Rho Signaling in Synaptic Plasticity, Memory, and Brain Disorders

Signal flow in the NMDA receptor-dependent phosphoproteome regulates postsynaptic plasticity for aversive learning

Structural plasticity of dendritic spines in the nucleus accumbens (NAc) is crucial for learning from aversive experiences. Activation of NMDA receptors (NMDARs) stimulates Ca2+-dependent signaling that leads to changes in the actin cytoskeleton, mediated by the Rho family of GTPases, resulting in postsynaptic remodeling essential for learning. We investigated how phosphorylation events downstream of NMDAR activation drive the changes in synaptic morphology that underlie aversive learning. Large-scale phosphoproteomic analyses of protein kinase targets in mouse striatal/accumbal slices revealed that NMDAR activation resulted in the phosphorylation of 194 proteins, including RhoA regulators such as ARHGEF2 and ARHGAP21. Phosphorylation of ARHGEF2 by the Ca2+-dependent protein kinase CaMKII enhanced its RhoGEF activity, thereby activating RhoA and its downstream effector Rho-associated kinase (ROCK/Rho-kinase). Further phosphoproteomic analysis identified 221 ROCK targets, including the postsynaptic scaffolding protein SHANK3, which is crucial for its interaction with NMDARs and other postsynaptic scaffolding proteins. ROCK-mediated phosphorylation of SHANK3 in the NAc was essential for spine growth and aversive learning. These findings demonstrate that NMDAR activation initiates a phosphorylation cascade crucial for learning and memory.

DCC, a potential target for controlling fear memory extinction and hippocampal LTP in male mice receiving single prolonged stress

Post-traumatic stress disorder (PTSD) is a severe stress-dependent psychiatric disorder characterized by impairment of fear memory extinction; however, biological markers to determine impaired fear memory extinction in PTSD remain unclear. In male mice with PTSD-like behaviors elicited by single prolonged stress (SPS), 19 differentially expressed proteins in the hippocampus were identified compared with controls. Among them, a biological macromolecular protein named deleted in colorectal cancer (DCC) was highly upregulated. Specific overexpression of DCC in the hippocampus induced similar impairment of long-term potentiation (LTP) and fear memory extinction as observed in SPS mice. The impairment of fear memory extinction in SPS mice was improved by inhibiting the function of hippocampal DCC using a neutralizing antibody. Mechanistic studies have shown that knocking down or inhibiting μ-calpain in hippocampal neurons increased DCC expression and induced impairment of fear memory extinction. Additionally, SPS-triggered impairment of hippocampal LTP and fear memory extinction could be rescued through activation of the Rac1-Pak1 signaling pathway. Our study provides evidence that calpain-mediated regulation of DCC controls hippocampal LTP and fear memory extinction in SPS mice, which likely through activation of the Rac1-Pak1 signaling pathway.

Nascimento J, Domith I, Karmirian K, Feilding A, Trindade P, Martins-de-Souza D, K. Rehen S. LSD Modulates Proteins Involved in Cell Proteostasis, Energy Metabolism and Neuroplasticity in Human Cerebral Organoids

Proteomic analysis of human cerebral organoids may reveal how psychedelics regulate biological processes, shedding light on drug-induced changes in the brain. This study elucidates the proteomic alterations induced by lysergic acid diethylamide (LSD) in human cerebral organoids. By employing high-resolution mass spectrometry-based proteomics, we quantitatively analyzed the differential abundance of proteins in cerebral organoids exposed to LSD. Our findings indicate changes in proteostasis, energy metabolism, and neuroplasticity-related pathways. Specifically, LSD exposure led to alterations in protein synthesis, folding, autophagy, and proteasomal degradation, suggesting a complex interplay in the regulation of neural cell function. Additionally, we observed modulation in glycolysis and oxidative phosphorylation, crucial for cellular energy management and synaptic function. In support of the proteomic data, complementary experiments demonstrated LSD's potential to enhance neurite outgrowth in vitro, confirming its impact on neuroplasticity. Collectively, our results provide a comprehensive insight into the molecular mechanisms through which LSD may affect neuroplasticity and potentially contribute to therapeutic effects for neuropsychiatric disorders.

