Calcium/calmodulin-dependent protein kinase II in squid synaptosomes

Antidepressant-like effects of the Guanxin Danshen formula via mediation of the CaMK II-CREB-BDNF signalling pathway in chronic unpredictable mild stress-induced depressive rats

Background

Depression is a chronic and recurrent syndrome of mood disorder causing immense social and economic burden; thus, treatment should be improved. Guanxin Danshen formula (GXDSF), a natural botanical drug composition prescription, has significant cardiovascular protective effects and is widely used in the clinical treatment of myocardial ischaemic diseases. However, it is still unclear and seldom studied whether GXDSF has neuroprotective effects against depressive disorders. This study explored whether GXDSF has antidepressant-like effects in rats exposed to chronic unpredictable mild stress (CUMS) and analysed the possible underlying neurotrophic expression and psychotropic mechanisms.

Methods

The present study was designed to investigate the antidepressant effects of GXDSF treatment in a CUMS-induced rat model. Based on the clinical doses, the drug-treated group was intragastrically administered GXDSF for 30 days, and rats were simultaneously exposed to CUMS stimulation for 30 days. After induction and drug administration, the depression-like behaviours were determined via the sucrose preference test (SPT), the open field test (OFT), the tail suspension test (TST), and the forced swim test (FST). ELISA kits were used to examine the monoaminergic neurotransmitters, monoamine oxidase (MAO) and Ca²⁺ levels in the hippocampus. Moreover, we measured and analysed the brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) levels and the upstream regulation and signal pathways of BDNF and NGF to explore their related mechanisms in this animal model of depression, including calcium-calmodulin dependent protein kinase-II (CaMKII) and cAMP response element-binding (CREB).

Results

The results revealed that GXDSF may possess significant antidepressant-like effects via improving body weight, raising the sucrose preference in the SPT, increasing the total distance, the number of upright stands, and the residence time of the central zone in the open field test (OPF) and reducing the immobility time in the TST and FST. In addition, GXDSF significantly upregulated the relative levels of neurotransmitters, including dopamine (DA), norepinephrine (NE), and serotonin (5-HT), in a dose-dependent manner and inhibited MAO activities in the hippocampus. Moreover, GXDSF reversed the decline in intracellular CREB and p-CREB expression induced by CUMS, downregulated the phosphorylation levels of intracellular CaMKII and its two subunits CaMKIIα and CaMKIIβ in the hippocampus, and thus, clearly upregulated the downstream effector protein expression levels of BDNF, NGF, and synitaxine-1 in the hippocampus. These data suggest that the antidepressant effects of GXDSF have a potential relationship with regulating changes in the CaMKII-CREB-BDNF pathway.

Conclusions

Despite several limitations of this study, the results have suggested that GXDSF administration possesses antidepressant-like effects in CUMS-treated rats and provide the first in vivo demonstration of a possible mechanism of GXDSF via regulating changes in the CaMKII-CREB-BDNF signalling pathway. These findings provide a novel potential substrate by which herbal antidepressants may exert therapeutic effects in the treatment of depression.

The sympathetic nervous system regulates skeletal muscle motor innervation and acetylcholine receptor stability

AIM

Symptoms of autonomic failure are frequently the presentation of advanced age and neurodegenerative diseases that impair adaptation to common physiologic stressors. The aim of this work was to examine the interaction between the sympathetic and motor nervous system, the involvement of the sympathetic nervous system (SNS) in neuromuscular junction (NMJ) presynaptic motor function, the stability of postsynaptic molecular organization, and the skeletal muscle composition and function.

METHODS

Since muscle weakness is a symptom of diseases characterized by autonomic dysfunction, we studied the impact of regional sympathetic ablation on muscle motor innervation by using transcriptome analysis, retrograde tracing of the sympathetic outflow to the skeletal muscle, confocal and electron microscopy, NMJ transmission by electrophysiological methods, protein analysis, and state of the art microsurgical techniques, in C57BL6, MuRF1KO and Thy-1 mice.

RESULTS

We found that the SNS regulates motor nerve synaptic vesicle release, skeletal muscle transcriptome, muscle force generated by motor nerve activity, axonal neurofilament phosphorylation, myelin thickness, and myofibre subtype composition and CSA. The SNS also modulates the levels of postsynaptic membrane acetylcholine receptor by regulating the Gαi2 -Hdac4-Myogenin-MuRF1pathway, which is prevented by the overexpression of the guanine nucleotide-binding protein Gαi2 (Q205L), a constitutively active mutant G protein subunit.

CONCLUSION

The SNS regulates NMJ transmission, maintains optimal Gαi2 expression, and prevents any increase in Hdac4, myogenin, MuRF1, and miR-206. SNS ablation leads to upregulation of MuRF1, muscle atrophy, and downregulation of postsynaptic AChR. Our findings are relevant to clinical conditions characterized by progressive decline of sympathetic innervation, such as neurodegenerative diseases and aging.

