Biology subjects

Meagher, R. B.

Publications and source records attributed to Meagher, R. B..

3 recordsLinked to original sources

bioRxiv2021

DectiSomes: Glycan Targeting of Liposomal Drugs Improves the Treatment of Disseminated Candidiasis

Candida albicans causes life-threatening disseminated candidiasis. Individuals at greatest risk have weakened immune systems. An outer cell wall, exopolysaccharide matrix, and biofilm rich in oligoglucans and oligomannans help Candida spp. evade host defenses. Even after antifungal drug treatment the one-year mortality rate exceeds 25%. Undoubtedly there is room to improve antifungal drug performance. The mammalian C-type lectin pathogen receptors Dectin-1 and Dectin-2 bind to fungal oligoglucans and oligomannans, respectively. We previously coated amphotericin B-loaded liposomes, AmB-LLs, pegylated analogs of AmBisome, with the ligand binding domains of these two Dectins. DectiSomes, DEC1-AmB-LLs and DEC2-AmB-LLs, showed two distinct patterns of binding to the exopolysaccharide matrix surrounding C. albicans hyphae grown in vitro, while untargeted AmB-LLs did not bind. DectiSomes were preferentially associated with fungal colonies in the kidneys. In a neutropenic mouse model of candidiasis, DEC1-AmB-LLs and DEC2-AmB-LLs delivering only one dose of 0.2 mg/kg AmB significantly reduced the kidney fungal burden several fold relative to AmB-LLs, based on either colony forming units (P= 0.013 to 8.8 x 10-5) or quantitative PCR of fungal rRNA ITS (P= 5.5x10-5 to 3.0x10-10). DEC1-AmB-LLs and DEC2-AmB-LLs significantly increased the percent of surviving mice relative to AmB-LLs. Dectin-2 targeted anidulafungin loaded liposomes and AmBisomes, DEC2-AFG-LLs and DEC2-AmBisome reduced fungal burden in the kidneys several fold over their untargeted counterparts (P=7.8x10-5 and 0.0020, respectively). The data herein suggest that targeting of a variety of antifungal drugs to fungal glycans may achieve lower safer effective doses and improve drug efficacy against a variety of invasive fungal infections.

microbiology↗

bioRxiv2019

Targeted antifungal liposomes

Aspergillus species cause pulmonary invasive aspergillosis resulting in nearly a hundred thousand deaths each year. Patients at the greatest risk of developing life-threatening aspergillosis have weakened immune systems and/or various lung disorders. Patients are treated with antifungals such as amphotericin B (AmB), casofungin acetate, or triazoles (itraconazole, voriconazole etc.), but these antifungal agents have serious limitations due to lack of sufficient fungicidal effect and human toxicity. Liposomes with AmB intercalated into the lipid membrane (AmBisomes, AmB-LLs), have several-fold reduced toxicity compared to detergent solubilized drug. However, even with the current antifungal therapies, one-year survival among patients is only 25 to 60%. Hence, there is a critical need for improved antifungal therapeutics.\n\nDectin-1 is a mammalian innate immune receptor in the membrane of some leukocytes that binds as a dimer to beta-glucans found in fungal cell walls, signaling fungal infection. Using a novel protocol, we coated AmB-LLs with Dectin-1s beta-glucan binding domain to make DEC-AmB-LLs. DEC-AmB-LLs bound rapidly, efficiently, and with great strength Aspergillus fumigatus and to Candida albicans and Cryptococcus neoformans, highly divergent fungal pathogens of global importance. By contrast, un-targeted AmB-LLs and BSA-coated BSA-AmB-LLs showed 200-fold lower affinity for fungal cells. DEC-AmB-LLs reduced the growth and viability of A. fumigatus an order of magnitude more efficiently than untargeted control liposomes delivering the same concentrations of AmB, in essence increasing the effective dose of AmB. Future efforts will focus on examining pan-antifungal targeted liposomal drugs in animal models of disease.\n\nTweetWe coated anti-fungal drug loaded liposomes to fungal cell walls with a beta-glucan binding protein and thereby increased drug effectiveness by an order of magnitude.\n\nImportanceThe fungus Aspergillus fumigatus causes pulmonary invasive aspergillosis resulting in nearly a hundred thousand deaths each year. Patients are often treated with antifungal drugs such as amphotericin B loaded into liposomes, AmB-LLs, but all antifungal drugs including AmB-LLs have serious limitations due to human toxicity and insufficient fungal cell killing. Even with the best current therapies, one-year survival among patients with invasive aspergillosis is only 25 to 60%. Hence, there is a critical need for improved antifungal therapeutics.\n\nDectin-1 is a mammalian protein that binds to beta-glucan polysaccharides found in nearly all fungal cell walls. We coated AmB-LLs with Dectin-1 to make DEC-AmB-LLs. DEC-AmB-LLs bond strongly to fungal cells, while AmB-LLs had little affinity. DEC-AmB-LLs killed or inhibited A. fumigatus ten times more efficiently than untargeted lipsomes, increasing the effective dose of AmB. Dectin-1 coated liposomes targeting fungal pathogens have the potential to greatly enhance antifungal therapeutics.

molecular biology↗

bioRxiv2017

Chromatin accessibility changes between Arabidopsis stem cells and mesophyll cells illuminate cell type-specific transcription factor networks

BackgroundCell differentiation is driven by changes in transcription factor (TF) activity and subsequent alterations in transcription. To study this process, differences in TF binding between cell types can be deduced by methods that probe chromatin accessibility. We used cell type-specific nuclei purification followed by the Assay for Transposase Accessible Chromatin (ATAC-seq) to delineate differences in chromatin accessibility and TF regulatory networks between stem cells of the shoot apical meristem (SAM) and differentiated leaf mesophyll cells of Arabidopsis thaliana.\n\nResultsChromatin accessibility profiles of SAM stem cells and leaf mesophyll cells were highly similar at a qualitative level, yet thousands of regions of quantitatively different chromatin accessibility were also identified. We found that chromatin regions preferentially accessible in mesophyll cells tended to also be substantially accessible in the stem cells as compared to the genome-wide average, whereas the converse was not true. Analysis of genomic regions preferentially accessible in each cell type identified hundreds of overrepresented TF binding motifs, highlighting a set of TFs that are likely important for each cell type. Among these, we found evidence for extensive co-regulation of target genes by multiple TFs that are preferentially expressed in one cell type or the other. For example, a set of zinc-finger TFs appear to control a suite of growth-and development-related genes specifically in stem cells, while another TF set co-regulates genes involved in light responses and photosynthesis specifically in mesophyll cells. Interestingly, the TFs within both of these sets also show evidence of extensively co-regulating each other.\n\nConclusionsQuantitative analysis of chromatin accessibility differences between stem cells and differentiated mesophyll cells allowed us to identify TF regulatory networks and downstream target genes that are likely to be functionally important in each cell type. Our findings that mesophyll cell-enriched accessible sites tend to already be substantially accessible in stem cells, but not vice versa, suggests that widespread regulatory element accessibility may be important for the developmental plasticity of stem cells. This work also demonstrates the utility of cell type-specific chromatin accessibility profiling in quickly developing testable models of regulatory control differences between cell types.

plant biology↗