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Open Access Publications from the University of California

Scholarly Works (8 results)

  • Thesis
  • Peer Reviewed
UC San Francisco Electronic Theses and Dissertations (2023)

After damage to white matter tracts in central nervous system (CNS) diseases such as multiple sclerosis (MS), myelin sheaths can be regenerated by activated oligodendrocyte precursor cells (OPCs). Failure of this remyelination program often occurs due to the improper expansion of the OPC population within sites of injury, contributing significantly to ongoing neurological dysfunction and disease progression. Understanding the biological underpinnings of developmental myelination and remyelination will reveal novel therapeutic strategies for disorders involving dysfunctional myelin regeneration. Importantly, OPCs dynamically produce primary cilia, microtubule-based organelles that transduce cues in a specialized signaling compartment. Here, we show that OPCs require primary cilia to respond properly to white matter injury (WMI). We demonstrate that removing primary cilia from OPCs results in significantly reduced OPC proliferation during both CNS development and WMI repair. Furthermore, we uncover a role for cAMP and CREB-mediated transcription, but not Hedgehog (Hh) signaling, in the ciliary control of OPC proliferation. This leads us to propose a G-protein coupled receptor (GPCR)/cAMP/CREB signaling axis initiated at the primary cilium as a crucial regulator of OPC biology. These findings advance our understanding of how OPCs coordinate complex cellular cues during remyelination in the CNS and presents the primary cilium as an organelle from which novel targets for remyelinating therapies may be identified.