The Small G-Protein Rac1 in the Dorsomedial Striatum Promotes Alcohol-Dependent Structural Plasticity and Goal-Directed Learning in Mice

The small G-protein Ras-related C3 botulinum toxin substrate 1 (Rac1) promotes the formation of filamentous actin (F-actin). Actin is a major component of dendritic spines, and we previously found that alcohol alters actin composition and dendritic spine structure in the nucleus accumbens (NAc) and the dorsomedial striatum (DMS). To examine if Rac1 contributes to these alcohol-mediated adaptations, we measured the level of GTP-bound active Rac1 in the striatum of mice following 7 weeks of intermittent access to 20% alcohol. We found that chronic alcohol intake activates Rac1 in the DMS of male mice. In contrast, Rac1 is not activated by alcohol in the NAc and DLS of male mice or in the DMS of female mice. Similarly, closely related small G-proteins are not activated by alcohol in the DMS, and Rac1 activity is not increased in the DMS by moderate alcohol or natural reward. To determine the consequences of alcohol-dependent Rac1 activation in the DMS of male mice, we inhibited endogenous Rac1 by infecting the DMS of mice with an adeno-associated virus (AAV) expressing a dominant negative form of the small G-protein (Rac1-DN). We found that overexpression of AAV-Rac1-DN in the DMS inhibits alcohol-mediated Rac1 signaling and attenuates alcohol-mediated F-actin polymerization, which corresponded with a decrease in dendritic arborization and spine maturation. Finally, we provide evidence to suggest that Rac1 in the DMS plays a role in alcohol-associated goal-directed learning. Together, our data suggest that Rac1 in the DMS plays an important role in alcohol-dependent structural plasticity and aberrant learning.

Forebrain excitatory neuron-specific loss of Brpf1 attenuates excitatory synaptic transmission and impairs spatial and fear memory

Bromodomain and plant homeodomain (PHD) finger containing protein 1 (Brpf1) is an activator and scaffold protein of a multiunit complex that includes other components involving lysine acetyltransferase (KAT) 6A/6B/7. Brpf1, KAT6A, and KAT6B mutations were identified as the causal genes of neurodevelopmental disorders leading to intellectual disability. Our previous work revealed strong and specific expression of Brpf1 in both the postnatal and adult forebrain, especially the hippocampus, which has essential roles in learning and memory. Here, we hypothesized that Brpf1 plays critical roles in the function of forebrain excitatory neurons, and that its deficiency leads to learning and memory deficits. To test this, we knocked out Brpf1 in forebrain excitatory neurons using CaMKIIa-Cre. We found that Brpf1 deficiency reduced the frequency of miniature excitatory postsynaptic currents and downregulated the expression of genes Pcdhgb1, Slc16a7, Robo3, and Rho, which are related to neural development, synapse function, and memory, thereby damaging spatial and fear memory in mice. These findings help explain the mechanisms of intellectual impairment in patients with BRPF1 mutation.

Function and Mechanism of Abscisic Acid on Microglia-Induced Neuroinflammation in Parkinson's Disease

Parkinson's disease (PD), as a neurologically implemented disease with complex etiological factors, has a complex and variable pathogenesis. Accompanying further research, neuroinflammation has been found to be one of the possible factors in its pathogenesis. Microglia, as intrinsic immune cells in the brain, play an important role in maintaining microenvironmental homeostasis in the brain. However, over-activation of neurotoxic microglia in PD promotes neuroinflammation, which further increases dopaminergic (DA) neuronal damage and exacerbates the disease process. Therefore, targeting and regulating the functional state of microglia is expected to be a potential avenue for PD treatment. In addition, plant extracts have shown great potential in the treatment of neurodegenerative disorders due to their abundant resources, mild effects, and the presence of multiple active ingredients. However, it is worth noting that some natural products have certain toxic side effects, so it is necessary to pay attention to distinguish medicinal ingredients and usage and dosage when using to avoid aggravating the progression of diseases. In this review, the roles of microglia with different functional states in PD and the related pathways inducing microglia to transform into neuroprotective states are described. At the same time, it is discussed that abscisic acid (ABA) may regulate the polarization of microglia by targeting them, promote their transformation into neuroprotective state, reduce the neuroinflammatory response in PD, and provide a new idea for the treatment of PD and the selection of drugs.

