Alterations of CaMKII after hypoxia-ischemia during brain development

TRPM7 Mediates Neuronal Cell Death Upstream of Calcium/Calmodulin-Dependent Protein Kinase II and Calcineurin Mechanism in Neonatal Hypoxic-Ischemic Brain Injury

Transient receptor potential melastatin 7 (TRPM7), a calcium-permeable, ubiquitously expressed ion channel, is critical for axonal development, and mediates hypoxic and ischemic neuronal cell death in vitro and in vivo. However, the downstream mechanisms underlying the TRPM7-mediated processes in physiology and pathophysiology remain unclear. In this study, we employed a mouse model of hypoxic-ischemic brain cell death which mimics the pathophysiology of hypoxic-ischemic encephalopathy (HIE). HIE is a major public health issue and an important cause of neonatal deaths worldwide; however, the available treatments for HIE remain limited. Its survivors face life-long neurological challenges including mental retardation, cerebral palsy, epilepsy and seizure disorders, motor impairments, and visual and auditory impairments. Through a proteomic analysis, we identified calcium/calmodulin-dependent protein kinase II (CaMKII) and phosphatase calcineurin as potential mediators of cell death downstream from TRPM7 activation. Further analysis revealed that TRPM7 mediates cell death through CaMKII, calmodulin, calcineurin, p38, and cofilin cascade. In vivo, we found a significant reduction of brain injury and improvement of short- and long-term functional outcomes after HI after administration of specific TRPM7 blocker waixenicin A. Our data demonstrate a molecular mechanism of TRPM7-mediated cell death and identifies TRPM7 as a promising therapeutic and drug development target for HIE.

Nest-building activity as a reproducible and long-term stroke deficit test in a mouse model of stroke

INTRODUCTION

Neuroprotective therapeutics achieved from animal studies have not been able to translate into clinical stroke therapies. A major reason may be that the functional tests and outcomes between animal stroke studies and clinical trials are significantly different. Ultimately, functional recovery is most important for stroke patients, but it remains challenging to identify animal functional tests that reflect human stroke deficits. This study aimed to explore whether the nest-building activity can be used as a functional test of mouse stroke deficit.

METHODS

Forty-one C57B6 male mice were randomly assigned into a sham-operated control group and 20-, 40- and 60-min middle cerebral artery occlusion (MCAO) groups. Mice were perfusion-fixed at 21 days following sham surgery or MCAO. Infarct volumes were assessed under the light microscopy. The nest-building activity was characterized and quantitatively evaluated.

RESULTS

The results show that only a small portion of striatum was damaged after 20-min MCAO. The brain damage areas were expanded from striatum to the neocortex and hippocampus proportionally after 40-min and 60-min MCAO, respectively. Consistently, relative to that of the sham-operated mice, the nest-building activity was insignificantly altered after 20-min MCAO, but dramatically and significantly reduced proportionally following 40-min and 60-min MCAO, respectively. The nest-building deficit was a long-lasting event and could be seen for as long as 14-21 days of recovery, the longest endpoint of this study.

CONCLUSIONS

The results suggest that the nest-building activity may be a novel, objective, easy to use, highly sensitive, and long-lasting test that may reflect the multifaceted sensorimotor and cognitive deficits after stroke in humans. Our findings may provide a novel multifaceted test for bridging the gap between animal stroke studies and clinical trials.

Dysfunction of Membrane Trafficking Leads to Ischemia-Reperfusion Injury After Transient Cerebral Ischemia

