Cannabinoid Receptors and Ligands: Lessons from CNS Disorders and the Quest for Novel Treatment Venues.

The potential use of cannabinoids for therapeutic purposes is at the forefront of cannabinoid research which aims to develop innovative strategies to prevent, manage and treat a broad spectrum of human diseases. This chapter briefly reviews the pivotal role of the endocannabinoid system in modulating the central nervous system and its roles on neurodegenerative diseases and brain disorders. Ligand-induced modulation of cannabinoid 1 and 2 receptors to modulate immune response, decrease neurodegeneration and pain are aspects that are also discussed.

Adhesion G protein-coupled receptor, ELTD1, is a potential therapeutic target for retinoblastoma migration and invasion.

BACKGROUND: Prognosis for pediatric metastatic Retinoblastoma (Rb) is poor and current therapies are limited by high systemic toxicity rates and insufficient therapeutic efficacy for metastatic Rb. Tumor dissemination to the brain is promoted by the heterogeneous adhesive and invasive properties of Rb cells within the tumor. In this study we evaluate, for the first time, the expression, and roles of the ELTD1 and GPR125 adhesion G protein-coupled receptors (GPCRs) in Rb cell migration, viability and invasion. METHODS: We characterized the RNA expression of adhesion-GPCRs in 64 Rb tumors compared to 11 fetal retinas using the database from the Childhood Solid Tumor Network from St Jude Children's Research Hospital. The role of ELTD1 and GPR125 in Rb were investigated ex vivo by microarray analysis, in vitro by cell viability, Western blot and migration assays, in addition to imaging of the subcellular localization of the GPCRs. To elucidate their role in vivo we utilized siRNA technology in an established Rb orthotopic xenograft murine model. RESULTS: Our investigation demonstrates, for the first time, that ELTD1 but not GPR125, is significantly increased in Rb tumors compared to fetal retinas. We utilized established the Rb cell lines Y79 and Weri-Rb-1, which represent an aggressive, metastatic, and non-metastatic phenotype, respectively, for the in vitro analyses. The studies demonstrated that ELTD1 is enriched in Weri-Rb-1 cells, while GPR125 is enriched in Y79 cells. The measured differences extended to their subcellular localization as ELTD1 labeling displayed punctate clusters in cell-to-cell adhesion sites of Weri-Rb-1 cells, while GPR125 displayed a polarized distribution in Y79 cells. Lastly, we demonstrated the lack of both adhesion receptors does not affect Rb cell viability, yet inhibition of ELTD1 decreases Y79 cell migration in vitro and invasion in vivo. CONCLUSION: Taken together, our data suggest that ELTD1, is a potential target to prevent extraocular Rb. The results within establish ELTD1 as a potential therapeutic target for metastatic Rb.

Targeting the Platelet-Derived Growth Factor-beta Stimulatory Circuitry to Control Retinoblastoma Seeds.

Purpose: Vitreous seeding remains the primary reason for treatment failure in eyes with retinoblastoma (Rb). Systemic and intra-arterial chemotherapy, each with its own inherent set of complications, have improved salvage rates for eyes with advanced disease, but the location and biology of vitreous seeds present a fundamental challenge in developing treatments with minimal toxicity and risk. The aim of this study was to target the platelet-derived growth factor (PDGF)- PDGF-receptor ß (PDGFRß) signaling pathway and investigate its role in the growth of Rb seeds, apoptotic activity, and invasive potential. Methods: We performed ex vivo analyses on vitreous samples from Rb patients that underwent enucleation and from patient-derived xenografts. These samples were evaluated by quantitative PCR, immunohistochemistry, and ELISA. The effects of disruption of the PDGF-PDGFRß signaling pathway, both by pharmacologic and genomic knockdown approaches, were evaluated in vitro by cell proliferation and apoptotic assays, quantitative PCR analyses, Western blotting, flow cytometry, and imaging flow cytometry. A three-dimensional cell culture system was generated for in-depth study of Rb seeds. Results: Our results demonstrated that PDGFRß signaling is active in the vitreous of Rb patients and patient-derived xenografts, sustaining growth and survival in an AKT-, MDM2-, and NF-κB-dependent manner. The novel three-dimensional cell culture system mimics Rb seeds, as the in vitro generated spheroids have similar morphologic features to Rb seeds and mimicked their natural physiology. Conclusions: Targeting the PDGFRß pathway in vitro reduces Rb cell growth, survival, and invasiveness and could augment current therapies. This represents a novel signaling pathway for potential targeted therapy to further improve ocular survival in advanced Rb.

Assessing a Science Graduate School Recruitment Symposium.

Ciencia Puerto Rico, a non-profit organization dedicated to promoting science, research and scientific education among Latinos, organized an educational symposium to provide college science majors the tools, opportunities and advice to pursue graduate degrees and succeed in the STEM disciplines. In this article we share our experiences and lessons learned, for others interested in developing large-scale events to recruit underrepresented minorities to STEM and in evaluating the effectiveness of these efforts.

