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Fischer QS, Kalikulov D, Viana DI Prisco G, Williams CA, Baldwin PR, Friedlander MJ. SYNAPTIC PLASTICITY IN THE INJURED BRAIN DEPENDS ON THE TEMPORAL PATTERN OF STIMULATION. J Neurotrauma 2024. [PMID: 38818799 DOI: 10.1089/neu.2024.0129] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/01/2024] Open
Abstract
Neurostimulation protocols are increasingly used as therapeutic interventions, including for brain injury. In addition to the direct activation of neurons, these stimulation protocols are also likely to have downstream effects on those neurons' synaptic outputs. It is well known that alterations in the strength of synaptic connections (long-term potentiation, LTP; long-term depression, LTD) are sensitive to the frequency of stimulation used for induction, however little is known about the contribution of the temporal pattern of stimulation to the downstream synaptic plasticity that may be induced by neurostimulation in the injured brain. We explored interactions of the temporal pattern and frequency of neurostimulation in the normal cerebral cortex and after mild traumatic brain injury (mTBI), to inform therapies to strengthen or weaken neural circuits in injured brains, as well as to better understand the role of these factors in normal brain plasticity. Whole-cell (WC) patch-clamp recordings of evoked postsynaptic potentials (PSPs) in individual neurons, as well as field potential (FP) recordings, were made from layer 2/3 of visual cortex in response to stimulation of layer 4, in acute slices from control (naïve), sham operated, and mTBI rats. We compared synaptic plasticity induced by different stimulation protocols, each consisting of a specific frequency (1 Hz, 10 Hz, or 100 Hz), continuity (continuous or discontinuous), and temporal pattern (perfectly regular, slightly irregular, or highly irregular). At the individual neuron level, dramatic differences in plasticity outcome occurred when the highly irregular stimulation protocol was used at 1 Hz or 10 Hz, producing an overall LTD in controls and shams, but a robust overall LTP after mTBI. Consistent with the individual neuron results, the plasticity outcomes for simultaneous FP recordings were similar, indicative of our results generalizing to a larger scale synaptic network than can be sampled by individual WC recordings alone. In addition to the differences in plasticity outcome between control (naïve or sham) and injured brains, the dynamics of the changes in synaptic responses that developed during stimulation were predictive of the final plasticity outcome. Our results demonstrate that the temporal pattern of stimulation plays a role in the polarity and magnitude of synaptic plasticity induced in the cerebral cortex while highlighting differences between normal and injured brain responses. Moreover, these results may be useful for optimization of neurostimulation therapies to treat mTBI and other brain disorders, in addition to providing new insights into downstream plasticity signaling mechanisms in the normal brain.
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Affiliation(s)
- Quentin S Fischer
- Fralin Biomedical Research Institute at VTC, Roanoke, Virginia, United States
- Baylor College of Medicine Department of Neuroscience, Houston, Texas, United States;
| | - Djanenkhodja Kalikulov
- Fralin Biomedical Research Institute at VTC, Roanoke, Virginia, United States
- Baylor College of Medicine Department of Neuroscience, Houston, Texas, United States;
| | | | - Carrie A Williams
- Fralin Biomedical Research Institute at VTC, Roanoke, Virginia, United States;
| | - Philip R Baldwin
- Baylor College of Medicine Department of Neuroscience, Houston, Texas, United States;
| | - Michael J Friedlander
- Fralin Biomedical Research Institute at VTC, Roanoke, Virginia, United States
- Baylor College of Medicine Department of Neuroscience, Houston, Texas, United States;
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Chen Y, Matveev V. Stationary Ca 2+ nanodomains in the presence of buffers with two binding sites. Biophys J 2021; 120:1942-1956. [PMID: 33771472 DOI: 10.1016/j.bpj.2021.03.015] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Revised: 03/06/2021] [Accepted: 03/11/2021] [Indexed: 10/21/2022] Open
Abstract
We examine closed-form approximations for the equilibrium Ca2+ and buffer concentrations near a point Ca2+ source representing a Ca2+ channel, in the presence of a mobile buffer with two Ca2+ binding sites activated sequentially and possessing distinct binding affinities and kinetics. This allows us to model the impact on Ca2+ nanodomains of realistic endogenous Ca2+ buffers characterized by cooperative Ca2+ binding, such as calretinin. The approximations we present involve a combination or rational and exponential functions, whose parameters are constrained using the series interpolation method that we recently introduced for the case of simpler Ca2+ buffers with a single Ca2+ binding site. We conduct extensive parameter sensitivity analysis and show that the obtained closed-form approximations achieve reasonable qualitative accuracy for a wide range of buffer's Ca2+ binding properties and other relevant model parameters. In particular, the accuracy of the derived approximants exceeds that of the rapid buffering approximation in large portions of the relevant parameter space.
