Mouse brain and muscle tissues constitutively express high levels of Homer proteins

Replication and extension of the subregion selectivity of glutamate-related changes within the nucleus accumbens associated with the incubation of cocaine-craving

Cue-elicited drug-seeking behavior intensifies with the passage of time during withdrawal from drug taking and this "incubation of cocaine-craving" involves alterations in nucleus accumbens (NA) glutamate transmission. Here, we employed a combination of in vivo microdialysis and immunoblotting approaches to further examine changes in biochemical indices of glutamate transmission within NA subregions that accompany the incubation of cocaine-craving exhibited by male rats with a 10-day history of 6-h access to intravenous cocaine (0.25 mg/infusion). Immunoblotting on whole cell lysates from the core subregion (NAc core) revealed interactions between cocaine self-administration history, withdrawal and drug cue re-exposure for Homer2a/b, mGlu1, and GluN2b expression, as well as indices of Akt and ERK activity. With the exception of PKCε phosphorylation, most protein changes within the shell subregion (NAc shell) depended on drug cue re-exposure and cocaine history rather than varying in a consistent time-dependent manner. Reduced basal extracellular glutamate content was apparent only in the NAc core of cocaine-experienced rats during protracted (30 days) withdrawal and this was accompanied by a markedly blunted capacity of the mGlu1/5 agonist DHPG to elevate glutamate levels within this subregion. Finally, over-expressing neither Homer1c nor Homer2b within the NAc core during protracted cocaine withdrawal altered the magnitude of cue-elicited responding, its extinction or cocaine-primed reinstatement of drug-seeking behavior. The present findings are consistent with the extant literature implicating changes in Group 1 mGlu receptor function within the NAc core subregion as central to incubated cocaine-craving and provide further evidence against a major role for Homer proteins in gating incubated cocaine-craving. Further, our results provide novel correlational evidence implicating elevated Akt and blunted ERK activity within the NAc core as potential contributors to the expression of incubated cocaine-craving, worthy of future investigation.

Increased Homer Activity and NMJ Localization in the Vestibular Lesion het-/- Mouse soleus Muscle

We investigated the shuttling of Homer protein isoforms identified in soluble (cytosolic) vs. insoluble (membrane-cytoskeletal) fraction and Homer protein-protein interaction/activation in the deep postural calf soleus (SOL) and non-postural gastrocnemius (GAS) muscles of het-/- mice, i.e., mice with an autosomal recessive variant responsible for a vestibular disorder, in order to further elucidate a) the underlying mechanisms of disrupted vestibular system-derived modulation on skeletal muscle, and b) molecular signaling at respective neuromuscular synapses. Heterozygote mice muscles served as the control (CTR). An increase in Homer cross-linking capacity was present in the SOL muscle of het-/- mice as a compensatory mechanism for the altered vestibule system function. Indeed, in both fractions, different Homer immunoreactive bands were detectable, as were Homer monomers (~43-48 kDa), Homer dimers (~100 kDa), and several other Homer multimer bands (>150 kDA). The het-/- GAS particulate fraction showed no Homer dimers vs. SOL. The het-/- SOL soluble fraction showed a twofold increase (+117%, p ≤ 0.0004) in Homer dimers and multimers. Homer monomers were completely absent from the SOL independent of the animals studied, suggesting muscle-specific changes in Homer monomer vs. dimer expression in the postural SOL vs. the non-postural GAS muscles. A morphological assessment showed an increase (+14%, p ≤ 0.0001) in slow/type-I myofiber cross-sectional area in the SOL of het-/- vs. CTR mice. Homer subcellular immuno-localization at the neuromuscular junction (NMJ) showed an altered expression in the SOL of het-/-mice, whereas only not-significant changes were found for all Homer isoforms, as judged by RT-qPCR analysis. Thus, muscle-specific changes, myofiber properties, and neuromuscular signaling mechanisms share causal relationships, as highlighted by the variable subcellular Homer isoform expression at the instable NMJs of vestibular lesioned het-/- mice.

Molecular mechanisms of alcohol's effects on the human body: A review and update

Alcohol consumption has been linked to numerous negative health outcomes although it has some beneficial effects on moderate dosages, the most severe of which being alcohol-induced hepatitis. The number of people dying from this liver illness has been shown to climb steadily over time, and its prevalence has been increasing. Researchers have found that alcohol consumption primarily affects the brain, leading to a wide range of neurological and psychological diseases. High-alcohol-consumption addicts not only experienced seizures, but also ataxia, aggression, social anxiety, and variceal hemorrhage that ultimately resulted in death, ascites, and schizophrenia. Drugs treating this liver condition are limited and can cause serious side effects like depression. Serine-threonine kinases, cAMP protein kinases, protein kinase C, ERK, RACK 1, Homer 2, and more have all been observed to have their signaling pathways disrupted by alcohol, and alcohol has also been linked to epigenetic changes. In addition, alcohol consumption induces dysbiosis by changing the composition of the microbiome found in the gastrointestinal tract. Although more studies are needed, those that have been done suggest that probiotics aid in keeping the various microbiota concentrations stable. It has been argued that reducing one's alcohol intake may seem less harmful because excessive drinking is a lifestyle disorder.

Homer 1 genotype AA variant relates to congenital splay leg syndrome in piglets by repressing Pax7 in myogenic progenitors

Introduction

Porcine congenital splay leg syndrome (PCS) is a major birth defect in piglets, resulting in lameness and high mortality rates. The multifactorial pathogenesis of PSC is not well understood but includes a polygenic inheritance.

Methods

Here, in addition to morphological investigations, we characterized the expression of myogenic genes and functional (proliferation and differentiation) properties of myogenic precursor/satellite cells (SATCs) in 1 day-old PCS piglets, non-affected littermates (LCs), and piglets from PCS-free healthy litters (HCs). In addition, PCS phenotypes were related to the SNP Homer1_rs325197091 within the Homer1 locus, which has been identified as a potential hereditary cause of PCS.

Results and discussion

Samples from musculus semitendinosus (ST) of PCS piglets had a higher proportion of type II fibers, reflecting myofiber immaturity. In addition, myofiber atrophy, a lower number of myonuclei per fiber (ST), and a higher apoptotic activity (in ST and longissimus dorsi muscle; LD) were found in the PCS group. A higher proportion of cycling committed myoblasts (Pax7+/Ki67+ cells) occurred in samples from PCS-affected piglets, and on the other hand, the mRNA expression of genes involved in differentiation (muscle differentiation 1; MyoD, myogenin; MyoG) was repressed compared with HCs. Cultured SATCs from PCS-affected animals showed a temporal shift in peak expression of Pax7, MyoD, and MyoG toward days 3 and 4 of their 7 days differentiation regime. In vitro experiments with isolated SATCs confirmed the lower differentiation potential and the delayed progression of the myogenic processes in cells from piglets with PCS phenotype. In addition, Pax7 and desmin were differently expressed in Homer1_rs325197091 genotype variants (GG, GA, and AA). Both genes showed the lowest expression in the homozygous AA-variant, which was most frequently found in PCS-affected animals. The homozygous AA-variant was also associated with lower expression of the truncated Homer1-subtype 205. Thus, we hypothesize that in PCS, the balance between Homer1 proteins and its signaling functions is changed in a way detrimental to the myogenic differentiation program. Our results demonstrated direct negative effects of the Homer1 AA genotype on Pax7 expression, but the exact mode of action still needs to be elucidated.

Dysregulated Signaling at Postsynaptic Density: A Systematic Review and Translational Appraisal for the Pathophysiology, Clinics, and Antipsychotics' Treatment of Schizophrenia

Emerging evidence from genomics, post-mortem, and preclinical studies point to a potential dysregulation of molecular signaling at postsynaptic density (PSD) in schizophrenia pathophysiology. The PSD that identifies the archetypal asymmetric synapse is a structure of approximately 300 nm in diameter, localized behind the neuronal membrane in the glutamatergic synapse, and constituted by more than 1000 proteins, including receptors, adaptors, kinases, and scaffold proteins. Furthermore, using FASS (fluorescence-activated synaptosome sorting) techniques, glutamatergic synaptosomes were isolated at around 70 nm, where the receptors anchored to the PSD proteins can diffuse laterally along the PSD and were stabilized by scaffold proteins in nanodomains of 50-80 nm at a distance of 20-40 nm creating "nanocolumns" within the synaptic button. In this context, PSD was envisioned as a multimodal hub integrating multiple signaling-related intracellular functions. Dysfunctions of glutamate signaling have been postulated in schizophrenia, starting from the glutamate receptor's interaction with scaffolding proteins involved in the N-methyl-D-aspartate receptor (NMDAR). Despite the emerging role of PSD proteins in behavioral disorders, there is currently no systematic review that integrates preclinical and clinical findings addressing dysregulated PSD signaling and translational implications for antipsychotic treatment in the aberrant postsynaptic function context. Here we reviewed a critical appraisal of the role of dysregulated PSD proteins signaling in the pathophysiology of schizophrenia, discussing how antipsychotics may affect PSD structures and synaptic plasticity in brain regions relevant to psychosis.

