Adhara Gaminde-Blasco

Alzheimer′s disease (AD) is characterized not only by neuronal loss and synaptic dysfunction but also by emerging evidence of oligodendrocyte and myelin pathology. Amyloid-β (Aβ), a hallmark of AD, disrupts oligodendrocyte homeostasis through mechanisms that remain poorly understood. Here, we investigated the role of the myelin regulatory factor (MYRF), a transcription factor essential for oligodendrocyte maturation, in AD-related glial dysfunction. Using the 3xTg-AD mouse model, we observed aberrantly induced maturation dynamics and reduced oligodendrocyte lineage cell density at 12 months in the dentate gyrus, accompanied by increased MYRF expression. Interestingly, sustained MYRF overexpression was found to be toxic for oligodendrocytes in vitro. Moreover, in vitro and in vivo experiments further demonstrated that Aβ exposure elevates MYRF protein levels and enhances its transcriptional activity, pointing to post-translational regulation. Mechanistically, Aβ impaired GSK3-dependent phosphorylation and Fbxw7-mediated ubiquitination of MYRF, prolonging N-MYRF stability, an effect prevented by PKC inhibition in vitro. Intracerebroventricular infusion of PKC inhibitor Gö6983 normalized MYRF levels, restored oligodendrocyte populations and myelin integrity, and improved hippocampal-dependent spatial learning in 3xTg-AD mice, with locomotor activity and anxiety-like behavior remaining unaffected. Together, these findings identify MYRF dysregulation as a mechanistic link between Aβ/PKC signaling and oligodendrocyte pathology, and highlight PKC inhibition as a potential strategy to restore oligodendroglial function and cognition in AD.

Oligodendrocyte dysfunction, myelin degeneration, and white matter changes are critical events in the cognitive decline of Alzheimer’s disease (AD). Amyloid-β peptide (Aβ), a hallmark of AD, disrupts oligodendrocyte and myelin homeostasis, through mechanisms that remain poorly understood. Here, transcriptomic profiling of Aβ-exposed oligodendrocytes revealed widespread gene expression changes, particularly in RNA-related processes. Among these, hnRNP A2, a key regulator of RNA transport and myelin protein regulation, was aberrantly upregulated in hippocampal oligodendrocytess from AD patients with high Aβ levels, from AD mouse models, and in Aβ-treated oligodendrocytes. RNA-immunoprecipitation sequencing of the hnRNP A2 interactome revealed Aβ-induced changes in mRNA interactions, particularly enriched binding to Mbp and Mobp, indicating impaired RNA metabolism of myelin components. Furthermore, Aβ, through hnRNP A2 disruption, increased the number, cargo and dynamics of Mbp- and Mobp-containing granules, enhanced MBP and MOBP synthesis, and decreased oligodendroglial voltage-gated Ca²⁺ influx in an MBP-dependent manner. These findings suggest that Aβ-induced dysregulation of hnRNP A2 impairs RNA metabolism and myelin protein synthesis, altering the intracellular Ca²⁺ homeostasis critical for oligodendrocyte function. Graphical abstract

Soluble forms of amyloid‐β (Aβ) peptide have been proposed as candidates to induce oligodendrocyte (OL) and myelin dysfunctions in the early stages of Alzheimer's disease (AD) pathology. Nevertheless, little is known about how Aβ affects OL differentiation and myelination in vivo, and the underlying molecular mechanisms. In this study, we explored the effects of a brain intraventricular injection of Aβ on OLs and myelin in the developing spinal cord of zebrafish larvae. Using quantitative fluorescent in situ RNA hybridization assays, we demonstrated that Aβ altered myrf and mbp mRNA levels and the regional distribution of mbp during larval development, suggesting an early differentiation of OLs. Through live imaging of Tg(myrf:mScarlet) and Tg(mbpa:tagRFP) zebrafish lines, both crossed with Tg(olig2:EGFP), we found that Aβ increased the number of myrf ⁺ and mbp ⁺ OLs in the dorsal spinal cord at 72 hpf and 5 dpf, respectively, without affecting total cell numbers. Furthermore, Aβ also increased the number of Sox10⁺cells, myelin sheaths per OL, and the number of myelinated axons in the dorsal spinal cord at 8 dpf compared to vehicle‐injected control animals. Interestingly, the treatment of Aβ‐injected zebrafish with the pan‐PKC inhibitor Gö6983 restored the aforementioned alterations in OLs and myelin to control levels. Altogether, not only do we demonstrate that Aβ induces a precocious oligodendroglial differentiation leading to dysregulated myelination, but we also identified PKC as a key player in Aβ‐induced pathology.

