Enzyme-Constrained Metabolic Modeling of the Tripartite Synapse Links Astrocyte-Neuron Lactate Shuttle to Lipid Trafficking and Redox Homeostasis
- 1Washington State University
Abstract
Neuron-astrocyte metabolic coupling sustains synaptic function through coordinated substrate exchange, redox homeostasis, and lipid handling, yet the systems-level mechanism remains poorly understood. Here, we developed an enzyme-constrained, genome-scale metabolic model of the mouse tripartite synapse to test whether protein allocation can reproduce the astrocyte-neuron lactate shuttle (ANLS). Starting from the iMM1865 mouse metabolic model, we corrected mass and charge imbalances, expanded fatty acid and lipid pathways, and standardized annotations to obtain a high-quality, generic mouse model, improving the MEMOTE score from 46% to 83%. Cell type-specific astrocyte and neuron models were reconstructed using the integrative metabolic analysis tool (iMAT) with cell type-resolved mouse brain proteomics, and were further extended to represent the tripartite synapse. Enzyme-constrained resource allocation models (RAMs) were reconstructed for the astrocyte and neuron models using the GECKO 3.0 pipeline and integrated into a tripartite synapse community model via a modified SteadyCom framework. In the stoichiometry-only model, minimum lactate exchange remained at zero under ATP-maintenance and biomass objectives, indicating no coupling between astrocyte lactate secretion and neuronal uptake arising from the metabolic network itself. Imposing enzyme constraints made lactate secretion obligatory, with corresponding neuronal lactate uptake. Across 100 turnover-number bootstrap parameterizations, lactate coupling became obligatory under both objectives, with median onsets at 0.770 of maximal ATP-maintenance demand and 0.879 of maximal growth. This indicates that protein limitation can drive astrocyte-neuron lactate coupling consistent with ANLS, independent of modeling assumptions. Incorporation of reactive oxygen species (ROS) and lipid peroxidation pathways demonstrated that the brain-type fatty acid binding protein (FABP7) knockout redistributed flux away from astrocytic detoxification, increased neuronal ROS burden, and produced cell-type-specific changes in lipid-associated reporter metabolites, with prostaglandin J2 as the highest-ranked reporter metabolite. Model predictions, including lactate shuttling and lipid metabolic shifts in FABP7 knockout, align with published experimental studies, supporting the biological relevance of this framework. These findings indicate that ANLS emerges, at least in part, from enzyme limitation in the tripartite synapse model and that FABP7-mediated lipid trafficking is essential for lipid-redox homeostasis at the tripartite synapse.
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BibTeX
@misc{ayensu2026enzymeconstrained,
title = {{Enzyme-Constrained Metabolic Modeling of the Tripartite Synapse Links Astrocyte-Neuron Lactate Shuttle to Lipid Trafficking and Redox Homeostasis}},
author = {S. H. Ayensu and D. H. Horimoto and C. C. Flores and J. R. Gerstner and W. L. Schroeder},
howpublished = {bioRxiv},
year = {2026},
month = jun,
doi = {10.64898/2026.06.15.732277},
url = {https://www.biorxiv.org/content/10.64898/2026.06.15.732277v2},
note = {CC0},
}
RIS
TY - UNPB
TI - Enzyme-Constrained Metabolic Modeling of the Tripartite Synapse Links Astrocyte-Neuron Lactate Shuttle to Lipid Trafficking and Redox Homeostasis
AU - S. H. Ayensu
AU - D. H. Horimoto
AU - C. C. Flores
AU - J. R. Gerstner
AU - W. L. Schroeder
PY - 2026
DA - 2026/06/15
PB - bioRxiv
DO - 10.64898/2026.06.15.732277
UR - https://www.biorxiv.org/content/10.64898/2026.06.15.732277v2
AB - Neuron-astrocyte metabolic coupling sustains synaptic function through coordinated substrate exchange, redox homeostasis, and lipid handling, yet the systems-level mechanism remains poorly understood. Here, we developed an enzyme-constrained, genome-scale metabolic model of the mouse tripartite synapse to test whether protein allocation can reproduce the astrocyte-neuron lactate shuttle (ANLS). Starting from the iMM1865 mouse metabolic model, we corrected mass and charge imbalances, expanded fatty acid and lipid pathways, and standardized annotations to obtain a high-quality, generic mouse model, improving the MEMOTE score from 46% to 83%. Cell type-specific astrocyte and neuron models were reconstructed using the integrative metabolic analysis tool (iMAT) with cell type-resolved mouse brain proteomics, and were further extended to represent the tripartite synapse. Enzyme-constrained resource allocation models (RAMs) were reconstructed for the astrocyte and neuron models using the GECKO 3.0 pipeline and integrated into a tripartite synapse community model via a modified SteadyCom framework. In the stoichiometry-only model, minimum lactate exchange remained at zero under ATP-maintenance and biomass objectives, indicating no coupling between astrocyte lactate secretion and neuronal uptake arising from the metabolic network itself. Imposing enzyme constraints made lactate secretion obligatory, with corresponding neuronal lactate uptake. Across 100 turnover-number bootstrap parameterizations, lactate coupling became obligatory under both objectives, with median onsets at 0.770 of maximal ATP-maintenance demand and 0.879 of maximal growth. This indicates that protein limitation can drive astrocyte-neuron lactate coupling consistent with ANLS, independent of modeling assumptions. Incorporation of reactive oxygen species (ROS) and lipid peroxidation pathways demonstrated that the brain-type fatty acid binding protein (FABP7) knockout redistributed flux away from astrocytic detoxification, increased neuronal ROS burden, and produced cell-type-specific changes in lipid-associated reporter metabolites, with prostaglandin J2 as the highest-ranked reporter metabolite. Model predictions, including lactate shuttling and lipid metabolic shifts in FABP7 knockout, align with published experimental studies, supporting the biological relevance of this framework. These findings indicate that ANLS emerges, at least in part, from enzyme limitation in the tripartite synapse model and that FABP7-mediated lipid trafficking is essential for lipid-redox homeostasis at the tripartite synapse.
ER -