Faculty Bibliography

OBJECTIVES/OBJECTIVE:The gut microbiome plays a crucial role in regulating systemic immunity and has been implicated in several chronic inflammatory diseases. Intestinal expansions of Ruminococcus gnavus (RG), a dominant gut commensal, correlate with disease flares in lupus nephritis (LN), but the underlying mechanism remains unknown. METHODS:In a Pilot cohort of patients with biopsy-proven LN, subsetted by gut microbiota community, immune status was characterised using bulk-blood RNA sequencing libraries, serum levels of representative host proteins, and levels of immunoglobulin (Ig)G antibodies to the novel lipoglycan (LG) produced by pathogenic RG strains. A Validation LN cohort was evaluated for blood transcriptomic profiles and levels of anti-LG antibodies. In murine models, mechanistic hypotheses were tested after RG gut colonisation or after intraperitoneal injection with an LG preparation, with outcomes determined by transcriptomic analyses, platelet functional readouts, and tissue histology. RESULTS:In a Pilot cohort of patients with LN, RG gut expansions were associated with high-level platelet, neutrophil, and monocyte activation. Serum levels of platelet factor 4 and release of neutrophil extracellular traps (NETs) were significantly higher in patients with high serum IgG antibody against the novel RG-specific LG, a marker of in vivo immune exposure. An LN Validation cohort confirmed these correlates and showed that anti-LG antibodies serve as a surrogate for thromboinflammatory profile in this LN-associated endotype. In mice, gut colonisation with LG-producing RG strains or a single LG injection caused megakaryocytosis and platelet activation; RG colonisation with LG-producing strains induced tubulointerstitial injury with NETosis. In vivo responses to LG toxin were Toll-like receptor 2-dependent. CONCLUSIONS:Gut expansions of the RG pathobiont may contribute to autoimmune pathogenesis through the LG toxin and cause LN flares through thromboinflammatory mechanisms in this previously unrecognised LN endotype.

Lysosomal phospholipid degradation produces two types of metabolites, either 2-lysophospholipids with saturated fatty acids in sn-1 position or 1-lysophospholipids with unsaturated fatty acids in sn-2 position. They may either be degraded further or re-used for phospholipid synthesis. We found that LPLAT7 (LPGAT1), an acyltransferase of the endoplasmic reticulum, re-acylates specifically lysosome-derived 1-lysophospholipids that carry an unsaturated chain. The enzymatic activity of LPLAT7 was specific for stearoyl-CoA and 1-lyso-2-acyl positional isomers of unsaturated lysophospholipids. In Huh7 cells, Lplat7 knockout prevented the reacylation of 1-lysophospholipids generated by the lysosomal degradation of exogenous ²H-phosphatidylcholine. Inhibition of lysosomal phospholipid degradation reduced the abundance of 1-stearoyl-2-unsaturated PC in Huh7 cells. Lplat7 knockout blunted the loss of unsaturated lysophosphatidylcholine (LPC) in response to lysosomal inhibition, suggesting that LPLAT7 consumes unsaturated LPC formed by lysosomes. In mice, Lplat7 knockout increased the concentration of unsaturated lysophospholipids, reduced the abundance of 1-stearoyl-2-unsaturated species of phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine, and inhibited the regeneration of cellular membranes. It also triggered the accumulation of triglycerides, confirming earlier reports that unsaturated lysophospholipids induce lipid droplet formation. Thus, by re-acylating unsaturated 1-lysophospholipids, LPLAT7 shifts lipid metabolism from the biogenesis of lipid droplets to the biogenesis of membranes.

A deficit in dietary protein elicits a nutrient-specific appetite, yet the underlying mechanisms remain poorly understood. In this work, we identify coordinated neuronal and systemic mechanisms in Drosophila that drive an essential amino acid (EAA)-specific appetite. EAA deprivation increases neuropeptide CNMamide (CNMa) expression in gut enterocytes, activating enteric neurons and ellipsoid body neurons in the brain to promote EAA intake through two complementary pathways: a rapid neuronal gut-brain axis and a slower hormonal route. CNMa suppresses the activity of sugar-sensing diuretic hormone 44 (DH44) neurons, thereby reducing carbohydrate intake and biasing feeding toward EAAs. Similarly, protein deprivation in mice promotes an EAA-specific appetite independently of fibroblast growth factor 21 (FGF21). Together, these findings reveal multilayered gut-brain mechanisms that regulate nutrient-specific feeding and maintain EAA homeostasis across species.

