Deciphering autism heterogeneity: a molecular stratification approach in four mouse models.

Autism spectrum disorder (ASD) is a complex neurodevelopmental condition characterized by impairments in social interaction and communication, as well as restrained or stereotyped behaviors. The inherent heterogeneity within the autism spectrum poses challenges for developing effective pharmacological treatments targeting core features. Successful clinical trials require the identification of robust markers to enable patient stratification. In this study, we identified molecular markers within the oxytocin and immediate early gene families across five interconnected brain structures of the social circuit. We used wild-type and four heterogeneous mouse models, each exhibiting unique autism-like behaviors modeling the autism spectrum. While dysregulations in the oxytocin family were model-specific, immediate early genes displayed widespread alterations, reflecting global changes across the four models. Through integrative analysis, we identified Egr1, Foxp1, Homer1a, Oxt, and Oxtr as five robust and discriminant molecular markers that allowed the successful stratification of the four models. Importantly, our stratification demonstrated predictive values when challenged with a fifth mouse model or identifying subgroups of mice potentially responsive to oxytocin treatment. Beyond providing insights into oxytocin and immediate early gene mRNA dynamics, this proof-of-concept study represents a significant step toward the potential stratification of individuals with ASD. This work has implications for the success of clinical trials and the development of personalized medicine in autism.

The mGluR5-mediated Arc activation protects against experimental traumatic brain injury in rats.

INTRODUCTION: Traumatic brain injury (TBI) is a complex pathophysiological process, and increasing attention has been paid to the important role of post-synaptic density (PSD) proteins, such as glutamate receptors. Our previous study showed that a PSD protein Arc/Arg3.1 (Arc) regulates endoplasmic reticulum (ER) stress and neuronal necroptosis in traumatic injury in vitro. AIM: In this study, we investigated the expression, regulation and biological function of Arc in both in vivo and in vitro experimental TBI models. RESULTS: Traumatic neuronal injury (TNI) induced a temporal upregulation of Arc in cortical neurons, while TBI resulted in sustained increase in Arc expression up to 24 h in rats. The increased expression of Arc was mediated by the activity of metabotropic glutamate receptor 5 (mGluR5), but not dependent on the intracellular calcium (Ca2+) release. By using inhibitors and antagonists, we found that TNI regulates Arc expression via Gq protein and protein turnover. In addition, overexpression of Arc protects against TBI-induced neuronal injury and motor dysfunction both in vivo and in vitro, whereas the long-term cognitive function was not altered. To determine the role of Arc in mGluR5-induced protection, lentivirus-mediated short hairpin RNA (shRNA) transfection was performed to knockdown Arc expression. The mGluR5 agonist (RS)-2-chloro-5-hydroxyphenylglycine (CHPG)-induced protection against TBI was partially prevented by Arc knockdown. Furthermore, the CHPG-induced attenuation of Ca2+ influx after TNI was dependent on Arc activation and followed regulation of AMPAR subunits. The results of Co-IP and Ca2+ imaging showed that the Arc-Homer1 interaction contributes to the CHPG-induced regulation of intracellular Ca2+ release. CONCLUSION: In summary, the present data indicate that the mGluR5-mediated Arc activation is a protective mechanism that attenuates neurotoxicity following TBI through the regulation of intracellular Ca2+ hemostasis. The AMPAR-associated Ca2+ influx and ER Ca2+ release induced by Homer1-IP3R pathway might be involved in this protection.

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.

Prefrontal cortex molecular clock modulates development of depression-like phenotype and rapid antidepressant response in mice.

Depression is associated with dysregulated circadian rhythms, but the role of intrinsic clocks in mood-controlling brain regions remains poorly understood. We found increased circadian negative loop and decreased positive clock regulators expression in the medial prefrontal cortex (mPFC) of a mouse model of depression, and a subsequent clock countermodulation by the rapid antidepressant ketamine. Selective Bmal1KO in CaMK2a excitatory neurons revealed that the functional mPFC clock is an essential factor for the development of a depression-like phenotype and ketamine effects. Per2 silencing in mPFC produced antidepressant-like effects, while REV-ERB agonism enhanced the depression-like phenotype and suppressed ketamine action. Pharmacological potentiation of clock positive modulator ROR elicited antidepressant-like effects, upregulating plasticity protein Homer1a, synaptic AMPA receptors expression and plasticity-related slow wave activity specifically in the mPFC. Our data demonstrate a critical role for mPFC molecular clock in regulating depression-like behavior and the therapeutic potential of clock pharmacological manipulations influencing glutamatergic-dependent plasticity.

