Hélène Lemieux

Mitochondria are central regulators of cellular metabolism, integrating energy production, redox balance, and signaling pathways that shape aging trajectories. If mitochondrial organization contributes to lifespan divergence, exceptionally long‐lived species should exhibit distinctive metabolic signatures reflecting adaptations promoting long‐term cellular maintenance. Comparative approaches across species with extreme lifespan variation provide a powerful framework for identifying potential metabolic strategies underlying longevity. We conducted targeted metabolomic profiling of five marine bivalve species spanning a lifespan gradient from approximately 30 to more than 500 years, including the exceptionally long‐lived ocean quahog, Arctica islandica . Fifty metabolites were quantified in gill and mantle tissue to determine whether lifespan variation is associated with coordinated changes in metabolic organization. Lifespan emerged as a dominant axis of metabolomic variation across species. Long‐lived bivalves exhibited a distinct metabolic phenotype characterized by a global reduction in free amino acid pools and coordinated changes in metabolites associated with mitochondrial metabolism. Longevity was associated with increased succinate‐to‐fumarate ratios, reduced fumarate and malate concentrations, and reduced engagement of pyruvate‐derived anaerobic pathways under basal conditions. Although these patterns varied in magnitude across tissues, they converged on a common longevity‐associated metabolic signature. Together, these patterns suggest that exceptional longevity is associated with a distinct organization of mitochondrial‐related metabolism and a more selective allocation of metabolic resources, rather than a generalized suppression of metabolism. Our findings identify metabolomic signatures associated with exceptional longevity across the bivalve species studied and support the hypothesis that long lifespan is characterized by a distinctive metabolic architecture favoring long‐term cellular maintenance.

“Alternative” or integrated role of mitochondrial glycerol-3-phosphate dehydrogenase

Aim: Maternal iron deficiency (ID) during pregnancy induces cardiovascular adaptations, including reduced blood pressure and improved cardiac efficiency in hypertensive pregnancy. Iron is essential for mitochondrial function, particularly oxidative phosphorylation, where it serves as a cofactor within electron transfer complexes. Given the high metabolic demands of the maternal heart and iron’s central role in mitochondrial metabolism, we examined how maternal ID affects cardiac mitochondrial ultrastructure, respiration, dynamics, and redox status in pregnant spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. Methods and Results: Female SHR and WKY rats were fed iron-replete or iron-restricted diets before and throughout gestation. On gestational day 21, cardiac mitochondrial ultrastructure was assessed by transmission electron microscopy (TEM), respiration by high-resolution respirometry, and the expression of proteins involved in fusion, fission, autophagy, and apoptosis markers by immunoblotting. Antioxidant gene expression was quantified by RT-qPCR. Data were analyzed by two-way ANOVA with Holm-Sidak’s post hoc test. Maternal iron restriction reduced hemoglobin levels in both strains. TEM revealed enlarged, morphologically heterogeneous mitochondria with reduced and disrupted cristae architecture in ID dams of both strains. Iron restriction reduced succinate-supported respiration and tended to reduce NADH-supported respiration, in both strains. SHR dams exhibited reduced fusion signalling, reflected by a lower L-OPA1:S-OPA1 ratio. MFN1 expression was reduced by ID in both strains, whereas MFN2 expression was lower in SHR and further reduced by ID. In contrast, DRP1 phosphorylation increased selectively in ID-WKY dams. Iron restriction increased LC3-II:I ratio and BNIP3 in SHR, and increased PINK1 in both strains, while Parkin and p62 were unchanged. Antioxidant gene expression increased in ID-SHR but decreased in ID-WKY dams. Despite these alterations, markers of oxidative damage and apoptosis were unchanged by iron restriction. Conclusion: Maternal ID induces marked remodeling of myocardial mitochondrial ultrastructure and selectively constrains iron-dependent respiration in hypertensive pregnancy without overt oxidative damage or apoptosis. These mitochondrial alterations occur alongside previously observed reductions in blood pressure and improved cardiac efficiency, suggesting favorable hemodynamic adaptations may coexist with underlying bioenergetic constraints in the maternal heart. Translational Perspective: Maternal iron deficiency anemia (IDA) may alter the course of hypertensive pregnancy in ways not evident from hemodynamic indices alone. Here, IDA was associated with abnormal myocardial mitochondrial ultrastructure, selective reductions in respiratory capacity and stress response pathways, despite previously observed improvements in blood pressure and cardiac efficiency. These findings suggest that favourable hemodynamic changes may reflect reduced metabolic demand rather than enhanced bioenergetic capacity. If confirmed in human pregnancy, management of ID in women with underlying hypertension may need closer attention to cardiac metabolic health, as cardiovascular adaptions could coexist with myocardial stress and may vary with anemia severity and duration.

