DCP-LA stimulates AMPA receptor exocytosis through CaMKII activation due to PP-1 inhibition

An optogenetic tool to recruit individual PKC isozymes to the cell surface and promote specific phosphorylation of membrane proteins

The PKC family consists of several closely related kinases. These enzymes regulate the function of proteins through the phosphorylation of hydroxyl groups on serines and/or threonines. The selective activation of individual PKC isozymes has proven challenging because of a lack of specific activator molecules. Here, we developed an optogenetic blue light-activated PKC isozyme that harnesses a plant-based dimerization system between the photosensitive cryptochrome-2 (CRY2) and the N terminus of the transcription factor calcium and integrin-binding protein 1 (CIB1) (N-terminal region of the CRY2-binding domain of CIB1). We show that tagging CRY2 with the catalytic domain of PKC isozymes can efficiently promote its translocation to the cell surface upon blue light exposure. We demonstrate this system using PKCε and show that this leads to robust activation of a K+ channel (G protein-gated inwardly rectifying K+ channels 1 and 4), previously shown to be activated by PKCε. We anticipate that this approach can be utilized for other PKC isoforms to provide a reliable and direct stimulus for targeted membrane protein phosphorylation by the relevant PKCs.

FORTIS: a live-cell assay to monitor AMPA receptors using pH-sensitive fluorescence tags

The real-time live fluorescent monitoring of surface AMPA receptors (AMPARs) could open new opportunities for drug discovery and phenotypic screening concerning neuropsychiatric disorders. We have developed FORTIS, a tool based on pH sensitivity capable of detecting subtle changes in surface AMPARs at a neuronal population level. The expression of SEP-GluA1 or pHuji-GluA1 recombinant AMPAR subunits in mammalian neurons cultured in 96-well plates enables surface AMPARs to be monitored with a microplate reader. Thus, FORTIS can register rapid changes in surface AMPARs induced by drugs or genetic modifications without having to rely on conventional electrophysiology or imaging. By combining FORTIS with pharmacological manipulations, basal surface AMPARs, and plasticity-like changes can be monitored. We expect that employing FORTIS to screen for changes in surface AMPARs will accelerate both neuroscience research and drug discovery.

DCP-LA Exerts an Antiaging Action on the Skin

The present study assessed the possibility for the linoleic acid derivative 8-[2-(2-pentyl-cyclopropylmethyl)-cyclopropyl]-octanoic acid (DCP-LA) as an antiaging compound for the skin by assaying senescence-associated β-galactosidase (SA-β-Gal), a biomarker of senescence and cell viability. The nitric oxide (NO) donor sodium nitroprusside (SNP) increased in SA-β-Gal-positive cells in cultured human fibroblasts and mouse keratinocytes, and DCP-LA significantly inhibited the effect of SNP. Moreover, SNP induced cell death in cultured mouse keratinocytes, and DCP-LA significantly prevented NO stress-induced death of keratinocytes. Taken together, these results indicate that DCP-LA exerts an antiaging action on the skin.

Effects of intraplantar botulinum toxin-B on carrageenan-induced changes in nociception and spinal phosphorylation of GluA1 and Akt

Increasing evidence suggests that botulinum neurotoxins (BoNTs) delivered into the skin and muscle in certain human and animal pain states may exert antinociceptive efficacy though their uptake and transport to central afferent terminals. Cleavage of soluble N-methylaleimide-sensitive attachment protein receptor by BoNTs can impede vesicular mediated neurotransmitter release as well as transport/insertion of channel/receptor subunits into plasma membranes, an effect that can reduce activity-evoked facilitation. Here, we explored the effects of intraplantar botulinum toxin- B (BoNT-B) on peripheral inflammation and spinal nociceptive processing in an inflammatory model of pain. C57BL/6 mice (male) received unilateral intraplantar BoNT (1 U, 30 μL) or saline prior to intraplantar carrageenan (20 μL, 2%) or intrathecal N-methyl-D-aspartate (NMDA), substance P or saline (5 μL). Intraplantar carrageenan resulted in edema and mechanical allodynia in the injected paw and increased phosphorylation of a glutamate subunit (pGluA1ser845) and a serine/threonine-specific protein kinase (pAktser473) in spinal dorsal horn along with an increased incidence of spinal c-Fos positive cells. Pre-treatment with intraplantar BoNT-B reduced carrageenan evoked: (i) allodynia, but not edema; (ii) pGluA1 and pAkt and (iii) c-Fos expression. Further, intrathecal NMDA and substance P each increased dorsal horn levels of pGluA1 and pAkt. Intraplantar BoNT-B inhibited NMDA, but not substance P evoked phosphorylation of GluA1 and Akt. These results suggest that intraplantar toxin is transported centrally to block spinal activation and prevent phosphorylation of a glutamate receptor subunit and a kinase, which otherwise contribute to facilitated states.