Elaboration of the Homer1 recognition landscape reveals incomplete divergence of paralogous EVH1 domains.

Short sequences that mediate interactions with modular binding domains are ubiquitous throughout eukaryotic proteomes. Networks of short linear motifs (SLiMs) and their corresponding binding domains orchestrate many cellular processes, and the low mutational barrier to evolving novel interactions provides a way for biological systems to rapidly sample selectable phenotypes. Mapping SLiM binding specificity and the rules that govern SLiM evolution is fundamental to uncovering the pathways regulated by these networks and developing the tools to manipulate them. We used high-throughput screening of the human proteome to identify sequences that bind to the Enabled/VASP homology 1 (EVH1) domain of the postsynaptic density scaffolding protein Homer1. This expanded our understanding of the determinants of Homer EVH1 binding preferences and defined a new motif that can facilitate the discovery of additional Homer-mediated interactions. Interestingly, the Homer1 EVH1 domain preferentially binds to sequences containing an N-terminally overlapping motif that is bound by the paralogous family of Ena/VASP actin polymerases, and many of these sequences can bind to EVH1 domains from both protein families. We provide evidence from orthologous EVH1 domains in pre-metazoan organisms that the overlap in human Ena/VASP and Homer binding preferences corresponds to an incomplete divergence from a common Ena/VASP ancestor. Given this overlap in binding profiles, promiscuous sequences that can be recognized by both families either achieve specificity through extrinsic regulatory strategies or may provide functional benefits via multi-specificity. This may explain why these paralogs incompletely diverged despite the accessibility of further diverged isoforms.

Perinatal stress modulates glutamatergic functional connectivity: A post-synaptic density immediate early gene-based network analysis.

Early life stress may induce synaptic changes within brain regions associated with behavioral disorders. Here, we investigated glutamatergic functional connectivity by a postsynaptic density immediate-early gene-based network analysis. Pregnant female Sprague-Dawley rats were randomly divided into two experimental groups: one exposed to stress sessions and the other serving as a stress-free control group. Homer1 expression was evaluated by in situ hybridization technique in eighty-eight brain regions of interest of male rat offspring. Differences between the perinatal stress exposed group (PRS) (n = 5) and the control group (CTR) (n = 5) were assessed by performing the Student's t-test via SPSS 28.0.1.0 with Bonferroni correction. Additionally, all possible pairwise Spearman's correlations were computed as well as correlation matrices and networks for each experimental group were generated via RStudio and Cytoscape. Perinatal stress exposure was associated with Homer1a reduction in several cortical, thalamic, and striatal regions. Furthermore, it was found to affect functional connectivity between: the lateral septal nucleus, the central medial thalamic nucleus, the anterior part of the paraventricular thalamic nucleus, and both retrosplenial granular b cortex and hippocampal regions; the orbitofrontal cortex, amygdaloid nuclei, and hippocampal regions; and lastly, among regions involved in limbic system. Finally, the PRS networks showed a significant reduction in multiple connections for the ventrolateral part of the anteroventral thalamic nucleus after perinatal stress exposure, as well as a decrease in the centrality of ventral anterior thalamic and amygdaloid nuclei suggestive of putative reduced cortical control over these regions. Within the present preclinical setting, perinatal stress exposure is a modifier of glutamatergic early gene-based functional connectivity in neuronal circuits involved in behaviors relevant to model neurodevelopmental disorders.

Changes in SLITRK1 Level in the Amygdala Mediate Chronic Neuropathic Pain-Induced Anxio-Depressive Behaviors in Mice.