Loss of neuromuscular junction integrity and muscle atrophy in skeletal muscle disuse

Physical inactivity (PI) is a major risk factor of chronic diseases. A major aspect of PI is loss of muscle mass and strength. The latter phenomenon significantly impacts daily life and represent a major issue for global health. Understandably, skeletal muscle itself has been the major focus of studies aimed at understanding the mechanisms underlying loss of mass and strength. Relatively lesser attention has been given to the contribution of alterations in somatomotor control, despite the fact that these changes can start very early and can occur at multiple levels, from the cortex down to the neuromuscular junction (NMJ). It is well known that exposure to chronic inactivity or immobilization causes a disproportionate loss of force compared to muscle mass, i.e. a loss of specific or intrinsic whole muscle force. The latter phenomenon may be partially explained by the loss of specific force of individual muscle fibres, but several other players are very likely to contribute to such detrimental phenomenon. Irrespective of the length of the disuse period, the loss of force is, in fact, more than two-fold greater than that of muscle size. It is very likely that somatomotor alterations may contribute to this loss in intrinsic muscle force. Here we review evidence that alterations of one component of somatomotor control, namely the neuromuscular junction, occur in disuse. We also discuss some of the novel players in NMJ stability (e.g., homer, bassoon, pannexin) and the importance of new established and emerging molecular markers of neurodegenerative processes in humans such as agrin, neural-cell adhesion molecule and light-chain neurofilaments.

The Homer1 family of proteins at the crossroad of dopamine-glutamate signaling: An emerging molecular "Lego" in the pathophysiology of psychiatric disorders. A systematic review and translational insight

Once considered only scaffolding proteins at glutamatergic postsynaptic density (PSD), Homer1 proteins are increasingly emerging as multimodal adaptors that integrate different signal transduction pathways within PSD, involved in motor and cognitive functions, with putative implications in psychiatric disorders. Regulation of type I metabotropic glutamate receptor trafficking, modulation of calcium signaling, tuning of long-term potentiation, organization of dendritic spines' growth, as well as meta- and homeostatic plasticity control are only a few of the multiple endocellular and synaptic functions that have been linked to Homer1. Findings from preclinical studies, as well as genetic studies conducted in humans, suggest that both constitutive (Homer1b/c) and inducible (Homer1a) isoforms of Homer1 play a role in the neurobiology of several psychiatric disorders, including psychosis, mood disorders, neurodevelopmental disorders, and addiction. On this background, Homer1 has been proposed as a putative novel target in psychopharmacological treatments. The aim of this review is to summarize and systematize the growing body of evidence on Homer proteins, highlighting the role of Homer1 in the pathophysiology and therapy of mental diseases.

Congenital Splay Leg Syndrome in Piglets-Current Knowledge and a New Approach to Etiology

The porcine congenital splay leg syndrome (PCS), even though being of transient nature, is still one of the most important causes for piglet losses due to its high incidence and mortality. Although, described decades ago, the pathogenetic mechanism is still elusive. Numerous, mostly descriptive studies characterized the syndrome at clinical, histological and cellular levels but resulted in a highly diverse picture of the syndrome. Broad variability in phenotypical expression and, in case of proper care, the rapid recovery of affected animals complicated a systematical analysis of the underlying pathogenesis. Although, several environmental factors were discussed as potential causes of PCS, most of the evidence points to a hereditary basis of PCS. Nevertheless, only few of the suggested candidate genes from transcriptome and mapping analyses, like F-box protein 32 (FBXO32), could be confirmed so far. Only recently, a genome wide association study revealed genomic regions on five porcine chromosomes and named a number of potential candidate genes, among them homer scaffold protein 1 (HOMER1). This new candidate-a cellular scaffold protein-plays a role in a plethora of cellular signaling cascades, and is not only involved in skeletal muscle differentiation but also critical for muscular function. In this review, we critically elucidate the current state of knowledge in the field and evaluate current achievements in the identification of the pathogenetic mechanism for the syndrome.

Homer1 is a Potential Biomarker for Prognosis in Human Colorectal Carcinoma, Possibly in Association with G3BP1 Signaling

Background

Homer scaffolding protein 1 (Homer1) is a postsynaptic scaffold protein that regulates the structure and function of excitatory synaptic as well as its intracellular signal transduction. However, the role of Homer1 in colorectal cancer as well as the underlying molecular mechanisms has not been elucidated.

Materials and Methods

To evaluate the alternations of gene expression during colorectal cancer, Homer1 expression was analyzed using the gene expression profiling interactive analysis and Oncomine analyses. The prognostic value of Homer1 expression was validated by our own colorectal cancer specimens using RT-PCR. Then, the cell viability, migration and invasion of colorectal cancer cell lines were detected by CCK-8 and transwell assay.

Results

We obtained the following important results. (1) Homer1 expression was significantly higher in colorectal cancer than normal samples. (2) Among patients with colorectal cancer, those with higher Homer1 expression had a lower survival rate. (3) The major mutation type of Homer1 in colorectal cancer samples was missense mutation. (4) Homer1 was able to promote colorectal cancer cell proliferation, migration, and invasion through up-regulating G3BP1 in vitro.

Conclusion

Our findings suggest that Homer1 may play a role in malignancy of colorectal cancer mainly through the G3BP1 signaling pathway, which might be a potential indicator of poor prognosis.

Distinct and Overlapping Expression Patterns of the Homer Family of Scaffolding Proteins and Their Encoding Genes in Developing Murine Cephalic Tissues

In mammals Homer1, Homer2 and Homer3 constitute a family of scaffolding proteins with key roles in Ca²⁺ signaling and Ca²⁺ transport. In rodents, Homer proteins and mRNAs have been shown to be expressed in various postnatal tissues and to be enriched in brain. However, whether the Homers are expressed in developing tissues is hitherto largely unknown. In this work, we used immunohistochemistry and in situ hybridization to analyze the expression patterns of Homer1, Homer2 and Homer3 in developing cephalic structures. Our study revealed that the three Homer proteins and their encoding genes are expressed in a wide range of developing tissues and organs, including the brain, tooth, eye, cochlea, salivary glands, olfactory and respiratory mucosae, bone and taste buds. We show that although overall the three Homers exhibit overlapping distribution patterns, the proteins localize at distinct subcellular domains in several cell types, that in both undifferentiated and differentiated cells Homer proteins are concentrated in puncta and that the vascular endothelium is enriched with Homer3 mRNA and protein. Our findings suggest that Homer proteins may have differential and overlapping functions and are expected to be of value for future research aiming at deciphering the roles of Homer proteins during embryonic development.

Transgenic Analyses of Homer2 Function Within Nucleus Accumbens Subregions in the Regulation of Methamphetamine Reward and Reinforcement in Mice

Problems associated with the abuse of amphetamine-type stimulants, including methamphetamine (MA), pose serious health and socioeconomic issues world-wide. While it is well-established that MA's psychopharmacological effects involve interactions with monoamine neurotransmission, accumulating evidence from animal models implicates dysregulated glutamate in MA addiction vulnerability and use disorder. Recently, we discovered an association between genetic vulnerability to MA-taking and increased expression of the glutamate receptor scaffolding protein Homer2 within both the shell and core subregions of the nucleus accumbens (NAC) and demonstrated a necessary role for Homer2 within the shell subregion in MA reward and reinforcement in mice. This report extends our earlier work by interrogating the functional relevance of Homer2 within the NAC core for the conditioned rewarding and reinforcing properties of MA. C57BL/6J mice with a virus-mediated knockdown of Homer2b expression within the NAC core were first tested for the development and expression of a MA-induced conditioned place-preference/CPP (four pairings of 2 mg/kg MA) and then were trained to self-administer oral MA under operant-conditioning procedures (5-80 mg/L). Homer2b knockdown in the NAC core augmented a MA-CPP and shifted the dose-response function for MA-reinforced responding, above control levels. To determine whether Homer2b within NAC subregions played an active role in regulating MA reward and reinforcement, we characterized the MA phenotype of constitutive Homer2 knockout (KO) mice and then assayed the effects of virus-mediated overexpression of Homer2b within the NAC shell and core of wild-type and KO mice. In line with the results of NAC core knockdown, Homer2 deletion potentiated MA-induced CPP, MA-reinforced responding and intake, as well as both cue- and MA-primed reinstatement of MA-seeking following extinction. However, there was no effect of Homer2b overexpression within the NAC core or the shell on the KO phenotype. These data provide new evidence indicating a globally suppressive role for Homer2 in MA-seeking and MA-taking but argue against specific NAC subregions as the neural loci through which Homer2 actively regulates MA addiction-related behaviors.

