Evidence suggests that increased glucocorticoid receptor (GR) signaling may contribute to cognitive decline with age. We hypothesized that alterations in GR signaling pathway molecules, FK506 binding protein (FKBP) 51 and FKBP52, were associated with memory impairment in aged mice. We used the single-trial object recognition test to measure short-term memory in 18 aged mice compared to 22 young mice, and employed quantitative immunohistochemistry to assess cellular expression of those three proteins in the frontal cortex, hippocampal CA1, and dentate gyrus. Values of the discrimination ratio (DR, a measure of novelty preference) in aged mice were significantly lower than those in young mice (mean 0.54 vs. 0.67, p = 0.003, t test). Aged mice with DR below 0.54 were considered impaired (n = 9). In the three neuroanatomic regions studied, the immunoreactivity normalized to the area measured (IRn) for GR was significantly increased in aged mice regardless of their task performance compared to young mice (p < 0.005), as was the FKBP52 IRn (p < 0.007, U test). In the frontal cortex and CA1, the FKBP51 IRn was significantly lower in impaired aged mice than in unimpaired aged mice (p < 0.01 and <0.05, respectively) and in young mice (p < 0.05 and <0.01, respectively, Dunn’s post hoc test). In aged mice, the frontal cortex FKBP51 IRn correlated directly with DR (rs = 0.68, p = 0.002, Spearman rank correlation). These observations suggest that recognition memory impairment in aged mice is associated with decreased FKBP51 expression that may promote GR-mediated glucocorticoid signaling to a greater extent than in unimpaired aged mice.
Aging; Brain immunophilins; FKBP51; FKBP52; Glucocorticoid receptor signaling; Object recognition test
► GluA1 AMPAR subunit is important for short-term recognition memory. ► We tested whether GluA1 is necessary for short-term memory in trace conditioning. ► GluA1 deletion impaired rewarded alternation, but not trace conditioning. ► The dissociation may reflect processing of different short-term memory traces.
GluA1 AMPA receptor subunit knockout mice display a selective impairment on short-term recognition memory tasks. In this study we tested whether GluA1 is important for short-term memory that is necessary for bridging the discontiguity between cues in trace conditioning. GluA1 knockout mice were not impaired at using short-term memory traces of T-maze floor inserts, made of different materials, to bridge the temporal gap between conditioned stimuli and reinforcement during appetitive discrimination tasks. Thus, different aspects of short-term memory are differentially sensitive to GluA1 deletion. This dissociation may reflect processing of qualitatively different short-term memory traces. Memory that results in performance of short-term recognition (e.g. for objects or places) may be different from the memory required for associative learning in trace conditioning.
AMPA receptors; Conditional learning; Trace conditioning; Non-spatial memory; Spatial memory
Macroautophagy, a major pathway for organelle and protein turnover, has been implicated in the neurodegeneration of Alzheimer's disease (AD). The basis for the profuse accumulation of autophagic vacuoles (AVs) in affected neurons of the AD brain, however, is unknown. In this study, we show that constitutive macroautophagy in primary cortical neurons is highly efficient, as newly formed autophagosomes are rapidly cleared by fusion with lysosomes, accounting for their scarcity in the healthy brain. Even after macroautophagy is strongly induced by suppressing mTOR kinase activity with rapamycin or nutrient deprivation, active cathepsin-positive autolysosomes rather than LC3-II-positive autophagosomes predominate, implying efficient autophagosome clearance in healthy neurons. By contrast, selectively impeding late steps in macroautophagy by inhibiting cathepsin-mediated proteolysis within autophagosomes with cysteine- and aspartyl-protease inhibitors caused a marked accumulation of electron-dense double membrane-limited AVs, containing cathepsin D and incompletely degraded LC3-II in perikarya and neurites. Similar structures accumulated in large numbers when fusion of autophagosomes with lysosomes was slowed by disrupting their transport on microtubules with vinblastine. Finally, we find that the autophagic vacuoles accumulating after protease inhibition or prolonged vinblastine treatment strongly resembled AVs that collect in dystrophic neurites in the AD brain and in an AD mouse model. We conclude that macroautophagy is constitutively active and highly efficient in healthy neurons, and that the autophagic pathology observed in AD most likely arises from impaired clearance of AVs rather than strong autophagy induction alone. Therapeutic modulation of autophagy in AD may, therefore, require targeting late steps in the autophagic pathway.
