An independent regulator of global release pathways in astrocytes generates a subtype of extracellular vesicles required for postsynaptic function

Extracellular vesicles (EVs) are heterogeneous in size, composition, and function. Researchers at Johns Hopkins University School of Medicine show that the six-transmembrane protein glycerophosphodiester phosphodiesterase 3 (GDE3) regulates actin remodeling, a global EV biogenic pathway, to release an EV subtype with distinct functions. GDE3 is necessary and sufficient for releasing EVs containing annexin A1 and GDE3 from the plasma membrane via Wiskott-Aldrich syndrome protein family member 3 (WAVE3), a major regulator of actin dynamics. GDE3 is expressed in astrocytes but not neurons, yet mice lacking GDE3 [Gde3 knockout (KO)] have decreased miniature excitatory postsynaptic current (mEPSC) amplitudes in hippocampal CA1 neurons. EVs from cultured wild-type astrocytes restore mEPSC amplitudes in Gde3 KOs, while EVs from Gde3 KO astrocytes or astrocytes inhibited for WAVE3 actin branching activity do not. Thus, GDE3-WAVE3 is a nonredundant astrocytic pathway that remodels actin to release a functionally distinct EV subtype, supporting the concept that independent regulation of global EV release pathways differentially regulates EV signaling within the cellular EV landscape.

GDE3 regulates postsynaptic responses via mGluR1/5.

(A and B) Measurements of mEPSC amplitudes in P12–15 Gde3 KO CA1 cells treated with Bay/MPEP. (A) Left: Superimposed representative averaged traces aligned by rise time. Middle: Graph quantifying the mean amplitude of each cell. Right: Cumulative distribution of amplitudes. WT and Gde3KO data are reproduced from Fig. 4A. (B) Graph quantifying the mean frequency of each cell. WT and Gde3KO data are reproduced from Fig. 4B. (C) Schematic of a model that posits that GDE3-WAVE3 is one of several pathways in astrocytes that integrate with the actin network to generate distinct MV subtypes with unique functions. GDE3 regulates WAVE3 to remodel the actin cytoskeleton to release MVs from the plasma membrane that contains GDE3 and annexin A1 (green, MVGDE3). MVGDE3s act on postsynaptic neurons to regulate postsynaptic responses through the inhibition of mGluR1/5. We hypothesize that alternative MV release pathways shown in purple and blue (1 and 2) can remodel actin to independently release distinct MV subtypes (MV1 and MV2) that have separate functions unrelated to MVGDE3. Thus, designated EV release pathways can independently regulate general mechanisms of EV release to control EV functional outputs. All bar graphs are means ± SEM; data points correspond to cells from six WT animals and four Gde3 KO animals treated with Bay/MPEP. ns, P > 0.05; *P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001. See table S1 for statistical details.