Nerve Growth Factor-induced Gene Research Articles

Lower Plasma Levels of Selective VGF (Non-Acronymic) Peptides in Bipolar Disorder: Comparative Analysis Reveals Distinct Patterns across Mood Disorders and Healthy Controls

Introduction: Discriminating bipolar disorder (BD) from major depressive disorder (MDD) remains a challenging clinical task. Identifying specific peripheral biosignatures that can differentiate between BD and MDD would significantly increase diagnostic accuracy. Dysregulated neuroplasticity is implicated in BD and MDD, and psychotropic medications restore specific disrupted processes by increasing neurotrophic signalling. The nerve growth factor inducible vgf gene (non-acronymic) encodes a precursor protein named proVGF, which undergoes proteolytic processing to produce several VGF peptides, some of which were suggested to be implicated in mood disorders and have antidepressant effects. Since the presence of VGF peptides in humans has been exclusively investigated in brain and cerebrospinal fluid, we aimed to identify which VGF peptides are present in the plasma and to investigate whether their levels could differentiate BD from MDD as well as responders from non-responders to pharmacological interventions. Methods: VGF peptides were investigated in plasma from patients diagnosed with MDD (n = 37) or BD (n = 40 under lithium plus n = 29 never exposed to lithium), as well as healthy controls (HC; n = 36). Results: Three VGF peptides (TLQP-11, AQEE-14, and NAPP-19) were identified using spectrometry analysis of plasma from HC. These peptides were then measured in the entire sample using ELISA, which showed significantly lower levels of AQEE and NAPP in BD than in HC and MDD (p = 5.0 × 10−5, p = 0.001, respectively). Conclusion: Our findings suggest that lower plasma levels of NAPP and AQEE are specifically associated with BD, thus possibly representing a diagnostic biomarker in mood disorders.

Nur77 improves ovarian function in reproductive aging mice by activating mitophagy and inhibiting apoptosis

Reproductive aging not only affects the fertility and physical and mental health of women but also accelerates the aging process of other organs. There is an urgent need newfor novel mechanisms, targets, and drugs to break the vicious cycle of mitochondrial dysfunction, redox imbalance, and germ cell apoptosis associated with ovarian aging. Autophagy, recognized as a longevity mechanism, has recently become a focal point in anti-aging research. Although mitophagy is a type of autophagy, its role and regulatory mechanisms in ovarian aging, particularly in age-related ovarian function decline, remain unclear. Nerve growth factor inducible gene B (Nur77) is an early response gene that can be stimulated by oxidative stress, DNA damage, metabolism, and inflammation. Recent evidence recommends that decreased expression of Nur77 is associated with age-related myocardial fibrosis, renal dysfunction, and Parkinson's disease; however, its association with ovarian aging has not been studied yet. We herein identified Nur77 as a regulator of germ cell senescence, apoptosis, and mitophagy and found that overexpression of Nur77 can activate mitophagy, improve oxidative stress, reduce apoptosis, and ultimately enhance ovarian reserve in aged mice ovaries. Furthermore, we discovered an association between Nur77 and the AKT pathway through String and molecular docking analyses. Experimental confirmation revealed that the AKT/mTOR signaling pathway is involved in the regulation of Nur77 in ovarian function. In conclusion, our results suggest Nur77 as a promising target for preventing and treating ovarian function decline related to reproductive aging.

Nur77 alleviates cardiac fibrosis by upregulating GSK-3β transcription during aging

