Browsing by Author "Tjahjono, Elissa"
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Item Box C/D small nucleolar ribonucleoproteins regulate mitochondrial surveillance and innate immunity(Public Library of Science, 2022) Tjahjono, Elissa; Revtovich, Alexey V.; Kirienko, Natalia V.Monitoring mitochondrial function is crucial for organismal survival. This task is performed by mitochondrial surveillance or quality control pathways, which are activated by signals originating from mitochondria and relayed to the nucleus (retrograde response) to start transcription of protective genes. In Caenorhabditis elegans, several systems are known to play this role, including the UPRmt, MAPKmt, and the ESRE pathways. These pathways are highly conserved and their loss compromises survival following mitochondrial stress. In this study, we found a novel interaction between the box C/D snoRNA core proteins (snoRNPs) and mitochondrial surveillance and innate immune pathways. We showed that box C/D, but not box H/ACA, snoRNPs are required for the full function of UPRmt and ESRE upon stress. The loss of box C/D snoRNPs reduced mitochondrial mass, mitochondrial membrane potential, and oxygen consumption rate, indicating overall degradation of mitochondrial function. Concomitantly, the loss of C/D snoRNPs increased immune response and reduced host intestinal colonization by infectious bacteria, improving host resistance to pathogenesis. Our data may indicate a model wherein box C/D snoRNP machinery regulates a “switch” of the cell’s activity between mitochondrial surveillance and innate immune activation. Understanding this mechanism is likely to be important for understanding multifactorial processes, including responses to infection and aging.Item Development and Characterization of High-Throughput Caenorhabditis elegans – Enterococcus faecium Infection Model(Frontiers Media S.A., 2021) Revtovich, Alexey V.; Tjahjono, Elissa; Singh, Kavindra V.; Hanson, Blake M.; Murray, Barbara E.; Kirienko, Natalia V.The genus Enterococcus includes two Gram-positive pathogens of particular clinical relevance: E. fae-calis and E. faecium. Infections with each of these pathogens are becoming more frequent, particular-ly in the case of hospital-acquired infections. Like most other bacterial species of clinical importance, antimicrobial resistance (and, specifically, multi-drug resistance) is an increasing threat, with both species considered to be of particular importance by the World Health Organization and the US Cen-ters for Disease Control. The threat of antimicrobial resistance is exacerbated by the staggering dif-ference in the speeds of development for the discovery and development of the antimicrobials versus resistance mechanisms . In the search for alternative strategies, modulation of host-pathogen interac-tions in general, and virulence inhibition in particular, has drawn substantial attention. Unfortunately, these approaches require a fairly comprehensive understanding of virulence determinants. This re-quirement is complicated by the fact that enterococcal infection models generally require vertebrates, making them slow, expensive, and ethically problematic, particularly when considering the thousands of animals that would be needed for the early stages of experimentation. To address this problem, we developed the first high-throughput C. elegans–E. faecium infection model involving host death. Im-portantly, this model recapitulates many key aspects of murine peritonitis models, including utilizing similar virulence determinants. Additionally, host death is independent of peroxide production, un-like other E. faecium–C. elegans virulence models, which allows the assessment of other virulence factors. Using this system, we analyzed a panel of lab strains with deletions of targeted virulence fac-tors. Although removal of certain virulence factors (e.g., Δfms15) was sufficient to affect virulence alone, multiple deletions were generally required to affect pathogenesis, suggesting that host-pathogen interactions are multifactorial. These data were corroborated by genomic analysis of select-ed isolates with high and low levels of virulence. We anticipate that this platform will be useful for identifying new treatments for E. faecium infection.Item ESRE Network Activation and Regulation Provide Insight into Mitochondrial Surveillance(2020-04-22) Tjahjono, Elissa; Bartel, Bonnie; Kirienko, Natalia VAll living organisms exist in a precarious state of homeostasis that requires constant maintenance. A wide variety of stresses, including hypoxia, heat, and infection by pathogens perpetually threaten to imbalance this state. Organisms use a battery of defenses to mitigate damage and restore normal function. In a pyoverdine-dependent Caenorhabditis elegans-Pseudomonas aeruginosa assay, C. elegans’ defense response utilizes the phylogenetically conserved ESRE (Ethanol and Stress Response Element) network, which has previously been shown to mitigate damage from a variety of abiotic stresses. It is intriguing that this network is involved in innate immunity; it indicates that host innate immune responses overlap with responses to abiotic stresses. I further investigated the ESRE defense network following exposure to P. aeruginosa and showed that mitochondrial damage leads to ESRE activation both in C. elegans and in mammals. Mitochondrial dysfunction contributes to a wide variety of pathologies, including neurodegenerative diseases, cancer, metabolic diseases, and aging. Mitochondrial status is actively surveilled by several different systems to ensure the preservation of cellular viability. I characterized the ESRE pathway, a novel mitochondrial surveillance system, and showed that it is robustly activated in response to increased superoxide radical. This differentiates ESRE from other existing mitochondrial surveillance pathways, such as the mitochondrial unfolded protein response (UPRmt) that monitors disruption of mitochondrial protein import and the mitochondrial MAPK (MAPKmt) pathway that responds to mitochondrial bioenergetic disruption. I also observed multiple interactions between the ESRE, UPRmt, and MAPKmt