Aging [Ageing]; Alzheimer; Autophagy; Culture; Lysosome; Neuron; Neuron Death; neuronal death; Neuropathology; neuroprotection; Neurotoxicity; Storage
(Macro)Autophagy is a phylogenetically conserved membrane-trafficking process that functions to deliver cytoplasmic cargoes to lysosomes for digestion. The process is a major mechanism for turnover of cellular constituents and is therefore critical for maintaining cellular homeostasis. Macroautophagy is characteristically distinct from other forms of autophagy due to the formation of double-membraned vesicles termed autophagosomes which encapsulate cargoes prior to fusion with lysosomes. Autophagosomes contain an integral membrane-bound form (LC3-II) of the microtubule-associated protein 1 light chain 3 β (MAP1LC3B), which has become a gold-standard marker to detect accumulation of autophagosomes and thereby changes in macroautophagy. Due to the role played by macroautophagy in various diseases, the detection of autophagosomes in tissue sections is frequently desired. To date, however, the detection of endogenous LC3-II on paraffin-embedded tissue sections has proved problematic. We report here a simple, optimized and validated method for the detection of LC3-II by immunohistochemistry in human and mouse tissue samples that we believe will be a useful resource for those wishing to study macroautophagy ex vivo.
autophagy; LC3; tissue sections; immunohistochemistry
Selective macroautophagy uses double-membrane vesicles, termed autophagosomes, to transport cytoplasmic pathogens, organelles and protein complexes to the vacuole for degradation. Autophagosomes are formed de novo by membrane fusion events at the phagophore assembly site (PAS). Therefore, precursor membrane material must be targeted and transported to the PAS. While some autophagy-related (Atg) proteins, such as Atg9 and Atg11, are known to be involved in this process, most of the mechanistic details are not understood. Previous work has also implicated the small Rab-family GTPase Ypt1 in the process, identifying Trs85 as a unique subunit of the TRAPPIII targeting complex and showing that it plays a macroautophagy-specific role; however, the relationship between Ypt1, Atg9 and Atg11 was not clear. Now, a recent report shows that Atg11 is a Trs85-specific effector of the Rab Ypt1, and may act as a classic coiled-coil membrane tether that targets Atg9-containing membranes to the PAS. Here, we review this finding in the context of what is known about Atg11, other Rab-dependent coiled-coil tethers, and other tethering complexes involved in autophagosome formation.
Atg9; membrane trafficking; stress; Trs85; vacuole; Ypt1
The GAP activity of OATL1, which is recruited to autophagosomes by Atg8, regulates autophagosome–lysosome fusion.
Macroautophagy is a bulk degradation system conserved in all eukaryotic cells. A ubiquitin-like protein, Atg8, and its homologues are essential for autophagosome formation and act as a landmark for selective autophagy of aggregated proteins and damaged organelles. In this study, we report evidence demonstrating that OATL1, a putative Rab guanosine triphosphatase–activating protein (GAP), is a novel binding partner of Atg8 homologues in mammalian cells. OATL1 is recruited to isolation membranes and autophagosomes through direct interaction with Atg8 homologues and is involved in the fusion between autophagosomes and lysosomes through its GAP activity. We further provide evidence that Rab33B, an Atg16L1-binding protein, is a target substrate of OATL1 and is involved in the fusion between autophagosomes and lysosomes, the same as OATL1. Because both its GAP activity and its Atg8 homologue–binding activity are required for OATL1 to function, we propose a model that OATL1 uses Atg8 homologues as a scaffold to exert its GAP activity and to regulate autophagosomal maturation.