BACKGROUND: Comorbid chronic neuropathic pain (NPP) and anxio-depressive disorders (ADD) have become a serious global public-health problem. The SLIT and NTRK-like 1 (SLITRK1) protein is important for synaptic remodeling and is highly expressed in the amygdala, an important brain region involved in various emotional behaviors. We examined whether SLITRK1 protein in the amygdala participates in NPP and comorbid ADD. METHODS: A chronic NPP mouse model was constructed by L5 spinal nerve ligation; changes in chronic pain and ADD-like behaviors were measured in behavioral tests. Changes in SLITRK1 protein and excitatory synaptic functional proteins in the amygdala were measured by immunofluorescence and Western blot. Adeno-associated virus was transfected into excitatory synaptic neurons in the amygdala to up-regulate the expression of SLITRK1. RESULTS: Chronic NPP-related ADD-like behavior was successfully produced in mice by L5 ligation. We found that chronic NPP and related ADD decreased amygdalar expression of SLITRK1 and proteins important for excitatory synaptic function, including Homer1, postsynaptic density protein 95 (PSD95), and synaptophysin. Virally-mediated SLITRK1 overexpression in the amygdala produced a significant easing of chronic NPP and ADD, and restored the expression levels of Homer1, PSD95, and synaptophysin. CONCLUSION: Our findings indicated that SLITRK1 in the amygdala plays an important role in chronic pain and related ADD, and may prove to be a potential therapeutic target for chronic NPP-ADD comorbidity.

Identification of BMAL1-Regulated circadian genes in mouse liver and their potential association with hepatocellular carcinoma: Gys2 and Upp2 as promising candidates.

Identification and functional analysis of key genes regulated by the circadian clock system will provide a comprehensive understanding of the underlying mechanisms through which circadian clock disruption impairs the health of living organisms. The initial phase involved bioinformatics analysis, drawing insights from three RNA-seq datasets (GSE184303, GSE114400, and GSE199061) derived from wild-type mouse liver tissues, which encompassed six distinct time points across a day. As expected, 536 overlapping genes exhibiting rhythmic expression patterns were identified. By intersecting these genes with differentially expressed genes (DEGs) originating from liver RNA-seq data at two representative time points (circadian time, CT: CT2 and CT14) in global Bmal1 knockout mice (Bmal1-/-), hepatocyte-specific Bmal1 knockout mice (L-Bmal1-/-), and their corresponding control groups, 80 genes potentially regulated by BMAL1 (referred to as BMAL1-regulated genes, BRGs) were identified. These genes were significantly enriched in glycolipid metabolism, immune response, and tumorigenesis pathways. Eight BRGs (Nr1d1, Cry1, Gys2, Homer2, Serpina6, Slc2a2, Nmrk1, and Upp2) were selected to validate their expression patterns in both control and L-Bmal1-/- mice livers over 24 h. Real-time quantitative polymerase chain reaction results demonstrated a comprehensive loss of rhythmic expression patterns in the eight selected BRGs in L-Bmal1-/- mice, in contrast to the discernible rhythmic patterns observed in the livers of control mice. Additionally, significant reductions in the expression levels of these selected BRGs, excluding Cry1, were also observed in L-Bmal1-/- mice livers. Chromatin immunoprecipitation (ChIP)-seq (GSE13505 and GSE39860) and JASPAR analyses validated the rhythmic binding of BMAL1 to the promoter and intron regions of these genes. Moreover, the progression of conditions, from basic steatosis to non-alcoholic fatty liver disease, and eventual malignancy, demonstrated a continuous gradual decline in Bmal1 transcripts in the human liver. Combining the aforementioned BRGs with DEGs derived from human liver cancer datasets identified Gys2 and Upp2 as potential node genes bridging the circadian clock system and hepatocellular carcinoma (HCC). In addition, CCK8 and wound healing assays demonstrated that the overexpression of human GYS2 and UPP2 proteins inhibited the proliferation and migration of HepG2 cells, accompanied by elevated expression of p53, a tumor suppressor protein. In summary, this study systematically identified rhythmic genes in the mouse liver, and a subset of circadian genes potentially regulated by BMAL1. Two circadian genes, Gys2 and Upp2, have been proposed and validated as potential candidates for advancing the prevention and treatment of HCC.

Homer1 ameliorates ischemic stroke by inhibiting necroptosis-induced neuronal damage and neuroinflammation.

