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

Role of Ca2+/Calmodulin-Dependent Protein Kinase Type II in Mediating Function and Dysfunction at Glutamatergic Synapses

Glutamatergic synapses harbor abundant amounts of the multifunctional Ca²⁺/calmodulin-dependent protein kinase type II (CaMKII). Both in the postsynaptic density as well as in the cytosolic compartment of postsynaptic terminals, CaMKII plays major roles. In addition to its Ca²⁺-stimulated kinase activity, it can also bind to a variety of membrane proteins at the synapse and thus exert spatially restricted activity. The abundance of CaMKII in glutamatergic synapse is akin to scaffolding proteins although its prominent function still appears to be that of a kinase. The multimeric structure of CaMKII also confers several functional capabilities on the enzyme. The versatility of the enzyme has prompted hypotheses proposing several roles for the enzyme such as Ca²⁺ signal transduction, memory molecule function and scaffolding. The article will review the multiple roles played by CaMKII in glutamatergic synapses and how they are affected in disease conditions.

Calcium/Calmodulin-Dependent Protein Kinase II in Cerebrovascular Diseases

Cerebrovascular disease is the most common life-threatening and debilitating condition that often leads to stroke. The multifunctional calcium/calmodulin-dependent protein kinase II (CaMKII) is a key Ca2+ sensor and an important signaling protein in a variety of biological systems within the brain, heart, and vasculature. In the brain, past stroke-related studies have been mainly focused on the role of CaMKII in ischemic stroke in neurons and established CaMKII as a major mediator of neuronal cell death induced by glutamate excitotoxicity and oxidative stress following ischemic stroke. However, with growing understanding of the importance of neurovascular interactions in cerebrovascular diseases, there are clearly gaps in our understanding of how CaMKII functions in the complex neurovascular biological processes and its contributions to cerebrovascular diseases. Additionally, emerging evidence demonstrates novel regulatory mechanisms of CaMKII and potential roles of the less-studied CaMKII isoforms in the ischemic brain, which has sparked renewed interests in this dynamic kinase family. This review discusses past findings and emerging evidence on CaMKII in several major cerebrovascular dysfunctions including ischemic stroke, hemorrhagic stroke, and vascular dementia, focusing on the unique roles played by CaMKII in the underlying biological processes of neuronal cell death, neuroinflammation, and endothelial barrier dysfunction triggered by stroke. We also highlight exciting new findings, promising therapeutic agents, and future perspectives for CaMKII in cerebrovascular systems.

Biological Properties of JNK3 and Its Function in Neurons, Astrocytes, Pancreatic β-Cells and Cardiovascular Cells

JNK is a protein kinase, which induces transactivation of c-jun. The three isoforms of JNK, JNK1, JNK2, and JNK3, are encoded by three distinct genes. JNK1 and JNK2 are expressed ubiquitously throughout the body. By contrast, the expression of JNK3 is limited and observed mainly in the brain, heart, and testes. Concerning the biological properties of JNKs, the contribution of upstream regulators and scaffold proteins plays an important role in the activation of JNKs. Since JNK signaling has been described as a form of stress-response signaling, the contribution of JNK3 to pathophysiological events, such as stress response or cell death including apoptosis, has been well studied. However, JNK3 also regulates the physiological functions of neurons and non-neuronal cells, such as development, regeneration, and differentiation/reprogramming. In this review, we shed light on the physiological functions of JNK3. In addition, we summarize recent advances in the knowledge regarding interactions between JNK3 and cellular reprogramming.

Tissue-type plasminogen activator is a homeostatic regulator of synaptic function in the central nervous system

Membrane depolarization induces the release of the serine proteinase tissue-type plasminogen activator (tPA) from the presynaptic terminal of cerebral cortical neurons. Once in the synaptic cleft this tPA promotes the exocytosis and subsequent endocytic retrieval of glutamate-containing synaptic vesicles, and regulates the postsynaptic response to the presynaptic release of glutamate. Indeed, tPA has a bidirectional effect on the composition of the postsynaptic density (PSD) that does not require plasmin generation or the presynaptic release of glutamate, but varies according to the baseline level of neuronal activity. Hence, in inactive neurons tPA induces phosphorylation and accumulation in the PSD of the Ca²⁺/calmodulin-dependent protein kinase IIα (pCaMKIIα), followed by pCaMKIIα-induced phosphorylation and synaptic recruitment of GluR1-containing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. In contrast, in active neurons with increased levels of pCaMKIIα in the PSD tPA induces pCaMKIIα and pGluR1 dephosphorylation and their subsequent removal from the PSD. These effects require active synaptic N-methyl-D-aspartate (NMDA) receptors and cyclin-dependent kinase 5 (Cdk5)-induced phosphorylation of the protein phosphatase 1 (PP1) at T320. These data indicate that tPA is a homeostatic regulator of the postsynaptic response of cerebral cortical neurons to the presynaptic release of glutamate via bidirectional regulation of the pCaMKIIα /PP1 switch in the PSD.

