Sandip De

Flaviviruses such as Dengue virus (DENV), Zika virus (ZIKV) and West Nile Virus (WNV) pose growing public health threats, exacerbated by asymptomatic infections and non-vector transmission. Current diagnostics, including nucleic acid tests and serology, are limited by transient viremia and antibody cross-reactivity, underscoring the need for improved detection methods. We utilized untargeted metabolomics to differentiate DENV and ZIKV infections in human induced pluripotent stem cells (hiPSCs), a model relevant to study virus–host interactions, drug screening, and therapeutic safety. LC-MSbased profiling revealed virus-specific metabolic reprogramming during both acute and long-term infections. DENV3 induced early and sustained activation of metabolic features, while ZIKV-MR766 triggered transient suppression. Long term infection with DENV2, DENV3, or ZIKV-PRV resulted in distinct metabolic signatures in hiPSCs, with ZIKV-PRV showing the greatest divergence. Shared metabolite changes across conditions included amino acids (e.g., tryptophan, glutamate), lipids, and nucleosides. Functional studies demonstrated that tryptophan metabolism regulates infection dynamics: inhibiting serotonin biosynthesis reduced viral load, whereas blocking kynurenine synthesis enhanced viral replication. These findings position metabolomics as a viable approach for flavivirus detection and highlight metabolic pathways as potential therapeutic targets. Importance: Accurate diagnosis of flavivirus infections remains challenging due to short periods of viremia, high rates of asymptomatic infection, and extensive serologic cross-reactivity among related viruses such as DENV and ZIKV. These limitations complicate clinical diagnosis, surveillance, and screening of human donor tissues. In this study, we demonstrate that untargeted metabolomics can distinguish ZIKV and DENV infections by identifying virus-specific host metabolic signatures during both acute and long-term infection. Using human induced pluripotent stem cells as a clinically relevant model, we show that metabolic reprogramming persists even in the absence of overt cytopathic effects and can reveal functional pathways that regulate viral replication. Our findings highlight host metabolite profiling as a complementary diagnostic strategy that may improve detection of flavivirus exposure, particularly in asymptomatic individuals or settings where conventional molecular and serologic tests are insufficient.

Changes in global climate have contributed to increased tick and mosquito (vector) populations and subsequent vector-borne flavivirus infections in humans. This increase poses a threat to the safety of human-derived biologics such as cell and gene therapy. We conducted time-course transcriptomic and protein analyses to uncover host molecular factors driving the virulence of Zika virus (ZIKV) and Dengue virus (DENV) in relation to host defense mechanisms, as these viruses have caused recent flavivirus outbreaks. Compared to DENV, ZIKV exhibited stronger virulence and cytopathic effects. RNA-seq analysis revealed differential expression of various cellular factors, including RNA processing factors. Protein analysis showed ZIKV, unlike DENV, degrades nonsense-mediated RNA decay (NMD) factors in host cells, resulting in accumulated host intronic transcripts. We found that active nuclear transport is required for ZIKV replication. From our findings, we hypothesize that ZIKV drives early host cell cytopathy through targeted protein degradation. Studies are underway to develop novel strategies to detect flaviviruses in biologics based on transcriptomics and proteomics.

Tick-borne diseases are a growing public health concern in the United States, with cases rising steadily each year. Lyme borreliosis, or Lyme disease, remains the most prevalent, affecting approximately 476,000 individuals annually. Human-driven changes in climate and ecosystems have expanded the habitat of pathogen-carrying ticks, facilitating the spread of these infections. Additionally, increased instances of tick-borne diseases transmission through human tissues have been reported. Despite ongoing efforts to manage these infections, their incidence continues to rise. To develop effective control measures against these diseases and prevent the transmission of tick-borne infections through human and animal tissues, it is very important to develop detection assays and understand the transmission mechanisms of tick-borne infections. In this study, we provide detailed descriptions and visual references for larval and nymphal tick feeding on mice, focusing on the transmission and acquisition of Borrelia burgdorferi (sensu stricto). These methodologies can be applied to study other tick-borne diseases, tick vectorial capacity, and tick biology, aiding in the development of detection strategies to combat these infections.

Tick-borne diseases are a growing public health concern in the United States, with cases rising steadily each year. Lyme borreliosis, or Lyme disease, remains the most prevalent, affecting approximately 476,000 individuals annually. Human-driven changes in climate and ecosystems have expanded the habitat of pathogen-carrying ticks, facilitating the spread of these infections. Additionally, increased instances of tick-borne diseases transmission through human tissues have been reported. Despite ongoing efforts to manage these infections, their incidence continues to rise. To develop effective control measures against these diseases and prevent the transmission of tick-borne infections through human and animal tissues, it is very important to develop detection assays and understand the transmission mechanisms of tick-borne infections. In this study, we provide detailed descriptions and visual references for larval and nymphal tick feeding on mice, focusing on the transmission and acquisition of Borrelia burgdorferi (sensu stricto). These methodologies can be applied to study other tick-borne diseases, tick vectorial capacity, and tick biology, aiding in the development of detection strategies to combat these infections.