Alpha2-adrenoceptor and adenosine A1 receptor within the nucleus tractus solitarii in hypertension development

Alpha2-adrenoceptor and A1 adenosine receptor systems within the nucleus tractus solitarii (NTS) play an important role in cardiovascular control. Deregulation of these systems may result in an elevated sympathetic tone, one of the root causes of neurogenic hypertension. The dorsomedial/dorsolateral and subpostremal NTS subnuclei of spontaneously hypertensive rats (SHR) show density changes in both receptors, even at 15 days of age, prior to the onset of hypertension. In addition, adenosine A1 receptors have been specifically reported to modulate alpha2-adrenoceptors in several brain regions, including the NTS, via a PLC-dependent pathway involving cross regulation between sympathetic neurons and astrocytes. The physiological cross talk between these receptor systems is also deregulated in SHR suggesting that alpha2-adrenoceptor and A1 adenosine receptor might be germane to the development of hypertension. In this review, we will focus on these systems within the NTS during development, pointing out some interesting modulations in processes, and chemical changes within specific subnuclei of NTS circuitry, that might have implications for neurogenic hypertension.

Linoleic acid derivative DCP-LA ameliorates stress-induced depression-related behavior by promoting cell surface 5-HT1A receptor translocation, stimulating serotonin release, and inactivating GSK-3β

Impairment of serotonergic neurotransmission is the major factor responsible for depression and glycogen synthase kinase 3β (GSK-3β) participates in serotonergic transmission-mediated signaling networks relevant to mental illnesses. In the forced-swim test to assess depression-like behavior, the immobility time for mice with restraint stress was significantly longer than that for nonstressed control mice. Postsynaptic cell surface localization of 5-HT1A receptor, but not 5-HT2A receptor, in the hypothalamus for mice with restraint stress was significantly reduced as compared with that for control mice, which highly correlated to prolonged immobility time, i.e., depression-like behavior. The linoleic acid derivative 8-[2-(2-pentyl-cyclopropylmethyl)-cyclopropyl]-octanoic acid (DCP-LA) restored restraint stress-induced reduction of cell surface 5-HT1A receptor and improved depression-like behavior in mice with restraint stress. Moreover, DCP-LA stimulated serotonin release from hypothalamic slices and cancelled restraint stress-induced reduction of GSK-3β phosphorylation at Ser9. Taken together, the results of the present study indicate that DCP-LA could ameliorate depression-like behavior by promoting translocation of 5-HT1A receptor to the plasma membrane on postsynaptic cells, stimulating serotonin release, and inactivating GSK-3β.

PKC-epsilon activation is required for recognition memory in the rat

Activation of PKCɛ, an abundant and developmentally regulated PKC isoform in the brain, has been implicated in memory throughout life and across species. Yet, direct evidence for a mechanistic role for PKCɛ in memory is still lacking. Hence, we sought to evaluate this in rats, using short-term treatments with two PKCɛ-selective peptides, the inhibitory ɛV1-2 and the activating ψɛRACK, and the novel object recognition task (NORT). Our results show that the PKCɛ-selective activator ψɛRACK, did not have a significant effect on recognition memory. In the short time frames used, however, inhibition of PKCɛ activation with the peptide inhibitor ɛV1-2 significantly impaired recognition memory. Moreover, when we addressed at the molecular level the immediate proximal signalling events of PKCɛ activation in acutely dissected rat hippocampi, we found that ψɛRACK increased in a time-dependent manner phosphorylation of MARCKS and activation of Src, Raf, and finally ERK1/2, whereas ɛV1-2 inhibited all basal activity of this pathway. Taken together, these findings present the first direct evidence that PKCɛ activation is an essential molecular component of recognition memory and point toward the use of systemically administered PKCɛ-regulating peptides as memory study tools and putative therapeutic agents.

