Myristoylated alanine rich C kinase substrate (MARCKS) heterozygous mutant mice exhibit deficits in hippocampal mossy fiber-CA3 long-term potentiation

Q241R mutation of Braf causes neurological abnormalities in a mouse model of cardio-facio-cutaneous syndrome, independent of developmental malformations

Constitutively active mutants of BRAF cause cardio-facio-cutaneous (CFC) syndrome, characterized by growth and developmental defects, cardiac malformations, facial features, cutaneous manifestations, and mental retardation. An animal model of human CFC syndrome, the systemic BrafQ241R/+ mutant mouse, has been reported to exhibit multiple CFC syndrome-like phenotypes. In this study, we analyzed the effects of Braf mutations on neural function, separately from their effects on developmental processes. To this end, we generated Braf mutant mice expressing BRAFQ241R specifically in mature excitatory neurons (n-BrafQ241R/+). We found no growth retardation or cardiac malformations in n-BrafQ241R/+ mice, indicating normal development. Behavioral analysis revealed that n-BrafQ241R/+ mice exhibited reduced home cage activity and learning disability, which were similar to those of systemic BrafQ241R/+ mice. The active form of ERK was increased in the hippocampus of n-BrafQ241R/+ mice, whereas basal synaptic transmission and synaptic plasticity in hippocampal Schaffer collateral-CA1 synapses seems to be normal. Transcriptome analysis of the hippocampal tissue revealed significant changes in the expression of genes involved in regulation of the RAS/mitogen-activated protein kinase (MAPK) signaling pathway, synaptic function and memory formation. These data suggest that the neuronal dysfunction observed in the systemic CFC mouse model is due to the disruption of homeostasis of the RAS/MAPK signaling pathway by the activated Braf mutant after maturation, rather than abnormal development of the brain. A similar mechanism may be possible in human CFC syndrome.

TESC overexpression mitigates amyloid-β-induced hippocampal atrophy and memory decline

BACKGROUND AND OBJECTIVES

Genome-wide association studies (GWASs) have identified numerous candidate genes for human brain-imaging phenotypes; however, the biological relevance of many of these genes remains unconfirmed. This study aimed to investigate the causal relationships among tescalcin (TESC) (a GWAS-indicated gene), hippocampal volume, Alzheimer's disease (AD), and the underlying biological mechanisms.

METHODS

Human transcriptional data were analyzed to confirm relative TESC expression in the hippocampus. In cell experiments, RNA-seq analysis was used to identify the potential biological pathways for TESC overexpression, and immunofluorescence imaging and cell viability assays were used to evaluate the effect of TESC overexpression on neuronal structure and survival. In animal experiments, the effects of TESC overexpression on hippocampal volume and cognitive function in normal mice and amyloid-β (Aβ)-induced AD mice were investigated by 9.4 T magnetic resonance imaging and behavioral tests. Underlying mechanisms were further assessed via western blotting and electrophysiological recordings.

RESULTS

Human transcriptional data demonstrated that TESC is primarily expressed in the hippocampus and neurons. TESC overexpression enhanced the viability of HT22 cells and reduced Aβ-induced cell death. In mouse models, Tesc-overexpressing mice revealed increased hippocampal volume, likely owing to enhanced cell viability and long-term potentiation (LTP), and reducing apoptotic- and oxidation-induced hippocampal damage. TESC overexpression could significantly mitigate Aβ-induced hippocampal atrophy and memory impairment, potentially by reducing Aβ-induced neuronal apoptosis and LTP weakening.

CONCLUSION

This study exemplifies the translation of GWAS findings into actionable biological knowledge and suggests that upregulation of TESC may offer a promising therapeutic strategy for AD.