Characterization of calcium/calmodulin-dependent protein kinase II activity in the nervous system of the lobster, Panulirus interruptus

Nervous system tissue from Panulirus interruptus has an enzyme activity that behaves like calcium/calmodulin-dependent protein kinase II (CaM KII) This activity phosphorylates known targets of CaM KII, such as synapsin I and autocamtide 3. It is inhibited by a CaM KII-specific autoinhibitory domain peptide. In addition, this lobster brain activity displays calcium-independent activity after autophosphorylation, another characteristic of CaM KII. A cDNA from the lobster nervous system was amplified using polymerase chain reaction. The fragment was cloned and found to be structurally similar to CaM KII. Serum from rabbits immunized with a fusion protein containing part of this sequence immunoprecipitated a CaM KII enzyme activity and a family of phosphoproteins of the appropriate size for CaM KII subunits. Lobster CaM KII activity is found in the brain and stomatogastric nervous system including the commissural ganglia, commissures, stomatogastric ganglion and stomatogastric nerve. Immunoblot analysis of these same regions also identifies bands at an apparent molecular weight characteristic of CaM KII.

Ca(2+)-mediated phosphorylation and proteolysis activity associated with the cytoskeletal fraction from cerebral cortex of rats

We describe a Triton-insoluble cytoskeletal fraction extracted from cerebral cortex of young rats retaining an endogenous Ca(2+)-mediated mechanism acting in vitro on Ca2+/calmodulin-dependent protein kinase II (CaM-KII) activity and on phosphorylation and proteolysis of the 150 kDa neurofilament subunit (NF-M), alpha and beta tubulin. Exogenous Ca2+ induced a 70% decrease in the in vitro phosphorylation of the NF-M and tubulins and a 30-50% decrease in the total amount of these proteins. However, when calpastatin was added basal phosphorylation and NF-M and tubulin content were recovered. Furthermore, exogenous Ca2+/calmodulin induced increased in vitro phosphorylation of the cytoskeletal proteins and CaM-KII activity only in the presence of calpastatin, suggesting the presence of Ca(2+)-induced calpain-mediated proteolysis. This fraction could be an interesting model to further studies concerning the in vitro effects of Ca(2+)-mediated protein kinases and proteases associated with the cytoskeletal fraction.

Characterization of synthetic peptide substrates for p34cdc2 protein kinase

Synthetic peptide substrates for the cell division cycle regulated protein kinase, p34cdc2, have been developed and characterized. These peptides are based on the sequences of two known substrates of the enzyme, Simian Virus 40 Large T antigen and the human cellular recessive oncogene product, p53. The peptide sequences are H-A-D-A-Q-H-A-T-P-P-K-K-K-R-K-V-E-D-P-K-D-F-OH (T antigen) and H-K-R-A-L-P-N-N-T-S-S-S-P-Q-P-K-K-K-P-L-D-G-E-Y-NH2 (p53), and they have been employed in a rapid assay of phosphorylation in vitro. Both peptides show linear kinetics and an apparent Km of 74 and 120 microM, respectively, for the purified human enzyme. The T antigen peptide is specifically phosphorylated by p34cdc2 and not by seven other protein serine/threonine kinases, chosen because they represent major classes of such enzymes. The peptides have been used in whole cell lysates to detect protein kinase activity, and the cell cycle variation of this activity is comparable to that measured with specific immune and affinity complexes of p34cdc2. In addition, the peptide phosphorylation detected in mitotic cells is depleted by affinity adsorption of p34cdc2 using either antibodies to p34cdc2 or by immobilized p13, a p34cdc2-binding protein. Purification of peptide kinase activity from mitotic HeLa cells yields an enzyme indistinguishable from p34cdc2. These peptides should be useful in the investigation of p34cdc2 protein kinase and their regulation throughout the cell division cycle.

Calcium/calmodulin-dependent protein kinase II increases glutamate and noradrenaline release from synaptosomes

A variety of evidence indicates that calcium-dependent protein phosphorylation modulates the release of neurotransmitter from nerve terminals. For instance, the injection of rat calcium/calmodulin-dependent protein kinase II (Ca2+/CaM-dependent PK II) into the preterminal digit of the squid giant synapse leads to an increase in the release of a so-far unidentified neurotransmitter induced by presynaptic depolarization. But until now, it has not been demonstrated that Ca2+/CaM-dependent PK II can also regulate neurotransmitter release in the vertebrate nervous system. Here we report that the introduction of Ca2+/CaM-dependent PK II, autoactivated by thiophosphorylation, into rat brain synaptosomes (isolated nerve terminals) increases the initial rate of induced release of two neurotransmitters, glutamate and noradrenaline. We also show that introduction of a selective peptidergic inhibitor of Ca2+/CaM-dependent PK II inhibits the initial rate of induced glutamate release. These results support the hypothesis that activation of Ca2+/CaM-dependent PK II in the nerve terminal removes a constraint on neurotransmitter release.