Imaging of kiss-and-run exocytosis of surface receptors in neuronal cultures.

Transmembrane proteins are continuously shuttled from the endosomal compartment to the neuronal plasma membrane by highly regulated and complex trafficking steps. These events are involved in many homeostatic and physiological processes such as neuronal growth, signaling, learning and memory among others. We have previously shown that endosomal exocytosis of the B2 adrenergic receptor (B2AR) and the GluR1-containing AMPA receptor to the neuronal plasma membrane is mediated by two different types of vesicular fusion. A rapid type of exocytosis in which receptors are delivered to the plasma membrane in a single kinetic step, and a persistent mode in which receptors remain clustered at the insertion site for a variable period of time before delivery to the cell surface. Here, by comparing the exocytosis of multiple receptors in dissociated hippocampal and striatal cultures, we show that persistent events are a general mechanism of vesicular delivery. Persistent events were only observed after 10 days in vitro, and their frequency increased with use of the calcium ionophore A23187 and with depolarization induced by KCl. Finally, we determined that vesicles producing persistent events remain at the plasma membrane, closing and reopening their fusion pore for a consecutive release of cargo in a mechanism reminiscent of synaptic kiss-and-run. These results indicate that the delivery of transmembrane receptors to the cell surface can be dynamically regulated by kiss-and-run exocytosis.

Ligand-specific endocytic dwell times control functional selectivity of the cannabinoid receptor 1.

G protein-coupled receptors (GPCRs) are the major transducers of external stimuli and key therapeutic targets in many pathological conditions. When activated by different ligands, one receptor can elicit multiple signalling cascades that are mediated by G proteins or ß-arrestin, a process defined as functional selectivity or ligand bias. However, the dynamic mechanisms underlying ß-arrestin signalling remain unknown. Here by studying the cannabinoid receptor 1 (CB1R), we identify ligand-specific endocytic dwell times, that is, the time during which receptors are clustered into clathrin pits together with ß-arrestins before endocytosis, as the mechanism controlling ß-arrestin signalling. Agonists inducing short endocytic dwell times produce little or no ß-arrestin signalling, whereas those eliciting prolonged dwell times induce robust signalling. Remarkably, extending CB1R dwell times by preventing endocytosis substantially increased ß-arrestin signalling. These studies reveal how receptor activation translates into ß-arrestin signalling and identify a mechanism to control this pathway.

A novel retinoblastoma therapy from genomic and epigenetic analyses.

Retinoblastoma is an aggressive childhood cancer of the developing retina that is initiated by the biallelic loss of RB1. Tumours progress very quickly following RB1 inactivation but the underlying mechanism is not known. Here we show that the retinoblastoma genome is stable, but that multiple cancer pathways can be epigenetically deregulated. To identify the mutations that cooperate with RB1 loss, we performed whole-genome sequencing of retinoblastomas. The overall mutational rate was very low; RB1 was the only known cancer gene mutated. We then evaluated the role of RB1 in genome stability and considered non-genetic mechanisms of cancer pathway deregulation. For example, the proto-oncogene SYK is upregulated in retinoblastoma and is required for tumour cell survival. Targeting SYK with a small-molecule inhibitor induced retinoblastoma tumour cell death in vitro and in vivo. Thus, retinoblastomas may develop quickly as a result of the epigenetic deregulation of key cancer pathways as a direct or indirect result of RB1 loss.

Coexpression of normally incompatible developmental pathways in retinoblastoma genesis.

It is widely believed that the molecular and cellular features of a tumor reflect its cell of origin and can thus provide clues about treatment targets. The retinoblastoma cell of origin has been debated for over a century. Here, we report that human and mouse retinoblastomas have molecular, cellular, and neurochemical features of multiple cell classes, principally amacrine/horizontal interneurons, retinal progenitor cells, and photoreceptors. Importantly, single-cell gene expression array analysis showed that these multiple cell type-specific developmental programs are coexpressed in individual retinoblastoma cells, which creates a progenitor/neuronal hybrid cell. Furthermore, neurotransmitter receptors, transporters, and biosynthetic enzymes are expressed in human retinoblastoma, and targeted disruption of these pathways reduces retinoblastoma growth in vivo and in vitro.

Synaptic proteins are tonotopically graded in postnatal and adult type I and type II spiral ganglion neurons.

Inherent in the design of the mammalian auditory system is the precision necessary to transduce complex sounds and transmit the resulting electrical signals to higher neural centers. Unique specializations in the organ of Corti are required to make this conversion, such that mechanical and electrical properties of hair cell receptors are tailored to their specific role in signal coding. Electrophysiological and immunocytochemical characterizations have shown that this principle also applies to neurons of the spiral ganglion, as evidenced by distinctly different firing features and synaptic protein distributions of neurons that innervate high- and low-frequency regions of the cochlea. However, understanding the fine structure of how these properties are distributed along the cochlear partition and within the type I and type II classes of spiral ganglion neurons is necessary to appreciate their functional significance fully. To address this issue, we assessed the localization of the postsynaptic AMPA receptor subunits GluR2 and GluR3 and the presynaptic protein synaptophysin by using immunocytochemical labeling in both postnatal and adult tissue. We report that these presynaptic and postsynaptic proteins are distributed oppositely in relation to the tonotopic map and that they are equally distributed in each neuronal class, thus having an overall gradation from one end of the cochlea to the other. For synaptophysin, an additional layer of heterogeneity was superimposed orthogonal to the tonotopic axis. The highest anti-synaptophysin antibody levels were observed within neurons located close to the scala tympani compared with those located close to the scala vestibuli. Furthermore, we noted that the protein distribution patterns observed in postnatal preparations were largely retained in adult tissue sections, indicating that these features characterize spiral ganglion neurons in the fully developed ear.

