Biology subjects

Dupree, J. L.

Publications and source records attributed to Dupree, J. L..

8 recordsLinked to original sources

bioRxiv2026

ORMDL3-mediated SPT regulation Coordinates Myelin Sphingolipid and Protein Synthesis in Oligodendrocytes

Myelin is an essential and highly specialized membrane in the central and peripheral nervous systems that enwraps axons to accelerate electrical transmission and support neuronal health. The generation of this multilamellar structure requires a tightly coordinated synthesis of specific proteins and lipids. Among these are sphingolipids (SLs), which are major components of myelin. SL production is initiated by the serine palmitoyltransferase (SPT) enzyme complex, the rate-limiting enzyme in the de novo SL biosynthesis pathway. ORMDL proteins (ORMDL1-3) are the regulatory subunits of SPT, which, by sensing ceramide levels, tune SL flux. Although ORMDL3 has been linked to asthma and peripheral myelination, its role in CNS myelination and the CNS myelin-making oligodendrocytes (OLGs) remains unclear. We therefore assessed the function of ORMDL3 in OLs by generating a Cnp-Cre-driven, oligodendrocyte-specific Ormdl3 conditional knockout (cKO) mouse model. Loss of Ormdl3 selectively increased myelin SLs, particularly long-chain sulfatides, without altering ceramide or galactosylceramide abundance. These changes are most prominent around postnatal day 35, a developmental period of active myelin turnover. Ultrastructural analysis of optic nerves shows a thicker myelin sheath and increased axon caliber in cKO mice. Unexpectedly, deletion of Ormdl3 also increases levels of major myelin proteins (MBP, MOG, and PLP) and is accompanied by dynamic, region- and sex-dependent regulation of enzymes involved in sulfatide biosynthesis, without altering OLGs number or maturation. Together, for the first time, these findings identify Ormdl3 as a key regulator of SL homeostasis during developmental myelination and suggest that it helps synchronize lipid synthesis with myelin protein expression.

biochemistry↗

bioRxiv2024

Endosome maturation is orchestrated by inside-out proton signaling through a Na+/H+ exchanger and pH-dependent Rab GTPase cycling

Endosome maturation requires progressive lumen acidification. To what extent is lumen acidification sensed by cytosolic-side molecules that drive endosome maturation? We show here that "inside-out" proton signaling through the endosomal Na+/H+ Exchanger 6 (NHE6) activates the late endosome master regulator Rab7. The mechanism involves potent inactivation of the Rab7 GTPase-activating protein (GAP) TBC1D5 with decreasing pH. NHE6 interacts with TBC1D5 in a complex with Rab7. Neurons from NHE6-null mice or mice engineered with a selective defect in NHE6 proton efflux exhibit blocked endosome maturation and decreased active Rab7, consistent with an overactive Rab7 GAP. Finally, epistatic knock-down of TBC1D5, thereby reducing Rab7 GAP activity, in NHE6-null neurons rescues Rab7 GTPase cycling and endosome maturation. Importantly, NHE6 is mutated in Christianson Syndrome underscoring the significance of these mechanisms to neurodegeneration. We conclude that lumen acidification regulates pH-dependent Rab GTPase cycling to coordinate late endosome maturation by a process involving proton signaling.

cell biology↗

bioRxiv2024

Sulfatide deficiency-induced astrogliosis and myelin lipid dyshomeostasis are independent of Trem2-mediated microglial activation

Disrupted lipid homeostasis and neuroinflammation often co-exist in neurodegenerative disorders including Alzheimers disease (AD). However, the intrinsic connection and causal relationship between these deficits remain elusive. Our previous studies show that the loss of sulfatide (ST), a class of myelin-enriched lipids, causes AD-like neuroinflammatory responses, cognitive impairment, bladder enlargement, as well as lipid dyshomeostasis. To better understand the relationship between neuroinflammation and lipid disruption induced by ST deficiency, we established a ST-deficient mouse model with constitutive Trem2 knockout and studied the impact of Trem2 in regulating ST deficiency-induced microglia-mediated neuroinflammation, astrocyte activation and lipid disruption. Our study demonstrates that Trem2 regulates ST deficiency-induced microglia-mediated neuroinflammatory pathways and astrogliosis at the transcriptomic level, but not astrocyte activation at the protein level, suggesting that Trem2 is indispensable for ST deficiency-induced microglia-mediated neuroinflammation but not astrogliosis. Meanwhile, ST loss-induced lipidome disruption and free water retention were consistently observed in the absence of Trem2. Collectively, these results emphasize the essential role of Trem2 in mediating lipid loss-associated microglia-mediated neuroinflammation, but not both astrogliosis and myelin lipid disruption. Moreover, we demonstrated that attenuating neuroinflammation has a limited impact on brain ST loss-induced lipidome alteration or AD-like peripheral disorders. Our findings suggest that preserving lipidome and astrocyte balance may be crucial in decelerating the progression of AD.

neuroscience↗

bioRxiv2024

A Statistically-Robust Model Of The Axomyelin Unit Under Normal Physiologic Conditions With Application To Disease States