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Affiliation(s)
- Yinbo Chen
- Department of Mathematical Sciences, New Jersey Institute of Technology, Newark, New Jersey
| | - Victor Matveev
- Department of Mathematical Sciences, New Jersey Institute of Technology, Newark, New Jersey.
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Li L, Lai M, Cole S, Le Novère N, Edelstein SJ. Neurogranin stimulates Ca2+/calmodulin-dependent kinase II by suppressing calcineurin activity at specific calcium spike frequencies. PLoS Comput Biol 2020; 16:e1006991. [PMID: 32049957 PMCID: PMC7041932 DOI: 10.1371/journal.pcbi.1006991] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2019] [Revised: 02/25/2020] [Accepted: 11/18/2019] [Indexed: 11/18/2022] Open
Abstract
Calmodulin sits at the center of molecular mechanisms underlying learning and memory. Its complex and sometimes opposite influences, mediated via the binding to various proteins, are yet to be fully understood. Calcium/calmodulin-dependent protein kinase II (CaMKII) and calcineurin (CaN) both bind open calmodulin, favoring Long-Term Potentiation (LTP) or Depression (LTD) respectively. Neurogranin binds to the closed conformation of calmodulin and its impact on synaptic plasticity is less clear. We set up a mechanistic computational model based on allosteric principles to simulate calmodulin state transitions and its interactions with calcium ions and the three binding partners mentioned above. We simulated calcium spikes at various frequencies and show that neurogranin regulates synaptic plasticity along three modalities. At low spike frequencies, neurogranin inhibits the onset of LTD by limiting CaN activation. At intermediate frequencies, neurogranin facilitates LTD, but limits LTP by precluding binding of CaMKII with calmodulin. Finally, at high spike frequencies, neurogranin promotes LTP by enhancing CaMKII autophosphorylation. While neurogranin might act as a calmodulin buffer, it does not significantly preclude the calmodulin opening by calcium. On the contrary, neurogranin synchronizes the opening of calmodulin's two lobes and promotes their activation at specific frequencies. Neurogranin suppresses basal CaN activity, thus increasing the chance of CaMKII trans-autophosphorylation at high-frequency calcium spikes. Taken together, our study reveals dynamic regulatory roles played by neurogranin on synaptic plasticity, which provide mechanistic explanations for opposing experimental findings.
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Affiliation(s)
- Lu Li
- Babraham Institute, Cambridge, United Kingdom
| | - Massimo Lai
- Quantitative Systems Pharmacology, CERTARA, Canterbury, United Kingdom
| | - Stephen Cole
- Cambridge Systems Biology Centre, University of Cambridge, Cambridge, United Kingdom
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Mahajan G, Nadkarni S. Intracellular calcium stores mediate metaplasticity at hippocampal dendritic spines. J Physiol 2019; 597:3473-3502. [PMID: 31099020 PMCID: PMC6636706 DOI: 10.1113/jp277726] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2019] [Accepted: 05/16/2019] [Indexed: 12/21/2022] Open
Abstract
Key points Calcium (Ca2+) entry mediated by NMDA receptors is considered central to the induction of activity‐dependent synaptic plasticity in hippocampal area CA1; this description does not, however, take into account the potential contribution of endoplasmic reticulum (ER) Ca2+ stores. The ER has a heterogeneous distribution in CA1 dendritic spines, and may introduce localized functional differences in Ca2+ signalling between synapses, as suggested by experiments on metabotropic receptor‐dependent long‐term depression. A physiologically detailed computational model of Ca2+ dynamics at a CA3–CA1 excitatory synapse characterizes the contribution of spine ER via metabotropic signalling during plasticity induction protocols. ER Ca2+ release via IP3 receptors modulates NMDA receptor‐dependent plasticity in a graded manner, to selectively promote synaptic depression with relatively diminished effect on LTP induction; this may temper further strengthening at the stronger synapses which are preferentially associated with ER‐containing spines. Acquisition of spine ER may thus represent a local, biophysically plausible ‘metaplastic switch’ at potentiated CA1 synapses, contributing to the plasticity–stability balance in neural circuits.