Neurons require an extraordinarily high level of membrane trafficking activities because of enriched axonal terminals and dendritic branches. For that reason, defects in the membrane trafficking pathway are a hallmark of most, and may be all, neurodegenerative disorders. A major cellular membrane trafficking pathway is the Golgi apparatus (Golgi hereafter)-late endosome-lysosome axis for supplying lysosomal enzymes. This pathway is regulated by N-ethylmaleimide-sensitive factor (NSF) ATPase. This review article is to discuss a novel hypothesis that brain ischemia inactivates NSF ATPase, resulting in a cascade of events of disruption of the Golgi-endosome-lysosome pathway, release of cathepsin B (CTSB), and induction of mitochondrial outer membrane permeabilization (MOMP) during the postischemic phase. This hypothesis is supported by recent studies demonstrating that NSF is trapped into inactive protein aggregates in neurons destined to die after brain ischemia. Consequently, Golgi, transport vesicles (TVs), and late endosomes (LEs) are accumulated and damaged, which is followed by CTSB release from these damaged structures. Moderate release of CTSB cleaves Bax-like BH3 protein (Bid) to become active truncated Bid (tBid). Active tBid is then translocated to the mitochondrial outer membrane, resulting in oligomerization of BCL2-associated X protein (Bax) forming the mitochondrial outer membrane pores, and releasing mitochondrial intramembranous proteins. Extensive CTSB release, however, can digest cellular proteins indiscriminately to induce cell death. Based on these new observations, we propose a novel hypothesis, i.e., brain ischemia leads to NSF inactivation, resulting in a massive buildup of damaged Golgi, TVs and LEs, fatal release of CTSB, induction of MOMP, and eventually brain ischemia-reperfusion injury.

Paeoniflorin Attenuates Cerebral Ischemia-Induced Injury by Regulating Ca2+/CaMKII/CREB Signaling Pathway

Paeoniflorin (PF) is an active ingredient of Paeoniae Radix which possesses the neuroprotective effect. However, so far, the neuroprotective mechanism of PF has still not been fully uncovered. The Ca²⁺/Ca²⁺/calmodulin-dependent protein kinase II (CaMKII)/cAMP response element-binding (CREB) signaling pathway plays an important role in the intracellular signal transduction pathway involved in cell proliferation, cell survival, inflammation and metabolism. Herein, the neuroprotective roles of PF in the models of middle cerebral artery occlusion (MCAO) followed by reperfusion in rats and N-methyl-d-aspartic acid (NMDA)-induced excitotoxicity in primary hippocampal neurons were investigated. Moreover, we attempted to confirm the hypothesis that its protection effect is via the modulation of the Ca²⁺/CaMKI)/CREB signaling pathway. In this study, PF not only significantly decreased neurological deficit scores and infarct volume in vivo, but also improved neurons’ cell viability, and inhibited neurons’ apoptosis and intracellular Ca²⁺ concentration in vitro. Furthermore, PF significantly up-regulated p-CREB and p-CaMKII, and down-regulated calmodulin (CaM) in vivo and in vitro. The results indicate that the protective effect of PF on cerebral ischemia reperfusion injury is possible through regulating the Ca²⁺/CaMKII/CREB signaling pathway.

Bryonolic Acid, a Triterpenoid, Protect Against N-methyl-d-Aspartate-Induced Neurotoxicity in PC12 Cells

Calcium overload is considered to be one of the mechanisms of cerebral ischemia. Ca(2+) influx and Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and cAMP response element-binding protein (CREB) phosphorylation are considered to be involved in N-Methyl-d-aspartate (NMDA)-induced apoptosis process. This study investigated the neuroprotective effects of bryonolic acid (BA) in an NMDA-induced rat adrenal pheochromocytoma cell line (PC12) cells and the potential mechanism. PC12 was treated by NMDA to establish an excitotoxicity model. BA (110,100 and 1000 μM final concentration) was added to the medium 24 h prior to the addition of NMDA. Subsequently, a methyl thiazolyl tetrazolium (MTT) assay and a lactate dehydrogenase (LDH) release were performed. Ca(2+) concentration was demonstrated using a scanning-dual wavelength fluorimetric method. In addition, protein and mRNA levels were determined via Western blot and real-time PCR. In the presence of BA, MTT assay and LDH assay showed that more cells were viable in comparison with the NMDA group. Moreover, the concentration of Ca(2+) decreased with the addition of BA in culture. Furthermore, BA could upregulate protein expressions of Bcl-2, p-CREB, and p-CaMKII and downregulate protein expression of Bax. The mRNA results showed that the pattern of mRNA expression were similar to their respective protein levels. All these results indicate that BA protected PC12 cells against NMDA-induced apoptosis by inhibiting Ca(2+) influx and regulating gene expression in the Ca(2+)-CaMKII-CREB signal pathway. Therefore, the present study supports the notion that BA may be a promising neuroprotective agent for the treatment of cerebral ischemia disease.

