Enhanced synaptic plasticity and spatial memory in female but not male FLRT2-haplodeficient mice

miRNA-132/212 Deficiency Disrupts Selective Corticosterone Modulation of Dorsal vs. Ventral Hippocampal Metaplasticity

Cortisol is a potent human steroid hormone that plays key roles in the central nervous system, influencing processes such as brain neuronal synaptic plasticity and regulating the expression of emotional and behavioral responses. The relevance of cortisol stands out in the disease, as its dysregulation is associated with debilitating conditions such as Alzheimer's Disease, chronic stress, anxiety and depression. Among other brain regions, cortisol importantly influences the function of the hippocampus, a structure central for memory and emotional information processing. The mechanisms fine-tuning the different synaptic responses of the hippocampus to steroid hormone signaling remain, however, poorly understood. Using ex vivo electrophysiology and wild type (WT) and miR-132/miR-212 microRNAs knockout (miRNA-132/212-/-) mice, we examined the effects of corticosterone (the rodent's equivalent to cortisol in humans) on the synaptic properties of the dorsal and ventral hippocampus. In WT mice, corticosterone predominantly inhibited metaplasticity in the dorsal WT hippocampi, whereas it significantly dysregulated both synaptic transmission and metaplasticity at dorsal and ventral regions of miR-132/212-/- hippocampi. Western blotting further revealed significantly augmented levels of endogenous CREB and a significant CREB reduction in response to corticosterone only in miR-132/212-/- hippocampi. Sirt1 levels were also endogenously enhanced in the miR-132/212-/- hippocampi but unaltered by corticosterone, whereas the levels of phospo-MSK1 were only reduced by corticosterone in WT, not in miR-132/212-/- hippocampi. In behavioral studies using the elevated plus maze, miRNA-132/212-/- mice further showed reduced anxiety-like behavior. These observations propose miRNA-132/212 as potential region-selective regulators of the effects of steroid hormones on hippocampal functions, thus likely fine-tuning hippocampus-dependent memory and emotional processing.

FIBCD1 is an endocytic GAG receptor associated with a novel neurodevelopmental disorder

Whole-exome sequencing of two patients with idiopathic complex neurodevelopmental disorder (NDD) identified biallelic variants of unknown significance within FIBCD1, encoding an endocytic acetyl group-binding transmembrane receptor with no known function in the central nervous system. We found that FIBCD1 preferentially binds and endocytoses glycosaminoglycan (GAG) chondroitin sulphate-4S (CS-4S) and regulates GAG content of the brain extracellular matrix (ECM). In silico molecular simulation studies and GAG binding analyses of patient variants determined that such variants are loss-of-function by disrupting FIBCD1-CS-4S association. Gene knockdown in flies resulted in morphological disruption of the neuromuscular junction and motor-related behavioural deficits. In humans and mice, FIBCD1 is expressed in discrete brain regions, including the hippocampus. Fibcd1 KO mice exhibited normal hippocampal neuronal morphology but impaired hippocampal-dependent learning. Further, hippocampal synaptic remodelling in acute slices from Fibcd1 KO mice was deficient but restored upon enzymatically modulating the ECM. Together, we identified FIBCD1 as an endocytic receptor for GAGs in the brain ECM and a novel gene associated with an NDD, revealing a critical role in nervous system structure, function and plasticity.

A Novel and Selective Dopamine Transporter Inhibitor, (S)-MK-26, Promotes Hippocampal Synaptic Plasticity and Restores Effort-Related Motivational Dysfunctions