Abstract Long‐term plasticity mediated by NMDA receptors supports input‐specific, Hebbian forms of learning at excitatory CA3–CA1 connections in the hippocampus. There exists an additional layer of stabilizing mechanisms that act globally as well as locally over multiple time scales to ensure that plasticity occurs in a constrained manner. Here, we investigated the role of calcium (Ca2+) stores associated with the endoplasmic reticulum (ER) in the local regulation of plasticity at individual CA1 synapses. Our study was spurred by (1) the curious observation that ER is sparsely distributed in dendritic spines, but over‐represented in larger spines that are likely to have undergone activity‐dependent strengthening, and (2) evidence suggesting that ER motility at synapses can be rapid, and accompany activity‐regulated spine remodelling. We constructed a physiologically realistic computational model of an ER‐bearing CA1 spine, and examined how IP3‐sensitive Ca2+ stores affect spine Ca2+ dynamics during activity patterns mimicking the induction of long‐term potentiation and long‐term depression (LTD). Our results suggest that the presence of ER modulates NMDA receptor‐dependent plasticity in a graded manner that selectively enhances LTD induction. We propose that ER may locally tune Ca2+‐based plasticity, providing a braking mechanism to mitigate runaway strengthening at potentiated synapses. Our study provides a biophysically accurate description of postsynaptic Ca2+ regulation, and suggests that ER in the spine may promote the re‐use of hippocampal synapses with saturated strengths. Calcium (Ca2+) entry mediated by NMDA receptors is considered central to the induction of activity‐dependent synaptic plasticity in hippocampal area CA1; this description does not, however, take into account the potential contribution of endoplasmic reticulum (ER) Ca2+ stores. The ER has a heterogeneous distribution in CA1 dendritic spines, and may introduce localized functional differences in Ca2+ signalling between synapses, as suggested by experiments on metabotropic receptor‐dependent long‐term depression. A physiologically detailed computational model of Ca2+ dynamics at a CA3–CA1 excitatory synapse characterizes the contribution of spine ER via metabotropic signalling during plasticity induction protocols. ER Ca2+ release via IP3 receptors modulates NMDA receptor‐dependent plasticity in a graded manner, to selectively promote synaptic depression with relatively diminished effect on LTP induction; this may temper further strengthening at the stronger synapses which are preferentially associated with ER‐containing spines. Acquisition of spine ER may thus represent a local, biophysically plausible ‘metaplastic switch’ at potentiated CA1 synapses, contributing to the plasticity–stability balance in neural circuits.
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Affiliation(s)
- Gaurang Mahajan
- Indian Institute of Science Education and Research, Pune, 411 008, India
| | - Suhita Nadkarni
- Indian Institute of Science Education and Research, Pune, 411 008, India
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Danielik V, Fellner P, Králik M, Baďurová B, Gabčová J, Jurišová J, Foltinovič T. Relation between the reactivity and surface area of gypsum. J Mol Liq 2019. [DOI: 10.1016/j.molliq.2019.03.121] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Abstract
Fundamental cell processes such as synaptic neurotransmitter release, endocrine hormone secretion, and myocyte contraction are controlled by highly localized calcium (Ca2+) signals resulting from brief openings of trans-membrane Ca2+ channels. On short temporal and spatial scales, the corresponding local Ca2+ nanodomains formed in the vicinity of a single or several open Ca2+ channels can be effectively approximated by quasi-stationary solutions. The rapid buffering approximation (RBA) is one of the most powerful of such approximations, and is based on the assumption of instantaneous equilibration of the bimolecular Ca2+ buffering reaction, combined with the conservation condition for the total Ca2+ and buffer molecule numbers. Previously, RBA has been generalized to an arbitrary arrangement of Ca2+ channels on a flat membrane, in the presence of any number of simple Ca2+ buffers with one-to-one Ca2+ binding stoichiometry. However, many biological buffers have multiple binding sites. For example, buffers and sensors phylogenetically related to calmodulin consist of two Ca2+-binding domains (lobes), with each domain binding two Ca2+ ions in a cooperative manner. Here we consider an extension of RBA to such buffers with two interdependent Ca2+ binding sites. We show that in the presence of such buffers, RBA solution is given by the solution to a cubic equation, analogous to the quadratic equation describing RBA in the case of a simple, one-to-one Ca2+ buffer. We examine in detail the dependence of RBA accuracy on buffering parameters, to reveal conditions under which RBA provides sufficient precision.
