Biology subjects

Ruhwedel, T.

Publications and source records attributed to Ruhwedel, T..

12 recordsLinked to original sources

bioRxiv2025

Tether-mediated extraction of myelinoid bodies by microglia and astrocytes can maintain myelin integrity

Oligodendrocytes make myelin for the electrical insulation of axons and saltatory impulse conduction. Myelin lipids and proteins undergo a slow turnover, but exactly how the multilamellar and compacted membrane sheaths are remodeled without compromising myelin sheath integrity has remained puzzling, in particular at advanced age when myelin abnormalities increase. Earlier EM studies had suggested myelin membranes are shed and subsequently phagocytosed by microglia. However, the formation of multilamellar myelinoid bodies (MBs), leaving a well-ordered myelin sheath behind, is difficult to reconcile with simple shedding mechanisms. Here, we show by three-dimensional FIB-SEM reconstructions of optic nerves in mice and by two-photon live-imaging of myelinated cortical slices that MBs are initially connected to their parental sheaths by long tethers, which are stretched by trogocytosing microglia and astrocytes. We observe ruptured tethers attached to both MBs and sheaths, suggesting a novel mechanism of tension-driven tether scission. Importantly, the successive fusion of the corresponding innermost myelin membranes in an extended tether can preserve myelin sheath integrity. Thus, the remodeling by tether-mediated MB extraction emerges as a mechanism of physiological maintenance of myelin sheaths in the CNS.

neuroscience↗

bioRxiv2025

Charting the nanotopography of inner hair cell synapses using MINFLUX nanoscopy

For us to hear, the cochlea encodes sounds into neural signals at synapses of inner hair cells (IHCs) and the auditory nerve with remarkable fidelity. To achieve the high rates of temporally precise synaptic transmission over long periods of time, IHCs employ sophisticated ribbon-type active zones (AZ). In order for us to understand synaptic sound encoding, we need to decipher the underpinning molecular topography of these synapse which had remained challenging due to technological limitations. Here we applied 3-dimensional minimal flux optical nanoscopy to mouse IHC synapses to chart the position of key pre- and postsynaptic proteins with single digit nanometre resolution of imaging. We demonstrate that nanoclusters of channels and interacting proteins govern the topography of AZs and postsynaptic densities (PSDs). We count synaptic proteins, their nanoclusters and determine their spatial organization feeding into computational modelling of AZ function. In conclusion, this study reveals a nanocluster-based molecular AZ and PSD topography, likely serving as functional modules in synaptic sound encoding.

neuroscience↗

bioRxiv2025

Neuropeptide CRH prevents premature differentiation of OPCs following CNS injury and in early postnatal development

The role of neuropeptides and their receptors in oligodendrocyte progenitor cells (OPCs) has largely been overlooked so far. Here, we describe a new subpopulation of corticotropin-releasing hormone (CRH)-expressing OPCs that aggregate around acute brain injuries and exhibit an elevated capacity to differentiate into myelinating oligodendrocytes (OLs). We found that CRH expression in OPCs is rapidly induced de novo as a transient response within the first 72 hours after injury. As target cells, we identified CRH receptor type 1 (CRHR1)-expressing OPCs which show a decreased differentiation velocity. We demonstrate that CRH/CRHR1 system inactivation increases the speed of OL generation compromising the long-term survival of OLs after acute injury. Furthermore, we prove that a CRH/CRHR1 system deficiency under non-injury conditions leads to increased early postnatal oligodendrogenesis and alterations in adult myelination. Altogether, we show that OPC-derived CRH not only actively influences the injury environment through the interaction with CRHR1-expressing OPCs, but also identify the G-protein coupled receptor CRHR1 as a critical modulator of oligodendrogenesis at early postnatal stages with lasting effects on adult myelination.

neuroscience↗

bioRxiv2024

Axon demyelination and degeneration in a zebrafishspastizin model of hereditary spastic paraplegia