Fragile X Syndrome FMRP Co-localizes with Regulatory Targets PSD-95, GABA Receptors, CaMKIIα, and mGluR5 at Fiber Cell Membranes in the Eye Lens

Fmr1 and FMRP underlie Fragile X Syndrome (FXS) and are linked with related autism spectrum disorders (ASD). Fmr1 also has an essential role in eye and lens development. Lenses express FMRP along with γ-aminobutyric acid (GABA) receptors (GABARs), post-synaptic density protein 95 (PSD-95), Tyr-phosphatase STEP, CaMKIIα and Alzheimer's disease Aβ precursor protein, which are verified targets of FMRP regulation in neurons and outline major topics in FXS/ASD research. PSD-95 as well as CaMKIIα transcripts undergo polypryimidine tract binding protein dependent alternative splicing in lens, consistent with PSD-95 translation in lens. At least 13 GABAR subunits and GAD25/65/67 GABA metabolism enzymes are expressed in lenses beginning in embryonic development, matching neural development. Interestingly, GABAergic drugs (e.g. baclofen) studied as FXS/ASD therapeutics are shown to resolve developmental vision defects in experimental myopia. Here, we demonstrated that FMRP co-localizes at fiber cell membranes with PSD-95, GABAAδ, GABAAβ3, GABBR1, STEP, CaMKIIα, and mGluR5 in young adult lenses. GAD65 and GABA detection was greatest at the peri-nuclear lens region where fiber cell terminal differentiation occurs. These findings add to an extensive list of detailed parallels between fiber cell and neuron morphology and their lateral membrane spine/protrusions, also reflected in the shared expression of genes involved in the morphogenesis and function of these membrane structures, and shared use of associated regulatory mechanisms first described as distinguishing the neuronal phenotype. Future studies can determine if GABA levels currently studied as a FXS/ASD biomarker in the brain, and generated by GAD25/65/67 in a comparable cell environment in the lens, may be similarly responsive to Fmr1 mutation in lens. The present demonstration of FMRP and key regulatory targets in the lens identifies a potential for the lens to provide a new research venue, in the same individual, to inform about Fmr1/FMRP pathobiology in brain as well as lens.

Curcumin Inhibits Neuronal Loss in the Retina and Elevates Ca²⁺/Calmodulin-Dependent Protein Kinase II Activity in Diabetic Rats

PURPOSE

To determine whether curcumin offers neuroprotection to minimize the apoptosis of neural cells in the retina of diabetic rats.

METHODS

Streptozotocin (STZ)-induced diabetic rats and control rats were used in this study. A subgroup of STZ-induced diabetic rats were treated with curcumin for 12 weeks. Retinal histology, apoptosis of neural cells in the retina, electroretinograms, and retinal glutamate content were evaluated after 12 weeks. Retinal levels of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII), phospho-CaMKII (p-CaMKII), and cleaved caspase-3 were determined by Western blot analysis.

RESULTS

The amplitudes a-wave, b-wave, and oscillatory potential were reduced by diabetes, but curcumin treatment suppressed this reduction of amplitudes. Curcumin also prevented cell loss from the outer nuclear, inner nuclear, and ganglion cell layers. Apoptosis of retinal neurons was detected in diabetic rats. The concentration of glutamate in the retina was higher in diabetic rats, but was significantly reduced in the curcumin-treated group. Furthermore, p-CaMKII and cleaved caspase-3 expression were upregulated in the diabetic retina, but reduced in curcumin-treated rats.

CONCLUSIONS

Curcumin attenuated diabetes-induced apoptosis in retinal neurons by reducing the glutamate level and downregulating CaMKII. Thus, curcumin might be used to prevent neuronal damage in the retina of patients with diabetes mellitus.

