Spinal sympathetic preganglionic neurons (SSPNs) are oxygen sensitive. These spinal oxygen sensors (SOS) increase sympathetic output when subjected to acute hypoxia, orchestrating cardiorespiratory responses to protect against the deleterious effects of oxygen deprivation. Most other oxygen-sensing systems rely on mitochondrial mechanisms to detect and signal decreases in oxygen. Here, we apply pharmacological blockers of the mitochondrial respiratory chain and a mitochondrial-targeted antioxidant to a rat perfused in situ spinal cord preparation to test the role of mitochondria in the SOS. We demonstrate that, unlike other oxygen-sensitive cells, the mitochondrial respiratory chain is not essential for the SOS. Nonetheless, blockade of mitochondrial respiratory complexes augments SSPN activity. These results indicate that mitochondrial reactive oxygen species (ROS) can increase SSPN activity but do not appear to drive the SOS. We propose that, in chronic diseases prone to oxidative stress and/or frequent hypoxic events, SSPN mitochondrial ROS directly contribute to sympathetic overactivity. KEY POINTS: Decreases in oxygen concentration are detected by oxygen-sensitive cells that orchestrate cardiorespiratory and vascular adjustments to avoid oxygen deprivation to vital tissues. Recently discovered spinal oxygen sensors (SOS) increase sympathetic and respiratory activity in response to hypoxia. Unlike other oxygen-sensitive cells, here we report that the SOS do not rely on the mitochondrial electron transport chain for oxygen sensing. Our findings show that pharmacological blockade of mitochondrial respiratory complexes can increase sympathetic activity but does not inhibit the hypoxic response. These results indicate that mitochondrial reactive oxygen species can affect sympathetic activity, but that mitochondria do not appear to play a key role in spinal oxygen sensing.

The intracardiac nervous system is a complex neural network formed by a diffuse plexus, the so-called intracardiac ganglion (ICG). These ganglia locally innervate and control heart function, but little is known about how ICG neuronal activity is regulated. Although various ionic currents have been characterized in cardiac tissue, the expression and role of TWIK-related K+ (TREK) channels in ICG neurons remain unexplored. TREK channels, members of the two-pore domain potassium channel family, are essential regulators of neuronal membrane resting potential and excitability, with recognized neuroprotective functions. In this study, we have characterized different ionic currents present in mouse ICG neurons, including tetrodotoxin-sensitive Na+ currents, delayed K+ rectifiers, Ca+2-dependent K+ currents and A, H and M currents. Notably, we provide the first evidence of functional TREK channel expression in these neurons. Our findings suggest that TREK channels contribute to excitability control and cellular homoeostasis in ICG neurons, highlighting their potential relevance to cardiac physiology and disease. KEY POINTS: This study provides the first evidence of functional TWIK-related K+ (TREK) channel expression in intracardiac ganglion (ICG) neurons. Comprehensive profiling of ionic currents shaping excitability in ICG neurons. Neuroprotective TREK channels might emerge as potential therapeutic targets for cardiac disorders.