Hereditary spastic paraplegias (HSPs) are a diverse set of neurological disorders characterized by progressive spasticity and weakness in the lower limbs caused by damage to the axons of the corticospinal tract. More than 88 genetic mutations have been associated with HSP, yet the mechanisms underlying these disorders are little understood. We studied the pathogenesis of one form of HSP known as spastic paraplegia 15 (SPG15). This disorder is caused by mutations in the ZFYVE26 gene, which codes for a protein called SPASTIZIN. We show that, in zebrafish, the significant reduction of Spastizin caused degeneration of Mauthner (M)-cells. M-cell degeneration is associated with axon demyelination in the spinal cord and impaired locomotion in the spastizin mutants. Our findings reveal that the mutation not only compromises axonal integrity but also affects the structural molecules of the myelin sheath, laying the foundation for degeneration and advancing our understanding of the intricate mechanisms underlying HSPs.

neuroscience↗

bioRxiv2023

Oligodendrocytes and neurons contribute to amyloid-β deposition in Alzheimer's disease

In Alzheimers disease (AD), amyloid-{beta} (A{beta}) is thought to be of neuronal origin. However, in single-cell RNAseq datasets from mouse and human, we found transcripts of amyloid precursor protein (APP) and the amyloidogenic-processing machinery equally abundant in oligodendrocytes (OLs). By cell-type-specific deletion of Bace1 in a humanized knock-in AD model, APPNLGF, we demonstrate that almost a third of cortical A{beta} deposited in plaques is derived from OLs. However, excitatory projection neurons must provide a threshold level of A{beta} production for plaque deposition to occur and for oligodendroglial A{beta} to co-aggregate. Indeed, very few plaques are deposited in the absence of neuronally-derived A{beta}, although soluble A{beta} species are readily detected, especially in subcortical white matter. Our data identify OLs as a source of A{beta} in vivo and further underscore a non-linear relationship between cellular A{beta} production and resulting plaque formation. Ultimately, our observations are relevant for therapeutic strategies aimed at disease prevention in AD.

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↗

bioRxiv2022

Myelin lipids as nervous system energy reserves

Neuronal functions and impulse propagation depend on the continuous supply of glucose1,2. Surprisingly, the mammalian brain has no obvious energy stores, except for astroglial glycogen granules3. Oligodendrocytes make myelin for rapid axonal impulse conduction4 and also support axons metabolically with lactate5-7. Here, we show that myelin itself, a lipid-rich membrane compartment, becomes a local energy reserve when glucose is lacking. In the mouse optic nerve, a model white matter tract, oligodendrocytes survive glucose deprivation far better than astrocytes, by utilizing myelin lipids which requires oxygen and fatty acid beta-oxidation. Importantly, fatty acid oxidation also contributes to axonal ATP and basic conductivity. This metabolic support by fatty acids is an oligodendrocyte function, involving mitochondria and myelin-associated peroxisomes, as shown with mice lacking Mfp2. To study reduced glucose availability in vivo without physically starving mice, we deleted the Slc2a1 gene from mature oligodendrocytes. This caused a significant decline of the glucose transporter GLUT1 from the myelin compartment leading to myelin sheath thinning. We suggest a model in which myelin turnover under low glucose conditions can transiently buffer axonal energy metabolism. This model may explain the gradual loss of myelin in a range of neurodegenerative diseases8 with underlying hypometabolism9.

neuroscience↗

bioRxiv2021

Progressive axonopathy when oligodendrocytes lack the myelin protein CMTM5

Oligodendrocytes facilitate rapid impulse propagation along the axons they myelinate and support their long-term integrity. However, the functional relevance of many myelin proteins has remained unknown. Here we find that expression of the tetraspan-transmembrane protein CMTM5 (Chemokine-like factor-like MARVEL-transmembrane domain containing protein 5) is highly enriched in oligodendrocytes and CNS myelin. Genetic disruption of the Cmtm5-gene in oligodendrocytes of mice does not impair the development or ultrastructure of CNS myelin. However, oligodendroglial Cmtm5-deficiency causes an early-onset progressive axonopathy, which we also observe in global and in tamoxifen-induced oligodendroglial Cmtm5-mutants. Presence of the Wlds mutation ameliorates the axonopathy, implying a Wallerian degeneration-like pathomechanism. These results indicate that CMTM5 is involved in the function of oligodendrocytes to maintain axonal integrity rather than myelin biogenesis.

neuroscience↗

bioRxiv2021

Myelin biogenesis is associated with pathological ultrastructure that is resolved by microglia during development

