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Sigma-1 receptor knockout impairs neurogenesis in dentate gyrus of adult hippocampus via down-regulation of NMDA receptors.

This study investigated the influence of sigma‐1 receptor (σ1R) deficiency on adult neurogenesis.

Sex-related neurogenesis decrease in hippocampal dentate gyrus with depressive-like behaviors in sigma-1 receptor knockout mice

Male sigma-1 receptor knockout (σ1R(-/-)) mice showed depressive-like phenotype with deficit in the survival of newly generated neuronal cells in the hippocampal dentate gyrus (DG), but female σ1R(-/-) mice did not. The level of serum estradiol (E2) at proestrus or diestrus did not differ between female σ1R(-/-) mice and wild-type (WT) mice. Ovariectomized (OVX) female σ1R(-/-) mice, but not WT mice, presented the same depressive-like behaviors and neurogenesis decrease as male σ1R(-/-) mice. Treatment of male σ1R(-/-) mice with E2 could alleviate the depressive-like behaviors and rescue the neurogenesis decrease. In addition, E2 could correct the decline in the density of NMDA-activated current (INMDA) in granular cells of DG and the phosphorylation of NMDA receptor (NMDAr) subtype 2B (NR2B) in male σ1R(-/-) mice, which was associated with the elevation of Src phosphorylation. The neuroprotection and antidepressant effects of E2 in male σ1R(-/-) mice were blocked by the inhibitor of Src or NR2B. The NMDAr agonist showed also the neuroprotection and antidepressant effects in male σ1R(-/-) mice, which were insensitive to the Src inhibitor. On the other hand, either the deprivation of E2 or the inhibition of Src in female σ1R(-/-) mice rather than WT mice led to a distinct decline in INMDA and NR2B phosphorylation. Similarly, the Src inhibitor could cause neurogenesis decrease and depressive-like behaviors in female σ1R(-/-) mice, but not in WT mice. These results indicate that the σ1R deficiency impairs neurogenesis leading to a depressive-like phenotype, which is alleviated by the neuroprotection of E2.

Sigma-1 (σ1) receptor deficiency reduces β-amyloid25–35-induced hippocampal neuronal cell death and cognitive deficits through suppressing phosphorylation of the NMDA receptor NR2B

In early Alzheimers disease (AD) brain, reduction of sigma-1 receptors (σ1R) is detected. In this study, we employed male heterozygous σ1R knockout (σ1R(+/-)) mice showing normal cognitive performance to investigate association of σ1R deficiency with AD risk. Herein we report that a single injection (i.c.v.) of Aβ(25-35) impaired spatial memory with approximately 25% death of pyramidal cells in the hippocampal CA1 region of WT mice (Aβ(25-35)-WT mice), whereas it did not cause such impairments in σ1R(+/-) mice (Aβ(25-35)-σ1R(+/-) mice). Compared with WT mice, Aβ(25-35)-WT mice showed increased levels of NMDA-activated currents (INMDA) and NR2B phosphorylation (phospho-NR2B) in the hippocampal CA1 region at 48 h after Aβ25-35-injection (post-Aβ(25-35)) followed by approximately 40% decline at 72 h post-Aβ(25-35) of their respective control levels, which was inhibited by the σ1R antagonist NE100. In Aβ(25-35)-WT mice, the administration of NR2B inhibitor Ro25-6981 or NE100 on day 1-4 post-Aβ(25-35) attenuated the memory deficits and loss of pyramidal cells. By contrast, Aβ(25-35)-σ1R(+/-) mice showed a slight increase in the INMDA density and the phospho-NR2B at 48 h or 72 h post-Aβ25-35 compared to σ1R(+/-) mice. Treatment with σ1R agonist PRE084 in Aβ(25-35)-σ1R(+/-) mice caused the same changes in the INMDA density and the phospho-NR2B as those in Aβ(25-35)-WT mice. Furthermore, Aβ(25-35)-σ1R(+/-) mice treated with the NMDA receptor agonist NMDA or PRE084 on day 1-4 post-Aβ(25-35) showed a loss of neuronal cells and memory impairment. These results indicate that the σ1R deficiency can reduce Aβ(25-35)-induced neuronal cell death and cognitive deficits through suppressing Aβ(25-35)-enhanced NR2B phosphorylation.