BACKGROUND:Exercise links with improved cancer outcomes following a diagnosis of primary breast cancer but experimental evidence and molecular mechanistic interrogation from preclinical studies are limited. The purpose of this study was to evaluate the effects, and dose‒response, of exercise in mouse models of breast cancer, as well as elucidate cancer cell extrinsic and intrinsic responses. METHODS:Independent in vivo modeling was used to investigate the effects of exercise across distinct breast cancer models. Unbiased transcriptomic and metabolomic analyses, alongside cellular and proteomic interrogation, were used to determine tumor microenvironment (TME)- and cancer cell-specific effects. RESULTS:Exercise inhibited breast cancer growth and metastasis across multiple syngeneic mouse models compared to sham control. Tumor growth inhibition was independent of estrogen receptor status, and in the 4T1 model, exercise exerted non-dose-dependent effects. In the Met1 model, exercise decreased TME immune cell content, particularly tumor-associated macrophages, while promoting an activated anticancer innate immune cell gene signature. Concurrent in vivo cancer cell-intrinsic effects were characterized by broad transcriptomic reprogramming including downregulation of metabolic pathways and upregulation of pathways regulating proliferation and apoptosis. Whole tumor metabolomic analyses unveiled broad shifts including decreased nicotinamide adenine dinucleotide (NAD+) and lactate, as well as availability of biosynthetic precursors. Finally, in silico analyses identified TME ligands, such as High Mobility Group Box 2 (HMGB2) and Cardiotrophin-1 (CTF1) as candidate drivers of downstream gene expression changes in cancer cells. CONCLUSION/CONCLUSIONS:Exercise suppresses breast cancer progression, which occurs in conjunction with broad reprogramming of immune TME-cancer processes and their interaction.

UNLABELLED:LKB1 mutations in lung cancer promote an immunosuppressive tumor microenvironment, but the underlying mechanisms remain unknown. Using genetically engineered mouse models and human tumor samples, we demonstrate that LKB1 loss leads to high expression of the cytokine leukemia-inhibitory factor (LIF), which through a cancer cell-autonomous autocrine loop, orchestrates the infiltration of immunosuppressive SiglecFHi neutrophils and Arg1+ interstitial macrophages. Genetic deletion of Lifr, the receptor for LIF, on Lkb1-mutant lung tumors revealed that autocrine LIF signaling induces tumor plasticity and the emergence of a Sox17+ dedifferentiated inflammatory cell state. Antibody-mediated LIF neutralization selectively eliminates the Sox17+ tumor cell state, reduces immunosuppressive myeloid cells, and enhances antitumor T-cell responses. Our study uncovers a novel LKB1-LIF axis driving immune evasion and identifies LIF as a potential therapeutic target in LKB1-mutant lung cancer. This work highlights the interplay between tumor genetics, cellular plasticity, and immune regulation in lung cancer progression. SIGNIFICANCE/UNASSIGNED:LKB1-mutant lung cancers express LIF, which induces an immunosuppressive Sox17+ tumor state. Anti-LIF therapy eliminates this state and restores antitumor immunity, revealing a novel vulnerability in this aggressive cancer subtype lacking effective targeted therapies.

Donnai-Barrow Syndrome (DBS) arises from loss-of-function (LoF) variants in the endocytic receptor LRP2/megalin and is characterized by low molecular weight (LMW) proteinuria and developmental abnormalities. Urinary proteomics of nine DBS patients revealed that the urinary proteome of a DBS patient with the missense variant LRP2 p.C1400R was indistinguishable from that of patients with splice site, nonsense, or frameshift mutations. A CRISPR mouse model of the variant was generated to determine the mechanism of LoF and proteinuria. The mutant LRP2 was expressed and observed to dimerize and localize to the proximal tubule apical membrane. However, both fluid-phase and receptor-mediated endocytosis were impaired in the context of a general perturbation of endocytic flux. Immunofluorescence revealed aberrant endocytic recycling with mislocalized RAB11+ and TFR1+ compartments and enlarged lysosomes. Structural modeling showed the LRP2 assembly likely tolerates the cysteine to arginine substitution at the cell surface, but at endosomal pH the variant introduced steric clashes that may disrupt intramolecular interfaces and disturb receptor recycling. These findings point to the importance of LRP2 recycling for global endocytic flux and offer a blueprint for leveraging patient-specific alleles to dissect proximal tubule function.

Breast cancer remains the second leading cause of cancer-related mortality among women, with triple-negative breast cancer (TNBC) exhibiting a particularly poor five-year prognosis. Here, we demonstrated that, among genetic and pharmacological perturbations targeting DNA replication, suppression of DNA polymerase epsilon (POLE) induced a potent, TNBC-specific gene expression signature enriched in inflammatory cytokines that are transcriptional targets of NF-κB. TNBC cells exhibited markedly higher levels of DNA damage and canonical NF-κB activation compared to luminal breast cancer cells. Notably, NF-κB activation in this context depended on the canonical component RELA but not the non-canonical component RELB. Mechanistically, ATM, STING, and RIG-I each contributed to NF-κB activation following POLE suppression. POLE suppression in an in vivo murine TNBC model led to cancer cell-intrinsic elimination of tumor burden and increased immune cell infiltration. Together, these findings support a model in which replication stress from POLE inhibition triggers robust NF-κB-mediated inflammation and immune microenvironment remodeling in TNBC and can independently trigger tumor eradication. These results suggest a potential therapeutic avenue for targeting POLE in TNBC.

