An Efficient Platform for Astrocyte Differentiation from Human Induced Pluripotent Stem Cells

Abstract

Growing evidence implicates the importance of glia, particularly astrocytes, in neurological and psychiatric diseases. Here, we describe a rapid and robust method for the differentiation of highly pure populations of replicative astrocytes from human induced pluripotent stem cells (hiPSCs), via a neural progenitor cell (NPC) intermediate. We evaluated this protocol across 42 NPC lines (derived from 30 individuals). Transcriptomic analysis demonstrated that hiPSC-astrocytes from four individuals are highly similar to primary human fetal astrocytes and characteristic of a non-reactive state. hiPSC-astrocytes respond to inflammatory stimulants, display phagocytic capacity, and enhance microglial phagocytosis. hiPSC-astrocytes also possess spontaneous calcium transient activity. Our protocol is a reproducible, straightforward (single medium), and rapid (<30 days) method to generate populations of hiPSC-astrocytes that can be used for neuron-astrocyte and microglia-astrocyte co-cultures for the study of neuropsychiatric disorders.

Keywords: astrocyte; human induced pluripotent stem cell; iPSC.

Figure 1

Rapid Differentiation of hiPSC-Derived NPCs to Astrocyte-like Identity (A) Representative flow-cytometry analysis of S100β (top) and GFAP (bottom) for four 30-day hiPSC-astrocyte differentiations. Arrows indicate the cells positive for each marker protein. Appropriate secondary-only control is shown in black. (B) Graphs of flow-cytometry analysis across 35 hiPSC-astrocyte differentiations from 26 NPC lines from three independent hiPSC cohorts. S100β (left) and GFAP (right) immunostaining is shown, with primary human fetal astrocytes (positive control) and hiPSCs (negative control). (C) Representative immunofluorescence images of hiPSC-astrocytes stained for astrocyte markers, glutamate transporters GLAST (green), VIMENTIN (green), ALDH1L1 (red), and APOE (green). Scale bars, 100 μm. (D) mRNA levels of astrocyte markers: S100β, GFAP, VIM, AQU4, ACSBG1, and APOE in hiPSC-astrocytes (n = 3 from four different lines) and primary human fetal astrocytes (pAstrocytes; n = 3 from cerebral cortex astrocytes). Primer sequences are listed in Table S3. n, the number of independent experiments. (E) mRNA levels of neuronal markers: TUJ1, MAP2AB, RELN, and CACNA1C in hiPSC-astrocytes (n = 3 from four different lines) and pAstrocytes (n = 3 from cerebral cortex astrocytes), relative to hNGN2-induced neurons (n = 3 from two lines). Primer sequences are listed in Table S3. (F) Principal component analysis of lineage-specific marker expression in 23 pairs of hiPSC-astrocytes and isogenic source NPCs, together with four pAstrocyte lines isolated from fetal cerebral cortex, midbrain, cerebellum, and whole brain. (G) Flow-cytometry analysis of S100β (top) and GFAP (bottom) for pAstrocytes from the cerebral cortex, midbrain, cerebellum, and whole brain. Appropriate secondary-only control is shown in black. CC, cerebral cortex; Mid, midbrain; Cereb, cerebellum; Mixed, whole brain; hiPSC-Astros, hiPSC-astrocytes; pAstros, primary human fetal astrocytes. Data are presented as mean ± SD using two-tailed homoscedastic Student's t test. ^∗∗p < 0.01, ^∗∗∗p < 0.001.

Figure 2

Transcriptional Profile of hiPSC-Astrocytes and Primary Human Fetal Astrocytes RNA-seq analysis of hiPSC-derived NPCs (n = 8), neurons (n = 6), and astrocytes (n = 4) together with pAstrocytes from human fetal cerebral cortex and midbrain. (A and B) Principal component (P.Co) analysis (A) and clustering diagram (B) of hiPSC-derived NPCs, neurons, and astrocytes, together with pAstrocytes. (C) Volcano plot comparison of hiPSC-astrocytes to pAstrocytes (top), as well as to hiPSC-derived NPCs (middle) and neurons (bottom). Average log₂(fold change) versus −log₁₀(FDR) is shown for all genes. Genes upregulated and downregulated by 2-fold change and FDR < 0.05 are labeled by red dots. The number of genes differentially expressed between different cell types is indicated by the red color density and quantified in Figure S2B. (D) Scatterplot (left) comparing gene expression in hiPSC-astrocytes and pAstrocytes. r represents the Spearman correlation coefficient. Venn diagram (right) of overlapping gene expression (CPM > 5) between hiPSC-astrocytes and pAstrocytes. (E) Functional pathway enrichment analysis of differentially expressed genes between hiPSC-astrocytes and pAstrocytes (left), hiPSC-astrocytes and NPCs (middle), and pAstrocytes and NPCs (right); hiPSC-astrocytes and pAstrocytes express increased extracellular cell communication signals, but decreased neuronal signals relative to NPCs. (F) Heatmap produced by Wilcoxon's rank-sum comparisons of hiPSC-derived NPCs, neurons, and astrocytes, as well as pAstrocytes, relative to the Allen BrainSpan Atlas. (G) Fold enrichment from functional pathway analysis of astrocyte-enriched genes, group G2 sorted from top 100 most variable genes from Figure S3A and Table 2.