The Hsc/Hsp70 co-chaperones of the BAG (Bcl-2-associated athanogene) protein family are modulators of protein quality control. We examined the specific roles of BAG1 and BAG3 in protein degradation during the aging process. We show that BAG1 and BAG3 regulate proteasomal and macroautophagic pathways, respectively, for the degradation of polyubiquitinated proteins. Moreover, using models of cellular aging, we find that a switch from BAG1 to BAG3 determines that aged cells use more intensively the macroautophagic system for turnover of polyubiquitinated proteins. This increased macroautophagic flux is regulated by BAG3 in concert with the ubiquitin-binding protein p62/SQSTM1. The BAG3/BAG1 ratio is also elevated in neurons during aging of the rodent brain, where, consistent with a higher macroautophagy activity, we find increased levels of the autophagosomal marker LC3-II as well as a higher cathepsin activity. We conclude that the BAG3-mediated recruitment of the macroautophagy pathway is an important adaptation of the protein quality control system to maintain protein homeostasis in the presence of an enhanced pro-oxidant and aggregation-prone milieu characteristic of aging.
BAG1; p62; proteasome; SQSTM1; ubiquitination
COG subunits localize to the phagophore assembly site where they interact with autophagy proteins and are required for double-membrane Cvt vesicle and autophagosome formation.
Macroautophagy is a catabolic pathway used for the turnover of long-lived proteins and organelles in eukaryotic cells. The morphological hallmark of this process is the formation of double-membrane autophagosomes that sequester cytoplasm. Autophagosome formation is the most complex part of macroautophagy, and it is a dynamic event that likely involves vesicle fusion to expand the initial sequestering membrane, the phagophore; however, essentially nothing is known about this process including the molecular components involved in vesicle tethering and fusion. In this study, we provide evidence that the subunits of the conserved oligomeric Golgi (COG) complex are required for double-membrane cytoplasm to vacuole targeting vesicle and autophagosome formation. COG subunits localized to the phagophore assembly site and interacted with Atg (autophagy related) proteins. In addition, mutations in the COG genes resulted in the mislocalization of Atg8 and Atg9, which are critical components involved in autophagosome formation.
Macroautophagy, which is a lysosomal pathway for the turnover of organelles and long-lived proteins, is a key determinant of cell survival and longevity. In this study, we show that neuronal macroautophagy is induced early in Alzheimer's disease (AD) and before β-amyloid (Aβ) deposits extracellularly in the presenilin (PS) 1/Aβ precursor protein (APP) mouse model of β-amyloidosis. Subsequently, autophagosomes and late autophagic vacuoles (AVs) accumulate markedly in dystrophic dendrites, implying an impaired maturation of AVs to lysosomes. Immunolabeling identifies AVs in the brain as a major reservoir of intracellular Aβ. Purified AVs contain APP and β-cleaved APP and are highly enriched in PS1, nicastrin, and PS-dependent γ-secretase activity. Inducing or inhibiting macroautophagy in neuronal and nonneuronal cells by modulating mammalian target of rapamycin kinase elicits parallel changes in AV proliferation and Aβ production. Our results, therefore, link β-amyloidogenic and cell survival pathways through macroautophagy, which is activated and is abnormal in AD.
Autophagosomes are double-membrane vesicles characteristic of macroautophagy, a degradative pathway for cytoplasmic material and organelles terminating in the lysosomal or vacuole compartment for mammals and yeast, respectively. This highly dynamic, multi-step process requires significant membrane reorganization events at different stages of the macroautophagic process. Such events include exchange and flow of lipids and proteins between membranes and vesicles (e.g., during initiation and growth of the phagophore), vesicular positioning and trafficking within the cell (e.g., autophagosome location and movement) and fusion of autophagosomes with the boundary membranes of the degradative compartment. Here, we review current knowledge on the contribution of different organelles to the formation of autophagosomes, their trafficking and fate within the cell. We will consider some of the unresolved questions related to the molecular mechanisms that regulate the “life and death” of the autophagosome.
