BDNF-mediated cerebellar granule cell development is impaired in mice null for CaMKK2 or CaMKIV

Unique genetic loci identified for emotional behavior in control and chronic stress conditions

An individual's genetic background affects their emotional behavior and response to stress. Although studies have been conducted to identify genetic predictors for emotional behavior or stress response, it remains unknown how prior stress history alters the interaction between an individual's genome and their emotional behavior. Therefore, the purpose of this study is to identify chromosomal regions that affect emotional behavior and are sensitive to stress exposure. We utilized the BXD behavioral genetics mouse model to identify chromosomal regions that predict fear learning and emotional behavior following exposure to a control or chronic stress environment. 62 BXD recombinant inbred strains and C57BL/6 and DBA/2 parental strains underwent behavioral testing including a classical fear conditioning paradigm and the elevated plus maze. Distinct quantitative trait loci (QTLs) were identified for emotional learning, anxiety and locomotion in control and chronic stress populations. Candidate genes, including those with already known functions in learning and stress were found to reside within the identified QTLs. Our data suggest that chronic stress history reveals novel genetic predictors of emotional behavior.

Convergent lines of evidence support CAMKK2 as a schizophrenia susceptibility gene

Genes that are differentially expressed between schizophrenia patients and healthy controls may have key roles in the pathogenesis of schizophrenia. We analyzed two large-scale genome-wide expression studies, which examined changes in gene expression in schizophrenia patients and their matched controls. We found calcium/calmodulin (CAM)-dependent protein kinase kinase 2 (CAMKK2) is significantly downregulated in individuals with schizophrenia in both studies. To seek the potential genetic variants that may regulate the expression of CAMKK2, we investigated the association between single-nucleotide polymorphisms (SNPs) within CAMKK2 and the expression level of CAMKK2. We found one SNP, rs1063843, which is located in intron 17 of CAMKK2, is strongly associated with the expression level of CAMKK2 in human brains (P=1.1 × 10(-6)) and lymphoblastoid cell lines (the lowest P=8.4 × 10(-6)). We further investigated the association between rs1063843 and schizophrenia in multiple independent populations (a total of 130 623 subjects) and found rs1063843 is significantly associated with schizophrenia (P=5.17 × 10(-5)). Interestingly, we found the T allele of rs1063843, which is associated with lower expression level of CAMKK2, has a higher frequency in individuals with schizophrenia in all of the tested samples, suggesting rs1063843 may be a causal variant. We also found that rs1063843 is associated with cognitive function and personality in humans. In addition, protein-protein interaction (PPI) analysis revealed that CAMKK2 participates in a highly interconnected PPI network formed by top schizophrenia genes, which further supports the potential role of CAMKK2 in the pathogenesis of schizophrenia. Taken together, these converging lines of evidence strongly suggest that CAMKK2 may have pivotal roles in schizophrenia susceptibility.

Ethanol induced acetylation of histone at G9a exon1 and G9a-mediated histone H3 dimethylation leads to neurodegeneration in neonatal mice

The transient exposure of immature rodents to ethanol during postnatal day 7 (P7), comparable to a time point within the third trimester of human pregnancy, induces neurodegeneration. However, the molecular mechanisms underlying the deleterious effects of ethanol on the developing brain are poorly understood. In our previous study, we showed that a high dose administration of ethanol at P7 enhances G9a and leads to caspase-3-mediated degradation of dimethylated H3 on lysine 9 (H3K9me2). In this study, we investigated the potential role of epigenetic changes at G9a exon1, G9a-mediated H3 dimethylation on neurodegeneration and G9a-associated proteins in the P7 brain following exposure to a low dose of ethanol. We found that a low dose of ethanol induces mild neurodegeneration in P7 mice, enhances specific acetylation of H3 on lysine 14 (H3K14ace) at G9a exon1, G9a protein levels, augments the dimethylation of H3K9 and H3 lysine 27 (H3K27me2). However, neither dimethylated H3K9 nor K27 underwent degradation. Pharmacological inhibition of G9a activity prior to ethanol treatment prevented H3 dimethylation and neurodegeneration. Further, our immunoprecipitation data suggest that G9a directly associates with DNA methyltransferase (DNMT3A) and methyl-CpG-binding protein 2 (MeCP2). In addition, DNMT3A and MeCP2 protein levels were enhanced by a low dose of ethanol that was shown to induce mild neurodegeneration. Collectively, these epigenetic alterations lead to association of G9a, DNMT3A and MeCP2 to form a larger repressive complex and have a significant role in low-dose ethanol-induced neurodegeneration in the developing brain.