Stable breathing depends on the integrated action of central and peripheral chemoreceptors, but the nature of this interaction in humans and its physiological importance remain controversial. Previous studies reported additive, hypo-additive and hyper-additive responses across species, preparations and protocols. Here, we used a novel method to quantify peripheral chemoreflex sensitivity across graded levels of central chemoreceptor activation to test whether central-peripheral chemoreceptor interaction in awake humans is fixed or state dependent. At low altitude, the form of interaction varied across individuals, with most showing additive responses (12/17) and a substantial subset showing hypo-additivity (5/17). After 7-10 days of acclimatization to 3500 m, all five hypo-additive individuals became additive, and four additive participants became hyper-additive. This shift in interaction towards hyper-additivity provides the first evidence that central-peripheral chemoreceptor integration is plastic. Plasticity during wakefulness was not associated with individual differences in central sleep apnoea severity at high altitude. Thus, our findings confirm that central-peripheral chemoreceptor interaction differs among individuals and suggest that the form of interaction can be reshaped by hypobaric hypoxic stress. KEY POINTS: How central and peripheral chemoreceptor drives to breathe interact in humans and whether this process is plastic remains uncertain. We quantified peripheral chemoreflex sensitivity to hypoxia (PChS) across graded levels of central chemoreceptor activation at low altitude and after 7-10 days of high-altitude exposure (3500 m). Seventeen participants performed repeated modified rebreathing tests with end-tidal P O 2 fixed at 150 (hyperoxia), 60 and 45 mmHg (hypoxia). PChS was computed at 1 mmHg intervals of end-tidal P C O 2 ( P ETC O 2 ) from linear regression of the difference in ventilation between hypoxic and hyperoxic conditions vs. calculated arterial oxygen saturation (ScO2) (L·min-1·mmHg-1·%ScO2 -1). At low altitude, PChS increased with P ETC O 2 in all individuals; the relationship was linear (no interaction) in 12 participants, and 5 showed hypo-additivity. After acclimatization, central and peripheral chemoreflex sensitivities increased. All hypo-additive individuals became additive; four additive individuals became hyper-additive. Central-peripheral chemoreceptor interaction is plastic in humans and can shift towards hyper-additivity with sustained hypobaric hypoxia.

Despite significant advances in early detection and therapeutic opportunities, cancer remains a critical global health challenge. The greatest barrier to reducing cancer-associated mortality is the persistent problem of therapeutic resistance and metastasis. Standard treatment approaches, including surgery combined with chemotherapy and radiation, are effective for many patients with localised disease. However, a substantial proportion of patients will experience recurrence and therapy resistance, leading to treatment failure and poor outcomes. This adverse prognosis for patients highlights the critical need to identify new therapeutic targets capable of improving long-term survival. The ion transportome comprises ion channels, solute transporters and pumps that regulate controlled movement of sodium (Na[+]), potassium (K[+]), calcium (Ca[2+]), chloride (Cl[-]) and hydrogen (H[+]) across cell membranes. Ion transport is central to many cellular processes, including cell growth, volume regulation, proliferation and migration. In many solid tumours, the finely tuned ionic balance becomes dysregulated, with aberrant expression or activity of membrane transport proteins being closely linked to many of the hallmarks of cancer. Ion channel modulation using pharmacological agents designed to treat channelopathies has demonstrated promise in suppressing cancer progression in preclinical models. Thus, targeting ion-driven vulnerabilities within solid tumours may complement existing therapies to overcome resistance and improve patient outcomes. The dynamic nature of ion transport mechanisms means that addressing critical research questions regarding their suitability as pharmacological targets is challenging, highlighting the need to develop innovative approaches to study these processes in oncology.

