DNA polymerase kappa supports repair-associated DNA synthesis and neuronal genome resilience
Postmitotic neurons must preserve genome integrity for decades despite continuous oxidative, transcription-associated, and environmental DNA damage. Although recent studies have established ongoing repair-associated DNA synthesis in mature neurons, the polymerases that execute this synthesis remain incompletely defined. DNA polymerase kappa (POLK), a Y-family translesion synthesis polymerase, is highly expressed in neurons and undergoes an age-associated redistribution from the nucleus to the cytoplasm, suggesting that loss of nuclear POLK may compromise neuronal genome maintenance. Here, we investigated the consequences of POLK loss and augmentation in primary mouse cortical neurons and human induced pluripotent stem cell-derived forebrain neurons, including APOE e4/e4 backgrounds. Partial POLK depletion reduced neuronal arbor complexity, enlarged neuronal nuclei, increased LAMIN A/C and nuclear-envelope abnormalities, and induced a multidimensional senescence-like stress phenotype characterized by increased senescence-associated {beta}-galactosidase, p21, nuclear p38 MAPK, inflammatory signaling, lysosomal remodeling, and reduced mitochondrial-associated staining. POLK localized in proximity to EdU-labeled DNA in mature neurons, and POLK depletion reproducibly reduced EdU incorporation across independent human neuronal backgrounds and maturation stages. Exploratory nuclear POLK immunoprecipitation-mass spectrometry, together with proximity ligation assays, placed POLK near proteins involved in nucleotide excision repair, base-excision/single-strand break repair, DNA-end repair, checkpoint signaling, and specialized polymerase regulation, including PCNA-Ub and RAD18. POLK loss also produced Alzheimer disease-relevant cellular phenotypes. In wild-type neurons, POLK depletion increased 6E10 immunoreactivity and was accompanied by remodeling of APP/endosomal, lipid/cholesterol, and lysosomal pathways. In APOE e4/e4 neurons, POLK depletion increased cytoplasmic dsDNA and phospho-tau. Conversely, neuron-directed POLK augmentation increased EdU incorporation while reducing 53BP1 and {gamma}H2AX signals, p38 MAPK, cytoplasmic dsDNA, 6E10 immunoreactivity, and phospho-tau. Together, these findings identify POLK as a component of repair-associated DNA synthesis in mature neurons and support a model in which neuronal POLK availability contributes to genome maintenance, stress resilience, and vulnerability in aging and Alzheimer disease-relevant states.