Biology subjects

Cammer, M.

Publications and source records attributed to Cammer, M..

11 recordsLinked to original sources

bioRxiv2026

Plasmodium falciparum hemozoin-associated biomolecules induce brain endothelial cell barrier disruption in an in vitro model of cerebral malaria

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 P. 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-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.

microbiology↗

bioRxiv2025

Lymphatic constraint of germinal centers optimizes protective antibody responses

Immunization strategies are central to pathogen control, where efficacy relies on antigen uptake, distribution, persistence, and inflammatory context. We recently demonstrated that dermal lymphatic capillaries regulate antigen presentation in lymph nodes (LN) by restraining fluid and virion transport following vaccinia virus (VACV) infection by skin scarification. Concurrently, a perifollicular, LN lymphangiogenic response encapsulates expanding B cell follicles. Given the important role of antigen transport and uptake on humoral immunity, we tested the hypothesis that lymphatic remodeling in the skin and LNs regulates germinal center (GC)-dependent antibody responses during infection. Using a model of lymphatic-specific VEGFR2 inhibition, we found that inhibiting viral-induced lymphatic remodeling in skin and LNs prompted significant GC expansion but paradoxically decreases protective VACV-specific class-switched antibodies. While the larger GC responses appeared structurally normal, they failed to support a proliferative burst consistent with clonal selection. Mathematical modeling revealed that this disconnect between GC size and function arises from impaired productive T follicular cell interactions in larger GC volumes and consistent with this finding, the optimal GC size was evolutionarily conserved across diverse mammals. Finally, we found that the presence of virus in the LN initiates these changes in GC function, inhibits LN lymphangiogenesis, increases B cell follicle size, and reduces selection efficiency. Therefore, protecting LN lymphatic vessels from virus-induced interferons rescues perifollicular lymphatic growth and follicle size, indicating that LN lymphangiogenesis directly constrains the follicular response. In summary, this study underscores the central role of lymphatic remodeling in compartmentalizing antigen and inflammatory signals to optimize GC fitness and protective antibody responses.

immunology↗

bioRxiv2025

Cardiomyocyte-specific plakophilin-2 loss is sufficient to induce aging and senescence of nonmyocytes. Relevance to arrhythmogenic cardiomyopathy.

IntroductionPathogenic variants in PKP2 are the most common cause of familial arrhythmogenic right ventricular cardiomyopathy (ARVC). ObjectiveTo test whether PKP2 deficiency only in cardiomyocytes is sufficient to provoke premature aging and pro-inflammatory senescence in non-myocytes, cardiac resident cells. MethodsWe studied mice with cardiomyocyte-specific, tamoxifen-activated loss of PKP2 (PKP2cKO) using conventional and multiplex imaging, cytokine arrays, epigenetic clocks, spatial transcriptomics, expansion and structured illumination microscopy, and correlative data analysis. We examined non-myocytes and cardiomyocytes for premature aging and senescence. ResultsWe observed senescence-associated heterochromatin foci (SAHFs) and p21 staining in non-myocytes. Cytokines in media of non-myocyte cells were consistent with senescence-associated secretory phenotype (SASP). Epigenetic clocks identified premature aging. Multiplex immunohistochemistry showed non-myocyte cells in niches, intermingled with cardiomyocytes. Spatial transcriptomics showed over-representation of SASP-related transcripts, predominantly in myocyte-rich areas of the left ventricle. SAHFs, p21 staining and increased epigenetic age were not found in cardiomyocytes from PKP2cKO hearts, though we observed structural features associated to premature aging. Cross-reference analysis showed correlation between the PKP2cKO cardiac proteome and that of mice 5 or 6 times their chronological age, as well as transcriptional signatures of neurodegenerative diseases. ConclusionLoss of PKP2 expression only in adult cardiac myocytes is sufficient to induce pro-inflammatory senescence in non-myocytes, and overall premature cardiac aging. This is the first study to intersect cellular senescence and premature aging in desmosomal arrhythmogenic cardiomyopathies. We speculate that cell-agnostic molecular signatures, biomarkers, and pharmacology of senescence and of neurodegenerative diseases may be relevant to diagnose or treat PKP2-ARVC. UNSTRUCTURED ABSTRACTPathogenic variants in PKP2 are the most common cause of familial arrhythmogenic right ventricular cardiomyopathy. We used the PKP2cKO model (cardiomyocyte-specific, tamoxifen-activated PKP2 knockout) to examine whether PKP2 deficiency only in cardiomyocytes is sufficient to provoke premature aging and pro-inflammatory senescence in non-myocyte, cardiac resident cells. Through a variety of methods, we identified senescence-associated heterochromatin foci (SAHFs), p21 staining, and cytokines consistent with senescence-associated secretory phenotype (SASP) in cells and media of non-myocytes. Epigenetic clocks identified premature aging. Spatial transcriptomics showed over-representation of SASP-related transcripts, predominantly in myocyte-rich areas of the left ventricle. SAHFs, p21 staining and epigenetics suggesting advanced age were not found in cardiomyocytes, though we observed structural features associated to premature aging. Cross-reference analysis showed correlation between the PKP2cKO cardiac proteome and that of mice 5 or 6 times their chronological age, as well as transcriptional signatures of neurodegenerative diseases. HIGHLIGHTSO_LIPKP2-ARVC is a leading cause of sudden unexpected death in the young. C_LIO_LIThe molecular path from the variant of a gene to the clinical disease remains unclear. An inflammatory component has been postulated. C_LIO_LIWe show that loss of PKP2 only in myocytes is sufficient to induce a pro-inflammatory senescence in non-myocytes and premature aging of cardiac cells. C_LIO_LISimilarities to the molecular profile of neurodegenerative diseases and novel paths to therapy are discussed. C_LI

