Biology subjects

Neumann, A. K.

Publications and source records attributed to Neumann, A. K..

5 recordsLinked to original sources

bioRxiv2025

Plasma Membrane Damage by Environmental Materials Enhances Cell-Cell Fusion and Impairs Immune Functions of Macrophages

Macrophages are the most abundant phagocytes and play an essential role in host defense. Previous studies have shown that many environmental materials can activate macrophages and trigger inflammatory responses. However, whether these exposures alter macrophage function in host defense remains unclear. This study found that many environmental materials (such as carbon nanotubes, tungsten carbide [WC], and detergents) can damage the plasma membranes of macrophages. This damage leads to decreased reactive oxygen species (ROS) production and phagocytosis but elevated cell-cell fusion. In vivo, airway exposure to laundry detergent impaired the recruitment of macrophages and other myeloid cells to the lung and dramatically dampened protective TH1 and TH17 cell responses, leading to increased susceptibility to Candida infection in mice. Overall, our data indicate that exposure to environmental materials compromises macrophage membrane integrity and impairs host defense. These findings may aid in the development of effective preventive and therapeutic strategies.

immunology↗

bioRxiv2022

Quantifying formations of Neutravidin clusters on biotinylated mixed silane Self-Assembled Monolayers.

Towards the goal of developing bio-chip / lab-on-a-chip substrates capable of performing highly specific bio-chemical reactions, Neutravidin binding to mixed Biotinylated Silane Self-Assembled Monolayers were studied using Confocal Fluorescence Light Microscopy. Non-specific bindings, specifically the formations of Neutravidin clusters, were quantified. Several experiments were conducted to determine the concentrations of Neutravidin necessary to not saturate surface binding to Biotinylated Self-Assembled Monolayers, determine the effectiveness of using FBS blocking buffers to reduce non-specific binding, optimize the repeatability of Neutravidin binding to Biotinlyated mixed Self-Assembled Monolayers with Silane-PEG-Biotin compositions ranging from 0 to 15%, and quantify background Neutravidin bindings and the corresponding formations of Neutravidin clusters to Self-Assembled Monolayers as Silane-PEG-Biotin percent compositions increase from 0 to 15%. The Neutravidin, Silane-PEG-Biotin, and Silane mPEG concentrations and ratios needed to develop homogeneous Neutravidin films, without the formations of clusters, on the Self-Assembled Monolayers have been determined.

bioengineering↗

bioRxiv2020

Dectin-1 mediated DC-SIGN Recruitment to Candida albicans Contact Sites

At host-pathogen contact sites with Candida albicans, Dectin-1 activates pro-inflammatory signaling, while DC-SIGN promotes adhesion to the fungal surface. We observed that Dectin-1 and DC-SIGN collaborate to enhance capture/retention of C. albicans under fluid shear culture conditions. Therefore, we devised a cellular model system wherein we could investigate the interaction between these two receptors during the earliest stages of host-pathogen interaction. In cells expressing both receptors, DC-SIGN was quickly recruited to contact sites (103.15% increase) but Dectin-1 did not similarly accumulate. Once inside the contact site, FRAP studies revealed a strong reduction in lateral mobility of DC-SIGN (but not Dectin-1), consistent with DC-SIGN engaging in multivalent adhesive binding interactions with cell wall mannoprotein ligands. Interestingly, in the absence of Dectin-1 co-expression, DC-SIGN recruitment to the contact was much poorer--only 35.04%. These data suggested that Dectin-1 promotes the active recruitment of DC-SIGN to the contact site. We proposed that Dectin-1 signaling activates the RHOA pathway, leading to actomyosin contractility that promotes DC-SIGN recruitment, perhaps via the formation of a centripetal ActoMyosin Flow (AMF) directed into the contact site. Indeed, RHOA pathway inhibitors significantly reduced Dectin-1 associated DC-SIGN recruitment to the contact site. We used agent based modeling to predict DC-SIGN transport kinetics with ("Directed+Brownian") and without ("Brownian") the hypothesized actomyosin flow-mediated transport. The Directed+Brownian transport model predicted a DC-SIGN contact site recruitment (108.72%), similar to that we observed experimentally under receptor co-expression. Brownian diffusive transport alone predicted contact site DC-SIGN recruitment of only 54.02%. However, this value was similar to experimentally observed recruitment in cells without Dectin-1 or treated with RHOA inhibitor, suggesting that it accurately predicted DC-SIGN recruitment when a contact site AMF would not be generated. TIRF microscopy of nascent cell contacts on glucan-coated glass revealed Dectin-1 dependent DC-SIGN and F-actin (LifeAct) recruitment kinetics to early-stage contact site membranes. DC-SIGN entry followed F-actin with a temporal lag of 8.35 {+/-} 4.57 seconds, but this correlation was disrupted by treatment with RHOA inhibitor. Thus, computational and experimental evidence provides support for the existence of a Dectin-1/RHOA-dependent AMF that produces a force to drive DC-SIGN recruitment to pathogen contact sites, resulting in improved pathogen capture and retention by immunocytes. These data suggest that the rapid collaborative response of Dectin-1 and DC-SIGN in early contact sties might be important for the efficient acquisition of yeast under flow conditions, such as those that prevail in circulation or mucocutaneous sites of infection.

