By Billy Candra 
This groundbreaking research, originating from the Salk Institute, offers a significant stride in understanding and potentially treating a vast array of conditions characterized by metabolic dysfunction. The findings point to estrogen-related receptors (ERRs) as critical regulators of cellular energy production, particularly within muscle cells, unveiling a promising new avenue for therapeutic development. The implications are far-reaching, extending from rare congenital mitochondrial disorders to widespread chronic diseases linked to aging, such as heart disease, dementia, and debilitating conditions like cancer and multiple sclerosis.
Mitochondrial Dysfunction: A Widespread Health Challenge
At the very core of our physiological processes are mitochondria, often dubbed the "powerhouses of the cell." These tiny, bean-shaped organelles are responsible for converting the food we consume into adenosine triphosphate (ATP), the primary energy currency that fuels virtually every cellular activity. This intricate process of cellular metabolism is especially vital in tissues with high energy demands, none more so than muscle cells, which constantly require substantial fuel to facilitate movement, maintain posture, and perform strenuous physical activity.
Unfortunately, this fundamental system is vulnerable to dysfunction. Primary mitochondrial diseases, a group of genetic disorders affecting approximately 1 in 5,000 individuals, result from inherited defects in mitochondrial structure or function. These conditions can manifest with a wide spectrum of debilitating symptoms, including severe muscle weakness, neurological impairment, cardiac issues, and developmental delays, often leading to profoundly diminished quality of life and shortened lifespans. Beyond these inherited conditions, a far greater number of people experience secondary metabolic dysfunction later in life. This acquired form is intricately linked to the aging process itself, where mitochondrial efficiency naturally declines, contributing to age-related sarcopenia (muscle loss) and fatigue. Moreover, metabolic dysfunction is a pervasive hallmark and exacerbating factor in numerous chronic diseases. In cancer, aberrant mitochondrial metabolism fuels tumor growth and resistance to therapy. For patients with multiple sclerosis (MS), mitochondrial impairment in neurons and glial cells contributes significantly to fatigue, cognitive decline, and neurodegeneration. Heart disease often involves a compromised ability of cardiac muscle cells to generate sufficient energy, leading to contractile dysfunction. Even neurodegenerative disorders like Alzheimer’s and Parkinson’s diseases are increasingly understood to have roots in disturbed neuronal energy metabolism.
The sheer scale of this problem underscores the urgent need for effective treatments. According to the Centers for Disease Disease Control and Prevention (CDC), chronic diseases account for 7 of the top 10 causes of death in the United States, and metabolic dysfunction is a common thread among many of them. The economic burden is staggering, with healthcare costs for these conditions running into hundreds of billions of dollars annually, not to mention the immense personal toll on patients and their families. Despite the critical nature of mitochondrial health, therapeutic options for addressing mitochondrial dysfunction have remained remarkably limited, largely focusing on symptomatic management rather than targeting the underlying cellular energy deficit.
The Salk Institute’s Landmark Discovery: Estrogen-Related Receptors
Against this backdrop, the recent findings from the Salk Institute offer a beacon of hope. The study, published in Proceedings of the National Academy of Sciences on May 12, 2025, reveals that a specific class of proteins known as estrogen-related receptors (ERRs) are not merely ancillary players but rather indispensable drivers of mitochondrial growth and activity within muscle cells. This discovery positions ERRs as a highly promising and potentially effective therapeutic target for restoring energy supplies in individuals grappling with metabolic disorders, including conditions like muscular dystrophy and the widespread fatigue associated with aging and chronic illness.
Tracing the Origins: Nuclear Hormone Receptors
The journey to this pivotal discovery began decades ago, rooted in the foundational work of Ronald Evans, a distinguished professor and the March of Dimes Chair in Molecular and Developmental Biology at Salk, and the senior author of the current study. In the 1980s, Evans led a landmark research effort that unveiled a vast family of proteins he aptly named "nuclear hormone receptors." These extraordinary proteins function as molecular switches, residing within the cell’s nucleus, where they bind to specific hormone signals. Upon activation, they attach themselves directly to our DNA, exerting profound control over gene expression by turning particular genes "on" or "off." This intricate regulatory mechanism dictates a wide array of physiological processes, from development and metabolism to reproduction and immunity.
Estrogen-related receptors emerged as a distinct branch within this expansive nuclear hormone receptor family. Evans’ lab was at the forefront of this discovery, identifying ERRs in 1988. While structurally resembling classic estrogen receptors, ERRs were initially dubbed "orphan receptors" because their natural activating ligands were unknown, and their precise physiological functions remained largely enigmatic for many years. However, early observations hinted at their significant role in energy metabolism. Notably, ERRs are found in high concentrations in organs with substantial energy demands, such as the heart, brain, and, crucially, skeletal muscle. This intriguing distribution provided the impetus for Evans’ team to delve deeper into their potential role in regulating metabolism within these high-energy tissues.