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Affiliation(s)
- Victor Matveev
- Department of Mathematical Sciences, New Jersey Institute of Technology, Newark, New Jersey.
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7
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Griffith T, Tsaneva-Atanasova K, Mellor JR. Control of Ca2+ Influx and Calmodulin Activation by SK-Channels in Dendritic Spines. PLoS Comput Biol 2016; 12:e1004949. [PMID: 27232631 PMCID: PMC4883788 DOI: 10.1371/journal.pcbi.1004949] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2015] [Accepted: 04/28/2016] [Indexed: 11/18/2022] Open
Abstract
The key trigger for Hebbian synaptic plasticity is influx of Ca2+ into postsynaptic dendritic spines. The magnitude of [Ca2+] increase caused by NMDA-receptor (NMDAR) and voltage-gated Ca2+ -channel (VGCC) activation is thought to determine both the amplitude and direction of synaptic plasticity by differential activation of Ca2+ -sensitive enzymes such as calmodulin. Ca2+ influx is negatively regulated by Ca2+ -activated K+ channels (SK-channels) which are in turn inhibited by neuromodulators such as acetylcholine. However, the precise mechanisms by which SK-channels control the induction of synaptic plasticity remain unclear. Using a 3-dimensional model of Ca2+ and calmodulin dynamics within an idealised, but biophysically-plausible, dendritic spine, we show that SK-channels regulate calmodulin activation specifically during neuron-firing patterns associated with induction of spike timing-dependent plasticity. SK-channel activation and the subsequent reduction in Ca2+ influx through NMDARs and L-type VGCCs results in an order of magnitude decrease in calmodulin (CaM) activation, providing a mechanism for the effective gating of synaptic plasticity induction. This provides a common mechanism for the regulation of synaptic plasticity by neuromodulators. Hebbian or associative plasticity is triggered by postsynaptic Ca2+ influx which activates calmodulin and CaMKII. The influx of Ca2+ through voltage-dependent NMDA receptors and Ca2+ channels is regulated by Ca2+ -activated K+ channels (SK-channels) providing negative feedback regulation of postsynaptic [Ca2+]. Using 3-dimensional modeling of Ca2+ and calmodulin dynamics within dendritic spines we show that the non-linear relationship between Ca2+ influx and calmodulin activation endows SK-channels with the ability to “gate” calmodulin activation and therefore the induction of Hebbian synaptic plasticity. Since SK-channels are inhibited by several neuromodulator receptors including acetylcholine and noradrenaline, the gating of synaptic plasticity by SK-channels could represent a common mechanism by which neuromodulators control the induction of synaptic plasticity.
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Affiliation(s)
- Thom Griffith
- Department of Engineering Mathematics, University of Bristol, Bristol, United Kingdom
- Bristol Centre for Complexity Sciences, University of Bristol, Bristol, United Kingdom
| | - Krasimira Tsaneva-Atanasova
- Department of Mathematics, College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, United Kingdom
- EPSRC Centre for Predictive Modelling in Healthcare, University of Exeter, Exeter, United Kingdom
- * E-mail: (KTA); (JRM)
| | - Jack R. Mellor
- Centre for Synaptic Plasticity, School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom
- * E-mail: (KTA); (JRM)
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8
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Abstract
Calcium plays a role in long-term plasticity by triggering postsynaptic signaling pathways for both the strengthening (LTP) and weakening (LTD) of synapses. Since these are opposing processes, several hypotheses have been developed to explain how calcium can trigger LTP in some situations and LTD in others. These hypotheses fall broadly into three categories, based on the amplitude of calcium concentration, the duration of the calcium elevation, and the location of the calcium influx. Here we review the experimental evidence for and against each of these hypotheses and the recent computational models utilizing each. We argue that with new experimental techniques for the precise visualization of calcium and new computational techniques for the modeling of calcium diffusion, it is time to take a new look at the location hypothesis.