immunology↗

bioRxiv2019

Innate Antifungal Immune Receptor, Dectin-1, Undergoes Ligand-Induced Oligomerization with Highly Structured β-Glucans and at Fungal Cell Contact Sites

Dectin-1A is a C-type Lectin innate immunoreceptor that recognizes {beta}-(1,3;1,6)-glucan, a structural component of Candida species cell walls. The higher order structure of {beta}-glucans ranges from random coil to insoluble fiber due to varying degrees of tertiary (helical) and quaternary structure. Model Saccharomyces cerevisiae {beta}-glucans of medium and high molecular weight (MMW and HMW, respectively) are highly structured. In contrast, low MW glucan (LMW) is much less structured. Despite similar affinity for Dectin-1A, the ability of glucans to induce Dectin-1A mediated calcium influx and Syk phosphorylation positively correlates with their degree of higher order structure. Chemical denaturation and renaturation of MMW glucan showed that glucan structure determines agonistic potential, but not binding affinity, for Dectin-1A. We explored the role of glucan structure on Dectin-1A oligomerization, which is thought to be required for Dectin-1 signaling. Glucan signaling decreased Dectin-1A diffusion coefficient in inverse proportion to glucan structural content, which was consistent with Dectin-1A aggregation. Forster Resonance Energy Transfer (FRET) measurements revealed that molecular aggregation of Dectin-1 occurs in a manner dependent upon glucan higher order structure. Number and Brightness analysis specifically confirmed an increase in the Dectin-1A dimer and oligomer populations that is correlated with glucan structure content. Comparison of receptor modeling data with FRET measurements confirms that in resting cells, Dectin-1A is predominantly in a monomeric state. Super Resolution Microscopy revealed that glucan-stimulated Dectin-1 aggregates are very small (<15 nm) collections of a few engaged receptors. Finally, FRET measurements confirmed increased molecular aggregation of Dectin-1A at fungal particle contact sites in a manner that positively correlated with the degree of exposed glucan on the particle surface. These results indicate that Dectin-1A senses the solution conformation of {beta}-glucans through their varying ability to drive receptor dimer/oligomer formation and activation of membrane proximal signaling events.

immunology↗

bioRxiv2019

RHOA mediated mechanical force generation through Dectin-1

Dectin-1 is an innate immune pattern recognition receptor which recognizes {beta}-glucan on the Candida albicans (C. albicans) cell wall. Recognition of {beta}-glucan by immune cells leads to phagocytosis, oxidative burst, cytokine and chemokine production. We looked for specific mechanisms that coordinate phagocytosis downstream of Dectin-1 leading to actin reorganization and internalization of fungus. We found that stimulation of Dectin-1 by soluble {beta}-glucan leads to mechanical force generation and areal contraction in Dectin-1 transfected HEK-293 cells and M1 macrophages. With inhibitor studies, we found this force generation is a SYK-independent, SFK (SRC Family Kinase)-dependent process mediated through the RHOA-ROCK-MLC pathway. We confirmed activation of RHOA downstream of Dectin-1 using G-LISA and stress fiber formation. Through phagocytosis assays, we found direct evidence for importance of RHOA-ROCK-MLC pathway in process of phagocytosis of C. albicans. In conclusion, we found evidence for RHOA-ROCK-MLC mediated mechanical force generation downstream of Dectin-1 for C. albicans phagocytosis.

immunology↗