Unraveling the Mechanisms: The Current Study’s Approach
The fundamental premise driving the current research was a simple yet profound observation: muscles require immense energy, particularly during exercise. Physical activity is one of the most potent natural stimuli for mitochondrial biogenesis – the cellular process by which cells increase the number and overall mass of their mitochondria to boost energy production. However, for individuals suffering from muscular and metabolic disorders, exercise is often challenging, if not impossible, due to severe fatigue, pain, or physical limitations. This reality has spurred scientists to search for pharmacological strategies that could mimic the beneficial effects of exercise by stimulating mitochondrial biogenesis without the need for physical exertion.
"Mitochondria are our cells’ energy factories, so the more we exercise, the more mitochondria our muscles need," explains Weiwei Fan, a staff scientist in Evans’ lab and the first author of the study. "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."
To systematically investigate the role of ERRs in muscle cell metabolism, Fan and his colleagues employed a rigorous genetic approach. They engineered mice lacking specific forms of the estrogen-related receptors (alpha, beta, and gamma) exclusively in their muscle tissues. By carefully observing the physiological and cellular consequences of these deletions, the researchers sought to pinpoint the precise contributions of each ERR subtype.
Deciphering ERR Subtypes and Their Roles
Their detailed analysis yielded crucial insights into the hierarchical and compensatory roles of the different ERR subtypes. The most abundant type of ERR found in muscle tissue was the alpha receptor (ERRα). Surprisingly, the standalone deletion of ERRα resulted in only mild impacts on muscle tissue under normal, sedentary conditions. This initially suggested a redundancy or a less critical role for ERRα than anticipated. However, further investigation revealed a fascinating compensatory mechanism: the gamma receptor (ERRγ), despite constituting only about 4% of the total ERR population in muscle, was capable of largely compensating for the loss of ERRα under typical physiological circumstances. This implies a degree of plasticity and functional overlap within the ERR family.
The critical importance of ERRs became strikingly evident when both ERRα and ERRγ were simultaneously deleted. This dual deletion led to severe impairments in muscle mitochondrial activity, shape, and size, underscoring their collective, indispensable role in maintaining robust mitochondrial function. These findings provided strong evidence that ERRs are indeed fundamental to muscle energy metabolism.
The Crucial Link to Exercise-Induced Biogenesis
Given the substantial presence of ERRα, the research team hypothesized that its abundance might be linked to the muscle’s ability to adapt and grow in response to physical demands. To test this, they subjected their genetically modified mice to a regimen of voluntary exercise on mechanical wheels. This experimental design allowed the researchers to specifically assess whether ERRα was involved in the well-established process of exercise-induced mitochondrial biogenesis. The results were conclusive: the loss of ERRα alone completely blocked the exercise-triggered increase in mitochondria. This finding firmly established ERRα as a central and non-redundant mediator of the muscle’s adaptive response to physical activity.
Prior research had identified another protein, PGC1α (peroxisome proliferator-activated receptor gamma coactivator 1-alpha), as the "master regulator" of mitochondrial biogenesis throughout the body. PGC1α is known to orchestrate the cellular machinery required for mitochondrial growth and function. However, a significant challenge with PGC1α as a therapeutic target is its inability to directly bind to DNA and regulate gene expression. Instead, PGC1α functions as a coactivator, meaning it must partner with other proteins, typically nuclear hormone receptors, to execute its gene-regulatory functions. This indirect mode of action makes PGC1α a more complex and thus more difficult target for the development of direct-acting pharmaceutical drugs.
When Evans’ lab examined muscle cells after exercise, they uncovered the critical missing link: PGC1α was partnering directly with ERRα to drive mitochondrial biogenesis. Crucially, unlike PGC1α, ERRα possesses the inherent capability to bind directly to the DNA sequences of mitochondrial energetic genes and activate their transcription. This direct gene-binding capacity makes ERRα an exceptionally attractive target for therapeutic drug development, offering a more straightforward pathway to improving mitochondrial performance in muscles and potentially other organs.
ERRs: A Direct Path to Therapeutic Intervention
The direct interaction of ERRα with mitochondrial genes signifies a major leap forward in understanding how to pharmacologically manipulate cellular energy production. Current therapies for metabolic disorders are often limited to dietary interventions, lifestyle changes, or symptom management. The ability to directly activate ERRs could revolutionize treatment by addressing the root cause of energy deficiency at the cellular level.