physiology↗

bioRxiv2025

Astrocytes connect specific brain regions through plastic gap junctional networks

Traditionally, neuronal axons have been considered the primary mediators of functional connectivity among brain regions. However, the role of astrocyte-mediated communication has been largely underappreciated. While astrocytes communicate with one another through gap junctions, the extent and specificity of this communication remain poorly understood. Astrocyte gap junctions are necessary for memory formation1,2, synaptic plasticity3-5, coordination of neuronal signaling6, and closing the visual and motor critical periods7,8. These findings indicate that this form of communication is essential for proper central nervous system development and function. Despite their significance, studying astrocyte gap junctional networks has been challenging. Current methods like slice electrophysiology disrupt network connectivity and introduce artifacts due to tissue damage. To overcome these limitations, we developed a vector-based approach that labels molecules as they are fluxed by astrocyte gap junctions in awake, behaving animals. We then used whole-brain tissue clearing9,10 to image these intact, three-dimensional astrocyte networks. We show that multiple astrocyte networks traverse the mouse brain. These networks selectively connect specific regions, rather than diffusing indiscriminately, and vary in size and organization. We observe local networks are confined to single brain regions and long-range networks robustly interconnecting multiple regions across hemispheres, often exhibiting patterns distinct from known neuronal networks. Further, we demonstrate that astrocyte networks undergo structural reorganization in adult brain following sensory deprivation. These discoveries reveal a previously unrecognized mode of communication between distant brain regions, mediated by plastic networks of gap junction-coupled astrocytes.

neuroscience↗

bioRxiv2025

Inhibitory effect of capsule on natural transformation of Streptococcus pneumoniae

The capsule of Streptococcus pneumoniae (Spn) is highly heterogeneous based on expression of distinct polysaccharides. Spn transformation, controlled by the Com regulon, has been predominantly focused on unencapsulated laboratory strains. However, genomic studies revealed different rates of recombination events in clinical isolates of different serotypes. As these isolates were genetically distinct beyond capsule-encoding genes, the exact relationship between transformation and capsule remains unclear. Herein, we compared the transformability of a collection of isogenic capsule-switch strains. Strains with different capsule types and amounts significantly differed in their transformation frequency, with the unencapsulated strain having a higher frequency compared to encapsulated strains. A GFP-reporter of each strain monitoring the expression of a Com regulon-controlled gene showed similar kinetics, indicating differences in transformability were due to processes downstream of competence activation. The Com pilus, induced by competence, binds and takes in the donor DNA, and is the central component of the transformation apparatus. The surface exposure of Com pilus significantly differed among serotypes with highly transformable strains having more cells binding ComGC antibody. Further, electron microscopy demonstrated that transformability correlated with the proportion of cells bearing a Com pilus, which was affected by both the presence of capsule and serotype. Additionally, the unencapsulated strain displayed longer pili than encapsulated strains. Examination of capsule porosity revealed that serotypes with higher transformation frequencies had more porous capsules. Together, these results indicate that the capsule interferes with the assembly of Com pilus, thereby inhibiting the natural transformation of Spn. IMPORTANCEThe capsule is a major virulence factor of Streptococcus pneumoniae (Spn), providing a physical shield and exhibiting extensive diversity across at least 100 serotypes. Although natural transformation of Spn has predominantly been characterized in unencapsulated laboratory strains, clinical encapsulated isolates also exhibit transformability and demonstrate varied recombination rates during host carriage. We utilized otherwise genetically identical capsule-switch strains to isolate the effect of capsule on transformation. We demonstrate serotype- and quantity-dependent inhibition of transformation by the capsule, mediated through hindrance with the transformation pilus assembly and function. This study challenges the paradigm that unencapsulated laboratory strains fully recapitulate natural transformation dynamics. By redefining capsule as a multifunctional modulator of Spn biology, balancing virulence and adaptability, our findings advance our understanding of pneumococcal evolution.

