LA JOLLA, CA – May 12, 2025 – In a discovery poised to revolutionize the treatment of metabolic disorders, scientists at the Salk Institute have identified a crucial role for a group of proteins known as estrogen-related receptors (ERRs) in repairing cellular energy metabolism and combating muscle fatigue. Published today in the prestigious Proceedings of the National Academy of Sciences, the groundbreaking study reveals that these receptors act as indispensable drivers of mitochondrial growth and activity within muscle cells, offering a powerful new therapeutic target for a wide array of debilitating conditions, from muscular dystrophy to the metabolic challenges associated with aging and chronic diseases.
The findings illuminate a previously underappreciated mechanism by which our bodies generate and utilize energy, suggesting that developing drugs to activate ERRs could restore vital energy supplies in individuals struggling with muscle weakness and fatigue. This research brings hope to millions affected by conditions where dysfunctional mitochondria – the "powerhouses" of our cells – are a central problem.
The Unseen Battle: Understanding Mitochondrial Dysfunction
At the heart of every cell, tiny, bean-shaped structures called mitochondria tirelessly convert the food we eat into adenosine triphosphate (ATP), the usable energy currency that fuels virtually all biological processes. This cellular-level metabolism is particularly vital in muscle cells, which demand immense amounts of energy to power movement, from the subtle twitch of an eyelid to the vigorous exertion of athletic performance.
However, this intricate energy production system is remarkably vulnerable. A significant number of individuals, estimated at 1 in 5,000, are born with congenital mitochondrial dysfunction, facing lifelong challenges with energy production. Furthermore, countless others acquire metabolic dysfunction later in life, a pervasive issue strongly linked to the natural aging process and a constellation of severe diseases, including certain cancers, multiple sclerosis (MS), heart disease, and neurodegenerative conditions like Alzheimer’s and Parkinson’s disease.
The consequences of mitochondrial dysfunction are profound and far-reaching. Patients often experience chronic fatigue, muscle weakness, exercise intolerance, cognitive impairments, and a general decline in organ function. Despite the widespread impact, effective treatments for these disorders remain elusive, often focusing on symptom management rather than addressing the root cause of energy deficit. This therapeutic void underscores the urgent need for novel approaches capable of restoring robust mitochondrial function.
A Legacy of Discovery: The Salk Institute’s Pioneering Role
The current breakthrough is built upon decades of foundational research at the Salk Institute, particularly the pioneering work of senior author Ronald Evans. In the 1980s, Evans led the landmark discovery of a vast family of proteins he named "nuclear hormone receptors." These extraordinary receptors, which include classic estrogen receptors, act as molecular switches, attaching themselves to our DNA and precisely controlling which genes get turned "on" or "off." This fundamental mechanism allows our bodies to respond to hormones and regulate a myriad of physiological processes.
Among the branches of this expansive family, Evans’s lab was also instrumental in discovering estrogen-related receptors (ERRs) in 1988. While structurally similar to classic estrogen receptors, their functional roles, particularly in energy metabolism, remained less understood. ERRs are notably abundant in organs with high energy demands, such as the heart and the brain, hinting at their potential involvement in critical metabolic processes. This observation naturally led Evans’s team to investigate their role in another high-energy organ: skeletal muscle.
"Estrogen-related receptors look a lot like classic estrogen receptors, but their function has been much less understood," explains Professor Evans, who holds the March of Dimes Chair in Molecular and Developmental Biology at Salk. "Our lab discovered estrogen-related receptors in 1988 and was one of the first to recognize their role in energy metabolism. Now 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 words underscore the culmination of years of dedicated scientific inquiry, bridging historical discovery with a critical contemporary application.
Targeting the Engine: Estrogen-Related Receptors Emerge as a Therapeutic Pathway
Skeletal muscles are voracious consumers of energy, especially during physical activity. Exercise, in fact, serves as one of the most potent natural signals for muscle cells to initiate mitochondrial biogenesis – a remarkable process wherein a cell increases both the number and efficiency of its mitochondria to generate more fuel. This adaptive response is what allows muscles to grow stronger and more enduring.
However, for individuals grappling with muscular and metabolic disorders, the very act of exercising can be excruciatingly difficult, often impossible. This creates a cruel paradox: the mechanism that could improve their condition is inaccessible to them. Recognizing this challenge, scientists have long sought an alternative, pharmacological pathway to stimulate mitochondrial biogenesis, effectively mimicking the beneficial effects of exercise without the physical exertion.
"Mitochondria are our cells’ energy factories, so the more we exercise, the more mitochondria our muscles need," says first author Weiwei Fan, a staff scientist in Evans’s lab. "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 line of reasoning formed the bedrock of their current investigation, aiming to provide a lifeline to those whose bodies cannot meet their own energy demands.
Unraveling the Mechanisms: The Mouse Model Study
To definitively determine whether estrogen-related receptors played a direct role in muscle cell metabolism, Fan and his colleagues embarked on a meticulously designed study using mouse models. Their approach involved genetically deleting three different forms, or isoforms, of these receptors – alpha (ERRα), beta (ERRβ), and gamma (ERRγ) – specifically within the muscle tissues of the mice. By observing the resulting effects, they could pinpoint the precise contributions of each receptor type.
