Detailed Three- Dimensional Modeling of Cellular Signaling M. - - PowerPoint PPT Presentation

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Detailed Three- Dimensional Modeling of Cellular Signaling M. - - PowerPoint PPT Presentation

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Detailed Three- Dimensional Modeling of Cellular Signaling M. Wittmann, A. Eder, J.S. Wiegert, C.P. Bengtson, A. Hellwig, M. Knodel, R. Geiger, L.H. Ge, D. Bucher, C.M. Schuster, H. Bading, G. Wittum, G. Queisser Gillian Queisser G-CSC

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Gillian Queisser G-CSC University of Frankfurt

  • M. Wittmann, A. Eder, J.S. Wiegert, C.P. Bengtson, A. Hellwig, M. Knodel, R. Geiger,

L.H. Ge, D. Bucher, C.M. Schuster, H. Bading, G. Wittum, G. Queisser

Detailed Three- Dimensional Modeling

  • f Cellular Signaling
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Gillian Queisser G-CSC University of Frankfurt

Detailed Modeling

  • Describe biophysical processes in space and time

=> Set up systems of partial differential equations.

  • Resolve morphology, ideally from microscopy

image reconstruction => Discretization of computational domain.

  • Simulate biophysical signal processing on detailed

morphologies in space and time => Numerics: Discretization schemes, fast solvers.

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Gillian Queisser G-CSC University of Frankfurt

  • 1. Modeling Nuclear

Calcium Dynamics

  • 2. Modeling Synaptic

Transmission at the Drosophila NMJ

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Gillian Queisser G-CSC University of Frankfurt

  • 1. Modeling Nuclear

Calcium Dynamics

Wittmann et al. (2009) The Journal of Neuroscience 29(47):14687-14700

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Gillian Queisser G-CSC University of Frankfurt

Infoldings are formed by a membrane bilayer

Dissociated hippocampal culture Hippocampal brain slice

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Gillian Queisser G-CSC University of Frankfurt

Surface Reconstructions

Cell nuclei from hippocampal neurons

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Gillian Queisser G-CSC University of Frankfurt

Volume Reconstruction

  • Create volume mesh by tetrahedra grid generation (TetGen, http://tetgen.berlios.de/).
  • Integrate TetGen with Simulation Environment UG.
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Gillian Queisser G-CSC University of Frankfurt

Synapse to nucleus communication

Simulations on Reconstructed Morphologies – Cellular Calcium

Signaling

  • M. Wittmann, H. Bading (2006)
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Gillian Queisser G-CSC University of Frankfurt

Single CCT Simulation

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Gillian Queisser G-CSC University of Frankfurt

  • Infolded nuclei have larger surface area

compared to spherical nuclei.

  • Volume of nuclei is nearly constant

independent of morphology.

Reconstructed Nuclei – Measurements

Increased membrane area leads to increase in nuclear pore complexes (NPCs) Nuclear pore counts by imunoreactivity

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Gillian Queisser G-CSC University of Frankfurt

  • Depending on the compartment size, nuclei

show different calcium dynamics in their microdomains (A-D).

  • With increased compartment ratio

microdomain calcium levels become significantly higher (E).

Nuclei form nuclear signaling microdomains

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Gillian Queisser G-CSC University of Frankfurt

Frequency dependent dynamics

Changes of activity dynamics due to a change in frequency

0.1 Hz 0.5 Hz 1 Hz

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Queisser, G., Wiegert, S., Bading, H. (in press) Nucleus

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Gillian Queisser G-CSC University of Frankfurt

Large Small

1s 0.05 !F/F 1s

0.01 !F/F 0.2s

0.2s

2 4 6 8 10 2 4 6 8 10 12

Power x10

  • 3

Frequency (Hz)

2 4 6 8 10 0.0 0.1 0.2 0.3 0.4 0.5

Power x10

  • 3

Frequency (Hz)

Small Compartments Better Resolve Oscillating Ca2+ Signals

Experiment Model

ER Tracker Blue White DPX AM

  • 70mV

5mV 0.2s

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Gillian Queisser G-CSC University of Frankfurt

Integration vs. Detection

Nuclear Read-Out

Signal Integration Frequency Detection Queisser, G., Wiegert, S., Bading, H. (in press) Nucleus

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Gillian Queisser G-CSC University of Frankfurt Signal-regulation of Nuclear Geometry

  • Neuronal nuclei are extremely plastic and their geometry is controlled by NMDA receptor

activation.

  • Synaptic NMDA receptors promote the formation of infoldings.
  • Extrasynaptic NDMA receptors – they direct neurons towards degeneration and cell death –

lead to loss of nuclear infoldings.

  • How calcium signals are translated into structural alterations is still unknown.
  • ERK-MAP kinase pathway is required for the formation of infoldings (not presented).

Nucleoplasmic Reticulum - Yes or No?