Dopamine (DA), the most abundant human brain catecholaminergic neurotransmitter, modulates key behavioral and neurological processes in young and senescent brains, including motricity, sleep, attention, emotion, learning and memory, and social and reward-seeking behaviors. The DA transporter (DAT) regulates transsynaptic DA levels, influencing all these processes. Compounds targeting DAT (e.g., cocaine and amphetamines) were historically used to shape mood and cognition, but these substances typically lead to severe negative side effects (tolerance, abuse, addiction, and dependence). DA/DAT signaling dysfunctions are associated with neuropsychiatric and progressive brain disorders, including Parkinson’s and Alzheimer diseases, drug addiction and dementia, resulting in devastating personal and familial concerns and high socioeconomic costs worldwide. The development of low-side-effect, new/selective medicaments with reduced abuse-liability and which ameliorate DA/DAT-related dysfunctions is therefore crucial in the fields of medicine and healthcare. Using the rat as experimental animal model, the present work describes the synthesis and pharmacological profile of (S)-MK-26, a new modafinil analogue with markedly improved potency and selectivity for DAT over parent drug. Ex vivo electrophysiology revealed significantly augmented hippocampal long-term synaptic potentiation upon acute, intraperitoneally delivered (S)-MK-26 treatment, whereas in vivo experiments in the hole-board test showed only lesser effects on reference memory performance in aged rats. However, in effort-related FR5/chow and PROG/chow feeding choice experiments, (S)-MK-26 treatment reversed the depression-like behavior induced by the dopamine-depleting drug tetrabenazine (TBZ) and increased the selection of high-effort alternatives. Moreover, in in vivo microdialysis experiments, (S)-MK-26 significantly increased extracellular DA levels in the prefrontal cortex and in nucleus accumbens core and shell. These studies highlight (S)-MK-26 as a potent enhancer of transsynaptic DA and promoter of synaptic plasticity, with predominant beneficial effects on effort-related behaviors, thus proposing therapeutic potentials for (S)-MK-26 in the treatment of low-effort exertion and motivational dysfunctions characteristic of depression and aging-related disorders.

Epigenome-wide DNA methylation in obsessive-compulsive disorder

In adult patients with obsessive-compulsive disorder (OCD), altered DNA methylation has been discerned in several candidate genes, while DNA methylation on an epigenome-wide level has been investigated in only one Chinese study so far. Here, an epigenome-wide association study (EWAS) was performed in a sample of 76 OCD patients of European ancestry (37 women, age ± SD: 33.51 ± 10.92 years) and 76 sex- and age-matched healthy controls for the first time using the Illumina MethylationEPIC BeadChip. After quality control, nine epigenome-wide significant quantitative trait methylation sites (QTMs) and 21 suggestive hits were discerned in the final sample of 68 patients and 68 controls. The top hit (cg24159721) and four other significant QTMs (cg11894324, cg01070250, cg11330075, cg15174812) map to the region of the microRNA 12136 gene (MIR12136). Two additional significant CpG sites (cg05740793, cg20450977) are located in the flanking region of the MT-RNR2 (humanin) like 8 gene (MT-RNRL8), while two further QTMs (cg16267121, cg15890734) map to the regions of the MT-RNR2 (humanin) like 3 (MT-RNRL3) and MT-RNR2 (humanin) like 2 (MT-RNRL2) genes. Provided replication of the present findings in larger samples, the identified QTMs might provide more biological insight into the pathogenesis of OCD and thereby could in the future serve as peripheral epigenetic markers of OCD risk with the potential to inform targeted preventive and therapeutic efforts.

Age-Dependent and Pathway-Specific Bimodal Action of Nicotine on Synaptic Plasticity in the Hippocampus of Mice Lacking the miR-132/212 Genes

