Cytochrome c oxidase adaptation to hypoxia in systemic vascular cells - From structure to function

• Applicant: Professorin Natascha Sommer, Ph.D.
• Subject Area: Biochemistry ; Cell Biology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 521904638

A decrease in physiological oxygen level (hypoxia) is one of the most challenging threats that aerobic organisms face. One recently uncovered mechanism of adaptation to hypoxia is the reconfiguration of cytochrome c oxidase (COX or complex IV), the final and regulatory electron donor to oxygen of the mitochondrial electron transport chain (ETC). It does so by changing the expression of some of the 14 COX subunits, although much remains unknown about the regulation of expression, downstream signaling consequences, and the exchange (“remodeling”) process itself, especially in primary cells. We have previously shown that superoxide release regulated by isoform 2 of subunit 4 of COX (Cox4i2) is essential for acute oxygen sensing in the pulmonary vasculature and the carotid body resulting in an optimal systemic oxygenation of the blood. Furthermore, RNA sequencing analysis showed upregulation of Cox4i2, and two other subunits of COX, the hypoxia inducible domain family member 1B (Higd1b) and Ndufa mitochondrial complex associated like 2 (Ndufa4l2) in the murine pulmonary vasculature after in vivo chronic hypoxic exposure. These subunits are highly expressed in pulmonary and systemic pericytes, confirmed by our single-cell RNA sequencing of mouse lungs. We hypothesize that expression of Cox4i2, Higd1b, and Ndufa4l2 regulates COX function in specific cell types (pericytes and other vascular cells) under physiological conditions and/or chronic stress stimuli such as chronic hypoxia. We speculate that Cox4i2, Ndufa4l2, and Higd1b, interact with each other, may act as redox sensors, and regulate COX activity, mitochondrial membrane potential, supercomplex formation, ETC redox state, and superoxide release, with consequences on cell proliferation, apoptosis, and viability. Our goal is to identify fundamental regulatory mechanisms of mitochondrial signaling depending on COX subunit expression mainly in primary systemic vascular cells and thereby answer three major questions: 1) How does COX adapt structurally and functionally to chronic hypoxia and oxidative stress stimuli? 2) What is the specific role of cysteine-containing isoforms in Cox4i2, Ndufa4l2, and Higd1b? 3) How does COX remodeling affect mitochondrial and cellular functions, in particular redox sensing and signaling? In the long term, the physiological and pathological mechanisms of vasoconstriction and remodeling processes can be clarified. To test our hypothesis, we will: 1. characterize the dynamic regulation of COX subunit isoform composition in systemic pericytes in response to chronic hypoxia and compare to systemic vascular cells by determining transcriptomic and proteomic COX composition, and identifying transcriptional regulators. 2. analyze structural consequences of COX remodeling upon chronic hypoxia by testing interactions between COX subunits, and supercomplex formation. 3.characterize functional consequences of COX remodeling on mitochondrial and cellular function.

• DFG Programme: Research Grants
• International Connection: USA
• Partner Organisation: National Science Foundation (NSF)
• Cooperation Partners: Professor Lawrence I. Grossman, Ph.D.; Professor Maik Hüttemann, Ph.D.