Oligodendrocyte NRF2 deficiency drives myelin pathology in age-related cognitive decline
核心洞察
A study of the Lothian Birth Cohort 1936 links severe cognitive decline to thicker myelin, smaller myelinated axons, and increased degenerating axon profiles in the corpus callosum.
Single-nucleus RNA sequencing revealed an enrichment of oligodendrocytes with reduced NRF2 (搜索) expression in individuals with more severe cognitive decline.
Oligodendrocyte-specific NRF2 (搜索) knockout in mice blunted cognitive improvement over time and recapitulated the smaller-axon, thicker-myelin pathology seen in human aging.
A landmark investigation into the biology of age-related cognitive decline (搜索) has identified a previously unrecognized role for oligodendrocytes—the myelin-producing cells of the brain—and the transcription factor NRF2 (搜索) in driving white matter pathology associated with worsening cognition. Drawing on the Lothian Birth Cohort 1936 (LBC1936), the longest-running study of human cognition, researchers linked the severity of cognitive decline in aging to a shift in myelinated axon profiles, thicker myelin, and an accumulation of oligodendrocytes deficient in NRF2.
White matter pathology tracks cognitive decline in aging humans
The study examined samples from LBC1936, a cohort of individuals born in 1936 and living in the Lothian regions of Scotland, who were tested for IQ at age 11 and followed up at age 70 and every three years thereafter. Cognition from age 70 to 82 was measured using standardized tests across visuospatial, processing speed, and memory domains (Wechsler Adult Intelligence Scale III/Memory Scale III), with individual rates of cognitive decline modeled using latent growth curve modeling.
Almost all individuals with follow-up testing beyond age 70 exhibited cognitive decline (865 of 866), with an average rate of decline of −0.26 standard deviation units per year. Individuals with steeper-than-average decline were classified as "severe," while those with less negative trajectories were classified as "mild." Notably, cognitive decline trajectories beyond age 70 did not relate to age 11 IQ.
Focusing on the corpus callosum—a large white matter region involved in cognitive processing and vulnerable to age-related pathology—the researchers used spectral confocal reflectance (SCoRe) microscopy to detect compacted myelin, revealing a significant decrease in individuals with severe cognitive decline. Transmission electron microscopy of corpus callosum samples showed no differences in the density or percentage of myelinated axons. However, individuals with more severe cognitive decline displayed a shift in myelinated axon profiles toward smaller axon diameters, and myelin thickness was increased—measured by a reduced g ratio—but only for large-diameter axons (>1 µm).
The team also observed an increased frequency of "empty" myelinated profiles lacking an apparent axon, suggestive of the early stages of Wallerian degeneration, which rose with worse cognitive decline. Importantly, neither axon diameter, myelin thickness, nor the density of degenerating myelinated axon profiles was associated with age at death, sex, age 11 IQ, technical variables, or neuropathological indices of small vessel disease. A significant negative association between Braak stage and axon diameter suggested that smaller axons may be a shared pathological feature between age-associated cognitive decline and Alzheimer's disease (搜索) pathology.
Oligodendrocytes deficient in NRF2 accumulate in severe cognitive decline
To uncover mechanisms underlying this pathology, the researchers optimized a single-nucleus RNA sequencing (snRNA-seq) protocol for adult and aged human white matter. Fluorescence-activated nuclei sorting (FANS) improved yield tenfold without compromising nuclei quality or cell type proportions. Applying this pipeline to fresh-frozen corpus callosum samples from 14 individuals, the team retained 45,437 high-quality nuclei after quality control (97% of all nuclei), with an average of 2,740 genes and 7,706 unique molecular identifiers per nucleus.
Unexpectedly, oligodendrocyte abundance was increased with more severe cognitive decline, a finding validated by immunofluorescence staining for Olig2. Subclustering oligodendrocytes into seven subpopulations revealed that subclusters Oligo4 and Oligo5 showed the highest number of differentially expressed genes between mild and severe cognitive decline (167 and 113 genes, respectively). Ingenuity Pathway Analysis of these differentially expressed genes identified NRF2 (搜索) as the only upstream regulator shared across both Oligo4 and Oligo5, predicted to be downregulated with more severe cognitive decline (Z = 2.217 and Z = 2.183, respectively).
Immunostaining validated that the proportion of Olig2+ cells expressing NRF2 (搜索) protein was decreased with severe cognitive decline. The authors noted that global knockout of the gene encoding NRF2 (Nfe2l2 (搜索)) worsens cognitive impairment in mouse models of aging, Alzheimer's disease (搜索), vascular dementia, and infection, "yet the contributing cell types are unclear." Data-mining of a mouse model in which oligodendrocytes accumulate in excess (Olig2-Cre;Tfebfl/fl) showed that Nfe2l2 was significantly downregulated versus floxed controls (P = 2.6 × 10⁻⁶), indicating that accumulation of oligodendrocytes is sufficient to downregulate NRF2 gene expression.
NRF2 loss in oligodendrocytes recapitulates human pathology in mice
To test the functional consequences of NRF2 (搜索) downregulation, the researchers generated an oligodendrocyte-specific inducible conditional knockout of NRF2 (Plp-CreERT;Nfe2l2fl/fl), with recombination induced at 6 months of age. Behavioral testing using the Morris water maze (MWM) at 12 months—when wild-type mice begin to show learning and memory impairment—revealed that conditional knockout animals showed attenuated cognitive improvement over time. When percentage time spent in the target quadrant was plotted as a fold change relative to testing day 1, controls improved by an average of 57.75%, whereas conditional knockouts improved by only 27.82%.
Correlating individual cognitive performance with white matter histology, the researchers found that both axon diameter and g ratio were significantly reduced in poorer performers, indicating that smaller axons and thicker myelin are correlates of worse cognitive performance in aging mice. In late aging (15–18 months), myelinated axon diameter and g ratio were significantly reduced in conditional knockouts versus controls, suggesting that loss of NRF2 (搜索) in oligodendrocytes exacerbates the neuropathological features associated with age-related cognitive decline (搜索).
"These findings demonstrate that NRF2 (搜索) downregulation in oligodendrocytes is sufficient to blunt cognitive performance over time in aging and induce thicker myelin and a shift to smaller myelinated axon diameters, mirroring observations in severe cognitive decline in human aging," the authors wrote. "Altogether, these results indicate a novel role for oligodendroglial NRF2 in contributing to cognitive impairment in aging."
The study was conducted with ethics permission from the Multi-Centre Research Ethics Committee for Scotland, the Lothian Research Ethics Committee, and the Scotland A Research Ethics Committee, using brain samples from the Medical Research Council Brain Bank at The University of Edinburgh. Power calculations reached greater than 80% power for all experiments.