Biology subjects

Jung, R. B.

Publications and source records attributed to Jung, R. B..

3 recordsLinked to original sources

bioRxiv2026

Fatty acid binding protein-8 (FABP8/PMP2) reveals molecular heterogeneity of myelin sheaths in the human CNS

Myelin is classically viewed as a uniform axon-insulating membrane, yet its molecular composition may differ between species and even within one species. Fatty acid binding protein-8 (FABP8/PMP2) was previously identified in CNS myelin of humans but not mice. Here we show that FABP8/PMP2 is a defining feature of CNS myelin in humans and old-world-monkeys, but absent from CNS myelin in other mammals, indicating evolutionary neofunctionalization of this lipid-binding protein in the primate lineage. In the human CNS, FABP8/PMP2 marks a subset of myelin sheaths that preferentially ensheath large-diameter axons, revealing sheath-to-sheath molecular heterogeneity correlated with axonal geometry. Chromatin is accessible at the PMP2/Pmp2 gene locus in oligodendrocytes of humans but not mice. Human oligodendrocytes intrinsically express FABP8/PMP2 when transplanted into mouse brains, demonstrating species-specific competence independent of environmental cues. Humanized transgenic mice expressing FABP8/PMP2 in oligodendrocytes form morphologically normal but developmentally transiently thicker myelin sheaths, and show elevated cholesterol content in purified myelin. Because FABP8/PMP2 binds cholesterol, we propose that its emergence in primate CNS myelin contributes to the cholesterol enrichment of human myelin. Thus, CNS myelin protein composition is evolvable and modular, with relevance for myelin lipids and morphology, and previously unrecognized complexity in neuron-glia co-adaptation. Main points- Fatty acid binding protein 8 (FABP8/PMP2) is present in CNS myelin of humans and old-world monkeys - PMP2 defines sheath-to-sheath heterogeneity in the human CNS - PMP2-immunopositive myelin ensheaths large-diameter axons - Human oligodendrocytes intrinsically express PMP2 upon transplantation into mice - Humanized PMP2-transgenic mice show thicker myelin and altered myelin lipid composition

neuroscience↗

bioRxiv2025

Adaptor protein complex 2 (AP2) participates in biogenesis and homeostasis of myelin sheaths in the central nervous system

Myelination of CNS axons requires oligodendrocytes to undergo extensive morphological changes by producing large amounts of myelin membrane with defined protein composition and structure. The formation of myelin sheaths thus involves efficient trafficking and sorting of future myelin constituents via vesicles that fuse with prospective myelin membranes by exocytotic mechanisms. However, the functional relevance of other trafficking steps in oligodendocytes for myelin biogenesis is largely unknown. Here, we followed the hypothesis that developmental myelination involves endocytic mechanisms. In this model, Golgi-derived vesicles fuse with the oligodendroglial plasma membrane, from which myelin constituents are retrieved by endocytosis into endosomal/lysosomal organelles before their final integration into the growing sheath. Considering that adaptor protein complex-2 subunit-{micro} (AP2M) facilitates AP2-dependent endocytosis, we recombined the Ap2m-gene in myelin-forming oligodendrocytes, causing both hypomyelination and specific changes in the myelin proteome. Most strikingly, lysosomal membrane proteins accumulate in the abaxonal (outermost) myelin layer, identifying this membrane as an active site for retrieving constituents from myelin sheaths. These data demonstrate that the AP2 complex serves a critical function in developmental myelination in vivo. Unexpectedly, we also observed pathological myelin outfoldings indicative of focal hypermyelination. Consistent with the hypothesis that this phenotype reflects impaired maintenance rather than biogenesis of myelin sheaths, recombination of the Ap2m-gene in oligodendrocytes of adult mice caused late-onset progressive focal hypermyelination. These results indicate that, in addition to astrocytic and microglial phagocytosis, oligodendrocytes cell-autonomously contribute to maintaining the structure of healthy myelin sheaths via AP2-dependent mechanisms.

neuroscience↗

bioRxiv2022

Potassium regulates axon-oligodendrocyte signaling and metabolic coupling in white matter

The integrity of myelinated axons relies on homeostatic support from oligodendrocytes (OLs), which is essential for brain function. However, the mechanisms by which OLs detect axonal spiking and rapidly control axon-OL metabolic coupling are largely unknown. Here, we combine optic nerve electrophysiology and two-photon imaging to study activity-dependent calcium (Ca2+) dynamics in OLs and metabolite fluxes in myelinated axons. Both high-frequency axonal firing and extracellular potassium (K+) elevations trigger a fast Ca2+ response in OLs that is facilitated by barium-sensitive, inwardly rectifying K+ channels. Using OL-specific Kir4.1 knockout mice (Kir4.1 cKO) we now demonstrate that, in addition to being crucial for K+ clearance, oligodendroglial Kir4.1 regulates axonal energy metabolism and long-term axonal integrity. Before the manifestation of axonal damage, we observed reduced glucose transporter GLUT1 and monocarboxylate transporter MCT1 expression in myelin of young Kir4.1 cKO mice, suggesting early deficits in metabolite supply to axons. Strikingly, we found lower resting lactate levels and activity-induced lactate surges in optic nerve axons of young Kir4.1 cKO mice. Moreover, both axonal glucose uptake and consumption were hampered in the absence of oligodendroglial Kir4.1, uncovering a new role of OLs in regulating axonal glucose metabolism. Our findings reveal a novel model of axon-OL signaling and metabolic coupling in which OLs detect high-frequency axonal activity through K+ signaling, which is critical in adjusting the axon-OL metabolic unit and in preserving long-term axonal health.

neuroscience↗