Scaffold Proteins: From Coordinating Signaling Pathways to Metabolic Regulation

Among their pleiotropic functions, scaffold proteins are required for the accurate coordination of signaling pathways. It has only been within the past 10 years that their roles in glucose homeostasis and metabolism have emerged. It is well appreciated that changes in the expression or function of signaling effectors, such as receptors or kinases, can influence the development of chronic diseases such as diabetes and obesity. However, little is known regarding whether scaffolds have similar roles in the pathogenesis of metabolic diseases. In general, scaffolds are often underappreciated in the context of metabolism or metabolic diseases. In the present review, we discuss various scaffold proteins and their involvement in signaling pathways related to metabolism and metabolic diseases. The aims of the present review were to highlight the importance of scaffold proteins and to raise awareness of their physiological contributions. A thorough understanding of how scaffolds influence metabolism could aid in the discovery of novel therapeutic approaches to treat chronic conditions, such as diabetes, obesity, and cardiovascular disease, for which the incidence of all continue to increase at alarming rates.

Homer2 within the central nucleus of the amygdala modulates withdrawal-induced anxiety in a mouse model of binge-drinking

A history of binge-drinking decreases protein expression of the glutamate-related scaffolding protein Homer2 within the central nucleus of the amygdala (CEA), coinciding with behavioral signs of negative affect. To assess the functional relevance of this protein change for withdrawal-induced hyper-anxiety, adult (PND 56) and adolescent (PND 28) male C57BL/6J mice were administered an intra-CEA infusion of an adeno-associated viral vector (AAV) carrying either cDNA to express Homer2 (H2-cDNA) or GFP as control. Mice underwent 14 days of binge-drinking under multi-bottle, limited-access conditions and were assayed for behavioral signs of negative affect during withdrawal using the light-dark box, marble burying, and forced swim tests (FST). Following behavioral testing, all animals experienced 5 days of drinking to evaluate the effects of prior alcohol experience and Homer2 manipulation on subsequent alcohol consumption. During protracted (4 weeks) withdrawal, adolescent alcohol-experienced GFP controls showed increased signs of negative affect across all 3 assays, compared to water-drinking GFP animals, and also showed elevated alcohol consumption during the subsequent drinking period. Homer2-cDNA infusion in adolescent-onset alcohol-drinking animals was anxiolytic and reduced subsequent alcohol consumption. Conversely, Homer2-cDNA was anxiogenic and increased drinking in water-drinking adolescents. Unfortunately, the data from adult-onset alcohol-drinking animals were confounded by low alcohol consumption and negligible behavioral signs of anxiety. Nevertheless, the present results provide novel cause-effect evidence supporting a role for CEA Homer2 in the regulation of both basal anxiety and the time-dependent intensification of negative affective states in individuals with a history of binge-drinking during adolescence.

Behavioral and Neurochemical Phenotyping of Mice Incapable of Homer1a Induction

Immediate early and constitutively expressed products of the Homer1 gene regulate the functional assembly of post-synaptic density proteins at glutamatergic synapses to influence excitatory neurotransmission and synaptic plasticity. Earlier studies of Homer1 gene knock-out (KO) mice indicated active, but distinct, roles for IEG and constitutively expressed Homer1 gene products in regulating cognitive, emotional, motivational and sensorimotor processing, as well as behavioral and neurochemical sensitivity to cocaine. More recent characterization of transgenic mice engineered to prevent generation of the IEG form (a.k.a Homer1a KO) pose a critical role for Homer1a in cocaine-induced behavioral and neurochemical sensitization of relevance to drug addiction and related neuropsychiatric disorders. Here, we extend our characterization of the Homer1a KO mouse and report a modest pro-depressant phenotype, but no deleterious effects of the KO upon spatial learning/memory, prepulse inhibition, or cocaine-induced place-conditioning. As we reported previously, Homer1a KO mice did not develop cocaine-induced behavioral or neurochemical sensitization within the nucleus accumbens; however, virus-mediated Homer1a over-expression within the nucleus accumbens reversed the sensitization phenotype of KO mice. We also report several neurochemical abnormalities within the nucleus accumbens of Homer1a KO mice that include: elevated basal dopamine and reduced basal glutamate content, Group1 mGluR agonist-induced glutamate release and high K⁺-stimulated release of dopamine and glutamate within this region. Many of the neurochemical anomalies exhibited by Homer1a KO mice are recapitulated upon deletion of the entire Homer1 gene; however, Homer1 deletion did not affect NAC dopamine or alter K⁺-stimulated neurotransmitter release within this region. These data show that the selective deletion of Homer1a produces a behavioral and neurochemical phenotype that is distinguishable from that produced by deletion of the entire Homer1 gene. Moreover, the data indicate a specific role for Homer1a in regulating cocaine-induced behavioral and neurochemical sensitization of potential relevance to the psychotogenic properties of this drug.

Homer1 (VesL-1) in the rat esophagus: focus on myenteric plexus and neuromuscular junction

Homer1, a scaffolding protein of the postsynaptic density (PSD), enriched at excitatory synapses is known to anchor and modulate group I metabotropic glutamate receptors (mGluRs) and different channel- and receptor-proteins. Homer proteins are expressed in neurons of different brain regions, but also in non-neuronal tissues like skeletal muscle. Occurrence and location of Homer1 and mGluR5 in myenteric plexus and neuromuscular junctions (NMJ) of rat esophagus have yet not been characterized. We located Homer1 and mGluR5 immunoreactivity (-iry) in rat esophagus and focused on myenteric neurons, intraganglionic laminar endings (IGLEs) and NMJs, using double- and triple-label immunohistochemistry and confocal laser scanning microscopy. Homer1-iry was found in a subpopulation of vesicular glutamate transporter 2 (VGLUT2) positive IGLEs and cholinergic varicosities within myenteric ganglia, but neither in nitrergic nor cholinergic myenteric neuronal cell bodies. Homer1-iry was detected in 63% of esophageal and, for comparison, in 35% of sternomastoid NMJs. Besides the location in the PSD, Homer1-iry colocalized with cholinergic markers, indicating a presynaptic location in coarse VAChT/CGRP/NF200- immunoreactive (-ir) terminals of nucleus ambiguus neurons supplying striated esophageal muscle. mGluR5-iry was found in subpopulations of myenteric neuronal cell bodies, VGLUT2-ir IGLEs and cholinergic varicosities within the myenteric neuropil and NMJs of esophagus and sternomastoid muscles. Thus, Homer1 may anchor mGluR5 at presynaptic sites of cholinergic boutons at esophageal motor endplates, in a small subpopulation of VGLUT2-ir IGLEs and cholinergic varicosities within myenteric ganglia possibly modulating Ca²⁺-currents and neurotransmitter release.

Effects of Vesl/Homer Proteins on Intracellular Signaling

The clustering of signaling molecules at specialized cellular sites allows cells to effectively convert extracellular signals into intracellular signals and to produce a concerted functional output with specific temporal and spatial patterns. A prime example for these molecules and their effects on cellular signaling are the postsynaptic density proteins of the central nervous system. Recently, one group of these proteins, the Vesl/Homer protein family has received increased attention because of its unique molecular properties that allow both the clustering end functional modulation of a plethora of different binding Proteins. Within multlprotein signaling complexes, Vesl/Homer Proteins influence proteins as diverse as metabotropic glutamate receptors; transient receptor potential channels; intracellular calcium channels; the scaffolding protein, Shank; small GTPases; transcription factors; and cytoskeletal proteins. Furthermore, interaction with such functionally relevant proteins also links Vesl/Homer proteins indirectly to an even larger group of cellular effector proteins, putting the Vesl/Homer Proteins at the crossroads of several critical intracellular signaling processes. In addition to the initial reports of Vesl/Homer protein expression in the central nervous system, members of this protein family have now been identified in other excitable cells in various muscle types and in a large number of nonexcitable cells. The widespread expression of Vesl/Homer proteins in different organs and their functional importance in cellular protein signaling complexes is further evidenced by their conservation in organisms from Drosoohila to humans.