The initial findings revealed a nuanced interplay among the ERR isoforms. The alpha receptor (ERRα) proved to be the most abundant type in muscle tissue. Interestingly, the loss of ERRα alone had only mild impacts on muscle mitochondrial activity under normal, resting conditions. This seemingly surprising observation was explained by the compensatory role of the gamma receptor (ERRγ). Although ERRγ constituted only about 4% of the total estrogen-related receptors, it was capable of stepping in and maintaining mitochondrial function when ERRα was absent. However, this compensatory capacity had its limits. When both the alpha and gamma types were deleted simultaneously, the consequences were severe: the mice exhibited profound impairments in muscle mitochondrial activity, as well as significant alterations in their shape and size, underscoring the critical, albeit sometimes redundant, roles these receptors play.
The researchers then turned their attention to the enigma of ERRα’s sheer abundance. If ERRγ could compensate under normal circumstances, what was the primary purpose of having such an excess of ERRα? Hypothesizing that ERRα’s prominence was linked to the muscle’s ability to adapt and grow in response to exercise, the team subjected their mice to controlled exercise regimens on mechanical wheels. This exercise predictably triggered mitochondrial biogenesis in wild-type mice, allowing the scientists to assess ERRα’s involvement in this vital process. The results were striking: the loss of ERRα alone completely blocked exercise-induced mitochondrial biogenesis. This finding unequivocally established ERRα as the central mediator of the muscle’s adaptive response to physical demand.
The PGC1α Puzzle: Why ERRs are a Better Bet
Prior scientific investigations had already identified another key player in exercise-induced mitochondrial growth: a protein called PGC1α. Known as the "master regulator" of mitochondria throughout the body, PGC1α orchestrates many aspects of mitochondrial function and biogenesis. However, PGC1α presents a significant challenge for therapeutic drug development. Unlike nuclear hormone receptors such as ERRs, PGC1α cannot bind directly to genes to turn them on or off. Instead, it relies on partner proteins to execute its commands. This indirect mode of action makes PGC1α a more complex and difficult target for developing specific, small-molecule drugs.
The Salk team’s new research elegantly resolves this puzzle. When Evans’s lab meticulously examined muscle cells after exercise, they discovered a critical partnership: PGC1α was indeed at work, but it was collaborating directly with ERRα to drive mitochondrial biogenesis. Crucially, unlike PGC1α, ERRα possesses the inherent ability to bind directly to the DNA sequences of mitochondrial energetic genes and activate them. This direct interaction makes ERRα a far more "druggable" target, offering a more straightforward path for pharmacological intervention to improve muscle’s mitochondrial performance. This revelation fundamentally shifts the paradigm for targeting mitochondrial dysfunction, moving from an indirect, multi-step approach to a direct, receptor-mediated one.
A Promising Pathway: Activating Cellular Energy Factories
The implications of this discovery are profound and extend far beyond the realm of muscle tissue. The ability to pharmacologically activate estrogen-related receptors holds immense promise for restoring energy supplies and improving mitochondrial function in individuals suffering from a wide spectrum of metabolic disorders. Conditions like muscular dystrophy, characterized by progressive muscle weakness and degeneration, could see revolutionary new treatments. Moreover, the metabolic decline associated with aging, leading to sarcopenia (age-related muscle loss) and frailty, could potentially be mitigated.
"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," emphasizes Weiwei Fan. "Improving mitochondrial function and energy metabolism could help strengthen many different organ systems, including the brain and heart." This holistic perspective highlights the systemic impact of enhanced mitochondrial health. Given that the brain and heart are also high-energy organs rich in ERRs, boosting their mitochondrial output could potentially offer protection against neurodegenerative diseases and cardiovascular conditions, opening doors to preventative strategies as well as treatments.
Beyond Muscle: Systemic Implications and Future Horizons
The discovery of ERRα’s pivotal role as a direct activator of mitochondrial genes represents a significant leap forward in our understanding of cellular energy regulation. It provides a tangible, actionable target for drug developers to explore. The potential to create "exercise in a pill" for those unable to perform physical activity is a long-held dream in medicine, and this research moves that dream closer to reality by identifying a key molecular switch.
Furthermore, the study’s insights into the compensatory roles of different ERR isoforms (ERRα and ERRγ) open new avenues for highly specific therapeutic strategies. Future research will undoubtedly delve deeper into the unique functions and regulatory mechanisms of both alpha- and gamma-type receptors. Understanding these nuances could lead to the development of highly targeted drugs designed to selectively activate specific ERRs, tailoring treatments to individual patient needs and minimizing potential off-target effects. This precision medicine approach holds the key to maximizing efficacy and safety.
The collaborative nature of this work is also noteworthy. The study involved a dedicated team of researchers, including 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. Their combined expertise across various scientific disciplines was instrumental in bringing this complex research to fruition.
This paradigm-shifting research was made possible through the generous support of numerous organizations, including 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. Their investment in fundamental scientific inquiry continues to yield discoveries that promise to transform human health.
In conclusion, the Salk Institute’s latest findings herald a new era in the fight against metabolic dysfunction. By identifying estrogen-related receptors as indispensable drivers of mitochondrial health, scientists have illuminated a powerful therapeutic pathway, offering a beacon of hope for improving the quality of life for millions affected by muscle weakness, fatigue, and the myriad diseases stemming from compromised cellular energy. The journey from fundamental discovery to therapeutic application is often long, but this breakthrough marks a decisive and exciting step forward.
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