LA JOLLA, CA – May 12, 2025 – In a discovery poised to revolutionize the treatment of a myriad of debilitating conditions, scientists at the Salk Institute for Biological Studies have identified a crucial set of proteins, known as estrogen-related receptors (ERRs), as indispensable drivers of energy metabolism and muscle function. A new study, published today in the prestigious journal Proceedings of the National Academy of Sciences, reveals that these receptors hold the key to repairing dysfunctional mitochondria, offering a powerful new therapeutic target for everything from age-related fatigue to severe metabolic and muscular disorders.
The findings highlight that ERRs, particularly ERRα, play a central role in orchestrating the cellular machinery responsible for producing energy within our muscles. By directly influencing the growth and activity of mitochondria – the microscopic powerhouses of our cells – these receptors offer an unprecedented pathway to restore vital energy supplies in individuals struggling with chronic fatigue and muscle weakness. This breakthrough opens the door to developing novel drugs that could mimic the beneficial effects of exercise, providing hope for millions currently facing limited treatment options.
The Silent Epidemic: Understanding Mitochondrial Dysfunction
At the core of this discovery lies the fundamental importance of mitochondria. These tiny, bean-shaped organelles are ubiquitous across the body, serving as the cellular engines that convert the food we eat into adenosine triphosphate (ATP), the primary energy currency of life. This intricate process of cellular-level metabolism is particularly critical in muscle cells, which demand vast amounts of fuel to power every movement, from a gentle blink to a strenuous sprint.
However, for a significant portion of the global population, this vital energy production system is compromised. Approximately 1 in 5,000 people are born with genetic defects that lead to dysfunctional mitochondria, resulting in severe and often life-limiting metabolic disorders like mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) or Leigh syndrome. Beyond these congenital conditions, millions more develop metabolic dysfunction later in life. This acquired impairment is frequently associated with the natural aging process, contributing to age-related muscle loss (sarcopenia) and frailty. Moreover, mitochondrial dysfunction is a hallmark of numerous pervasive diseases, including various forms of cancer, neurodegenerative disorders such as multiple sclerosis (MS) and dementia, cardiovascular ailments like heart disease, and metabolic syndrome.
The consequences of impaired mitochondrial function are profound and far-reaching. Patients often experience debilitating muscle weakness, chronic fatigue, exercise intolerance, and a cascade of systemic issues affecting organ systems that rely heavily on energy, such as the brain and heart. Despite the widespread impact, effective treatments for mitochondrial dysfunction remain largely elusive. Current approaches often focus on symptom management or supportive care, underscoring the urgent need for therapies that address the root cause of energy deficits at the cellular level. The Salk Institute’s latest research offers a beacon of hope in this challenging landscape, proposing a direct and powerful means to restore the very foundation of cellular energy.
A Legacy of Discovery: The Salk Institute’s Chronology of Breakthroughs
The journey to this pivotal discovery traces back decades, rooted in the foundational work of Professor Ronald Evans, a towering figure in molecular biology and the senior author of the new study. His laboratory at the Salk Institute has consistently been at the forefront of understanding how our bodies regulate gene expression and metabolism.
The Nuclear Hormone Receptor Era (1980s): The story begins in the 1980s when Evans led the landmark discovery of a vast family of proteins he named "nuclear hormone receptors." These extraordinary receptors act as molecular switches within cells. Upon binding to specific hormones (like steroids, thyroid hormones, or vitamins), they translocate to the cell nucleus, where they attach directly to specific sequences of our DNA. This binding event then controls which genes get turned "on" or "off," thereby orchestrating a vast array of physiological processes, from development and metabolism to inflammation and reproduction. This discovery fundamentally reshaped our understanding of how hormones exert their profound effects on the body.