Development-dependent regulation of molecular chaperones after hypoxia-ischemia

Cellular stress response after hypoxia-Ischemia (HI) may be substantially different between immature and mature brains. To study this phenomenon, postnatal day 7 (P7) and P26 rats were subjected to HI followed by different periods of recovery. Nuclear accumulation of heat-shock transcription factor-1 (HSF1) and expression of molecular chaperone proteins and mRNAs were analyzed by in situ hybridization, Western blotting and confocal microscopy. Nuclear accumulation of HSF1 protein and induction of hsp70 mRNA occurred dramatically in P26 neurons, but minimally in P7 neurons and moderately in microglial cells after HI. Consistently, the level of HSF1 was significantly higher in P26 brain samples, compared with that in P7 brain. Translation of hsp70 mRNA into proteins in P26 mature neurons was seen at 4h and peaked at 24h, when some neurons had already died after HI. Induction of ER glucose-regulated protein-78 (grp78) and mitochondrial hsp60 mRNAs and proteins was moderate and occurred also only in P26 mature brain after HI. These results suggest that the cellular stress response after HI is development-dependent, being pronounced in mature but virtually negligible in neonatal neurons. Therefore, the effectiveness of therapeutic strategies targeting the stress pathway against HI may be significantly different between immature and mature brains. The delayed induction of molecular chaperones in mature brain may be somewhat late for protecting HI neurons from acute HI injury.

Excitotoxic insult results in a long-lasting activation of CaMKIIα and mitochondrial damage in living hippocampal neurons

Over-activation of excitatory NMDA receptors and the resulting Ca2+ overload is the main cause of neuronal toxicity during stroke. CaMKII becomes misregulated during such events. Biochemical studies show either a dramatic loss of CaMKII activity or its persistent autonomous activation after stroke, with both of these processes being implicated in cell toxicity. To complement the biochemical data, we monitored CaMKII activation in living hippocampal neurons in slice cultures using high spatial/temporal resolution two-photon imaging of the CaMKIIα FRET sensor, Camui. CaMKII activation state was estimated by measuring Camui fluorescence lifetime. Short NMDA insult resulted in Camui activation followed by a redistribution of its protein localization: an increase in spines, a decrease in dendritic shafts, and concentration into numerous clusters in the cell soma. Camui activation was either persistent (> 1-3 hours) or transient (~20 min) and, in general, correlated with its protein redistribution. After longer NMDA insult, however, Camui redistribution persisted longer than its activation, suggesting distinct regulation/phases of these processes. Mutational and pharmacological analysis suggested that persistent Camui activation was due to prolonged Ca2+ elevation, with little impact of autonomous states produced by T286 autophosphorylation and/or by C280/M281 oxidation. Cell injury was monitored using expressible mitochondrial marker mito-dsRed. Shortly after Camui activation and clustering, NMDA treatment resulted in mitochondrial swelling, with persistence of the swelling temporarily linked to the persistence of Camui activation. The results suggest that in living neurons excitotoxic insult produces long-lasting Ca2+-dependent active state of CaMKII temporarily linked to cell injury. CaMKII function, however, is to be restricted due to strong clustering. The study provides the first characterization of CaMKII activation dynamics in living neurons during excitotoxic insults.

Conditional deletion of α-CaMKII impairs integration of adult-generated granule cells into dentate gyrus circuits and hippocampus-dependent learning

New granule cells are continuously integrated into hippocampal circuits throughout adulthood, and the fine-tuning of this process is likely important for efficient hippocampal function. During development, this integration process is critically regulated by the α-calcium/calmodulin-dependent protein kinase II (α-CaMKII), and here we ask whether this role is conserved in the adult brain. To do this, we developed a transgenic strategy to conditionally delete α-CaMKII from neural progenitor cells and their progeny in adult mice. First, we found that the selective deletion of α-CaMKII from newly generated dentate granule cells led to an increase in dendritic complexity. Second, α-CaMKII deletion led to a reduction in number of mature synapses and cell survival. Third, consistent with altered morphological and synaptic development, acquisition of one-trial contextual fear conditioning was impaired after deletion of α-CaMKII from newly generated dentate granule cells. Previous work in Xenopus identified α-CaMKII as playing a key role in the stabilization of dendritic and synaptic structure during development. The current study indicates that α-CaMKII plays a plays a similar, cell-autonomous role in the adult hippocampus and, in addition, reveals that the loss of α-CaMKII from adult-generated granule cells is associated with impaired hippocampus-dependent learning.