Cardiac fibrosis is associated with aging, for which no targeted therapies are available. With aging, the levels of nerve growth factor-induced gene B (Nur77) are reduced during cardiac remodelling; however, its role in cardiac fibrosis in aging remains unclear. Here, we found that Nur77 knockout increased cardiac structure abnormalities, systolic and diastolic dysfunction, cardiac hypertrophy, and fibrotic marker expression in 15-month-old mice. Furthermore, Nur77 deficiency induced collagen type I (Col-1) and α-smooth muscle actin overproduction in transforming growth factor beta (TGF-β) treated H9c2 cells, whereas Nur77 overexpression attenuated this effect. Nur77 deficiency in vivo and in vitro downregulated glycogen synthase kinase (GSK)-3β expression and increased β-catenin activity, while its overexpression increased GSK-3β expression. GSK-3β knockdown counteracted the anti-fibrotic effect of Nur77 on TGF-β-treated H9c2 cells. Chromatin immunoprecipitation and luciferase reporter assay results suggested GSK-3β as the direct target of Nur77. Our findings suggest that Nur77 directly initiates GSK-3β transcription and age-related cardiac fibrosis partly through the GSK-3β/β-catenin pathway. This study proposes a novel mechanism for Nur77 regulating cardiac fibrosis and suggests Nur77 as a target for the prevention and treatment of aging-associated cardiac fibrosis and heart failure.

Nur77 ameliorates age-related renal tubulointerstitial fibrosis by suppressing the TGF-β/Smads signaling pathway.

Nerve growth factor-induced gene B (Nur77) has been shown to ameliorate several biological processes in chronic diseases, including inflammatory response, cellular proliferation, and metabolism. Chronic kidney disease (CKD) is characterized by tubulointerstitial fibrosis for which no targeted therapies are available as yet. In this study, we performed in vivo and in vitro experiments to demonstrate that Nur77 targets fibrosis signals and attenuates renal tubulointerstitial fibrosis during the aging process. We observed that the TGF-β/Smads signal pathway was significantly suppressed by Nur77, suggesting that Nur77 controlled the activation of key steps in TGF-β/Smads signaling. We further showed that Nur77 interacted with Smad7, the main repressor of nuclear translocation of Smad2/3, and stabilized Smad7 protein homeostasis. Nur77 deficiency resulted in Smad7degradation, aggravating Smad2/3 phosphorylation, and promoting transcription of its downstream target genes, ACTA2 and collagen I. Our findings demonstrate that Nur77 is a potential therapeutic target for age-related kidney diseases including CKD. Maintenance of Nur77may be an effective strategy for blocking renal tubulointerstitial fibrosis and improving renal function in the elderly.

SOX9 promotes stress-responsive transcription of VGF nerve growth factor inducible gene in renal tubular epithelial cells

Acute kidney injury (AKI) is a common clinical condition associated with diverse etiologies and abrupt loss of renal function. In patients with sepsis, rhabdomyolysis, cancer, and cardiovascular disorders, the underlying disease or associated therapeutic interventions can cause hypoxia, cytotoxicity, and inflammatory insults to renal tubular epithelial cells (RTECs), resulting in the onset of AKI. To uncover stress-responsive disease-modifying genes, here we have carried out renal transcriptome profiling in three distinct murine models of AKI. We find that Vgf nerve growth factor inducible gene up-regulation is a common transcriptional stress response in RTECs to ischemia-, cisplatin-, and rhabdomyolysis-associated renal injury. The Vgf gene encodes a secretory peptide precursor protein that has critical neuroendocrine functions; however, its role in the kidneys remains unknown. Our functional studies show that RTEC-specific Vgf gene ablation exacerbates ischemia-, cisplatin-, and rhabdomyolysis-associated AKI in vivo and cisplatin-induced RTEC cell death in vitro Importantly, aggravation of cisplatin-induced renal injury caused by Vgf gene ablation is partly reversed by TLQP-21, a Vgf-derived peptide. Finally, in vitro and in vivo mechanistic studies showed that injury-induced Vgf up-regulation in RTECs is driven by the transcriptional regulator Sox9. These findings reveal a crucial downstream target of the Sox9-directed transcriptional program and identify Vgf as a stress-responsive protective gene in kidney tubular epithelial cells.

Nur77 attenuates inflammatory responses and oxidative stress by inhibiting phosphorylated IκB-α in Parkinson's disease cell model.