autophagosome; degradation; lysosome; macroautophagy; mammals; membrane; organelle; yeast
The sorting nexins Atg20/Snx42 and Snx41 regulate membrane traffic and endosomal protein sorting and are essential for Cvt and/or pexophagy in yeast. Previously, we showed that macroautophagy is necessary for conidiation in the rice-blast fungus Magnaporthe oryzae. Here, we analyzed the physiological function(s) of selective autophagy in Magnaporthe through targeted deletion of MGG_12832, an ortholog of yeast SNX41 and ATG20/SNX42. Loss of MGG_12832 (hereafter SNX41) abolished conidia formation and pathogenesis in M. oryzae. Snx41-GFP localized as dynamic puncta or short tubules that are partially associated with autophagosomes and/or autophagic vacuoles. PX domain, but not macroautophagy per se, was required for such localization of Snx41-GFP in Magnaporthe. Although not required for nonselective autophagy, Snx41 was essential for pexophagy in Magnaporthe. We identified Oxp1, an ATP-dependent oxoprolinase in the gamma-glutamyl cycle, as a binding partner and potential retrieval target of Snx41-dependent protein sorting. The substrate of Oxp1, 5-oxoproline, could partially restore conidiation in the snx41Δ. Exogenous glutathione, a product of the gamma-glutamyl cycle, significantly restored pathogenicity in the snx41Δ mutant, likely through counteracting the oxidative stress imposed by the host. We propose that the gamma-glutamyl cycle and glutathione biosynthesis are subject to regulation by Snx41-dependent vesicular trafficking, and mediate antioxidant defense crucial for in planta growth and pathogenic differentiation of Magnaporthe at the onset of blast disease in rice.
Atg20; Snx41; fungal virulence; Magnaporthe; antioxidant; GSH; sorting nexin
Neuregulin 1 (NRG1) is a growth factor involved in neurodevelopment and plasticity. It is a schizophrenia candidate gene, and hippocampal expression of the NRG1 type I isoform is increased in the disorder. We have studied transgenic mice overexpressing NRG1 type I (NRG1tg-type I) and their wild-type littermates and measured hippocampal electrophysiological and behavioral phenotypes. Young NRG1tg-type I mice showed normal memory performance, but in older NRG1tg-type I mice, hippocampus-dependent spatial working memory was selectively impaired. Hippocampal slice preparations from NRG1tg-type I mice exhibited a reduced frequency of carbachol-induced gamma oscillations and an increased tendency to epileptiform activity. Long-term potentiation in NRG1tg-type I mice was normal. The results provide evidence that NRG1 type I impacts on hippocampal function and circuitry. The effects are likely mediated via inhibitory interneurons and may be relevant to the involvement of NRG1 in schizophrenia. However, the findings, in concert with those from other genetic and pharmacological manipulations of NRG1, emphasize the complex and pleiotropic nature of the gene, even with regard to a single isoform.
gamma oscillation; hippocampus; neuregulin; schizophrenia; synaptic plasticity
Proper control of mitochondrial turnover is critical for maintenance of cellular energetics under basal and stressed conditions, and for prevention of endogenous oxidative stress. Whole organelle turnover is mediated through macroautophagy, a process by which autophagosomes deliver mitochondria to the lysosome for hydrolytic degradation. While mitochondrial autophagy can occur as part of a nonselective upregulation of autophagy, selective degradation of damaged or unneeded mitochondria (mitophagy) is a rapidly growing area in development, cancer, and neurodegeneration, particularly with regard to Parkinson’s disease. Due to its dynamic nature, and the potential for regulatory perturbation by disease processes, no single technique is sufficient to evaluate mitophagy. Here, we describe several complementary techniques that include electron microscopy, single cell analysis of LC3 fluorescent puncta, and Western blot, each used in conjunction with a flux inhibitor to trap newly formed autophagosomes in order to monitor mitophagy in neuronal cells.
Autophagy; Mitophagy; Electron microscopy; Western Blot; RFP-LC3; GFP-LC3; Immunofluorescence
CREB binding protein (CBP) is a transcriptional co-activator with histone acetyltransferase activity. Our prior study suggested that CBP might be a key target of presenilins in the regulation of memory formation and neuronal survival. To elucidate the role of CBP in the adult brain, we generated conditional knockout (cKO) mice in which CBP is completely inactivated in excitatory neurons of the postnatal forebrain. Histological analysis revealed normal neuronal morphology and absence of age-dependent neuronal degeneration in the CBP cKO cerebral cortex. CBP cKO mice exhibited robust impairment in the formation of spatial, associative and object recognition memory. In addition to impaired long-term memory, CBP cKO mice also displayed deficits in short-term associative and object recognition memory. Administration of a histone deacetylase inhibitor, TSA, rescued the reduction of acetylated histones in the CBP cKO cortex but failed to rescue either short-term or long-term memory deficits, suggesting that the memory impairment may not be caused by general reduction of histone acetyltransferase activity in CBP cKO mice. Further microarray and Western analysis showed decreased expression of calcium-calmodulin-dependent kinase isoforms and NMDA and AMPA receptor subunits in the cerebral cortex of CBP cKO mice. Collectively, these findings suggest a crucial role for CBP in the formation of both short-term and long-term memory.