Characterization of the ubiquitin-modified proteome regulated by transient forebrain ischemia

Ubiquitylation is a posttranslational protein modification that modulates various cellular processes of key significance, including protein degradation and DNA damage repair. In animals subjected to transient cerebral ischemia, ubiquitin-conjugated proteins accumulate in Triton-insoluble aggregates. Although this process is widely considered to modulate the fate of postischemic neurons, few attempts have been made to characterize the ubiquitin-modified proteome in these aggregates. We performed proteomics analyses to identify ubiquitylated proteins in postischemic aggregates. Mice were subjected to 10 minutes of forebrain ischemia and 4 hours of reperfusion. The hippocampi were dissected, aggregates were isolated, and trypsin-digested after spiking with GG-BSA as internal standard. K-ɛ-GG-containing peptides were immunoprecipitated and analyzed by label-free quantitative liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis. We identified 1,664 peptides to 520 proteins containing at least one K-ɛ-GG. Sixty-six proteins were highly ubiquitylated, with 10 or more K-ɛ-GG peptides. Based on selection criteria of greater than fivefold increase and P<0.001, 763 peptides to 272 proteins were highly enriched in postischemic aggregates. These included proteins involved in important neuronal functions and signaling pathways that are impaired after ischemia. Results of this study could serve as an important platform to uncover the mechanisms linking insoluble ubiquitin aggregates to the functions of postischemic neurons.

Ca²⁺/calmodulin-dependent protein kinase II contributes to hypoxic ischemic cell death in neonatal hippocampal slice cultures

We have recently shown that p38MAP kinase (p38MAPK) stimulates ROS generation via the activation of NADPH oxidase during neonatal hypoxia-ischemia (HI) brain injury. However, how p38MAPK is activated during HI remains unresolved and was the focus of this study. Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) plays a key role in brain synapse development, neural transduction and synaptic plasticity. Here we show that CaMKII activity is stimulated in rat hippocampal slice culture exposed to oxygen glucose deprivation (OGD) to mimic the condition of HI. Further, the elevation of CaMKII activity, correlated with enhanced p38MAPK activity, increased superoxide generation from NADPH oxidase as well as necrotic and apoptotic cell death. All of these events were prevented when CaMKII activity was inhibited with KN93. In a neonatal rat model of HI, KN93 also reduced brain injury. Our results suggest that CaMKII activation contributes to the oxidative stress associated with neural cell death after HI.

Bi-directional regulation of CaMKIIα phosphorylation at Thr286 by NMDA receptors in cultured cortical neurons

The N-methyl-D-aspartate (NMDA) receptor (NMDAR)-stimulated autophosphorylation of calmodulin-dependent kinase IIα at Thr286 may regulate many aspects of neuroplasticity. Here, we show that low NMDA concentration (20 μM) up-regulated Thr286 phosphorylation, and high concentration (100 μM) caused dephosphorylation. We next modulated the strength of NMDAR activation by manipulating NMDAR 2A subunit (NR2A) and NMDAR 2B subunit (NR2B), which represent the major NMDAR subtypes in forebrain regions. Pharmacological inhibition and molecular knockdown of NR2A or NR2B blocked 20 μM NMDA-induced phosphorylation. Conversely, over-expression of NR2A or NR2B enhanced phosphorylation by 20 μM NMDA. The 100 μM NMDA-induced dephosphorylation was suppressed by inhibition or knockdown of NR2A or NR2B, and enhanced by over-expression of NR2A or NR2B. Compared to NR2A, NR2B showed a higher impact on the NMDA-stimulated bi-directional regulation of Thr286 phosphorylation. We further found that activation of NR2A and NR2B by 100 μM NMDA-induced dephosphorylation through protein phosphatases (PP) that are inhibited by high concentration okadaic acid (1 μM), but not by PP2A and PP2B inhibitors. This novel function of NMDAR in dynamic regulation of calmodulin-dependent kinase IIα activity provides new evidence to support the current understanding that, depending on the degree of activation, NMDAR may lead to different and even opposing effects on intracellular signaling.