Despite tremendous progress in characterizing the myriad cellular structures in the nervous system, a full appreciation of the interdependent and intricate interactions between these structures is as yet unfulfilled. Indeed, few more so than the interaction between the myelin internode and its ensheathed axon. More than a half-century after the ultrastructural characterization of this axomyelin unit, we lack a reliable understanding of the physiological properties, the significance and consequence of pathobiological processes, and the means to gauge success or failure of interventions designed to mitigate disease. Herein, we highlight shortcomings in the most common statistical procedures used to characterize the axomyelin unit, with particular emphasis on the underlying principles of simple linear regression. These shortcomings lead to insensitive detection and/or ambiguous interpretation of normal physiology, disease mechanisms and remedial methodologies. To address these problems, we syndicate insights from early seminal myelin studies and use a statistical model of the axomyelin unit that is established in the accompanying article. Herein, we develop and demonstrate a statistically-robust analysis pipeline with which to examine and interpret axomyelin physiology and pathobiology in two disease states, experimental autoimmune encephalomyelitis and the rumpshaker mouse model of leukodystrophy. On a cautionary note, our pipeline is a relatively simple and streamlined approach that is not necessarily a panacea for all g ratio analyses. Rather, it approximates a minimum effort needed to elucidate departures from normal physiology and to determine if more comprehensive studies may lead to deeper insights.

neuroscience↗

bioRxiv2023

Adult-onset CNS sulfatide deficiency causes sex-dependent metabolic disruption in aging

The interconnection between obesity and central nervous system (CNS) neurological dysfunction has been widely appreciated. Accumulating evidence demonstrates that obesity is a risk factor for CNS neuroinflammation and cognitive impairment. However, the extent to which CNS disruption influences peripheral metabolism remains to be elucidated. We previously reported that myelin-enriched sulfatide loss leads to CNS neuroinflammation and cognitive decline. In this study, we further investigated the impact of CNS sulfatide deficiency on peripheral metabolism while considering sex- and age-specific effects. We found that female sulfatide-deficient mice gained significantly more body weight, exhibited higher basal glucose levels, and were glucose intolerant during glucose-tolerance test (GTT) compared to age-matched controls under a normal diet, whereas male sulfatide-deficient mice only displayed glucose intolerance at a much older age compared to female sulfatide-deficient mice. Mechanistically, we found the increased body weight was associated with increased food intake and elevated neuroinflammation, especially in the hypo-thalamus, in a sex-specific manner. Our results suggest that CNS sulfatide deficiency leads to sex-specific alterations in energy homeostasis via dysregulated hypothalamic control of food-intake.

neuroscience↗

bioRxiv2022

Alterations of the axon initial segment in multiple sclerosis

Grey matter damage has been established as a key contributor to disability progression in multiple sclerosis. Aside from neuronal loss and axonal transections, which predominate in cortical demyelinated lesions, synaptic alterations have been detected in both demyelinated plaques and normal-appearing grey matter, resulting in functional neuronal damage. The axon initial segment is a key element of neuronal function, responsible for action potential initiation and maintenance of neuronal polarity. Despite several reports of profound axon initial segment alterations in different pathological models, among which experimental auto-immune encephalomyelitis, whether the axon initial segment is affected in multiple sclerosis is still unknown. Using immunohistochemistry, we analyzed axon initial segments from control and multiple sclerosis tissue, focusing on layer 5/6 pyramidal neurons in the neocortex and Purkinje cells in the cerebellum and performed analysis on the parameters known to control neuronal excitability, i.e., axon initial segment length and position. We found that the axon initial segment length was unchanged among the different multiple sclerosis samples, and not different from controls. In contrast, in both cell types, the axon initial segment position was altered, with an increased soma-axon initial segment gap, in both active and inactive demyelinated lesions. In addition, using a computational model, we show that this increased gap between soma and axon initial segment might increase neuronal excitability. Taken together, these results show for the first time changes of axon initial segments in multiple sclerosis, in active as well as inactive grey matter lesions in both neocortex and cerebellum, which might alter neuronal function.

neuroscience↗

bioRxiv2021

The Long Noncoding RNA FEDORA is a Cell-Type- and Sex-Specific Regulator of Depression

Women suffer from depression at twice the rate of men, but the underlying molecular mechanisms are poorly understood. Here, we identify dramatic baseline sex differences in expression of long noncoding RNAs (lncRNAs) in human postmortem brain tissue that are profoundly lost in depression. One such lncRNA, RP11-298D21.1 (which we termed FEDORA), is enriched in oligodendrocytes and neurons and upregulated in several cortical regions of depressed females but not males. We found that virally-expressing FEDORA selectively either in neurons or in oligodendrocytes of prefrontal cortex promoted depression-like behavioral abnormalities in female mice only, changes associated with cell-type-specific regulation of synaptic properties, myelin thickness, and gene expression. We also found that blood FEDORA levels have diagnostic significance for depressed women. These findings demonstrate the important role played by lncRNAs, and FEDORA in particular, in shaping the sex-specific landscape of the brain and contributing to sex differences in depression.

neuroscience↗

bioRxiv2021

Yin Yang 1 sets up the stage for cerebellar astrocyte maturation

Diverse subpopulations of astrocytes tile different brain regions to accommodate local requirements of neurons and associated neuronal circuits. Nevertheless, molecular mechanisms governing astrocyte diversity remain mostly unknown. We explored the role of a zinc finger transcription factor Yin Yang 1 (YY1) that is expressed in astrocytes. We found that specific deletion of YY1 from astrocytes causes severe motor deficits in mice, induces Bergmann gliosis, and results in simultaneous loss of GFAP expression in velate and fibrous cerebellar astrocytes. Single cell RNA-seq analysis showed that YY1 exerts specific effects on gene expression in subpopulations of cerebellar astrocytes. We found that although YY1 is dispensable for the initial stages of astrocyte development, it regulates subtype-specific gene expression during astrocyte maturation. Moreover, YY1 is continuously needed to maintain mature astrocytes in the adult cerebellum. Our findings suggest that YY1 plays critical roles regulating cerebellar astrocyte maturation during development and maintaining a mature phenotype of astrocytes in the adult cerebellum.

neuroscience↗