pathways. Understanding mitochondrial surveillance and the interplay that occurs among these pathways is crucial for the advancement and understanding of cell biology. Considering that the ESRE motif and its role in response to mitochondrial damage is conserved in humans, modulation of mitochondrial pathways could confer resistance to stress and improve health span, leading to a direct benefit to human health.Item Examining Sporadic Cancer Mutations Uncovers a Set of Genes Involved in Mitochondrial Maintenance(MDPI, 2023) Moreno, Armando; Taffet, Allison; Tjahjono, Elissa; Anderson, Quinton L.; Kirienko, Natalia V.Mitochondria are key organelles for cellular health and metabolism and the activation of programmed cell death processes. Although pathways for regulating and re-establishing mitochondrial homeostasis have been identified over the past twenty years, the consequences of disrupting genes that regulate other cellular processes, such as division and proliferation, on affecting mitochondrial function remain unclear. In this study, we leveraged insights about increased sensitivity to mitochondrial damage in certain cancers, or genes that are frequently mutated in multiple cancer types, to compile a list of candidates for study. RNAi was used to disrupt orthologous genes in the model organism Caenorhabditis elegans, and a series of assays were used to evaluate these genes’ importance for mitochondrial health. Iterative screening of ~1000 genes yielded a set of 139 genes predicted to play roles in mitochondrial maintenance or function. Bioinformatic analyses indicated that these genes are statistically interrelated. Functional validation of a sample of genes from this set indicated that disruption of each gene caused at least one phenotype consistent with mitochondrial dysfunction, including increased fragmentation of the mitochondrial network, abnormal steady-state levels of NADH or ROS, or altered oxygen consumption. Interestingly, RNAi-mediated knockdown of these genes often also exacerbated α-synuclein aggregation in a C. elegans model of Parkinson’s disease. Additionally, human orthologs of the gene set showed enrichment for roles in human disorders. This gene set provides a foundation for identifying new mechanisms that support mitochondrial and cellular homeostasis.Item Mitochondria-affecting small molecules ameliorate proteostasis defects associated with neurodegenerative diseases(Springer Nature, 2021) Tjahjono, Elissa; Pei, Jingqi; Revtovich, Alexey V.; Liu, Terri-Jeanne E.; Swadi, Alisha; Hancu, Maria C.; Tolar, Joe G.; Kirienko, Natalia V.Macroautophagic recycling of dysfunctional mitochondria, known as mitophagy, is essential for mitochondrial homeostasis and cell viability. Accumulation of defective mitochondria and impaired mitophagy have been widely implicated in many neurodegenerative diseases, and loss-of-function mutations of PINK1 and Parkin, two key regulators of mitophagy, are amongst the most common causes of heritable parkinsonism. This has led to the hypothesis that pharmacological stimulation of mitophagy may be a feasible approach to combat neurodegeneration. Toward this end, we screened ~ 45,000 small molecules using a high-throughput, whole-organism, phenotypic screen that monitored accumulation of PINK-1 protein, a key event in mitophagic activation, in a Caenorhabditis elegans strain carrying a Ppink-1::PINK-1::GFP reporter. We obtained eight hits that increased mitochondrial fragmentation and autophagosome formation. Several of the compounds also reduced ATP production, oxygen consumption, mitochondrial mass, and/or mitochondrial membrane potential. Importantly, we found that treatment with two compounds, which we named PS83 and PS106 (more commonly known as sertraline) reduced neurodegenerative disease phenotypes, including delaying paralysis in a C. elegans β-amyloid aggregation model in a PINK-1-dependent manner. This report presents a promising step toward the identification of compounds that will stimulate mitochondrial turnover.Item The evolutionarily conserved ESRE stress response network is activated by ROS and mitochondrial damage(Springer Nature, 2020) Tjahjono, Elissa; McAnena, Aidan P.; Kirienko, Natalia V.Background: Mitochondrial dysfunction causes or contributes to a wide variety of pathologies, including neurodegenerative diseases, cancer, metabolic diseases, and aging. Cells actively surveil a number of mitochondrial readouts to ensure that cellular homeostasis is maintained. Results: In this article, we characterize the role of the ethanol and stress response element (ESRE) pathway in mitochondrial surveillance and show that it is robustly activated when the concentration of reactive oxygen species (ROS) in the cell increases. While experiments were mostly performed in Caenorhabditis elegans, we observed similar gene activation profile in human cell lines. The linear relationship between ROS and ESRE activation differentiates ESRE from known mitochondrial surveillance pathways, such as the mitochondrial unfolded protein response (UPRmt), which monitor mitochondrial protein import. The ability of the ESRE network to be activated by increased ROS allows the cell to respond to oxidative and reductive stresses. The ESRE network works in tandem with other mitochondrial surveillance mechanisms as well, in a fashion that suggests a partially redundant hierarchy. For example, mutation of the UPRmt pathway results in earlier and more robust activation of the ESRE pathway. Interestingly, full expression of ATFS-1, a key transcription factor for the UPRmt, requires the presence of an ESRE motif in its promoter region. Conclusion: The ESRE pathway responds to mitochondrial damage by monitoring ROS levels. This response is conserved in humans. The ESRE pathway is activated earlier when other mitochondrial surveillance pathways are unavailable during mitochondrial crises, potentially to mitigate stress and restore health. However, the exact mechanisms of pathway activation and crosstalk remain to be elucidated. Ultimately, a better understanding of this network, and its role in the constellation of mitochondrial and cellular stress networks, will improve healthspan