Unraveling ChR2-driven stochastic Ca²⁺ dynamics in astrocytes – A call for new interventional paradigms

Abstract

26Control of astrocytes via modulation of Ca 2+ oscillations using techniques like optogenetics can prove to be crucial 27 in therapeutic intervention of a variety of neurological disorders. However, a systematic study quantifying the 28 effect of optogenetic stimulation in astrocytes is yet to be performed. Here, we propose a novel stochastic 29 Ca 2+ dynamics model that incorporates the light sensitive component -channelrhodopsin 2 (ChR2). Utilizing this 30 model, we studied the effect of various pulsed light stimulation paradigms on astrocytes for select variants of 31 ChR2 (wild type, ChETA, and ChRET/TC) in both an individual and a network of cells. Our results exhibited a 32 consistent pattern of Ca 2+ activity among individual cells in response to optogenetic stimulation, i.e., showing 33 steady state regimes with increased Ca 2+ basal level and Ca 2+ spiking probability. Furthermore, we performed a 34 global sensitivity analysis to assess the effect of stochasticity and variation of model parameters on astrocytic 35 Ca 2+ dynamics in the presence and absence of light stimulation, respectively. Results indicated that directing 36 variants towards the first open state of the photo-cycle of ChR2 (o 1 ) enhances spiking activity in astrocytes during 37 optical stimulation. Evaluation of the effect of astrocytic ChR2 expression (heterogeneity) on Ca 2+ signaling 38 revealed that the optimal stimulation paradigm of a network does not necessarily coincide with that of an 39 individual cell. Simulation for ChETA-incorporated astrocytes suggest that maximal activity of a single cell 40 reduced the spiking probability of the network of astrocytes at higher degrees of ChR2 expression efficiency due 41 to an elevation of basal Ca 2+ beyond physiological levels. Collectively, the framework presented in this study 42 provides valuable information for the selection of light stimulation paradigms that elicit optimal astrocytic activity 43 using existing ChR2 constructs, as well as aids in the engineering of future optogenetic constructs. 44 45 3 46 Author summary 47Optogenetics -an avant-garde technique involves targeted delivery of light sensitive ion channels to cells. 48Channelrhodopsin 2 (ChR2), an algal derived light sensitive ion channel has extensively been used in 49 neuroscience to manipulate various cell types in a guided and controlled manner. Despite being predominantly 50 used in neurons, recent advancements have led to the expansion of the application of optogenetics in non-neuronal 51 cell types, like astrocytes. These cells play a key role in various aspects of the central nervous system and 52 alteration of their signaling is associated with various disorders, including epilepsy, stroke and Alzheimer's 53 disease. Hence, invaluable information for therapeutic intervention can be obtained from using optogenetics to 54 regulate astrocytic activity in a strategic manner. Here, we propose a novel computational model to assess 55 astrocytic response to optogenetic stimulation which implicitly accounts for ...

Engaging Biological Oscillators through Second Messenger Pathways Permits Emergence of a Robust Gastric Slow-Wave during Peristalsis

“…An exchange of second messengers, namely, Ca 2+ and IP 3 can occur via gap junctions [22][23][24]81]. The flux describing Ca 2+ exchange between adjacent ICCs is modeled by a term…”

“…Previous modeling studies of intercellular Ca 2+ waves in astrocytes [35] and smooth muscle cells [24] support this approach of modeling Ca 2+ and IP 3 permeability. The exchange of IP 3 was modeled as proportional to the IP 3 concentration gradient between adjacent cells (see Methods, also [81]). Although IP 3 can diffuse within the cell cytoplasm and not necessarily through the gap junctions, we assumed that IP 3 only moves to the adjacent cells based on the concentration gradient.…”

A Digital Realization of Neuroglial Interaction Model and Its Network Structure

“…This network is called astroglia syncytium and a pair of coupled neurons is interacting with an astrocyte. Thus, gap junction flow for IP3 (𝐽𝐼𝑃3) and calcium (𝐽𝐶𝑎 2+ ) between two neighboring cells through GJs, are governed by the following equations respectively [42]:…”