The Emergence of Estrogen-Related Receptors (1988): Building on this foundational work, Evans’ lab made another significant stride in 1988 with the discovery of estrogen-related receptors (ERRs). While their name suggests a connection to classic estrogen receptors, the researchers quickly recognized that ERRs, despite their structural similarity, operated independently of estrogen. Their precise physiological function, however, remained a compelling mystery for many years. Initial investigations revealed that ERRs were particularly abundant in organs with high energy demands, such as the heart and the brain. This observation naturally piqued the researchers’ interest, hinting at a potential role for ERRs in regulating energy metabolism.
Focusing on Skeletal Muscle and Exercise: With this clue in hand, Evans’ team embarked on a focused exploration of ERRs’ potential role in skeletal muscle – another organ renowned for its intense energy requirements, especially during physical activity. It has long been understood that exercise is one of the most potent natural signals for muscle cells to trigger "mitochondrial biogenesis." This is a remarkable cellular adaptation wherein a cell increases both the number and efficiency of its mitochondria to produce more fuel, enhancing endurance and performance.
However, this natural adaptive mechanism presents a cruel paradox for individuals suffering from muscular and metabolic disorders. For these patients, the very act of exercising is difficult, often impossible, trapping them in a cycle of declining muscle function and energy deficit. This realization spurred the Salk scientists to seek an alternative: if they could decipher the molecular mechanisms by which exercise induces mitochondrial biogenesis, they might be able to pharmacologically stimulate this process, offering a lifeline to those too weak to benefit from physical training. This quest set the stage for the groundbreaking experiments that would finally unveil the indispensable role of estrogen-related receptors.
Unveiling the Mechanism: Experimental Insights and Supporting Data
The meticulous research conducted by first author Dr. Weiwei Fan, a staff scientist in Evans’ lab, and his colleagues, was designed to precisely determine the role of ERRs in muscle cell metabolism. Their approach involved sophisticated genetic manipulation in mouse models, allowing them to selectively remove specific ERR subtypes from muscle tissue and observe the consequences.
Targeted Gene Deletion: The team focused on the three known forms of estrogen-related receptors: alpha (ERRα), beta (ERRβ), and gamma (ERRγ). By genetically deleting these receptors, either individually or in combination, from the muscle tissues of mice, the researchers could unravel their distinct and overlapping functions.
Differential Roles and Compensation: The initial findings revealed a nuanced picture. They observed that ERRα was the most abundant type of receptor in muscle tissue. Surprisingly, however, the loss of ERRα alone had only mild impacts on muscle function under normal, resting conditions. This suggested a compensatory mechanism at play. Further investigation pointed to ERRγ, which, despite making up only a small fraction (around 4%) of the total estrogen-related receptors, demonstrated a remarkable ability to compensate for the absence of ERRα, maintaining mitochondrial function. This delicate balance highlighted the redundancy and robustness built into the body’s energy regulation systems.
Profound Impairment with Combined Deletion: The true significance of ERRs became starkly apparent when both ERRα and ERRγ were simultaneously deleted. This combined loss led to severe and undeniable impairments in muscle mitochondrial activity, shape, and size. The "cellular powerhouses" became fewer, smaller, and less efficient, directly impacting the muscle’s ability to generate energy. These findings underscored that while ERRα was the predominant form, ERRγ played a critical, albeit smaller, compensatory role in maintaining baseline mitochondrial health.
The Exercise Challenge: ERRα’s Indispensable Role: The most compelling evidence for ERRα’s crucial function emerged from an exercise experiment. To simulate the physiological demands that naturally trigger mitochondrial growth, the researchers had their genetically modified mice exercise on mechanical wheels. This setup allowed them to directly assess whether ERRα was involved in the exercise-induced mitochondrial biogenesis. The results were unequivocal: losing ERRα alone completely blocked the muscle’s ability to undergo exercise-induced mitochondrial biogenesis. Without ERRα, the muscles could not adapt and grow their energy infrastructure in response to physical exertion, confirming its indispensable role in this vital adaptive process.