The small G-protein Rac1 in the dorsomedial striatum promotes alcohol-dependent structural plasticity and goal-directed learning in mice

The small G-protein Rac1 promotes the formation of filamentous actin (F-Actin). Actin is a major component of dendritic spines, and we previously found that alcohol alters actin composition and dendritic spine structure in the nucleus accumbens (NAc) and the dorsomedial striatum (DMS). To examine if Rac1 contributes to these alcohol-mediated adaptations, we measured the level of GTP-bound active Rac1 in the striatum of mice following 7 weeks of intermittent access to 20% alcohol. We found that chronic alcohol intake activates Rac1 in the DMS of male mice. In contrast, Rac1 is not activated by alcohol in the NAc and DLS of male mice, or in the DMS of female mice. Similarly, closely related small G-proteins are not activated by alcohol in the DMS, and Rac1 activity is not increased in the DMS by moderate alcohol or natural reward. To determine the consequences of alcohol-dependent Rac1 activation in the DMS of male mice, we inhibited endogenous Rac1 by infecting the DMS of mice with an AAV expressing a dominant negative form of the small G-protein (Rac1-DN). We found that overexpression of AAV-Rac1-DN in the DMS inhibits alcohol-mediated Rac1 signaling and attenuates alcohol-mediated F-actin polymerization, which corresponded with a decrease in dendritic arborization and spine maturation. Finally, we provide evidence to suggest that Rac1 in the DMS plays a role in alcohol-associated goal-directed learning. Together, our data suggest that Rac1 in the DMS plays an important role in alcohol-dependent structural plasticity and aberrant learning.

Significance Statement

Addiction, including alcohol use disorder, is characterized by molecular and cellular adaptations that promote maladaptive behaviors. We found that Rac1 was activated by alcohol in the dorsomedial striatum (DMS) of male mice. We show that alcohol-mediated Rac1 signaling is responsible for alterations in actin dynamics and neuronal morphology. We also present data to suggest that Rac1 is important for alcohol-associated learning processes. These results suggest that Rac1 in the DMS is an important contributor to adaptations that promote alcohol use disorder.

Oligomeric Amyloid-β and Tau Alter Cell Adhesion Properties and Induce Inflammatory Responses in Cerebral Endothelial Cells Through the RhoA/ROCK Pathway

Dysfunction of cerebral endothelial cells (CECs) has been implicated in the pathology of Alzheimer's disease (AD). Despite evidence showing cytotoxic effects of oligomeric amyloid-β (oAβ) and Tau (oTau) in the central nervous system, their direct effects on CECs have not been fully investigated. In this study, we examined the direct effects of oAβ, oTau, and their combination on cell adhesion properties and inflammatory responses in CECs. We found that both oAβ and oTau increased cell stiffness, as well as the p-selectin/Sialyl-LewisX (sLeX) bonding-mediated membrane tether force and probability of adhesion in CECs. Consistent with these biomechanical alterations, treatments with oAβ or oTau also increased actin polymerization and the expression of p-selectin at the cell surface. These toxic oligomeric peptides also triggered inflammatory responses, including upregulations of p-NF-kB p65, IL-1β, and TNF-α. In addition, they rapidly activated the RhoA/ROCK pathway. These biochemical and biomechanical changes were further enhanced by the treatment with the combination of oAβ and oTau, which were significantly suppressed by Fasudil, a specific inhibitor for the RhoA/ROCK pathway. In conclusion, our data suggest that oAβ, oTau, and their combination triggered subcellular mechanical alterations and inflammatory responses in CECs through the RhoA/ROCK pathway.

Linkage of CDC42 and T-helper cell ratio with anxiety, depression and quality of life in ST-elevation myocardial infarction

Objective: To investigate the correlations between CDC42 and T-cell subsets concerning anxiety, depression and quality of life in ST-elevation myocardial infarction patients undergoing percutaneous coronary intervention. Methods: Sera from 156 participants were analyzed for CDC42 levels and Th1, Th2, Th17 and Treg cells. Results: CDC42 correlated with reduced Th1/Th2 and Th17/Treg ratios, lower anxiety and depression, and higher EuroQol visual analog scale (EQ-VAS) score. The Th17/Treg ratio correlated with elevated anxiety, depression, EuroQol-5 dimensions score and decreased EQ-VAS score. The Th1/Th2 ratio was positively related to the EQ-VAS score. Conclusion: CDC42 correlates with reduced Th1/Th2 and Th17/Treg ratios, reduced anxiety and depression, and improved quality of life in ST-elevation myocardial infarction patients undergoing percutaneous coronary intervention.

