Biology subjects

Rizzuto, R.

Publications and source records attributed to Rizzuto, R..

4 recordsLinked to original sources

bioRxiv2025

YME1L-dependent regulation of mitochondrial Ca2+ transport: a role for mitochondrial uptake protein 1 (MICU1) in nutrient sensing

Mitochondrial calcium uptake via the mitochondrial calcium uniporter complex (MCUc) is tightly regulated by gatekeeper proteins such as MICU1 and MICU2. While long-term nutritional interventions have been shown to remodel the MCUc, its short-term regulation during postprandial transitions and acute nutrient stress remains unclear. Here, we demonstrate that non-gated MCUc increases in the postprandial liver due to a transient loss of mature MICU1 (m-MICU1), accompanied by changes in its precursor form (p-MICU1). These changes are more pronounced and occur earlier than the general increase in mitochondrial mass and respiratory protein content, indicating that they are independent of mitochondrial remodelling during refeeding. In vitro, serum deprivation, insulin signalling, modulation of mTOR activity, and glutamine starvation all affect mature or precursor MICU1 protein levels, indicating that multiple nutritional changes promote MICU1 processing alterations, leading to the formation of a non-gated, MICU-deficient MCUc. Under these conditions, mitochondrial, but not cytosolic, Ca{superscript 2} levels increase in intact cells. Moreover, mitochondrial Ca{superscript 2} uptake rates are enhanced, which correlates with higher mitochondrial oxygen consumption, increased reactive oxygen species (ROS) production, and enhanced sensitivity to mitochondrial permeability transition. We identify the mitochondrial protease YME1L as essential for MICU1 turnover in response to nutrient availability. YME1L silencing prevents MICU1 degradation and suppresses the enhanced Ca{superscript 2} uptake induced by glutamine deprivation. Together, these results reveal nutrient-sensitive, YME1L-dependent remodelling of the MCU complex and establish MICU1 degradation as a key mechanism linking metabolic signals to mitochondrial Ca{superscript 2} transport.

physiology↗

bioRxiv2023

TMEM65-dependent Ca2+ extrusion safeguards mitochondrial homeostasis

The bidirectional transport of Ca2+ into and out of mitochondria is a conserved biological process controlling multiple events, including metabolism, signaling, and cell fate. In the presence of membrane potential driving mitochondrial Ca2+ accumulation, transient changes of [Ca2+]mt in response to cytosolic [Ca2+] variations are ensured by a molecular machinery for Ca2+ influx and efflux embedded in the inner mitochondrial membrane (IMM). While it is well established that influx relies on the Mitochondrial Calcium Uniporter (MCU), efflux was expected to be molecularly diversified, given the occurrence of functionally different exchange pathways with either Na+ or H+1. Accordingly, dedicated transporters ensure proper Ca2+ homeostasis and tightly regulated mitochondrial bioenergetics, but the process is not yet fully elucidated. We here demonstrate that TMEM65, a protein with an unknown biological function, is a fundamental component of the Ca2+ efflux machinery of mitochondria. As the MCU, TMEM65 has a broad tissue expression and localizes to the IMM. Its overexpression dramatically enhances Na+- and Li+-dependent mitochondrial Ca2+ extrusion, which is abrogated by the pharmacological inhibitor CGP-37157. Conversely, its downregulation chronically elevates resting mitochondrial Ca2+ levels and inhibits efficient Ca2+ efflux upon cellular activation, culminating in mitochondrial calcium overload and causing organelle dysfunction. Since TMEM65 has been associated with a severe human mitochondrial disease2, we deleted the TMEM65 homologues in Caenorhabditis elegans (CeTMEM65). While the two CeTMEM65 orthologs are dispensable for the survival at permissive growing conditions, their loss undermines embryonic developments when eggs are exposed to mild temperature-stress. In this regard, we find that CeTMEM65 (null) alleles cause necrotic lesions that are suppressed by inhibiting the mitochondrial calcium uniporter MCU-1. Overall, these results unambiguously assign a primary role in mitochondrial Ca2+ homeostasis to the orphan protein TMEM65. More importantly, our findings describe a novel molecular component that may be relevant in pathological settings in which excessive mitochondrial Ca2+ accumulation critically contribute to degenerative pathways.

biochemistry↗

bioRxiv2023

Mitochondrial Calcium Uptake Declines during Aging and is Directly Activated by Oleuropein to Boost Energy Metabolism and Skeletal Muscle Performance

Mitochondrial calcium (mtCa2+) uptake via the Mitochondrial Calcium Uniporter (MCU) couples the regulation of calcium homeostasis to energy production. mtCa2+ uptake is rate-limiting for mitochondrial activation during muscle contraction, but how MCU is affected during physiopathology and whether it can be stimulated therapeutically remains largely uncharacterized. By profiling human and preclinical aging of skeletal muscle, we discovered a conserved down-regulation of MCUR1 during aging that decreases mtCa2+ uptake and drives sarcopenia. Through a screen of 5000 bioactive nutrients, we identify the natural polyphenol Oleuropein as a specific MCU activator that stimulates mitochondrial respiration via binding to MICU1. Oleuropein activates mtCa2+ uptake and oxidative energy metabolism to enhance endurance and limit fatigue in vivo both in young and aged. These effects of Oleuropein are mediated by an MCU-dependent mechanism in skeletal muscle as they are lost upon muscle-specific MCU KO. Our work demonstrates that impaired mtCa2+ uptake causes mitochondrial dysfunction during aging and establishes Oleuropein as a novel nutrient that specifically targets MCU to stimulate mitochondrial bioenergetics and muscle performance.

physiology↗

bioRxiv2019

The mitochondrial Ca2+ uniporter MCU is required for normal glucose-stimulated insulin secretion in vitro and in vivo

Mitochondrial oxidative metabolism is central to glucose-stimulated insulin secretion (GSIS). Whether Ca2+ uptake into pancreatic {beta}-cell mitochondria potentiates or antagonises this process is still a matter of debate. Although the mitochondrial importer (MCU) complex is thought to represent the main route for Ca2+ transport across the inner mitochondrial membrane, its role in {beta}-cells has not previously been examined in vivo. Here, we inactivated the pore-forming subunit MCUa (MCU) selectively in the {beta}-cell in mice using Ins1Cre-mediated recombination. Glucose-stimulated mitochondrial Ca2+ accumulation, ATP production and insulin secretion were strongly (p<0.05 and p<0.01) inhibited in MCU null animals ({beta}MCU-KO) in vitro. Interestingly, cytosolic Ca2+ concentrations increased (p<0.001) whereas mitochondrial membrane depolarisation improved in {beta}MCU-KO animals. Male {beta}MCU-KO mice displayed impaired in vivo insulin secretion at 5 (p<0.001) but not 15 min. post intraperitoneal (IP) injection of glucose while the opposite phenomenon was observed following an oral gavage at 5 min. Unexpectedly, glucose tolerance was improved (p<0.05) in young {beta}MCU-KO (<12 weeks), but not older animals. We conclude that MCU is crucial for mitochondrial Ca2+ uptake in pancreatic {beta}-cells and is required for normal GSIS. The apparent compensatory mechanisms which maintain glucose tolerance in {beta}MCU-KO mice remain to be established.

physiology↗