  • 3D reconstructions and EM results show that the invaginations are lined by both the inner and
  • uter nuclear envelope, therefore the invaginated space is filled with cytosol, NOT ER lumen.
  • Nucleoplasmic reticulum does not exist in hippocampal neurons.
  • Infoldings enhance nuclear calcium signaling:

1.larger nuclear surface and increased number of NPCs 2.diffusion distances from cytosolic to nuclear locations are smaller. 3.Compartmentalization occurs allowing microdomains to regulate calcium dynamics differently from one another.

Some Results

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Gillian Queisser G-CSC University of Frankfurt

Some Results

Nuclear Geometry and Calcium Signaling

  • Compartments are often unequal in size, smaller ones better resolve high frequency calcium

signals.

  • May be relevant for activation of calmodulin, the principal calcium sensor.
  • Calcium oscillations may be important to activate CREB-dependent transcription during LTP

and memory formation.

  • This information relay may be optimized in small microdomains.
  • Spatial re-organization of chromosome territories may be caused due to changes in nuclear

architecture and therefore affect gene transcription.

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Gillian Queisser G-CSC University of Frankfurt

  • 2. Modeling Synaptic

Transmission at the Drosophila NMJ

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Gillian Queisser G-CSC University of Frankfurt

Biological Framework

  • The morphology of presynaptic specializations can vary

greatly ranging from classical single-release-site boutons in the central nervous system to boutons of various sizes harboring multiple vesicle release sites.

  • Basis of this analysis were the well-characterized

glutamatergic synapses of larval neuromuscular junctions (NMJs) of Drosophila.

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Gillian Queisser G-CSC University of Frankfurt

Two types of Boutons

  • Larval bodywall muscles of Drosophila are typically

innervated by two motor neurons of which one forms large ball-like Ib boutons and a second motor neuron forms smaller type Is boutons.

  • Generate three-dimensional density profiles of presynaptic

vesicles to monitor the local distribution and dynamics of vesicles as a function of bouton morphology.

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Gillian Queisser G-CSC University of Frankfurt

Important Parameters

  • Frequency
  • Vesicle output probability Po
  • Bouton size
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Gillian Queisser G-CSC University of Frankfurt

Simulations

Is bouton, Po = 90% Ib bouton, Po = 5% Simulation on 3D-reconstruction

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Gillian Queisser G-CSC University of Frankfurt

Synaptic Transmission at different input Frequencies

10 20 30 40 50 1 2 3 4 5 eEJP [mV]

Stimulus number [X1000]

15 Hz 30 Hz 60 Hz 80 Hz

In vivo In silico

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Gillian Queisser G-CSC University of Frankfurt

Output Probability, Size and Frequency

5 10 3 6

  • Av. ves/AP

time [s]

Po = 5 % Po = 40 % Po = 90 %

1 2 350 700

  • Av. ves/AP

time [s]

Po = 5 % Po = 40 % Po = 90 %

5 10 3 6

  • Av. ves/AP

time [s]

10% 20% 30% 40% 50% 60% 70% 80%

0,5 1 350 700

  • Av. ves/AP

time [s]

It Ib Is

0,5 1 1000 2000

  • Av. ves/AP

time [s]

It Ib Is

0,5 1 600 1200

  • Av. ves/AP

time [s]

10 Hz 20 Hz 32 Hz 40 Hz 50 Hz 64 Hz 80 Hz 100 Hz

0,5 1 600 1200

  • Av. ves/AP

time [s]

10 Hz 20 Hz 30 Hz 40 Hz 50 Hz 64 Hz 80 Hz 100 Hz

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Gillian Queisser G-CSC University of Frankfurt

Bouton Configurations

!

13

0,7 1,4 100 200

Averaged vesicle release per AP

time [sec]

Ib bouton, Po = 5 % Is bouton, Po = 90 %

10 20 30 40 0,4 0,8 1,2 Vesicle release time [s] Ib bouton Is bouton

Optimal bouton configurations predicted by model Native pattern – in vivo vs. in silico

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Gillian Queisser G-CSC University of Frankfurt

Conclusions

  • Po strongly affects the magnitude of total vesicle release at the beginning of

stimulation

  • Bouton size primarily affects the endurance of active vesicle release suggesting

that larger boutons are better suited for long bouts of synaptic activity whereas smaller boutons are only reliable with short trains of stimulation.

  • The model predicts that Ib boutons are utilized to transmit longer-lasting high-

frequency stimuli whereas Is boutons are better suited for few low-frequency events at high amplitudes.

  • Taken together Is and Ib boutons complement each others functionality,

forming an efficient system across different time scales.

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Gillian Queisser G-CSC University of Frankfurt

Thanks To

C.P. Bengtson

  • D. Bucher
  • A. Eder

L.H. Ge

  • R. Geiger
  • A. Hellwig
  • M. Knodel

J.S. Wiegert

  • H. Bading

C.M. Schuster

  • G. Wittum