Neuroinflammation and oxidative stress play key roles in the pathological development of Parkinson’s disease (PD). Nerve growth factor-induced gene B (Nur77) is closely related to dopamine neurotransmission, and its pathogenesis is unclear. This study aims to investigate the role and mechanism of Nur77 in a cell model of Parkinson’s disease. Silencing Nur77 with siRNA can aggravate intracellular LDH release, increase the expression of pro-inflammatory genes (such as tumor necrosis factor α, nuclear factor κB (p65), monocyte chemotactic protein 1, interleukin-6), and decrease cell survival, decrease expression of nuclear factor E2-related factor(Nrf2), heme oxygenase 1, NADPH quinineoxidoreductase-1. Cytosporone B (Nur77 agonist) has the opposite effect to Nur77 silencing. PDTC (NF-κB inhibitor / antioxidant) can also inhibit pro-inflammatory genes to a similar degree as Cytosporone B. Phosphorylated IκB-α can be inhibited by Cytosporone B, while silencing Nur77 can increase the protein expression level of phosphorylated IκB-α. After silencing IκB-α, both Cytosporone B and siNur77 did not affect pro-inflammatory genes and antioxidant stress. These findings reveal the first evidence that Nur77 exerts anti-inflammatory and antioxidant stress effects by inhibiting IκB-α phosphorylation expression in a Parkinson cell model. Nur77 may be a potential therapeutic target for Parkinson’s disease.

Pharmacological inhibition of G9a/GLP restores cognition and reduces oxidative stress, neuroinflammation and β-Amyloid plaques in an early-onset Alzheimer's disease mouse model.

The implication of epigenetic mechanisms in Alzheimer’s disease (AD) has been demonstrated in several studies. UNC0642, a specific and potent inhibitor of methyltransferase activity G9a/GLP (G9a-like) complex, was evaluated in the 5XFAD mouse model. UNC0642 treatment rescued 5XFAD cognition impairment, reduced DNA-methylation (5-mC), increased hydroxymethylation (5-hmC), and decreased the di-methylation of lysine 9 of histone H3 (H3K9me2) levels in the hippocampus. Increases in the Nuclear Factor erythroid-2-Related Factor 2 (NRF2), Heme oxygenase decycling 1 (Hmox1) gene expression, and diminution in Reactive Oxygen Species (ROS) were also reported. Moreover, neuroinflammatory markers, such as Interleukin 6 (Il-6), Tumor necrosis factor-alpha (Tnf-α) gene expression, and Glial fibrillary acidic protein (GFAP) immunofluorescence were reduced by UNC0642 treatment. An increase in Nerve growth factor (Ngf), Nerve growth factor inducible (Vgf) gene expression, Brain-derived neurotrophic factor (BDNF), and Synaptophysin (SYN) were found after UNC0642 treatment. Importantly, a reduction in β-amyloid plaques was also observed. In conclusion, our work demonstrates that the inhibition of the G9a/GLP complex by UNC0642 delivered significant neuroprotective effects in 5XFAD mice, point out G9a/GLP as a new target for AD.

Nur77 promotes embryo adhesion by transcriptionally regulating HOXA10 expression

ABSTRACTHOXA10 is an important regulator of embryo adhesion. Reduced expression may contribute to embryo implantation failure. The expression of Nur77 and HOXA10 has been shown to be reduced in the endometrium of patients with recurrent implantation failure. In this study, we found that Nur77 was directly bound to the HOXA10 promoter and promoted HOXA10 protein expression in a dose-dependent manner in Ishikawa cells. Furthermore, the promoting effect of Nur77 on embryo adhesion was significantly blocked when endogenous HOXA10 expression was knocked down in Ishikawa cells. Moreover, the Nur77 agonist 6-MP was also confirmed to promote embryo adhesion. This study is the first to show that Nur77 promotes embryo adhesion by transcriptionally regulating HOXA10 expression. Nur77 and 6-MP may provide a basis to develop a new treatment for patients who suffer from embryo adhesion dysfunction.Abbreviations: HB-EGF: heparin-binding epidermal growth factor-like growth factor; HOXA10: homeobox A10; NGFI-B: nerve growth factor-induced gene B; RIF: recurrent implantation failure; RPL: recurrent pregnancy loss; 6-MP: 6-mercaptopurine; IGFBP-1: insulin-like growth factor binding protein-1; LIF: leukemia inhibitory factor; IL-1β: Interleukin - 1β; CRISPR/Cas9: Clustered Regularly Interspaced Short Palindromic Repeats; AF-1: activation function-1 domain; HIF-1α: hypoxia-inducible factor 1α; CREB: cAMP response element binding