presenilin; learning and memory; neurodegeneration; conditional knockout
The study investigates long-term recognition memory in congenital prosopagnosia (CP), a lifelong impairment in face identification that is present from birth. Previous investigations of processing deficits in CP have mostly relied on short-term recognition tests to estimate the scope and severity of individual deficits. We firstly report on a controlled test of long-term (one year) recognition memory for faces and objects conducted with a large group of participants with CP. Long-term recognition memory is significantly impaired in eight CP participants (CPs). In all but one case, this deficit was selective to faces and didn't extend to intra-class recognition of object stimuli. In a test of famous face recognition, long-term recognition deficits were less pronounced, even after accounting for differences in media consumption between controls and CPs. Secondly, we combined test results on long-term and short-term recognition of faces and objects, and found a large heterogeneity in severity and scope of individual deficits. Analysis of the observed heterogeneity revealed a dissociation of CP into subtypes with a homogeneous phenotypical profile. Thirdly, we found that among CPs self-assessment of real-life difficulties, based on a standardized questionnaire, and experimentally assessed face recognition deficits are strongly correlated. Our results demonstrate that controlled tests of long-term recognition memory are needed to fully assess face recognition deficits in CP. Based on controlled and comprehensive experimental testing, CP can be dissociated into subtypes with a homogeneous phenotypical profile. The CP subtypes identified align with those found in prosopagnosia caused by cortical lesions; they can be interpreted with respect to a hierarchical neural system for face perception.
Macroautophagy is an evolutionarily conserved mechanism for bulk intracellular degradation of proteins and organelles. Pathological studies have implicated macroautophagy defects in human neurodegenerative disorders of aging including Alzheimer’s disease and tauopathies. Neuronal deficiency of macroautophagy throughout mouse embryonic development results in neurodevelopmental defects and early postnatal mortality. However, the role of macroautophagy in mature CNS neurons, and the relationship with human disease neuropathology, remains unclear. Here we describe mice deficient in an essential macroautophagy component, Atg7, specifically within postnatal CNS neurons.
Postnatal forebrain-specific Atg7 conditional knockout (cKO) mice displayed age-dependent neurodegeneration and ubiquitin- and p62-positive inclusions. Phosphorylated tau was significantly accumulated in Atg7 cKO brains, but neurofibrillary tangles that typify end-stage human tauopathy were not apparent. A major tau kinase, glycogen synthase kinase 3β (GSK3β), was also accumulated in Atg7 cKO brains. Chronic pharmacological inhibition of tau phosphorylation, or genetic deletion of tau, significantly rescued Atg7-deficiency-mediated neurodegeneration, but did not suppress inclusion formation.
These data elucidate a role for macroautophagy in the long-term survival and physiological function of adult CNS neurons. Neurodegeneration in the context of macroautophagy deficiency is mediated through a phospho-tau pathway.
ERK 1,2 pathway mediates experience-dependent gene transcription in neurons and several studies have identified its pivotal role in experience-dependent synaptic plasticity and in forms of long term memory involving hippocampus, amygdala, or striatum. The perirhinal cortex (PRHC) plays an essential role in familiarity-based object recognition memory. It is still unknown whether ERK activation in PRHC is necessary for recognition memory consolidation. Most important, it is unknown whether by modulating the gain of the ERK pathway it is possible to bidirectionally affect visual recognition memory and PRHC synaptic plasticity. We have first pharmacologically blocked ERK activation in the PRHC of adult mice and found that this was sufficient to impair long term recognition memory in a familiarity-based task, the object recognition task (ORT). We have then tested performance in the ORT in Ras-GRF1 knock-out (KO) mice, which exhibit a reduced activation of ERK by neuronal activity, and in ERK1 KO mice, which have an increased activation of ERK2 and exhibit enhanced striatal plasticity and striatal mediated memory. We found that Ras-GRF1 KO mice have normal short term memory but display a long term memory deficit; memory reconsolidation is also impaired. On the contrary, ERK1 KO mice exhibit a better performance than WT mice at 72 h retention interval, suggesting a longer lasting recognition memory. In parallel with behavioral data, LTD was strongly reduced and LTP was significantly smaller in PRHC slices from Ras-GRF1 KO than in WT mice while enhanced LTP and LTD were found in PRHC slices from ERK1 KO mice.
