Biology subjects

Flick, M. J.

Publications and source records attributed to Flick, M. J..

8 recordsLinked to original sources

bioRxiv2026

Aquaporin-4 Regulates Edema, Sustains Astrocyte Differentiation, and Constrains Immunosuppressive Remodeling in Glioblastoma

Vasogenic cerebral edema is a severe complication that affects most patients with glioblastoma (GBM). It leads to an increase in intracranial pressure, neurological deficits, and increased mortality rates. While there is considerable research on edema formation, the molecular and cellular mechanisms of edema resolution in GBM, particularly in response to dexamethasone or other anti-edema therapies, remain largely undefined. Our findings demonstrate that the water channel aquaporin-4 (AQP4), a key regulator of brain water homeostasis, is upregulated in human GBM compared to the normal brain. AQP4 expression correlates with peritumoral edema in GBM patients, with the classical (CL) GBM subtype exhibiting the highest AQP4 levels but the lowest edema content relative to the proneural (PN) and mesenchymal (MES) subtypes. Using the RCAS/tv-a system, we generated de novo GBM with defined driver mutations in Aqp4-proficient and -deficient mice. Loss of Aqp4 shortened survival and exacerbated edema, accompanied by reduced astrocytic coverage within the tumor core, but not at the tumor margin. Single-cell RNA-sequencing and spatial transcriptomics revealed that Aqp4 loss reprograms astrocytes toward an immature, progenitor-like state and alters their crosstalk with other cell types in the GBM microenvironment. Additionally, loss of Aqp4 skewed myeloid populations toward immunosuppressive phenotypes while reducing lymphoid infiltration. Treatment with anti-VEGFA antibody, an established anti-edema therapy, increased expression of Aqp4 and reduced vessel leakage, underscoring the role of AQP4 in the therapeutic modulation of brain water balance. Overall, this study highlights the important role of AQP4 in resolving edema and its critical function in maintaining astrocyte identity and shaping the immune landscape of GBM.

cancer biology↗

bioRxiv2026

Lack of canonical PAR4 activation is associated with reduced arterial and venous thrombosis in mice.

BackgroundProtease-activated receptor 4 (PAR4) is the only functional thrombin receptor on mouse platelets. Expression and activation of platelet PAR4 was shown to influence hemostatic plug stability and contributes to thrombosis in different murine arterial and venous thrombosis models. PAR4 activation by thrombin and other serine proteases occurs at the canonical activation site at Arginine (Arg) 59 in mice and Arg47 in humans. If murine PAR4 has functional non-canonical activation sites as shown for other PARs is unknown. ObjectiveTo investigate canonical and potentially non-canonical PAR4 signaling in mice, we generated a mouse model expressing a functional, thrombin-cleavage resistant PAR4 by changing Arg59 to Alanine (Ala) 59 in murine PAR4 (PAR4R59A). PAR4R59A mice were used to assess the impact of impaired canonical (thrombin)-dependent PAR4 signaling on hemostasis and thrombosis in mice. MethodsWe analyzed platelet aggregation, platelet integrin activation and -granule release ex vivo. Hemostasis and thrombosis in PAR4R59A and their control mice was compared using the jugular vein needle puncture injury-induced hemostasis model, and the ferric chloride-induced carotid artery and electrolytic injury-induced femoral vein thrombosis models. ResultsPlatelets of PAR4R59A mice did not response to thrombin but responded normally to PAR4 agonist peptide (PAR4AP) stimulation in aggregation assays. Platelets of PAR4R59A and their control mice exhibited comparable responses to ADP, convulxin or PAR4AP regarding integrin activation and -granular release. PAR4R59A mice exhibited impaired hemostasis in the jugular vein needle puncture model, and were protected from ferric chloride-induced arterial thrombosis and from electrolytic injury induced thrombosis in the femoral vein. ConclusionThe novel PAR4R59A mouse expresses a thrombin-insensitive but still functional PAR4. We propose that the new mouse line will increase the in vivo investigation of canonical PAR4 signaling pathways and may reveal unknown non-canonical PAR4 signaling in different pathologies.

pathology↗

bioRxiv2026

Graph-based modeling of multiparametric MRI deciphers molecular states of high-grade glioma invasion with prognostic implications