Mitochondrial metabolism plays a critical role in determining lifespan across animal taxa. In our study, we used the Western honeybee ( Apis mellifera ) as a model, capitalizing on the stark lifespan difference between queens, which often live more than two years, and summer workers, which survive only about 30 days, despite sharing the same genetic background. We investigated mitochondrial function in head tissue, thoracic muscle, and abdominal fat tissue of queens and workers, comparing early (7 days) and late adult stages (28–30 days in workers; 2 years in queens). No significant differences in mitochondrial flux control ratio for the NADH- Succinate- and glycerophosphate (Gp) pathways were found in thoracic muscles across castes or age groups. In head and abdominal fat tissues, early-life queens showed reduced reliance on NADH-linked pathways for maximal respiratory flux compared to workers. The decrease in the NADH-pathway was compensated by an increase in the Gp-pathway contribution. Queens exhibited reduced phosphorylation-pathway control over OXPHOS compared to workers, both in head tissue during early life and in abdominal fat tissue later in life. These findings reveal caste- and tissue-specific patterns of mitochondrial regulation that may contribute to dramatic lifespan divergence observed in eusocial insects. They suggest that early-life metabolic flexibility could play an important role in shaping life history evolution in Apis mellifera .

Preeclampsia is a serious pregnancy complication and increases the risk of cardiovascular disease in offspring later in life. Cardiac development includes maturation of cardiomyocytes, a process that is intricately dependent on proper mitochondrial function. However, it remains unclear whether preeclampsia impairs mitochondrial function and alters cardiac maturation of fetal hearts during late gestation. Herein we induced selective reduced uterine placental perfusion (sRUPP), as a model of preeclampsia in rats, to investigate fetal cardiac myosin heavy chain (MYH) expression, reactive oxygen species (ROS) production, mitochondrial respiration, mitochondrial content and dynamics in male and female fetuses at gestational day (GD) 20 (term = GD 22). Litter size was reduced, while pup reabsorptions were increased in sRUPP compared to Sham controls. In only the male fetuses of sRUPP dams, cardiac MYH7/MYH6 ratio was reduced and MYH6 expression increased. Complex IV activity was elevated in sRUPP male fetuses, with no changes in mitochondrial citrate synthase or ATP synthase activities in either sex. However, ROS production increased in only sRUPP female fetuses. In male fetal hearts, sRUPP increased fusion protein MFN1 expression, tended to decrease fusion protein OPA1 expression, and decreased fission protein FIS1 expression. In contrast, MFN2 and OPA1 were reduced in sRUPP female fetuses. In conclusion, the sRUPP model of preeclampsia affected cardiac maturation and mitochondrial function in late gestation fetuses in a sex-specific manner. As prenatal strategies are being developed to improve pregnancy outcomes, sex-specific fetal effects should be taken into consideration.

Mitochondria play a key role in aging. Here, we measured integrated mitochondrial functions in experimentally evolved lines of the seed beetle Acanthoscelides obtectus that were selected for early (E) or late (L) reproduction for nearly 4 decades. The 2 lines have markedly different lifespans (8 days and 13 days in the E and L lines, respectively). The contribution of the NADH pathway to maximal flux was lower in the L compared to the E beetles at young stages, associated with increased control by complex I. In contrast, the contribution of the Succinate pathway was higher in the L than in the E line, whereas the Proline pathway showed no differences between the lines. Our data suggest that selection of age at reproduction leads to a modulation of complex I activity in mitochondria and that mitochondria are a functional link between evolutionary and mechanistic theories of aging.

For ectothermic species, adaptation to thermal changes is of critical importance. Mitochondrial oxidative phosphorylation (OXPHOS), which leverages multiple electron pathways to produce energy needed for survival, is among the crucial metabolic processes impacted by temperature. Our aim in this study was to identify how changes in temperature affect the less-studied electron transferring flavoprotein pathway, fed by fatty acid substrates. We used the planarian Dugesia tigrina, acclimated for 4 weeks at 10°C (cold acclimated) or 20°C (normothermic). Respirometry experiments were conducted at an assay temperature of either 10 or 20°C to study specific states of the OXPHOS process using the fatty acid substrates palmitoylcarnitine (long chain), octanoylcarnitine (medium chain) or acetylcarnitine (short chain). Following cold acclimation, octanoylcarnitine exhibited increases in both the OXPHOS and electron transfer (ET, non-coupled) states, indicating that the pathway involved in medium-chain length fatty acids adjusts to cold temperatures. Acetylcarnitine only showed an increase in the OXPHOS state as a result of cold acclimation, but not in the ET state, indicative of a change in phosphorylation system capacity rather than fatty acid β-oxidation. Palmitoylcarnitine oxidation was unaffected. Our results show that cold acclimation in D. tigrina caused a specific adjustment in the capacity to metabolize medium-chain fatty acids rather than an adjustment in the activity of the enzymes carnitine-acylcarnitine translocase, carnitine acyltransferase and carnitine palmitoyltransferase-2. Here, we provide novel evidence of the alterations in fatty acid β-oxidation during cold acclimation in D. tigrina.