OBJECTIVE: Proinflammatory necroptosis is the main pathological mechanism of ischemic stroke. Homer scaffolding protein 1 (Homer1) is a postsynaptic scaffolding protein that exerts anti-inflammatory effects in most central nervous system diseases. However, the relationship between Homer1 and proinflammatory necroptosis in ischemic stroke remains unclear. AIM: This study aimed to investigate the role of Homer1 in ischemia-induced necroptosis. METHODS: C57BL/6 mice were used to establish a model of permanent middle cerebral artery occlusion model (pMCAO). Homer1 knockdown mice were generated using adeno-associated virus (AAV) infection to explore the role of Homer1 and its impact on necroptosis in pMCAO. Finally, Homer1 protein was stereotaxically injected into the ischemic cortex of Homer1flox/flox/Nestin-Cre +/- mice, and the efficacy of Homer1 was investigated using behavioral assays and molecular biological assays to explore potential mechanisms. RESULTS: Homer1 expression peaked at 8 h in the ischemic penumbral cortex after pMCAO and colocalized with neurons. Homer1 knockdown promoted neuronal death by enhancing necroptotic signaling pathways and aggravating ischemic brain damage in mice. Furthermore, the knockdown of Homer1 enhanced the expression of proinflammatory cytokines. Moreover, injection of Homer1 protein reduced necroptosis-induced brain injury inhibited the expression of proinflammatory factors, and ameliorated the outcomes in the Homer1flox/flox/Nestin-Cre+/- mice after pMCAO. CONCLUSIONS: Homer1 ameliorates ischemic stroke by inhibiting necroptosis-induced neuronal damage and neuroinflammation. These data suggested that Homer1 is a novel regulator of neuronal death and neuroinflammation.

Homer1 Protects against Retinal Ganglion Cell Pyroptosis by Inhibiting Endoplasmic Reticulum Stress-Associated TXNIP/NLRP3 Inflammasome Activation after Middle Cerebral Artery Occlusion-Induced Retinal Ischemia.

Retinal ischemia, after cerebral ischemia, is an easily overlooked pathophysiological problem in which inflammation is considered to play an important role. Pyroptosis is a kind of cell death pattern accompanied by inflammation. Homer scaffold protein 1 (Homer1) has anti-inflammation properties and protects against ischemic injury. However, little is known about pyroptosis following middle cerebral artery occlusion (MCAO)-induced retinal ischemia and the regulatory mechanisms involved by Homer1 for the development of pyroptosis. In the present study, retinal ischemic injury was induced in mice by permanent MCAO in vivo, and retinal ganglion cells (RGCs) were subjected to Oxygen and Glucose Deprivation (OGD) to establish an in vitro model. It was shown that TXNIP/NLRP3-mediated pyroptosis was located predominantly in RGCs, which gradually increased after retinal ischemia and peaked at 24 h after retinal ischemia. Interestingly, the RGCs pyroptosis occurred not only in the cell body but also in the axon. Notably, the occurrence of pyroptosis coincided with the change of Homer1 expression in the retina after retinal ischemia and Homer1 also co-localized with RGCs. It was demonstrated that overexpression of Homer1 not only alleviated RGCs pyroptosis and inhibited the release of pro-inflammatory factors but also led to the increase in phosphorylation of AMPK, inhibition of ER stress, and preservation of visual function after retinal ischemia. In conclusion, it was suggested that Homer1 may protect against MCAO-induced retinal ischemia and RGCs pyroptosis by inhibiting endoplasmic reticulum stress-associated TXNIP/NLRP3 inflammasome activation after MCAO-induced retinal ischemia.

HOMER3 promotes non-small cell lung cancer growth and metastasis primarily through GABPB1-mediated mitochondrial metabolism.

