Biology subjects

Popper, B.

Publications and source records attributed to Popper, B..

6 recordsLinked to original sources

bioRxiv2026

Neutrophils are critical for placental and fetal infection with the human pathogen Listeria monocytogenes

Fetal listeriosis, caused by Listeria monocytogenes (Lm), represents a severe infectious disease. During pregnancy, the unique intrauterine environment permits Lm to breach the maternal-fetal barrier by infiltrating the placental trophoblast layer and ultimately leading to significant fetal morbidity and mortality. However, the exact pathways remain incompletely understood. In this study, we sought to elucidate the molecular mechanisms underlying the early stages of placental and fetal Lm infection. Our results reveal that neutrophils serve as a survival niche for Lm within the vasculature, facilitating placental and fetal infection in the mouse in vivo. This finding was further substantiated by in vitro studies using TLR2-stimulated trophoblast cells and Lm-infected neutrophils. Additionally, tissue-clearing analysis of Lm-infected placentas demonstrated neutrophil colocalization with Lm is rare within placental tissue. Collectively, our findings identify maternal neutrophils as an essential viability niche for Lm enabling their entry into trophoblast cells, thereby promoting placental and fetal infection. One Sentence SummaryMaternal circulating neutrophils act as survival niche for Listeria monocytogenes and facilitate placental/fetal infection with Listeria during pregnancy.

immunology↗

bioRxiv2025

Mutations in VPS18 lead to a neutrophil maturation defect associated with disturbed vesicle homeostasis

Neutrophils, the first cells to arrive at the site of inflammation, are rather short-lived cells and thus have to be constantly replenished. During neutrophil development, vesicle dynamics need to be fine-tuned and impaired vesicle trafficking has been linked to failure in neutrophil maturation. Here, we characterized the role of VPS18 as a central core component of CORVET & HOPS tethering complexes for neutrophil development. Using CRISPR/Cas9-engineered Hoxb8 cells with heterozygous mutations in Vps18, we found that VPS18 deficiency interfered with neutrophil development due to tethering complex instability. As a result, vesicle dynamics were impaired with a strong increase in LC3-II and p62 levels, indicating autophagosome accumulation and reduced autophagic flux. With transmission electron microscopy, we verified the increase in autophagosomes and also found irregularly shaped vesicular structures in Vps18 mutants. Subsequently, Vps18 mutant neutrophil progenitors underwent premature apoptosis. We described a novel patient with a heterozygous stop-gain mutation in VPS18 suffering from neutropenia and recurrent infections. To verify our findings in the human system, we used human induced pluripotent stem cells (iPSCs). Upon differentiation into neutrophils, loss of VPS18 resulted in an almost complete absence of iPSC-derived developing neutrophils. Heterozygous VPS18 mutant and patient mutation-harboring iPSCs were characterized by strongly reduced numbers of developing neutrophils. Zebrafish larvae with heterozygous mutations in vps18 were also characterized by significantly reduced neutrophil numbers. This study shows the pivotal impact of VPS18 for adequate vesicle dynamics during neutrophil development which might be relevant in the context of vesicle trafficking during granulopoiesis and congenital neutropenia.

physiology↗

bioRxiv2022

Neomorphic DNA-binding enables tumor-specific therapeutic gene expression in fusion-addicted childhood sarcoma

Chimeric fusion transcription factors are oncogenic hallmarks of several devastating cancer types including pediatric sarcomas, such as Ewing sarcoma (EwS) and alveolar rhabdomyosarcoma (ARMS). Despite their exquisite specificity, these driver oncogenes have been considered largely undruggable due to their lack of enzymatic activity. Here, we show in the EwS model that - capitalizing on neomorphic DNA-binding preferences - the addiction to the respective fusion transcription factor EWSR1-FLI1 can be leveraged to express therapeutic genes. We genetically engineered a de novo enhancer-based, synthetic and highly potent expression cassette that can elicit EWSR1-FLI1-dependent expression of a therapeutic payload as evidenced by episomal and CRISPR-edited genomic reporter assays. Combining in silico screens and immunohistochemistry, we identified GPR64 as a highly specific cell surface antigen for targeted transduction strategies in EwS. Functional experiments demonstrated that anti-GPR64-pseudotyped lentivirus harboring our expression cassette can specifically transduce EwS cells to promote the expression of viral thymidine kinase sensitizing EwS for treatment to the otherwise relatively non-toxic (Val)ganciclovir and leading to strong anti-tumorigenic, but no adverse effects in vivo. Further, we prove that similar vector designs can be applied in PAX3-FOXO1-driven ARMS, and to express immunomodulatory cytokines, such as IL-15 and XCL1, in tumor types typically considered to be immunologically cold. Collectively, these results generated in pediatric sarcomas indicate that exploiting, rather than suppressing, the neomorphic functions of chimeric transcription factors may open inroads to innovative and personalized therapies, and that our highly versatile approach may be translatable to other cancers addicted to oncogenic transcription factors with unique DNA-binding properties.