Deep sequencing reveals increased DNA methylation in chronic rat epilepsy

Epilepsy is a frequent neurological disorder, although onset and progression of seizures remain difficult to predict in affected patients, irrespective of their epileptogenic condition. Previous studies in animal models as well as human epileptic brain tissue revealed a remarkably diverse pattern of gene expression implicating epigenetic changes to contribute to disease progression. Here we mapped for the first time global DNA methylation patterns in chronic epileptic rats and controls. Using methyl-CpG capture associated with massive parallel sequencing (Methyl-Seq) we report the genomic methylation signature of the chronic epileptic state. We observed a predominant increase, rather than loss of DNA methylation in chronic rat epilepsy. Aberrant methylation patterns were inversely correlated with gene expression changes using mRNA sequencing from same animals and tissue specimens. Administration of a ketogenic, high-fat, low-carbohydrate diet attenuated seizure progression and ameliorated DNA methylation mediated changes in gene expression. This is the first report of unsupervised clustering of an epigenetic mark being used in epilepsy research to separate epileptic from non-epileptic animals as well as from animals receiving anti-convulsive dietary treatment. We further discuss the potential impact of epigenetic changes as a pathogenic mechanism of epileptogenesis.

Inhibition of calcium/calmodulin-dependent protein kinase kinase β and calcium/calmodulin-dependent protein kinase IV is detrimental in cerebral ischemia

BACKGROUND AND PURPOSE

Elevation of intracellular calcium was traditionally thought to be detrimental in stroke pathology. However, clinical trials testing treatments that block calcium signaling have failed to improve outcomes in ischemic stroke. Emerging data suggest that calcium may also trigger endogenous protective pathways after stroke. Calcium/calmodulin-dependent protein kinase kinase (CaMKK) is a major kinase activated by rising intracellular calcium. Compelling evidence has suggested that CaMKK and its downstream kinase CaMK IV are critical in neuronal survival when cells are under ischemic stress. We examined the functional role of CaMKK/CaMK IV signaling in stroke.

METHODS

We used a middle cerebral artery occlusion model in mice.

RESULTS

Our data demonstrated that pharmacological and genetic inhibition of CaMKK aggravated stroke injury. Additionally, deletion of CaMKK β, one of the 2 CaMKK isoforms, reduced CaMK IV activation, and CaMK IV deletion in mice worsened stroke outcome. Finally, CaMKK β or CaMK IV knockout mice had exacerbated blood-brain barrier disruption evidenced by increased hemorrhagic transformation and activation of matrix metalloproteinase. We observed transcriptional inactivation including reduced levels of histone deacetylase 4 phosphorylation in mice with CaMKK β or CaMK IV deletion after stroke.

CONCLUSIONS

Our data have established that the CaMKK/CaMK IV pathway is a key endogenous protective mechanism in ischemia. Our results suggest that this pathway serves as an important regulator of blood-brain barrier integrity and transcriptional activation of neuroprotective molecules in stroke.

CREB phosphorylation regulates striatal transcriptional responses in the self-administration model of methamphetamine addiction in the rat

Neuroplastic changes in the dorsal striatum participate in the transition from casual to habitual drug use and might play a critical role in the development of methamphetamine (METH) addiction. We examined the influence of METH self-administration on gene and protein expression that may form substrates for METH-induced neuronal plasticity in the dorsal striatum. Male Sprague-Dawley rats self-administered METH (0.1mg/kg/injection, i.v.) or received yoked saline infusions during eight 15-h sessions and were euthanized 2h, 24h, or 1month after cessation of METH exposure. Changes in gene and protein expression were assessed using microarray analysis, RT-PCR and Western blots. Chromatin immunoprecipitation (ChIP) followed by PCR was used to examine epigenetic regulation of METH-induced transcription. METH self-administration caused increases in mRNA expression of the transcription factors, c-fos and fosb, the neurotrophic factor, Bdnf, and the synaptic protein, synaptophysin (Syp) in the dorsal striatum. METH also caused changes in ΔFosB, BDNF and TrkB protein levels, with increases after 2 and 24h, but decreases after 1month of drug abstinence. Importantly, ChIP-PCR showed that METH self-administration caused enrichment of phosphorylated CREB (pCREB), but not of histone H3 trimethylated at lysine 4 (H3K4me3), on promoters of c-fos, fosb, Bdnf and Syp at 2h after cessation of drug intake. These findings show that METH-induced changes in gene expression are mediated, in part, by pCREB-dependent epigenetic phenomena. Thus, METH self-administration might trigger epigenetic changes that mediate alterations in expression of genes and proteins serving as substrates for addiction-related synaptic plasticity.

Involvement of CaMKIV in neurogenic effect with chronic fluoxetine treatment

Calcium-calmodulin dependent protein kinase IV (CaMKIV) is a protein kinase that has been suggested to participate in fluoxetine (FLX)-induced phosphorylation of cyclic AMP-response element binding protein (CREB). CREB is a key transcription factor in adult neurogenesis. The present study aimed at evaluating whether CaMKIV is involved in adult hippocampal neurogenesis with FLX treatment. Effects of chronic FLX on hippocampal cell proliferation, survival and phenotypes were assessed using bromodeoxyuridine (BrdU) immunohistochemistry or BrdU/neuronal nuclei (NeuN)/S100β immunofluorescence staining in wild-type (WT) and CaMKIV knockout (KO) mice. Expression and phosphorylation of CaMKIV and CREB were assessed using RT-PCR and Western blotting. The behavioural action with FLX was assessed in the novelty suppressed feeding test (NSF), which is considered neurogenesis-dependent. CaMKIV KO mice have reduced cell proliferation, but not survival in the dentate gyrus of hippocampus with chronic treatment of FLX when compared to wild littermates. Phenotype analysis showed that most newborn cells matured into neurons. Phosphorylation of CaMKIV was up-regulated in WT mice and phosphorylation of CREB was impaired in CaMKIV KO mice after FLX treatment. The behavioural effects of FLX in NSF were similar in both types. These data suggest that CaMKIV is involved in some aspects of FLX-promoting hippocampal neurogenesis.