The PGC1α Connection: A Therapeutic Dilemma Solved: The scientific community has long recognized PGC1α as a "master regulator" of mitochondria throughout the body. Previous studies had established that PGC1α was a key driver of exercise-induced mitochondrial growth. However, PGC1α presents a significant challenge for therapeutic drug development: it cannot bind directly to genes in the DNA. Instead, it relies on "partner proteins" to physically attach to the DNA and activate gene expression, making it an indirect and therefore more difficult target for small-molecule drugs.
The Salk team’s breakthrough was in identifying ERRα as PGC1α’s crucial partner in muscle cells. When Evans’ lab examined muscle cells after exercise, they found that PGC1α was indeed partnering with ERRα to drive mitochondrial biogenesis. But unlike PGC1α, ERRα possesses the critical ability to bind directly to the promoters of mitochondrial energetic genes and turn them "on." This direct action makes ERRα an exceptionally promising and tractable target for therapeutic intervention. By developing a drug that boosts ERRα activity, scientists could potentially bypass the complexities of PGC1α and directly stimulate mitochondrial growth and function.
Expert Perspectives and Optimism: A New Horizon for Treatment
The implications of this discovery are resonating deeply within the scientific community, particularly with the researchers who have dedicated their careers to understanding these complex cellular processes.
Professor Ronald Evans, a recipient of numerous accolades for his pioneering work, expressed profound optimism about the therapeutic potential of ERRs. "Estrogen-related receptors look a lot like classic estrogen receptors, but their function has been much less understood," Evans commented, reflecting on the long journey of discovery. "Our lab discovered estrogen-related receptors in 1988 and was one of the first to recognize their role in energy metabolism. Now, after decades of dedicated research, we’ve learned that estrogen-related receptors are indispensable drivers of mitochondrial growth and activity in our muscles. This makes them a really promising target to treat muscle weakness and fatigue in many different diseases that involve metabolic dysfunction." His emphasis on "indispensable drivers" underscores the non-negotiable role ERRs play in this fundamental biological process, elevating them from mere players to essential orchestrators of cellular energy.
Dr. Weiwei Fan, the study’s first author, articulated the practical vision for this research. "Mitochondria are our cells’ energy factories, so the more we exercise, the more mitochondria our muscles need," Fan explained. "This got us thinking – if we could understand how exercise induces mitochondrial biogenesis, we might be able to target those same mechanisms pharmacologically to trigger this process in people who are too weak to exercise." This pharmacological mimicry of exercise is a holy grail for patients suffering from conditions like muscular dystrophy, chronic heart failure, or severe sarcopenia, for whom physical activity is either limited or contraindicated. The ability to enhance mitochondrial function without the physical strain of exercise could significantly improve their quality of life and potentially slow disease progression.
Fan also highlighted the broader systemic benefits of activating ERRs. "Our findings suggest that activating estrogen-related receptors could not only help fuel people’s muscles, but it could also have other beneficial effects across the whole body," he stated. "Improving mitochondrial function and energy metabolism could help strengthen many different organ systems, including the brain and heart." This holistic perspective underscores the far-reaching impact of mitochondrial health, extending beyond muscle strength to critical functions of cognition and cardiovascular health, areas where mitochondrial dysfunction is increasingly implicated in disease pathology.
Far-Reaching Implications: A New Era of Therapeutic Development
The Salk Institute’s groundbreaking identification of estrogen-related receptors as direct regulators of mitochondrial biogenesis marks a pivotal moment in the quest to combat metabolic dysfunction. The implications are vast, promising a new era of therapeutic development that could significantly alter the landscape of chronic disease management.
Targeted Drug Development: The immediate and most exciting implication is the potential for developing novel drugs that specifically target and activate ERRs. Because ERRα can directly bind to DNA and regulate gene expression, it presents a highly "druggable" target. Pharmaceutical researchers can now focus on identifying small molecules that can precisely enhance ERR activity, effectively "turning on" the genes responsible for mitochondrial growth and energy production. Such drugs could provide a powerful, non-invasive means to improve energy metabolism in patients who currently have few options. This could lead to a new class of therapeutics for conditions such as muscular dystrophy, chronic fatigue syndrome, age-related muscle decline (sarcopenia), and even metabolic syndrome, which often involves impaired energy utilization.