The Implication of Androgens in the Presence of Protein Kinase C to Repair Alzheimer’s Disease-Induced Cognitive Dysfunction

Aging, as a major risk factor of memory deficiency, affects neural signaling pathways in hippocampus. In particular, age-dependent androgens deficiency causes cognitive impairments. Several enzymes like protein kinase C (PKC) are involved in memory deficiency. Indeed, PKC regulatory process mediates α-secretase activation to cleave APP in β-amyloid cascade and tau proteins phosphorylation mechanism. Androgens and cortisol regulate PKC signaling pathways, affecting the modulation of receptor for activated C kinase 1. Mitogen-activated protein kinase/ERK signaling pathway depends on CREB activity in hippocampal neurons and is involved in regulatory processes via PKC and androgens. Therefore, testosterone and PKC contribute in the neuronal apoptosis. The present review summarizes the current status of androgens, PKC, and their influence on cognitive learning. Inconsistencies in experimental investigations related to this fundamental correlation are also discussed, with emphasis on the mentioned contributors as the probable potent candidates for learning and memory improvement.

Proteomic analyses of limbic regions in neonatal male, female and androgen receptor knockout mice

Background

It is well-established that organizational effects of sex steroids during early development are fundamental for sex-typical displays of, for example, mating and aggressive behaviors in rodents and other species. Male and female brains are known to differ with respect to neuronal morphology in particular regions of the brain, including the number and size of neurons, and the density and length of dendrites in nuclei of hypothalamus and amygdala. The aim of the present study was to use global proteomics to identify proteins differentially expressed in hypothalamus/amygdala during early development (postnatal day 8) of male, female and conditional androgen receptor knockout (AR^NesDel) male mice, lacking androgen receptors specifically in the brain. Furthermore, verification of selected sexually dimorphic proteins was performed using targeted proteomics.

Results

Our proteomic approach, iTRAQ, allowed us to investigate expression differences in the 2998 most abundantly expressed proteins in our dissected tissues. Approximately 170 proteins differed between the sexes, and 38 proteins between AR^NesDel and control males (p < 0.05). In line with previous explorative studies of sexually dimorphic gene expression we mainly detected subtle protein expression differences (fold changes <1.3). The protein MARCKS (myristoylated alanine rich C kinase substrate), having the largest fold change of the proteins selected from the iTRAQ analyses and of known importance for synaptic transmission and dendritic branching, was confirmed by targeted proteomics as differentially expressed between the sexes.

Conclusions

Overall, our results provide solid evidence that a large number of proteins show sex differences in their brain expression and could potentially be involved in brain sexual differentiation. Furthermore, our finding of a sexually dimorphic expression of MARCKS in the brain during development warrants further investigation on the involvement in sexual differentiation of this protein.

Electronic supplementary material

The online version of this article (doi:10.1186/s12868-016-0332-1) contains supplementary material, which is available to authorized users.

Protein Kinase C Activation as a Potential Therapeutic Strategy in Alzheimer's Disease: Is there a Role for Embryonic Lethal Abnormal Vision-like Proteins?

Alzheimer's disease (AD), the most common cause of dementia, is an irreversible and progressive neurodegenerative disorder. It affects predominantly brain areas that are critical for memory and learning and is characterized by two main pathological hallmarks: extracellular amyloid plaques and intracellular neurofibrillary tangles. Protein kinase C (PKC) has been classified as one of the cognitive kinases controlling memory and learning. By regulating several signalling pathways involved in amyloid and tau pathologies, it also plays an inhibitory role in AD pathophysiology. Among downstream targets of PKC are the embryonic lethal abnormal vision (ELAV)-like RNA-binding proteins that modulate the stability and the translation of specific target mRNAs involved in synaptic remodelling linked to cognitive processes. This MiniReview summarizes the current evidence on the role of PKC and ELAV-like proteins in learning and memory, highlighting how their derangement can contribute to AD pathophysiology. This last aspect emphasizes the potential of pharmacological activation of PKC as a promising therapeutic strategy for the treatment of AD.