Profiling the autoantibody repertoire reveals autoantibodies associated with mild cognitive impairment and dementia

Background

Dementia is a debilitating neurological disease affecting millions of people worldwide. The exact mechanisms underlying the initiation and progression of the disease remain to be fully defined. There is an increasing body of evidence for the role of immune dysregulation in the pathogenesis of dementia, where blood-borne autoimmune antibodies have been studied as potential markers associated with pathological mechanisms of dementia.

Methods

This study included plasma from 50 cognitively normal individuals, 55 subjects with MCI (mild cognitive impairment), and 22 subjects with dementia. Autoantibody profiling for more than 1,600 antigens was performed using a high throughput microarray platform to identify differentially expressed autoantibodies in MCI and dementia.

Results

The differential expression analysis identified 33 significantly altered autoantibodies in the plasma of patients with dementia compared to cognitively normal subjects, and 38 significantly altered autoantibodies in the plasma of patients with dementia compared to subjects with MCI. And 20 proteins had significantly altered autoantibody responses in MCI compared to cognitively normal individuals. Five autoantibodies were commonly dysregulated in both dementia and MCI, including anti-CAMK2A, CKS1B, ETS2, MAP4, and NUDT2. Plasma levels of anti-ODF3, E6, S100P, and ARHGDIG correlated negatively with the cognitive performance scores (MoCA) (r2 -0.56 to -0.42, value of p < 0.001). Additionally, several proteins targeted by autoantibodies dysregulated in dementia were significantly enriched in the neurotrophin signaling pathway, axon guidance, cholinergic synapse, long-term potentiation, apoptosis, glycolysis and gluconeogenesis.

Conclusion

We have shown multiple dysregulated autoantibodies in the plasma of subjects with MCI and dementia. The corresponding proteins for these autoantibodies are involved in neurodegenerative pathways, suggesting a potential impact of autoimmunity on the etiology of dementia and the possible benefit for future therapeutic approaches. Further investigations are warranted to validate our findings.

Case report: Anti-ARHGAP26 autoantibodies in atypical dementia with Lewy bodies

Background

Dementia with Lewy bodies (DLB) is the second most common type of neurodegenerative dementia. Here, we report a case of dementia associated with anti-Rho-GTPase-activating protein 26 (ARHGAP26) autoantibodies, which have never been previously linked to DLB.

Methods

We describe the case of a 78-year-old man who underwent cerebrospinal fluid (CSF) analysis, magnetic resonance imaging (MRI), 18F-fluorodesoxyglucose positron emission tomography (FDG-PET), and a detailed neuropsychological evaluation.

Results

The patient presented with mild dementia syndrome associated with extrapyramidal symptoms. Neuropsychological testing revealed impaired cognitive flexibility, figural memory, and verbal memory. Fluctuating cognitive abilities with deficits in attention-executive dysfunction and visuoconstruction also developed over time. A brain MRI showed reduced biparietal and cerebellar brain volume with generalized accentuation of the outer CSF spaces. The patient's CSF revealed anti-ARHGAP26 autoantibodies, which were also detectable in serum. In the differential complementary imaging diagnosis at 2 years, an FDG-PET revealed decreased occupancy of the posterior cingulum and precuneus. Although the FDG-PET, MRI, and clinical findings were potentially consistent with Alzheimer's disease, negative amyloid biomarkers in the CSF made an AD diagnosis highly unlikely. Single photon emission computed tomography (SPECT) with [(123)I] N-omega-fluoropropyl-2beta-carbomethoxy-3beta-{4-iodophenyl}nortropane ([(123)I]FP-CIT) showed right-sided predominance, reduced dopamine transporter uptake in the putamen, consistent with a positive indicative biomarker finding typical of DLB. Considering the clinically probable DLB associated with the two core features of Parkinsonism and fluctuating cognition with deficits in attention, supported by an abundant tracer uptake in the right putamen and lower uptake in the left putamen on 123I-FP-CIT-SPECT as an indicative biomarker, we started an antidementia drug using a cholinesterase inhibitor.

