Rotenone as a Probe for Mitochondrial Proteostasis and Complex I Dysfunction

Introduction

Mitochondria are the metabolic hub of eukaryotic cells, integrating energy production, redox homeostasis, and cell fate decisions. Disruption of mitochondrial function is central to the pathogenesis of neurodegenerative diseases and metabolic disorders. Rotenone, a naturally occurring isoflavonoid, has emerged as a widely used mitochondrial Complex I inhibitor and mitochondrial dysfunction inducer, offering a powerful tool to dissect the mechanisms underlying mitochondrial impairment, apoptosis, and autophagy. This article provides a rigorous examination of how Rotenone enables experimental interrogation of mitochondrial proteostasis and signaling networks, with particular emphasis on its utility in the context of recent advances in mitochondrial enzyme regulation and proteostatic control.

Rotenone: Biochemical Properties and Mechanistic Actions

Rotenone (CAS 83-79-4) is a lipophilic compound derived from the roots of several plant species. Its primary mode of action is the inhibition of NADH:ubiquinone oxidoreductase (Complex I) within the electron transport chain, with an IC₅₀ of 1.7–2.2 μM. This blockade impedes electron flow from NADH to ubiquinone, collapsing the mitochondrial proton gradient and impairing ATP synthesis. As a consequence, electron leakage occurs, driving the overproduction of reactive oxygen species (ROS) and initiating ROS-mediated cell death. Rotenone is a solid, insoluble in water and ethanol but highly soluble in DMSO (≥77.6 mg/mL), and requires storage below -20°C for optimal stability.

Experimentally, Rotenone is a classical tool for inducing mitochondrial dysfunction, facilitating the study of downstream effects such as apoptosis, autophagy, and the activation of stress-responsive signaling pathways including p38 MAPK and JNK. Its utility as an apoptosis inducer in SH-SY5Y cells and in animal models of Parkinson's disease stems from its ability to elicit selective vulnerability in dopaminergic neurons and modulate neuronal survival pathways.

Rotenone in Mitochondrial Proteostasis and OGDH Regulation

The interplay between mitochondrial bioenergetics and proteostasis is increasingly recognized as a determinant of cellular health. While rotenone's inhibition of Complex I is well characterized, its broader influence on mitochondrial proteostasis, including the regulation of metabolic enzymes, is of growing interest. Recent work by Wang et al. (Molecular Cell, 2025) has elucidated a novel post-translational regulatory mechanism involving the co-chaperone TCAIM, which binds and reduces the protein levels of α-ketoglutarate dehydrogenase (OGDH) via HSPA9 and LONP1. This targeted degradation of OGDH suppresses OGDH complex activity, thereby altering TCA cycle flux and mitochondrial metabolism.

Rotenone-induced mitochondrial stress provides a unique experimental context to interrogate such proteostatic mechanisms. By elevating mitochondrial ROS and impairing electron transport, rotenone creates a proteotoxic milieu that challenges protein quality control systems. Researchers can exploit this to study how chaperones and proteases respond to acute mitochondrial dysfunction, and how selective degradation of enzymes like OGDH influences cellular adaptation, metabolic reprogramming, and stress signaling.

Experimental Applications in Cellular and Animal Models

Rotenone has become indispensable in modeling mitochondrial impairment and neurodegeneration. In differentiated SH-SY5Y neuroblastoma cells, exposure to nanomolar concentrations of rotenone induces apoptosis, reduces mitochondrial motility, and produces a biphasic survival response over extended culture periods. These effects are mediated in part by ROS generation, caspase activation (enabling caspase activation assay readouts), and the engagement of autophagy pathways, supporting its use in autophagy pathway research.

In vivo, intranasal administration of rotenone in rodents recapitulates key features of Parkinson's disease, including selective dopaminergic neurite degeneration in the substantia nigra and olfactory impairment. As such, rotenone models facilitate the study of neurodegenerative disease research and the interrogation of neuronal vulnerability to mitochondrial toxins. Importantly, these models allow for the parallel assessment of mitochondrial proteostasis, providing a platform to test hypotheses arising from recent discoveries in enzyme regulation, such as those involving TCAIM and OGDH.