X MARCKS the spot: myristoylated alanine-rich C kinase substrate in neuronal function and disease

Intracellular protein-protein interactions are dynamic events requiring tightly regulated spatial and temporal checkpoints. But how are these spatial and temporal cues integrated to produce highly specific molecular response patterns? A helpful analogy to this process is that of a cellular map, one based on the fleeting localization and activity of various coordinating proteins that direct a wide array of interactions between key molecules. One such protein, myristoylated alanine-rich C-kinase substrate (MARCKS) has recently emerged as an important component of this cellular map, governing a wide variety of protein interactions in every cell type within the brain. In addition to its well-documented interactions with the actin cytoskeleton, MARCKS has been found to interact with a number of other proteins involved in processes ranging from intracellular signaling to process outgrowth. Here, we will explore these diverse interactions and their role in an array of brain-specific functions that have important implications for many neurological conditions.

Improvement of biochemical and behavioral defects in the Niemann-Pick type A mouse by intraventricular infusion of MARCKS

Niemann-Pick disease type A (NPDA) is a fatal disease due to mutations in the acid sphingomyelinase (ASM) gene, which triggers the abnormal accumulation of sphingomyelin (SM) in lysosomes and the plasma membrane of mutant cells. Although the disease affects multiple organs, the impact on the brain is the most invalidating feature. The mechanisms responsible for the cognitive deficit characteristic of this condition are only partially understood. Using mice lacking the ASM gene (ASMko), a model system in NPDA research, we report here that high sphingomyelin levels in mutant neurons lead to low synaptic levels of phosphoinositide PI(4,5)P2 and reduced activity of its hydrolyzing phosphatase PLCγ, which are key players in synaptic plasticity events. In addition, mutant neurons have reduced levels of membrane-bound MARCKS, a protein required for PI(4,5)P2 membrane clustering and hydrolysis. Intracerebroventricular infusion of a peptide that mimics the effector domain of MARCKS increases the content of PI(4,5)P2 in the synaptic membrane and ameliorates behavioral abnormalities in ASMko mice.

The effects of aging on the BTBR mouse model of autism spectrum disorder

Autism spectrum disorder (ASD) is a complex heterogeneous neurodevelopmental disorder characterized by alterations in social functioning, communicative abilities, and engagement in repetitive or restrictive behaviors. The process of aging in individuals with autism and related neurodevelopmental disorders is not well understood, despite the fact that the number of individuals with ASD aged 65 and older is projected to increase by over half a million individuals in the next 20 years. To elucidate the effects of aging in the context of a modified central nervous system, we investigated the effects of age on the BTBR T + tf/j mouse, a well characterized and widely used mouse model that displays an ASD-like phenotype. We found that a reduction in social behavior persists into old age in male BTBR T + tf/j mice. We employed quantitative proteomics to discover potential alterations in signaling systems that could regulate aging in the BTBR mice. Unbiased proteomic analysis of hippocampal and cortical tissue of BTBR mice compared to age-matched wild-type controls revealed a significant decrease in brain derived neurotrophic factor and significant increases in multiple synaptic markers (spinophilin, Synapsin I, PSD 95, NeuN), as well as distinct changes in functional pathways related to these proteins, including “Neural synaptic plasticity regulation” and “Neurotransmitter secretion regulation.” Taken together, these results contribute to our understanding of the effects of aging on an ASD-like mouse model in regards to both behavior and protein alterations, though additional studies are needed to fully understand the complex interplay underlying aging in mouse models displaying an ASD-like phenotype.

Lipid dynamics at dendritic spines

Dynamic changes in the structure and composition of the membrane protrusions forming dendritic spines underlie memory and learning processes. In recent years a great effort has been made to characterize in detail the protein machinery that controls spine plasticity. However, we know much less about the involvement of lipids, despite being major membrane components and structure determinants. Moreover, protein complexes that regulate spine plasticity depend on specific interactions with membrane lipids for proper function and accurate intracellular signaling. In this review we gather information available on the lipid composition at dendritic spine membranes and on its dynamics. We pay particular attention to the influence that spine lipid dynamism has on glutamate receptors, which are key regulators of synaptic plasticity.