Impairment of TrkB-PSD-95 signaling in Angelman syndrome

Brain-derived neurotrophic factor signaling is defective in Angelman syndrome and can be rescued by disruption of Arc/PSD95 binding.

Angelman syndrome (AS) is a neurodevelopment disorder characterized by severe cognitive impairment and a high rate of autism. AS is caused by disrupted neuronal expression of the maternally inherited Ube3A ubiquitin protein ligase, required for the proteasomal degradation of proteins implicated in synaptic plasticity, such as the activity-regulated cytoskeletal-associated protein (Arc/Arg3.1). Mice deficient in maternal Ube3A express elevated levels of Arc in response to synaptic activity, which coincides with severely impaired long-term potentiation (LTP) in the hippocampus and deficits in learning behaviors. In this study, we sought to test whether elevated levels of Arc interfere with brain-derived neurotrophic factor (BDNF) TrkB receptor signaling, which is known to be essential for both the induction and maintenance of LTP. We report that TrkB signaling in the AS mouse is defective, and show that reduction of Arc expression to control levels rescues the signaling deficits. Moreover, the association of the postsynaptic density protein PSD-95 with TrkB is critical for intact BDNF signaling, and elevated levels of Arc were found to impede PSD-95/TrkB association. In Ube3A deficient mice, the BDNF-induced recruitment of PSD-95, as well as PLCγ and Grb2-associated binder 1 (Gab1) with TrkB receptors was attenuated, resulting in reduced activation of PLCγ-α-calcium/calmodulin-dependent protein kinase II (CaMKII) and PI3K-Akt, but leaving the extracellular signal-regulated kinase (Erk) pathway intact. A bridged cyclic peptide (CN2097), shown by nuclear magnetic resonance (NMR) studies to uniquely bind the PDZ1 domain of PSD-95 with high affinity, decreased the interaction of Arc with PSD-95 to restore BDNF-induced TrkB/PSD-95 complex formation, signaling, and facilitate the induction of LTP in AS mice. We propose that the failure of TrkB receptor signaling at synapses in AS is directly linked to elevated levels of Arc associated with PSD-95 and PSD-95 PDZ-ligands may represent a promising approach to reverse cognitive dysfunction.

Angelman syndrome (AS) is a debilitating neurological disorder caused by a dysfunctional Ube3A gene. Most children with AS exhibit developmental delay, movement disorders, speech impairment, and often autistic features. The Ube3A enzyme normally regulates the degradation of the synaptic protein Arc, and in its absence the resulting elevated levels of Arc weaken synaptic contacts, making it difficult to generate long-term potentiation (LTP) and to process and store memory. In this study, we show that increased levels of Arc disrupt brain-derived neurotrophic factor (BDNF) signaling through the TrkB receptor (which is important for both the induction and maintenance of LTP). We find that the association of the postsynaptic density protein PSD-95 with TrkB is critical for intact BDNF signaling, and that the high levels of Arc in AS interfere with BDNF-induced recruitment of postsynaptic density protein-95 (PSD-95) and other effectors to TrkB. By disrupting the interaction between Arc and PSD-95 with the novel cyclic peptidomimetic compound CN2097, we were able to restore BDNF signaling and improve the induction of LTP in a mouse model of AS. We propose that the disruption of TrkB receptor signaling at synapses contributes to the cognitive dysfunction that occurs in Angelman syndrome.

G9a-mediated histone methylation regulates ethanol-induced neurodegeneration in the neonatal mouse brain

Rodent exposure to binge-like ethanol during postnatal day 7 (P7), which is comparable to the third trimester of human pregnancy, induces neuronal cell loss. However, the molecular mechanisms underlying these neuronal losses are still poorly understood. Here, we tested the possibility of histone methylation mediated by G9a (lysine dimethyltransferase) in regulating neuronal apoptosis in P7 mice exposed to ethanol. G9a protein expression, which is higher during embryogenesis and synaptogenic period compared to adult brain, is entirely confined to the cell nuclei in the developing brain. We found that ethanol treatment at P7, which induces apoptotic neurodegeneration in neonatal mice, enhanced G9a activity followed by increased histone H3 lysine 9 (H3K9me2) and 27 (H3K27me2) dimethylation. In addition, it appears that increased dimethylation of H3K9 makes it susceptible to proteolytic degradation by caspase-3 in conditions in which ethanol induces neurodegeneration. Further, pharmacological inhibition of G9a activity prior to ethanol treatment at P7 normalized H3K9me2, H3K27me2 and total H3 proteins to basal levels and prevented neurodegeneration in neonatal mice. Together, these data demonstrate that G9a mediated histone H3K9 and K27 dimethylation critically regulates ethanol-induced neurodegeneration in the developing brain. Furthermore, these findings reveal a novel link between G9a and neurodegeneration in the developing brain exposed to postnatal ethanol and may have a role in fetal alcohol spectrum disorders.

