Biology subjects

Warnhoff, K.

Publications and source records attributed to Warnhoff, K..

5 recordsLinked to original sources

bioRxiv2026

Paralogous guanine deaminases likely acquired from bacteria by horizontal gene transfer promote purine homeostasis in Caenorhabditis elegans

Disruptions in purine metabolism contribute to a range of human diseases, from rare genetic disorders such as Lesch-Nyhan syndrome and xanthinuria to common conditions including gout and cancer. To better understand the metabolic networks that regulate purine homeostasis, we developed a Caenorhabditis elegans model of xanthine dehydrogenase (xdh-1) deficiency. Remarkably, xdh-1 mutant animals form rare xanthine stones, recapitulating a hallmark of human xanthinuria. To uncover genetic regulators of purine homeostasis, we performed a forward genetic screen for mutations that exacerbate xanthine stone formation in xdh-1 mutants. This approach identified multiple loss-of-function alleles in a previously uncharacterized gene, which we named gda-1. We show that gda-1 encodes an intestinal guanine deaminase that mediates a key enzymatic step in purine catabolism. The C. elegans genome also encodes a paralog, gda-2, which shares guanine deaminase activity but is expressed in distinct tissues. While gda-2 can compensate for gda-1 loss in guanine metabolism, the two genes exhibit non-redundant roles in regulating xanthine accumulation and stone formation. Interestingly, our evolutionary analyses suggest that gda-2 was acquired by nematodes via horizontal gene transfer from bacteria. These findings reveal a spatially regulated purine catabolism pathway in C. elegans and suggest that acquisition of bacterial genes has shaped a core nematode metabolic network.

genetics↗

bioRxiv2025

XDH-1 inactivation causes xanthine stone formation in C. elegans which is inhibited by SULP-4-mediated anion exchange in the excretory cell

Xanthine dehydrogenase (XDH) is a molybdenum cofactor (Moco) requiring enzyme that catabolizes hypoxanthine into xanthine and xanthine into uric acid, the final steps in purine catabolism. Human patients with mutations in XDH develop xanthinuria which can lead to xanthine stones in the kidney, recurrent urinary tract infections, and renal failure. Currently there are no therapies for treating human XDH deficiency. Thus, understanding mechanisms that maintain purine homeostasis is an important goal of human health. Here, we used the nematode C. elegans to model human XDH deficiency using 2 clinically relevant paradigms: Moco deficiency or loss-of-function mutations in xdh-1, the C. elegans ortholog of XDH. Both Moco deficiency and xdh-1 loss of function caused the formation of autofluorescent xanthine stones in C. elegans. Surprisingly, only 2% of xdh-1 null mutant C. elegans developed a xanthine stone, suggesting additional pathways may regulate this process. To uncover such pathways, we performed a forward genetic screen for mutations that enhance the penetrance of xanthine stone formation in xdh-1 null mutant C. elegans. We isolated multiple loss-of-function mutations in the gene sulp-4 which encodes a sulfate permease homologous to human SLC26 anion exchange proteins. We demonstrated that SULP-4 acts cell-nonautonomously in the excretory cell to limit xanthine stone accumulation. Interestingly, sulp-4 mutant phenotypes were suppressed by mutations in genes that encode for cystathionase (cth-2) or cysteine dioxygenase (cdo-1), members of the sulfur amino acid catabolism pathway required for production of sulfate, a substrate of SULP-4. We propose that sulfate accumulation caused by sulp-4 loss of function promotes xanthine stone accumulation. We speculate that sulfate accumulation causes osmotic imbalance, creating conditions in the intestinal lumen that favor xanthine stone accumulation. Supporting this model, a mutation in osm-8 that constitutively activates the osmotic stress response also promoted xanthine stone accumulation in an xdh-1 mutant background. Thus, our work establishes a C. elegans model for human XDH deficiency and identifies the sulfate permease sulp-4 as a critical player controlling xanthine stone accumulation.