microbiology↗

bioRxiv2024

Integrin-deficient T cell leukemia accumulates in the central nervous system

T-cell acute lymphoblastic leukemia (T-ALL) spreads aggressively to the central nervous system (CNS), particularly the leptomeninges. Children with T-ALL are treated with high-dose, CNS-directed chemotherapy, which can cause lasting neurotoxicity and is not always effective. Little is known about how T-ALL enters and persists within the CNS. However, normal T cell migration into the CNS has been extensively studied. Two integrins--VLA-4 and LFA-1--mediate normal T cell entry to the CNS, and VLA-4 blockade effectively treats multiple sclerosis by excluding T cells from the brain. We hypothesized that these integrins would likewise be required for T-ALL CNS entry. Unexpectedly, not only were VLA-4 and LFA-1 dispensable for T-ALL to reach the CNS, integrin-deficient T-ALL accumulated in the CNS compared to control. Mechanistically, integrin loss accelerated T-ALL proliferation in the CNS, suggesting that integrin-mediated interactions may promote quiescence in this space. Integrin blockade synergized with chemotherapy targeting proliferating cells, raising the possibility that combination therapy might be a powerful strategy.

immunology↗

bioRxiv2023

Pulses of RhoA Signaling Stimulate Actin Polymerization and Flow in Protrusions to Drive Collective Cell Migration

In animals, cells often move as collectives to shape organs, close wounds, or--in the case of disease--metastasize. To accomplish this, cells need to generate force to propel themselves forward. The motility of singly migrating cells is driven largely by an interplay between Rho GTPase signaling and the actin network (Yamada and Sixt, 2019). Whether cells migrating as collectives use the same machinery for motility is unclear. Using the zebrafish posterior lateral line primordium as a model for collective cell migration, we find that active RhoA and myosin II cluster on the basal sides of the primordium cells and are required for primordium motility. Positive and negative feedbacks cause RhoA and myosin II activities to pulse. These pulses of RhoA signaling stimulate actin polymerization at the tip of the protrusions and myosin II-dependent actin flow and protrusion retraction at the base of the protrusions, and deform the basement membrane underneath the migrating primordium. This suggests that RhoA-induced actin flow on the basal sides of the cells constitutes the motor that pulls the primordium forward, a scenario that likely underlies collective migration in other--but not all (Bastock and Strutt, 2007; Lebreton and Casanova, 2013; Matthews et al., 2008)--contexts.

developmental biology↗

bioRxiv2023

Bacterial contact induces polar plug disintegration to mediate whipworm egg hatching

The bacterial microbiota promotes the life cycle of the intestine-dwelling whipworm Trichuris by mediating hatching of parasite eggs ingested by the mammalian host. Despite the enormous disease burden associated with Trichuris colonization, the mechanisms underlying this transkingdom interaction have been obscure. Here, we used a multiscale microscopy approach to define the structural events associated with bacteria-mediated hatching of eggs for the murine model parasite Trichuris muris. Through the combination of scanning electron microscopy (SEM) and serial block face SEM (SBFSEM), we visualized the outer surface morphology of the shell and generated 3D structures of the egg and larva during the hatching process. These images revealed that exposure to hatching-inducing bacteria catalyzed asymmetric degradation of the polar plugs prior to exit by the larva. Although unrelated bacteria induced similar loss of electron density and dissolution of the structural integrity of the plugs, egg hatching was most efficient in the presence of bacteria that bound poles with high density such as Staphylococcus aureus. Consistent with the ability of taxonomically distant bacteria to induce hatching, additional results suggest chitinase released from larva within the eggs degrade the plugs from the inside instead of enzymes produced by bacteria in the external environment. These findings define at ultrastructure resolution the evolutionary adaptation of a parasite for the microbe-rich environment of the mammalian gut.

microbiology↗

bioRxiv2023

Too bad to be fraud, Midjourney has yet to embark in science.