Cancer metabolism has emerged as a major target for cancer therapy, while the state of mitochondrial drugs has remained largely unexplored, partly due to an inadequate understanding of various mitochondrial functions in tumor contexts. Here, we report that HOMER3 is highly expressed in non-small cell lung cancer (NSCLC) and is closely correlated with poor prognosis. Lung cancer cells with low levels of HOMER3 are found to show significant mitochondrial dysfunction, thereby suppressing their proliferation and metastasis in vivo and in vitro. At the mechanistic level, we demonstrate that HOMER3 and platelet-activating factor acetylhydrolase 1b catalytic subunit 3 cooperate to upregulate the level of GA-binding protein subunit beta-1 (GABPB1), a key transcription factor involved in mitochondrial biogenesis, to control mitochondrial inner membrane genes and mitochondrial function. Concurrently, low levels of HOMER3 and its downstream target GABPB1 led to mitochondrial dysfunction and decreased proliferation and invasive activity of lung cancer cells, which raises the possibility that targeting mitochondrial synthesis is an important and promising therapeutic approach for NSCLC.

Phase separation-mediated actin bundling by the postsynaptic density condensates.

The volume and the electric strength of an excitatory synapse is near linearly correlated with the area of its postsynaptic density (PSD). Extensive research in the past has revealed that the PSD assembly directly communicates with actin cytoskeleton in the spine to coordinate activity-induced spine volume enlargement as well as long-term stable spine structure maintenance. However, the molecular mechanism underlying the communication between the PSD assembly and spine actin cytoskeleton is poorly understood. In this study, we discover that in vitro reconstituted PSD condensates can promote actin polymerization and F-actin bundling without help of any actin regulatory proteins. The Homer scaffold protein within the PSD condensates and a positively charged actin-binding surface of the Homer EVH1 domain are essential for the PSD condensate-induced actin bundle formation in vitro and for spine growth in neurons. Homer-induced actin bundling can only occur when Homer forms condensate with other PSD scaffold proteins such as Shank and SAPAP. The PSD-induced actin bundle formation is sensitively regulated by CaMKII or by the product of the immediate early gene Homer1a. Thus, the communication between PSD and spine cytoskeleton may be modulated by targeting the phase separation of the PSD condensates.

hsa_circ_0006916 Exerts Effect on Amyloid Beta-Induced Neuron Injury by Targeting miR-217/HOMER1.

OBJECTIVE: Circular RNAs (circRNAs) are rich in miRNA-binding sites, which serve as miRNA sponges or competitive endogenous RNAs (ceRNAs). In the central nervous system, circRNAs are relevant to many neurological disorders including Alzheimer's disease (AD). Dementia associated with AD is correlated with the conversion of the ß-Amyloid (Aß) peptides from soluble monomers to aggregated oligomers and insoluble fibrils. Downregulation of circHOMER1 (circ_0006916) expression level is observed in AD female cases. Thus, this study investigates whether circHOMER1 prevents fibrillar Aß (fAß)-induced cell damage. METHODS: The levels of sAß42 in cerebrospinal fluid (CSF) of amyloid-positive normal cognition (NC) individuals, mild cognitive impairment (MCI) individuals, and AD patients were measured. For in vitro studies, the SH-SY5Y cells were treated with 10 µM of fAß42 or soluble Aß42 (sAß42). RNase R treatment and actinomycin D treatment were used to identify the characteristics of circHOMER1. Gene expression was measured by RT-qPCR. Protein levels were measured using western blotting. Cell viability and apoptosis were estimated by MTT assays and flow cytometry. The binding relationship of miR-217 and circHOMER1 (HOMER1) was verified by luciferase reporter assays. RESULTS: CircHOMER1 was more stable in SH-SY5Y cells than linear HOMER1. CircHOMER1 upregulation ameliorates the fAß42-induced cell apoptosis and circHOMER1 downregulation reversed the anti-apoptotic roles of sAß42. Mechanistically, miR-217 interacted with circHOMER1 (HOMER1). Moreover, miR-217 upregulation or HOMER1 downregulation exacerbates the fAß42-induced cell damage. CONCLUSIONS: CircHOMER1 (hsa_circ_0006916) ameliorates the fAß42-induced cell injury via the miR-217/HOMER1 axis.

Ndufa4 Regulates the Proliferation and Apoptosis of Neurons via miR-145a-5p/Homer1/Ccnd2.