Homer2 within the nucleus accumbens core bidirectionally regulates alcohol intake by both P and Wistar rats

In murine models of alcoholism, the glutamate receptor scaffolding protein Homer2 bidirectionally regulates alcohol intake. Although chronic alcohol drinking increases Homer2 expression within the core subregion of the nucleus accumbens (NAc) of alcohol-preferring P rats, the relevance of this neuroadaptation for alcohol intake has yet to be determined in rats. Thus, the present study employed an adeno-associated viral vector (AAV) strategy to over-express and knock down the major rodent isoform Homer2b within the NAc of both P and outbred Wistar rats to examine for changes in alcohol preference and intake (0-30% v/v) under continuous-access procedures. The generalization of AAV effects to non-drug, palatable, sweet solutions was also determined in tests of sucrose (0-5% w/v) and saccharin (0-0.125% w/v) intake/preference. No net-flux in vivo microdialysis was conducted for glutamate in the NAc to relate Homer2-dependent changes in alcohol intake to extracellular levels of glutamate. Line differences were noted for sweet solution preference and intake, but these variables were not affected by intra-NAc AAV infusion in either line. In contrast, Homer2b over-expression elevated, while Homer2b knock-down reduced, alcohol intake in both lines, and this effect was greatest at the highest concentration. Strikingly, in P rats there was a direct association between changes in Homer2b expression and NAc extracellular glutamate levels, but this effect was not seen in Wistar rats. These data indicate that NAc Homer2b expression actively regulates alcohol consumption by rats, paralleling this previous observation in mice. Overall, these findings underscore the importance of mesocorticolimbic glutamate activity in alcohol abuse/dependence and suggest that Homer2b and/or its constituents may serve as molecular targets for the treatment of these disorders.

Expression and function of ryanodine receptor related pathways in PCB tolerant Atlantic killifish (Fundulus heteroclitus) from New Bedford Harbor, MA, USA

Atlantic killifish (Fundulus heteroclitus) thrive in New Bedford Harbor (NBH), MA, highly contaminated with polychlorinated biphenyls (PCBs). Resident killifish have evolved tolerance to dioxin-like (DL) PCBs, whose toxic effects through the aryl hydrocarbon receptor (AhR) are well studied. In NBH, non-dioxin like PCBs (NDL PCBs), which lack activity toward the AhR, vastly exceed levels of DL congeners yet how killifish counter NDL toxic effects has not been explored. In mammals and fish, NDL PCBs are potent activators of ryanodine receptors (RyR), Ca(2+) release channels necessary for a vast array of physiological processes. In the current study we compared the expression and function of RyR related pathways in NBH killifish with killifish from the reference site at Scorton Creek (SC, MA). Relative to the SC fish, adults from NBH displayed increased levels of skeletal muscle RyR1 protein, and increased levels of FK506-binding protein 12 kDa (FKBP12) an accessory protein essential for NDL PCB-triggered changes in RyR channel function. In accordance with increased RyR1 levels, NBH killifish displayed increased maximal ligand binding, increased maximal response to Ca(2+) activation and increased maximal response to activation by the NDL PCB congener PCB 95. Compared to SC, NBH embryos and larvae had increased levels of mtor and ryr2 transcripts at multiple stages of development, and generations, while levels of serca2 were decreased at 9 days post-fertilization in the F1 and F2 generations. These findings suggest that there are compensatory and heritable changes in RyR mediated Ca(2+) signaling proteins or potential signaling partners in NBH killifish.

Identification of Homer1 as a potential prognostic marker for intrahepatic cholangiocarcinoma

BACKGROUND

The aim of the present study was to analyze whether Homer1 is a potential prognostic marker for intrahepatic cholangiocarcinoma (ICC).

MATERIALS AND METHODS

The expression of Homer1 in ICC tissue was detected with immunohistochemistry and levels of protein in ICC and paratumor tissues were evaluated by Western blotting. Survival analysis by the Kaplan-Meier method was performed to assess prognostic significance.

RESULTS

Homer1 expression was high in 67.4% (58/86) of ICC samples, and there was significant difference between ICC and adjacent noncancerous tissues (p<0.001); high expression was associated with poor histologic differentiation (p=0.019), TNM stage (p=0.014), lymph node metastasis (p=0.040), and lymphatic invasion (p=0.025). On Kaplan-Meier analysis, a comparison of survival curves of low versus high expressors of Homer1 revealed a highly significant difference in OS (p=0.001) and DFS (p=0.006), indicating that high expression of Homer1 was linked with a worse prognosis. Multivariate analyses showed that Homer1 expression was an independent risk factor predicting overall survival[Hazard ratio(HR), 7.52; 95% confidence interval (CI), 2.63- 21.47; p=0.002] and disease-free survival (HR, 11.56; 95%CI, 5.17-25.96; p<0.001) in ICC.

CONCLUSIONS

Homer1 promotes lymphatic invasion and associates with lymph node metastasis and poor prognosis of ICC. The current study shows that Homer1 may be an independent prognostic factor for ICC patients after curative resection, and it provides an important basis for screening/treating high-risk patients.

Cocaine-elicited imbalances in ventromedial prefrontal cortex Homer1 versus Homer2 expression: implications for relapse

Withdrawal from a history of extended access to self-administered cocaine produces a time-dependent intensification of drug seeking, which might relate to a cocaine-induced imbalance in the relative expression of constitutively expressed Homer1 versus Homer2 isoforms within the ventromedial aspect of the prefrontal cortex (vmPFC). Thus, we employed immunoblotting to examine the relation between cue-reinforced lever pressing at 3- versus 30-day withdrawal from a 10-day history of extended access (6 hours/day) to intravenous cocaine (0.25 mg/infusion) or saline (Sal6h), and the expression of Homer1b/c and Homer2a/b within the vmPFC versus the more dorsomedial aspect of this structure (dmPFC). Behavioral studies employed adeno-associated virus (AAV) vectors to reverse cocaine-elicited changes in the relative expression of Homer1 versus Homer2 isoforms and tested animals for cocaine prime-, and cue-induced responding following extinction training. Cocaine self-administration elevated both Homer1b/c and Homer2a/b levels within the vmPFC at 3-day withdrawal, and the rise in Homer2a/b persisted for at least 30 days. dmPFC Homer levels did not change as a function of self-administration history. Reversing the relative increase in Homer2 versus Homer1 expression via Homer1c overexpression or Homer2b knockdown failed to influence cue-reinforced lever pressing when animals were tested in a drug-free state, but both AAV treatments prevented cocaine-primed reinstatement of lever-pressing behavior. These data suggest that a cocaine-elicited imbalance in the relative expression of constitutively expressed Homer2 versus Homer1 within the vmPFC is necessary for the capacity of cocaine to reinstate drug-seeking behavior, posing drug-induced changes in vmPFC Homer expression as a molecular trigger contributing to drug-elicited relapse.

De novo copy number variants are associated with congenital diaphragmatic hernia

BACKGROUND

Congenital diaphragmatic hernia (CDH) is a common birth defect with significant morbidity and mortality. Although the aetiology of CDH remains poorly understood, studies from animal models and patients with CDH suggest that genetic factors play an important role in the development of CDH. Chromosomal anomalies have been reported in CDH.

METHODS

In this study, the authors investigated the frequency of chromosomal anomalies and copy number variants (CNVs) in 256 parent-child trios of CDH using clinical conventional cytogenetic and microarray analysis. The authors also selected a set of CDH related training genes to prioritise the genes in those segmental aneuploidies and identified the genes and gene sets that may contribute to the aetiology of CDH.