Functional role of the interaction between polysialic acid and myristoylated alanine-rich C kinase substrate at the plasma membrane

Polysialic acid (PSA) is a homopolymeric glycan that plays crucial roles in the developing and adult nervous system. So far only a few PSA-binding proteins have been identified. Here, we identify myristoylated alanine-rich C kinase substrate (MARCKS) as novel PSA binding partner. Binding assays showed a direct interaction between PSA and a peptide comprising the effector domain of MARCKS (MARCKS-ED). Co-immunoprecipitation of PSA-carrying neural cell adhesion molecule (PSA-NCAM) with MARCKS and co-immunostaining of MARCKS and PSA at the cell membrane of hippocampal neurons confirm the interaction between PSA and MARCKS. Co-localization and an intimate interaction of PSA and MARCKS at the cell surface was seen by confocal microscopy and fluorescence resonance energy transfer (FRET) analysis after the addition of fluorescently labeled PSA or PSA-NCAM to live CHO cells or hippocampal neurons expressing MARCKS as a fusion protein with green fluorescent protein (GFP). Cross-linking experiments showed that extracellularly applied PSA or PSA-NCAM and intracellularly expressed MARCKS-GFP are in close contact, suggesting that PSA and MARCKS interact with each other at the plasma membrane from opposite sides. Insertion of PSA and MARCKS-ED peptide into lipid bilayers from opposite sides alters the electric properties of the bilayer confirming the notion that PSA and the effector domain of MARCKS interact at and/or within the plane of the membrane. The MARCKS-ED peptide abolished PSA-induced enhancement of neurite outgrowth from cultured hippocampal neurons indicating an important functional role for the interaction between MARCKS and PSA in the developing and adult nervous system.

Low hippocampal PI(4,5)P₂ contributes to reduced cognition in old mice as a result of loss of MARCKS

Cognitive and motor performances decline during aging. Although it is clear that such signs reflect synaptic compromise, the underlying mechanisms have not been defined. We found that the levels and activity of the synaptic plasticity modulators phosphatidylinositol-(4,5)-bisphosphate (PI(4,5)P₂) and phospholipase Cγ (PLCγ) were substantially reduced in hippocampal synaptic membranes from old mice. In addition, these membranes contained reduced levels of the PI(4,5)P₂-clustering molecule myristoylated alanine-rich C kinase substrate (MARCKS). Consistent with a cause-effect relationship, raising MARCKS levels in the brain of old mice led to increased synaptic membrane clustering of PI(4,5)P₂ and to PLCγ activation. MARCKS overexpression in the hippocampus of old mice or intraventricular perfusion of MARCKS peptide resulted in enhanced long-term potentiation and improved memory. These results reveal one of the mechanisms involved in brain dysfunction during aging.

Angiotensin-II and MARCKS: a hydrogen peroxide- and RAC1-dependent signaling pathway in vascular endothelium

MARCKS is an actin-binding protein that modulates vascular endothelial cell migration and cytoskeleton signaling (Kalwa, H., and Michel, T. (2011) J. Biol. Chem. 286, 2320-2330). Angiotensin-II is a vasoactive peptide implicated in vascular physiology as well as pathophysiology; the pathways connecting angiotensin-II and cytoskeletal remodeling are incompletely understood. Here we show that MARCKS is expressed in intact arterial preparations, with prominent staining of the endothelium. In endothelial cells, angiotensin-II-promoted MARCKS phosphorylation is abrogated by PEG-catalase, implicating endogenous H(2)O(2) in the angiotensin-II response. Studies using the H(2)O(2) biosensor HyPer2 reveal that angiotensin-II promotes increases in intracellular H(2)O(2). We used a Rac1 FRET biosensor to show that angiotensin-II promotes Rac1 activation that is attenuated by PEG-catalase. siRNA-mediated Rac1 knockdown blocks angiotensin-II-stimulated MARCKS phosphorylation. Cell imaging studies using a phosphoinositide 4,5-bisphosphate (PIP(2)) biosensor revealed that angiotensin-II PIP(2) regulation depends on MARCKS and H(2)O(2). siRNA-mediated knockdown of MARCKS or Rac1 attenuates receptor-mediated activation of the tyrosine kinase c-Abl and disrupts actin fiber formation. These studies establish a critical role for H(2)O(2) in angiotensin-II signaling to the endothelial cytoskeleton in a novel pathway that is critically dependent on MARCKS, Rac1, and c-Abl.