Figure 3

Characterization of the Neuroinflammatory Status and Reactivity of hiPSC-Astrocytes (A) Cluster analysis of hiPSC-derived NPCs, neurons, and astrocytes, as well as pAstrocytes, combined with a human adult brain dataset (Zhang et al., 2016). hiPSC-Astros, hiPSC-astrocytes; pAstros, primary human fetal astrocytes; FDR, false discovery rate; CPM, counts per million. (B) Cluster diagram of hiPSC-astrocytes and pAstrocytes compared with the astrocyte reactivity dataset (Zamanian et al., 2012), which was sorted by reactivity genes enriched in the A1 (LPS-treatment), A2 (MCAO ischemia), and pan-reactive phenotypes, or related controls (saline and sham, respectively). (C) IL-6 secretion from pAstrocytes (cerebral cortex, midbrain, cerebellum and whole brain [mixed regions]) and negative controls (fibroblasts and NPCs), after 24-hr treatment with 50 ng/mL or 100 ng/mL poly(I:C), 10 μg/mL or 50 μg/mL LPS, or 5 μM or 10 μM Aβ42 and its relative vehicle controls (saline for poly(I:C) and LPS, and Tris-HCl [pH 8] for Aβ(1–42)), as measured by ELISA. (D) IL-6 secretion following 24-hr treatment with poly(I:C), LPS, and Aβ42 across hiPSC-astrocyte differentiations from nine NPC lines from three independent hiPSC cohorts. hiPSC-Astros, hiPSC-astrocytes; pAstros, primary human fetal astrocytes. Data are presented as mean ± SD using one-way ANOVA with Tukey multiple comparison test. n.s., not significant; ^∗p < 0.05, ^∗∗∗p < 0.001.

Figure 4

Impact of hiPSC-Astrocytes on the Phagocytic Capacity of BV2 Microglial Cells (A) Phagocytic indices of BV2 cells, hiPSC-astrocytes, and pAstrocytes incubated with 20 μg of pHrodo-labeled myelin for 3 hr and analyzed by flow cytometry. (B) Amnis images representative of pHrodo red myelin after engulfment in hiPSC-astrocytes, pAstrocytes, and BV2 cells. (C) Phagocytic indices of BV2 microglia co-cultured with hiPSC-astrocytes and pAstrocytes that were treated with 30 μg of pHrodo-labeled zymosan for 3 hr and analyzed by flow cytometry, F(3, 33) = 79.33. (D) Phagocytic indices of BV2 microglia treated with astrocyte conditioned medium for 20 hr and then incubated with 30 μg of pHrodo-labeled zymosan for 3 hr for analysis by flow cytometry, F(3, 13) = 30.80. Data are representative of three independent experiments from 6–8 different control hiPSC-astrocytes and 2–4 different pAstrocytes and are shown as mean ± SEM. Similar significance was obtained in two other independent experiments. hiPSC-Astros, hiPSC-astrocytes; pAstros, primary human fetal astrocytes. Treatment with 2 μM cytochalasin D (Cyt) was used as a negative control for phagocytosis inhibition.

Figure 5

Spontaneous and Glutamate-Responsive Calcium Transients in hiPSC-Astrocytes and Primary Astrocytes (A and C) Representative Fluo-4-stained hiPSC-astrocytes and pAstrocytes. Note similarity in shape of cells. (B and D) Plots of fluorescence (RFUs) versus time for 25 regions of interest from hiPSC-astrocytes and pAstrocytes. (E) Average number of spontaneously active cells per field (318 μm²) for hiPSC-astrocytes (n = 22 fields from four different lines) and pAstrocytes (n = 12 fields from three different preparations of cerebral cortex astrocytes). n, the number of fields. (F) Average number of calcium spikes per 348-s trace for hiPSC-astrocytes (n = 22) and pAstrocytes (n = 12). (G) Average amplitude of calcium spike in each 348-s trace for hiPSC-astrocytes (n = 22) and pAstrocytes (n = 12). Peak excludes the amplitude of the glutamate-induced spike. Each point represents the average multiple regions of interest per 318 μm². Line shows mean ± SEM. hiPSC-Astros, hiPSC-astrocytes, pAstros, primary human fetal astrocytes. Using a two-tailed Student's t test, n.s., not significant; ^∗∗p < 0.05.