ERK1,2; recognition memory; perirhinal cortex; synaptic plasticity
Previous work from our laboratory has shown that the ability of estradiol to enhance object memory consolidation in young ovariectomized mice is dependent on dorsal hippocampal activation of the extracellular signal-regulated kinase/mitogen activated protein kinase (ERK/MAPK) signaling pathway (Fernandez et al., 2008). However, it is unclear if estradiol modulates memory or ERK activation similarly in the presence of progesterone. Therefore, the present study investigated effects of combined estradiol and progesterone treatment on object memory consolidation and dorsal hippocampal ERK activation in young ovariectomized C57BL/6 mice. Object memory was tested in a novel object recognition task. Immediately after training, mice received intraperitoneal (i.p.) injections of vehicle, 17β-estradiol (E2; 0.2 mg/kg), or E2 plus 5, 10, or 20 mg/kg progesterone (P). Forty-eight hours later, mice receiving E2 alone or E2 plus 10 or 20 mg/kg P exhibited significantly enhanced memory for the novel object relative to chance, whereas those receiving vehicle or E2 plus 5 mg/kg P spent no more time than chance with the novel object. Two weeks later, ERK phosphorylation was measured in the dorsal hippocampus 1 hour after i.p. injection of vehicle, E2, or E2 plus P. Consistent with our previous work (Fernandez et al., 2008), E2 alone significantly increased phospho-p42 ERK protein levels in the dorsal hippocampus relative to vehicle controls. In contrast, no combination of E2 and P affected dorsal hippocampal phosphoERK levels. These data indicate that, unlike E2 alone, the beneficial effects of combined E2 plus P treatment on memory are not associated with ERK activation in the dorsal hippocampus 1 hour after treatment, and suggest that E2 alone and combined E2 plus P may influence ERK activation in different timeframes or enhance memory through different mechanisms.
Object recognition; Non-spatial memory; Mouse; Estrogen; Progestin; MAPK
Spatial alternation, win-shift behavior has been claimed to be a test of working memory in rodents that requires active maintenance of relevant, trial-specific information. In this review, we describe work with GluA1 AMPA receptor subunit knockout mice that show impaired spatial alternation, but normal spatial reference memory. Due to their selective impairment on spatial alternation, GluA1 knockout mice provide a means by which the psychological processes underlying alternation can be examined. We now argue that the spatial alternation deficit in GluA1 knockout mice is due to an inability to show stimulus-specific, short-term habituation to recently experienced stimuli. Short-term habituation involves a temporary reduction in attention paid to recently presented stimuli, and is thus a distinct process from those that are involved in working memory in humans. We have recently demonstrated that GluA1 knockout mice show impaired short-term habituation, but, surprisingly, show enhanced long-term spatial habituation. Thus, GluA1 deletion reveals that there is competition between short-term and long-term processes in memory. © 2010 Wiley Periodicals, Inc.
hippocampus; working memory; mice; habituation; plasticity; AMPA receptors
Patients with chronic pain usually suffer from working memory deficits, which may decrease their intellectual ability significantly. Despite intensive clinical studies, the mechanism underlying this form of memory impairment remains elusive. In this study, we investigated this issue in the spared nerve injury (SNI) model of neuropathic pain, a most common form of chronic pain. We found that SNI impaired working memory and short-term memory in rats and mice. To explore the potential mechanisms, we studied synaptic transmission/plasticity in hippocampus, a brain region critically involved in memory function. We found that frequency facilitation, a presynaptic form of short-term plasticity, and long-term potentiation at CA3–CA1 synapses were impaired after SNI. Structurally, density of presynaptic boutons in hippocampal CA1 synapses was reduced significantly. At the molecular level, we found that tumor necrosis factor-α (TNF-α) increased in cerebrospinal fluid, in hippocampal tissue and in plasma after SNI. Intracerebroventricular or intrahippocampal injection of recombinant rat TNF mimicked the effects of SNI in naive rats, whereas inhibition of TNF-α or genetic deletion of TNF receptor 1 prevented both memory deficits and synaptic dysfunction induced by SNI. As TNF-α is critical for development of neuropathic pain, we suggested that the over-production of TNF-α following peripheral nerve injury might lead to neuropathic pain and memory deficits, simultaneously.
