Biology subjects

Lewis, R. W.

Publications and source records attributed to Lewis, R. W..

3 recordsLinked to original sources

bioRxiv2025

CNS Myelin Sheath Lengths Locally Scale to Axon Diameter via Piezo1

Myelin sheath lengths vary by an order of magnitude in the central nervous system (CNS) and tune the timing of neuronal signaling. Thus, variation in myelin sheath length has been proposed to coordinate the timing of neuronal signaling to ultimately impact behavior. The mechanisms to establish myelin sheath length are unknown. For decades, reports have documented that in vivo myelin sheath size scales with the diameter of the ensheathed axon. We previously demonstrated diameter is sufficient to instruct myelin sheath lengths formed by oligodendrocytes using a synthetic axon culture system. The mechanisms of oligodendrocyte diameter-sensing and its translation into sheath elongation are still unknown. Here we demonstrate that diameter-sensing and sheath length is locally regulated: each individual myelin sheath responds to the underlying fiber diameter. We uncover a novel mechanism for scaling myelin sheath length to fiber diameter, through mechanosensitive ion channel Piezo1. In vivo, Piezo1 impacts the elongation of myelin sheaths on large diameter axons, recapitulating our in vitro results. Yet, surprisingly, there is no impact on myelin thickness with conditional Piezo1 loss. We propose Piezo1 provides a mechanism to establish hard-wired myelin sheath patterns, where oligodendrocytes transduce axon diameter into generating myelin segments with vastly different lengths.

neuroscience↗

bioRxiv2025

Dominant MLC-causing mutations alter hepaCAM subcellular localization and protein interactome in astrocytes of the developing mouse cortex

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is a rare leukodystrophy characterized by early-onset macrocephaly, white matter edema, seizures, and motor and cognitive decline. Missense mutations to hepatic and glial cell adhesion molecule (hepaCAM), also known as GlialCAM, are responsible for approximately twenty-five percent of MLC cases. HepaCAM is highly enriched in astrocytes and plays important roles in astrocyte territory establishment, gap junction coupling, branching organization, synaptic function, and development of the gliovascular unit. The molecular mechanisms through which MLC-causing missense mutations alter hepaCAM function in vivo and facilitate MLC pathogenesis during brain development remain largely unknown. Here, we used new viral tools and proximity-based proteomics to examine how three different dominant MLC-causing mutations impact hepaCAM subcellular localization and protein interactome in astrocytes of the developing mouse cortex. We found dramatic defects in hepaCAM distribution throughout the astrocyte, which were common to all mutants tested. We also observed significant changes in protein interactome between wild type and mutant hepaCAM, including decreased association with previously described hepaCAM-interacting proteins Connexin 43 and CLC-2. Moreover, we identified changes in association between hepaCAM and a number of previously undescribed potential hepaCAM-interaction partners, including the epilepsy-associated potassium channel KCNQ2. Collectively, our data provide new insights into hepaCAM function in astrocytes during brain development, reveal altered hepaCAM protein dynamics with MLC missense mutations, and provide a new resource to explore the molecular underpinnings of MLC pathogenesis.

neuroscience↗

bioRxiv2022

The AMPK activator A-769662 inhibits human TASK3 potassium channels in an AMPK-independent manner

Heteromeric TASK1/3 channels play a fundamental role in oxygen-sensing by carotid body type 1 cells, where hypoxia-induced inhibition of TASK3 and/or TASK1/3 potassium currents leads to depolarisation, voltage-gated calcium entry, exocytotic transmitter release and increases in carotid body afferent input responses that initiate corrective changes in breathing patterns. However, the mechanism by which hypoxia leads to TASK-1/3 channel inhibition is still debated. It had been proposed that the AMP-activated protein kinase (AMPK) might directly phosphorylate and inhibit TASK channels, in particular TASK-3, although subsequent studies on rat type I cells argued against this view. Here we report on the effects of novel, highly selective AMPK activators on recombinant human TASK-3 potassium channels. Sequence alignment identified an AMPK recognition motif in TASK-3, but not TASK-1, with Ser55 representing a potential site for AMPK-dependent phosphorylation in TASK-3. However, neither of the AMPK activators, AICAR or MK-8722, caused a significant reduction of human TASK-3 current amplitude. By contrast, high concentrations of the AMPK activator A-769662 (100-500 {micro}M) inhibited human TASK-3 currents in a concentration-dependent manner. Importantly, A-769662 (300 {micro}M) also inhibited human TASK-3 channels in HEK293 cells that stably over-expressed an AMPK-{beta}1 subunit mutant (S108A) that renders AMPK insensitive to activators binding the Allosteric Drug and Metabolite (ADaM) site, such as A-769662. We therefore identify A-769662 as a novel human TASK-3 channel inhibitor and provide conclusive evidence that AMPK does not regulate TASK-3 channel currents.

pharmacology and toxicology↗