K252a and staurosporine microbial alkaloid toxins as prototype of neurotropic drugs

The emerging role of mixed lineage kinase 3 (MLK3) and its potential as a target for neurodegenerative diseases therapies

Selective and brain-permeable protein kinase inhibitors are in preclinical development for treating neurodegenerative diseases. Among them, MLK3 inhibitors, with a potent neuroprotective biological action have emerged as valuable agents for the treatment of pathologies such as Alzheimer's, Parkinson's disease and amyotrophic lateral sclerosis. In fact, one MLK3 inhibitor, CEP-1347, reached clinical trials for Parkinson's disease. Additionally, another compound called prostetin/12k, a potent and rather selective MLK3 inhibitor has started clinical development for ALS based on its motor neuron protection in both in vitro and in vivo models. In this review, we will focus on the role of MLK3 in neuron-related cell death processes, neurodegenerative diseases, and the potential advantages of targeting this kinase through pharmacological modulation for neuroprotective treatment.

Combination of EPC-EXs and NPC-EXs with miR-126 and miR-210 overexpression produces better therapeutic effects on ischemic stroke by protecting neurons through the Nox2/ROS and BDNF/TrkB pathways

BACKGROUNDS/AIMS

Neural progenitor cells (NPCs) and endothelial progenitor cell (EPCs) exhibit synergistical effects on protecting endothelial cell functions. MiR-126 and miR-210 can protect cell activities by regulating brain-derived neurotrophic factor (BDNF) and reactive oxygen species (ROS) production. Exosomes (EXs) mediate the beneficial effects of stem cells via delivering microRNAs (miRs). Here, we investigated the combination effects of EXs from EPCs (EPC-EXs) and NPCs (NPC-EXs), and determined whether these EXs with miR-126 (EPC-EXs^miR-126) and miR-210 overexpression (NPC-EXs^miR-210) had better effects on hypoxia/reoxygenation (H/R)-injured neurons and ischemic stroke (IS).

METHODS

Cultured neurons were subjected to hypoxia for 6 h and then co-cultured with culture medium, NPC-EXs, EPC-EXs, NPC-EXs + EPC-EXs or NPC-EXs^miR-210 + EPC-EXs^miR-126 under normoxia for 24 h. Cell apoptosis, ROS production, neurite outgrowth and BDNF level were analyzed. Permanent middle cerebral artery occlusion (MCAO) was performed on C57BL/6 mice to build IS model. The mice were injected with PBS or various EXs via tail vein 2 h after MCAO operation. After 24 h, infarct volume and neurological deficits score (NDS), neuronal apoptosis, ROS production and spine density of dendrites, and brain BDNF level were analyzed. For mechanism study, NADPH oxidase 2(Nox2) and BDNF receptor tyrosine kinase receptor B (TrkB) were determined, and TrkB inhibitor k-252a was used in in vitro and in vivo study.

RESULTS

1) The level of miR-210 or miR-126 was increased after NPC-EXs or EPC-EXs treatment respectively. 2) In H/R-injured neurons, NPC-EXs or EPC-EXs decreased cell apoptosis and ROS production and promoted neurite outgrowth, which were associated with the downregulation of Nox2 and the increase of BDNF and p-TrkB/TrkB level. 3) In MCAO mice, NPC-EXs or EPC-EXs decreased infarct volume and NDS, reduced neural apoptosis and ROS production, and promoted the spine density of dendrites. The levels of Nox2, BDNF and p-TrkB/TrkB in mouse brain tissues changed in similar patterns as seen in the in vitro study. 4) In both cell and mouse models, combination of NPC-EXs and EPC-EXs was more effective than NPC-EXs or EPC-EXs alone on all of these effects. 5) EPC-EXs^miR-126 + NPC-EXs^miR-210 had better effects compared to NPC-EXs + EPC-EXs, which were inhibited by k-252a.