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Affiliation(s)
- R C Evans
- George Mason University, The Krasnow Institute for Advanced Studies, MS 2A1, Fairfax, Virginia 22030-444
| | - K T Blackwell
- George Mason University, The Krasnow Institute for Advanced Studies, MS 2A1, Fairfax, Virginia 22030-444
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9
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Ebrahimi S, Okabe S. Structural dynamics of dendritic spines: Molecular composition, geometry and functional regulation. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1838:2391-8. [DOI: 10.1016/j.bbamem.2014.06.002] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2014] [Revised: 05/18/2014] [Accepted: 06/02/2014] [Indexed: 12/16/2022]
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10
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Hoffman L, Chandrasekar A, Wang X, Putkey JA, Waxham MN. Neurogranin alters the structure and calcium binding properties of calmodulin. J Biol Chem 2014; 289:14644-55. [PMID: 24713697 DOI: 10.1074/jbc.m114.560656] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Neurogranin (Ng) is a member of the IQ motif class of calmodulin (CaM)-binding proteins, and interactions with CaM are its only known biological function. In this report we demonstrate that the binding affinity of Ng for CaM is weakened by Ca(2+) but to a lesser extent (2-3-fold) than that previously suggested from qualitative observations. We also show that Ng induced a >10-fold decrease in the affinity of Ca(2+) binding to the C-terminal domain of CaM with an associated increase in the Ca(2+) dissociation rate. We also discovered a modest, but potentially important, increase in the cooperativity in Ca(2+) binding to the C-lobe of CaM in the presence of Ng, thus sharpening the threshold for the C-domain to become Ca(2+)-saturated. Domain mapping using synthetic peptides indicated that the IQ motif of Ng is a poor mimetic of the intact protein and that the acidic sequence just N-terminal to the IQ motif plays an important role in reproducing Ng-mediated decreases in the Ca(2+) binding affinity of CaM. Using NMR, full-length Ng was shown to make contacts largely with residues in the C-domain of CaM, although contacts were also detected in residues in the N-terminal domain. Together, our results can be consolidated into a model where Ng contacts residues in the N- and C-lobes of both apo- and Ca(2+)-bound CaM and that although Ca(2+) binding weakens Ng interactions with CaM, the most dramatic biochemical effect is the impact of Ng on Ca(2+) binding to the C-terminal lobe of CaM.
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Affiliation(s)
| | | | - Xu Wang
- Biochemistry and Molecular Biology, University of Texas Medical School at Houston, Houston, Texas 77030
| | - John A Putkey
- Biochemistry and Molecular Biology, University of Texas Medical School at Houston, Houston, Texas 77030
| | - M Neal Waxham
- From the Departments of Neurobiology and Anatomy and
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Evans RC, Maniar YM, Blackwell KT. Dynamic modulation of spike timing-dependent calcium influx during corticostriatal upstates. J Neurophysiol 2013; 110:1631-45. [PMID: 23843436 DOI: 10.1152/jn.00232.2013] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The striatum of the basal ganglia demonstrates distinctive upstate and downstate membrane potential oscillations during slow-wave sleep and under anesthetic. The upstates generate calcium transients in the dendrites, and the amplitude of these calcium transients depends strongly on the timing of the action potential (AP) within the upstate. Calcium is essential for synaptic plasticity in the striatum, and these large calcium transients during the upstates may control which synapses undergo plastic changes. To investigate the mechanisms that underlie the relationship between calcium and AP timing, we have developed a realistic biophysical model of a medium spiny neuron (MSN). We have implemented sophisticated calcium dynamics including calcium diffusion, buffering, and pump extrusion, which accurately replicate published data. Using this model, we found that either the slow inactivation of dendritic sodium channels (NaSI) or the calcium inactivation of voltage-gated calcium channels (CDI) can cause high calcium corresponding to early APs and lower calcium corresponding to later APs. We found that only CDI can account for the experimental observation that sensitivity to AP timing is dependent on NMDA receptors. Additional simulations demonstrated a mechanism by which MSNs can dynamically modulate their sensitivity to AP timing and show that sensitivity to specifically timed pre- and postsynaptic pairings (as in spike timing-dependent plasticity protocols) is altered by the timing of the pairing within the upstate. These findings have implications for synaptic plasticity in vivo during sleep when the upstate-downstate pattern is prominent in the striatum.