Activation of PPARγ Ameliorates Spatial Cognitive Deficits through Restoring Expression of AMPA Receptors in Seipin Knock-Out Mice

A characteristic phenotype of congenital generalized lipodystrophy 2 (CGL2) that is caused by loss-of-function of seipin gene is mental retardation. Here, we show that seipin deficiency in hippocampal CA1 pyramidal cells caused the reduction of peroxisome proliferator-activated receptor gamma (PPARγ). Twelve-week-old systemic seipin knock-out mice and neuronal seipin knock-out (seipin-nKO) mice, but not adipose seipin knock-out mice, exhibited spatial cognitive deficits as assessed by the Morris water maze and Y-maze, which were ameliorated by the treatment with the PPARγ agonist rosiglitazone (rosi). In addition, seipin-nKO mice showed the synaptic dysfunction and the impairment of NMDA receptor-dependent LTP in hippocampal CA1 regions. The density of AMPA-induced current (IAMPA) in CA1 pyramidal cells and GluR1/GluR2 expression were significantly reduced in seipin-nKO mice, whereas the NMDA-induced current (INMDA) and NR1/NR2 expression were not altered. Rosi treatment in seipin-nKO mice could correct the decrease in expression and activity of AMPA receptor (AMPAR) and was accompanied by recovered synaptic function and LTP induction. Furthermore, hippocampal ERK2 and CREB phosphorylation in seipin-nKO mice were reduced and this could be rescued by rosi treatment. Rosi treatment in seipin-nKO mice elevated BDNF concentration. The MEK inhibitor U0126 blocked rosi-restored AMPAR expression and LTP induction in seipin-nKO mice, but the Trk family inhibitor K252a did not. These findings indicate that the neuronal seipin deficiency selectively suppresses AMPAR expression through reducing ERK-CREB activities, leading to the impairment of LTP and spatial memory, which can be rescued by PPARγ activation. SIGNIFICANCE STATEMENT Congenital generalized lipodystrophy 2 (CGL2), caused by loss-of-function mutation of seipin gene, is characterized by mental retardation. By the generation of systemic or neuronal seipin knock-out mice, the present study provides in vivo evidence that neuronal seipin deficiency causes deficits in spatial memory and hippocampal LTP induction. Neuronal seipin deficiency selectively suppresses AMPA receptor expression, ERK-CREB phosphorylation with the decline of PPARγ. The PPARγ agonist rosiglitazone can ameliorate spatial cognitive deficits and rescue the LTP induction in seipin knock-out mice by restoring AMPA receptor expression and ERK-CREB activities.

Postpartum estrogen withdrawal impairs hippocampal neurogenesis and causes depression- and anxiety-like behaviors in mice

Postpartum estrogen withdrawal is known to be a particularly vulnerable time for depressive symptoms. Ovariectomized adult mice (OVX-mice) treated with hormone-simulated pregnancy (HSP mice) followed by a subsequent estradiol benzoate (EB) withdrawal (EW mice) exhibited depression- and anxiety-like behaviors, as assessed by forced swim, tail suspension and elevated plus-maze, while HSP mice, OVX mice or EB-treated OVX mice (OVX/EB mice) did not. The survival and neurite growth of newborn neurons in hippocampal dentate gyrus were examined on day 5 after EW. Compared with controls, the numbers of 28-day-old BrdU(+) and BrdU(+)/NeuN(+) cells were increased in HSP mice but significantly decreased in EW mice; the numbers of 10-day-old BrdU(+) cells were increased in HSP mice and OVX/EB mice; and the density of DCX(+) fibers was reduced in EW mice and OVX mice. The phosphorylation of hippocampal NMDA receptor (NMDAr) NR2B subunit or Src was increased in HSP mice but decreased in EW mice. NMDAr agonist NMDA prevented the loss of 28-day-old BrdU(+) cells and the depression- and anxiety-like behaviors in EW mice. NR2B inhibitor Ro25-6981 or Src inhibitor dasatinib caused depression- and anxiety-like behaviors in HSP mice with the reduction of 28-day-old BrdU(+) cells. The hippocampal BDNF levels were reduced in EW mice and OVX mice. TrkB receptor inhibitor K252a reduced the density of DCX(+) fibers in HSP mice without the reduction of 28-day-old BrdU(+) cells, or the production of affective disorder. Collectively, these results indicate that postpartum estrogen withdrawal impairs hippocampal neurogenesis in mice that show depression- and anxiety-like behaviors.