Long-term neuronal survival, regeneration, and transient target reconnection after optic nerve crush and mesenchymal stem cell transplantation

BackgroundRetina and/or optic nerve injury may cause irreversible blindness, due to degeneration of retinal ganglion cells. We and others have previously shown that the intravitreal injection of mesenchymal stem cells (MSCs) protects injured retinal ganglion cells and stimulates their regeneration after optic nerve injury, but the long-term effects of this therapy are still unknown.MethodsWe injected rat MSC (rMSC) intravitreally in adult (3–5 months) Lister Hooded rats of either sex after optic nerve crush. Retinal ganglion cell survival, axonal regeneration, and reconnection were analyzed 60 and 240 days after crush by immunohistochemistry for Tuj1, anterograde labeling with cholera-toxin B and by immunohistochemistry for nerve growth factor-induced gene A (NGFI-A, driven by light stimulation) in the superior colliculus after a cycle of light deprivation-stimulation. Visual behaviors (optokinetic reflex, looming response, and preference for dark) were analyzed 70 days after crush.ResultsrMSC treatment doubled the number of surviving retinal ganglion cells, preferentially of a larger subtype, and of axons regenerating up to 0.5 mm. Some axons regenerated to the lateral geniculate nucleus and superior colliculus. NGFI-A+ cells were doubled in rMSC-treated animals 60 days after crush, but equivalent to vehicle-injected animals 240 days after crush, suggesting that newly formed synapses degenerated. Animals did not recover visual behaviors.ConclusionsWe conclude that rMSC-induced neuroprotection is sustained at longer time points. Although rMSCs promoted long-term neuroprotection and long-distance axon regeneration, the reconnection of retinal ganglion cells with their targets was transitory, indicating that they need additional stimuli to make stable reconnections.

The Pathways Involved in TLQP-62 Mediated Biological Functions

VGF is neurosecretory protein, belongs to the extendedgranin family of proteins, originallyrecognized as a nerve growth factor (NGF) inducible gene product. It is selectively synthesized mostly in neuronal and neuroendocrine cells. It has a very simple organization. It has several biologically active peptides, described as VGF-derived peptides including APPG-40, APPG-37, GRPE-37, NERP-1, NERP-2, NAPP-129 (VGF 20), VGF 18, HFHH-51 (VGF 6), HHPD-1, AQEE-30 (Peptide V), LQEQ-19, TLQP-21 and TLQP-62 (VGF 10). Among these peptides TLQP-62 is of great significance because of its several remarkable biological effects like regulation of memory formation, glucose homeostasis and insulin secretion, gene transcription, neurogenesis, etc. Although in light of these outstanding behavioral and physiological roles, very few information are available regarding its mode of action. Still, no receptor has been found for TLQP-62 mediated cascading pathways. However, considering the significant biological function of TLQP-62, this review study was done to summarize the pathways involved in TLQP-62 mediated action, based on the information till now. TLQP-62 activates signal transduction cascades by two mechanisms including opening of the calcium channels and modulating the AMPK, PKC and ERK pathways. These events result in an increase in intracellular Ca2+ concentration which permits the secretion of insulin. TLQP-62 would be a significant therapeutics and drug discovery tool for a wide range of diseases to which the peptide related, if TLQP-62 mediated pathways are known, as a whole.

