ISR/eIF2α~P Overflow Represses Synaptic Proteostasis in Cortical Neurons in TDP-43-Type Frontotemporal Dementia

In ALS, chronic ISR activation creates an eIF2α~P state that represses axonal protein synthesis below synaptic maintenance thresholds, causing NMJ denervation. Analogously, in TDP-43-type FTD, chronic ISR activation driven by TDP-43 aggregates and proteostatic stress may repress local dendritic/synaptic protein synthesis required for glutamatergic synapse stability, contributing to early cortical synaptic loss and frontotemporal network dysfunction. The prediction is that cortical neurons in FTD patients will show elevated eIF2α~P and repressed synaptic proteome expression correlating with cognitive decline.

Analogy rationale: TDP-43 pathology is a shared hallmark of both ALS and FTD (FTD-TDP type B), and both diseases involve proteostatic stress from protein aggregation, providing a plausible mechanistic analog where ISR overflow similarly disrupts local protein synthesis essential for neuronal connectivity.

In ALS, chronic ISR activation creates an eIF2α~P state that represses axonal protein synthesis below synaptic maintenance thresholds, causing NMJ denervation. Analogously, in TDP-43-type FTD, chronic ISR activation driven by TDP-43 aggregates and proteostatic stress may repress local dendritic/synaptic protein synthesis required for glutamatergic synapse stability, contributing to early cortical synaptic loss and frontotemporal network dysfunction. The prediction is that cortical neurons in FTD patients will show elevated eIF2α~P and repressed synaptic proteome expression correlating with cognitive decline.

Analogy rationale: TDP-43 pathology is a shared hallmark of both ALS and FTD (FTD-TDP type B), and both diseases involve proteostatic stress from protein aggregation, providing a plausible mechanistic analog where ISR overflow similarly disrupts local protein synthesis essential for neuronal connectivity.

Disanalogies: ALS primarily affects motor neurons with peripheral NMJ denervation, whereas FTD targets cortical neurons involved in cognitive networks, and the predominance of tau (FTD-tau) or FUS (FTD-FUS) pathology in many FTD cases may not engage the same ISR activation dynamics as TDP-43 pathology.

Falsifiable prediction: Post-mortem frontal cortex tissue from FTD-TDP patients (vs. age-matched controls) will show: (1) elevated eIF2α~P (Ser51) by western blot, (2) decreased polysome association of synaptic mRNAs (CAMKIIα, Arc, PSD-95), and (3) the magnitude of eIF2α~P elevation will correlate inversely with synaptic density markers and antemortem cognitive decline scores.
This hypothesis was generated from `h-alsmnd-870c6115d68c` in `ALS` — judge it on its own merits but acknowledge the source.