RESULTS

The authors identified chromosomal anomalies in 16 patients (6.3%) of the series including three aneuploidies, two unbalanced translocation, and 11 patients with de novo CNVs ranging in size from 95 kb to 104.6 Mb. The authors prioritised the genes in the CNV segments and identified KCNA2, LMNA, CACNA1S, MYOG, HLX, LBR, AGT, GATA4, SOX7, HYLS1, FOXC1, FOXF2, PDGFA, FGF6, COL4A1, COL4A2, HOMER2, BNC1, BID, and TBX1 as genes that may be involved in diaphragm development. Gene enrichment analysis identified the most relevant gene ontology categories as those involved in tissue development (p=4.4×10(-11)) or regulation of multicellular organismal processes (p=2.8×10(-10)) and 'receptor binding' (p=8.7×10(-14)) and 'DNA binding transcription factor activity' (p=4.4×10(-10)).

CONCLUSIONS

The present findings support the role of chromosomal anomalies in CDH and provide a set of candidate genes including FOXC1, FOXF2, PDGFA, FGF6, COL4A1, COL4A2, SOX7, BNC1, BID, and TBX1 for further analysis in CDH.

Cytoskeletal and scaffolding proteins as structural and functional determinants of TRP channels

Transient receptor potential (TRP) channels are six transmembrane-spanning proteins, with variable selectivity for cations, that play a relevant role in intracellular Ca(2+) homeostasis. There is a large body of evidence that shows association of TRP channels with the actin cytoskeleton or even the microtubules and demonstrating the functional importance of this interaction for TRP channel function. Conversely, cation currents through TRP channels have also been found to modulate cytoskeleton rearrangements. The interplay between TRP channels and the cytoskeleton has been demonstrated to be essential for full activation of a variety of cellular functions. Furthermore, TRP channels have been reported to take part of macromolecular complexes including different signal transduction proteins. Scaffolding proteins play a relevant role in the association of TRP proteins with other signaling molecules into specific microdomains. Especially relevant are the roles of the Homer family members for the regulation of TRPC channel gating in mammals and INAD in the modulation of Drosophila TRP channels. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé.

Signaling pathways mediating alcohol effects

Ethanol's effects on intracellular signaling pathways contribute to acute effects of ethanol as well as to neuroadaptive responses to repeated ethanol exposure. In this chapter we review recent discoveries that demonstrate how ethanol alters signaling pathways involving several receptor tyrosine kinases and intracellular tyrosine and serine-threonine kinases, with consequences for regulation of cell surface receptor function, gene expression, protein translation, neuronal excitability and animal behavior. We also describe recent work that demonstrates a key role for ethanol in regulating the function of scaffolding proteins that organize signaling complexes into functional units. Finally, we review recent exciting studies demonstrating ethanol modulation of DNA and histone modification and the expression of microRNAs, indicating epigenetic mechanisms by which ethanol regulates neuronal gene expression and addictive behaviors.

Homer 2 antagonizes protein degradation in slow-twitch skeletal muscles

Homer represents a new and diversified family of proteins made up of several isoforms. The presence of Homer isoforms, referable to 1b/c and 2a/b, was investigated in fast- and slow-twitch skeletal muscles from both rat and mouse. Homer 1b/c was identical irrespective of the muscle, and Homer 2a/b was instead characteristic of the slow-twitch phenotype. Transition in Homer isoform composition was studied in two established experimental models of atrophy, i.e., denervation and disuse of slow-twitch skeletal muscles of the rat. No change of Homer 1b/c was observed up to 14 days after denervation, whereas Homer 2a/b was found to be significantly decreased at 7 and 14 days after denervation by 70 and 90%, respectively, and in parallel to reduction of muscle mass; 3 days after denervation, relative mRNA was reduced by 90% and remained low thereafter. Seven-day hindlimb suspension decreased Homer 2a/b protein by 70%. Reconstitution of Homer 2 complement by in vivo transfection of denervated soleus allowed partial rescue of the atrophic phenotype, as far as muscle mass, muscle fiber size, and ubiquitinazion are concerned. The counteracting effects of exogenous Homer 2 were mediated by downregulation of MuRF1, Atrogin, and Myogenin, i.e., all genes known to be upregulated at the onset of atrophy. On the other hand, slow-to-fast transition of denervated soleus, another landmark of denervation atrophy, was not rescued by Homer 2 replacement. The present data show that 1) downregulation of Homer 2 is an early event of atrophy, and 2) Homer 2 participates in the control of ubiquitinization and ensuing proteolysis via transcriptional downregulation of MuRF1, Atrogin, and Myogenin. Homers are key players of skeletal muscle plasticity, and Homer 2 is required for trophic homeostasis of slow-twitch skeletal muscles.

Proteasomal degradation of the metabotropic glutamate receptor 1α is mediated by Homer-3 via the proteasomal S8 ATPase: Signal transduction and synaptic transmission

The metabotropic glutamate receptors (mGluRs) fine-tune the efficacy of synaptic transmission. This unique feature makes mGluRs potential targets for the treatment of various CNS disorders. There is ample evidence to show that the ubiquitin proteasome system mediates changes in synaptic strength leading to multiple forms of synaptic plasticity. The present study describes a novel interaction between post-synaptic adaptors, long Homer-3 proteins, and one of the 26S proteasome regulatory subunits, the S8 ATPase, that influences the degradation of the metabotropic glutamate receptor 1α (mGluR1α). We have shown that the two human long Homer-3 proteins specifically interact with human proteasomal S8 ATPase. We identified that mGluR1α and long Homer-3s immunoprecipitate with the 26S proteasome both in vitro and in vivo. We further found that the mGluR1α receptor can be ubiquitinated and degraded by the 26S proteasome and that Homer-3A facilitates this process. Furthermore, the siRNA mediated silencing of Homer-3 led to increased levels of total and plasma membrane-associated mGluR1α receptors. These results suggest that long Homer-3 proteins control the degradation of mGluR1α receptors by shuttling ubiquitinated mGluR-1α receptors to the 26S proteasome via the S8 ATPase which may modulate synaptic transmission.

Scaffolding protein Homer 1c mediates hypertrophic responses downstream of Gq in cardiomyocytes

Activation of the heterotrimeric G protein, Gq, causes cardiomyocyte hypertrophy in vivo and in cell models. Responses to activated Gq in cardiomyocytes are mediated exclusively by phospholipase Cβ1b (PLCβ1b), because it localizes at the sarcolemma by binding to Shank3, a high-molecular-weight (MW) scaffolding protein. Shank3 can bind to the Homer family of low-MW scaffolding proteins that fine tune Ca(2+) signaling by facilitating crosstalk between Ca(2+) channels at the cell surface with those on intracellular Ca(2+) stores. Activation of α(1)-adrenergic receptors, expression of constitutively active Gαq (GαqQL), or PLCβ1b initiated cardiomyocyte hypertrophy and increased Homer 1c mRNA expression, by 1.6 ± 0.18-, 1.9 ± 0.17-, and 1.5 ± 0.07-fold, respectively (means ± se, 6 independent experiments, P<0.05). Expression of Homer 1c induced an increase in cardiomyocyte area from 853 ± 27 to 1146 ± 31 μm(2) (P<0.05); furthermore, expression of dominant-negative Homer (Homer 1a) reversed the increase in cell size caused by α(1)-adrenergic agonist or PLCβ1b treatment (1503±48 to 996±28 and 1626±48 to 828±31 μm(2), respectively, P<0.05). Homer proteins were localized near the sarcolemma, associated with Shank3 and phospholipase Cβ1b. We conclude that Gq-mediated hypertrophy involves activation of PLCβ1b scaffolded onto a Shank3/Homer complex. Signaling downstream of Homer 1c is necessary and sufficient for Gq-initiated hypertrophy.

Homer-1 polymorphisms are associated with psychopathology and response to treatment in schizophrenic patients

The HOMER 1 protein plays a crucial role in mediating glutamatergic neurotransmission. It has previously shown to be a candidate gene for etiology and pathophysiology of different psychiatric diseases such as schizophrenia. To identify genes involved in response to antipsychotics, subgroups of animals were treated with haloperidol (1 mg/kg, n = 11) or saline (n = 12) for one week. By analyzing microarray data, we replicated the observed increase of Homer 1 gene expression. Furthermore, we genotyped 267 schizophrenic patients, who were treated monotherapeutically with different antipsychotics within randomized-controlled trials. Psychopathology was measured weekly using the PANSS for a minimum of four and a maximum of twelve weeks. Correlations between PANSS subscale scores at baseline and PANSS improvement scores after four weeks of treatment and genotypes were calculated by using a linear model for all investigated SNP's. We found an association between two HOMER 1 polymorphisms (rs2290639 and rs4704560) and different PANSS subscales at baseline. Furthermore all seven investigated polymorphisms were found to be associated with therapy response in terms of a significant correlation with different PANSS improvement subscores after four weeks of antipsychotic treatment. Most significant associations have been shown between the rs2290639 HOMER 1 polymorphism and PANSS subscales both at baseline conditions and after four weeks of antipsychotic treatment. This is the first study which shows an association between HOMER 1 polymorphisms and psychopathology data at baseline and therapy response in a clinical sample of schizophrenic patients. Thus, these data might further help in detecting differential therapy response in individuals with schizophrenia.