Tis21 knock-out enhances the frequency of medulloblastoma in Patched1 heterozygous mice by inhibiting the Cxcl3-dependent migration of cerebellar neurons

A failure in the control of proliferation of cerebellar granule neuron precursor cells (GCPs), located in the external granular layer (EGL) of the cerebellum, gives rise to medulloblastoma. To investigate the process of neoplastic transformation of GCPs, we generated a new medulloblastoma model by crossing Patched1 heterozygous mice, which develop medulloblastomas with low frequency, with mice lacking the Tis21 gene. Overexpression of Tis21 is known to inhibit proliferation and trigger differentiation of GCPs; its expression decreases in human medulloblastomas. Double-knock-out mice show a striking increase in the frequency of medulloblastomas and hyperplastic EGL lesions, formed by preneoplastic GCPs. Tis21 deletion does not affect the proliferation of GCPs but inhibits their differentiation and, chiefly, their intrinsic ability to migrate outside the EGL. This defect of migration may represent an important step in medulloblastoma formation, as GCPs, remaining longer in the EGL proliferative niche, may become more prone to transformation. By genome-wide analysis, we identified the chemokine Cxcl3 as a target of Tis21. Cxcl3 is downregulated in Tis21-null GCPs of EGL and lesions; addition of Cxcl3 to cerebellar slices rescues the defective migration of Tis21-null GCPs and, remarkably, reduces the area of hyperplastic lesions. As Tis21 activates Cxcl3 transcription, our results suggest that Tis21 induces migration of GCPs through Cxcl3, which may represent a novel target for medulloblastoma therapy.

Activation of PAC1 Receptors in Rat Cerebellar Granule Cells Stimulates Both Calcium Mobilization from Intracellular Stores and Calcium Influx through N-Type Calcium Channels

High concentrations of pituitary adenylate cyclase-activating polypeptide (PACAP) and a high density of PACAP binding sites have been detected in the developing rat cerebellum. In particular, PACAP receptors are actively expressed in immature granule cells, where they activate both adenylyl cyclase and phospholipase C. The aim of the present study was to investigate the ability of PACAP to induce calcium mobilization in cerebellar granule neurons. Administration of PACAP-induced a transient, rapid, and monophasic rise of the cytosolic calcium concentration ([Ca(2+)]i), while vasoactive intestinal peptide was devoid of effect, indicating the involvement of the PAC1 receptor in the Ca(2+) response. Preincubation of granule cells with the Ca(2+) ATPase inhibitor, thapsigargin, or the d-myo-inositol 1,4,5-trisphosphate (IP3) receptor antagonist, 2-aminoethoxydiphenyl borate, markedly reduced the stimulatory effect of PACAP on [Ca(2+)]i. Furthermore, addition of the calcium chelator, EGTA, or exposure of cells to the non-selective Ca(2+) channel blocker, NiCl2, significantly attenuated the PACAP-evoked [Ca(2+)]i increase. Preincubation of granule neurons with the N-type Ca(2+) channel blocker, ω-conotoxin GVIA, decreased the PACAP-induced [Ca(2+)]i response, whereas the L-type Ca(2+) channel blocker, nifedipine, and the P- and Q-type Ca(2+) channel blocker, ω-conotoxin MVIIC, had no effect. Altogether, these findings indicate that PACAP, acting through PAC1 receptors, provokes an increase in [Ca(2+)]i in granule neurons, which is mediated by both mobilization of calcium from IP3-sensitive intracellular stores and activation of N-type Ca(2+) channel. Some of the activities of PACAP on proliferation, survival, migration, and differentiation of cerebellar granule cells could thus be mediated, at least in part, through these intracellular and/or extracellular calcium fluxes.

C1q-induced LRP1B and GPR6 proteins expressed early in Alzheimer disease mouse models, are essential for the C1q-mediated protection against amyloid-β neurotoxicity

