Glutamatergic dysfunction precedes neuron loss in cerebral organoids with MAPT mutation

Abstract

Frontotemporal dementia (FTD) due to MAPT mutation causes pathological accumulation of tau and glutamatergic cortical neuronal death by unknown mechanisms. We used human induced pluripotent stem cell (iPSC)-derived cerebral organoids expressing tau-V337M and isogenic corrected controls to discover early alterations due to the mutation that precede neurodegeneration. At 2 months, mutant organoids show upregulated expression of MAPT, and glutamatergic signaling pathways and regulators including the RNA-binding protein ELAVL4. Over the following 4 months, mutant organoids accumulate splicing changes, disruption of autophagy function and build-up of tau and P-tau S396. By 6 months, tau-V337M organoids show specific loss of glutamatergic neurons of layers affected in patients. Mutant neurons are susceptible to glutamate toxicity which was rescued pharmacologically by treatment with the PIKFYVE kinase inhibitor apilimod. Our results demonstrate a sequence of events that precede cell death, revealing molecular pathways associated with glutamate signaling as potential targets for therapeutic intervention in FTD.

Single cell transcriptomic profiling of tauopathy in a novel 3D neuron-astrocyte coculture model

“…Human oTau seeding in hiNCs before combination with hiACs allows for a discrete analysis of how neuronal tau pathology develops and interacts with neighboring astrocytes in a physiologically relevant spatial context. This targeted and controlled methodology allows for a deeper level of study of tau induced phenotypes in vitro beyond that previously shown [28][29][30]32,33,83,84 . Previous studies with microfluidic and organoid models have developed some phenotypes of interest such as tau hyperphosphorylation and neurodegeneration in glutamate toxicity challenged MAPT mutant iPSCs 83 , 29 .…”

“…The AstTau system allows for a detailed analysis of astrocytic phenotypes that are associated with tau pathology in a manner not easily studied with in vivo models that take 6-8 months to develop glial populations 29, 77 . The incorporation of hiACs in the AstTau model is necessary for neuronal survival in 3D culture, while also enabling study of the evolution of the interaction over the disease course.…”

“…This targeted and controlled methodology allows for a deeper level of study of tau induced phenotypes in vitro beyond that previously shown 28–30, 32, 33, 75, 76 . Previous studies with microfluidic and organoid models have developed some phenotypes of interest such as tau hyperphosphorylation and neurodegeneration in glutamate toxicity challenged MAPT mutant iPSCs 29, 75 . Models such as these and others including 2D models develop tau hyper-phosphorylation but no neurodegeneration 12–20 , and represent partial models of tauopathy.…”

“…Increasingly, investigators are turning to human induced pluripotent stem cells (hiPSCs) to overcome such challenges, but such 2D models typically exhibit limited arborization, neuron-neuron, neuron-glial interactions, and the extensive tau pathology and degeneration present in tauopathies [12][13][14][15][16][17][18][19][20][21][22][23][24][25] . Three-dimensional (3D) organoid models of tauopathies show great promise, but most require maturation over an extended time frame of months or years, lack an explicit ratio of neuron and glial compartments, and develop limited pathology and neurodegeneration [26][27][28][29][30][31][32][33][34][35] . This difficulty in producing an expedient human organoid model combined with the inadequacies of current animal models for tauopathies has stymied the development of effective research and therapeutics.…”

“…Three-dimensional (3D) organoid models of tauopathies show great promise, but most require maturation over an extended time frame of months or years, lack an explicit ratio of neuron and glial compartments, and develop limited pathology and neurodegeneration [26][27][28][29][30][31][32][33][34][35] . This difficulty in producing an expedient human organoid model combined with the inadequacies of current animal models for tauopathies has stymied the development of effective research and therapeutics.…”