AbstractThe infiltrative, non-enhancing margin of IDH wildtype high grade glioma (IDHwt HGG) harbors distinct molecular programs that drive invasion and therapeutic resistance, yet remains largely unevaluable by conventional tissue sampling approaches and by conventional imaging. Here we show that this invasive architecture is encoded within multiparametric MRI (mpMRI) feature relationships and can be decoded using a graph-based framework trained on multiregional image-localized biopsies. Across 134 spatially matched biopsy-imaging pairs from 35 patients with primary IDHwt HGG (29 glioblastomas (GBM) and 6 non-glioblastoma HGGs), unsupervised graph community detection identifies two imaging-defined clusters that localize to invasive tumor regions without molecular supervision. Transcriptomic profiling associates these clusters with neuronal (NEU) and glycolytic-plurimetabolic (GPM) molecular programs. Building on this framework, a graph convolutional network (GCN) accurately predicts NEU and GPM transcriptional states in independent training and validation cohorts and significantly outperforms conventional convolutional neural networks. Applied to whole-tumor mpMRI volumes, the trained GCN generates spatially resolved probability maps that quantify the distribution and relative burden of NEU and GPM programs across both MRI contrast-enhancing and non-enhancing invasive regions. These imaging-derived molecular maps stratify patients by overall survival. Increased GPM burden is associated with poorer survival, consistent with the aggressive behavior associated with mesenchymal-like transcriptional programs in IDHwt HGG. In contrast, increased NEU burden is associated with improved survival, identifying a previously unrecognized imaging-derived prognostic biomarker that was not detected by biopsy-based molecular classification alone. Together, these findings establish a graph-based imaging framework for spatially resolved molecular classification of invasive IDHwt HGG and demonstrate that whole-tumor molecular state architecture carries prognostic information beyond conventional tissue sampling.

cancer biology↗

bioRxiv2026

Extravascular coagulation stabilizes pro-fibrotic stromal states via tumor-intrinsic PAR1 signaling in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) exhibits a desmoplastic stroma with context-dependent tumor-restraining and tumor-promoting functions, highlighting the need to selectively reprogram stromal states. Extravascular coagulation is a prominent feature of the PDAC tumor microenvironment, yet whether it functions as an upstream regulator of fibrotic stromal states, rather than merely a byproduct of tumor-associated vascular dysfunction, has remained unclear. Here, we identify extravascular coagulation as a tumor-amplified regulatory module that stabilizes pro-fibrotic stromal states via tumor-intrinsic protease-activated receptor-1 (PAR1) signaling. To interrogate this axis mechanistically, we integrated human tumor bioinformatics with microphysiological tumor-stroma (MPTS) models that reconstruct tumor-stroma interactions under controlled coagulation exposure, followed by cross-scale validation in vivo. Analysis of The Cancer Genome Atlas (TCGA) revealed heterogeneous F2R (PAR1) expression across tumors, with elevated expression associated with fibrotic transcriptional programs and reduced survival. Consistently, thrombin induced coordinated pro-fibrotic programs in tumor cells and cancer-associated fibroblasts (CAFs), which were recapitulated in MPTS where tumor-intrinsic PAR1 was required for amplification of extracellular matrix deposition and CAF activation. Mechanistically, PAR1 signaling amplified tumor-stroma communication, in part through induction of TGF-{beta}1-dependent pathways, establishing a reinforcing feedback loop that stabilizes fibrotic remodeling. Pharmacologic inhibition of PAR1 selectively suppressed the fibrotic transcriptional program within myofibroblastic CAFs while reducing the abundance of other CAF subtypes, reprogramming stromal states and attenuating tumor progression across MPTS and in vivo models. These findings establish a coagulation-PAR1 axis as an upstream organizer of PDAC stromal architecture and identify pharmacologic PAR1 inhibition as a mechanistically grounded strategy for selectively reprogramming the tumor-promoting stroma.

cancer biology↗

bioRxiv2024

The catheterized bladder environment induces dysregulation of macrophage polarization exacerbating bacterial UTI

