White matter injury across neurodegenerative disease.

Oligodendrocytes (OLs), the myelin-generating cells of the central nervous system (CNS), are active players in shaping neuronal circuitry and function. It has become increasingly apparent that injury to cells within the OL lineage plays a central role in neurodegeneration. In this review, we focus primarily on three degenerative disorders in which white matter loss is well documented: Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). We discuss clinical data implicating white matter injury as a key feature of these disorders, as well as shared and divergent phenotypes between them. We examine the cellular and molecular mechanisms underlying the alterations to OLs, including chronic neuroinflammation, aggregation of proteins, lipid dysregulation, and organellar stress. Last, we highlight prospects for therapeutic intervention targeting the OL lineage to restore function.

Antiretroviral treatment reveals a novel role for lysosomes in oligodendrocyte maturation.

White matter deficits are a common neuropathologic finding in neurologic disorders, including HIV-associated neurocognitive disorders (HAND). In HAND, the persistence of white matter alterations despite suppressive antiretroviral (ARV) therapy suggests that ARVs may be directly contributing to these impairments. Here, we report that a frontline ARV, bictegravir (BIC), significantly attenuates remyelination following cuprizone-mediated demyelination, a model that recapitulates acute demyelination, but has no impact on already formed mature myelin. Mechanistic studies utilizing primary rat oligodendrocyte precursor cells (OPCs) revealed that treatment with BIC leads to significant decrease in mature oligodendrocytes accompanied by lysosomal deacidification and impairment of lysosomal degradative capacity with no alterations in lysosomal membrane permeability or total lysosome number. Activation of the endolysosomal cation channel TRPML1 prevents both lysosomal deacidification and impairment of oligodendrocyte differentiation by BIC. Lastly, we show that deacidification of lysosomes by compounds that raise lysosomal pH is sufficient to prevent maturation of oligodendrocytes. Overall, this study has uncovered a critical role for lysosomal acidification in modulating oligodendrocyte function and has implications for neurologic diseases characterized by lysosomal dysfunction and white matter abnormalities.

CXCL12-induced rescue of cortical dendritic spines and cognitive flexibility.

Synaptodendritic pruning is a common cause of cognitive decline in neurological disorders, including HIV-associated neurocognitive disorders (HAND). HAND persists in treated patients as a result of chronic inflammation and low-level expression of viral proteins, though the mechanisms involved in synaptic damage are unclear. Here, we report that the chemokine CXCL12 recoups both cognitive performance and synaptodendritic health in a rodent model of HAND, which recapitulates the neuroinflammatory state of virally controlled individuals and the associated structural/functional deficiencies. CXCL12 preferentially regulates plastic thin spines on layer II/III pyramidal neurons of the medial prefrontal cortex via CXCR4-dependent stimulation of the Rac1/PAK actin polymerization pathway, leading to increased spine density and improved flexible behavior. Our studies unveil a critical role of CXCL12/CXCR4 signaling in spine dynamics and cognitive flexibility, suggesting that HAND - or other diseases driven by spine loss - may be reversible and upturned by targeting Rac1-dependent processes in cortical neurons.