Lack of JWA Enhances Neurogenesis and Long-Term Potentiation in Hippocampal Dentate Gyrus Leading to Spatial Cognitive Potentiation

JWA (Arl6ip5), a homologous gene of glutamate-transporter-associated protein 3-18 (GTRAP3-18) and addicsin, is highly expressed in hippocampus. We generated systemic and neuronal JWA knockout (JWA-KO and JWA-nKO) mice to investigate the influence of JWA deficiency on spatial cognitive performance, process of neurogenesis, and induction of long-term potentiation (LTP) in hippocampal dentate gyrus (DG). In comparison with wild-type (WT) mice and JWAloxP/loxP (control of JWA-nKO) mice, 8-week-old JWA-KO mice and JWA-nKO mice showed spatial cognitive potentiation as assessed by Morris water maze test. In hippocampal DG of JWA-nKO mice, either survival and migration or neurite growth of newborn neurons were significantly enhanced without the changes in proliferation and differentiation of stem cells. In addition, the increase of LTP amplitude and the decline of LTP threshold were observed in DG, but not in CA1 region, of JWA-nKO mice compared to control mice. The levels of hippocampal FAK, Akt, and mTOR phosphorylation in JWA-nKO mice were higher than those in control mice. The PI3K or FAK inhibitor could abolish the enhanced neurogenesis and LTP induction in JWA-nKO mice, which was accompanied by disappearance of the spatial cognitive potentiation. The treatment of JWA-nKO mice with 3′-azido-3′-deoxythymidine (AZT), a telomerase inhibitor, suppressed not only the enhanced neurogenesis but also the enhanced LTP induction in DG, but it did not affect the LTP induction in CA1 region. The results suggest that the JWA deficiency through cascading FAK-PI3K-Akt-mTOR pathway increases the newborn neurons and enhances the LTP induction in hippocampal DG, which leads to the spatial cognitive potentiation.

Seipin knockout in mice impairs stem cell proliferation and progenitor cell differentiation in the adult hippocampal dentate gyrus via reduced levels of PPARγ.

ABSTRACT The seipin gene (BSCL2) was originally identified in humans as a loss-of-function gene associated with congenital generalized lipodystrophy type 2 (CGL2). Neuronal seipin-knockout (seipin-nKO) mice display a depression-like phenotype with a reduced level of hippocampal peroxisome proliferator-activated receptor gamma (PPARγ). The present study investigated the influence of seipin deficiency on adult neurogenesis in the hippocampal dentate gyrus (DG) and the underlying mechanisms of the effects. We show that the proliferative capability of stem cells in seipin-nKO mice was substantially reduced compared to in wild-type (WT) mice, and that this could be rescued by the PPARγ agonist rosiglitazone (rosi). In seipin-nKO mice, neuronal differentiation of progenitor cells was inhibited, with the enhancement of astrogliogenesis; both of these effects were recovered by rosi treatment during early stages of progenitor cell differentiation. In addition, rosi treatment could correct the decline in hippocampal ERK2 phosphorylation and cyclin A mRNA level in seipin-nKO mice. The MEK inhibitor U0126 abolished the rosi-rescued cell proliferation and cyclin A expression in seipin-nKO mice. In seipin-nKO mice, the hippocampal Wnt3 protein level was less than that in WT mice, and there was a reduction of neurogenin 1 (Neurog1) and neurogenic differentiation 1 (NeuroD1) mRNA, levels of which were corrected by rosi treatment. STAT3 phosphorylation (Tyr705) was enhanced in seipin-nKO mice, and was further elevated by rosi treatment. Finally, rosi treatment for 10 days could alleviate the depression-like phenotype in seipin-nKO mice, and this alleviation was blocked by the MEK inhibitor U0126. The results indicate that, by reducing PPARγ, seipin deficiency impairs proliferation and differentiation of neural stem and progenitor cells, respectively, in the adult DG, which might be responsible for the production of the depression-like phenotype in seipin-nKO mice. Summary: By reducing PPARγ, neuronal seipin deficiency impairs adult neurogenesis in the hippocampal dentate gyrus to produce a depression-like phenotype in mice.

Deficits in cognitive function and hippocampal plasticity in GM2/GD2 synthase knockout mice

In this study, we used GM2/GD2 synthase knockout (GM2/GD2−/−) mice to examine the influence of deficiency in ganglioside “a‐pathway” and “b‐pathway” on cognitive performances and hippocampal synaptic plasticity. Eight‐week‐old GM2/GD2−/− male mice showed a longer escape‐latency in Morris water maze test and a shorter latency in step‐down inhibitory avoidance task than wild‐type (WT) mice. Schaffer collateral‐CA1 synapses in the hippocampal slices from GM2/GD2−/− mice showed an increase in the slope of EPSPs with reduced paired‐pulse facilitation, indicating an enhancement of their presynaptic glutamate release. In GM2/GD2−/− mice, NMDA receptor (NMDAr)‐dependent LTP could not be induced by high‐frequency (100–200 Hz) tetanus or θ‐burst conditioning stimulation (CS), whereas NMDAr‐independent LTP was induced by medium‐frequency CS (20–50 Hz). The application of mono‐sialoganglioside GM1 in the slice from GM2/GD2−/− mice, to specifically recover the a‐pathway, prevented the increased presynaptic glutamate release and 20 Hz‐LTP induction, whereas it could not rescue the impaired NMDAr‐dependent LTP. These findings suggest that b‐pathway deficiency impairs cognitive function probably through suppression of NMDAr‐dependent LTP, while a‐pathway deficiency may facilitate NMDAr‐independent LTP through enhancing presynaptic glutamate release. As both of the NMDAr‐independent LTP and increased presynaptic glutamate release were sensitive to the blockade of L‐type voltage‐gated Ca2+ channels (L‐VGCC), a‐pathway deficiency may affect presynaptic L‐VGCC.