spared nerve injury; chronic neuropathic pain; working memory; long-term potentiation; presynaptic boutons; tumor necrosis factor-α; pain/analgesics; learning & memory; neuropharmacology; plasticity; peripheral nerve injury; chronic neuropathic pain; working memory; long-term potentiation; presynaptic boutons; tumor necrosis factor alpha
Cognitive impairments are common in depression and involve dysfunctional serotonin neurotransmission. The 5-HT1B receptor (5-HT1BR) regulates serotonin transmission, via presynaptic receptors, but can also affect transmitter release at heterosynaptic sites. This study aimed at investigating the roles of the 5-HT1BR, and its adapter protein p11, in emotional memory and object recognition memory processes by the use of p11 knockout (p11KO) mice, a genetic model for aspects of depression-related states. 5-HT1BR agonist treatment induced an impairing effect on emotional memory in wild type (WT) mice. In comparison, p11KO mice displayed reduced long-term emotional memory performance. Unexpectedly, 5-HT1BR agonist stimulation enhanced memory in p11KO mice, and this atypical switch was reversed after hippocampal adeno-associated virus mediated gene transfer of p11. Notably, 5-HT1BR stimulation increased glutamatergic neurotransmission in the hippocampus in p11KO mice, but not in WT mice, as measured by both pre- and postsynaptic criteria. Magnetic resonance spectroscopy demonstrated global hippocampal reductions of inhibitory GABA, which may contribute to the memory enhancement and potentiation of pre- and post-synaptic measures of glutamate transmission by a 5-HT1BR agonist in p11KO mice. It is concluded that the level of hippocampal p11 determines the directionality of 5-HT1BR action on emotional memory processing and modulates hippocampal functionality. These results emphasize the importance of using relevant disease models when evaluating the role of serotonin neurotransmission in cognitive deficits related to psychiatric disorders.
AAV; biosensor; MRS; novel object recognition; passive avoidance; S100A10
Cognitive impairments are common in depression and involve dysfunctional serotonin neurotransmission. The 5-HT1B receptor (5-HT1BR) regulates serotonin transmission, via presynaptic receptors, but can also affect transmitter release at heterosynaptic sites. This study aimed at investigating the roles of the 5-HT1BR, and its adaptor protein p11, in emotional memory and object recognition memory processes by the use of p11 knockout (p11KO) mice, a genetic model for aspects of depression-related states. 5-HT1BR agonist treatment induced an impairing effect on emotional memory in wild type (WT) mice. In comparison, p11KO mice displayed reduced long-term emotional memory performance. Unexpectedly, 5-HT1BR agonist stimulation enhanced memory in p11KO mice, and this atypical switch was reversed after hippocampal adeno-associated virus mediated gene transfer of p11. Notably, 5-HT1BR stimulation increased glutamatergic neurotransmission in the hippocampus in p11KO mice, but not in WT mice, as measured by both pre- and postsynaptic criteria. Magnetic resonance spectroscopy demonstrated global hippocampal reductions of inhibitory GABA, which may contribute to the memory enhancement and potentiation of pre- and post-synaptic measures of glutamate transmission by a 5-HT1BR agonist in p11KO mice. It is concluded that the level of hippocampal p11 determines the directionality of 5-HT1BR action on emotional memory processing and modulates hippocampal functionality. These results emphasize the importance of using relevant disease models when evaluating the role of serotonin neurotransmission in cognitive deficits related to psychiatric disorders.
passive avoidance; novel object recognition; S100A10; biosensor; AAV; MRS
A major goal of biomedical research has been the identification of molecular mechanisms that can enhance memory. Here we report a novel signaling pathway that regulates the conversion from short- to long-term memory. The mTOR complex 2 (mTORC2), which contains the key regulatory protein Rictor (Rapamycin-Insensitive Companion of mTOR), was discovered only recently, and little is known about its physiological role. We show that conditional deletion of rictor in the postnatal murine forebrain greatly reduces mTORC2 activity and selectively impairs both long-term memory (LTM) and the late (but not the early) phase of hippocampal long-term potentiation (LTP). Actin polymerization is reduced in the hippocampus of mTORC2-deficient mice and its restoration rescues both L-LTP and LTM. More importantly, a compound that selectively promotes mTORC2 activity converts early-LTP into late-LTP and enhances LTM. These findings indicate that mTORC2 could be a novel therapeutic target for the treatment of cognitive dysfunction.