Haloperidol-induced striatalNur77expression in a non-human primate model of tardive dyskinesia

Tardive dyskinesia (TD) is a delayed and potentially irreversible motor complication arising in patients chronically exposed to antipsychotic drugs. As several modern (so-called atypical) antipsychotic drugs are common offenders, combined with the widening clinical indications for prescription as well as exposure of vulnerable individuals, TD will remain a significant drug-induced unwanted side effect. In addition, the pathophysiology of TD remains elusive and therapeutics are difficult. Based on rodent experiments, we have previously shown that the transcriptional factor Nur77 (also known as nerve growth factor inducible gene B or Nr4a1) is induced in the striatum following antipsychotic drug exposure as part of a long-term neuroadaptive process. To confirm this, we exposed adult capuchin (Cebus apella) monkeys to prolonged treatments with haloperidol (median 18.5months, N=11) or clozapine (median 6months, N=6). Six untreated animals were used as controls. Five haloperidol-treated animals developed mild TD movements similar to those found in humans. No TD was observed in the clozapine group. Postmortem analysis of Nur77 expression measured by in situ hybridization revealed a stark contrast between the two drugs, as Nur77 mRNA levels in the caudate-putamen were strongly upregulated in animals exposed to haloperidol but were spared following clozapine treatment. Interestingly, within the haloperidol-treated group, TD-free animals showed higher Nur77 expression in putamen subterritories compared with dyskinetic animals. This suggests that Nur77 expression might be associated with a reduced risk of TD in this experimental model and could provide a novel target for drug intervention.

Upregulation of Neurodevelopmental Genes During Scarless Healing

Scarless fetal skin wound healing is a paradigm for ideal skin repair and is dependent on peripheral nerve function.To further explore neurogenic mechanisms influence on the scarless skin repair, fetal rats were wounded on gestational days 16 (E16; n = 24) and 18 (E18; n = 8) and wounds were harvested at 1 and 3 days after injury. Unwounded skin at identical gestational age was used for control comparison. The scarless E16 and scarring E18 wounds underwent macroarray gene expression analysis (1172 genes).During the scarless healing period, 53 (4.5%) genes had a statistically significant upregulation post-injury with at least a 2- to 3-fold change 1 day after wounding and 14 (1.2%) genes 3 days after wounding (P < 0.05). Many neurodevelopmental genes were increased during scarless repair on post-injury days 1 and 3. Neuropeptide Y Receptor type I, cJun related Transcription Factor (junD), Synaptophysin, SNAP 25, Neuronal calcium sensor 1 (NCS1), neural visine-like calcium binding protein 1 (NVP1), nerve growth factor-induced gene A (NGFI-A/EGR1), VGF8A protein, p27kip1, and members of the GABA and serotonin family each had 2- to 3-fold expression increases (P < 0.05).We speculate that fetal skin cells express neurotrophins during skin development that regulate peripheral neuron formation. During injury these factors promote the survival and regeneration of peripheral neurons; this interaction of neuropeptides, neuropeptide receptors, and neurotrophins may modulate the fetal scarless repair mechanisms in response to injury. Identification of these neurodevelopmental candidate genes provides insight for new investigation into mechanisms regulating scarless healing.

Orphan Nuclear Receptor DAX-1 Acts as a Novel Corepressor of Liver X Receptor α and Inhibits Hepatic Lipogenesis