Nicotine addiction develops predominantly during human adolescence through smoking. Self-administration experiments in rodents verify this biological preponderance to adolescence, suggesting evolutionary-conserved and age-defined mechanisms which influence the susceptibility to nicotine addiction. The hippocampus, a brain region linked to drug-related memory storage, undergoes major morpho-functional restructuring during adolescence and is strongly affected by nicotine stimulation. However, the signaling mechanisms shaping the effects of nicotine in young vs. adult brains remain unclear. MicroRNAs (miRNAs) emerged recently as modulators of brain neuroplasticity, learning and memory, and addiction. Nevertheless, the age-dependent interplay between miRNAs regulation and hippocampal nicotinergic signaling remains poorly explored. We here combined biophysical and pharmacological methods to examine the impact of miRNA-132/212 gene-deletion (miRNA-132/212-/-) and nicotine stimulation on synaptic functions in adolescent and mature adult mice at two hippocampal synaptic circuits: the medial perforant pathway (MPP) to dentate yrus (DG) synapses (MPP-DG) and CA3 Schaffer collaterals to CA1 synapses (CA3-CA1). Basal synaptic transmission and short-term (paired-pulse-induced) synaptic plasticity was unaltered in adolescent and adult miRNA-132/212-/- mice hippocampi, compared with wild-type controls. However, nicotine stimulation promoted CA3-CA1 synaptic potentiation in mature adult (not adolescent) wild-type and suppressed MPP-DG synaptic potentiation in miRNA-132/212-/- mice. Altered levels of CREB, Phospho-CREB, and acetylcholinesterase (AChE) expression were further detected in adult miRNA-132/212-/- mice hippocampi. These observations propose miRNAs as age-sensitive bimodal regulators of hippocampal nicotinergic signaling and, given the relevance of the hippocampus for drug-related memory storage, encourage further research on the influence of miRNAs 132 and 212 in nicotine addiction in the young and the adult brain.

Expression of FLRT2 in Postnatal Central Nervous System Development and After Spinal Cord Injury

Fibronectin and leucine-rich transmembrane (FLRT) proteins are necessary for various developmental processes and in pathological conditions. FLRT2 acts as a homophilic cell adhesion molecule, a heterophilic repulsive ligand of Unc5/Netrin receptors, and a synaptogenic molecule; the last feature is mediated by binding to latrophilins. Although the function of FLRT2 in regulating cortical migration at the late gestation stage has been analyzed, little is known about the expression pattern of FLRT2 during postnatal central nervous system (CNS) development. In this study, we used Flrt2-LacZ knock-in (KI) mice to analyze FLRT2 expression during CNS development. At the early postnatal stage, FLRT2 expression was largely restricted to several regions of the striatum and deep layers of the cerebral cortex. In adulthood, FLRT2 expression was more prominent in the cerebral cortex, hippocampus, piriform cortex (PIR), nucleus of the lateral olfactory tract (NLOT), and ventral medial nucleus (VM) of the thalamus, but lower in the striatum. Notably, in the hippocampus, FLRT2 expression was confined to the CA1 region and partly localized on pre- and postsynapses whereas only few expression was observed in CA3 and dentate gyrus (DG). Finally, we observed temporally limited FLRT2 upregulation in reactive astrocytes around lesion sites 7 days after thoracic spinal cord injury. These dynamic changes in FLRT2 expression may enable multiple FLRT2 functions, including cell adhesion, repulsion, and synapse formation in different regions during CNS development and after spinal cord injury.

miRNA-132/212 Gene-Deletion Aggravates the Effect of Oxygen-Glucose Deprivation on Synaptic Functions in the Female Mouse Hippocampus

Cerebral ischemia and its sequelae, which include memory impairment, constitute a leading cause of disability worldwide. Micro-RNAs (miRNA) are evolutionarily conserved short-length/noncoding RNA molecules recently implicated in adaptive/maladaptive neuronal responses to ischemia. Previous research independently implicated the miRNA-132/212 cluster in cholinergic signaling and synaptic transmission, and in adaptive/protective mechanisms of neuronal responses to hypoxia. However, the putative role of miRNA-132/212 in the response of synaptic transmission to ischemia remained unexplored. Using hippocampal slices from female miRNA-132/212 double-knockout mice in an established electrophysiological model of ischemia, we here describe that miRNA-132/212 gene-deletion aggravated the deleterious effect of repeated oxygen-glucose deprivation insults on synaptic transmission in the dentate gyrus, a brain region crucial for learning and memory functions. We also examined the effect of miRNA-132/212 gene-deletion on the expression of key mediators in cholinergic signaling that are implicated in both adaptive responses to ischemia and hippocampal neural signaling. miRNA-132/212 gene-deletion significantly altered hippocampal AChE and mAChR-M1, but not α7-nAChR or MeCP2 expression. The effects of miRNA-132/212 gene-deletion on hippocampal synaptic transmission and levels of cholinergic-signaling elements suggest the existence of a miRNA-132/212-dependent adaptive mechanism safeguarding the functional integrity of synaptic functions in the acute phase of cerebral ischemia.