To enable rapid propagation of action potentials, axons are ensheathed by myelin, a multilayered insulating membrane formed by oligodendrocytes. Most of the myelin is generated early in development, in a process thought to be error-free, resulting in the generation of long-lasting stable membrane structures. Here, we explored structural and dynamic changes in CNS myelin during development by combining ultrastructural analysis of mouse optic nerves by serial block face scanning electron microscopy and confocal time-lapse imaging in the zebrafish spinal cord. We found that myelin undergoes extensive ultrastructural changes during early postnatal development. Myelin degeneration profiles were engulfed and phagocytosed by microglia in a phosphatidylserine-dependent manner. In contrast, retractions of entire myelin sheaths occurred independently of microglia and involved uptake of myelin by the oligodendrocyte itself. Our findings show that the generation of myelin early in development is an inaccurate process associated with aberrant ultrastructural features that requires substantial refinement.

neuroscience↗

bioRxiv2020

WNT11 is a novel ligand for ROR2 in human breast cancer

Breast cancer has been associated with activation of the WNT signaling pathway, although the underlying molecular mechanisms are still unclear. Here, we found the WNT receptor ROR2 to be highly expressed in aggressive breast tumors and associated with worse metastasis-free survival. In order to understand the molecular basis of these observations, we overexpressed ROR2 in human breast cancer cell lines, inducing a BRCAness-like phenotype and rendering them resistant to PARP inhibition. High levels of ROR2 were associated with defects in cell morphology and cell-cell-contacts leading to increased tumor invasiveness. Using gene expression analysis we demonstrated an upregulation of several non-canonical WNT ligands in ROR2-overexpressing breast cancer cells, in particular WNT11. Co-immunoprecipitation confirmed that WNT11 is indeed a novel ligand for ROR2 that interacts with its cysteine-rich domain and triggers the invasion-promoting signaling via RHO/ROCK. Knockdown of WNT11 reversed the pro-invasive phenotype and the cellular changes in ROR2-overexpressing cells. Taken together, our studies revealed a novel auto-stimulatory loop in which ROR2 triggers the expression of its own ligand, WNT11, resulting in enhanced tumor invasion associated with breast cancer metastasis.

cancer biology↗

bioRxiv2020

White matter integrity requires continuous myelin synthesis at the inner tongue

Myelin, the electrically insulating axonal sheath, is composed of lipids and proteins with exceptionally long lifetime. This raises the question how myelin function is affected by myelin turnover. We have studied the integrity of myelinated tracts after experimentally preventing the formation of new myelin in the CNS of adult mice, using an inducible Mbp null allele. Oligodendrocytes survived recombination, continued expressing myelin genes, but failed to maintain compacted myelin sheaths. Using 3D electron microscopy and mass spectrometry imaging we visualized myelin-like membranes that failed to incorporate adaxonally, most prominently at juxta-paranodes. Myelinoid body formation indicated degradation of existing myelin at the abaxonal side and at the inner tongue of the sheath. Compacted myelin thinning and shortening of internodes, with about 50% myelin lost after 20 weeks (=5 months), ultimately led to axonal pathology and neurological disease. These data reveal that functional axon-myelin units require the continuous incorporation of new myelin membranes.

neuroscience↗

bioRxiv2019

A role of oligodendrocytes in information processing independent of conduction velocity

Myelinating oligodendrocytes enable fast impulse propagation along axons as revealed through studies of homogeneously myelinated white matter tracts. However, gray matter myelination patterns are different, with sparsely myelinated sections leaving large portions of the axons naked. The consequences of this patchy myelination for oligodendrocyte function are not understood but suggest other roles in information processing beyond the regulation of axonal conduction velocity. Here, we analyzed the contribution of myelin to auditory information processing using paradigms that are good predictors of speech understanding in humans. We compared mice with different degrees of dysmyelination using acute cortical multiunit recordings in combination with behavioral readouts. We identified complex alterations of neuronal responses that reflect fatigue and temporal acuity deficits. Partially discriminable but overall similar deficits were observed in mice with oligodendrocytes that can myelinate but cannot fully support axons metabolically. Thus, myelination contributes to sustained stimulus perception in temporally complex paradigms, revealing a role of oligodendrocytes in the CNS beyond the increase of axonal conduction velocity.

neuroscience↗