Michael J. Holtzman

Viral infection induces robust reprogramming of metabolic pathways in host cells. However, whether host metabolic enzymes detect viral components remains unknown. Our group and others previously identified O-GlcNAc transferase (OGT), an important glucose metabolic enzyme, as a crucial mediator of the antiviral immune responses. Here, by studying a mouse model with a catalytically impaired OGT, we discover a catalytic activity-independent function of OGT in restraining influenza A virus (IAV) infection in addition to its catalytic activity-dependent effect on MAVS-mediated antiviral immunity. Biochemical studies reveal a critical antiviral effect based on OGT interacting with IAV genomic RNA that requires its N-terminal tetracopeptide repeat-4 motif. This interaction causes the translocation of nuclear OGT to cytosolic lipid droplets (LDs) to destabilize LDs-coating perilipin 2, thereby limiting LDs accumulation and in turn virus replication. In sum, our findings reveal OGT as a multifaceted metabolic sensor that integrates MAVS signaling and lipid metabolism to combat viral infection.

The choroid plexus (ChP) regulates cerebrospinal fluid (CSF) composition, providing essential molecular cues for brain development; yet, embryonic ChP secretory mechanisms remain poorly defined. Here we identify apocrine secretion by embryonic ChP epithelial cells as a key regulator of the CSF proteome and neurodevelopment in male and female mice. We demonstrate that the activation of serotonergic 5-HT_2C receptors (by WAY-161503) triggers sustained Ca²⁺ signaling, driving high-volume apocrine secretion in mouse and human ChP. This secretion alters the CSF proteome, stimulating neural progenitors lining the brain’s ventricles and shifting their developmental trajectory. Inducing ChP secretion in utero in mice disrupts neural progenitor dynamics, cerebral cortical architecture and offspring behavior. Additionally, illness or lysergic acid diethylamide exposure during pregnancy provokes coordinated ChP secretion in the mouse embryo. Our findings reveal a fundamental secretory pathway in the ChP that shapes brain development, highlighting how its disruption can have lasting consequences for brain health.

Epithelial injury calls for a regenerative response from a coordinated network of epithelial stem cells and immune cells. Defining this network is key to preserving the repair process for acute resolution, but also for preventing a remodeling process with chronic dysfunction. We recently identified an immune niche for basal-epithelial stem cells using mouse models of injury after respiratory viral infection. Niche function depended on an early sentinel population of monocyte-derived dendritic cells (moDCs) that provided ligand GPNMB to basal-ESC receptor CD44 for reprogramming towards chronic lung disease. These same cell and molecular control points worked directly in mouse and human basal-ESC organoids, but the findings were not yet validated in vivo in human disease. Further, persistence of GPNMB expression in moDCs and M2-macrophages in mouse models suggested utility as a long-term disease biomarker in humans. Here we show increased expression of GPNMB localized to moDC-macrophage populations in lung tissue samples from long-term Covid, asthma, and COPD. The findings thereby provide initial evidence of a persistent and correctable pathway from acute injury to chronic disease with implications for cellular reprogramming and inflammatory memory. New and noteworthy Recent work indicates that a sentinel immune niche provides GPNMB to epithelial stem cells to drive structural remodeling and disease as exemplified by the response to respiratory viral injury. The present study provides initial evidence that this niche can be detected in humans in the context of comparable diseases (long-term Covid, asthma, and COPD) also linked to viral infection. The results support a persistent mechanism for inflammatory disease that might be correctable with GPNMB blockade directly or indirectly through related signaling pathways.

The stress kinase MAPK13 (aka p38delta-MAPK) is an attractive entry point for therapeutic intervention because it regulates the structural remodeling that can develop after epithelial injury in the lung and likely other tissue sites. However, a selective, safe, and effective MAPK13 inhibitor is not yet available for experimental or clinical application. Here we identify a first-in-kind MAPK13 inhibitor using structure-based drug design combined with a screening funnel for cell safety and molecular specificity. This inhibitor (designated NuP-4A for intravenous or Nu4-B for inhaled delivery) down-regulates basal-epithelial stem cell reprogramming, structural remodeling, and pathophysiology equivalently to Mapk13 gene-knockout in mouse and mouse organoid models of muco-obstructive lung disease after viral infection. Treatment prevents and reverses disease biomarkers, and this benefit persists after stopping treatment as a sign of disease modification. Similarly, NuP-4 treatment can directly control stimulated growth, immune activation, and mucinous differentiation in human basal-cell organoids. The results thereby provide a new tool and potential correction for stem cell reprogramming towards muco-obstructive lung diseases like asthma and COPD and related diseases that might depend on overactivation of MAPK13. New and noteworthy: This study identifies a highly selective and potent small-molecule inhibitor for stress kinase MAPK13 in controlling the basal-epithelial stem cell response to viral infection and the consequent development of muco-obstructive lung disease. The present model has direct implications for diseases like asthma and COPD that are triggered by respiratory viruses and other inhaled toxins. Further, the tissue distribution of MAPK13 implies related actions at other epithelial sites. The findings also refine a hypothesis for therapeutic intervention based on proper scaling of MAPK13 function including precise down-regulation with a highly selective MAPK13 inhibitor.

Epithelial barriers are programmed for defense and repair but are also the site of long-term structural remodeling and disease. In general, this paradigm features epithelial stem cells (ESCs) that are called on to regenerate damaged tissues but can also be reprogrammed for detrimental remodeling. Here we identified a Wfdc21- dependent monocyte-derived dendritic cell (moDC) population that functioned as an early sentinel niche for basal ESC reprogramming in mouse models of epithelial injury after respiratory viral infection. Niche function depended on moDC delivery of ligand GPNMB to the basal ESC receptor CD44 so that properly timed antibody blockade of ligand or receptor provided long-lasting correction of reprogramming and broad disease phenotypes. These same control points worked directly in mouse and human basal ESC organoids. Together, the findings identify a mechanism to explain and modify what is otherwise a stereotyped but sometimes detrimental response to epithelial injury.

All living organisms are charged with repair after injury particularly at epithelial barrier sites, but in some cases this response leads instead to structural remodeling and long-term disease. Identifying the molecular and cellular control of this divergence is key to disease modification. In that regard, stress kinase control of epithelial stem cells is a rational entry point for study. Here we examine the potential for mitogen-activated protein kinase 13 (MAPK13) regulation of epithelial stem cells using models of respiratory viral injury and post-viral lung disease. We show that Mapk13 gene-knockout mice handle acute infectious illness as expected but are protected against structural remodeling manifest as basal-epithelial stem cell (basal-ESC) hyperplasia-metaplasia, immune activation, and mucinous differentiation. In corresponding cell models, Mapk13 -deficiency directly attenuates basal-ESC growth and organoid formation. Extension to human studies shows marked induction/activation of basal-cell MAPK13 in clinical samples of comparable remodeling found in asthma and COPD. Here again, MAPK13 gene-knockdown inhibits human basal-ESC growth in culture. Together, the data identify MAPK13 as a control for structural remodeling and disease after epithelial injury and as a suitable target for down-regulation as a disease-modifying strategy. New and noteworthy: This study identifies a distinct role for stress kinase MAPK13 in controlling the epithelial stem cell response to injury and the consequent development of tissue remodeling. The present model has direct implications for lung injury and subsequent disease triggered by respiratory viruses and other inhaled toxins, but the tissue distribution of MAPK13 implies related actions at other barrier sites. The findings also refine a hypothesis for therapeutic intervention based on proper scaling of MAPK13 function including down-regulation with selective kinase inhibitors.