Cardiac re-entrant arrhythmias are a major cause of sudden cardiac death. Optogenetic defibrillation has emerged as a promising anti-arrhythmic strategy based on photoactivation of channelrhodopsins, yet the efficacy and potential adverse consequences of activating different classes of light-gated ion channels have not been systematically evaluated. Previous studies assessed either cation (e.g. ChR2) or anion (e.g. GtACR1) non-selective channels, both of which depolarize resting cardiomyocytes. Recently identified light-gated K[+] channels (e.g. WiChR) suppress cardiomyocyte activity while maintaining the membrane potential near its resting state, but their defibrillation potential remains unexplored. We used computational simulations to compare ChR2, GtACR1 and WiChR. Single-cell simulations showed that ChR2 and GtACR1 markedly increased diastolic intracellular Ca[2+] (by 42.6% and 52.6%, respectively), whereas WiChR induced only minimal changes (by 4.0%), suggesting lower pro-arrhythmogenic risk. WiChR, however, slightly increased intracellular Na[+] (by 15.1% vs. 0.1% and 3.4% for ChR2 and GtACR1), consistent with the residual Na[+] permeability of currently available K[+]-conducting channelrhodopsins. Simulations in human ventricles and atria showed that GtACR1 most effectively terminated re-entrant arrhythmias at low light intensities, whereas WiChR achieved comparable efficacy at ≥5 mW/mm[2]. Complementary tissue-scale simulations revealed that defibrillation occurs through depolarization within the excitable gap followed by fast Na[+] channel inactivation (ChR2 and partly GtACR1), or through reduced membrane resistance at sufficiently high light intensities (large-conductance channels GtACR1 and WiChR). Overall, we demonstrate that channelrhodopsin ion selectivity is a key determinant of both optogenetic defibrillation efficacy and its underlying mechanisms. TRANSLATIONAL PERSPECTIVE: Re-entrant arrhythmias are a leading cause of sudden cardiac death. Standard therapies, including the activation of implantable cardioverter-defibrillators, carry burdens such as pain and myocardial injury. Optogenetic defibrillation has been suggested as a potentially gentler alternative, replacing high-voltage electrical shocks by photoactivation of light-gated ion channels expressed in cardiac cells. Determining which light-gated ion channel optimally balances efficacy and adverse effects on cardiac electrophysiology is critical for clinical translation. We addressed this question using computational simulations and validation experiments in zebrafish hearts. We identify ion selectivity as a key determinant of both the success rate for arrhythmia termination and the underlying mechanisms: non-selective cation- and anion-conducting channels terminate re-entry efficiently while promoting intracellular Ca[2+] accumulation, a plausible substrate for pro-arrhythmic side effects that could undermine therapeutic safety. K[+]-conducting channels largely avoid this pro-arrhythmic risk by holding cardiomyocytes near their resting potential, albeit at the cost of requiring transmural illumination, while also causing mild Na[+] accumulation attributable to residual Na[+] permeability. Together, these trade-offs define clear clinical implications: K[+]-conducting channels may provide the safest option for optogenetic defibrillation, particularly once variants with further enhanced K[+] selectivity and red-shifted activation spectra for improved operation within blood-perfused myocardium become available. KEY POINTS: We use computational simulations to compare cation non-selective (ChR2), anion non-selective (GtACR1) and K[+]-selective (WiChR) channelrhodopsins for optogenetic termination of re-entrant arrhythmia. Single-cardiomyocyte simulations suggest that ChR2 and GtACR1 activation can cause progressive accumulation of intracellular Ca[2+], which is minimized when using WiChR. Intracellular microelectrode recordings from hearts of transgenic adult zebrafish validate the simulated voltage dynamics seen with ChR2, GtACR1 or WiChR activation. Simulations of human left ventricles and atria indicate that GtACR1 is most effective in terminating re-entrant arrhythmia at low light intensities, whereas WiChR becomes similarly effective at higher intensities. Tissue-scale simulations indicate distinct defibrillation mechanisms: excitable gap extinction by de novo action potential initiation followed by inactivation of fast Na[+] channels for depolarizing channelrhodopsins (ChR2, GtACR1), and reduction in membrane resistance for the large-conductance channels (GtACR1, WiChR), effectively clamping the membrane potential at each channel's reversal potential at high light levels.

Nearly 100 years ago, Otto Warburg observed that cancer cells preferentially use glycolysis even in the presence of oxygen, supporting rapid cell growth. Since then, the concept of the Warburg effect has expanded far beyond tumour bioenergetics and is now recognised as a key feature of immune cell activation. A notable example is in macrophages, which, following pro-inflammatory stimulation, undergo Warburg-like metabolic reprogramming, characterised by increased glycolysis. Recent studies have shown that accumulated metabolites such as lactate have a range of immunoregulatory functions that shape macrophage inflammatory responses. In addition, glycolytic enzymes have been found to exert non-canonical functions that directly regulate macrophage immune signalling. Mitochondria, once considered suppressed during Warburg reprogramming, also undergo profound changes, with the electron transport chain generating reactive oxygen species and metabolites such as succinate, fumarate and itaconate playing complex immunoregulatory roles, and mitochondrial dynamics actively shaping metabolism and immune responses. Together, these findings redefine the Warburg effect in macrophages as a coordinated metabolic and signalling process that integrates glycolysis, mitochondrial function and immunometabolite signalling to optimise context-dependent immune responses.