Regulation of GluA1 AMPA receptor through PKC phosphorylation induced by free fatty acid derivative HUHS2002

The present study investigated the effect of 4-[4-(Z)-hept-1-enyl-phenoxy] butyric acid (HUHS2002), a newly synthesized free fatty acid derivative, on α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor responses. HUHS2002 potentiated currents through GluA1 AMPA receptors expressed in Xenopus oocytes in a bell-shaped concentration (1 nM–1 μM)-dependent manner, the maximum reaching nearly 140 % of original amplitude at 100 nM. The potentiation was significantly inhibited by GF109203X, an inhibitor of protein kinase C (PKC), but not KN-93, an inhibitor of Ca²⁺/calmodulin-dependent protein kinase II (CaMKII). HUHS2002 had no potentiating effect on currents through mutant GluA1 AMPA receptors with replacement of Ser831, a PKC/CaMKII phosphorylation site, by Ala. In the in situ PKC assay using rat PC-12 cells, HUHS2002 significantly enhanced PKC activity, that is suppressed by GF109203X. Overall, the results of the present study show that HUHS2002 potentiates GluA1 AMPA receptor responses by activating PKC and phosphorylating the receptors at Ser831, regardless of CaMKII activation and phosphorylation.

Free fatty acid derivative HUHS2002 potentiates α7 ACh receptor responses through indirect activation of CaMKII

The present study examined the effect of 4-[4-(Z)-hept-1-enyl-phenoxy] butyric acid (HUHS2002), a free fatty acid derivative, on α7 acetylcholine (ACh) receptor responses. HUHS2002 potentiated whole-cell membrane currents through α7 ACh receptors expressed in Xenopus oocytes in a concentration (1-100 nM)-dependent manner, reaching about 140 % of the original amplitude at 100 nM 50 min after a 10-min treatment. The HUHS2002 effect was prevented by KN-93, an inhibitor of Ca²⁺/calmodulin-dependent protein kinase II (CaMKII), while it was not affected by GF109203X, an inhibitor of protein kinase C (PKC), or H-89, an inhibitor of protein kinase A (PKA). In the in situ CaMKII assay using cultured rat hippocampal neurons, HUHS2002 activated CaMKII and the activation was abolished by KN-93. In the cell-free assay of protein phosphatase 1 (PP1), HUHS2002 partially inhibited PP1 activity. Taken together, these results indicate that HUHS2002 potentiates α7 ACh receptor responses by indirectly activating CaMKII, possibly via inhibition of PP1.

Indomethacin enhances learning and memory potential by interacting with CaMKII

The present study examined the effect of indomethacin (IM), a cyclooxygenase inhibitor, on learning and memory functions. IM activated Ca(2+) /calmodulin-dependent protein kinase II (CaMKII) in cultured rat hippocampal neurons. IM (100 µM) significantly increased the rate of spontaneous AMPA receptor-mediated miniature excitatory postsynaptic currents elicited from CA1 pyramidal neurons of rat hippocampal slices, without affecting the amplitude, and enhanced extracellular high K(+) (20 mM)-induced glutamate release from rat hippocampal slices, indicating that IM stimulates presynaptic glutamate release. Those IM effects were clearly inhibited by the CaMKII inhibitor KN-93. IM persistently facilitated synaptic transmission monitored from the CA1 region of rat hippocampal slices in a concentration (1-100 µM)-dependent manner that was also abolished by KN-93. In the water maze test, IM (1 mg/kg, i.p.) enhanced spatial learning and memory ability for normal rats, and ameliorated scopolamine-induced spatial learning and memory impairment or age-related spatial learning and memory deterioration for senescence-accelerated mouse-prone 8 mice. In the test to learn 15 numbers consisting of three patterns of five digit number for healthy human subjects, oral intake with IM (25 mg/kg) significantly raised the scores of correct number arrangements that subjects memorized 5 min and 3 days after the test. The results of the present study indicate that IM could enhance learning and memory potential by facilitating hippocampal synaptic transmission as a result from stimulating presynaptic glutamate release under the control of CaMKII.