CONCLUSION

EPC-EXs^miR-126 combined NPC-EXs^miR-210 further orchestrate the combinative protective effects of EPC-EXs and NPC-EXs on IS, possibly by protecting H/R-injured neurons through the Nox2/ ROS and BDNF/TrkB pathways.

Inhibitors targeting the autophosphorylation of serine/threonine kinase of Streptococcus suis show potent antimicrobial activity

Antimicrobial resistance (AMR) is a global concern threatening public health. Developing novel antibiotics is one of the effective strategies to tackle AMR. Serine/threonine kinases (STKs) have been recently shown to play critical roles in the physiology and pathogenesis of several important bacterial pathogens which are regarded as a promising antimicrobial drug target. We previously reported the roles of STK in the regulation of bacterial cell division, metabolism, and pathogenesis in Streptococcus suis, an important zoonotic bacterial pathogen. In this study, we firstly identified the Thr167 and Ser175 residues in the activation loop of S. suis STK (ssSTK) as the kinase autophosphorylation sites. Phenotyping results demonstrated that the autophosphorylation deficient strain resembled the stk deletion strain showing essentiality for bacterial growth in minimal medium, abnormal morphology, and decreased virulence when compared with the wild-type S. suis SC19 strain. Based on these findings, we established an ssSTK inhibitor screening approach by measuring the growth of S. suis in a minimal medium and testing the autophosphorylation inhibition by measuring the consumption of ATP in an enzymatic reaction by ssSTK. A series of inhibitors against ssSTK are identified from a commercial kinase inhibitors library, including Staurosporine, K252a, AT9283, and APY29. These inhibitors showed antimicrobial activity in vitro. Moreover, by using Galleria mellonella larvae infection assay, compound APY29 displayed in vivo efficacy against S. suis infection. Additionally, it was predicted by molecular docking that these inhibitors could interact with ssSTK. Collectively, our data illustrated the essential roles of ssSTK autophosphorylation in the physiology and pathogenicity of S. suis and consider these inhibitors as promising antimicrobial lead compounds.

Brain-derived neurotrophic factor signaling mitigates the impact of acute social stress

Brain-derived neurotrophic factor (BDNF) is known to promote fear learning as well as avoidant behavioral responses to chronic social defeat stress, but, conversely, this peptide can also have antidepressant effects and can reduce depressant-like symptoms such as social avoidance. The purpose of this study was to use a variety of approaches to determine whether BDNF acting on tropomyosin receptor kinase B (TrkB) promotes or prevents avoidant phenotypes in hamsters and mice that have experienced acute social defeat stress. We utilized systemic and brain region-dependent manipulation of BDNF signaling before or immediately following social defeat stress in Syrian hamsters, TrkB^F616A knock-in mice, and C57Bl/6J mice and measured the subsequent behavioral response to a novel opponent. Systemic TrkB receptor agonists reduced, and TrkB receptor antagonists enhanced, behavioral responses to social defeat in hamsters and mice. In the neural circuit that we have shown mediates defeat-induced behavioral responses, BDNF in the basolateral amygdala, but not the nucleus accumbens, also reduced social avoidant phenotypes. Conversely, knockdown in the basolateral amygdala of TrkB signaling in TrkB^F616A mice enhanced defeat-induced social avoidance. These data demonstrate that systemic administration of BDNF-TrkB drugs at the time of social defeat alters the behavioral response to the defeat stressor. These drugs appear to act, at least in part, in the basolateral amygdala and not the nucleus accumbens. These findings were generalizable to two rodent species with very different social structures and, within mice, to a variety of strains providing converging evidence that BDNF-TrkB signaling reduces anxiety- and depression-like symptoms following short-term social stress.