Conclusions

Our report shows that atypical DLB may be associated with anti-ARHGAP26 autoantibodies, although their role and significance in the pathogenesis of DLB are unknown. However, it has to be mentioned that it is also possible that antibody-specific synthesis of anti-ARHGAP26 autoantibodies is a hallmark of a rare autoimmune disease that may cause the clinical and laboratory features involving altered dopamine transporter uptake on 123I-FP-CIT-SPECT, dementia, and mild Parkinson's symptoms rather than idiopathic DLB with only two core DLB features and inconsistent cognitive and imaging findings. Further research is needed to investigate the role of these autoantibodies in different dementias, particularly in DLB and mixed DLB-AD types.

Involvement of brain cell phenotypes in stress-vulnerability and resilience

Stress-related disorders' prevalence is epidemically increasing in modern society, leading to a severe impact on individuals' well-being and a great economic burden on public resources. Based on this, it is critical to understand the mechanisms by which stress induces these disorders. The study of stress made great progress in the past decades, from deeper into the hypothalamic-pituitary-adrenal axis to the understanding of the involvement of a single cell subtype on stress outcomes. In fact, many studies have used state-of-the-art tools such as chemogenetic, optogenetic, genetic manipulation, electrophysiology, pharmacology, and immunohistochemistry to investigate the role of specific cell subtypes in the stress response. In this review, we aim to gather studies addressing the involvement of specific brain cell subtypes in stress-related responses, exploring possible mechanisms associated with stress vulnerability versus resilience in preclinical models. We particularly focus on the involvement of the astrocytes, microglia, medium spiny neurons, parvalbumin neurons, pyramidal neurons, serotonergic neurons, and interneurons of different brain areas in stress-induced outcomes, resilience, and vulnerability to stress. We believe that this review can shed light on how diverse molecular mechanisms, involving specific receptors, neurotrophic factors, epigenetic enzymes, and miRNAs, among others, within these brain cell subtypes, are associated with the expression of a stress-susceptible or resilient phenotype, advancing the understanding/knowledge on the specific machinery implicate in those events.

Basolateral Amygdala Corticotrophin Releasing Factor Receptor 2 Interacts with Nonmuscle Myosin II to Destabilize Memory

Inhibiting the actin motor ATPase nonmuscle myosin II (NMII) with blebbistatin (Blebb) in the basolateral amgydala (BLA) depolymerizes actin, resulting in an immediate, retrieval-independent disruption of methamphetamine (METH)-associated memory. The effect is highly selective, as NMII inhibition has no effect in other relevant brain regions (e.g. dorsal hippocampus [dPHC], nucleus accumbens [NAc]), nor does it interfere with associations for other aversive or appetitive stimuli, including cocaine (COC). To investigate a potential source of this specificity, pharmacokinetic differences in METH and COC brain exposure were examined. Replicating METH's longer half-life with COC did not render the COC association susceptible to disruption by NMII inhibition. Therefore, transcriptional differences were next assessed. Comparative RNA-seq profiling in the BLA, dHPC and NAc following METH or COC conditioning identified crhr2, which encodes the corticotrophin releasing factor receptor 2 (CRF2), as uniquely upregulated by METH in the BLA. CRF2 antagonism with Astressin-2B (AS2B) had no effect on METH-associated memory after consolidation, allowing for determination of CRF2 influences on NMII-based susceptibility after METH conditioning. Pretreatment with AS2B occluded the ability of Blebb to disrupt an established METH-associated memory. Alternatively, the Blebb-induced, retrieval-independent memory disruption seen with METH was mimicked for COC when combined with CRF2 overexpression in the BLA and its ligand, UCN3 during conditioning. These results indicate that BLA CRF2 receptor activation during learning can prevent stabilization of the actin-myosin cytoskeleton supporting the memory, rendering it vulnerable to disruption via NMII inhibition. CRF2 represents an interesting target for BLA-dependent memory destabilization via downstream effects on NMII.