Temperature shifts are a major challenge to animals; they drive adaptations in organisms and species, and affect all physiological functions in ectothermic organisms. Understanding the origin and mechanisms of these adaptations is critical for determining whether ectothermic organisms will be able to survive when faced with global climate change. Mitochondrial oxidative phosphorylation is thought to be an important metabolic player in this regard, since the capacity of the mitochondria to produce energy greatly varies according to temperature. However, organism survival and fitness depend not only on how much energy is produced, but, more precisely, on how oxidative phosphorylation is affected and which step of the process dictates thermal sensitivity. These questions need to be addressed from a new perspective involving a complex view of mitochondrial oxidative phosphorylation and its related pathways. In this review, we examine the effect of temperature on the commonly measured pathways, but mainly focus on the potential impact of lesser-studied pathways and related steps, including the electron-transferring flavoprotein pathway, glycerophosphate dehydrogenase, dihydroorotate dehydrogenase, choline dehydrogenase, proline dehydrogenase, and sulfide:quinone oxidoreductase. Our objective is to reveal new avenues of research that can address the impact of temperature on oxidative phosphorylation in all its complexity to better portray the limitations and the potential adaptations of aerobic metabolism.

Introduction: The impact of eccentric exercise on mitochondrial function has only been poorly investigated and remains unclear. This study aimed to identify the changes in skeletal muscle mitochondrial respiration, specifically triggered by a single bout of eccentric treadmill exercise. Methods: Male adult mice were randomly divided into eccentric (ECC; downhill running), concentric (CON; uphill running), and unexercised control groups (n = 5/group). Running groups performed 18 bouts of 5 min at 20 cm·s⁻¹ on an inclined treadmill (±15° to 20°). Mice were sacrificed 48 h after exercise for blood and quadriceps muscles collection. Deep proximal (red) and superficial distal (white) muscle portions were used for high-resolution respirometric measurements. Results: Plasma creatine kinase activity was significantly higher in the ECC compared with CON group, reflecting exercise-induced muscle damage (P < 0.01). The ECC exercise induced a significant decrease in oxidative phosphorylation capacity in both quadriceps femoris parts (P = 0.032 in proximal portion, P = 0.010 in distal portion) in comparison with the CON group. This observation was only made for the nicotinamide adenine dinucleotide (NADH) pathway using pyruvate + malate as substrates. When expressed as a flux control ratio, indicating a change related to mitochondrial quality rather than quantity, this change seemed more prominent in distal compared with proximal portion of quadriceps muscle. No significant difference between groups was found for the NADH pathway with glutamate or glutamate + malate as substrates, for the succinate pathway or for fatty acid oxidation. Conclusions: Our data suggest that ECC exercise specifically affects pyruvate mitochondrial transport and/or oxidation 48 h after exercise, and this alteration mainly concerns the distal white muscle portion. This study provides new perspectives to improve our understanding of the mitochondrial adaptation associated with ECC exercise.

Equine atypical myopathy is a seasonal intoxication of grazing equids. In Europe, this poisoning is associated with the ingestion of toxins contained in the seeds and seedlings of the sycamore maple (Acer pseudoplatanus). The toxins involved in atypical myopathy are known to inhibit ß-oxidation of fatty acids and induce a general decrease in mitochondrial respiration, as determined by high-resolution respirometry applied to muscle samples taken from cases of atypical myopathy. The severe impairment of mitochondrial bioenergetics induced by the toxins may explain the high rate of mortality observed: about 74% of horses with atypical myopathy die, most within the first two days of signs of poisoning. The mechanism of toxicity is not completely elucidated yet. To improve our understanding of the pathological process and to assess therapeutic candidates, we designed in vitro assays using equine skeletal myoblasts cultured from muscle biopsies and subjected to toxins involved in atypical myopathy. We established that equine primary myoblasts do respond to one of the toxins incriminated in the disease.