Leucine-rich repeats and immunoglobulin-like domains 1 deficiency affects hippocampal dendrite complexity and impairs cognitive function

Leucine-rich repeat (LRR) transmembrane proteins have been directly linked to neurodevelopmental and cognitive disorders. We have previously shown that the LRR transmembrane protein, leucine-rich repeats and immunoglobulin-like domains 1 (Lrig1), is a physiological regulator of dendrite complexity of hippocampal pyramidal neurons and social behavior. In this study, we performed a battery of behavioral tests to evaluate spatial memory and cognitive capabilities in Lrig1 mutant mice. The cognitive assessment demonstrated deficits in recognition and spatial memory, evaluated by novel object recognition and object location tests. Moreover, we found that Lrig1-deficient mice present specific impairments in the processing of similar but not dissimilar locations in a spatial pattern separation task, which was correlated with an enhanced dendritic growth and branching of Doublecortin-positive immature granule cells of the dentate gyrus. Altogether, these findings indicate that Lrig1 plays an essential role in controlling morphological and functional plasticity in the hippocampus.

Female dominance of both spatial cognitive dysfunction and neuropsychiatric symptoms in a mouse model of Alzheimer's disease

Alzheimer’s disease (AD) is a prevalent neurological disorder affecting memory function in elderly persons. Indeed, AD exhibits abnormality in cognitive behaviors and higher susceptibility to neuropsychiatric symptoms (NPS). Various factors including aging, sex difference and NPS severity, are implicated during in development of AD. In this study, we evaluated behavioral abnormalities of AD model, PDAPP transgenic mice at young age using the Morris Water Maze test, which was established to assess hippocampal-dependent learning and memory. We found that female AD model mice exhibited spatial learning dysfunction and highly susceptible to NPS such as anxiety and depression, whereas spatial reference memory function was comparable in female PDAPP Tg mice to female wild type (WT) mice. Spatial learning function was comparable in male AD model mice to male WT mice. Multiple regression analysis showed that spatial learning dysfunction was associated with NPS severity such as anxiety and depression. Furthermore, the analysis showed that spatial reference memory function was associated with status of depression, but not anxiety. Thus, these results suggest female dominance of spatial learning dysfunction in the AD model mice accompanying increased NPS severity. The understandings of AD model may be useful for the development of therapeutic agents and methods in human AD.

Nicotine abolishes memory-related synaptic strengthening and promotes synaptic depression in the neurogenic dentate gyrus of miR-132/212 knockout mice

Micro-RNAs (miRNAs) are highly evolutionarily conserved short-length/noncoding RNA molecules that modulate a wide range of cellular functions in many cell types by regulating the expression of a variety of targeted genes. miRNAs have also recently emerged as key regulators of neuronal genes mediating the effects of psychostimulant drugs and memory-related neuroplasticity processes. Smoking is a predominant addictive behaviour associated with millions of deaths worldwide, and nicotine is a potent natural psychoactive agonist of cholinergic receptors, highly abundant in cigarettes. The influence of miRNAs modulation on cholinergic signalling in the nervous system remains however poorly explored. Using miRNA knockout mice and biochemical, electrophysiological and pharmacological approaches, we examined the effects of miR-132/212 gene disruption on the levels of hippocampal nicotinic acetylcholine receptors, total ERK and phosphorylated ERK (pERK) and MeCP2 protein levels, and studied the impact of nicotine stimulation on hippocampal synaptic transmission and synaptic depression and strengthening. miR-132/212 deletion significantly altered α7-nAChR and pERK protein levels, but not total ERK or MeCP2, and resulted in both exacerbated synaptic depression and virtually abolished memory-related synaptic strengthening upon nicotine stimulation. These observations reveal a functional miRNAs/nicotinergic signalling interplay critical for nicotinic-receptor expression and neuroplasticity in brain structures relevant for drug addiction and learning and memory functions.