The Dandy-Walker malformation (DWM) is characterized by neuron dysregulation in embryonic development; however, the regulatory mechanisms associated with it are unclear. This study aimed to investigate the role of NADH dehydrogenase 1 alpha subcomplex 4 (NDUFA4) in regulating downstream signaling cascades and neuronal proliferation and apoptosis. Ndufa4 overexpression promoted the proliferation of neurons and inhibited their apoptosis in vitro, which underwent reverse regulation by the Ndufa4 short hairpin RNAs. Ndufa4-knockout (KO) mice showed abnormal histological alterations in the brain tissue, in addition to impaired spatial learning capacity and exploratory activity. Ndufa4 depletion altered the microRNA expressional profiles of the cerebellum: Ndufa4 inhibited miR-145a-5p expression both in the cerebellum and neurons. miR-145a-5p inhibited the proliferation of neurons and promoted their apoptosis. Ndufa4 promoted and miR-145a-5p inhibited the expression of human homer protein homolog 1 and cyclin D2 in neurons. Thus, Ndufa4 promotes the proliferation of neurons and inhibits their apoptosis by inhibiting miR-145a-5p, which directly targets and inhibits the untranslated regions of Homer1 and Ccnd2 expression.

Opposite Regulation of Homer Signal at the NMJ Postsynaptic Micro Domain between Slow- and Fast-Twitch Muscles in an Experimentally Induced Autoimmune Myasthenia Gravis (EAMG) Mouse Model.

Accelerated postsynaptic remodelling and disturbance of neuromuscular transmission are common features of autoimmune neurodegenerative diseases. Homer protein isoform expression, crosslinking activity and neuromuscular subcellular localisation are studied in mouse hind limb muscles of an experimentally induced autoimmune model of Myasthenia Gravis (EAMG) and correlated to motor end plate integrity. Soleus (SOL), extensor digitorum longus (EDL) and gastrocnemius (GAS) skeletal muscles are investigated. nAChR membrane clusters were studied to monitor neuromuscular junction (NMJ) integrity. Fibre-type cross-sectional area (CSA) analysis is carried out in order to determine the extent of muscle atrophy. Our findings clearly showed that crosslinking activity of Homer long forms (Homer 1b/c and Homer2a/b) are decreased in slow-twitch and increased in fast-twitch muscle of EAMG whereas the short form of Homer that disrupts Homer crosslinking (Homer1a) is upregulated in slow-twitch muscle only. Densitometry analysis showed a 125% increase in Homer protein expression in EDL, and a 45% decrease in SOL of EAMG mice. In contrast, nAChR fluorescence pixel intensity decreased in endplates of EAMG mice, more distinct in type-I dominant SOL muscle. Morphometric CSA of EAMG vs. control (CTR) revealed a significant reduction in EDL but not in GAS and SOL. Taken together, these results indicate that postsynaptic Homer signalling is impaired in slow-twitch SOL muscle from EAMG mice and provide compelling evidence suggesting a functional coupling between Homer and nAChR, underscoring the key role of Homer in skeletal muscle neurophysiology.

Homer1 promotes the conversion of A1 astrocytes to A2 astrocytes and improves the recovery of transgenic mice after intracerebral hemorrhage.

BACKGROUND: Inflammation induced by intracerebral hemorrhage (ICH) is one of the main causes of the high mortality and poor prognosis of patients with ICH. A1 astrocytes are closely associated with neuroinflammation and neurotoxicity, whereas A2 astrocytes are neuroprotective. Homer scaffolding protein 1 (Homer1) plays a protective role in ischemic encephalopathy and neurodegenerative diseases. However, the role of Homer1 in ICH-induced inflammation and the effect of Homer1 on the phenotypic conversion of astrocytes remain unknown. METHODS: Femoral artery autologous blood from C57BL/6 mice was used to create an ICH model. We use the A1 phenotype marker C3 and A2 phenotype marker S100A10 to detect astrocyte conversion after ICH. Homer1 overexpression/knock-down mice were constructed by adeno-associated virus (AAV) infection to explore the role of Homer1 and its mechanism of action after ICH. Finally, Homer1 protein and selumetinib were injected into in situ hemorrhage sites in the brains of Homer1flox/flox/Nestin-Cre+/- mice to study the efficacy of Homer1 in the treatment of ICH by using a mouse cytokine array to explore the potential mechanism. RESULTS: The expression of Homer1 peaked on the third day after ICH and colocalized with astrocytes. Homer1 promotes A1 phenotypic conversion in astrocytes in vivo and in vitro. Overexpression of Homer1 inhibits the activation of MAPK signaling, whereas Homer1 knock-down increases the expression of pathway-related proteins. The Homer1 protein and selumetinib, a non-ATP competitive MEK1/2 inhibitor, improved the outcome in ICH in Homer1flox/flox/Nestin-Cre+/- mice. The efficacy of Homer1 in the treatment of ICH is associated with reduced expression of the inflammatory factor TNFSF10 and increased expression of the anti-inflammatory factors activin A, persephin, and TWEAK. CONCLUSIONS: Homer1 plays an important role in inhibiting inflammation after ICH by suppressing the A1 phenotype conversion in astrocytes. In situ injection of Homer1 protein may be a novel and effective method for the treatment of inflammation after ICH.

