Fig 1.
Description and characterization of Ca2+ signaling in the astrocytic compartment.
(A) Schematic of the astrocytic compartment along with all the molecular components. (B) Representative Ca2+ events from an astrocytic compartment stimulated with DHPG (100 μM, 2 sec). (C) Raster plot of Ca2+ events. (D) Distribution of Ca2+ event peak amplitudes from 400 trials. (E) Distribution of Ca2+ event rise times. (F) Histogram of full width at half maximum (FWHM). (G) Decay time histogram. (H) Temporal distributions of Ca2+ events from the model and experimental data (Marchaland et al., 2008a). Error bars indicate the standard error of the mean computed from 6 independent datasets.
Fig 2.
Description and characterization of the Ca2+-dependent gliotransmitter release machinery.
(A) Schematic of the gliotransmitter release machinery. (B) Pathways of release, endocytosis, and recycling of docked and mobile vesicles. (C) Vesicular release rate through Synaptotagmin 4 (Syt4) in response to a range of steady state Ca2+ concentrations. (D) Peak release rates of Syt4 are fitted to a Hill function to estimate the dissociation constant (kd). (E) Time to peak release rate of Syt4 decays exponentially with Ca2+ concentration. (F) Release rates of Synaptotagmin 7 (Syt7) in response to a range of steady state Ca2+ concentrations. (G) Peak release rates of Syt7. (H) Time to peak release rate of Syt7.
Fig 3.
Validation of the gliotransmitter release model.
(A) Raster plot of kiss-and-run and full fusion releases from an astrocytic compartment stimulated with DHPG (100 μM, 2 sec). (B) Distribution of kiss-an-run release times shows the rapid rise in release events that decay exponentially within the stimulus duration. (C) Temporal distribution indicates the comparatively slow and low number of full-fusion events that extends beyond the stimulus duration. (D) Time courses indicate the dynamics of docked vesicle release, endocytosis and reacidification. (E) Time courses indicate the dynamics of mobile vesicle release, endocytosis and reacidification. (F) Temporal distribution of total release events is in good agreement with experimental data from Marchaland et al. (Marchaland et al., 2008a). Error bars indicate the standard error of the mean computed from 6 independent sets of simulation trials.
Fig 4.
Characterization of the astrocytic compartmental models with Aβ-induced molecular alterations.
(A) Peak amplitudes of IP3 generated by DHPG stimulation from control and an astrocytic compartment with altered mGluR function are fitted to Hill functions for estimating dissociation constants (kd). (B) Steady-state PMCA fluxes from control and Aβ-PMCA conditions fitted to Hill functions. (C) Resting cytosolic Ca2+, IP3, and ER Ca2+ levels in control and Aβ-conditions. (D) Representative heat maps of Ca2+ signaling from control and Aβ conditions stimulated with DHPG. (E) Peak amplitude of Ca2+ event evoked with different DHPG concentrations. (F) Rate of Ca2+ events evoked by different DHPG concentrations. (G) Percentage Ca2+ response evoked by DHPG stimulation is higher the presence of Aβ conditions. Error bars indicate the standard error of the mean computed from 6 independent sets of simulation trials.
Fig 5.
Quantification of the dynamics and kinetics of Ca2+ events from astrocytic compartments stimulated with glutamate vesicles.
(A) Representative heat maps highlight the differences in Ca2+ dynamics in the presence of Aβ conditions. (B) Peak Ca2+ amplitude averaged across different ranges of stimulation frequencies. (C) Glutamate-evoked Ca2+ events are more frequent in astrocytes with Aβ conditions when compared to control. (D) The presence of Aβ-PMCA condition increases the (E) rise time, (F) decay time and (F) Full width at half maximum of astrocytic Ca2+ events. Error bars indicate the standard error of the mean from 6 independent datasets.
Fig 6.
Quantification of gliotransmission in astrocytic compartments stimulated with glutamate.
(A) Raster plots of kiss-and-run and full-fusion releases in control astrocyte and in the presence of Aβ conditions. Top: temporal histograms. (B) Rate of full fusions for different glutamate stimulation rates. Right: release rates for the three stimulus groups (C) Rate of kiss-and-run exocytosis. Right: release rates pooled into three simulation groups. Error bars indicate the standard error of the mean computed from 6 independent datasets.
Fig 7.
Synchrony of Ca2+ and gliotransmitter release events from astrocytic compartments stimulated with glutamate.
(A) Heat maps of Ca2+ event synchrony at different inter-event intervals and stimulation frequencies in the presence and absence of Aβ conditions. (B) Ca2+ synchrony averaged across event intervals at different glutamate stimulation rates is different between control and Aβ conditions. Right: at low stimulation regime, synchrony is high with the Aβ-PMCA condition, whereas at high stimulation rates, synchrony is more in the Aβ-mGluR condition (C) Heat maps of release event synchrony at different inter-event intervals and stimulation frequencies in the presence and absence of Aβ conditions. (D) synchrony of release averaged across event intervals at different glutamate stimulation rates is different between control and Aβ conditions. Right: bar graph indicates the increase in release synchrony at different stimulation regimes in all the Aβ conditions. Error bars indicate the standard error of the mean computed by bootstrapping 100 times with a sample size of 1000.
Fig 8.
Cross-correlation between individual Ca2+ and gliotransmitter release events are disrupted in astrocytic compartments with Aβ pathology.
(A) Peak cross-correlations between Ca2+ and release events become low at higher stimulation rates in astrocytes with Aβ conditions when compared to control. (B) Higher stimulation rates decrease population of docked vesicles in astrocytes with Aβ conditions when compared to control. (C) The presence of Aβ conditions shifts the relationship between peak cross-correlation and docked vesicle population.