Nanoplastics impact the zebrafish (Danio rerio) transcriptome: Associated developmental and neurobehavioral consequences

Microplastics (MPs) are a ubiquitous pollutant detected not only in marine and freshwater bodies, but also in tap and bottled water worldwide. While MPs have been extensively studied, the toxicity of their smaller counterpart, nanoplastics (NPs), is not well documented. Despite likely large-scale human and animal exposure to NPs, the associated health risks remain unclear, especially during early developmental stages. To address this, we investigated the health impacts of exposures to both 50 and 200 nm polystyrene NPs in larval zebrafish. From 6 to 120 h post-fertilization (hpf), developing zebrafish were exposed to a range of fluorescent NPs (10-10,000 parts per billion). Dose-dependent increases in accumulation were identified in exposed larval fish, potentially coinciding with an altered behavioral response as evidenced through swimming hyperactivity. Notably, exposures did not impact mortality, hatching rate, or deformities; however, transcriptomic analysis suggests neurodegeneration and motor dysfunction at both high and low concentrations. Furthermore, results of this study suggest that NPs can accumulate in the tissues of larval zebrafish, alter their transcriptome, and affect behavior and physiology, potentially decreasing organismal fitness in contaminated ecosystems. The uniquely broad scale of this study during a critical window of development provides crucial multidimensional characterization of NP impacts on human and animal health.

Podoplanin Gene Disruption in Mice Promotes in vivo Neural Progenitor Cells Proliferation, Selectively Impairs Dentate Gyrus Synaptic Depression and Induces Anxiety-Like Behaviors

Podoplanin (Pdpn), a brain-tumor-related glycoprotein identified in humans and animals, is endogenously expressed in several organs critical for life support such as kidney, lung, heart and brain. In the brain, Pdpn has been identified in proliferative nestin-positive adult neural progenitor cells and in neurons of the neurogenic hippocampal dentate gyrus (DG), a structure associated to anxiety, critical for learning and memory functions and severely damaged in people with Alzheimer's Disease (AD). The in vivo role of Pdpn in adult neurogenesis and anxiety-like behavior remained however unexplored. Using mice with disrupted Pdpn gene as a model organism and applying combined behavioral, molecular biological and electrophysiological assays, we here show that the absence of Pdpn selectively impairs long-term synaptic depression in the neurogenic DG without affecting the CA3-Schaffer's collateral-CA1 synapses. Pdpn deletion also enhanced the proliferative capacity of DG neural progenitor cells and diminished survival of differentiated neuronal cells in vitro. In addition, mice with podoplanin gene disruption showed increased anxiety-like behaviors in experimentally validated behavioral tests as compared to wild type littermate controls. Together, these findings broaden our knowledge on the molecular mechanisms influencing hippocampal synaptic plasticity and neurogenesis in vivo and reveal Pdpn as a novel molecular target for future studies addressing general anxiety disorder and synaptic depression-related memory dysfunctions.

Western diet-induced fear memory impairment is attenuated by 6-shogaol in C57BL/6N mice

Dementia is a progressive cognitive diminution impeding with normal daily activities that is constantly on the increase. Currently, the estimated prevalence is 50 million affected people worldwide, a figure expected to triple within the next 30 years. While the pathophysiology of the different types of dementia is complex, likely involving the interplay between multiple genetic and environmental factors, strong evidence points towards an important link between diet and cognitive health. Here we examined the consequences of high-fat, high-sugar Western diet (HFSD)-induced obesity on cognitive performance in the fear conditioning task in mice and explored a possible beneficial effect of 6-shogaol (6S), an active constituent of ginger, in this model. Chronic exposure to HFSD significantly enhanced body weight gain in C57BL/6N mice and this effect was prevented by treatment with 6S. HFSD + vehicle-treated mice presented with a selective deficit in cued fear memory, which was not observed in HFSD + 6S-treated animals. The findings of this study provide first evidence for a beneficial effect of 6S on HFSD-induced obesity and emotional memory deficit in mice.