ApoE maintains neuronal integrity via microRNA and H3K27me3-mediated repression

ApoE regulates neurogenesis, although how it influences genetic programs remains elusive. Cortical neurons induced from isogenic control and ApoE-/- human neural stem cells (NSCs) recapitulated key transcriptomic signatures of in vivo counterparts identified from single-cell human midbrain. Surprisingly, ApoE expression in NSC and neural progenitor cells (NPCs) is not required for differentiation. Instead, ApoE prevents the over-proliferation of non-neuronal cells during extended neuronal culture when it is not expressed. Elevated miR-199a-5p level in ApoE-/- cells lowers the EZH1 protein and the repressive H3K27me3 mark, a phenotype rescued by miR-199a-5p steric inhibitor. Reduced H3K27me3 at genes linked to extracellular matrix organization and angiogenesis in ApoE-/- NPC correlates with their aberrant expression and phenotypes in neurons. Interestingly, the ApoE coding sequence, which contains many predicted miR-199a-5p binding sites, can repress miR-199a-5p without translating into protein. This suggests that ApoE maintains neurons integrity through the target-directed miRNA degradation of miR-199a-5p, imparting the H3K27me3-mediated repression of non-neuronal genes during differentiation.

Altered stability of nuclear lamin-B marks the onset of aging in male Drosophila

Epigenetic alterations occur during aging, but it remains unclear what epigenetic features are associated with the onset of physiological decline in animals. Nuclear lamin-B forms the filamentous meshwork underneath the nuclear envelope, providing the structural scaffold necessary for genome organization and gene regulation. We found that reduced level of nuclear lamin-B protein coincides with the decline in locomotor activity and stress resistance in young adult male Drosophila. Ubiquitous lamin-B expression improves locomotor activity of the male flies at the expense of lower stress resistance and shorten lifespan. This observation suggests that tissue-specific expression of lamin-B may regulate different aspects of animal physiology during aging. To test this hypothesis, specific GAL-4 lines were used to drive the expression of lamin-B in specific neuronal populations and muscle tissues in male flies. Ectopic expression of lamin-B in the dopaminergic neurons within the protocerebral anterior medial region of the brain improves the locomotor activity of the male flies with little impact on their stress responses and lifespan. Interestingly, age-dependent decrease in the level of lamin-B protein is independent of its mRNA expression. Instead, cellular thermal shift assay showed that lamin-B and CP190 insulator protein undergo significant change in their solubility during aging. This suggests that the increased solubility of lamin-B protein may contribute to its reduced stability and degradation during aging.