Universität zu Köln

Gehling, Titus ORCID: 0000-0001-5004-5061 (2025). Dual Role of Sulfite Oxidase in Mitochondrial Bioenergetics and Nitrite-Dependent Nitric Oxide Synthesis. PhD thesis, Universität zu Köln.

PDF Gehling_PhDThesis_public_version.pdf Download (5MB)

Abstract

Abstract Sulfite oxidase (SOX) is a vital mitochondrial enzyme requiring the molybdenum cofactor (Moco) to oxidize toxic sulfite to sulfate, a key step in sulfur metabolism. SOX deficiency (SOXD) causes neurodegeneration and has recently been linked to mitochondrial dysfunction. Thus, understanding the role of SOX for mitochondrial physiology and its regulation is crucial. While SOX loss of SOX is known to impact mitochondrial bioenergetics and morphology, the underlying mechanisms remain poorly understood. Additionally, SOX has been implicated in a distinct, non-canonical function: facilitating nitrite-dependent nitric oxide (NO) synthesis, the physiological significance of which has yet to be elucidated. This thesis explores both functional dimensions of SOX and investigates their broader physiological relevance. By using a combination of respiratory experiments and proteomic approaches this work revealed disruption of mitochondrial bioenergetics upon loss of SOX, specifically, a marked reduction in mitochondrial oxygen consumption and impairment of oxidative phosphorylation expanding from different In vivo to ex vivo model systems. Proteomics revealed that these impairments correlate with widespread downregulation of proteins involved in the tricarboxylic acid cycle and respiratory complexes and upregulation of glycolytic proteins, indicating metabolic rewiring. Whole-cell proteomic analysis uncovered extensive alterations in extracellular matrix proteins, linking SOX deficiency to impaired mitochondrial function and extracellular matrix remodeling. Additionally, nitrite exposure caused a slight, non-significant decrease in respiration, suggesting a potential role for SOX-dependent nitrite reduction in OXPHOS regulation. Furthermore, this work uncovered a protective role of SOX in hypoxic vasodilation. In the context of heart failure with preserved ejection fraction (HFpEF), loss of SOX resulted in increased right ventricular hypertrophy and cardiac remodeling. Spectroscopic experiments revealed that cytochrome c can serve as an electron donor for SOX in the absence of oxygen, suggesting an adaptive mechanism for NO generation under hypoxic conditions. Furthermore, characterization of SOX-deficient neuronal cultures revealed a novel mechanism underlying the characteristic neurodegeneration of SOXD. While the typical SSC-mediated neurodegeneration was absent, neuronal cultures exhibited a marked reduction in mitochondrial respiration. In combination with a neurodevelopment deficit in these cultures this highlights the contribution of mitochondrial dysfunction towards the pathomechanism of SOXD. Finally, regulatory studies identified molybdate supplementation, MOCS1AB overexpression, and the RNA-binding protein CLUH as modulators of SOX activity and expression. These findings offer potential therapeutic avenues for molybdenum cofactor deficiency and related metabolic disorders e.g. by dietary or pharmacological molybdate administration, gene therapy approaches aimed at boosting MOCS1AB expression or modulation of CLUH-mediated RNA regulation. Collectively, this work elucidates a dualistic role of SOX in sustaining mitochondrial bioenergetics and nitric oxide homeostasis, extending the understanding of sulfur metabolism in health and disease. These insights pave the way for mechanism-based therapeutic strategies aimed at mitigating bioenergetic deficits in SOX-related pathologies, while also identifying possible targets for these strategies.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Gehling, Titus titus.gehling@web.de https://orcid.org/0000-0001-5004-5061 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-791066
Date:	2025
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Chemistry > Institute of Biochemistry
Subjects:	Chemistry and allied sciences Life sciences
Uncontrolled Keywords:	Keywords Language Sulfite Oxidase UNSPECIFIED Nitrite-dependent NO synthesis UNSPECIFIED Mitochondria UNSPECIFIED Sulfite Oxidase Deficiency UNSPECIFIED CLUH UNSPECIFIED Bioenergetics UNSPECIFIED Mitochondrial Respiration UNSPECIFIED
Date of oral exam:	22 October 2025
Referee:	Name Academic Title Schwarz, Günter Prof. Dr. Riemer, Jan Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/79106