DAX-1 (dosage-sensitive sex reversal adrenal hypoplasia congenital critical region on X chromosome, gene 1) is a member of the nuclear receptor superfamily that can repress diverse nuclear receptors and has a key role in adreno-gonadal development. Our previous report has demonstrated that DAX-1 can inhibit hepatocyte nuclear factor 4alpha transactivity and negatively regulate gluconeogenic gene expression (Nedumaran, B., Hong, S., Xie, Y. B., Kim, Y. H., Seo, W. Y., Lee, M. W., Lee, C. H., Koo, S. H., and Choi, H. S. (2009) J. Biol. Chem. 284, 27511-27523). Here, we further expand the role of DAX-1 in hepatic energy metabolism. Transfection assays have demonstrated that DAX-1 can inhibit the transcriptional activity of nuclear receptor liver X receptor alpha (LXRalpha). Physical interaction between DAX-1 and LXRalpha was confirmed Immunofluorescent staining in mouse liver shows that LXRalpha and DAX-1 are colocalized in the nucleus. Domain mapping analysis shows that the entire region of DAX-1 is involved in the interaction with the ligand binding domain region of LXRalpha. Competition analyses demonstrate that DAX-1 competes with the coactivator SRC-1 for repressing LXRalpha transactivity. Chromatin immunoprecipitation assay showed that endogenous DAX-1 recruitment on the SREBP-1c gene promoter was decreased in the presence of LXRalpha agonist. Overexpression of DAX-1 inhibits T7-induced LXRalpha target gene expression, whereas knockdown of endogenous DAX-1 significantly increases T7-induced LXRalpha target gene expression in HepG2 cells. Finally, overexpression of DAX-1 in mouse liver decreases T7-induced LXRalpha target gene expression, liver triglyceride level, and lipid accumulation. Overall, this study suggests that DAX-1, a novel corepressor of LXRalpha, functions as a negative regulator of lipogenic enzyme gene expression in liver.

17β‐estradiol and enriched environment accelerate cognitive recovery after focal brain ischemia

Cognitive impairments, including spatial memory and learning deficiencies, are common after ischemic stroke. Estrogen substitution improves cognitive functions in post-menopausal women and ovariectomized rodents, partially through induction of neuroplasticity in the hippocampal formation. Post-ischemic housing of male rats in an enriched environment (EE) improves functional outcome, without changing infarct volume. We hypothesized that 17beta-estradiol combined with an EE would accelerate cognitive recovery after focal brain ischemia in ovariectomized rats and that recovery would be related to altered expression of nerve growth factor-induced gene (NGFI)-A in the hippocampus. 17beta-estradiol or placebo pellets were implanted 6 h after transient middle cerebral artery occlusion. Two days later, rats were placed in an EE or a deprived environment (DE) for 6 weeks. At 5 weeks after middle cerebral artery occlusion, 17beta-estradiol-treated rats housed in an EE showed improvements in cognitive function (i.e. shorter latency and path in the Morris water maze task) compared with placebo-treated animals housed in an EE. Furthermore, beneficial effects on latency and path were observed when comparing EE-housed vs. DE-housed 17beta-estradiol-treated rats. When comparing 17beta-estradiol-treated EE-housed rats vs. placebo-treated DE-housed rats, pronounced effects on latency and path were observed. Infarct volumes did not differ between groups. 17beta-estradiol-treated EE-housed rats had significantly higher NGFI-A mRNA expression bilaterally in the cornu ammonis 1 region and in the ipsilateral dentate gyrus of the hippocampus, compared with placebo-treated EE-housed rats. In conclusion, 17beta-estradiol treatment combined with an EE improved recovery of cognitive function after experimental brain ischemia, putatively through the upregulation of NGFI-A in hippocampal subregions.

Expression of the nerve growth factor-induced gene B-.BETA. in the developing rat brain and retina

The nerve growth factor-induced gene B-beta (NGFI-Bbeta, Nurr1) is a member of the nuclear receptor superfamily that is expressed predominantly in the central nervous system. We used an antibody against the human NGFI-Bbeta to observe the protein expression in neuronal cells in the retina, cerebral neocortex, and midbrain of humans and rats. To provide further insight into the role of NGFI-Bbeta in the differentiation of neuronal cells, we also examined the expression of NGFI-Bbeta in rat ontogeny. A few cells in the midbrain showed the expression of NGFIBbeta from 12 days of gestation, and NGFI-Bbeta positive cells increased in the neocortex, claustrum, thalamus and hypothalamus in the subsequent fetal days. NGFI-Bbeta-positive cells appeared in the inner nuclear layer of the retina at 18 days of gestation and also in the ganglion cell layer after birth. An immunohistochemical study on the expression of proliferating cell nuclear antigen (PCNA) demonstrated that NGFI-Bbeta-positive cells were not proliferating cells. These findings suggest that NGFI-Bbeta plays an important role during the postmitotic differentiation of neuronal cells in the brain and retina.