Apolipoprotein E3 (ApoE3) but not ApoE4 protects against synaptic loss through increased expression of protein kinase C epsilon

Synaptic loss is the earliest pathological change in Alzheimer disease (AD) and is the pathological change most directly correlated with the degree of dementia. ApoE4 is the major genetic risk factor for the age-dependent form of AD, which accounts for 95% of cases. Here we show that in synaptic networks formed from primary hippocampal neurons in culture, apoE3, but not apoE4, prevents the loss of synaptic networks produced by amyloid β oligomers (amylospheroids). Specific activators of PKCε, such as 8-(2-(2-pentyl-cyclopropylmethyl)-cyclopropyl)-octanoic acid methyl ester and bryostatin 1, protected against synaptic loss by amylospheroids, whereas PKCε inhibitors blocked this synaptic protection and also blocked the protection by apoE3. Blocking LRP1, an apoE receptor on the neuronal membrane, also blocked the protection by apoE. ApoE3, but not apoE4, induced the synthesis of PKCε mRNA and expression of the PKCε protein. Amyloid β specifically blocked the expression of PKCε but had no effect on other isoforms. These results suggest that protection against synaptic loss by apoE is mediated by a novel intracellular PKCε pathway. This apoE pathway may account for much of the protective effect of apoE and reduced risk for the age-dependent form of AD. This finding supports the potential efficacy of newly developed therapeutics for AD.

Indomethacin activates protein kinase C and potentiates α7 ACh receptor responses

BACKGROUND/AIMS

We have earlier found that indomethacin activates CaMKII, as a novel action distinct from COX inhibition. To explore further indomethacin actions, the present study focused upon PKC and examined the effect of indomethacin on α7 ACh receptor responses and hippocampal synaptic transmission through PKC.

METHODS

We recorded currents through α7 ACh receptors expressed in Xenopus oocytes, quantified PKC activity in the in situ and cell-free PKC assay, and monitored field excitatory postsynaptic potentials (fEPSPs) and miniature excitatory postsynaptic currents (mEPSCs) from the CA1 region of rat hippocampal slices.

RESULTS

Indomethacin potentiated α7 ACh receptor currents in a bell-shaped concentration (100 nM-1 mM)-dependent manner, and the potentiating effect was inhibited by the PKC inhibitor GF109203X. Indomethacin activated PKC in a concentration (1-100 μM)-dependent manner for cultured rat hippocampal neurons. Additionally, indomethacin (100 μM) significantly activated PKC-ε under the cell-free conditions. Indomethacin (100 μM) induced a transient huge increase in the fEPSP slope followed by persistent increase, and the former effect was attenuated by the α7 ACh receptor antagonist α-bungarotoxin or GF109203X. Indomethacin (100 μM) also increased the rate of nicotine-evoked mEPSCs, and the effect was prevented by α-bungarotoxin or GF109203X.

CONCLUSION

The results of the present study show that indomethacin activates PKC, possibly PKC-e in the brain, thereby potentiating α7 ACh receptor responses to stimulate presynaptic glutamate release, which in part contributes to facilitation of hippocampal transmission. This extends our knowledge about diverse indomethacin actions.

The role of glutamate receptors in traumatic brain injury: implications for postsynaptic density in pathophysiology

Traumatic brain injury (TBI) is the major cause of death and disability, and the incidence of TBI continues to increase rapidly. In recent years, increasing attention has been paid to an important structure at the postsynaptic membrane: the postsynaptic density (PSD). Glutamate receptors, as major components of the PSD, are highly responsive to alterations in the glutamate concentration at excitatory synapses and activate intracellular signal transduction via calcium and other second messengers following TBI. PSD scaffold proteins (PSD-95, Homer, and Shank), which anchor glutamate receptors and form a network structure, also have potential effects on these downstream signaling pathways. The changes in the function and structure of these major PSD proteins are also induced by TBI, indicating that there is a more complicated mechanism associated with PSD proteins in the pathophysiological process of TBI.