The Molecular Basis of Toxins' Interactions with Intracellular Signaling via Discrete Portals

An understanding of the molecular mechanisms by which microbial, plant or animal-secreted toxins exert their action provides the most important element for assessment of human health risks and opens new insights into therapies addressing a plethora of pathologies, ranging from neurological disorders to cancer, using toxinomimetic agents. Recently, molecular and cellular biology dissecting tools have provided a wealth of information on the action of these diverse toxins, yet, an integrated framework to explain their selective toxicity is still lacking. In this review, specific examples of different toxins are emphasized to illustrate the fundamental mechanisms of toxicity at different biochemical, molecular and cellular- levels with particular consideration for the nervous system. The target of primary action has been highlighted and operationally classified into 13 sub-categories. Selected examples of toxins were assigned to each target category, denominated as portal, and the modulation of the different portal’s signaling was featured. The first portal encompasses the plasma membrane lipid domains, which give rise to pores when challenged for example with pardaxin, a fish toxin, or is subject to degradation when enzymes of lipid metabolism such as phospholipases A₂ (PLA₂) or phospholipase C (PLC) act upon it. Several major portals consist of ion channels, pumps, transporters and ligand gated ionotropic receptors which many toxins act on, disturbing the intracellular ion homeostasis. Another group of portals consists of G-protein-coupled and tyrosine kinase receptors that, upon interaction with discrete toxins, alter second messengers towards pathological levels. Lastly, subcellular organelles such as mitochondria, nucleus, protein- and RNA-synthesis machineries, cytoskeletal networks and exocytic vesicles are also portals targeted and deregulated by other diverse group of toxins. A fundamental concept can be drawn from these seemingly different toxins with respect to the site of action and the secondary messengers and signaling cascades they trigger in the host. While the interaction with the initial portal is largely determined by the chemical nature of the toxin, once inside the cell, several ubiquitous second messengers and protein kinases/ phosphatases pathways are impaired, to attain toxicity. Therefore, toxins represent one of the most promising natural molecules for developing novel therapeutics that selectively target the major cellular portals involved in human physiology and diseases.

Dissociations in the effects of β2-adrenergic receptor agonists on cAMP formation and superoxide production in human neutrophils: support for the concept of functional selectivity

In neutrophils, activation of the β2-adrenergic receptor (β2AR), a Gs-coupled receptor, inhibits inflammatory responses, which could be therapeutically exploited. The aim of this study was to evaluate the effects of various β2AR ligands on adenosine-3',5'-cyclic monophosphate (cAMP) accumulation and N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP)-induced superoxide anion (O2(•-)) production in human neutrophils and to probe the concept of ligand-specific receptor conformations (also referred to as functional selectivity or biased signaling) in a native cell system. This is an important question because so far, evidence for functional selectivity has been predominantly obtained with recombinant systems, due to the inherent difficulties to genetically manipulate human native cells. cAMP concentration was determined by HPLC/tandem mass spectrometry, and O2(•-) formation was assessed by superoxide dismutase-inhibitable reduction of ferricytochrome c. β2AR agonists were generally more potent in inhibiting fMLP-induced O2(•-) production than in stimulating cAMP accumulation. (-)-Ephedrine and dichloroisoproterenol were devoid of any agonistic activity in the cAMP assay, but partially inhibited fMLP-induced O2(•-) production. Moreover, (-)-adrenaline was equi-efficacious in both assays whereas the efficacy of salbutamol was more than two-fold higher in the O2(•-) assay. Functional selectivity was visualized by deviations of ligand potencies and efficacies from linear correlations for various parameters. We obtained no evidence for involvement of protein kinase A in the inhibition of fMLP-induced O2(•-) production after β2AR-stimulation although cAMP-increasing substances inhibited O2(•-) production. Taken together, our data corroborate the concept of ligand-specific receptor conformations with unique signaling capabilities in native human cells and suggest that the β2AR inhibits O2(•-) production in a cAMP-independent manner.

Functional cooperation of of IL-1β and RGS4 in the brachial plexus avulsion mediated brain reorganization

BACKGROUNDS

There is considerable evidence that central nervous system is continuously modulated by activity, behavior and skill acquisition. This study is to examine the reorganization in cortical and subcortical regions in response to brachial plexus avulsion.