Targeting the p53 pathway in retinoblastoma with subconjunctival Nutlin-3a.

Retinoblastoma is a rare childhood cancer of the retina that begins in utero and is diagnosed in the first years of life. The goals of retinoblastoma treatment are ocular salvage, vision preservation, and reduction of short- and long-term side effects without risking mortality because of tumor dissemination. To identify better chemotherapeutic combinations for the treatment of retinoblastoma, several groups have developed genetic mouse models and orthotopic xenograft models of human retinoblastoma for preclinical testing. Previous studies have implicated the MDMX protein in the suppression of the p53 pathway in retinoblastoma and shown that the MDM2/MDMX antagonist, Nutlin-3a, can efficiently induce p53-mediated cell death in retinoblastoma cell lines. However, Nutlin-3a cannot be administered systemically to treat retinoblastoma, because it has poor penetration across the blood-ocular barrier. Therefore, we developed an ocular formulation of Nutlin-3a, Nutlin-3a(OC), and tested the pharmacokinetics and efficacy of this new formulation in genetic and human retinoblastoma orthotopic xenograft models of retinoblastoma. Here, we show that Nutlin-3a(OC) specifically and efficiently targets the p53 pathway and that the combination of Nutlin-3a(OC) with systemic topotecan is a significantly better treatment for retinoblastoma than currently used chemotherapy in human orthotopic xenografts. Our studies provide a new standardized approach to evaluate and prioritize novel agents for incorporation into future clinical trials for retinoblastoma.

Reciprocal regulation of presynaptic and postsynaptic proteins in bipolar spiral ganglion neurons by neurotrophins.

A unifying principle of sensory system organization is feature extraction by modality-specific neuronal maps in which arrays of neurons show systematically varied response properties and receptive fields. Only beginning to be understood, however, are the mechanisms by which these graded systems are established. In the peripheral auditory system, we have shown previously that the intrinsic firing features of spiral ganglion neurons are influenced by brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3). We now show that is but a part of a coordinated package of neurotrophin actions that also includes effects on presynaptic and postsynaptic proteins, thus encompassing the input, transmission, and output functions of the spiral ganglion neurons. Using immunocytochemical methods, we determined that proteins targeted to opposite ends of the neuron were organized and regulated in a reciprocal manner. AMPA receptor subunits GluR2 and GluR3 were enriched in base neurons compared with their apex counterparts. This distribution pattern was enhanced by exposure to BDNF but reduced by NT-3. SNAP-25 and synaptophysin were distributed and regulated in the mirror image: enriched in the apex, enhanced by NT-3 and reduced by BDNF. Moreover, we used a novel coculture to identify potential endogenous sources of neurotrophins by showing that sensory receptors from different cochlear regions were capable of altering presynaptic and postsynaptic protein levels in these neurons. From these studies, we suggest that BDNF and NT-3, which are systematically distributed in complementary gradients, are responsible for orchestrating a comprehensive set of electrophysiological specializations along the frequency contour of the cochlea.

Firing patterns of type II spiral ganglion neurons in vitro.

Type I and type II spiral ganglion neurons convey auditory information from the sensory receptors in the cochlea to the CNS. The numerous type I neurons have been extensively characterized, but the small population of type II neurons with their unmyelinated axons are undetectable with most recording methods. Despite the paucity of information about the type II neurons, it is clear that they must have a significant role in sound processing because they innervate the large number of outer hair cells that are critical for maintaining normal responses to stimuli. To elucidate the function of type II neurons, we have developed an approach for studying their electrophysiological features in vitro. Type II neurons obtained from postnatal day 6-7 mice displayed distinctly different firing properties than type I neurons. They showed slower accommodation, lower action potential thresholds, and more prolonged responses to depolarizing current injection than the type I neurons. These differences were most evident in neurons from the basal, high-frequency region of the cochlea. The basal type I neurons displayed uniformly fast firing features, whereas the basal type II neurons showed particularly slow accommodation and responses to depolarization. Interestingly, neurons from the apical, low-frequency region of the cochlea showed the opposite trend. These data suggest that the type I and type II neurons have specialized electrophysiological characteristics tailored to their different roles in auditory signal processing. In particular, the type II neuron properties are consistent with cells in other sensory systems that receive convergent synaptic input for high-sensitivity stimulus detection.