Functional and phosphoproteomic analysis of β-adrenergic receptor signaling at excitatory synapses in the CA1 region of the ventral hippocampus

Activation of β-adrenergic receptors (β-ARs) not only enhances learning and memory but also facilitates the induction of long-term potentiation (LTP), a form of synaptic plasticity involved in memory formation. To identify the mechanisms underlying β-AR-dependent forms of LTP we examined the effects of the β-AR agonist isoproterenol on LTP induction at excitatory synapses onto CA1 pyramidal cells in the ventral hippocampus. LTP induction at these synapses is inhibited by activation of SK-type K⁺ channels, suggesting that β-AR activation might facilitate LTP induction by inhibiting SK channels. However, although the SK channel blocker apamin enhanced LTP induction, it did not fully mimic the effects of isoproterenol. We therefore searched for potential alternative mechanisms using liquid chromatography-tandem mass spectrometry to determine how β-AR activation regulates phosphorylation of postsynaptic density (PSD) proteins. Strikingly, β-AR activation regulated hundreds of phosphorylation sites in PSD proteins that have diverse roles in dendritic spine structure and function. Moreover, within the core scaffold machinery of the PSD, β-AR activation increased phosphorylation at several sites previously shown to be phosphorylated after LTP induction. Together, our results suggest that β-AR activation recruits a diverse set of signaling pathways that likely act in a concerted fashion to regulate LTP induction.

Neurodevelopmental disorders, like cancer, are connected to impaired chromatin remodelers, PI3K/mTOR, and PAK1-regulated MAPK

Neurodevelopmental disorders (NDDs) and cancer share proteins, pathways, and mutations. Their clinical symptoms are different. However, individuals with NDDs have higher probabilities of eventually developing cancer. Here, we review the literature and ask how the shared features can lead to different medical conditions and why having an NDD first can increase the chances of malignancy. To explore these vital questions, we focus on dysregulated PI3K/mTOR, a major brain cell growth pathway in differentiation, and MAPK, a critical pathway in proliferation, a hallmark of cancer. Differentiation is governed by chromatin organization, making aberrant chromatin remodelers highly likely agents in NDDs. Dysregulated chromatin organization and accessibility influence the lineage of specific cell brain types at specific embryonic development stages. PAK1, with pivotal roles in brain development and in cancer, also regulates MAPK. We review, clarify, and connect dysregulated pathways with dysregulated proliferation and differentiation in cancer and NDDs and highlight PAK1 role in brain development and MAPK regulation. Exactly how PAK1 activation controls brain development, and why specific chromatin remodeler components, e.g., BAF170 encoded by SMARCC2 in autism, await clarification.

Crosstalk between the Rho and Rab family of small GTPases in neurodegenerative disorders

Neurodegeneration is associated with defects in cytoskeletal dynamics and dysfunctions of the vesicular trafficking and sorting systems. In the last few decades, studies have demonstrated that the key regulators of cytoskeletal dynamics are proteins from the Rho family GTPases, meanwhile, the central hub for vesicle sorting and transport between target membranes is the Rab family of GTPases. In this regard, the role of Rho and Rab GTPases in the induction and maintenance of distinct functional and morphological neuronal domains (such as dendrites and axons) has been extensively studied. Several members belonging to these two families of proteins have been associated with many neurodegenerative disorders ranging from dementia to motor neuron degeneration. In this analysis, we attempt to present a brief review of the potential crosstalk between the Rab and Rho family members in neurodegenerative pathologies such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington disease, and amyotrophic lateral sclerosis (ALS).

Cytoskeletal dysregulation and neurodegenerative disease: Formation, monitoring, and inhibition of cofilin-actin rods

The presence of atypical cytoskeletal dynamics, structures, and associated morphologies is a common theme uniting numerous diseases and developmental disorders. In particular, cytoskeletal dysregulation is a common cellular feature of Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease. While the numerous activators and inhibitors of dysregulation present complexities for characterizing these elements as byproducts or initiators of the disease state, it is increasingly clear that a better understanding of these anomalies is critical for advancing the state of knowledge and plan of therapeutic attack. In this review, we focus on the hallmarks of cytoskeletal dysregulation that are associated with cofilin-linked actin regulation, with a particular emphasis on the formation, monitoring, and inhibition of cofilin-actin rods. We also review actin-associated proteins other than cofilin with links to cytoskeleton-associated neurodegenerative processes, recognizing that cofilin-actin rods comprise one strand of a vast web of interactions that occur as a result of cytoskeletal dysregulation. Our aim is to present a current perspective on cytoskeletal dysregulation, connecting recent developments in our understanding with emerging strategies for biosensing and biomimicry that will help shape future directions of the field.