    Cover page: Ciliary signaling in oligodendroglial development and white matter injury repair
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2017)
    Amyloid β-protein (Aβ) assembly is hypothesized to be a seminal neuropathologic event in Alzheimer's disease (AD). We used an unbiased D-amino acid substitution strategy to determine structure-assembly relationships of 76 different Aβ40 and Aβ42 peptides. We determined the effects of the substitutions on peptide oligomerization, secondary structure dynamics, fibril assembly dynamics, and fibril morphology. Our experiments revealed that the assembly of Aβ42 was more sensitive to chiral substitutions than was Aβ40 assembly. Substitutions at identical positions in the two peptides often, but not always, produced the same effects on assembly. Sites causing substantial effects in both Aβ40 and Aβ42 include His14, Gln15, Ala30, Ile31, Met35, and Val36. Sites whose effects were unique to Aβ40 include Lys16, Leu17, and Asn 27, whereas sites unique to Aβ42 include Phe20 and Ala21. These sites may be appropriate targets for therapeutic agents that inhibit or potentiate, respectively, these effects.
      Cover page: Identification of key regions and residues controlling Aβ folding and assembly
      • Article
      • Peer Reviewed
      UC San Francisco Previously Published Works (2023)
      Remyelination after white matter injury (WMI) often fails in diseases such as multiple sclerosis because of improper recruitment and repopulation of oligodendrocyte precursor cells (OPCs) in lesions. How OPCs elicit specific intracellular programs in response to a chemically and mechanically diverse environment to properly regenerate myelin remains unclear. OPCs construct primary cilia, specialized signaling compartments that transduce Hedgehog (Hh) and G-protein-coupled receptor (GPCR) signals. We investigated the role of primary cilia in the OPC response to WMI. Removing cilia from OPCs genetically via deletion of Ift88 results in OPCs failing to repopulate WMI lesions because of reduced proliferation. Interestingly, loss of cilia does not affect Hh signaling in OPCs or their responsiveness to Hh signals but instead leads to dysfunctional cyclic AMP (cAMP)-dependent cAMP response element-binding protein (CREB)-mediated transcription. Because inhibition of CREB activity in OPCs reduces proliferation, we propose that a GPCR/cAMP/CREB signaling axis initiated at OPC cilia orchestrates OPC proliferation during development and in response to WMI.
        Cover page: Primary cilia control oligodendrocyte precursor cell proliferation in white matter injury via Hedgehog-independent CREB signaling.
        • Article
        • Peer Reviewed
        UC San Francisco Previously Published Works (2021)
        Oligodendrocyte (OL) maturation arrest in human white matter injury contributes significantly to the failure of endogenous remyelination in multiple sclerosis (MS) and newborn brain injuries such as hypoxic ischemic encephalopathy (HIE) that cause cerebral palsy. In this study, we identify an oligodendroglial-intrinsic factor that controls OL maturation specifically in the setting of injury. We find a requirement for the ring finger protein Rnf43 not in normal development but in neonatal hypoxic injury and remyelination in the adult mammalian CNS. Rnf43, but not the related Znrf3, is potently activated by Wnt signaling in OL progenitor cells (OPCs) and marks activated OPCs in human MS and HIE. Rnf43 is required in an injury-specific context, and it promotes OPC differentiation through negative regulation of Wnt signal strength in OPCs at the level of Fzd1 receptor presentation on the cell surface. Inhibition of Fzd1 using UM206 promotes remyelination following ex vivo and in vivo demyelinating injury.
          Cover page: Oligodendroglial ring finger protein Rnf43 is an essential injury-specific regulator of oligodendrocyte maturation
          • Article
          • Peer Reviewed
          UC San Francisco Previously Published Works (2019)
          Disruption of the blood-brain barrier (BBB) is critical to initiation and perpetuation of disease in multiple sclerosis (MS). We report an interaction between oligodendroglia and vasculature in MS that distinguishes human white matter injury from normal rodent demyelinating injury. We find perivascular clustering of oligodendrocyte precursor cells (OPCs) in certain active MS lesions, representing an inability to properly detach from vessels following perivascular migration. Perivascular OPCs can themselves disrupt the BBB, interfering with astrocyte endfeet and endothelial tight junction integrity, resulting in altered vascular permeability and an associated CNS inflammation. Aberrant Wnt tone in OPCs mediates their dysfunctional vascular detachment and also leads to OPC secretion of Wif1, which interferes with Wnt ligand function on endothelial tight junction integrity. Evidence for this defective oligodendroglial-vascular interaction in MS suggests that aberrant OPC perivascular migration not only impairs their lesion recruitment but can also act as a disease perpetuator via disruption of the BBB.
            Cover page: Aberrant oligodendroglial–vascular interactions disrupt the blood–brain barrier, triggering CNS inflammation
            • Article
            • Peer Reviewed
            UC San Diego Previously Published Works (2021)
            Fibrosis is a common pathological response to inflammation in many peripheral tissues and can prevent tissue regeneration and repair. Here, we identified persistent fibrotic scarring in the CNS following immune cell infiltration in the experimental autoimmune encephalomyelitis (EAE) mouse model of multiple sclerosis. Using lineage tracing and single-cell sequencing in EAE, we determined that the majority of the fibrotic scar is derived from proliferative CNS fibroblasts, not pericytes or infiltrating bone marrow-derived cells. Ablating proliferating fibrotic cells using cell-specific expression of herpes thymidine kinase led to an increase in oligodendrocyte lineage cells within the inflammatory lesions and a reduction in motor disability. We further identified that interferon-gamma pathway genes are enriched in CNS fibrotic cells, and the fibrotic cell-specific deletion of Ifngr1 resulted in reduced fibrotic scarring in EAE. These data delineate a framework for understanding the CNS fibrotic response.
              Cover page: CNS fibroblasts form a fibrotic scar in response to immune cell infiltration
              • Article
              • Peer Reviewed
              UC San Francisco Previously Published Works (2018)
              Hypoxia can injure brain white matter tracts, comprised of axons and myelinating oligodendrocytes, leading to cerebral palsy in neonates and delayed post-hypoxic leukoencephalopathy (DPHL) in adults. In these conditions, white matter injury can be followed by myelin regeneration, but myelination often fails and is a significant contributor to fixed demyelinated lesions, with ensuing permanent neurological injury. Non-myelinating oligodendrocyte precursor cells are often found in lesions in plentiful numbers, but fail to mature, suggesting oligodendrocyte precursor cell differentiation arrest as a critical contributor to failed myelination in hypoxia. We report a case of an adult patient who developed the rare condition DPHL and made a nearly complete recovery in the setting of treatment with clemastine, a widely available antihistamine that in preclinical models promotes oligodendrocyte precursor cell differentiation. This suggested possible therapeutic benefit in the more clinically prevalent hypoxic injury of newborns, and we demonstrate in murine neonatal hypoxic injury that clemastine dramatically promotes oligodendrocyte precursor cell differentiation, myelination, and improves functional recovery. We show that its effect in hypoxia is oligodendroglial specific via an effect on the M1 muscarinic receptor on oligodendrocyte precursor cells. We propose clemastine as a potential therapy for hypoxic brain injuries associated with white matter injury and oligodendrocyte precursor cell maturation arrest.
                Cover page: Clemastine rescues myelination defects and promotes functional recovery in hypoxic brain injury.
                • Article
                • Peer Reviewed
                UC San Francisco Previously Published Works (2023)
                Oligodendrocyte precursor cells (OPCs) undergo an extensive and coordinated migration in the developing CNS, using the pre-formed scaffold of developed blood vessels as their physical substrate for migration. While OPC association with vasculature is critical for dispersal, equally important for permitting differentiation and proper myelination of target axons is their appropriate and timely detachment, but regulation of this process remains unclear. Here we demonstrate a correlation between the developmental formation of astrocytic endfeet on vessels and the termination of OPC perivascular migration. Ex vivo and in vivo live imaging shows that astrocyte endfeet physically displace OPCs from vasculature, and genetic abrogation of endfoot formation hinders both OPC detachment from vessels and subsequent differentiation. Astrocyte-derived semaphorins 3a and 6a act to repel OPCs from blood vessels at the cessation of their perivascular migration and, in so doing, permit subsequent OPC differentiation by insulating them from a maturation inhibitory endothelial niche.
                  Cover page: Astrocyte endfoot formation controls the termination of oligodendrocyte precursor cell perivascular migration during development.
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