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Affiliation(s)
- R C Evans
- The Krasnow Institute for Advanced Studies, George Mason University, Fairfax, Virginia; and
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12
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13
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Agarwal A, Adams R, Castellani GC, Shouval HZ. On the precision of quasi steady state assumptions in stochastic dynamics. J Chem Phys 2012; 137:044105. [PMID: 22852595 DOI: 10.1063/1.4731754] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Many biochemical networks have complex multidimensional dynamics and there is a long history of methods that have been used for dimensionality reduction for such reaction networks. Usually a deterministic mass action approach is used; however, in small volumes, there are significant fluctuations from the mean which the mass action approach cannot capture. In such cases stochastic simulation methods should be used. In this paper, we evaluate the applicability of one such dimensionality reduction method, the quasi-steady state approximation (QSSA) [L. Menten and M. Michaelis, "Die kinetik der invertinwirkung," Biochem. Z 49, 333369 (1913)] for dimensionality reduction in case of stochastic dynamics. First, the applicability of QSSA approach is evaluated for a canonical system of enzyme reactions. Application of QSSA to such a reaction system in a deterministic setting leads to Michaelis-Menten reduced kinetics which can be used to derive the equilibrium concentrations of the reaction species. In the case of stochastic simulations, however, the steady state is characterized by fluctuations around the mean equilibrium concentration. Our analysis shows that a QSSA based approach for dimensionality reduction captures well the mean of the distribution as obtained from a full dimensional simulation but fails to accurately capture the distribution around that mean. Moreover, the QSSA approximation is not unique. We have then extended the analysis to a simple bistable biochemical network model proposed to account for the stability of synaptic efficacies; the substrate of learning and memory [J. E. Lisman, "A mechanism of memory storage insensitive to molecular turnover: A bistable autophosphorylating kinase," Proc. Natl. Acad. Sci. U.S.A. 82, 3055-3057 (1985)]. Our analysis shows that a QSSA based dimensionality reduction method results in errors as big as two orders of magnitude in predicting the residence times in the two stable states.
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Affiliation(s)
- Animesh Agarwal
- Department of Neurobiology and Anatomy, University of Texas Medical School, Houston, Texas 77030, USA
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Gorny X, Mikhaylova M, Seeger C, Reddy PP, Reissner C, Schott BH, Helena Danielson U, Kreutz MR, Seidenbecher C. AKAP79/150 interacts with the neuronal calcium-binding protein caldendrin. J Neurochem 2012; 122:714-26. [PMID: 22693956 DOI: 10.1111/j.1471-4159.2012.07828.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The A kinase-anchoring protein AKAP79/150 is a postsynaptic scaffold molecule and a key regulator of signaling events. At the postsynapse it coordinates phosphorylation and dephosphorylation of receptors via anchoring kinases and phosphatases near their substrates. Interactions between AKAP79 and two Ca(2+) -binding proteins caldendrin and calmodulin have been investigated here. Calmodulin is a known interaction partner of AKAP79/150 that has been shown to regulate activity of the kinase PKC in a Ca(2+) -dependent manner. Pull-down experiments and surface plasmon resonance biosensor analyses have been used here to demonstrate that AKAP79 can also interact with caldendrin, a neuronal calcium-binding protein implicated in regulation of Ca(2+) -influx and release. We demonstrate that calmodulin and caldendrin compete for a partially overlapping binding site on AKAP79 and that their binding is differentially dependent on calcium. Therefore, this competition is regulated by calcium levels. Moreover, both proteins have different binding characteristics suggesting that the two proteins might play complementary roles. The postsynaptic enrichment, the complex binding mechanism, and the competition with calmodulin, makes caldendrin an interesting novel player in the signaling toolkit of the AKAP interactome.