CaMKII antisense oligodeoxynucleotides protect against ischemia-induced neuronal death in the rat hippocampus

The present study was performed to investigate the effects of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) antisense oligodeoxynucleotides (ODNs) on the assembly of the CaMKII·GluR6·PSD-95 signaling module, GluR6 serine phosphorylation and c-Jun N-terminal kinase 3 (JNK3) activation. A further aim was to determine the neuroprotective mechanism of CaMKII antisense ODNs against ischemia-reperfusion (I/R)-induced neuronal death in the rat hippocampus. CaMKII antisense ODNs were intracerebroventricularly infused to inhibit CaMKII expression once daily for 3 days prior to the induction of ischemia. Transient cerebral ischemia (15 min) and reperfusion were induced by four-vessel occlusion in Sprague-Dawley rats as an animal model for transient cerebral I/R. The expression of related proteins was examined by immunoprecipitation and immunoblotting. Neuronal death in the rat hippocampus was detected by histology and histochemistry. The results indicate that CaMKII antisense ODNs inhibit several of the processes that are normally induced by cerebral I/R, including CaMKII expression, increased CaMKII·GluR6·PSD-95 signaling module assembly, GluR6 serine phosphorylation and JNK3 activation. Alternatively, CaMKII antisense ODNs also exhibit a significant neuroprotective role against cerebral I/R-induced cell death. These results provide the first evidence that CaMKII antisense ODNs can exert neuroprotective effects on cerebral I/R-induced cell death. The possible molecular mechanisms underlying this effect include 1) an inhibition of CaMKII expression and subsequent suppression of the assembly of the CaMKII·GluR6·PSD-95 signaling module, 2) GluR6 serine phosphorylation, and 3) reduced JNK3 activation.

Effect of maternal administration of allopregnanolone before birth asphyxia on neonatal hippocampal function in the spiny mouse

Clinically, treatment options where fetal distress is anticipated or identified are limited. Allopregnanolone is an endogenous steroid, that positively modulates the GABA(A) receptor, and that has anti-apoptotic and anti-excitotoxic actions, reducing brain damage in adult animal models of brain injury. We sought to determine if prophylactic treatment of the pregnant female with a single dose of this steroid could reduce birth asphyxia-induced losses in hippocampal function at 5 days of age (P5) in spiny mouse neonates (Acomys cahirinus). At 37 days gestation (term=39 days) and 1h before inducing birth asphyxia, spiny mice dams were injected subcutaneously (0.2 ml) with either 3mg/kg allopregnanolone or 20% w/v β-cyclodextrin vehicle. One hour later, fetuses were either delivered immediately by caesarean section (control group) or exposed to 7.5 min of in utero asphyxia, causing acidosis and hypoxia. At P5, ex vivo hippocampal plasticity was assessed, or brains collected to determine cell proliferation (proliferating cell nuclear antigen; PCNA) or calcium channel expression (inositol trisphosphate receptor type 1; IP(3)R1) using immunohistochemistry. Allopregnanolone partially prevented the decrease in long term potentiation at P5, and the asphyxia-induced increase in IP(3)R1 expression in CA1 pyramidal neurons. There was no effect of allopregnanolone on the asphyxia induced impairment of the input/output (I/O) curve and paired-pulse facilitation (PPF). In control birth pups, maternal allopregnanolone treatment caused significant changes in short term post-synaptic plasticity and also reduced hippocampal proliferation at P5. These findings show that allopregnanolone can modulate hippocampal development and synaptic function in a normoxic or hypoxic environment, possibly by modifying calcium metabolism. Best practice for treatment dose and timing of treatment will need to be carefully considered.