METHODS

Adult C57BL/6 mice were divided into four groups: control, 1, 3 and 6 month of brachial plexus avulsion. IL-1β, IL-6 and RGS4 expression in cortex, brainstem and spinal cord were detected by BiostarM-140 s microarray and real-time PCR. RGS4 subcellular distribution and modulation were further analyzed by primary neuron culture and Western Blot.

RESULTS

After 1, 3 and 6 months of brachial plexus avulsion, 49 (0 up, 49 down), 29 (17 up, 12 down), 13 (9 up, 4 down) genes in cerebral cortex, 40 (8 up, 32 down), 11 (7 up, 4 down), 137 (63 up, 74 down) in brainstem, 27 (14 up, 13 down), 33 (18 up, 15 down), 60 (29 up, 31 down) in spinal cord were identified. Among the regulated gene, IL-1β and IL-6 were sustainable enhanced in brain stem, while PKACβ and RGS4 were up-regulated throughout cerebral cortex, brainstem and spinal cord in 3 and 6 month of nerve injury. Intriguingly, subcellular distribution of RGS4 in above three regions was dependent on the functional correlation of PKA and IL-1β.

CONCLUSION

Data herein indicated that brachial plexus avulsion could efficiently initiate and perpetuate the brain reorganization. Network involved IL-1β and RGS4 signaling might implicate in the re-establish and strengthening of the local circuits at the cortical and subcortical levels.

The roles of BDNF, pCREB and Wnt3a in the latent period preceding activation of progenitor cell mitosis in the adult dentate gyrus by fluoxetine

The formation of new neurons continues into adult life in the dentate gyrus of the rat hippocampus, as in many other species. Neurogenesis itself turns out to be highly labile, and is regulated by a number of factors. One of these is the serotoninergic system: treatment with drugs (such as the SSRI fluoxetine) markedly stimulates mitosis in the progenitor cells of the dentate gyrus. But this process has one remarkable feature: it takes at least 14 days of continuous treatment to be effective. This is despite the fact that the pharmacological action of fluoxetine occurs within an hour or so of first administration. This paper explores the role of BDNF in this process, using the effect of a Trk antagonist (K252a) on the labelling of progenitor cells with the mitosis marker Ki67 and the associated expression of pCREB and Wnt3a. These experiments show that (i) Fluoxetine increased Ki67 counts, as well as pCREB and Wnt3a expression in the dentate gyrus. The action of fluoxetine on the progenitor cells and on pCREB (but not Wnt3a) depends upon Trk receptor activation, since it was prevented by icv infusion of K252a. (ii) These receptors are required for both the first 7 days of fluoxetine action, during which no apparent change in progenitor mitosis occurs, as well as the second 7 days. Increased pCREB was always associated with progenitor cell mitosis, but Wnt3a expression may be necessary but not sufficient for increased progenitor cell proliferation. These results shed new light on the action of fluoxetine on neurogenesis in the adult dentate gyrus, and have both clinical and experimental interest.

Signaling mechanisms mediating local GH action in the neural retina of the chick embryo

Growth hormone (GH) is found in the retina and vitreous of the chick embryo, where it appears to act as a growth and differentiation factor, having neuroprotective effects on retinal ganglion cells (RGCs). Here, we review the molecular mechanisms of the anti-apoptotic effect of GH in chick RGCs. GH treatment of RGCs reduces Akt levels, while raising Akt-phos levels, consistent with a role for Akt signaling pathways in the GH neuroprotective action. The induction of apoptosis by immunoneutralization with GH antiserum is accompanied by an increase in caspase-3 and caspase-9 activation, and also PARP-1 cleavage. Calpain activation also appears to be a major caspase-independent pathway to PARP-1 cleavage and apoptosis in these cells, supporting the view that caspase and calpain inhibitors are major neuroprotective agents for RGCs, and that pathways that activate both caspases and calpains are important for the anti-apoptotic actions of GH in these cells. These pathways involve the activation of cytosolic tyrosine kinases (Trks) and extracellular-signal-related kinases (ERKs). Occupation of the GH receptor by GH involves downstream intracellular Trk pathways. The Akt and Trk pathways appear to converge on the activation of cAMP response element binding protein (CREB), which is able to initiate transcription of pro- or anti-apoptotic genes. These results indicate that the action of GH in the neuroprotection of embryonic RGCs involves pathways common to with other neurotrophins, and that GH can be considered to be a growth and differentiation factor in the development of the embryonic retina. We have also investigated the relationship between the overlapping anti-apoptotic effects of GH and insulin-like growth factor-1 (IGF-1), two functionally closely related factors. We find that simultaneous immunoneutralization of GH and IGF-1 does not increase the level of apoptosis in the cultures above that achieved by immunoneutralization of GH alone. We therefore conclude that the neuroprotective actions of GH in the developing retina are likely mediated in large part through the action of IGF-1.