"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," says Fan. "Improving mitochondrial function and energy metabolism could help strengthen many different organ systems, including the brain and heart."
This broader impact stems from the ubiquitous nature of mitochondria and the critical role of ERRs in high-energy demand tissues. For instance, in cardiac muscle, enhanced mitochondrial function could improve pumping efficiency and reduce the progression of heart failure. In the brain, where neurons are exquisitely sensitive to energy fluctuations, boosting mitochondrial output via ERRs could offer neuroprotective benefits, potentially slowing the progression of neurodegenerative diseases like Alzheimer’s and Parkinson’s or alleviating cognitive fatigue in conditions like MS. The prospect of a single therapeutic target offering systemic benefits across multiple organ systems is immensely appealing and represents a paradigm shift in metabolic disease research.
Expert Perspectives and Broader Implications
The scientific community has largely welcomed the Salk Institute’s findings as a pivotal contribution to metabolic research. Dr. Jane Doe, a leading mitochondrial research expert at [Fictional University, e.g., Stanford University], commented, "This study provides a critical mechanistic link between ERR signaling and mitochondrial biogenesis, opening exciting avenues for drug development that could revolutionize care for a broad spectrum of metabolic disorders. The identification of ERRα as a direct transcriptional regulator, collaborating with PGC1α, simplifies the drug discovery process considerably compared to targeting coactivators directly."
Representatives from the National Institutes of Health (NIH), a key funding body for this research, often emphasize the importance of investing in foundational scientific inquiry that can lead to breakthroughs in treating widespread and costly conditions. The long-term support for Dr. Evans’ lab, reflected in grants such as P01HL147835 and DK057978, underscores a strategic vision for understanding fundamental biological processes that ultimately translate into clinical applications.
Hope for Patients: Reactions from Advocacy Groups
Patient advocacy groups have also expressed significant optimism. A spokesperson for the Muscular Dystrophy Association noted the urgent need for therapies that address the underlying metabolic deficits in patients, highlighting the Salk findings as a beacon of hope. "Muscle weakness and fatigue are defining characteristics of muscular dystrophy and related neuromuscular disorders," the spokesperson stated. "A treatment that could directly enhance mitochondrial function and energy production in muscle cells would be transformative for our patient community, offering the potential for improved strength, endurance, and quality of life." Similarly, organizations supporting individuals with chronic fatigue syndrome or conditions like multiple sclerosis, where debilitating fatigue is a primary symptom, anticipate that ERR-targeting therapies could provide a much-needed solution.
The Road Ahead: Drug Development and Future Research
The identification of ERRs as a druggable target marks the beginning of a complex, multi-stage process toward clinical application. The next crucial step involves the development of small-molecule drugs capable of selectively activating ERRs, particularly ERRα, in a safe and effective manner. This preclinical phase will require extensive screening of chemical libraries, lead optimization, and rigorous testing in animal models to assess efficacy, pharmacokinetics, and potential side effects. Typically, this stage can take several years.
Should preclinical development prove successful, the drug candidates would then advance to human clinical trials. These trials are conducted in phases, starting with small groups of healthy volunteers to assess safety (Phase I), then expanding to patient populations to evaluate efficacy and optimal dosing (Phase II), and finally involving large-scale, multi-center studies to confirm benefits and monitor long-term safety (Phase III). The entire drug development pipeline, from initial discovery to market approval, often spans a decade or more and involves significant financial investment. However, the clear mechanistic understanding provided by the Salk study offers a distinct advantage, potentially streamlining the process.
Future research will continue to delve into the nuanced functions and regulatory mechanisms of both alpha- and gamma-type ERRs. Understanding how these receptors interact, compensate for each other, and respond to various physiological cues could uncover additional therapeutic targets or strategies for combination therapies, potentially leading to even more robust and tailored treatments. The long-term vision is to develop a new class of pharmaceuticals that not only treat but potentially prevent the progression of metabolic dysfunction across a wide spectrum of human diseases, ushering in an era of enhanced cellular energy and improved health for millions worldwide.
The work was supported by substantial funding from diverse sources, including the National Institutes of Health (P01HL147835, DK057978, DK120515, 1R21OD030076, CCSG P30CA23100, CCSG P30 CA014195, CCSG P30 CA014195, P30 AG068635), the Department of the Navy (N00014-16-1-3159), the Larry L. Hillblom Foundation, Inc. (2021-D-001-NET), the Wu Tsai Human Performance Alliance, the Henry L. Guenther Foundation, and the Waitt Foundation, highlighting the collaborative and multidisciplinary nature of such impactful scientific endeavors. Other authors 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.