Role of ryanodine receptor subtypes in initiation and formation of calcium sparks in arterial smooth muscle: comparison with striated muscle

Calcium sparks represent local, rapid, and transient calcium release events from a cluster of ryanodine receptors (RyRs) in the sarcoplasmic reticulum. In arterial smooth muscle cells (SMCs), calcium sparks activate calcium-dependent potassium channels causing decrease in the global intracellular [Ca2+] and oppose vasoconstriction. This is in contrast to cardiac and skeletal muscle, where spatial and temporal summation of calcium sparks leads to global increases in intracellular [Ca2+] and myocyte contraction. We summarize the present data on local RyR calcium signaling in arterial SMCs in comparison to striated muscle and muscle-specific differences in coupling between L-type calcium channels and RyRs. Accordingly, arterial SMC Ca(v)1.2 L-type channels regulate intracellular calcium stores content, which in turn modulates calcium efflux though RyRs. Downregulation of RyR2 up to a certain degree is compensated by increased SR calcium content to normalize calcium sparks. This indirect coupling between Ca(v)1.2 and RyR in arterial SMCs is opposite to striated muscle, where triggering of calcium sparks is controlled by rapid and direct cross-talk between Ca(v)1.1/Ca(v)1.2 L-type channels and RyRs. We discuss the role of RyR isoforms in initiation and formation of calcium sparks in SMCs and their possible molecular binding partners and regulators, which differ compared to striated muscle.

Replicated genetic evidence supports a role for HOMER2 in schizophrenia

Schizophrenia is a heritable mental disorder with a complex genetic aetiology potentially implicating glutamatergic dysfunction. Following a search for functionally relevant genes with evidence of linkage to schizophrenia, we selected HOMER2 for as a candidate gene for investigation using a multi-stage association design. Twenty-six tagging SNPs were genotyped in 401 cases and 812 controls and associated SNPs were analysed in an independent sample of 408 cases and 804 controls, all from Ireland. Secondary replication analysis was undertaken using the International Schizophrenia Consortium (ISC) European sample of 1287 cases and 1128 controls. Significant associations were found at five SNPs in the first Irish sample (p<0.05), but were not replicated in the second Irish sample. SNP rs2306428 was significantly associated when the two samples were combined (p=0.008, OR=0.73) and also by proxy in the ISC sample (rs17158184, r(2)=1.0, p=0.019, OR=0.75). The protective allele at rs2306428 removes a predicted splice-enhancer binding site where Homer2 is naturally truncated. We did not detect an allelic effect of rs2306428 on neuropsychological function nor on HOMER2 splicing. This study supports a role for HOMER2 gene in schizophrenia susceptibility. Further work is required to confirm and elucidate the role of HOMER2 and interacting genes in schizophrenia aetiology.

Homer and the ryanodine receptor

Homer proteins have recently been identified as novel high-affinity ligands that modulate ryanodine receptor (RyR) Ca(2+) release channels in heart and skeletal muscle, through an EVH1 domain which binds to proline-rich regions in target proteins. Many Homer proteins can also self-associate through a coiled-coil domain that allows their multimerisation. In other tissues, especially neurons, Homer anchors proteins embedded in the surface membrane to the Ca(2+) release channel in the endoplasmic reticulum and can anchor membrane or cytosolic proteins to the cytoskeleton. Although this anchoring aspect of Homer function has not been extensively investigated in muscle, there are consensus sequences for Homer binding in the RyR and on many of the proteins that it interacts with in the massive RyR ion channel complex. In this review we explore the potential of Homer to contribute to a variety of cell processes in muscle and neurons that also involve RyR channels.

Simvastatin inhibits angiotensin II-induced cardiac cell hypertrophy: role of Homer 1a

1. The scaffolding protein Homer 1a is constitutively expressed in the myocardium, although its function in cardiomyocytes remains poorly understood. The aim of the present study was to investigate Homer 1a expression in hypertrophic cardiac cells and its role in angiotensin (Ang) II-induced cardiac hypertrophy. 2. After serum starvation for 24 h, cells were treated with 1 micromol/L simvastatin, 100 nmol/L angiotensin (Ang) II or their combination added to Dulbecco's modified Eagle's medium containing 0.5% serum. For combination treatment with AngII plus simvastatin, cells were exposed to simvastatin 12 h before the addition of AngII to the medium and cells were then incubated in the presence of both drugs for a further 24 h. Western blotting was used to determine Homer 1a protein expression. Hypertrophy was evaluated by determining the protein content per cell. 3. Homer 1a protein levels were upregulated following AngII-induced hypertrophy in H9C2 cells and neonatal rat cardiomyocytes, and these increases were augmented by simvastatin pretreatment. Concomitantly, simvastatin pretreatment inhibited extracellular signal-regulated kinase (ERK) 1/2 phosphorylation and AngII-induced hypertrophy. 4. The inhibitory effects of simvastatin against AngII-induced hypertrophy were attenuated by Homer 1a silencing, suggesting that simvastatin suppresses cardiac hypertrophy in a Homer 1a-dependent manner. Furthermore, AngII-induced hypertrophy and ERK1/2 phosphorylation in neonatal rat cardiomyocytes were significantly inhibited following the overexpression of Homer 1a using an adenovirus. 5. These results suggest a possible role for Homer 1a in inhibiting cardiac hypertrophy perhaps in part through inhibition of ERK1/2 activation.

In vitro modulation of the cardiac ryanodine receptor activity by Homer1

The Homer protein family allows clustering and/or functional modulation of many proteins from different calcium signalling complexes including those formed by the ryanodine receptor (RyR) Ca(2+) release channel in skeletal muscle and the heart. Homer1b/c and the cardiac RyR (RyR2) are strongly expressed in the heart and neurons where their interaction with each other may modulate Ca(2+) signalling. However, functional interactions between Homer1b and RyR2 have been poorly defined. Our preliminary data and similar consensus binding sites for Homer in RyR2 and skeletal RyR (RyR1) proteins, led to the hypothesis that Homer may similarly regulate both RyR isoforms. Single-channel and [(3)H]ryanodine binding data showed that RyR2 and RyR1 activity increased to a maximum with ~50-100 nM Homer1b and fell with Homer1b > 200 nM. Homer1b (50 nM) activated RyR2 and RyR1 at all cytosolic [Ca(2+)]; estimated EC(50) value of RyR2 diminished from ~2.8 microM Ca(2+) (control) to ~1.9 microM Ca(2+) in the presence of 50 nM Homer1b. Short Homer1 (lacking the coiled-coil multimerisation domain) and Homer1b similarly modulated RyR2, indicating an action through ligand binding, not mutimerisation. These actions of Homer were generally similar in RyR2 and RyR1. The strong functional interactions suggest that Homer1 is likely to be an endogenous modulator of RyR channels in the heart and neurons as well as in skeletal muscle.

Targeting Homer genes using adeno-associated viral vector: lessons learned from behavioural and neurochemical studies

Over a decade of in-vitro data support a critical role for members of the Homer family of postsynaptic scaffolding proteins in regulating the functional architecture of glutamate synapses. Earlier studies of Homer knockout mice indicated a necessary role for Homer gene products in normal mesocorticolimbic glutamate transmission and behaviours associated therewith. The advent of adeno-associated viral vectors carrying cDNA for, or short hairpin RNA against, specific Homer isoforms enabled the site-directed targeting of Homers to neurons in the brain. This approach has allowed our groups to address developmental issues associated with conventional knockout mice, to confirm active roles for distinct Homer isoforms in regulating glutamate transmission in vivo, as well as in mediating a variety of behavioural processes. This review summarizes the existing data derived from our studies using adeno-associated viral vector-mediated neuronal targeting of Homer in rodents, implicating this family of proteins in drug and alcohol addiction, learning/memory and emotional processing.