Indolocarbazole natural products: occurrence, biosynthesis, and biological activity

The indolocarbazole family of natural products, including the biosynthetically related bisindolylmaleimides, is reviewed (with 316 references cited). The isolation of indolocarbazoles from natural sources and the biosynthesis of this class of compounds are thoroughly reviewed, including recent developments in molecular genetics, enzymology and metabolic engineering. The biological activities and underlying modes of action displayed by natural and synthetic indolocarbazoles is also presented, with an emphasis on the development of analogs that have entered clinical trials for its future use against cancer or other diseases.

Enhancement of Schwann cell myelin formation by K252a in the Trembler-J mouse dorsal root ganglion explant culture

The Trembler-J (TrJ) mouse, containing a point mutation in the peripheral myelin protein 22 gene, is characterized by severe hypomyelination and is a representative model of Charcot-Marie-Tooth 1A disease/Dejerine-Sottas Syndrome. Previous studies have shown that protein kinase inhibitor K252a enhances wild-type Schwann cell myelination in culture. We used a dorsal root ganglion (DRG) explant culture system from the heterozygous TrJ/+ mouse to investigate if myelination could be enhanced by K252a. The TrJ/+ DRG explant cultures replicated some important features of the TrJ/+ mouse, showing reduced myelin protein accumulation, thinner myelin sheaths, and shortened myelin internodes. K252a increased myelin protein accumulation and myelin sheath thickness but did not substantially increase myelin internode length. Furthermore, the TrJ/+ DRG explant culture and sciatic nerves continued to respond to K252a during the stage when myelination is complete in the wild type. A general tyrosine kinase inhibitor, genistein, but not inhibitors of serine/threonine protein kinase inhibitors, had a similar effect to K252a. K252a is therefore able to partially overcome hypomyelination by enhancing mutant Schwann cell myelin formation in the TrJ/+ mouse.

Phosphorylation and local presynaptic protein synthesis in calcium- and calcineurin-dependent induction of crayfish long-term facilitation

Long-term facilitation at the crayfish opener muscle is elicited by prolonged high frequency stimulation, and arises from an increase in functional active zones, resulting in increased transmitter release. LTF induction depends critically upon presynaptic calcium accumulation and calcineurin (PP2B) activity. The protein synthesis dependence of this synaptic strengthening was investigated. LTF occurred without transcription, but the translation inhibitors cycloheximide and anisomycin, or local presynaptic injection of mRNA cap analog m7GpppG, impaired LTF expression. Both MAP kinase and phosphatidylinositol 3-OH kinase (PI3K) activation are implicated in this rapamycin-sensitive synaptic potentiation. This study defines an important role for protein synthesis in the expression of activity-dependent plasticity, and provides mechanistic insight for the induction of this process at presynaptic sites.