Effects of birth asphyxia on neonatal hippocampal structure and function in the spiny mouse

Studies of human neonates, and in animal experiments, suggest that birth asphyxia results in functional compromise of the hippocampus, even when structural damage is not observable or resolves in early postnatal life. The aim of this study was to determine if changes in hippocampal function occur in a model of birth asphyxia in the precocial spiny mouse where it is reported there is no major lesion or infarct. Further, to assess if, as in human infants, this functional deficit has a sex-dependent component. At 37 days gestation (term=39 days) spiny mice fetuses were either delivered immediately by caesarean section (control group) or exposed to 7.5min of in utero asphyxia causing systemic acidosis and hypoxia. At 5 days of age hippocampal function was assessed ex vivo in brain slices, or brains were collected for examination of structure or protein expression. This model of birth asphyxia did not cause infarct or cystic lesion in the postnatal day 5 (P5) hippocampus, and the number of proliferating or pyknotic cells in the hippocampus was unchanged, although neuronal density in the CA1 and CA3 was increased. Protein expression of synaptophysin, brain-derived neurotrophic factor (BDNF), and the inositol trisphosphate receptor 1 (IP(3)R1) were all significantly increased after birth asphyxia, while long-term potentiation (LTP), paired pulse facilitation (PPF), and post-tetanic potentiation (PTP) were all reduced at P5 by birth asphyxia. In control P5 pups, PPF and synaptic fatigue were greater in female compared to male pups, and after birth asphyxia PPF and synaptic fatigue were reduced to a greater extent in female vs. male pups. In contrast, the asphyxia-induced increase in synaptophysin expression and neuronal density were greater in male pups. Thus, birth asphyxia in this precocial species causes functional deficits without major structural damage, and there is a sex-dependent effect on the hippocampus. This may be a clinically relevant model for assessing treatments delivered either before or after birth to protect this vulnerable region of the developing brain.

Regulation of CaMKII by phospho-Thr253 or phospho-Thr286 sensitive targeting alters cellular function

Calcium/calmodulin-stimulated protein kinase II (CaMKII) is an important mediator of synaptic function that is regulated by multi-site phosphorylation and targeting through interactions with proteins. A new phosphorylation site at Thr253 has been identified in vivo, that does not alter CaMKII activity, but does alter CaMKII function through interactions with binding proteins. To identify these proteins, as well as to examine the specific effects following Thr253 or Thr286 phosphorylation on these interactions, we developed an in vitro overlay binding assay. We demonstrated that the interaction between CaMKII and its binding proteins was altered by the phosphorylation state of both the CaMKII and the partner, and identified a CaMKII-specific sequence that was responsible for the interaction between CaMKII and two interacting proteins. By comparing CaMKII binding profiles in tissue and cell extracts, we demonstrated that the CaMKII binding profiles varied with cell type, and also showed that overexpression of a CaMKII Thr253 phospho-mimic mutant in human neuroblastoma and breast cancer cells dramatically altered the morphology and growth rates when compared to overexpression of non-phosphorylated CaMKII. This data highlights the importance of the microenvironment in regulating CaMKII function, and describes a potentially new mechanism by which the functions of CaMKII can be regulated.

{beta}-Amyloid impairs AMPA receptor trafficking and function by reducing Ca2+/calmodulin-dependent protein kinase II synaptic distribution

A fundamental feature of Alzheimer disease (AD) is the accumulation of beta-amyloid (Abeta), a peptide generated from the amyloid precursor protein (APP). Emerging evidence suggests that soluble Abeta oligomers adversely affect synaptic function, which leads to cognitive failure associated with AD. The Abeta-induced synaptic dysfunction has been attributed to the synaptic removal of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors (AMPARs); however, it is unclear how Abeta induces the loss of AMPARs at the synapses. In this study we have examined the potential involvement of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII), a signaling molecule critical for AMPAR trafficking and function. We found that the synaptic pool of CaMKII was significantly decreased in cortical neurons from APP transgenic mice, and the density of CaMKII clusters at synapses was significantly reduced by Abeta oligomer treatment. In parallel, the surface expression of GluR1 subunit as well as AMPAR-mediated synaptic response and ionic current was selectively decreased in APP transgenic mice and Abeta-treated cultures. Moreover, the reducing effect of Abeta on AMPAR current density was mimicked and occluded by knockdown of CaMKII and blocked by overexpression of CaMKII. These results suggest that the Abeta-induced change in CaMKII subcellular distribution may underlie the removal of AMPARs from synaptic membrane by Abeta.

