The eukaryotic initiation factor 2α (eIF2α) phosphorylation pathway critically regulates both cytoplasmic and mitochondrial protein synthesis, with mitochondrial translation dysfunction representing a key pathogenic mechanism in neurodegeneration. While cytoplasmic eIF2α phosphorylation by PERK initially serves as an adaptive response to ER stress, sustained phosphorylation creates a secondary pathological cascade affecting mitochondrial function. The molecular mechanism involves the disruption of nuclear-encoded mitochondrial ribosomal protein synthesis due to global translation attenuation. When eIF2α remains chronically phosphorylated, the reduced synthesis of mitochondrial ribosomal proteins (MRPs) and mitochondrial translation factors leads to impaired assembly of mitochondrial ribosomes (mitoribosomes). This creates a bottleneck in mitochondrial protein synthesis, particularly affecting the 13 core subunits of the electron transport chain complexes that are encoded by mitochondrial DNA.

The eukaryotic initiation factor 2α (eIF2α) phosphorylation pathway critically regulates both cytoplasmic and mitochondrial protein synthesis, with mitochondrial translation dysfunction representing a key pathogenic mechanism in neurodegeneration. While cytoplasmic eIF2α phosphorylation by PERK initially serves as an adaptive response to ER stress, sustained phosphorylation creates a secondary pathological cascade affecting mitochondrial function. The molecular mechanism involves the disruption of nuclear-encoded mitochondrial ribosomal protein synthesis due to global translation attenuation. When eIF2α remains chronically phosphorylated, the reduced synthesis of mitochondrial ribosomal proteins (MRPs) and mitochondrial translation factors leads to impaired assembly of mitochondrial ribosomes (mitoribosomes). This creates a bottleneck in mitochondrial protein synthesis, particularly affecting the 13 core subunits of the electron transport chain complexes that are encoded by mitochondrial DNA. The pathological significance emerges through a feed-forward loop: mitochondrial dysfunction increases reactive oxygen species production, which further activates PERK and maintains eIF2α phosphorylation. Simultaneously, impaired ATP production compromises the energy-dependent processes required for proper protein folding in the ER, perpetuating ER stress. The dysfunction of PPP1R15B-mediated dephosphorylation prevents recovery from this state, while defective eIF2B recycling maintains the translation block. This mechanism explains the particular vulnerability of neurons, which have high energy demands and limited regenerative capacity. The hypothesis predicts that interventions targeting mitochondrial translation machinery, such as enhancing mitoribosome assembly or supplementing mitochondrial translation factors, could break this pathological cycle even in the presence of sustained eIF2α phosphorylation, offering a novel therapeutic approach for neurodegenerative diseases characterized by mitochondrial dysfunction.