Urinary catheterization causes bladder damage, predisposing hosts to catheter-associated urinary tract infections (CAUTIs). CAUTI pathogenesis is mediated by bladder damage-induced inflammation, resulting in accumulation and deposition of the blood-clotting protein fibrinogen (Fg) and its matrix form fibrin, which are exploited by uropathogens as biofilm platforms to establish infection. Catheter-induced inflammation also results in robust immune cell recruitment, including macrophages (M{phi}s). A fundamental knowledge gap is understanding the mechanisms by which the catheterized-bladder environment suppresses the M{phi} antimicrobial response, allowing uropathogen persistence. Here, we found that Fg and fibrin differentially modulate M1 and M2 M{phi} polarization, respectively. We unveiled that fibrin accumulation in catheterized mice induced an anti-inflammatory M2-like M{phi} phenotype, correlating with pathogen persistence. Even GM-CSF treatment of wildtype mice to promote M1 polarization was not sufficient to reduce bacterial burden and dissemination, indicating that the catheterized-bladder environment provides mixed signals, dysregulating M{phi} polarization, hindering its antimicrobial response against uropathogens.

immunology↗

bioRxiv2023

4D intravital imaging studies iden1fy platelets as the predominant cellular procoagulant surface in a mouse model of hemostasis

Interplay between platelets, coagulation/fibrinolytic factors, and endothelial cells (ECs) is necessary for effective hemostatic plug formation. This study describes a novel four-dimensional (4D) imaging platform to visualize and quantify hemostatic plug components with high spatiotemporal resolution. Fibrin accumulation following laser-induced endothelial ablation was observed at the EC-platelet plug interface, controlled by the antagonistic balance between fibrin generation and breakdown. Phosphatidylserine (PS) was first detected in close physical proximity to the fibrin ring, followed by exposure across the endothelium. Impaired PS exposure in cyclophilinD-/- mice resulted in a significant reduction in fibrin accumulation. Adoptive transfer and inhibitor studies demonstrated a key role for platelets, but not ECs, in fibrin generation during hemostatic plug formation. Inhibition of fibrinolysis with tranexamic acid (TXA) led to increased fibrin accumulation in WT mice, but not in cyclophilinD-/- mice or WT mice treated with antiplatelet drugs. These studies implicate platelets as the functionally dominant procoagulant surface during hemostatic plug formation. In addition, they suggest that impaired fibrin formation due to reduced platelet procoagulant activity is not reversed by TXA treatment.

cell biology↗

bioRxiv2021

FIBRIN POLYMER ON THE SURFACE OF BIOMATERIAL IMPLANTS DRIVES THE FOREIGN BODY REACTION

ABSTRACTImplantation of biomaterials and medical devices in the body triggers the foreign body reaction (FBR) which is characterized by macrophage fusion at the implant surface leading to the formation of foreign body giant cells and the development of the fibrous capsule enveloping the implant. While adhesion of macrophages to the surface is an essential step in macrophage fusion and implanted biomaterials are known to rapidly acquire a layer of host proteins, a biological substrate that is responsible for this process in vivo is unknown. Here we show that mice with genetically-imposed fibrinogen deficiency display a dramatic reduction of macrophage fusion on implanted biomaterials and are protected from the formation of fibrin-containing granulation tissue, a precursor of the fibrous capsule. Furthermore, macrophage fusion on biomaterials implanted in FibAEK mice that express a mutated form of fibrinogen incapable of thrombin-mediated polymerization was strongly reduced. Surprisingly, despite the lack of fibrin, the capsule was formed in FibAEK mice, although it had a different composition and distinct mechanical properties than that in wild-type mice. Specifically, while mononuclear -SMA-expressing macrophages embedded in the capsule of both strains of mice secreted collagen, the amount of collagen and its density in the tissue of FibAEK mice was reduced. These data identify fibrin polymer as a key biological substrate driving the development of the FBR.

immunology↗

bioRxiv2021

Fibrin is a critical regulator of neutrophil effector function at mucosal barrier sites

Tissue-specific cues are critical for homeostasis at mucosal barriers. Here, we document that the clotting factor fibrin is a critical regulator of neutrophil function at mucosal barriers. We demonstrate that fibrin engages neutrophils through the M{beta}2 integrin receptor and activates effector functions, including the production of reactive oxygen species and NET formation. These immune-protective neutrophil functions become tissue damaging in the context of impaired plasmin-mediated fibrinolysis. Indeed, the accumulation of fibrin due to Mendelian genetic defects in plasmin leads to severe oral mucosal immunopathology in mice and humans. Concordantly, genetic polymorphisms in the human PLG gene, encoding plasminogen, are associated with common forms of the oral mucosal disease periodontitis. Our work uncovers fibrin as a critical regulator of neutrophil effector function within the mucosal tissue microenvironment and suggests fibrin-neutrophil engagement as a pathogenic instigator and therapeutic target in common mucosal disease.

immunology↗