Rising global temperatures coupled with increasing international travel, and trade are contributing to spread of vectors such as ticks and mosquitoes, resulting in a surge of vector-borne flavivirus infection in human population. Furthermore, this increase in flavivirus infection pose threat to the safety of biologics such as cell and gene therapy products as human-derived materials are commonly used during manufacturing of these drug products. In this study, we conducted time-course transcriptomic and protein analyses to uncover the host molecular factors driving the virulence of Zika virus (ZIKV) and Dengue virus (DENV) in the context of host defense mechanisms, as these two viruses have caused the most recent and significant flavivirus outbreaks. Compared to DENV, ZIKV exhibited stronger virulence and cytopathic effects. RNA sequencing analysis revealed differential expression of various cellular factors, including RNA processing factors. Further investigation identified cell-type and time-dependent upregulation nonsense-mediated RNA decay (NMD), RNA degradation factors and nuclear pore complex (NPC) transcripts. Protein analysis showed that ZIKV, unlike DENV, degrades NMD factors in host cells, which along with mis-regulation of RNA degradation factors resulted in accumulation in host intronic transcripts as revealed by RNA-seq data. We also found that active nuclear transport is required for ZIKV replication, suggesting that therapeutic targeting of the NPC could potentially be effective in controlling ZIKV infection. Furthermore, from our findings we hypothesize that, ZIKV, but not DENV, drives early host cell cytopathy through targeted protein degradation. Current studies are underway to develop novel strategies to detect ZIKV, DENV and other flaviviruses in biologics based on transcriptomics and proteomics. Teaser: Exploring the molecular basis of flavivirus virulence in host cells.

Although all cells in the human body are made of the same DNA, these cells undergo differentiation and behave differently during development, through integration of external and internal stimuli via ‘specific mechanisms.’ Epigenetics is one such mechanism that comprises DNA/RNA, histone modifications, and non-coding RNAs that regulate transcription without changing the genetic code. The discovery of the first Polycomb mutant phenotype in Drosophila started the study of epigenetics more than 80 years ago. Since then, a considerable number of Polycomb Group (PcG) genes in Drosophila have been discovered to be preserved in mammals, including humans. PcG proteins exert their influence through gene repression by acting in complexes, modifying histones, and compacting the chromatin within the nucleus. In this article, we discuss how our knowledge of the PcG repression mechanism in Drosophila translates to human communicable disease research.

Polycomb group (PcG) proteins are an important group of transcriptional repressors that act by modifying chromatin. PcG target genes are covered by the repressive chromatin mark H3K27me3. Polycomb repressive complex 2 (PRC2) is a multiprotein complex that is responsible for generating H3K27me3. In Drosophila, PRC2 is recruited by Polycomb Response Elements (PREs) and then tri-methylates flanking nucleosomes, spreading the H3K27me3 mark over large regions of the genome, the "Polycomb domains". What defines the boundary of a Polycomb domain? There is experimental evidence that insulators, PolII, and active transcription can all form the boundaries of Polycomb domains. Here we divide the boundaries of larval Polycomb domains into six different categories. In one category, genes are transcribed toward the Polycomb domain, where active transcription is thought to stop the spreading of H3K27me3. In agreement with this, we show that introducing a transcriptional terminator into such a transcription unit causes an extension of the Polycomb domain. Additional data suggest that active transcription of a boundary gene may restrict the range of enhancer activity of a Polycomb-regulated gene.

Predicting regulatory potential from primary DNA sequences or transcription factor binding patterns is not possible. However, the annotation of the genome by chromatin proteins, histone modifications, and differential compaction is largely sufficient to reveal the locations of genes and their differential activity states. The Polycomb Group (PcG) and Trithorax Group (TrxG) proteins are the central players in this cell type–specific chromatin organization. PcG function was originally viewed as being solely repressive and irreversible, as observed at the homeotic loci in flies and mammals. However, it is now clear that modular and reversible PcG function is essential at most developmental genes. Focusing mainly on recent advances, we review evidence for how PcG and TrxG patterns change dynamically during cell type transitions. The ability to implement cell type–specific transcriptional programming with exquisite fidelity is essential for normal development.

UPF1 is an RNA helicase that is required for nonsense-mediated mRNA decay (NMD) in eukaryotes, and the predominant view is that UPF1 mainly operates on the 3’UTRs of mRNAs that are directed for NMD in the cytoplasm. Here we offer evidence, obtained from Drosophila, that UPF1 constantly moves between the nucleus and cytoplasm by a mechanism that requires its RNA helicase activity. UPF1 is associated, genome-wide, with nascent RNAs at most of the active Pol II transcription sites and at some Pol III-transcribed genes, as demonstrated microscopically on the polytene chromosomes of salivary glands and by ChIP-seq analysis in S2 cells. Intron recognition seems to interfere with association and translocation of UPF1 on nascent pre-mRNAs, and cells depleted of UPF1 show defects in the release of mRNAs from transcription sites and their export from the nucleus.