mTOR complexes; actin assembly; spatial memory; fear memory; cognitive enhancer
Macroautophagy is a conserved mechanism for the bulk degradation of proteins and organelles. Pathological studies have implicated defective macroautophagy in neurodegeneration, but physiological functions of macroautophagy in adult neurons remain unclear. Here we show that Atg7, an essential macroautophagy component, regulates dopaminergic axon terminal morphology. Mature Atg7-deficient midbrain dopamine (DA) neurons harbored selectively enlarged axonal terminals. This contrasted with the phenotype of DA neurons deficient in Pten – a key negative regulator of the mTOR kinase signaling pathway and neuron size – that displayed enlarged soma but unaltered axon terminals. Surprisingly, concomitant deficiency of both Atg7 and Pten led to a dramatic enhancement of axon terminal enlargement relative to Atg7 deletion alone. Similar genetic interactions between Atg7 and Pten were observed in the context of DA turnover and DA-dependent locomotor behaviors. These data suggest a model for morphological regulation of mature dopaminergic axon terminals whereby the impact of mTOR pathway is suppressed by macroautophagy.
Macroautophagy is a major recycling pathway in cells, and its dysfunction is associated with neurological disorders including Alzheimer's disease, Parkinson's disease, and frontotemporal dementia. Here we show that Atg7, an essential component of macroautophagy, regulates mature dopaminergic axon terminal morphology in coordination with the well-described role of the PI3K pathway. Deficiency of Pten, a negative regulator of the PI3K/mTOR pathway, leads primarily to enlarged dopaminergic cell soma but normal-appearing axonal terminals, whereas Atg7 deficiency primarily induces enlarged axonal terminals. Atg7 and Pten double deficiency leads to further axon terminal enlargement, suggesting that Atg7 deficiency unmasks the impact of PI3K/mTOR pathway on mature dopaminergic axon terminals. In addition, we show that Atg7 and Pten coordinately regulate striatal dopamine turnover and dopamine-dependent motor behaviors. Taken together, these data support a novel role for Atg7-dependent macroautophagy in the regulation of dopaminergic axon terminal morphology, in coordination with the PI3K/mTOR pathway.
Recent work [Sanderson, D., Good, M.A., Skelton, K., Sprengel, R., Seeburg, P. H., Nicholas, J., et al. Enhanced long-term and impaired short-term spatial memory in GluA1 AMPA receptor subunit knockout mice: Evidence for a dual-process memory model. Learning and Memory, in press] showed that short-term memory (STM) is selectively reduced in GluR1 knockout mice. This raises the possibility that a form of synaptic modification dependent on GluR1 might underlie STM. Studies of synaptic plasticity have shown that stimuli too weak to induce long-term potentiation induce short-term potentiation (STP), a phenomenon that has received little attention. Here we examined several properties of STP and tested the dependence of STP on GluR1. The minimal requirement for inducing STP was examined using a test pathway and a conditioning pathway. Several closely spaced stimuli in the test pathway, forming a single brief burst, were sufficient to induce STP. Thus, STP is likely to be induced by the similar bursts that occur in vivo. STP induction is associative in nature and dependent on the NMDAR. STP decays with two components, a fast component (1.6 ± 0.26 min) and a slower one (19 ± 6.6 min). To test the role of GluR1 in STP, experiments were conducted on GluR1 knockout mice. We found that STP was greatly reduced. These results, taken together with the behavioral work of D. Sanderson et al. [Sanderson, D., Good, M. A, Skelton, K., Sprengel, R., Seeburg, P. H., Nicholas, J., et al. Enhanced long-term and impaired short-term spatial memory in GluA1 AMPA receptor subunit knockout mice: Evidence for a dual-process memory model. Learning and Memory, in press], provide genetic evidence that STP is a likely mechanism of STM.