MARCKS dephosphorylation is involved in bradykinin-induced neurite outgrowth in neuroblastoma SH-SY5Y cells

Bradykinin (BK) plays a major role in producing peripheral sensitization in response to peripheral inflammation and in pain transmission in the central nerve system (CNS). Because BK activates protein kinase C (PKC) through phospholipase C (PLC)-β and myristoylated alanine-rich C kinase substrate (MARCKS) has been found to be a substrate of PKC, we explored the possibility that BK could induce MARCKS phosphorylation and regulate its function. BK stimulation induced transient MARCKS phosphorylation on Ser159 with a peak at 1  min in human neuroblastoma SH-SY5Y cells. By contrast, PKC activation by the phorbol ester phorbol 12,13-dibutyrate (PDBu) elicited MARCKS phosphorylation which lasted more than 10  min. Western blotting analyses and glutathione S-transferase (GST) pull-down analyses showed that the phosphorylation by BK was the result of activation of the PKC-dependent RhoA/Rho-associated coiled-coil kinase (ROCK) pathway. Protein phosphatase (PP) 2A inhibitors calyculin A and fostriecin inhibited the dephosphorylation of MARCKS after BK-induced phosphorylation. Moreover, immunoprecipitation analyses showed that PP2A interacts with MARCKS. These results indicated that PP2A is the dominant PP of MARCKS after BK stimulation. We established SH-SY5Y cell lines expressing wild-type MARCKS and unphosphorylatable MARCKS, and cell morphology changes after cell stimulation were studied. PDBu induced lamellipodia formation on the neuroblastoma cell line SH-SY5Y and the morphology was sustained, whereas BK induced neurite outgrowth of the cells via lamellipodia-like actin accumulation that depended on transient MARCKS phosphorylation. Thus these findings show a novel BK signal cascade-that is, BK promotes neurite outgrowth through transient MARCKS phosphorylation involving the PKC-dependent RhoA/ROCK pathway and PP2A in a neuroblastoma cell line.

Genetics of the hippocampal transcriptome in mouse: a systematic survey and online neurogenomics resource

Differences in gene expression in the CNS influence behavior and disease susceptibility. To systematically explore the role of normal variation in expression on hippocampal structure and function, we generated an online microarray database for a diverse panel of strains of mice, including most common inbred strains and numerous recombinant inbred lines (www.genenetwork.org). Using this resource, coexpression networks for families of genes can be generated rapidly to test causal models related to function. The data set is optimized for quantitative trait locus (QTL) mapping and was used to identify over 5500 QTLs that modulate mRNA levels. We describe a wide variety of analyses and novel synthetic approaches that take advantage of this resource, and demonstrate how both the data and associated tools can be applied to the study of gene regulation in the hippocampus and relations to structure and function.