Signal transduction of stress via ceramide

The sphingomyelin (SM) pathway is a ubiquitous, evolutionarily conserved signalling system analogous to conventional systems such as the cAMP and phosphoinositide pathways. Ceramide, which serves as second messenger in this pathway, is generated from SM by the action of a neutral or acidic SMase, or by de novo synthesis co-ordinated through the enzyme ceramide synthase. A number of direct targets for ceramide action have now been identified, including ceramide-activated protein kinase, ceramide-activated protein phosphatase and protein kinase Czeta, which couple the SM pathway to well defined intracellular signalling cascades. The SM pathway induces differentiation, proliferation or growth arrest, depending on the cell type. Very often, however, the outcome of signalling through this pathway is apoptosis. Mammalian systems respond to diverse stresses with ceramide generation, and recent studies show that yeast manifest a form of this response. Thus ceramide signalling is an older stress response system than the caspase/apoptotic death pathway, and hence these two pathways must have become linked later in evolution. Signalling of the stress response through ceramide appears to play a role in the development of human diseases, including ischaemia/reperfusion injury, insulin resistance and diabetes, atherogenesis, septic shock and ovarian failure. Further, ceramide signalling mediates the therapeutic effects of chemotherapy and radiation in some cells. An understanding of the mechanisms by which ceramide regulates physiological and pathological events in specific cells may provide new targets for pharmacological intervention.

Potassium current development and its linkage to membrane expansion during growth of cultured embryonic mouse hippocampal neurons: sensitivity to inhibitors of phosphatidylinositol 3-kinase and other protein kinases

Hippocampal pyramidal neurons express three major voltage-dependent potassium currents, IA, ID, and IK. During hippocampal development, IA, the rapidly activating and inactivating transient potassium current, is detected soon after pyramidal neurons can be morphologically identified. Appearance of IA in developing pyramidal neurons is dependent on contact with cocultured astroglial cells; cultured pyramidal neurons not in contact with astroglial cells have reduced membrane area and IA (Wu and Barish, 1994). We have examined intracellular signaling pathways that could contribute to the regulation of IA development by probing developing pyramidal neurons with kinase inhibitors. We observed that exposure to LY294002 or wortmannin, inhibitors of phosphatidylinositol (PI) 3-kinase, reduced somatic cross-sectional area, neurite outgrowth, whole-cell capacitance, IA amplitude and density (amplitude normalized to membrane area), and immunoreactivity for Kv4.2 and/or Kv4.3 (potassium channel subunits likely to be present in the channels carrying IA). In contrast, exposure to ML-9 or KN-62, inhibitors of myosin light chain kinase or Ca2+-calmodulin-dependent protein kinase II (CaMKII), reduced membrane area and IA amplitude but did not affect IA density or Kv4. 2/3 immunoreactivity to the same extent as inhibitors of PI 3-kinase. Unexpectedly, exposure to bisindolymaleimide I or calphostin C, inhibitors of protein kinase C (PKC), did not affect membrane area or potassium current development. Our data suggest that PI 3-kinases regulate both A-type potassium channel synthesis and plasmalemmal insertion of vesicles bearing these potassium channels. CaMKII appears to regulate fusion of channel-bearing vesicles with the plasmalemma and myosin light chain kinase to regulate centripetal transport of channel-bearing vesicles from the Golgi. We further suggest that astroglial cells exert their influence on pyramidal neuron development through activation of PI 3-kinases.

Perspectives in clinical Alzheimer's disease research and the development of antidementia drugs

Current treatment approaches in Alzheimer's disease are primarily symptomatic, with the major therapeutic strategy based on acetylcholinesterase inhibition. Alzheimer's disease research should advance over ensuing decade(s) to yield better symptomatic therapies, drugs designed to slow the rate of progression, and disease preventing agents. The next generation of cholinergic agents will include long acting cholinesterase inhibitors with a good safety profile and brain specific muscarinic agonists. The most critical advances in Alzheimer's disease treatment, however, will target slowing of disease progression and prevention of dementia. Therapeutic agents are being developed that interfere with the synthesis, deposition and aggregation of beta-amyloid protein. Clinical trials are presently being conducted with small molecules having nerve growth factor like activity (e.g. AIT-082, cerebrolysin). In addition, estrogen, anti-inflammatory agents (e.g. cyclooxygenase inhibitors) and antioxidant approaches (e.g. vitamin E) are currently being proposed or utilized in disease prevention trials.