Neuroprotective peptides fused to arginine-rich cell penetrating peptides: Neuroprotective mechanism likely mediated by peptide endocytic properties

Several recent studies have demonstrated that TAT and other arginine-rich cell penetrating peptides (CPPs) have intrinsic neuroprotective properties in their own right. Examples, we have demonstrated that in addition to TAT, poly-arginine peptides (R8 to R18; containing 8-18 arginine residues) as well as some other arginine-rich peptides are neuroprotective in vitro (in neurons exposed to glutamic acid excitotoxicity and oxygen glucose deprivation) and in the case of R9 in vivo (after permanent middle cerebral artery occlusion in the rat). Based on several lines of evidence, we propose that this neuroprotection is related to the peptide's endocytosis-inducing properties, with peptide charge and arginine residues being critical factors. Specifically, we propose that during peptide endocytosis neuronal cell surface structures such as ion channels and transporters are internalised, thereby reducing calcium influx associated with excitotoxicity and other receptor-mediated neurodamaging signalling pathways. We also hypothesise that a peptide cargo can act synergistically with TAT and other arginine-rich CPPs due to potentiation of the CPPs endocytic traits rather than by the cargo-peptide acting directly on its supposedly intended intracellular target. In this review, we systematically consider a number of studies that have used CPPs to deliver neuroprotective peptides to the central nervous system (CNS) following stroke and other neurological disorders. Consequently, we critically review evidence that supports our hypothesis that neuroprotection is mediated by carrier peptide endocytosis. In conclusion, we believe that there are strong grounds to regard arginine-rich peptides as a new class of neuroprotective molecules for the treatment of a range of neurological disorders.

CXCR-7 receptor promotes SDF-1α-induced migration of bone marrow mesenchymal stem cells in the transient cerebral ischemia/reperfusion rat hippocampus

The stromal cell-derived factor 1/C-X-C chemokine receptor type 4 (SDF-1/CXCR-4) axis plays an important role during stem cell recruitment. SDF-1 can also bind the more recently described CXCR-7 receptor, but effects of SDF-1/CXCR-7 signaling on stem cell migrating to ischemic brain injury area are little known. In the present study, we investigated the effect of CXCR-7 on bone marrow mesenchymal stem cell (BMSC) migration toward SDF-1α in the cerebral ischemia/reperfusion (I/R) rat hippocampus. We cultured BMSCs from rats and characterized them using flow cytometry, immunocytochemistry, western blotting, and immunofluorescence to detect SDF-1α, CXCR-4, and CXCR-7 expression in third passage BMSCs (P3-BMSCs). We also prepared the model of transient cerebral I/R by four-vessel occlusion (4-VO), and BMSCs were transplanted into I/R rat brain via lateral ventricle (LV) injection (20μl, 1×10(6)/ml). After that, we examined the effect of BMSCs migration in the cerebral I/R rat hippocampus through Transwell chamber assay. Our results show that SDF-1α, CXCR-4, and CXCR-7 were expressed in P3-BMSCs. Moreover, SDF-1α expression was increased in I/R hippocampus. At 48h after transplant, green fluorescent BrdU-BMSCs were observed in transplant groups, but no green fluorescent BrdU-BMSCs were seen in medium group. Among BMSCs transplant groups, the number of BrdU-BMSCs positive cell was the highest in BMSC group. Treatment with AMD3100 and/or CXCR-7 neutralizing antibody decreased the number of BMSC migration. Collectively, these findings indicate that CXCR-4 and -7 receptors were co-expressed in BMSCs and synergistically promoted BMSC migration. The effect of CXCR-7 was stronger than that of CXCR-4. Moreover, BMSCs that migrated to hippocampus promoted the autocrine and paracrine signaling of SDF-1α.