Accumbens Homer2 overexpression facilitates alcohol-induced neuroplasticity in C57BL/6J mice

Homer proteins are integral components of the postsynaptic density that are necessary for alcohol-induced neuroplasticity within the nucleus accumbens (NAC). In this report, we describe the effects of chronic alcohol consumption upon NAC Homer expression and investigate the functional consequences of mimicking the alcohol-induced changes in Homer expression vis-à-vis alcohol-induced changes in NAC neurochemistry and behavior. Chronic alcohol consumption under continuous access (3 months; daily intake approximately 11.2+/-1.5 g/kg/day) produced a robust increase in NAC Homer2 protein levels that was apparent at 2 days, 2 weeks, and 2 months following withdrawal from alcohol drinking. The increased Homer2 expression was accompanied by a less enduring elevation in total mGluR1 and NR2b levels that were evident at 2 days and 2 weeks but not at the 2-month time point. Mimicking the alcohol-induced increase in Homer2 levels by viral transfection of NAC neurons in alcohol-preferring C57BL/6J inbred mice enhanced behavioral output for alcohol reinforcement and increased alcohol intake under both preprandial and postprandial conditions. Moreover, NAC Homer2 overexpression facilitated the expression of an alcohol-conditioned place preference, as well as the development of motor tolerance. Finally, NAC Homer2 overexpression facilitated NAC glutamate and dopamine release following an acute alcohol injection and augmented alcohol-induced dopamine and glutamate sensitization, but did not affect NAC gamma-aminobutyric acid levels. Thus, an upregulation in NAC mGluR-Homer2-N-methyl-D-aspartic acid receptor signaling appears to be an important molecular adaptation to alcohol that promotes neuroplasticity facilitating motivational drive for alcohol and the development of alcoholism-related behaviors.

Mice lacking Homer 1 exhibit a skeletal myopathy characterized by abnormal transient receptor potential channel activity

Transient receptor potential (TRP) channels are nonselective cation channels, several of which are expressed in striated muscle. Because the scaffolding protein Homer 1 has been implicated in TRP channel regulation, we hypothesized that Homer proteins play a significant role in skeletal muscle function. Mice lacking Homer 1 exhibited a myopathy characterized by decreased muscle fiber cross-sectional area and decreased skeletal muscle force generation. Homer 1 knockout myotubes displayed increased basal current density and spontaneous cation influx. This spontaneous cation influx in Homer 1 knockout myotubes was blocked by reexpression of Homer 1b, but not Homer 1a, and by gene silencing of TRPC1. Moreover, diminished Homer 1 expression in mouse models of Duchenne's muscular dystrophy suggests that loss of Homer 1 scaffolding of TRP channels may contribute to the increased stretch-activated channel activity observed in mdx myofibers. These findings provide direct evidence that Homer 1 functions as an important scaffold for TRP channels and regulates mechanotransduction in skeletal muscle.

Homers regulate drug-induced neuroplasticity: implications for addiction

Drug addiction is a chronic, relapsing disorder, characterized by an uncontrollable motivation to seek and use drugs. Converging clinical and preclinical observations implicate pathologies within the corticolimbic glutamate system in the genetic predisposition to, and the development of, an addicted phenotype. Such observations pose cellular factors regulating glutamate transmission as likely molecular candidates in the etiology of addiction. Members of the Homer family of proteins regulate signal transduction through, and the trafficking of, glutamate receptors, as well as maintain and regulate extracellular glutamate levels in corticolimbic brain regions. This review summarizes the existing data implicating the Homer family of protein in acute behavioral and neurochemical sensitivity to drugs of abuse, the development of drug-induced neuroplasticity, as well as other behavioral and cognitive pathologies associated with an addicted state.

Dynamic regulation of ryanodine receptor type 1 (RyR1) channel activity by Homer 1

Homer, a family of scaffolding proteins originally identified in neurons, is also expressed in skeletal muscle. Previous studies showed that splice variants of Homer 1 (H1) amplify the gain of the ryanodine receptor type 1 (RyR1) channel complex. Using [3H]ryanodine ([3H]Ry) to probe the conformational state of RyR1, the actions of long- and short-forms of H1 are examined singly and in combination. At < or =200 nM, H1 long-forms (H1b or H1c possessing coiled-coil (CC) domains) and short-forms (H1a or H1EVH1 lacking CC domains) enhance specific [3H]Ry binding to RyR1. However, at a concentration > 200 nM, either H1 form completely inhibited [3H]Ry binding. Importantly, the combinations of H1c+H1EVH1, or H1b+H1a acted in an additive manner to enhance or inhibit [3H]Ry-binding activity. H1a and H1c individually or in combination produced the same dynamic pattern in regulating purified RyR1 channels reconstituted in planar lipid bilayers. In combination, their net action on RyR1 channels depends on total concentrations of H1. These data provide a mechanism by which constitutively and transiently expressed H1 forms can tightly regulate RyR1 channel activity in response to changing levels of expression and degradation of H1 proteins.

The Homer family proteins

The Homer family of adaptor proteins consists of three members in mammals, and homologs are also known in other animals but not elsewhere. They are predominantly localized at the postsynaptic density in mammalian neurons and act as adaptor proteins for many postsynaptic density proteins. As a result of alternative splicing each member has several variants, which are classified primarily into the long and short forms. The long Homer forms are constitutively expressed and consist of two major domains: the amino-terminal target-binding domain, which includes an Enabled/vasodilator-stimulated phosphoprotein (Ena/VASP) homology 1 (EVH1) domain, and the carboxy-terminal self-assembly domain containing a coiled-coil structure and leucine zipper motif. Multimers of long Homer proteins, coupled through their carboxy-terminal domains, are thought to form protein clusters with other postsynaptic density proteins, which are bound through the amino-terminal domains. Such Homer-mediated clustering probably regulates or facilitates signal transduction or cross-talk between target proteins. The short Homer forms lack the carboxy-terminal domain; they are expressed in an activity-dependent manner as immediate-early gene products, possibly disrupting Homer clusters by competitive binding to target proteins. Homer proteins are also involved in diverse non-neural physiological functions.

Homer proteins in Ca2+ signaling by excitable and non-excitable cells

Homers are scaffolding proteins that bind Ca(2+) signaling proteins in cellular microdomains. The Homers participate in targeting and localization of Ca(2+) signaling proteins in signaling complexes. However, recent work showed that the Homers are not passive scaffolding proteins, but rather they regulate the activity of several proteins within the Ca(2+) signaling complex in an isoform-specific manner. Homer2 increases the GAP activity of RGS proteins and PLCbeta that accelerate the GTPase activity of Galpha subunits. Homer1 gates the activity of TRPC channels, controls the rates of their translocation and retrieval from the plasma membrane and mediates the conformational coupling between TRPC channels and IP(3)Rs. Homer1 stimulates the activity of the cardiac and neuronal L-type Ca(2+) channels Ca(v)1.2 and Ca(v)1.3. Homer1 also mediates the communication between the cardiac and smooth muscle ryanodine receptor RyR2 and Ca(v)1.2 to regulate E-C coupling. In many cases the Homers function as a buffer to reduce the intensity of Ca(2+) signaling and create a negative bias that can be reversed by the immediate early gene form of Homer1. Hence, the Homers should be viewed as the buffers of Ca(2+) signaling that ensure a high spatial and temporal fidelity of the Ca(2+) signaling and activation of downstream effects.

Strain- and region-specific gene expression profiles in mouse brain in response to chronic nicotine treatment

A pathway-focused complementary DNA microarray and gene ontology analysis were used to investigate gene expression profiles in the amygdala, hippocampus, nucleus accumbens, prefrontal cortex (PFC) and ventral tegmental area of C3H/HeJ and C57BL/6J mice receiving nicotine in drinking water (100 mug/ml in 2% saccharin for 2 weeks). A balanced experimental design and rigorous statistical analysis have led to the identification of 3.5-22.1% and 4.1-14.3% of the 638 sequence-verified genes as significantly modulated in the aforementioned brain regions of the C3H/HeJ and C57BL/6J strains, respectively. Comparisons of differential expression among brain tissues showed that only a small number of genes were altered in multiple brain regions, suggesting presence of a brain region-specific transcriptional response to nicotine. Subsequent principal component analysis and Expression Analysis Systematic Explorer analysis showed significant enrichment of biological processes both in C3H/HeJ and C57BL/6J mice, i.e. cell cycle/proliferation, organogenesis and transmission of nerve impulse. Finally, we verified the observed changes in expression using real-time reverse transcriptase polymerase chain reaction for six representative genes in the PFC region, providing an independent replication of our microarray results. Together, this report represents the first comprehensive gene expression profiling investigation of the changes caused by nicotine in brain tissues of the two mouse strains known to exhibit differential behavioral and physiological responses to nicotine.