Complement protein C1q is induced in the brain in response to a variety of neuronal injuries, including Alzheimer disease (AD), and blocks fibrillar amyloid-β (fAβ) neurotoxicity in vitro. Here, we show that C1q protects immature and mature primary neurons against fAβ toxicity, and we report for the first time that C1q prevents toxicity induced by oligomeric forms of amyloid-β (Aβ). Gene expression analysis reveals C1q-activated phosphorylated cAMP-response element-binding protein and AP-1, two transcription factors associated with neuronal survival and neurite outgrowth, and increased LRP1B and G protein-coupled receptor 6(GPR6) expression in fAβ-injured neurons. Silencing of cAMP-response element-binding protein, LRP1B or GPR6 expression inhibited C1q-mediated neuroprotection from fAβ-induced injury. In addition, C1q altered the association of oligomeric Aβ and fAβ with neurons. In vivo, increased hippocampal expression of C1q, LRP1B, and GPR6 is observed as early as 2 months of age in the 3 × Tg mouse model of AD, whereas no such induction of LRP1B and GPR6 was seen in C1q-deficient AD mice. In contrast, expression of C1r and C1s, proteases required to activate the classical complement pathway, and C3 showed a significant age-dependent increase only after 10-13 months of age when Aβ plaques start to accumulate in this AD model. Thus, our results identify pathways by which C1q, up-regulated in vivo early in response to injury without the coordinate induction of other complement components, can induce a program of gene expression that promotes neuroprotection and thus may provide protection against Aβ in preclinical stages of AD and other neurodegenerative processes.

Calcium/calmodulin-dependent protein kinase kinase 2: roles in signaling and pathophysiology

Many cellular Ca(2+)-dependent signaling cascades utilize calmodulin (CaM) as the intracellular Ca(2+) receptor. Ca(2+)/CaM binds and activates a plethora of enzymes, including CaM kinases (CaMKs). CaMKK2 is one of the most versatile of the CaMKs and will phosphorylate and activate CaMKI, CaMKIV, and AMP-activated protein kinase. Cell expression of CaMKK2 is limited, yet CaMKK2 is involved in regulating many important physiological and pathophysiological processes, including energy balance, adiposity, glucose homeostasis, hematopoiesis, inflammation, and cancer. Here, we explore known functions of CaMKK2 and discuss its potential as a target for therapeutic intervention.

Regulation of retinal proteome by topical antiglaucomatous eye drops in an inherited glaucoma rat model

Examination of the response of the retinal proteome to elevated intraocular pressure (IOP) and to the pharmacological normalization of IOP is crucial, in order to develop drugs with neuroptorective potential. We used a hereditary rat model of ocular hypertension to lower IOP with travaprost and dorzolamide applied topically on the eye surface, and examine changes of the retinal proteome. Our data demonstrate that elevated IOP causes alterations in the retinal protein profile, in particular in high-mobility-group-protein B1 (HMGB1), calmodulin, heat-shock-protein (HSP) 70 and carbonic anhydrase II expression. The changes of the retinal proteome by dorzolamide or travoprost are different and independent of the IOP lowering effect. This fact suggests that the eye drops exert a direct IOP-independent effect on retinal metabolism. Further investigations are required to elucidate the potential neuroprotective mechanisms signaled through changes of HMGB1, calmodulin, HSP70 and carbonic anhydrase II expression in glaucoma. The data may facilitate development of eye drops that exert neuroprotection through direct pharmacological effect.

The Time Course of JNK and P38 Activation in Cerebellar Granule Neurons Following Glucose Deprivation and BDNF Treatment

Low glucose condition induces neuronal cell-death via intracellular mechanisms including mitogen-activated protein kinases (MAPK) signaling pathways. It has been shown that low glucose medium decreases neuronal survival in cerebellar granule neurons (CGNs). In this study, we have examined the activation of JNK, p38kinase and ERK1/2 pathways in low glucose medium in CGNs. The CGNs were prepared from new-born (P-2 and P-5) rats and cultured in Dulbecco's Modified Eagle's Medium high (DMEM-HIGH) glucose supplemented with Fetal Bovine Serum (FBS) 10% for 7 days. The glucose deprivation was induced through replacing the culture medium with the low glucose (5 mM) medium. The MAPK pathways activation was evaluated through phospho specific antibodies using western blot. The viability of cells was measuring using MTT assay. The results indicated that low glucose reduces the cell survival and brain-derived neurotrophic factor (BDNF) elevates the cell viability in CGNs. The basal c-Jun N-terminal kinase (JNK) activity was high in CGNs and glucose deprivation for 24 h had increased phospho-JNK level to 2-fold compared to basal. BDNF treatment reduced the basal JNK activity within 30 min but had no effect in longer incubations. BDNF also blocked the low glucose-induced JNK activation. In addition, CGNs exhibited high p38 phosphorylation in low glucose medium in 48 h. These results demonstrated that in sustained low glucose conditions, CGNs had high activity of stress-activated MAPK which could induce cellular damage. Moreover, BDNF can prevent JNK and p38 activation in stress conditions and increase cell viability. Our results suggest that in sustained stress conditions, inhibition of JNK and/or p38 pathways might protect neurons from damage in low glucose conditions.

