Biology subjects

Mehrad, B.

Publications and source records attributed to Mehrad, B..

3 recordsLinked to original sources

bioRxiv2022

Computational modeling of macrophage iron sequestration during host defense against Aspergillus

Iron is essential to the virulence of Aspergillus species, and restricting iron availability is a critical mechanism of antimicrobial host defense. Macrophages recruited to the site of infection are at the crux of this process, employing multiple intersecting mechanisms to orchestrate iron sequestration from pathogens. To gain an integrated understanding of how this is achieved in invasive aspergillosis, we generated a transcriptomic time-series of the response of human monocyte-derived macrophages to Aspergillus and used this and the available literature to construct a mechanistic computational model of iron handling of macrophages during this infection. We found an overwhelming macrophage response beginning 2-4 hours after exposure to the fungus, which included upregulated transcription of iron import proteins transferrin receptor-1, divalent metal transporter-1, and ZIP family transporters, and downregulated transcription of the iron exporter ferroportin. The computational model, based on a discrete dynamical systems framework, consisted of 21 3-state nodes, and was validated with additional experimental data that were not used in model generation. The model accurately captures the steady state and the trajectories of most of the quantitatively measured nodes. In the experimental data, we surprisingly found that transferrin receptor-1 upregulation preceded the induction of inflammatory cytokines, a feature that deviated from model predictions. Model simulations suggested that direct induction of TfR1 after fungal recognition, independent of the Iron Regulatory Protein - Labile Iron Pool system, explains this finding. We anticipate that this model will contribute to a quantitative understanding of iron regulation as a fundamental host defense mechanism during aspergillosis. ImportanceInvasive pulmonary aspergillosis is a major cause of death among immunosuppressed individuals despite the best available therapy. Depriving the pathogen of iron is an essential component of host defense in this infection, but the mechanisms by which the host achieves this are complex. To understand how recruited macrophages mediate iron deprivation during the infection, we developed and validated a mechanistic computational model that integrates the available information in the field. The insights provided by this approach can help in designing iron modulation therapies as anti-fungal treatments.

immunology↗

bioRxiv2021

The Innate Immune Response to Invasive Pulmonary Aspergillosis: A Systems Modeling Approach

Aspergillus species are ubiquitous environmental molds, the spores of which are inhaled daily by most humans. Immunocompromised hosts can develop an invasive infection resulting in high mortality. There is, therefore, a pressing need for host-centric therapeutics for this infection. To address this need, we created a multi-scale computational model of the infection, focused on its interaction with the innate immune system and iron, a critical nutrient for the pathogen. The model, parameterized using published data, was found to recapitulate a wide range of biological features and was experimentally validated in vivo. Conidial swelling was identified as critical in fungal strains with high growth, whereas the siderophore secretion rate is an essential prerequisite for establishment of the infection in low-growth strains. In immunocompetent hosts, high growth, high swelling probability, and impaired leukocyte activation lead to a high conidial germination rate. Similarly, in neutropenic mice, high fungal growth was achieved through synergy between high growth rate, high swelling probability, slow leukocyte activation, and high siderophore secretion. In summary, the model reveals a small set of parameters related to fungal growth, iron acquisition, and leukocyte activation as key determinants of the fate of the infection.

systems biology↗

bioRxiv2021

In vitro infection of human lung tissue with SARS-CoV-2: Heterogeneity in host defense and therapeutic response

Cell lines are the mainstay in understanding the biology of COVID-19 infection, but do not recapitulate many of the complexities of human infection. The use of human lung tissue is one solution for the study of such novel respiratory pathogens. We hypothesized that a cryopreserved bank of human lung tissue allows for the in vitro study of the inter-individual heterogeneity of host response to SARS-CoV-2 infection, thus providing a bridge between studies with cell lines and studies in animal models. We generated a cryobank of tissues from 16 donors, most of whom had risk factors for severe illness from COVID-19. Cryopreserved tissues preserved 90% of cell viability and contained heterogeneous populations of metabolically active epithelial, endothelial, and immune cell subsets of the human lung. Samples were readily infectible with HCoV-OC43 and SARS-CoV-2 coronavirus strains, and demonstrated comparable susceptibility to infection. In contrast, we observed a marked donor-dependent heterogeneity in the expression of IL-6, CXCL8 and IFN{beta} in response to SARS-CoV-2 infection. Treatment of tissues with dexamethasone and the experimental drug, N-hydroxycytidine, suppressed viral growth in all samples, whereas chloroquine and remdesivir had no detectable effect. Metformin and sirolimus, molecules with predicted antiviral activity, suppressed viral replication in tissues from a subset of donors. In summary, we developed a novel system for the in vitro study of human SARS-CoV-2 infection using primary human lung tissue from a library of donor tissues. This model may be useful for drug screening and for understanding basic mechanisms of COVID-19 pathogenesis. ImportanceThe current biological systems for the study of COVID-19 are in vitro systems that differ from the human lung in many respects, and animal hosts to which the virus is not adapted. We developed another alternative for studying pathogenesis and drug susceptibility of SARS-CoV-2 in a cryopreserved bank of human lung tissues. We consider the importance of this work to relate to the practical use of this culture system as a repeatable and scalable approach that allows for the study of an important infection in relevant tissues. The tissue bank highlights the heterogeneous response to SARS-CoV-2 infection and treatment, which allows researchers to investigate why treatments work in some donors but not others.

microbiology↗