ABSTRACT
Neurons are the longest-lived cells in our bodies and lack DNA replication, which makes them reliant on a limited repertoire of DNA repair mechanisms to maintain genome fidelity. These repair mechanisms decline with age, but we have limited knowledge of how genome instability emerges and what strategies neurons and other long-lived cells may have evolved to protect their genomes over the human life span. A targeted sequencing approach in human embryonic stem cell-induced neurons shows that, in neurons, DNA repair is enriched at well-defined hotspots that protect essential genes. These hotspots are enriched with histone H2A isoforms and RNA binding proteins and are associated with evolutionarily conserved elements of the human genome. These findings provide a basis for understanding genome integrity as it relates to aging and disease in the nervous system.
Subject(s)
DNA Repair , Genome, Human , Genomic Instability , Neurons/metabolism , Aging/genetics , DNA Damage , DNA, Intergenic , Deoxyuridine/analogs & derivatives , Deoxyuridine/metabolism , Embryonic Stem Cells , Histones/metabolism , Humans , Mitosis , Mutation , Nervous System Diseases/genetics , Neurons/cytology , Promoter Regions, Genetic , RNA-Binding Proteins/metabolism , Sequence Analysis, DNA , Transcription, GeneticABSTRACT
A complex therapeutic challenge for Alzheimer's disease (AD) is minimizing deleterious aspects of microglial activation while maximizing beneficial actions, including phagocytosis/clearance of amyloid beta (Abeta) peptides. One potential target is selective suppression of microglial prostaglandin E(2) receptor subtype 2 (EP2) function, which influences microglial phagocytosis and elaboration of neurotoxic cytokines. To test this hypothesis, we transplanted bone marrow cells derived from wild-type mice or mice homozygous deficient for EP2 (EP2(-/-)) into lethally irradiated 5-month-old wild-type or APPswe-PS1DeltaE9 double transgenic AD mouse model recipients. We found that cerebral engraftment by bone marrow transplant (BMT)-derived wild-type or EP2(-/-) microglia was more efficient in APPswe-PS1DeltaE9 than in wild-type mice, and APPswe-PS1DeltaE9 mice that received EP2(-/-) BMT had increased cortical microglia compared with APPswe-PS1DeltaE9 mice that received wild-type BMT. We found that myeloablative irradiation followed by bone marrow transplant-derived microglia engraftment, rather than cranial irradiation or BMT alone, was responsible for the approximate one-third reduction in both Abeta plaques and potentially more neurotoxic soluble Abeta species. An additional 25% reduction in cerebral cortical Abeta burden was achieved in mice that received EP2(-/-) BMT compared with mice that received wild-type BMT. Our results provide a foundation for an adult stem cell-based therapy to suppress soluble Abeta peptide and plaque accumulation in the cerebrum of patients with AD.