Preterm birth is a leading cause of neonatal morbidity and mortality worldwide, with ascending infection and inflammation at the fetal-maternal interface recognized as major contributors to its pathophysiology. Gardnerella spp., key species associated with bacterial vaginosis, have been implicated in adverse pregnancy outcomes; however, the mechanisms underlying their ability to ascend and trigger inflammatory responses remain poorly understood. In this study, we used a fetal-maternal interface organ-on-chip model to investigate the ascending infection of Gardnerella spp. and the resulting compartmentalized cytokine response. The device integrated decidual, chorionic trophoblast, amniotic mesenchymal and amniotic epithelial cells to mimic the in vivo architecture of the fetal membranes. Quantitative PCR revealed progressive bacterial ascension, with a significantly higher load of Gardnerella spp. in the amnion mesenchymal layer after 48 h of stimulation. Cytokine analysis demonstrated increased production of interleukin (IL)-1β, IL-6, C-X-C motif chemokine ligand 8 and IL-10 across cellular compartments, indicating a coordinated pro-inflammatory and compensatory anti-inflammatory response. These findings provide direct evidence of Gardnerella spp. invasion dynamics and immune activation at the fetal-maternal interface, supporting the use of microphysiological systems as translational tools to study infection-driven mechanisms of spontaneous preterm birth. KEY POINTS: Gardnerella spp. ascend rapidly across the fetal-maternal interface. Ascending infection induces compartmentalized inflammatory cytokine responses. Amnion mesenchymal cells exhibited the highest bacterial burden after 48 h. The fetal-maternal interface organ-on-chip provides a translational model for studying infection-driven preterm birth.

Stereotactic arrhythmia radioablation (STAR) has emerged as a promising non-invasive therapy for refractory ventricular tachycardia, yet its biological mechanisms remain poorly defined. While conventional catheter ablation achieves arrhythmia control through structural remodelling, radiotherapy was initially assumed to act similarly. However, STAR reduces ventricular arrhythmia burden within weeks, preceding the development of radiation-induced structural remodelling. This temporal mismatch indicates that early anti-arrhythmic effects are probably driven by functional adaptations. Human tissue findings and preclinical large- and small-animal models have provided the first insights into how the myocardium responds to focal high-dose radiation, yet experimental data on STAR's underlying cellular mechanisms remain limited. Across these studies, a consistent observation is the temporal dissociation between early functional effects and delayed structural remodelling, which provides a key framework for interpretating STAR's anti-arrhythmic action. In this review, we synthesize current evidence on cell-type-specific responses to ionizing radiation by integrating insights from the emerging STAR literature, oncology and radiation heart disease models. By linking time-resolved cellular responses to clinical observations, we aim to distinguish mechanisms most relevant to early therapeutic effects from those contributing to delayed remodelling, and to define key knowledge gaps for guiding safe and effective clinical implementation.