Calcium/calmodulin-dependent protein kinase II regulates the phosphorylation of CREB in NMDA-induced retinal neurotoxicity

We examined the role of the phosphorylation of calcium/calmodulin-dependent protein kinase II (CaMKII) and cyclic AMP-response element binding protein (CREB) in N-methyl-d-aspartate (NMDA)-induced neurotoxicity in the rat retina. Western blot analysis showed early elevation of phosphorylated CaMKII (p-CaMKII) protein levels and subsequential elevation of phosphorylated CREB (p-CREB) protein after NMDA injection. Immunohistochemistry showed that p-CaMKII was colocalized with Thy-1-positive retinal ganglion cells (RGCs) after NMDA injection. The increase in the p-CaMKII protein level was significantly inhibited by the preinjection of CaMKII small interfering RNA (siRNA), whereas negative control siRNA did not affect. Moreover, the increase in the p-CREB protein level after NMDA injection was also prevented by preinjection of CaMKII siRNA. In addition, our morphometric study of neurotracer retrograde labeling and Thy-1-positive cells showed that CaMKII siRNA significantly accelerated NMDA-induced RGC loss. Furthermore, the prevention of CREB binding by CRE decoy oligonucleotide also exacerbated RGC loss. These results suggest that the activation of CaMKII may regulate CREB phosphorylation and that the transient phosphorylation of CaMKII and CREB may be a neuroprotective response against NMDA-induced neurotoxicity.

alphaCaMKII autophosphorylation levels differ depending on subcellular localization

Calcium/calmodulin-dependent protein kinase II (CaMKII) has important roles in many processes in the central nervous system. It is enriched at the post-synaptic density (PSD), a localization which is thought to be critical for many of its proposed neuronal functions. In order to better understand the mechanisms that regulate association of CaMKII with the PSD, we compared the levels of autophosphorylation between PSD-associated kinase and kinase in other parts of the neuron. We were surprised to find that alphaCaMKII in a PSD-enriched fraction prepared from recovered hippocampal CA1-minislices had a relatively low level of threonine 286 (T286) phosphorylation and a relatively high level of threonine 305 (T305) phosphorylation. Furthermore, when the minislices were subjected to a treatment that mimics ischemic conditions, there was a significant translocation of alphaCaMKII to the PSD-enriched fraction accompanied with a dramatic reduction in T286 phosphorylation levels throughout the neuron. These findings have important implications for our understanding of the role of autophosphorylation in the localization of CaMKII.

Activation of calcium/calmodulin-dependent protein kinases after traumatic brain injury

A prominent cognitive impairment after traumatic brain injury (TBI) is hippocampal-dependent memory loss. Although the histopathologic changes in the brain are well documented after TBI, the underlying biochemical mechanisms that contribute to memory loss have yet to be thoroughly delineated. Thus, we determined if calcium/calmodulin-dependent protein kinases (CaMKs), known to be necessary for the formation of hippocampal-dependent memories, are regulated after TBI. Sprague-Dawley rats underwent moderate parasagittal fluid-percussion brain injury on the right side of the parietal cortex. The ipsilateral hippocampus and parietal cortex were Western blotted for phosphorylated, activated alpha-calcium/calmodulin-dependent protein kinase II (alpha-CaMKII), CaMKIV, and CaMKI. alpha-Calcium/calmodulin-dependent protein kinase II was activated in membrane subcellular fractions from the hippocampus and parietal cortex 30 mins after TBI. CaMKI and CaMKIV were activated in a more delayed manner, increasing in phosphorylation 1 h after TBI. The increase in activated alpha-CaMKII in membrane fractions was accompanied by a decrease in cytosolic total alpha-CaMKII, suggesting redistribution to the membrane. Using confocal microscopy, we observed that alpha-CaMKII was activated within hippocampal neurons of the dentate gyrus, CA3, and CA1 regions. Two downstream substrates of alpha-CaMKII, the AMPA-type glutamate receptor GluR1, and cytoplasmic polyadenylation element-binding protein, concomitantly increased in phosphorylation in the hippocampus and cortex 1 h after TBI. These results demonstrate that several of the biochemical cascades that subserve memory formation are activated unselectively in neurons after TBI. As memory formation requires activation of CaMKII signaling pathways at specific neuronal synapses, unselective activation of CaMKII signaling in all synapses may disrupt the machinery for memory formation, resulting in memory loss after TBI.