Biology subjects

Ortiz, S. C.

Publications and source records attributed to Ortiz, S. C..

4 recordsLinked to original sources

bioRxiv2025

The pre-mRNA Splicing Modulator Pladienolide B Inhibits Cryptococcus neoformans Germination and Growth

Cryptococcus neoformans is an opportunistic fungal pathogen responsible for life-threatening infections, particularly in immunocompromised individuals. The limitations of current antifungal therapies due to toxicity and the emergence of resistance highlight the need for novel treatment strategies and targets. C. neoformans has an intron-rich genome, and pre-mRNA splicing is required for expression of the vast majority of its genes. In this study, we investigated the efficacy of a human splicing inhibitor, pladienolide B (PladB), as an antifungal against C. neoformans. PladB inhibited growth of C. neoformans in liquid culture and spore germination. The potency of PladB could be increased by simultaneous treatment with either FK506 or clorgyline. This combination treatment resulted in significant reductions in fungal growth and prevented spore germination. Transcriptomic analysis revealed that PladB inhibits splicing in C. neoformans and results in wide-spread intron retention. In combination with FK506, this resulted in down-regulation of or intron-retention in transcripts from processes vital for cellular growth including translation, transcription, and RNA processing. Together, these results suggest that targeting RNA splicing pathways could be a promising antifungal strategy and that the effectiveness of splicing inhibitors as antifungals can be increased by co-administering drugs such as FK506. IMPORTANCEFungal infections, like those caused by Cryptococcus neoformans, can turn deadly for many patients. New treatments and therapeutic targets are needed to combat these pathogens. One potential target is the pre-mRNA processing pathway which is required for expression of nearly all protein-coding genes in C. neoformans. We have determined that a pre-mRNA splicing inhibitor can inhibit both C. neoformans growth and germination and that the potency of this drug can be increased when used in combination with other molecules. This work provides evidence that targeting steps in pre-mRNA processing may be an effective antifungal strategy and avenue for development of new medicines.

microbiology↗

bioRxiv2023

Airway epithelial cells as a novel intracellular host reservoir for Cryptococcus spores

Human fungal pathogens, including Cryptococcus neoformans, cause 1.5 million annual deaths. Cryptococcus causes disease when it disseminates out of the lung and into the brain which can occur years after initial exposure (latency) via mechanisms that remain unknown. Spores of Cryptococcus display distinct surface epitopes, host-interactions, and disease kinetics to the vegetatively growing yeast morphotype, yet they remain understudied likely contributing to our lack of understanding of pathogenesis. One of the first barriers spores encounter are non-professional phagocytic Airway Epithelial Cells (AECs). Here, we demonstrated that Cryptococcus spores preferentially invade AECs both in vitro and in vivo. Once inside spores can germinate, subsequently replicate, persist and/or escape. This ability to enter AECs correlates with a preferential ability of spore to cross AEC barriers. Together our work indicates that AECs can be invaded by Cryptococcus spores and may serve as a previously ignored intracellular host niche, providing alternative hypothesis for both Cryptococcus dissemination and latency.

microbiology↗

bioRxiv2023

Spores of the fungal pathogen Cryptococcus exhibit cell type-specific carbon source utilization during germination

Spores are critical morphotypes required for long-term survival of most fungi. Under the right environmental conditions, spores can escape dormancy and differentiate into vegetatively growing cells through the process of germination. For fatal human fungal pathogens like Cryptococcus, germination is the key differentiation process required for spores to initiate vegetative growth and ultimately cause disease; however, relatively little is known about the molecular mechanisms that control germination. To this end, we performed an extensive characterization of Cryptococcus spore germination through the morphological assessment of germinating spores, the inhibition of key eukaryotic processes, and the detailed quantification of fungal spore germination kinetics under numerous nutrient conditions. We identified temporal associations between molecular and morphological events and determined that carbon metabolism pathways (both glycolysis and oxidative phosphorylation) were required from the beginning of germination. We further determined that carbon sources are primarily used as fuel rather than as simply triggers of germination commitment, and identified spore-specific carbon source utilization that is absent in yeast. Finally, we discovered the first spore-specific enzyme, Nth2, a trehalase that is required for germination when trehalose is the primary available carbon source. Together this work provides an extensive characterization of Cryptococcus spore germination and suggests that germination is more than simply a modified cell cycle but is rather a highly adapted differentiation process.

microbiology↗

bioRxiv2021

Discovery of fungal-specific targets and inhibitors using chemical phenotyping of pathogenic spore germination

There is a critical need for new antifungal drugs; however, the lack of available fungal-specific targets is a major hurdle in the development of antifungal therapeutics. Spore germination is a differentiation process absent in humans that could harbor uncharacterized fungal-specific targets. To capitalize on this possibility, we developed novel phenotypic assays to identify and characterize inhibitors of spore germination of the human fungal pathogen Cryptococcus. Using these assays, we carried out a high throughput screen of ~75,000 drug-like small molecules and identified and characterized 191 novel inhibitors of spore germination, many of which also inhibited yeast replication and demonstrated low cytotoxicity against mammalian cells. Using an automated, microscopy-based, quantitative germination assay (QGA), we discovered that germinating spore populations can exhibit unique phenotypes in response to chemical inhibitors. Through the characterization of these spore population dynamics in the presence of the newly identified inhibitors, we classified 6 distinct phenotypes based on differences in germination synchronicity, germination rates, and overall population behavior. Similar chemical phenotypes were induced by inhibitors that targeted the same cellular function or had shared substructures. Leveraging these features, we used QGAs to identify outliers among compounds that fell into similar structural groups and thus refined relevant structural moieties, facilitating target identification. This approach led to the identification of complex II of the electron transport chain as the putative target of a promising structural cluster of germination inhibitory compounds. These inhibitors showed high potency against Cryptococcus spore germination, while maintaining low cytotoxicity against mammalian cells, making them prime candidates for development into novel antifungal therapeutics.

microbiology↗