Neurosteroid dehydroepiandrosterone enhances activity and trafficking of astrocytic GLT-1 via σ1 receptor-mediated PKC activation in the hippocampal dentate gyrus of rats.

Neurosteroid dehydroepiandrosterone (DHEA) has been reported to exert a potent neuroprotective effect against glutamate‐induced excitotoxicity. However, the underlying mechanism remains to be elucidated. One of the possible mechanisms may be an involvement of astrocytic glutamate transporter subtype‐1 (GLT‐1) that can quickly clear spilled glutamate at the synapse to prevent excitotoxicity. To examine the effect of DHEA on GLT‐1 activity, we measured synaptically induced glial depolarization (SIGD) in the dentate gyrus (DG) of adult rats by applying an optical recording technique to the hippocampal slices stained with voltage‐sensitive dye RH155. Bath‐application of DHEA for 10 min dose‐dependently increased SIGD without changing presynaptic glutamate releases, which was sensitive to the GLT‐1 blocker DHK. Patch‐clamp recordings in astrocytes showed that an application of 50 μM DHEA increased glutamate‐evoked inward currents (Iglu) by approximately 1.5‐fold, which was dependent on the GLT‐1 activity. In addition, the level of biotinylated GLT‐1 protein in the surface of astrocytes was significantly elevated by DHEA. The DHEA‐increased SIGD, Iglu, and GLT‐1 translocation to the cell surface were blocked by the σ1R antagonist NE100 and mimicked by the σ1R agonist PRE084. DHEA elevated the phosphorylation level of PKC in a σ1R‐dependent manner. Furthermore, the PKC inhibitor chelerythrine could prevent the DHEA‐increased SIGD, Iglu, and GLT‐1 translocation. Collectively, present results suggest that DHEA enhances the activity and translocation to cell surface of astrocytic GLT‐1 mainly via σ1R‐mediated PKC cascade.

Sigma-1 receptor deficiency reduces GABAergic inhibition in the basolateral amygdala leading to LTD impairment and depressive-like behaviors

&NA; Sigma‐1 receptor knockout (&sgr;1R−/−) in male mice causes depressive‐like phenotype. We observed the expression of &sgr;1R in principal neurons of basolateral amygdala (BLA), a main region for affective regulation. The present study investigated the influence of &sgr;1R deficiency in BLA neurons on synaptic properties and plasticity at cortico‐BLA pathway. In comparison with wild‐type (WT) mice, the slopes of field excitatory postsynaptic potentials (fEPSP) were reduced in &sgr;1R−/− mice with the increases in paired‐pulse facilitation (PPF) and paired‐pulse inhibition (PPI) values. Induction of NMDA receptor (NMDAr)‐dependent long‐term potentiation (LTP) and NMDAr‐independent long‐term depression (LTD) were impaired in &sgr;1R−/− mice. The NMDAr NR2B phosphorylation in BLA of &sgr;1R−/− mice was lower than in WT mice. The coupling of nNOS to PSD‐95 and nitric oxide (NO) level were reduced in BLA of &sgr;1R−/− mice, which were recovered by the BLA‐injection of NMDAr agonist NMDA. The bath‐application of NMDA in BLA slices from &sgr;1R−/− mice corrected the reduced fEPSP slopes and increased PPF and PPI and recovered the LTP and LTD induction, which were sensitive to nNOS inhibitor 7‐NI. NO donor DETA/NO or GABAAR agonist muscimol could correct the PPI and recover LTD in &sgr;1R−/− mice. In addition, the BLA‐injection of NMDA, DETA/NO or muscimol could relieve the depressive‐like behaviors in &sgr;1R−/− mice. These results indicate that the &sgr;1R deficiency in BLA principal neurons via NMDAr dysfunction suppresses nNOS activity and NO production to reduce GABAAR‐mediated inhibition, which impairs LTD induction and causes depressive‐like phenotype. Highlights&sgr;1R deficiency in BLA neurons reduces nNOS activity via low phosphorylation of NR2B.Reduced NO production in BLA neurons reduces presynaptic glutamate and GABA release.Decline of GABAAR‐mediated inhibition impairs LTD induction in BLA.Impaired LTD in BLA is associated with depressive‐like behaviors in &sgr;1R−/− mice.