Rotenone, Redox Signaling, and MAPK Pathway Activation

By driving ROS production, rotenone serves as a model for studying redox-regulated signaling cascades. ROS generated during Complex I inhibition can activate stress kinases such as p38 MAPK and JNK, which participate in the orchestration of apoptotic and autophagic responses. Detailed analysis of these pathways has revealed their involvement in both neuronal death and adaptive responses to mitochondrial stress. Rotenone-induced activation of these pathways is measurable via phospho-specific antibodies and kinase activity assays, supporting mechanistic studies on how mitochondrial dysfunction interfaces with cell signaling networks.

Moreover, the intersection of ROS signaling with mitochondrial proteostasis is an area of emerging research, as oxidative modification of mitochondrial proteins can influence their recognition by chaperones and proteases, as demonstrated by the TCAIM–OGDH regulatory axis. Rotenone thus provides a dual function: as a trigger of redox signaling and as a stressor to challenge mitochondrial protein quality control machinery.

Integrating Rotenone in the Study of Mitochondrial Enzyme Homeostasis

The recent findings by Wang et al. (Molecular Cell, 2025) highlight the importance of post-translational control in mitochondrial metabolic adaptation. While the reduction of OGDH protein by the TCAIM-HSPA9-LONP1 axis was elucidated independently of rotenone, combining rotenone-induced mitochondrial dysfunction with genetic or pharmacologic modulation of mitochondrial chaperones or proteases enables experimental dissection of compensatory and maladaptive responses to proteostatic stress.

For example, in SH-SY5Y or primary neuronal cultures, co-treatment with rotenone and modulators of HSPA9 or LONP1 can be used to determine the impact of mitochondrial protein turnover on cell survival, metabolic flux (using stable isotope tracing), and ROS-mediated cell death. Additionally, the application of rotenone in animal models with genetically altered proteostasis (e.g., TCAIM or LONP1 knockout mice) offers a platform to explore the pathophysiological consequences of disrupted enzyme homeostasis in the setting of mitochondrial dysfunction—a key question in the field of neurodegeneration and aging.

Practical Considerations and Protocol Optimization

When utilizing Rotenone in research, careful attention to dosing, solubilization, and storage is critical. Due to its poor solubility in aqueous solvents, preparation of concentrated stock solutions in DMSO (≥77.6 mg/mL) is recommended, with aliquots stored below -20°C to maintain stability. Once dissolved, prolonged storage should be avoided to prevent degradation. Appropriate vehicle controls and titration of concentrations are necessary, as rotenone exhibits cell-type and species-specific sensitivity, particularly in neuronal cultures.

In cellular assays, endpoints such as mitochondrial membrane potential, ROS production, caspase activation, and autophagic flux can be quantitatively assessed following rotenone exposure. For in vivo studies, the route and timing of administration (e.g., intranasal versus systemic) should be tailored to the experimental objectives, balancing model fidelity with animal welfare considerations.

Conclusion and Future Perspectives

Rotenone's role as a mitochondrial Complex I inhibitor extends beyond its established use in neurodegeneration models. Its ability to induce mitochondrial dysfunction and proteostatic stress positions it as a valuable probe for interrogating the interplay between electron transport, ROS signaling, enzyme turnover, and cell fate pathways. The integration of rotenone-based models with cutting-edge insights into mitochondrial proteostasis—such as the TCAIM-mediated regulation of OGDH—opens new avenues for mechanistic research and therapeutic exploration.

This article extends the discussion beyond previous overviews, such as "Rotenone: A Mitochondrial Complex I Inhibitor for Neurode...", by explicitly linking rotenone-induced mitochondrial stress to post-translational enzyme regulation and proteostasis. Through this lens, researchers are equipped to interrogate not only the bioenergetic consequences of Complex I inhibition, but also the adaptive and maladaptive proteostatic responses that shape cell survival and metabolic adaptation in health and disease.