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Affiliation(s)
- Xenia Gorny
- Leibniz Institute for Neurobiology, Magdeburg, Germany
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15
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Kamp MA, Shakeri B, Tevoufouet EE, Krieger A, Henry M, Behnke K, Herzig S, Hescheler J, Radhakrishnan K, Parent L, Schneider T. The C-terminus of human Ca(v)2.3 voltage-gated calcium channel interacts with alternatively spliced calmodulin-2 expressed in two human cell lines. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2012; 1824:1045-57. [PMID: 22633975 DOI: 10.1016/j.bbapap.2012.05.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2012] [Revised: 04/27/2012] [Accepted: 05/16/2012] [Indexed: 01/20/2023]
Abstract
Ca(v)2.3 containing voltage-activated Ca(2+) channels are expressed in excitable cells and trigger neurotransmitter and peptide-hormone release. Their expression remote from the fast release sites leads to the accumulation of presynaptic Ca(2+) which can both, facilitate and inhibit the influx of Ca(2+) ions through Ca(v)2.3. The facilitated Ca(2+) influx was recently related to hippocampal postsynaptic facilitation and long term potentiation. To analyze Ca(2+) mediated modulation of cellular processes more in detail, protein partners of the carboxy terminal tail of Ca(v)2.3 were identified by yeast-2-hybrid screening, leading in two human cell lines to the detection of a novel, extended and rarely occurring splice variant of calmodulin-2 (CaM-2), called CaM-2-extended (CaM-2-ext). CaM-2-ext interacts biochemically with the C-terminus of Ca(v)2.3 similar to the classical CaM-2 as shown by co-immunoprecipitation. Functionally, only CaM-2-ext reduces whole cell inward currents significantly. The insertion of the novel 46 nts long exon and the consecutive expression of CaM-2-ext must be dependent on a new upstream translation initiation site which is only rarely used in the tested human cell lines. The structure of the N-terminal extension is predicted to be more hydrophobic than the remaining CaM-2-ext protein, suggesting that it may help to dock it to the lipophilic membrane surrounding.
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Affiliation(s)
- Marcel A Kamp
- Institute for Neurophysiology, University of Cologne, Germany
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16
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Raghuram V, Sharma Y, Kreutz MR. Ca(2+) sensor proteins in dendritic spines: a race for Ca(2+). Front Mol Neurosci 2012; 5:61. [PMID: 22586368 PMCID: PMC3347464 DOI: 10.3389/fnmol.2012.00061] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2012] [Accepted: 04/18/2012] [Indexed: 12/21/2022] Open
Abstract
Dendritic spines are believed to be micro-compartments of Ca2+ regulation. In a recent study, it was suggested that the ubiquitous and evolutionarily conserved Ca2+ sensor, calmodulin (CaM), is the first to intercept Ca2+ entering the spine and might be responsible for the fast decay of Ca2+ transients in spines. Neuronal calcium sensor (NCS) and neuronal calcium-binding protein (nCaBP) families consist of Ca2+ sensors with largely unknown synaptic functions despite an increasing number of interaction partners. Particularly how these sensors operate in spines in the presence of CaM has not been discussed in detail before. The limited Ca2+ resources and the existence of common targets create a highly competitive environment where Ca2+ sensors compete with each other for Ca2+ and target binding. In this review, we take a simple numerical approach to put forth possible scenarios and their impact on signaling via Ca2+ sensors of the NCS and nCaBP families. We also discuss the ways in which spine geometry and properties of ion channels, their kinetics and distribution, alter the spatio-temporal aspects of Ca2+ transients in dendritic spines, whose interplay with Ca2+ sensors in turn influences the race for Ca2+.
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Affiliation(s)
- Vijeta Raghuram
- Centre for Cellular and Molecular Biology, CSIR Hyderabad, India
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Mikhaylova M, Hradsky J, Kreutz MR. Between promiscuity and specificity: novel roles of EF-hand calcium sensors in neuronal Ca2+ signalling. J Neurochem 2011; 118:695-713. [PMID: 21722133 DOI: 10.1111/j.1471-4159.2011.07372.x] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
In recent years, substantial progress has been made towards an understanding of the physiological function of EF-hand calcium sensor proteins of the Calmodulin (CaM) superfamily in neurons. This deeper appreciation is based on the identification of novel target interactions, structural studies and the discovery of novel signalling mechanisms in protein trafficking and synaptic plasticity, in which CaM-like sensor proteins appear to play a role. However, not all interactions are of plausible physiological relevance and in many cases it is not yet clear how the CaM signaling network relates to the proposed function of other EF-hand sensors. In this review, we will summarize these findings and address some of the open questions on the functional role of EF-hand calcium binding proteins in neurons.
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Affiliation(s)
- Marina Mikhaylova
- PG Neuroplasticity, Leibniz-Institute for Neurobiology, Magdeburg, Germany
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