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.

Activity dependent dissociation of the Homer1 interactome.

Neurons encode information by rapidly modifying synaptic protein complexes, which changes the strength of specific synaptic connections. Homer1 is abundantly expressed at glutamatergic synapses, and is known to alter its binding to metabotropic glutamate receptor 5 (mGlu5) in response to synaptic activity. However, Homer participates in many additional known interactions whose activity-dependence is unclear. Here, we used co-immunoprecipitation and label-free quantitative mass spectrometry to characterize activity-dependent interactions in the cerebral cortex of wildtype and Homer1 knockout mice. We identified a small, high-confidence protein network consisting of mGlu5, Shank2 and 3, and Homer1-3, of which only mGlu5 and Shank3 were significantly reduced following neuronal depolarization. We identified several other proteins that reduced their co-association in an activity-dependent manner, likely mediated by Shank proteins. We conclude that Homer1 dissociates from mGlu5 and Shank3 following depolarization, but our data suggest that direct Homer1 interactions in the cortex may be more limited than expected.

A bidirectional competitive interaction between circHomer1 and Homer1b within the orbitofrontal cortex regulates reversal learning.

Although circular RNAs (circRNAs) are enriched in the brain, their relevance for brain function and psychiatric disorders is poorly understood. Here, we show that circHomer1 is inversely associated with relative HOMER1B mRNA isoform levels in both the orbitofrontal cortex (OFC) and stem-cell-derived neuronal cultures of subjects with psychiatric disorders. We further demonstrate that in vivo circHomer1 knockdown (KD) within the OFC can inhibit the synaptic expression of Homer1b mRNA. Furthermore, we show that circHomer1 directly binds to Homer1b mRNA and that Homer1b-specific KD increases synaptic circHomer1 levels and improves OFC-mediated behavioral flexibility. Importantly, double circHomer1 and Homer1b in vivo co-KD results in a complete rescue in circHomer1-associated alterations in both chance reversal learning and synaptic gene expression. Lastly, we uncover an RNA-binding protein that can directly bind to circHomer1 and promote its biogenesis. Taken together, our data provide mechanistic insights into the importance of circRNAs in brain function and disease.

Homer1a regulates Shank3 expression and underlies behavioral vulnerability to stress in a model of Phelan-McDermid syndrome.

Mutations of SHANK3 cause Phelan-McDermid syndrome (PMS), and these individuals can exhibit sensitivity to stress, resulting in behavioral deterioration. Here, we examine the interaction of stress with genotype using a mouse model with face validity to PMS. In Shank3ΔC/+ mice, swim stress produces an altered transcriptomic response in pyramidal neurons that impacts genes and pathways involved in synaptic function, signaling, and protein turnover. Homer1a, which is part of the Shank3-mGluR-N-methyl-D-aspartate (NMDA) receptor complex, is super-induced and is implicated in the stress response because stress-induced social deficits in Shank3ΔC/+ mice are mitigated in Shank3ΔC/+;Homer1a-/- mice. Several lines of evidence demonstrate that Shank3 expression is regulated by Homer1a in competition with crosslinking forms of Homer, and consistent with this model, Shank3 expression and function that are reduced in Shank3ΔC/+ mice are rescued in Shank3ΔC/+;Homer1a-/- mice. Studies highlight the interaction between stress and genetics and focus attention on activity-dependent changes that may contribute to pathogenesis.