Regulation of Ca2+/calmodulin-dependent protein kinase II by brain gangliosides

Purified rat brain Ca2+/calmodulin-dependent protein kinase II (CaM-kinase II) is stimulated by brain gangliosides to a level of about 30% the activity obtained in the presence of Ca2+/calmodulin (CaM). Of the various gangliosides tested, GT1b was the most potent, giving half-maximal activation at 25 microM. Gangliosides GD1a and GM1 also gave activation, but asialo-GM1 was without effect. Activation was rapid and did not require calcium. The same gangliosides also stimulated the autophosphorylation of CaM-kinase II on serine residues, but did not produce the Ca2+-independent form of the kinase. Ganglioside stimulation of CaM-kinase II was also present in rat brain synaptic membrane fractions. Higher concentrations (125-250 microM) of GT1b, GD1a, and GM1 also inhibited CaM-kinase II activity. This inhibition appears to be substrate-directed, as the extent of inhibition is very dependent on the substrate used. The molecular mechanism of the stimulatory effect of gangliosides was further investigated using a synthetic peptide (CaMK 281-309), which contains the CaM-binding, inhibitory, and autophosphorylation domains of CaM-kinase II. Using purified brain CaM-kinase II in which these regulatory domains were removed by limited proteolysis. CaMK 281-309 strongly inhibited kinase activity (IC50 = 0.2 microM). GT1b completely reversed this inhibition, but did not stimulate phosphorylation of the peptide on threonine-286. These results demonstrate that GT1b can partially mimic the effects of Ca2+/CaM on native CaM-kinase II and on peptide CaMK 281-309.

Calcium/calmodulin-dependent protein kinase II

There is a great deal known about the in vitro properties of CaM kinase II, both in terms of its substrate specificity and its regulation by calmodulin and autophosphorylation. Much of this characterization is based on experiments performed with the rat brain isozyme of CaM kinase II, although in the aspects examined to date isozymes of the kinase from other tissues appear to behave in a broadly similar manner in vitro. However, relatively little is known about the functions of the kinase in vivo. The proteins phosphorylated by the kinase (with the probable exception of synapsin I and tyrosine hydroxylase) and the role of kinase autophosphorylation in vivo remain largely unknown. Investigation of the physiological role of the kinase in brain and other tissues will be a particularly exciting area for future work. The current knowledge of the in vitro properties and the availability of cDNA clones will hopefully expedite this research.

Calcium/calmodulin-stimulated phosphorylation of photoreceptor proteins in Limulus

Calcium (Ca2+) is thought to play a major role in the photoresponse of both vertebrates and invertebrates, but the mechanisms through which Ca2+ exerts its effects are unclear. In many systems, some effects of Ca2+ on cellular processes are thought to be mediated via activation of calcium/calmodulin protein kinase (CaCAM-PK) and the phosphorylation of specific proteins. Thus, protein substrates for CaCAM-PK in photoreceptor cells may be important in mediating the effects of Ca2+ on the photoresponse. In this study, we identify eight substrates for CaCAM-PK found in both the ventral and lateral eyes of Limulus. We focus on a characterization of one of these, a 46-kD substrate. We show that its subcellular distribution in ventral photoreceptors and its isoelectric forms are identical to the 46-kD light-stimulated phosphoprotein (46A) described by Edwards et al. (1989). Furthermore, we present evidence that 46A is unique to photoreceptor cells, and that it is present throughout the cell. Based on the results of this study, and the previous study by Edwards et al. (1989), we propose that 46A is involved in mediating the effects of Ca2+ on Limulus photoreceptor cell function, and that it may be involved in dark adaptation.

Calcium/calmodulin-dependent protein kinase II

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Dephosphorylation of neurofilament proteins enhances their susceptibility to degradation by calpain

The degradation of phosphorylated and dephosphorylated neurofilament proteins by the Ca2+-activated neutral proteinase calpain was studied. Neurofilaments were isolated from bovine spinal cord, dephosphorylated by alkaline phosphatase (from Escherichia coli) and radioiodinated with [125I]-Bolton-Hunter reagent. The radioiodinated neurofilament proteins (untreated and dephosphorylated) were incubated in the presence and absence of calpain from rabbit skeletal muscle, and the degradation rates of large (NF-H), mid-sized (NF-M) and small (NF-L) neurofilament polypeptides were analysed by SDS/polyacrylamide-gel electrophoresis and autoradiography. The degradation of dephosphorylated neurofilament proteins occurred at a higher rate, and to a greater extent, than did that of the phosphorylated (untreated) neurofilament proteins. The dephosphorylated high-molecular-mass neurofilament (NF-HD) was proteolyzed 6 times more quickly than the untreated NF-H. The degradation rate of the NF-M and NF-L neurofilament proteins was also enhanced after dephosphorylation, but less than that of NF-H. This indicates that the dephosphorylation of neurofilament proteins can increase their sensitivity to calpain degradation.