A cell-intrinsic role for CaMKK2 in granulocyte lineage commitment and differentiation

Granulocytes serve a critical function in host organisms by recognizing and destroying invading microbes, as well as propagating and maintaining inflammation at sites of infection. However, the molecular pathways underpinning the development of granulocytes are poorly understood. Here, we identify a role for CaMKK2 in the restriction of granulocytic fate commitment and differentiation of myeloid progenitor cells. Following BMT, engraftment by Camkk2(-/-) donor cells resulted in the increased production of mature granulocytes in the BM and peripheral blood. Similarly, Camkk2(-/-) mice possessed elevated numbers of CMP cells and exhibited an accelerated granulopoietic phenotype in the BM. Camkk2(-/-) myeloid progenitors expressed increased levels of C/EBPα and PU.1 and preferentially differentiated into Gr1(+)Mac1(+) granulocytes and CFU-G in vitro. During normal granulopoiesis in vivo or G-CSF-induced differentiation of 32D myeloblast cells in vitro, CaMKK2 mRNA and protein were decreased as a function of time and were undetectable in mature granulocytes. Expression of ectopic CaMKK2 in Camkk2(-/-) CMPs was sufficient to rescue aberrant granulocyte differentiation and when overexpressed in 32D cells, was also sufficient to impede granulocyte differentiation in a kinase activity-dependent manner. Collectively, our results reveal a novel role for CaMKK2 as an inhibitor of granulocytic fate commitment and differentiation in early myeloid progenitors.

The Ca2+/calmodulin-dependent protein kinase kinase, CaMKK2, inhibits preadipocyte differentiation

When fed a standard chow diet, CaMKK2 null mice have increased adiposity and larger adipocytes than do wild-type mice, whereas energy balance is unchanged. Here, we show that Ca(2+)/calmodulin-dependent protein kinase kinase 2 (CaMKK2) is expressed in preadipocytes, where it functions as an AMP-activated protein kinase (AMPK)α kinase. Acute inhibition or deletion of CaMKK2 in preadipocytes enhances their differentiation into mature adipocytes, which can be reversed by 5-aminoimidazole-4-carboxamide ribonucleotide-mediated activation of AMPK. During adipogenesis, CaMKK2 expression is markedly decreased and temporally accompanied by increases in mRNA encoding the early adipogenic genes CCAAT/enhancer binding protein (C/EBP) β and C/EBP δ. Preadipocyte factor 1 has been reported to inhibit adipogenesis by up-regulating sex determining region Y-box 9 (Sox9) expression in preadipocytes and Sox9 suppresses C/EBPβ and C/EBPδ transcription. We show that inhibition of the CaMKK2/AMPK signaling cascade in preadipocytes reduces preadipocyte factor 1 and Sox9 mRNA resulting in accelerated adipogenesis. We conclude that CaMKK2 and AMPK function in a signaling pathway that participates in the regulation of adiposity.

Calcium/calmodulin-dependent protein kinase IV mediates distinct features of basal and activity-dependent dendrite complexity

Intracellular signaling mechanisms translate extracellular signals, such as neuronal activity, into effects on dendrite complexity. Deciphering these mechanisms has considerable impact on understanding how the brain develops and what can go wrong in developmental disorders. How neurons regulate intracellular signaling to control their dendrite morphology remains poorly understood and is likely to be determined at the level of individual neuronal types. Calcium/calmodulin-dependent protein kinase IV (CaMKIV) is a signaling mechanism involved in the regulation of gene expression and dendrite growth. Expression of CaMKIV is developmentally regulated in the cerebral cortex, with highest expression occurring concomitant with the period of extensive dendrite growth and elaboration. Interestingly, cortical neurons heterogeneously expressed CaMKIV in postnatal rat cortices and cortical neurons in vitro. We tested if this differential CaMKIV expression mediated distinct arborization patterns in the dendrites of pyramidal and non-pyramidal neurons. In fact, CaMKIV mediated dendrite complexity via regulation of specific morphological features of the dendrite arbor: branching and elongation, but not primary dendrite formation. We found that small interfering RNA (siRNA) knockdown of CaMKIV decreased basal dendrite complexity indicating that endogenously expressed CaMKIV mediated dendrite complexity. CaMKIV was also required for activity-induced dendrite elaboration. Active CaMKIV expression in cortical neurons increased dendrite elaboration indicating that enzymatic activity was involved. These data indicated neuronal CaMKIV expression was required for basal and activity-induced dendrite complexity. Further, the data presented in this study indicate CaMKIV contributes to the diversity of dendrite arbors via restricted expression and regulation of distinct modes of dendrite elaboration.

Ca2+/Calmodulin-dependent protein kinase kinase beta is regulated by multisite phosphorylation

Ca(2+)/calmodulin-dependent protein kinase kinase β (CaMKKβ) is a serine/threonine-directed kinase that is activated following increases in intracellular Ca(2+). CaMKKβ activates Ca(2+)/calmodulin-dependent protein kinase I, Ca(2+)/calmodulin-dependent protein kinase IV, and the AMP-dependent protein kinase in a number of physiological pathways, including learning and memory formation, neuronal differentiation, and regulation of energy balance. Here, we report the novel regulation of CaMKKβ activity by multisite phosphorylation. We identify three phosphorylation sites in the N terminus of CaMKKβ, which regulate its Ca(2+)/calmodulin-independent autonomous activity. We then identify the kinases responsible for these phosphorylations as cyclin-dependent kinase 5 (CDK5) and glycogen synthase kinase 3 (GSK3). In addition to regulation of autonomous activity, we find that phosphorylation of CaMKKβ regulates its half-life. We find that cellular levels of CaMKKβ correlate with CDK5 activity and are regulated developmentally in neurons. Finally, we demonstrate that appropriate phosphorylation of CaMKKβ is critical for its role in neurite development. These results reveal a novel regulatory mechanism for CaMKKβ-dependent signaling cascades.

