Study uncovers a polyphenol’s mechanism in enhancing mitochondrial calcium uptake and muscle bioenergetics during aging.

In a recent study published in the Cell Metabolism, a group of researchers explored mitochondrial calcium (mtCa²⁺) uptake in muscle aging and identified oleuropein as a mitochondrial calcium uniporter (MCU) activator to boost energy and performance.

Background

Mitochondrial dysfunction is a key hallmark of aging, contributing to physiological decline and chronic diseases. In skeletal muscle, mtCa²⁺ uptake, regulated by the MCU, plays a vital role in oxidative metabolism and Adenosine trisphosphate (ATP) production during contraction.

Age-related declines in mitochondrial activity are linked to sarcopenia, characterized by reduced muscle mass, strength, and function. While exercise and nutrition reduce sarcopenia, direct therapeutic strategies targeting mtCa²⁺ uptake remain unexplored. Polyphenol-rich diets show promise, yet their molecular mechanisms are unclear.

Further research is needed to develop interventions enhancing mitochondrial bioenergetics and addressing age-related muscle dysfunction.

About the study

Human skeletal muscle transcriptomics utilized Ribonucleic Acid (RNA) sequencing data from the Singapore sarcopenia study to analyze genes regulating mtCa²⁺ uptake in muscle biopsies from older individuals with and without sarcopenia. After filtering genes with low expression, the data were normalized and subjected to statistical analysis using the Benjamini-Hochberg method for p-value correction. Protein interaction networks centered on mitochondrial calcium uniporter regulator 1 (MCUR1) were constructed using Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) and analyzed through Cytoscape to reveal functionally grouped gene ontologies.

In primary human skeletal muscle myotubes, mtCa²⁺ uptake was measured after inducing MCU or MCUR1 knockdown using adenoviral short hairpin (shRNA), followed by differentiation into myotubes. Oleuropein treatments involved mitochondrial-targeted aequorin to quantify Ca²⁺ uptake under various conditions, including stimulation with caffeine. Similar methods were applied to skeletal muscle myotubes derived from healthy and sarcopenic donors, enabling comparative analyses.

High-throughput screening employed aequorin-based luminescent sensors to identify compounds that modulate mtCa²⁺ uptake. Hits were validated through further testing. Additionally, ex vivo muscle force and fatigue assessments, in vivo exercise performance, and mitochondrial respiration analyses were conducted in murine models to evaluate oleuropein’s functional effects.

Study results

mtCa²⁺ uptake declines significantly during aging and sarcopenia in human skeletal muscle, driven by the downregulation of MCUR1. In primary human myotubes derived from aged donors, mtCa²⁺ uptake was impaired by 45%, demonstrating reduced mitochondrial bioenergetic capacity. This dysfunction was exacerbated in sarcopenic patients, where mtCa²⁺ uptake was further reduced, correlating with decreased MCUR1 expression.

Notably, MCUR1 levels were positively associated with muscle mass, strength, and physical performance, emphasizing its role in maintaining mtCa²⁺ homeostasis and skeletal muscle function during aging. Functional studies showed that MCUR1 knockdown in young myotubes recapitulated the impaired mtCa²⁺ uptake seen in aging, while MCUR1 overexpression restored mtCa²⁺ uptake in aged myotubes.

In a preclinical aging model, mtCa²⁺ uptake was similarly reduced in aged mouse muscle, accompanied by a 54% decline in MCUR1 expression. This impairment disrupted energy metabolism, increasing pyruvate dehydrogenase (PDH) phosphorylation, reducing mitochondrial respiration, and shifting substrate preference toward fatty acid oxidation.

Restoring MCUR1 expression or pharmacologically activating PDH using dichloroacetate (DCA) reversed these metabolic defects, demonstrating the central role of the MCU-PDH axis in age-related mitochondrial dysfunction.

To address these deficits, a high-throughput screen identified the olive-derived polyphenol oleuropein as a potent activator of mtCa²⁺ uptake. Oleuropein is directly bound to MICU1, a key regulatory subunit of the MCU complex, with high specificity and affinity. Functional assays confirmed that oleuropein stimulated mtCa²⁺ uptake without altering cytosolic calcium levels or mitochondrial membrane potential.

Oleuropein’s efficacy depended on the presence of MICU1 and MCU, as genetic knockdown of either abolished its effects on mtCa²⁺ uptake and mitochondrial respiration. In human myotubes, oleuropein enhanced mitochondrial energy metabolism and reduced fatigue during muscle contractions, demonstrating physiological benefits.

Dietary oleuropein treatments in young mice confirmed its ability to enhance mtCa²⁺ uptake, activate PDH, and improve exercise performance. These effects were abolished in MCU-deficient mice, confirming its mechanism of action via the MCU complex. Remarkably, oleuropein reversed age-related declines in mtCa²⁺ uptake, mitochondrial metabolism, and physical performance in aged human myotubes and animal models. Chronic oleuropein supplementation restored mitochondrial function, reduced muscle fatigue, and improved exercise endurance in sarcopenic rodents.

Conclusions

To summarize, targeting mitochondria to enhance energy production is a critical focus due to its role in health and disease. Oleuropein, a natural polyphenol, uniquely stimulates mitochondrial respiration and ATP production by directly enhancing mtCa²⁺ uptake via binding to MICU1 of the MCU complex. This mechanism transiently elevates mtCa²⁺ levels, activating PDH dephosphorylation and boosting bioenergetics. Unlike other mitochondrial therapies, oleuropein acts rapidly and specifically without altering cytosolic calcium.

Preclinical studies confirm its efficacy in reversing age-related declines in mtCa²⁺ uptake, mitochondrial respiration, and muscle performance. With a strong safety profile and benefits for sarcopenia and aging, oleuropein holds translational potential for clinical applications.