Molecular mechanisms of mitochondrial complex i rescue by hypoxia and genetic suppressors

The National Institute of Neurological Disorders and Stroke awarded Brandeis University $436,864 on September 1, 2026, under the Extramural Research Programs in the Neurosciences and Neurological Disorders program (CFDA 93.853) to investigate the molecular mechanisms by which hypoxia and genetic suppressors rescue mitochondrial Complex I function.

The research combines C. elegans genetics, mitochondrial biochemistry, and cryogenic electron microscopy to define the structural basis of hypoxia rescue in Complex I dysfunction, which underlies pediatric disorders such as Leigh syndrome and contributes to neurodegeneration including Parkinson's and Alzheimer's disease. The work will generate the first structures of C. elegans respiratory supercomplexes and compare wild-type configurations with reduction-of-function mutants, hypoxia-mimetic mutants, and hypoxia-resistant mutants to uncover the structural mechanisms enabling Complex I mutant rescue. In vitro electron transport chain activity assays on mitochondrial membranes will validate findings. The research integrates the Meisel Lab's expertise in C. elegans genetics and bioenergetics with the Letts Lab's expertise in electron transport chain supercomplex structural biology.

Performance of work occurs at Brandeis University in Waltham, Massachusetts. The period of performance runs from September 1, 2026, through August 31, 2028. This is a Project Grant, an assistance type supporting investigator-initiated research.

Abstract

Mitochondrial complex i (CI) dysfunction underlies devastating pediatric disorders such as leigh syndrome and contributes to age-associated neurodegeneration, including parkinson's and alzheimer's disease. Surprisingly, environmental hypoxia rescues c. Elegans and mouse CI mutants, even reversing neurodegeneration in a mouse model of leigh syndrome. Recent genetic screens in c. Elegans identified "hypoxia-mimetic" mutations in CI subunits that restore electron flow, however due to a lack of structural data the molecular mechanisms by which hypoxia and these mutations rescue CI function remain unknown. We hypothesize that hypoxia and hypoxia-mimetic mutations stabilize specific conformations or assembly states of CI supercomplexes (SCS) that reduce pathological reverse electron transfer (RET) and restore forward electron flow. We will test this hypothesis by combining c. Elegans genetics and mitochondrial biochemistry with state-of-the-art cryogenic electron microscopy (cryoem) to define the structural basis of hypoxia rescue. This work will solve the first structures of c. Elegans respiratory supercomplexes; wild-type structures alone will provide insights into longstanding mitochondrial mutant phenotypes such as volatile anesthetics sensitivity, neurodegeneration, and longevity. By then comparing wild type with CI reduction-of-function mutants, CI "hypoxia-mimetic" mutants, and CI "hypoxia-resistant" mutants, we will uncover the structural basis for CI mutant rescue. In vitro etc activity assays performed on mitochondrial membranes will then be used to functionally validate our hypotheses. Combining the meisel lab's expertise in c. Elegans genetics and bioenergetics with the letts lab's expertise in etc SC structural biology, the work proposed in this R21 will establish a hypothesis-generation/hypothesis-testing pipeline that will set the standard for elucidating mitochondrial respiratory physiology and pathophysiology, with important implications for translating hypoxia into a viable therapy for neurodegenerative diseases.