Neuronal activity-regulated gene transcription in synapse development and cognitive function

Activity-dependent plasticity of vertebrate neurons allows the brain to respond to its environment. During brain development, both spontaneous and sensory-driven neural activity are essential for instructively guiding the process of synapse development. These effects of neuronal activity are transduced in part through the concerted regulation of a set of activity-dependent transcription factors that coordinate a program of gene expression required for the formation and maturation of synapses. Here we review the cellular signaling networks that regulate the activity of transcription factors during brain development and discuss the functional roles of specific activity-regulated transcription factors in specific stages of synapse formation, refinement, and maturation. Interestingly, a number of neurodevelopmental disorders have been linked to abnormalities in activity-regulated transcriptional pathways, indicating that these signaling networks are critical for cognitive development and function.

Signaling in migrating neurons: from molecules to networks

During prenatal and postnatal development of the mammalian brain, new neurons are generated by precursor cells that are located in the germinal zones. Subsequently newborn neurons migrate to their destined location in the brain. On the migrational route immature neurons interact via a series of recognition molecules with a plethora of extracellular cues. Stimuli that are conveyed by extracellular cues are translated into complex intracellular signaling networks that eventually enable neuronal migration. In this Focused Review we discuss signaling networks underlying neuronal migration emphasizing molecules and pathways that appear to be neuron-specific.

Calmodulin-kinases regulate basal and estrogen stimulated medulloblastoma migration via Rac1

Medulloblastoma is a highly prevalent pediatric central nervous system malignancy originating in the cerebellum, with a strong propensity for metastatic migration to the leptomeninges, which greatly increases mortality. While numerous investigations are focused on the molecular mechanisms of medulloblastoma histogenesis, the signaling pathways regulating migration are still poorly understood. Medulloblastoma likely arises from aberrant proliferative signaling in cerebellar granule precursor cells during development, and estrogen is a morphogen that promotes medulloblastoma cell migration. It has been previously shown that the calcium/calmodulin activated kinase kinase (CaMKK) pathway promotes cerebellar granule precursor migration and differentiation during normal cerebellar development via CaMKIV. Here we investigate the regulatory role of the CaMKK pathway in migration of the human medulloblastoma DAOY and cerebellar granule cells. Using pharmacological inhibitors and dominant negative approaches, we demonstrate that the CaMKK/CaMKI cascade regulates basal medulloblastoma cell migration via Rac1, in part by activation of the RacGEF, βPIX. Additionally, pharmacological inhibition of CaMKK blocks both the estrogen induced Rac1 activation and medulloblastoma migration. The CaMKK signaling module described here is one of the first reported calcium regulated pathways that modulates medulloblastoma migration. Since tumor dissemination requires cell migration to ectopic sites, this CaMKK pathway may be a putative therapeutic target to limit medulloblastoma metastasis.

CaM kinase kinase beta-mediated activation of the growth regulatory kinase AMPK is required for androgen-dependent migration of prostate cancer cells

While patients with advanced prostate cancer initially respond favorably to androgen ablation therapy, most experience a relapse of the disease within 1-2 years. Although hormone-refractory disease is unresponsive to androgen-deprivation, androgen receptor (AR)-regulated signaling pathways remain active and are necessary for cancer progression. Thus, both AR itself and the processes downstream of the receptor remain viable targets for therapeutic intervention. Microarray analysis of multiple clinical cohorts showed that the serine/threonine kinase Ca2+/calmodulin-dependent protein kinase kinase β (CaMKKβ) is both highly expressed in the prostate and further elevated in prostate cancers. Using cellular models of prostate cancer, we have determined that androgens (a) directly increase the expression of a CaMKKβ splice variant and (b) increase functional CaMKKβ protein levels as determined by the phosphorylation of both CaMKI and AMP-activated protein kinase (AMPK), two of CaMKKβ's primary substrates. Importantly, inhibition of the CaMKKβ-AMPK, but not CaMKI, signaling axis in prostate cancer cells by pharmacological inhibitors or siRNA-mediated knockdown blocks androgen-mediated migration and invasion. Conversely, overexpression of CaMKKβ alone leads to both increased AMPK phosphorylation and cell migration. Given the key roles of CaMKKβ and AMPK in the biology of prostate cancer cells, we propose that these enzymes are potential therapeutic targets in prostate cancer.

Transcriptional upregulation of brain-derived neurotrophic factor in rostral ventrolateral medulla by angiotensin II: significance in superoxide homeostasis and neural regulation of arterial pressure

RATIONALE

Oxidative stress in rostral ventrolateral medulla (RVLM), where sympathetic premotor neurons for the maintenance of neurogenic vasomotor tone are located, contributes to neural mechanisms of hypertension. Emerging evidence suggests that brain-derived neurotrophic factor (BDNF) manifests "nontrophic" actions.