Artificial Intelligence (AI) promises great benefits for data management, for image analysis, and for new discovery, but also creates unprecedented potential for fraud. This brief study explores whether images created by AI pose a threat to the integrity of figures in scientific publications. An attempt was made to use a leading AI image-generation engine, Midjourney, to create plausible facsimiles of images that are commonly depicted in manuscripts in the biological sciences. We conclude that a widely available AI for generated images is not a threat to integrity, yet, but may be in the near future.

scientific communication and education↗

bioRxiv2020

3-Dimensional Organization and Dynamics of the Microsporidian Polar Tube Invasion Machinery

Microsporidia, a divergent group of single-celled eukaryotic parasites, harness a specialized harpoon-like invasion apparatus called the polar tube (PT) to gain entry into host cells. The PT is tightly coiled within the transmissible extracellular spore, and is about 20 times the length of the spore. Once triggered, the PT is rapidly ejected and is thought to penetrate the host cell, acting as a conduit for the transfer of infectious cargo into the host. The organization of this specialized infection apparatus in the spore, how it is deployed, and how the nucleus and other large cargo are transported through the narrow PT are not well understood. Here we use serial block-face scanning electron microscopy to reveal the 3-dimensional architecture of the PT and its relative spatial orientation to other organelles within the spore. Using high-speed optical microscopy, we also capture and quantify the entire PT germination process in vitro. Our results show that the emerging PT experiences very high accelerating forces to reach velocities exceeding 300 m.s-1, and that firing kinetics differ markedly between species. Live-cell imaging reveals that the nucleus, which is approximately 7 times larger than the diameter of the PT, undergoes extreme deformation to fit through the narrow tube, and moves at speeds comparable to PT extension. Our study sheds new light on the 3-dimensional organization, dynamics, and mechanism of PT extrusion, and shows how infectious cargo moves through the tube to initiate infection.

microbiology↗

bioRxiv2020

APOL1 Variant-Expressing Endothelial Cells Exhibit Autophagic Dysfunction and Mitochondrial Stress

Apolipoprotein L1 (APOL1) gene risk variants (RV) associate with renal and cardiovascular disease particularly in SLE. We hypothesized that in RV-carrying human umbilical vein endothelial cells (HUVECs) cytokine-induced APOL1 expression compromises mitochondrial respiration, lysosome integrity, and autophagic flux. HUVEC cultures of each APOL1 genotype were generated. APOL1 was expressed using IFN{gamma}; HUVEC mitochondrial function, lysosome integrity, and autophagic flux were measured. IFN{gamma} increased APOL1 expression across all genotypes 20-fold (p=0.001). Compared to the homozygous G0 (ancestral) allele (0RV), high risk (2RV) HUVECs showed both depressed baseline and maximum mitochondrial oxygen consumption (p<0.01), and impaired mitochondrial networking on MitoTracker assays. These cells also demonstrated a contracted lysosome compartment (p<0.001), and an accumulation of autophagosomes suggesting a defect in autophagic flux. Treatment of 0RV HUVECs with a non-selective lysosome inhibitor, hydroxychloroquine, produced autophagosome accumulations similar to the 2RV cells, thus implicating lysosome dysfunction in blocking autophagy. Compared to 0RV and 2RV HUVECs, 1 RV cells demonstrated an intermediate autophagy defect which was exacerbated by IFN{gamma}. Our findings implicate dysfunction of mitochondrial respiration, lysosome, and autophagy in APOL1 RV-mediated endothelial cytotoxicity. IFN{gamma} amplified this phenotype even in variant heterozygous cells-a potential underpin of the APOL1/inflammation interaction. This is the first description of APOL1 pathobiology in variant heterozygous cell cultures.

cell biology↗