Hippocampal infusions of MARCKS peptides impair memory of rats on the radial-arm maze

In vitro hippocampal studies by Gay et al. (2008) demonstrated that a myristoylated alanine-rich C kinase substrate (MARCKS) peptide comprising the phosphorylation site or effector domain of the protein acts as a powerful inhibitor of alpha7 nicotinic acetylcholine receptors (nAChRs), which are known to be critically involved in memory function. However, behavioral consequences of hippocampal MARCKS peptide infusions have not been investigated. The purpose of the current study was to determine if local infusions in the rat ventral hippocampus of long (comprising amino acids 151-175) and short (amino acids 159-165) forms of MARCKS peptides could affect memory performance in the 16-arm radial maze. Our results demonstrated a dramatic impairment of both working (changing) and reference (constant) memory with MARCKS(151-175) only. The shorter MARCKS peptide did not affect memory performance. This is in line with in vitro results reported by Gay et al. (2008) that long, but not short, MARCKS peptides inhibit alpha7 nAChRs. We also found that the effect of the MARCKS(151-175) peptide was dose-dependent, with a robust memory impairment at 10 microg/side, and smaller inconsistent effects at lower doses. Our present behavioral study, together with the earlier in vitro study by Gay et al. (2008), suggests that effector domain MARCKS peptides could play a significant role in memory regulation and impairment.

Palmitic acid mediates hypothalamic insulin resistance by altering PKC-theta subcellular localization in rodents

Insulin signaling can be modulated by several isoforms of PKC in peripheral tissues. Here, we assessed whether one specific isoform, PKC-theta, was expressed in critical CNS regions that regulate energy balance and whether it mediated the deleterious effects of diets high in fat, specifically palmitic acid, on hypothalamic insulin activity in rats and mice. Using a combination of in situ hybridization and immunohistochemistry, we found that PKC-theta was expressed in discrete neuronal populations of the arcuate nucleus, specifically the neuropeptide Y/agouti-related protein neurons and the dorsal medial nucleus in the hypothalamus. CNS exposure to palmitic acid via direct infusion or by oral gavage increased the localization of PKC-theta to cell membranes in the hypothalamus, which was associated with impaired hypothalamic insulin and leptin signaling. This finding was specific for palmitic acid, as the monounsaturated fatty acid, oleic acid, neither increased membrane localization of PKC-theta nor induced insulin resistance. Finally, arcuate-specific knockdown of PKC-theta attenuated diet-induced obesity and improved insulin signaling. These results suggest that many of the deleterious effects of high-fat diets, specifically those enriched with palmitic acid, are CNS mediated via PKC-theta activation, resulting in reduced insulin activity.

Inhibition of native and recombinant nicotinic acetylcholine receptors by the myristoylated alanine-rich C kinase substrate peptide

A variety of peptide ligands are known to inhibit the function of neuronal nicotinic acetylcholine receptors (nAChRs), including small toxins and brain-derived peptides such as beta-amyloid(1-42) and synthetic apolipoproteinE peptides. The myristoylated alanine-rich C kinase substrate (MARCKS) protein is a major substrate of protein kinase C and is highly expressed in the developing and adult brain. The ability of a 25-amino acid synthetic MARCKS peptide, derived from the effector domain (ED), to modulate nAChR activity was tested. To determine the effects of the MARCKS ED peptide on nAChR function, receptors were expressed in Xenopus laevis oocytes, and two-electrode voltage-clamp experiments were performed. The MARCKS ED peptide completely inhibited acetylcholine (ACh)-evoked responses from alpha7 nAChRs in a dose-dependent manner, yielding an IC(50) value of 16 nM. Inhibition of ACh-induced responses was both activity- and voltage-independent. The MARCKS ED peptide was unable to block alpha-bungarotoxin binding. A MARCKS ED peptide in which four serine residues were replaced with aspartate residues was unable to inhibit alpha7 nAChR-mediated currents. The MARCKS ED peptide inhibited ACh-induced alpha4beta2 and alpha2beta2 responses, although with decreased potency. The effects of the MARCKS ED peptide on native nAChRs were tested using acutely isolated rat hippocampal slices. In hippocampal interneurons, the MARCKS ED peptide was able to block native alpha7 nAChRs in a dose-dependent manner. The MARCKS ED peptide represents a novel antagonist of neuronal nAChRs that has considerable utility as a research tool.