Ca2+/Calmodulin Kinase Kinase α Is Dispensable for Brain Development but Is Required for Distinct Memories in Male, though Not in Female, Mice

In neurons, the Ca(2+)/calmodulin (CaM) kinase cascade transduces Ca(2+) signaling into gene transcription. The CaM kinase cascade is known to be important for brain development as well as memory formation in adult brain, although the functions of some cascade members remain unknown. Here we have generated null and hypomorphic mutants to study the physiological role of CaM kinase kinase alpha (CaMKKalpha), which phosphorylates and activates both CaM kinase I (CaMKI) and CaMKIV, the output kinases of the cascade. We show that CaMKKalpha is dispensable for brain development and long-term potentiation in adult hippocampal CA1 synapses. We find that CaMKKalpha is required for hippocampus-dependent contextual fear memory, but not spatial memory, formation. Surprisingly, CaMKKalpha is important for contextual fear memory formation in males but not in females. We show that in male mice, contextual fear conditioning induces up-regulation of hippocampal mRNA expression of brain-derived neurotrophic factor (BDNF) in a way that requires CaMKKalpha, while in female mice, contextual fear conditioning induces down-regulation of hippocampal BDNF mRNA expression that does not require CaMKKalpha. Additionally, we demonstrate sex-independent up-regulation in hippocampal nerve growth factor-inducible gene B mRNA expression that does not require CaMKKalpha. Thus, we show that CaMKKalpha has a specific complex role in memory formation in males.

Males Afraid, Females Brave

There are different kinds of memories. In mice, differences have been noted in contextual fear memory formation and spatial memory formation, although both forms of memory appear to involve a calcium signal and the activation of calcium/calmodulin-dependent kinases (CaMKs). In mice, there are two isoforms of CaMK that have been implicated in memory formation (CaMKI and CaMKIV) and two upstream kinases that phosphorylate CaMK (CaM kinase kinases: CaMKKα and CaMKKβ). CaMKKβ has been implicated in spatial memory formation, and CaMKIV has been implicated in long-term potentiation and fear conditioning. Two groups, Blaeser et al . and Mizuno et al ., created mice deficient in CaMKKα function and found that the mice showed normal spatial memory, normal motor activity, and normal sensory perception; however, male mice were impaired in the formation of contextual fear memories. Synaptic transmission was not impaired in the CamKKα-deficient mice, nor was formation of hippocampal long-term potentiation. Blaeser et al . showed that, compared with wild-type mice, the CamKKα-deficient male mice exhibited decreased phosphorylation of CaMKIV and the transcriptional regulator CREB (a substrate of CaMKIV) in response to fear conditioning. Phosphorylation of CREB under basal conditions was increased in the mutant mice in certain brain regions; however, the fear-induced increases in phosphorylation were absent. Mizuno et al . investigated memory formation in both male and female mice deficient for CaMKKα and noted that females did not show impairment of contextual fear conditioning. (It was known that female mice tend to exhibit contextual fear conditioning to a lesser extent than do male mice.) In wild-type mice, contextual fear conditioning promoted an increase in brain-derived neurotrophic factor (BDNF) in males only and a decrease in BDNF in females (transcript abundance was measured by real-time polymerase chain reaction). In the CaMKKα-deficient mice, the increase in BDNF in males was compromised, but the decrease in females was unaffected. The gene encoding BDNF is a CREB target; however, expression of another gene regulated by CREB, the gene encoding nerve growth factor-inducible gene B (NGF-1B), was increased in response to fear conditioning in both males and females and was not affected by lack of CaMKKα. Thus, in addition to specific forms of memory requiring specific signaling cascades, there is an additional gender-specific layer of regulation. F. Blaeser, M. J. Sanders, N. Truong, S. Ko, L. J. Wu, D. F. Wozniak. M. S. Fanselow, M. Zhuo, T. A. Chatila, Long-term memory deficits in Pavlovian fear conditioning in Ca 2+ /calmodulin kinase kinase α-deficient mice. Mol. Cell. Biol. 26 , 9105-9115 (2006). [Abstract] [Full Text] K. Mizuno, L. Ris, A. Sánchez-Capelo, E. Godaux, K. P. Giese, Ca 2+ /calmodulin kinase kinase α is dispensable for brain development but is required for distinct memories in male, though not in female, mice. Mol. Cell. Biol. 26 , 9094-9104 (2006). [Abstract] [Full Text]

