Astrocytes constitute a large portion of the brain’s total cell population and play specialized roles in ion homeostasis, neuronal function, synaptic transmission, blood-brain barrier integrity, and injury response. Astrocytes arise later than neurons during in vivo development as well as during in vitro differentiation protocols and contribute significantly to neural circuit development1. To model relevant neural cell-cell interactions in vitro, it is often advantageous to co-culture astrocytes with neurons. This protocol describes how complex intercellular interactions can be partially recapitulated in two-dimensional culture by separately deriving forebrain-type neurons and astrocytes from human pluripotent stem cells (hPSCs), then combining them into a co-culture.
* Required for forebrain-type neuron differentiation as outlined in the STEMdiff™ Forebrain Neuron Product Information Sheet.
✝ Required for astrocyte differentiation as outlined in the STEMdiff™ Astrocyte Product Information Sheet.
Figure 1. Schematic for Co-Culture of hPSC-Derived Forebrain Neurons with Astrocytes
hPSCs are independently differentiated into forebrain-type neurons and astrocytes that are then combined under optimized co-culture conditions.
Important Note: Prior to combining the cells (at Day 0 in Figure 1), differentiated astrocytes should be cultured in STEMdiff™ Astrocyte Maturation Medium for at least 3 weeks, and differentiated forebrain neurons should be cultured in STEMdiff™ Forebrain Neuron Maturation Medium for at least 1 week. The timeline depicted in Figure 1 is provided as a general guideline using these maturation periods. If desired, the maturation period for one or both cell types may be extended. As indicated in Figure 1, the timeline will also depend on whether the embryoid body (EB) protocol or monolayer protocol is used for each differentiation. Refer to the relevant Product Information Sheet (PIS) for protocol timelines prior to beginning your experiment. Co-cultures can be maintained for at least 1 - 2 weeks prior to performing analysis.
Note: When seeding neuronal precursors into STEMdiff™ Forebrain Neuron Maturation Medium (section C, step 1 of the PIS), the suggested density ranges from 1.5 x 104 - 6 x 104 cells/cm2, depending on the downstream application and intended culture length. The optimal density should be determined by the user.
Continue the forebrain neuron maturation phase until neurons have been cultured in STEMdiff™ Forebrain Neuron Maturation Medium for at least 1 week.
Verify successful forebrain neuron differentiation by performing immunocytochemistry on a subset of cultured cells:
Note: With conventional use of the STEMdiff™ forebrain neuron system, the cell population should be > 90% positive for ꞵIII-tubulin and FOXG1, and < 10% GFAP+.
Part III: Set Up Neuron-Astrocyte Co-Culture
Dissociate mature astrocytes from Part I according to steps 1 - 5 of section C (Astrocyte Maturation) of the STEMdiff™ Astrocyte PIS.
Note: Resuspend the cells in an appropriate volume of complete STEMdiff™ Astrocyte Maturation Medium, and perform a cell count using Trypan Blue and a hemocytometer.
Dilute the cell suspension in additional complete STEMdiff™ Astrocyte Maturation Medium to obtain the required cell concentration and volume.
Note: The concentration and volume of the astrocyte suspension should be optimized by the user and will depend on the desired astrocyte-to-neuron cell-type ratio, the number of culture wells used, and the initial cell density of forebrain neuronal precursors plated in Part II. The recommended astrocyte-to-neuron cell-type ratio ranges from 2:1 to 6:1.
Remove and discard the culture medium from the forebrain neurons generated in Part II.
Seed the resuspended astrocytes prepared in step 2 onto the forebrain neurons.
After 1 day, replace the medium with fresh STEMdiff™ Forebrain Neuron Maturation Medium.
Incubate the co-cultures at 37°C and 5% CO2. Perform a full-medium change with STEMdiff™ Forebrain Neuron Maturation Medium every 2 - 3 days. Co-cultures can be maintained for at least 1 - 2 weeks prior to analysis.
Scientific Resources for Neurological Disease Modeling
View webinars from leading researchers and browse scientific posters for examples of how to generate patient-specific neuronal cell types from induced pluripotent stem cells (iPSCs), bridging the gap between studies using animal models and clinical research.