Amyloid β oligomers (Aβo) have been proposed as candidates to induce oligodendrocyte (OL) and myelin dysfunctions in early stages of Alzheimer’s disease (AD) pathology. Nevertheless, little is known about how Aβo affect OL differentiation and myelination in vivo , and the underlying molecular mechanisms. In this study, we explored the effects of a brain intraventricular injection of Aβo on OLs and myelin in the developing spinal cord of zebrafish larvae. Using quantitative fluorescent in situ RNA hybridization assays, we demonstrated that Aβo altered myrf and mbp mRNA levels and the regional distribution of mbp during larval development, suggesting an early differentiation of OLs. Through live imaging of Tg( myrf :mScarlet) and Tg( mbp :tagRFP) zebrafish lines, both crossed with Tg( olig2 :EGFP), we found that Aβo increased the number of myrf ⁺ and mbp ⁺ OLs in the dorsal spinal cord at 72 hpf and 5 dpf, respectively, without affecting total cell numbers. Furthermore, Aβo also increased the number of myelin sheaths per OL and the number of myelinated axons in the dorsal spinal cord compared to vehicle-injected control animals. Interestingly, the treatment of Aβo-injected zebrafish with the pan-PKC inhibitor Gö6983 restored the aforementioned alterations in OLs and myelin to control levels. Altogether, not only do we demonstrate that Aβo induce a precocious oligodendroglial differentiation leading to dysregulated myelination, but we also identified PKC as a key player in Aβo-induced pathology.

Oligodendrocyte dysfunction, myelin degeneration, and white matter structural alterations are critical events in Alzheimer’s disease (AD) that contribute to cognitive decline. A key hallmark of AD, Aβ oligomers, disrupt oligodendrocyte and myelin homeostasis, but a comprehensive global analysis of the mechanisms involved is lacking. Here, transcriptomic profiling of Aβ-exposed oligodendrocytes revealed widespread gene expression changes, particularly affecting pathways related to RNA localisation. Among the genes identified, we focused on Hnrnpa2/b1, the gene encoding the hnRNP A2 protein, which is essential for RNA transport and translation of myelin proteins. We confirmed aberrant upregulation of hnRNP A2 in hippocampal oligodendrocytes from post-mortem human brains of early-stage AD patients, Aβ-injected mouse hippocampi and Aβ-treated disrupting cells in vitro. RIP-seq analysis of the hnRNP A2 interactome revealed attenuated interactions with Hnrnpk and Hnrnpa2/b1, while interactions with Mbp and Mobp were enriched, suggesting changes in RNA metabolism of molecules associated with mRNA transport of myelin proteins. Aβ increased the total number and dynamics of mRNA-containing granules, facilitating local translation of the myelin proteins MBP and MOBP and attenuating Ca²⁺ signalling. These findings suggest that Aβ oligomers disrupt RNA metabolism mechanisms crucial for oligodendrocyte myelination through dysregulation of hnRNP A2 and myelin protein levels, potentially affecting oligodendroglia Ca²⁺ homeostasis.

The pathophysiological process of Alzheimer’s disease (AD) is believed to begin many years before the formal diagnosis of AD dementia. This protracted preclinical phase offers a crucial window for potential therapeutic interventions, yet its comprehensive characterization remains elusive. Accumulating evidence suggests that amyloid-β (Aβ) may mediate neuronal hyperactivity in circuit dysfunction in the early stages of AD. At the same time, neural activity can also facilitate Aβ accumulation through intricate feed-forward interactions, complicating elucidating the conditions governing Aβ-dependent hyperactivity and its diagnostic utility. In this study, we use biophysical modeling to shed light on such conditions. Our analysis reveals that the inherently nonlinear nature of the underlying molecular interactions can give rise to various modes of hyperactivity emergence. This diversity in the mechanisms of hyperactivity may ultimately account for a spectrum of AD manifestations.

Oxidized cholesterol metabolite 27‐hydroxycholesterol (27‐OH) is a potential link between hypercholesterolemia and neurodegenerative diseases since unlike peripheral cholesterol, 27‐OH is transported across the blood–brain barrier. However, the effects of high 27‐OH levels on oligodendrocyte function remain unexplored. We hypothesize that during hypercholesterolemia 27‐OH may impact oligodendrocytes and myelin and thus contribute to the disconnection of neural networks in neurodegenerative diseases. To test this idea, we first investigated the effects of 27‐OH in cultured oligodendrocytes and found that it induces cell death of immature O4⁺/GalC⁺ oligodendrocytes along with stimulating differentiation of PDGFR⁺ oligodendrocyte progenitors (OPCs). Next, transgenic mice with increased systemic 27‐OH levels (Cyp27Tg) underwent behavioral testing and their brains were immunohistochemically stained and lysed for immunoblotting. Chronic exposure to 27‐OH in mice resulted in increased myelin basic protein (MBP) but not 2′,3′‐cyclic‐nucleotide 3′‐phosphodiesterase (CNPase) or myelin oligodendrocyte glycoprotein (MOG) levels in the corpus callosum and cerebral cortex. Intriguingly, we also found impairment of spatial learning suggesting that subtle changes in myelinated axons of vulnerable areas like the hippocampus caused by 27‐OH may contribute to impaired cognition. Finally, we found that 27‐OH levels in cerebrospinal fluid from memory clinic patients were associated with levels of the myelination regulating CNPase, independently of Alzheimer's disease markers. Thus, 27‐OH promotes OPC differentiation and is toxic to immature oligodendrocytes as well as it subtly alters myelin by targeting oligodendroglia. Taken together, these data indicate that hypercholesterolemia‐derived higher 27‐OH levels change the oligodendrocytic capacity for appropriate myelin remodeling which is a crucial factor in neurodegeneration and aging.