Homer 1a uncouples metabotropic glutamate receptor 5 from postsynaptic effectors

Metabotropic glutamate receptors (mGluRs) and Homer proteins play critical roles in neuronal functions including plasticity, nociception, epilepsy, and drug addiction. Furthermore, Homer proteins regulate mGluR1/5 function by acting as adapters and facilitating coupling to effectors such as the inositol triphosphate receptor. However, although Homer proteins and their interaction with mGluRs have been the subject of intense study, direct measurements of Homer-induced changes in postsynaptic mGluR-effector coupling have not been reported. This question was addressed here by examining glutamatergic excitatory postsynaptic currents (EPSCs) in rat autaptic hippocampal cultures. In most neurons, the group I mGluR agonist (S)-3,5-dihydroxyphenylglycine strongly inhibited the EPSC acutely. This modulation occurred postsynaptically, was mediated primarily by mGluR5, and was inositol triphosphate receptor-dependent. Expression of the dominant negative, immediate early form of Homer, Homer 1a, strongly reduced EPSC modulation, but the W24A mutant of Homer 1a, which cannot bind mGluRs, had no effect. (S)-3,5-dihydroxyphenylglycine-mediated intracellular calcium responses in the processes of Homer 1a-expressing neurons were reduced compared with those in Homer 1a W24A-expressing cells. However, neither the distribution of mGluR5 nor the modulation of somatic calcium channels was altered by Homer 1a expression. These data demonstrate that Homer 1a can reduce mGluR5 coupling to postsynaptic effectors without relying on large changes in the subcellular distribution of the receptor. Thus, alteration of mGluR signaling by changes in Homer protein expression may represent a viable mechanism for fine-tuning synaptic strength in neurons.

Ca2+ signaling in microdomains: Homer1 mediates the interaction between RyR2 and Cav1.2 to regulate excitation-contraction coupling

Excitation-contraction (E-C) coupling and Ca(2+)-induced Ca(2+) release in smooth and cardiac muscles is mediated by the L-type Ca(2+) channel isoform Ca(v)1.2 and the ryanodine receptor isoform RyR2. Although physical coupling between Ca(v)1.1 and RyR1 in skeletal muscle is well established, it is generally assumed that Ca(v)1.2 and RyR2 do not directly communicate either passively or dynamically during E-C coupling. In the present work, we re-examined this assumption by studying E-C coupling in the detrusor muscle of wild type and Homer1(-/-) mice and by demonstrating a Homer1-mediated dynamic interaction between Ca(v)1.2 and RyR2 using the split green fluorescent protein technique. Deletion of Homer1 in mice (but not of Homer2 or Homer3) resulted in impaired urinary bladder function, which was associated with higher sensitivity of the detrusor muscle to muscarinic stimulation and membrane depolarization. This was not due to an altered expression or function of RyR2 and Ca(v)1.2. Most notably, expression of Ca(v)1.2 and RyR2 tagged with the complementary C- and N-terminal halves of green fluorescent protein and in the presence and absence of Homer1 isoforms revealed that H1a and H1b/c reciprocally modulates a dynamic interaction between Ca(v)1.2 and RyR2 to regulate the intensity of Ca(2+)-induced Ca(2+) release and its dependence on membrane depolarization. These findings define the molecular basis of a "two-state" model of E-C coupling by Ca(v)1.2 and RyR2. In one state, Ca(v)1.2 couples to RyR2 by H1b/c, which results in reduced responsiveness to membrane depolarization and in the other state H1a uncouples Ca(v)1.2 and RyR2 to enhance responsiveness to membrane depolarization. These findings reveal an unexpected and novel mode of interaction and communication between Ca(v)1.2 and RyR2 with important implications for the regulation of smooth and possibly cardiac muscle E-C coupling.

Agonists and antagonists of the cardiac ryanodine receptor: Potential therapeutic agents?

This review addresses the potential use of the intracellular ryanodine receptor (RyR) Ca(2+) release channel as a therapeutic target in heart disease. Heart disease encompasses a wide range of conditions with the major contributors to mortality and morbidity being ischaemic heart disease and heart failure (HF). In addition there are many rare, but devastating conditions, some of which are either genetically linked to the RyR and its regulatory proteins or involve drug-induced modification of the proteins. The defects in Ca(2+) signalling vary with the nature of the heart disease and the stage in its progress and therefore specific corrections require different modifications of Ca(2+) signalling. Compounds that activate the RyR are potential inotropic agents to increase the Ca(2+) transient and strength of contraction. Compounds that reduce RyR activity are potentially useful in conditions where excess RyR activity initiates arrhythmias, or depletes the Ca(2+) store, as in end stage HF. It has recently been discovered that the cardio-protective action of the drug JTV519 can be attributed partly to its ability to stabilise the interaction between the RyR and the 12.6 kDa binding protein for the commonly used immunosuppressive drug FK506 (FKBP12.6, known as tacrolimus). This has established the credibility of the RyR as a therapeutic target. We explore the possibility that mutations causing the rare RyR-linked arrhythmias will open the door to identification of novel RyR-based therapeutic agents. The use of regulatory binding sites within the RyR complex or on its associated proteins as templates for drug design is discussed.

Generation and characterization of rabbit embryonic stem cells

We described the derivation of four stable pluripotent rabbit embryonic stem cell (ESC) lines, one (RF) from blastocysts fertilized in vivo and cultured in vitro and three (RP01, RP02, and RP03) from parthenogenetic blastocysts. These ESC lines have been cultivated for extended periods (RF >1 year, RP01 >8 months, RP02 >8 months, and RP03 >6 months) in vitro while maintaining expression of pluripotent ESC markers and a normal XY or XX karyotype. The ESCs from all lines expressed alkaline phosphatase, transcription factor Oct-4, stage-specific embryonic antigens (SSEA-1, SSEA-3, and SSEA-4), and the tumor-related antigens (TRA-1-60 and TRA-1-81). Similar to human and mouse ESCs, rabbit ESCs expressed pluripotency (Oct-4, Nanog, SOX2, and UTF-1) and signaling pathway genes (fibroblast growth factor, WNT, and transforming growth factor pathway). Morphologically, rabbit ESCs resembled primate ESCs, whereas their proliferation characteristics were more like those seen in mouse ESCs. Rabbit ESCs were induced to differentiate into many cell types in vitro and formed teratomas with derivatives of the three major germ layers in vivo when injected into severe combined immunodeficient mice. Our results showed that pluripotent, stable ESC lines could be derived from fertilized and parthenote-derived rabbit embryos.

Novel regulators of RyR Ca2+ release channels: insight into molecular changes in genetically-linked myopathies

There are many mutations in the ryanodine receptor (RyR) Ca2+ release channel that are implicated in skeletal muscle disorders and cardiac arrhythmias. More than 80 mutations in the skeletal RyR1 have been identified and linked to malignant hyperthermia, central core disease or multi-minicore disease, while more than 40 mutations in the cardiac RyR2 lead to ventricular arrhythmias and sudden cardiac death in patients with structurally normal hearts. These RyR mutations cause diverse changes in RyR activity which either excessively activate or block the channel in a manner that disrupts Ca2+ signalling in the muscle fibres. In a different myopathy, myotonic dystrophy (DM), a juvenile isoform of the skeletal RyR is preferentially expressed in adults. There are two regions of RyR1 that are variably spiced and developmentally regulated (ASI and ASII). The juvenile isoform (ASI(-)) is less active than the adult isoform (ASI(+)) and its over-expression in adults with DM may contribute to functional changes. Finally, mutations in an important regulator of the RyR, the Ca2+ binding protein calsequestrin (CSQ), have been linked to a disruption of Ca2+ homeostasis in cardiac myocytes that results in arrhythmias. We discuss evidence supporting the hypothesis that mutations in each of these situations alter protein/protein interactions within the RyR complex or between the RyR and its associated proteins. The disruption of these protein-protein interactions can lead either to excess Ca2+ release or reduced Ca2+ release and thus to abnormal Ca2+ homeostasis. Much of the evidence for disruption of protein-protein interactions has been provided by the actions of a group of novel RyR regulators, domain peptides with sequences that correspond to sequences within the RyR and which compete with the endogenous residues for their interaction sites.