensin-I, urocortin 2, and urocortin 3. Related to the CRF peptide family is the diuretic hormone family found in insects. This family consists of a number of paralogous lineages within the Insecta. The teneurin C-terminal-associated peptides (TCAP) are a recently described family of peptides with evolutionary origins around the same time as the CRF family. This family consists of four independent lineages in chordates that are orthologous to peptides in the Insecta. Like CRF, the peptides are 40 or 41 amino acids in length and share about 20% sequence identity to the CRF family members. Each of the four TCAP peptides is encoded by an exon that is closely associated with the teneurin gene. Recent studies indicate that TCAP can block CRF-mediated c-fos expression in the brain and modulate CRF-mediated behaviors. Thus, the TCAP family may act, in part, to modulate the physiological actions of the CRF family.