Systemic Health Benefits: The benefits of improved mitochondrial function are not confined to muscle tissue alone. As Dr. Fan emphasized, the potential for "other beneficial effects across the whole body" is immense. The brain and heart, two of the most energy-demanding organs, are particularly vulnerable to mitochondrial dysfunction. Enhancing mitochondrial performance through ERR activation could offer neuroprotective effects, potentially mitigating the progression of neurodegenerative diseases like Alzheimer’s, Parkinson’s, and multiple sclerosis, where neuronal energy deficits are a key pathological feature. Similarly, improving cardiac mitochondrial function could be transformative for patients with heart failure or other cardiovascular diseases, bolstering the heart’s pumping efficiency and overall health.
Addressing the Challenges of Aging: With global populations aging, the burden of age-related metabolic decline and muscle weakness is growing. By offering a pharmacological means to boost mitochondrial health, ERR activators could play a crucial role in promoting "healthspan" – the period of life spent in good health – enabling older adults to maintain strength, mobility, and cognitive function for longer.
Future Research Pathways and Challenges: While the promise is immense, the path from discovery to clinical application is long and complex. Future research will undoubtedly delve deeper into the intricate functions and regulatory mechanisms of both alpha- and gamma-type receptors. Understanding how these subtypes interact and are regulated could uncover even more refined therapeutic targets or strategies, perhaps involving combination therapies. Scientists will also need to explore potential side effects of ERR activation, ensuring that any developed drugs are both effective and safe. The journey will involve rigorous preclinical testing, followed by multiple phases of human clinical trials, a process that typically spans many years. However, the foundational understanding provided by the Salk Institute study offers a robust starting point.
Socio-Economic Impact: On a broader societal scale, the successful development of ERR-based therapies could significantly reduce the healthcare burden associated with chronic metabolic and muscular diseases. By improving quality of life, extending functional independence, and potentially slowing disease progression, these therapies could lead to substantial savings in long-term care costs and enhance overall societal productivity.
Conclusion
The Salk Institute’s latest research represents a profound leap forward in our understanding of cellular energy metabolism and offers a beacon of hope for millions worldwide. By definitively identifying estrogen-related receptors, particularly ERRα, as the indispensable drivers of mitochondrial biogenesis and function in muscle, Professor Ronald Evans, Dr. Weiwei Fan, and their team have unlocked a powerful new therapeutic avenue. This discovery has laid the groundwork for developing drugs that could effectively mimic the energy-boosting benefits of exercise, directly combating muscle weakness and fatigue in a wide array of debilitating conditions. As the scientific community moves forward, the promise of ERR-activating therapies shines brightly, heralding a future where mitochondrial dysfunction may no longer be a life sentence of decline, but a manageable condition, restoring vitality and improving the health of countless individuals.
Authors & Support: Other authors contributing to this significant work include Hui Wang, Lillian Crossley, Mingxiao He, Hunter Robbins, Chandra Koopari, Yang Dai, Morgan Truitt, Ruth Yu, Annette Atkins, and Michael Downes of Salk; Tae Gyu Oh of Salk and the University of Oklahoma; and Christopher Liddle of the University of Sydney, Australia.
The research was supported by generous funding from the National Institutes of Health (P01HL147835, DK057978, DK120515, 1R21OD030076, CCSG P30CA23100, CCSG P30 CA014195, CCSG P30 CA014195, P30 AG068635), Department of the Navy (N00014-16-1-3159), Larry L. Hillblom Foundation, Inc. (2021-D-001-NET), Wu Tsai Human Performance Alliance, Henry L. Guenther Foundation, and Waitt Foundation.
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