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Glutamate dehydrogenase (Gdh2)-dependent alkalization is dispensable for survival and escape of Candida albicans from macrophages
Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
(English)Manuscript (preprint) (Other academic)
National Category
Biochemistry and Molecular Biology
Research subject
Molecular Bioscience
Identifiers
URN: urn:nbn:se:su:diva-173431OAI: oai:DiVA.org:su-173431DiVA, id: diva2:1353782
Available from: 2019-09-24 Created: 2019-09-24 Last updated: 2019-09-25Bibliographically approved
In thesis
1. The Role of Proline Catabolism in Candida albicans Pathogenesis
Open this publication in new window or tab >>The Role of Proline Catabolism in Candida albicans Pathogenesis
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Candida albicans is an opportunistic fungal pathogen that has evolved in close association with human hosts. Pathogenicity is linked to an array of virulence characteristics expressed in response to environmental cues and that reflect the requirement to take up and metabolize nutrients available in the host. Metabolism generates the energy to support the bioenergetic demands of infectious growth, including the ability to reversibly switch morphologies from yeast to filamentous hyphal forms. Amino acids are among the most versatile nutrients available in the hosts as they can serve as both carbon and nitrogen sources, be transformed to key metabolic intermediates, or utilized to modulate extracellular pH via deamination forming ammonia. Of the proteinogenic amino acids, proline is unique in having a secondary amine covalently locked within an imine ring. Accumulating evidence implicates proline catabolism as being critical in the pathogenesis of many human diseases, ranging from bacterial and parasitic infections to cancer progression. This work focuses on the role of proline catabolism on C. albicans  pathogenesis.

Paper I describes how proline induces filamentous growth in C. albicans. Hyphal growth is induced by an increase in intracellular ATP, a positive regulator of the Ras1/cAMP/PKA pathway. Proline is a direct substrate for ATP production, its catabolism in the mitochondria by proline oxidase (Put1) and Δ1-pyrroline-5-carboxylate (P5C) dehydrogenase (Put2) leads to the generation of FADH2 and NADH, respectively. Arginine and ornithine induce filamentous growth due to being catabolized to proline. Strikingly, mitochondrial proline catabolism is essential for hyphal growth and escape from macrophages.

Paper II documents that proline catabolism is an important regulator of reactive oxygen species (ROS) homeostasis in C. albicans. When cells depend on proline as an energy source, the activities of the two catabolic enzymes Put1 and Put2 must operate in synchrony; perturbation of these highly regulated catabolic steps exerts deleterious effects on growth. Cells lacking PUT2 exhibit increased sensitivity to exogenous proline. This sensitivity is linked to ROS generation, likely due to the accumulation of the toxic intermediate P5C. Consistently, a put2-/- mutant is avirulent in Drosophila and in a 3D skin infection model, and hypovirulent in neutrophils and a systemic murine infection model.

Paper III shows that the enzymatic step directly downstream of Put2, the deamination of glutamate to α-ketoglutarate catalyzed by glutamate dehydrogenase (Gdh2), releases the ammonia responsible for the alkalization of the extracellular environment when C. albicans  cells grow in the presence of amino acids. Cells lacking GDH2 do not alkalinize the medium. Alkalization is thought to induce hyphal growth in cells engulfed by macrophages. Surprisingly, filamentous growth of gdh2-/- cells is not impaired in filament-inducing media, or importantly, in situ in the phagosome of primary murine macrophages. Thus, alkalization is not a requisite for filamentous growth within macrophages.

The results demonstrate that under physiologically relevant host conditions, proline catabolism is important for C. albicans pathogenesis. Further studies are warranted to determine the applicability of this pathway as a potential target for therapeutic approaches aimed at combating this major fungal pathogen.

Place, publisher, year, edition, pages
Stockholm: Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, 2019. p. 82
Keywords
Candida albicans, proline metabolism, ATP, P5C, virulence, macrophage, hyphae, filamentation, Ras1/cAMP/PKA, mitochondria, Proline dehydrogenase, P5C dehydrogenase, reactive oxygen species, Proline-P5C cycle
National Category
Biological Sciences
Research subject
Molecular Bioscience
Identifiers
urn:nbn:se:su:diva-173362 (URN)978-91-7797-837-4 (ISBN)978-91-7797-838-1 (ISBN)
Public defence
2019-11-08, Vivi Täckholmsalen (Q-salen), NPQ-huset, Svante Arrhenius väg 20, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript.

Available from: 2019-10-16 Created: 2019-09-23 Last updated: 2019-10-09Bibliographically approved

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