cancer biology↗

bioRxiv2020

Extratubular polymerized uromodulin induces leukocyte recruitment and inflammation in vivo

Uromodulin (UMOD) is produced and secreted by tubular epithelial cells. Secreted UMOD polymerizes (pUMOD) within the lumen, where it regulates salt transport and protects the kidney from bacteria and stone formation. Under various pathological conditions, pUMOD accumulates within the tubular lumen and reaches extratubular sites where it may interact with renal interstitial cells. Here, we investigated the potential of extratubular pUMOD to act as a damage associated molecular pattern (DAMP) molecule thereby creating local inflammation. We found that intrascrotal and intraperitoneal injection of pUMOD induced leukocyte recruitment in vivo and led to TNF- secretion by F4/80 positive macrophages. Additionally, pUMOD directly affected vascular permeability and increased neutrophil extravasation independent of macrophage-released TNF-. Interestingly, pUMOD did not directly upregulate adhesion molecules on endothelial cells and did not directly activate {beta}2 integrins on neutrophils. In obstructed neonatal murine kidneys, we observed extratubular UMOD accumulation with tubular atrophy and leukocyte infiltrates. Finally, we found extratubular UMOD deposits associated with peritubular leukocyte infiltration in kidneys from patients with inflammatory kidney diseases. Taken together, we identified extratubular pUMOD as a strong inducer of leukocyte recruitment, underlining its critical role in mounting an inflammatory response in various kidneys pathologies.

immunology↗

bioRxiv2020

Helicobacter hepaticus as disease driver in a novel CD40-mediated model of colitis

Gut microbiota and the immune system are in constant exchange, which shapes both, host immunity and microbial communities. Here, improper immune regulation can cause inflammatory bowel disease (IBD) and colitis. Antibody therapies blocking signaling through the CD40 - CD40L axis showed promising results as these molecules have been described to be deregulated in certain IBD patients. To better understand the mechanism, we used transgenic DC-LMP1/CD40 animals, which lack intestinal CD103+ dendritic cells (DCs) and therefore cannot induce regulatory T (iTreg) cells due to a constitutive CD40-signal in CD11c+ cells. These mice rapidly develop spontaneous fatal colitis with an increase of inflammatory IL-17+IFN-{gamma}+ Th17/Th1 and IFN-{gamma}+ Th1 cells. In the present study we analyzed the impact of the microbiota on disease development and detected elevated IgA- and IgG-levels in sera from DC-LMP1/CD40 animals. Their serum antibodies specifically bound intestinal bacteria and we identified a 60 kDa chaperonin GroEL (Hsp60) from Helicobacter hepaticus (Hh) as the main specific antigen targeted in absence of iTregs. When rederived to a different Hh-free SPF-microbiota, mice showed few signs of disease without fatalities, but upon recolonization of mice with Hh we found rapid disease onset and the generation of inflammatory Th17/Th1 and Th1 cells in the colon. Thus, the present work identifies a major bacterial antigen and highlights the impact of specific microorganisms on modulating the host immune response and its role on disease onset, progression and outcome in this colitis model.

immunology↗

bioRxiv2020

Adaptive mitochondrial regulation of the proteasome

The proteasome is the main proteolytic system for targeted protein degradation in the cell. Its function is fine-tuned according to cellular needs. Regulation of proteasome function by mitochondrial metabolism, however, is unknown. Here, we demonstrate that mitochondrial dysfunction reduces the assembly and activity of the 26S proteasome in the absence of oxidative stress. Impaired respiratory complex I function leads to metabolic reprogramming of the Krebs cycle and deficiency in aspartate. Aspartate supplementation activates assembly and activity of 26S proteasomes via transcriptional activation of the proteasome assembly factors p28 and Rpn6. This metabolic adaptation of 26S proteasome function involves sensing of aspartate via the mTORC1 pathway. Metformin treatment of primary human cells similarly reduced assembly and activity of 26S proteasome complexes, which was fully reversible and rescued by supplementation of aspartate or pyruvate. Of note, respiratory dysfunction conferred resistance towards the proteasome inhibitor Bortezomib. Our study uncovers a fundamental novel mechanism of how mitochondrial metabolism adaptively adjusts protein degradation by the proteasome. It thus unravels unexpected consequences of defective mitochondrial metabolism in disease or drug-targeted mitochondrial reprogramming for proteasomal protein degradation in the cell. As metabolic inhibition of proteasome function can be alleviated by treatment with aspartate or pyruvate, our results also have therapeutic implications.

cell biology↗