OBJECTIVE

We assessed the hypothesis that BDNF plays an active role in oxidative stress-associated neurogenic hypertension by maintaining superoxide anion (O⁻(.)₂) homeostasis in RVLM.

METHODS AND RESULTS

In Wistar-Kyoto rats, microinjection of angiotensin II (Ang II) bilaterally into RVLM upregulated BDNF mRNA and protein and induced cAMP response element binding protein (CREB) phosphorylation. The Ang II-induced BDNF upregulation in RVLM was attenuated by coadministration of the NADPH oxidase inhibitor apocynin; the superoxide dismutase mimetic tempol; or an antisense oligonucleotide against CREB. Intracisternal infusion of Ang II elicited phosphorylation of p47(phox) subunit of NADPH oxidase, suppression of mitochondrial electron coupling capacity, and augmentation in mitochondrial uncoupling protein (UCP)2 expression in RVLM. The former 2 cellular events were enhanced, whereas UCP2 upregulation was attenuated by gene knockdown of BDNF or depletion of tropomyosin receptor kinase (Trk)B ligands with recombinant human TrkB-Fc fusion protein. The same treatments also significantly potentiated both Ang II-induced (O⁻(.)₂) production in RVLM and chronic pressor response.

CONCLUSIONS

Ang II induces (O⁻(.)₂) -dependent upregulation of BDNF in RVLM via phosphorylation of CREB. The Ang II-activated BDNF/TrkB signaling, in turn, exerts negative-feedback regulation on tissue (O⁻(.)₂) level in RVLM through inhibition of p47(phox) phosphorylation, preservation of mitochondrial electron transport capacity, and upregulation of mitochondrial UCP2, resulting in protection against Ang II-induced oxidative stress and long-term pressor response.

Reduced blockade by extracellular Mg(2+) is permissive to NMDA receptor activation in cerebellar granule neurons that model a migratory phenotype

NMDA receptors (NMDAR) contribute to neuronal development throughout the CNS. However, their mode(s) of activation preceding synaptic maturation is unclear, as they are not co-localized with alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate receptors (AMPARs) which normally provide sufficient depolarization to relieve voltage-dependent blockade by Mg(2+). We used cerebellar granule neurons (CGNs) cultured at a near-physiological KCl concentration to examine maturation-dependent changes in NMDAR responses. In contrast, most studies use KCl-supplemented medium to promote survival. At 2-4 days in vitro CGNs: (i) express developmental markers resembling the in vivo migratory phenotype; (ii) maintain a basal amount of calcium responsive element-binding protein phosphorylation that requires NMDARs and calcium/calmodulin-dependent kinases, but not AMPARs; (iii) exhibit NMDA-mediated Ca(2+) influx not effectively blocked by ambient Mg(2+) (0.75 mM) or AMPARs; (iv) maintain a more depolarized resting membrane potential and increased resistance compared to synaptically-connected CGNs. Moreover, migrating CGNs in explant cultures demonstrate NMDA-mediated Ca(2+) influx not effectively blocked by 0.75 mM Mg(2+), and NMDAR but not AMPAR antagonists slow migration. These data suggest the biophysical properties of immature CGNs render NMDARs less sensitive to Mg(2+) blockade, enhancing the likelihood of activation in the absence of AMPAR depolarization.

Impaired cerebellar development and deficits in motor coordination in mice lacking the neuronal protein BM88/Cend1

During nervous system development, neural progenitors arise in proliferative zones, then exit the cell cycle and differentiate as they migrate away from these zones. The neuronal protein BM88/Cend1 has been implicated in coordination of cell cycle exit and differentiation of neuronal precursors. To further elucidate its function we generated Cend1 knock-out mice and analyzed their phenotype during postnatal cerebellar development. Cend1(-/-) mice showed no overt abnormalities in the gross anatomy of the cerebellum or other brain regions. However, detailed analysis revealed alterations in cerebellar layering arising from increased proliferation of granule cell precursors, delayed radial granule cell migration and impaired Purkinje cell differentiation. Accordingly, expression of Patched1, cyclin D1, reelin and brain-derived neurotrophic factor, which correlate with morphological development of the cerebellum, was altered in Cend1(-/-) mice. The observed anatomical and molecular alterations were accompanied by deficits in motor behaviour. Our results suggest that Cend1 is required for normal cerebellar development.

Should I stay or should I go? Becoming a granule cell

Cerebellar granule cells undergo profound and rapid morphological modifications during development while they migrate from their birthplace at the surface of the cerebellar cortex to its deepest layer. Post-mitotic granule cells extend bipolar axons and sequentially use the two main modes of migration, tangential and radial, to reach their final destinations. Recent studies show that protein degradation involving key cell-cycle regulators controls granule cell axon extension. The use of knockout mice deficient in different axon-guidance molecules combined with cutting-edge imaging methods has started to shed light on the molecular mechanisms that trigger granule cell migration. These studies suggest that a major reorganization of the cytoskeleton occurs as granule cells switch from tangential to radial migration.