Post-Synapses in the Brain: Role of Dendritic and Spine Structures

Brain synapses are neuronal structures of the greatest interest. For a long time, however, the knowledge about them was variable, and interest was mostly focused on their pre-synaptic portions, especially neurotransmitter release from axon terminals. In the present review interest is focused on post-synapses, the structures receiving and converting pre-synaptic messages. Upon further modulation, such messages are transferred to dendritic fibers. Dendrites are profoundly different from axons; they are shorter and of variable thickness. Their post-synapses are of two types. Those called flat/intended/aspines, integrated into dendritic fibers, are very frequent in inhibitory neurons. The spines, small and stemming protrusions, connected to dendritic fibers by their necks, are present in almost all excitatory neurons. Several structures and functions including the post-synaptic densities and associated proteins, the nanoscale mechanisms of compartmentalization, the cytoskeletons of actin and microtubules, are analogous in the two post-synaptic forms. However other properties, such as plasticity and its functions of learning and memory, are largely distinct. Several properties of spines, including emersion from dendritic fibers, growth, change in shape and decreases in size up to disappearance, are specific. Spinal heads correspond to largely independent signaling compartments. They are motile, their local signaling is fast, however transport through their thin necks is slow. When single spines are activated separately, their dendritic effects are often lacking; when multiple spines are activated concomitantly, their effects take place. Defects of post-synaptic responses, especially those of spines, take place in various brain diseases. Here alterations affecting symptoms and future therapy are shown to occur in neurodegenerative diseases and autism spectrum disorders.

Inhibition of Rac1 in ventral hippocampal excitatory neurons improves social recognition memory and synaptic plasticity

Rac1 is critically involved in the regulation of the actin cytoskeleton, neuronal structure, synaptic plasticity, and memory. Rac1 overactivation is reported in human patients and animal models of Alzheimer’s disease (AD) and contributes to their spatial memory deficits, but whether Rac1 dysregulation is also important in other forms of memory deficits is unknown. In addition, the cell types and synaptic mechanisms involved remain unclear. In this study, we used local injections of AAV virus containing a dominant-negative (DN) Rac1 under the control of CaMKIIα promoter and found that the reduction of Rac1 hyperactivity in ventral hippocampal excitatory neurons improves social recognition memory in APP/PS1 mice. Expression of DN Rac1 also improves long-term potentiation, a key synaptic mechanism for memory formation. Our results suggest that overactivation of Rac1 in hippocampal excitatory neurons contributes to social memory deficits in APP/PS1 mice and that manipulating Rac1 activity may provide a potential therapeutic strategy to treat social deficits in AD.

Delta-Catenin as a Modulator of Rho GTPases in Neurons

Small Rho GTPases are molecular switches that are involved in multiple processes including regulation of the actin cytoskeleton. These GTPases are activated (turned on) and inactivated (turned off) through various upstream effector molecules to carry out many cellular functions. One such upstream modulator of small Rho GTPase activity is delta-catenin, which is a protein in the p120-catenin subfamily that is enriched in the central nervous system. Delta-catenin affects small GTPase activity to assist in the developmental formation of dendrites and dendritic spines and to maintain them once they mature. As the dendritic arbor and spine density are crucial for synapse formation and plasticity, delta-catenin's ability to modulate small Rho GTPases is necessary for proper learning and memory. Accordingly, the misregulation of delta-catenin and small Rho GTPases has been implicated in several neurological and non-neurological pathologies. While links between delta-catenin and small Rho GTPases have yet to be studied in many contexts, known associations include some cancers, Alzheimer's disease (AD), Cri-du-chat syndrome, and autism spectrum disorder (ASD). Drawing from established studies and recent discoveries, this review explores how delta-catenin modulates small Rho GTPase activity. Future studies will likely elucidate how PDZ proteins that bind delta-catenin further influence small Rho GTPases, how delta-catenin may affect small GTPase activity at adherens junctions when bound to N-cadherin, mechanisms behind delta-catenin's ability to modulate Rac1 and Cdc42, and delta-catenin's ability to modulate small Rho GTPases in the context of diseases, such as cancer and AD.