Adenosine deaminase acting on RNA 1 (ADAR1) contributes to immunotherapy resistance by suppressing interferon signaling. Therapeutic targeting of ADAR1 has not been achieved to date in clinical settings. Here, we discover all-trans retinoic acid (ATRA) promotes ADAR1 protein degradation in cancer. In addition, ATRA induces PD-L1 and combination of ATRA and PD-1 blockade reprograms tumor microenvironments to unleash antitumor immunity, thereby impeding tumor growth. Mechanistically, we identify USP7 as a key regulator for ADAR1 protein stability. ATRA disrupts USP7-ADAR1 interaction and promotes ADAR1 ubiquitination and degradation. ATRA leads to ADAR1 retinoylation, which results in disruption of USP7-ADAR1 complex. Our clinical data shows a positive correlation between USP7 and ADAR1 in various types of cancer. Overall, this study sheds light on control of ADAR1 protein turnover and proposes a mechanism-driven combination therapy using ATRA and PD-1/PD-L1 blockade to convert immunologically "cold" into "hot" tumors, holding potential for clinical translation.

Reactivation of quiescent neural stem cells (NSCs) in the central nervous system (CNS) is a tightly controlled process that generates new neurons and glia to maintain homeostasis or enable repair post-injury, but it remains unclear if reactivation of distinct NSC populations is coupled. Here, we discovered that NSC quiescence exit in Drosophila follows a hierarchical sequence, whereby activation of anterior stem cells in the brain lobes precedes and is required for the timely state-transition of more posterior NSCs in the ventral nerve cord. To achieve this, quiescent NSCs transiently activate neuronal genes. This transient neuronal state is temporary and specific to NSC dormancy, as neuronal genes are switched off after stem cells resume proliferation. Blocking neuronal firing in brain lobe neurons delays the onset of posterior NSC reactivation. Our results reveal long-range communication between quiescent NSCs to coordinate reactivation across the CNS, enabled by a transient, plastic neuron-like state that allows direct interaction with neuronal axons.

Cerebral malaria is a major complication of Plasmodium falciparum infection that occurs upon the sequestration of infected red blood cells (iRBCs) in brain capillaries, resulting in the loss of endothelial barrier integrity, brain swelling, and frequently long-term sequelae or death. P. falciparum-iRBCs cause the disruption of human brain microvascular endothelial cell barrier integrity in vitro, mimicking the microenvironment of cerebral malaria, yet the specific mechanisms mediating this process remain unknown. Upon infection of the host RBCs, P. falciparum produces hemozoin, a crystal form of heme generated following the degradation of hemoglobin by the parasite. Here, we show that the endothelial barrier-disrupting activity is found entirely in the hemozoin fraction of P. falciparum-iRBCs. This activity is not caused by the hemozoin crystal itself, which is not able to induce barrier disruption, but by the biomolecules that are associated with it. Treatment of purified P. falciparum hemozoin with proteases inhibits the disruption of endothelial barrier integrity caused by the hemozoin, indicating an important role for proteins in the disruption of the barrier. Conversely, treatment with nucleases did not affect hemozoin barrier-disrupting activity. These results identify a key molecular mechanism in the P. falciparum-mediated brain endothelial barrier disruption during cerebral malaria and may open new avenues for the treatment of this complication.IMPORTANCEWhile several specific biomolecules have been proposed to contribute to the disruption of endothelial barrier integrity in cerebral malaria, no single Plasmodium falciparum- or host-derived factor has been definitively identified as the primary driver of this disruption. Here, we identify the brain endothelial barrier-disruptive P. falciparum-infected red blood cell (iRBC)-derived activity to be caused by biomolecules bound to hemozoin, identifying a key, novel mechanism in the pathogenesis of cerebral malaria. The finding that P. falciparum hemozoin also disrupts a pulmonary endothelial cell barrier opens the possibility that this mechanism underlies other severe malaria complications. The implication of P. falciparum-iRBC-derived proteins in this mechanism is in line with previous reports, providing a novel interpretation of these findings in the context of hemozoin-binding. This knowledge provides a new perspective in the search for specific molecules and mechanisms involved in barrier disruption, which may lead to the development of much-needed specific treatments for cerebral malaria.