Alpha-isoform of Ca2+/calmodulin-dependent kinase II autophosphorylation is required for memory consolidation-specific transcription

Autophosphorylation of the alpha-isoform of Ca2+/calmodulin-dependent kinase II switches the kinase into an autonomous activity mode. This molecular switch is important for hippocampal long-term memory formation, which requires de novo gene transcription and protein synthesis. Here, we have studied whether auto-phosphorylation of the alpha-isoform of Ca2+/calmodulin-dependent kinase II is required for gene transcription induced in the hippocampus by contextual fear conditioning. We have shown that upregulation of a nonassociative transcript, the serum and glucocorticoid-induced kinase-1 messenger RNA, is normal in alpha-isoform of Ca2+/calmodulin-dependent kinase II autophosphorylation-deficient mutant mice, whereas upregulation of an associative transcript, the nerve growth factor-inducible gene B messenger RNA, is impaired. Thus, we suggest that autophosphorylation of the alpha-isoform of Ca2+/calmodulin-dependent kinase II is a biochemical switch that regulates association-specific consolidation processes.

Enriched Environment Enhances Recovery of Motor Function after Focal Ischemia in Mice, and Downregulates the Transcription Factor NGFI-A

The purpose of this study was to investigate the effect of enriched environment on motor function after experimental stroke in mice, and to determine whether time in enriched environment affects functional recovery. Earlier investigations have shown that rats placed in an enriched environment after focal ischemia, remarkably improve motor function, but similar observations in mice have not been reported. In this study, we show that placing mice in an enriched environment for 3 h daily for 2 weeks, after transient (50 mins) occlusion of the middle cerebral artery, enhanced neurologic outcome. Continuous postischemic housing in the enriched environment likewise improved motor function, but mortality increased. Two weeks exposure to enriched environment followed by housing the mice in standard cages for 2 weeks, resulted in a loss of the improved motor function. In contrast, 4 weeks exposure to enriched environment led to an improved motor function and to a better maintenance of neurologic recovery. The expression levels of the immediate-early gene nerve growth factor-induced gene A at 2 to 3 weeks of recovery decreased in animals housed in enriched environment, implying this transcription factor in the recovery process. We conclude that housing mice in an enriched environment after experimental stroke improves functional outcome. Also, the presented experimental procedure is useful for further studies of the genomics of functional recovery after experimental stroke.

Memory Reconsolidation Engages Only a Subset of Immediate-Early Genes Induced during Consolidation

The relationship between memory consolidation and reconsolidation at the molecular level is poorly understood. Here, we identify three immediate-early genes that are differentially regulated in the mouse hippocampus after contextual fear conditioning and reactivation of the context-shock memory: serum- and glucocorticoid-induced kinase 1 (SGK1), SGK3, and nerve growth factor-inducible gene B (NGFI-B). The upregulation of SGK1 expression was not specific for the context-shock association and therefore not suitable for a comparison of contextual memory consolidation and reconsolidation. SGK3 expression was upregulated during both consolidation and reconsolidation. Analysis of SGK3 expression showed that expression changes elicited by a context-shock association during consolidation can subsequently be recapitulated during reconsolidation and that the transcriptional changes induced by retrieval depend on the remoteness of the memory. On the other hand, we found that NGFI-B is regulated during consolidation but not reconsolidation. This consolidation-specific regulation occurs in hippocampal area CA1. Our discovery of a consolidation-specific transcription indicates that reconsolidation is only a partial recapitulation of consolidation at the transcriptional level. Such partial rather than total recapitulation may have evolved as a more economic and reliable mechanism for organisms to modify memory.