The molecular and electrophysiological mechanism of buyanghuanwu decoction in learning and memory ability of vascular dementia rats

Buyanghuanwu Decoction (BYHWD), as a traditional Chinese medicine, has been developed to treat vascular dementia for hundreds of years, but the underlying mechanisms remain unknown. In this research, the protective effects of BYHWD on hippocampal neuron were examined in the rats of ischemia-reperfusion. Ischemia-reperfusion injury was induced by the four-vessel occlusion method and continued for 30 days. BYHWD (per 6.25g/kg/d) was orally given to rats twice each day for 30 days after ischemia-reperfusion, Nimodipine (per 10mg/kg/d) was orally given to rats twice each day for 30 days. In VD+BYHWD group rats, the neuronal injury in the hippocampal CA1 region was significantly less than that of VD group's. BYHWD of intragastric administration also markedly increased the expression of Extracellular signal-regulated kinase 2 (ERK2) and Calcium/calmodulin-dependent protein kinaseII (CaMKIIIy)in the CA1 region. Our results suggested that increased ERK2 and CaMKIIIy due to BYHWD may partially account for its effect of neuroprotection standing against ischemic injury in the hippocampal CA1 region, and participated in the rebuilding of synapse, strengthened the expression of LTP, promoted the ability recover of learning and memory in VD rats.

Convergent Ca2+ and Zn2+ signaling regulates apoptotic Kv2.1 K+ currents. Proc Natl Acad Sci U S A. 2013;110:13988-13993. [PMID: 23918396 DOI: 10.1073/pnas.1306238110]

A simultaneous increase in cytosolic Zn(2+) and Ca(2+) accompanies the initiation of neuronal cell death signaling cascades. However, the molecular convergence points of cellular processes activated by these cations are poorly understood. Here, we show that Ca(2+)-dependent activation of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is required for a cell death-enabling process previously shown to also depend on Zn(2+). We have reported that oxidant-induced intraneuronal Zn(2+) liberation triggers a syntaxin-dependent incorporation of Kv2.1 voltage-gated potassium channels into the plasma membrane. This channel insertion can be detected as a marked enhancement of delayed rectifier K(+) currents in voltage clamp measurements observed at least 3 h following a short exposure to an apoptogenic stimulus. This current increase is the process responsible for the cytoplasmic loss of K(+) that enables protease and nuclease activation during apoptosis. In the present study, we demonstrate that an oxidative stimulus also promotes intracellular Ca(2+) release and activation of CaMKII, which, in turn, modulates the ability of syntaxin to interact with Kv2.1. Pharmacological or molecular inhibition of CaMKII prevents the K(+) current enhancement observed following oxidative injury and, importantly, significantly increases neuronal viability. These findings reveal a previously unrecognized cooperative convergence of Ca(2+)- and Zn(2+)-mediated injurious signaling pathways, providing a potentially unique target for therapeutic intervention in neurodegenerative conditions associated with oxidative stress.

αCaMKII is differentially regulated in brain regions that exhibit differing sensitivities to ischemia and excitotoxicity

Different brain regions exhibit differing sensitivities to ischemia/excitotoxicity. Whether these differences are due to perfusion or intrinsic factors has not been established. Herein, we found no apparent association between sensitivity to ischemia/excitotoxicity and the level of expression or basal phosphorylation of calcium/calmodulin-stimulated protein kinase II (αCaMKII) or glutamate receptors. However, we demonstrated significant differences in CaMKII-mediated responses after ischemia/excitotoxic stimulation in striatum and cortex. In vivo ischemia and in vitro excitotoxic stimulation produced more rapid phosphorylation of Thr253-αCaMKII in striatum compared with cortex, but equal rates of Thr286-αCaMKII phosphorylation. Phosphorylation by CaMKII of Ser831-GluA1 and Ser1303-GluN2B occurred more rapidly in striatum than in cortex after either stimulus. The differences between brain regions in CaMKII activation and its effects were not accounted for by differences in the expression of αCaMKII, glutamate receptors, or density of synapses. These results implicate intrinsic tissue differences in Thr253-αCaMKII phosphorylation in the differential sensitivities of brain regions to ischemia/excitotoxicity.