genetics↗

bioRxiv2023

Hypoxia-inducible factor promotes cysteine homeostasis in Caenorhabditis elegans

Dedicated genetic pathways regulate cysteine homeostasis. For example, high levels of cysteine activate cysteine dioxygenase, a key enzyme in cysteine catabolism in most animal and many fungal species. The mechanism by which cysteine dioxygenase is regulated is largely unknown. In an unbiased genetic screen for mutations that activate cysteine dioxygenase (cdo-1) in the nematode C. elegans, we isolated loss-of-function mutations in rhy-1 and egl-9, which encode proteins that negatively regulate the stability or activity of the oxygen-sensing hypoxia inducible transcription factor (hif-1). EGL-9 and HIF-1 are core members of the conserved eukaryotic hypoxia response. However, we demonstrate that the mechanism of HIF-1-mediated induction of cdo-1 is largely independent of EGL-9 prolyl hydroxylase activity and the von Hippel-Lindau E3 ubiquitin ligase, the classical hypoxia signaling pathway components. We demonstrate that C. elegans cdo-1 is transcriptionally activated by high levels of cysteine and hif-1. hif-1-dependent activation of cdo-1 occurs downstream of an H2S-sensing pathway that includes rhy-1, cysl-1, and egl-9. cdo-1 transcription is primarily activated in the hypodermis where it is also sufficient to drive sulfur amino acid metabolism. Thus, the regulation of cdo-1 by hif-1 reveals a negative feedback loop that maintains cysteine homeostasis. High levels of cysteine stimulate the production of an H2S signal. H2S then acts through the rhy-1/cysl-1/egl-9 signaling pathway to increase HIF-1-mediated transcription of cdo-1, promoting degradation of cysteine via CDO-1.

genetics↗

bioRxiv2022

Dietary molybdenum cofactor promotes fitness by increasing Moco content and sulfite oxidase activity in the nematode C. elegans

Molybdenum cofactor (Moco) is a prosthetic group necessary for the activity of 4 unique enzymes, including the essential sulfite oxidase (SUOX-1). Moco is required for life; humans with inactivating mutations in the genes encoding Moco-biosynthetic enzymes display Moco deficiency, a rare and lethal inborn error of metabolism. Despite its importance to human health, little is known about how Moco moves among and between cells, tissues, and organisms. The prevailing view is that cells that require Moco must synthesize Moco de novo. Although, the nematode Caenorhabditis elegans appears to be an exception to this rule and has emerged as a valuable system for understanding fundamental Moco biology. C. elegans has the seemingly unique capacity to both synthesize its own Moco as well as acquire Moco from its microbial diet. However, the relative contribution of Moco from the diet or endogenous synthesis has not been rigorously evaluated or quantified biochemically. We genetically removed dietary or endogenous Moco sources in C. elegans and biochemically determined their impact on animal Moco content and SUOX-1 activity. We demonstrate that dietary Moco deficiency dramatically reduces both animal Moco content and SUOX-1 activity. Furthermore, these biochemical deficiencies have physiological consequences; we show that dietary Moco deficiency alone causes sensitivity to sulfite, the toxic substrate of SUOX-1. This work establishes the biochemical consequences of depleting dietary Moco or endogenous Moco synthesis in C. elegans and quantifies the surprising contribution of the diet to maintaining Moco homeostasis in C. elegans.

biochemistry↗

bioRxiv2020

Protein-bound molybdenum cofactor is bioavailable and rescues molybdenum cofactor-deficient C. elegans

The molybdenum cofactor (Moco) is a 520 dalton prosthetic group that is synthesized in all domains of life. In animals, four oxidases (among them sulfite oxidase) use Moco as a prosthetic group. Moco is essential in animals; humans with mutations in genes that encode Moco-biosynthetic enzymes display lethal neurological and developmental defects. Moco supplementation seems a logical therapy, however the instability of Moco has precluded biochemical and cell biological studies of Moco transport and bioavailability. The nematode Caenorhabditis elegans can take up Moco from its bacterial diet and transport it to cells and tissues that express Moco-requiring enzymes, suggesting a system for Moco uptake and distribution. Here we show that protein-bound Moco is the stable, bioavailable species of Moco taken up by C. elegans from its diet and is an effective dietary supplement, rescuing a C. elegans model of Moco deficiency. We demonstrate that diverse Moco:protein complexes are stable and bioavailable, suggesting a new strategy for the production and delivery of therapeutically active Moco to treat human Moco deficiency.

developmental biology↗