Rnd3 Expression is Necessary to Maintain Mitochondrial Homeostasis but Dispensable for Autophagy

Autophagy is a highly conserved process that mediates the targeting and degradation of intracellular components to lysosomes, contributing to the maintenance of cellular homeostasis and to obtaining energy, which ensures viability under stress conditions. Therefore, autophagy defects are common to different neurodegenerative disorders. Rnd3 belongs to the family of Rho GTPases, involved in the regulation of actin cytoskeleton dynamics and important in the modulation of cellular processes such as migration and proliferation. Murine models have shown that Rnd3 is relevant for the correct development and function of the Central Nervous System and lack of its expression produces several motor alterations and neural development impairment. However, little is known about the molecular events through which Rnd3 produces these phenotypes. Interestingly we have observed that Rnd3 deficiency correlates with the appearance of autophagy impairment profiles and irregular mitochondria. In this work, we have explored the impact of Rnd3 loss of expression in mitochondrial function and autophagy, using a Rnd3 KO CRISPR cell model. Rnd3 deficient cells show no alterations in autophagy and mitochondria turnover is not impaired. However, Rnd3 KO cells have an altered mitochondria oxidative metabolism, resembling the effect caused by oxidative stress. In fact, lack of Rnd3 expression makes these cells strictly dependent on glycolysis to obtain energy. Altogether, our results demonstrate that Rnd3 is relevant to maintain mitochondria function, suggesting a possible relationship with neurodegenerative diseases.

Acrolein, an endogenous aldehyde induces synaptic dysfunction in vitro and in vivo: Involvement of RhoA/ROCK2 pathway

Acrolein, an unsaturated aldehyde, is increased in the brain of Alzheimer's disease (AD) patients and identified as a potential inducer of sporadic AD. Synaptic dysfunction, as a typical pathological change occurring in the early stage of AD, is most closely associated with the severity of dementia. However, there remains a lack of clarity on the mechanisms of acrolein inducing AD-like pathology and synaptic impairment. In this study, acrolein-treated primary cultured neurons and mice were applied to investigate the effects of acrolein on cognitive impairment and synaptic dysfunction and their signaling mechanisms. In vitro, ROCK inhibitors, Fasudil, and Y27632, could attenuate the axon ruptures and synaptic impairment caused by acrolein. Meanwhile, RNA-seq distinct differentially expressed genes in acrolein models and initially linked activated RhoA/Rho-kinase2 (ROCK2) to acrolein-induced synaptic dysfunction, which could regulate neuronal cytoskeleton and neurite. The Morris water maze test and in vivo field excitatory postsynaptic potential (fEPSP) were performed to evaluate spatial memory and long-term potential (LTP), respectively. Acrolein induced cognitive impairment and attenuated LTP. Furthermore, the protein level of Synapsin 1 and postsynaptic density 95 (PSD95) and dendritic spines density were also decreased in acrolein-exposed mice. These changes were improved by ROCK2 inhibitor Fasudil or in ROCK2^+/- mice. Together, our findings suggest that RhoA/ROCK2 signaling pathway plays a critical role in acrolein-induced synaptic damage and cognitive dysfunction, suggesting inhibition of ROCK2 should benefit to the early AD.

Analysis of Faecal Microbiota and Small ncRNAs in Autism: Detection of miRNAs and piRNAs with Possible Implications in Host-Gut Microbiota Cross-Talk

Intestinal microorganisms impact health by maintaining gut homeostasis and shaping the host immunity, while gut dysbiosis associates with many conditions, including autism, a complex neurodevelopmental disorder with multifactorial aetiology. In autism, gut dysbiosis correlates with symptom severity and is characterised by a reduced bacterial variability and a diminished beneficial commensal relationship. Microbiota can influence the expression of host microRNAs that, in turn, regulate the growth of intestinal bacteria by means of bidirectional host-gut microbiota cross-talk. We investigated possible interactions among intestinal microbes and between them and host transcriptional modulators in autism. To this purpose, we analysed, by "omics" technologies, faecal microbiome, mycobiome, and small non-coding-RNAs (particularly miRNAs and piRNAs) of children with autism and neurotypical development. Patients displayed gut dysbiosis related to a reduction of healthy gut micro- and mycobiota as well as up-regulated transcriptional modulators. The targets of dysregulated non-coding-RNAs are involved in intestinal permeability, inflammation, and autism. Furthermore, microbial families, underrepresented in patients, participate in the production of human essential metabolites negatively influencing the health condition. Here, we propose a novel approach to analyse faeces as a whole, and for the first time, we detected miRNAs and piRNAs in faecal samples of patients with autism.