Oestradiol (E2) and progesterone (P4) fluctuate across the menstrual cycle and potentially influence motor function, which can be estimated from motor unit discharge patterns. To address the methodological limitations of prior menstrual cycle research, we established the motor units and sex hormones (MUSH) collaboration. This multisite investigation aimed to move beyond characterization of motor unit firing across the menstrual cycle and determine whether fluctuations in E2 and P4 influence motor unit activity. We hypothesized that discharge rates and persistent inward current (PIC)-related contributions to discharge would be greatest during the late follicular (LF) phase, when E2 concentrations were highest. Fifty women completed a comprehensive protocol involving menstrual cycle and ovulation tracking, serum hormone measurement and high-density surface electromyographic recordings from the tibialis anterior during isometric contractions to quantify motor unit activity in the early follicular, LF and mid-luteal phases. After 10 women with atypical hormone concentration profiles or insufficient motor unit yield were excluded, 40 remained for analysis. There were significant changes in several motor unit discharge variables between menstrual cycle phases and significant associations with hormone concentrations. Increased E2 was associated with higher peak discharge rates and ascending discharge rate non-linearity, whereas increased P4 was associated with higher peak discharge rates, more discharge rate hysteresis and ascending discharge rate non-linearity. Despite reaching statistical significance, the magnitudes of these effects (i.e. effect sizes) were small. Overall, these findings indicate that fluctuations in sex hormones influence motor unit behaviour, but the effects are subtle, highlighting the need for well-powered and methodologically rigorous menstrual cycle research. KEY POINTS: There are small but detectable differences in motor unit discharge rates between menstrual cycle phases, which are predicted by within-participant fluctuations in oestradiol (E2) and progesterone (P4). Discharge rate patterns that provide estimates of neuromodulatory and inhibitory input suggest that E2 and P4 can influence spinal cord circuitry differently than has previously been documented in the brain, highlighting an understudied aspect of female neurophysiology. Variability in menstrual cycles and associate hormones makes large-scale, rigorous studies especially valuable in female neuromuscular research.

The dynamics of calcium ions (Ca 2 +) in skeletal muscles link electrochemical activation and contractile force generation. Recent experimental data suggest that store-operated Ca 2 + entry (SOCE), the process of extracellular Ca 2 + influx upon the depletion of Ca 2 + from the sarcoplasmic reticulum (SR), helps delay the onset of muscle fatigue during exercise. We hypothesize that SOCE regulates force generation during prolonged muscle activity by allowing for sustained Ca 2 + release from the SR. We test this hypothesis with a quantitative biophysical model that simulates the biochemical events of muscle contraction, from depolarization at the T-tubules to Ca 2 + release from the SR to Ca 2 + binding and force generation throughout the myoplasm. We also consider the balance between Ca 2 + removal from the myoplasm and SOCE through the T-tubule membrane, along with mitochondrial uptake of free Ca 2 + and phosphate. We use the model to test the effects of SOCE inhibition on force production. The magnitude of myoplasmic Ca 2 + and force is lower in SOCE knockout cells, especially when SOCE reduction is combined with impaired uptake of phosphate by mitochondria. We then test the effects of SOCE during resistance exercise or high-intensity interval training. These simulations predict a context-dependent relationship between force generation and SOCE - increased SOCE is associated with greater force production during resistance exercise but worsens the effects of fatigue in certain cases of high-intensity training. Such SOCE-induced fatigue is attributed to phosphate accumulation in the myoplasm and can be mitigated by increased rates of mitochondrial phosphate uptake. KEY POINTS: Store-operated calcium entry (SOCE) provides a mechanism for calcium ion (Ca 2 +) influx following the depletion of Ca 2 + from intracellular stores such as the sarcoplasmic reticulum (SR). Recent experiments suggest that SOCE is an important modulator of contractile force generation in skeletal muscle. Here we develop a computational model of Ca 2 + handling in the myoplasm, SR, and mitochondria and the resulting effects on force generation in skeletal muscle fibres to examine the role of SOCE during extended periods of activity. Our model predicts that increasing SOCE leads to enhanced force over periods of repeated stimuli during resistance exercise due to sustained Ca 2 + release. Our simulations show a complex relationship between SOCE and force production during high-intensity interval training, with exacerbated phosphate accumulation in the myoplasm leading to force reduction for very high levels of SOCE. This effect can be mitigated by enhanced mitochondrial phosphate uptake.

Friedreich's ataxia (FA) is an inherited disorder caused by reduced expression of the mitochondrial protein frataxin (FXN). Although defined as a neurodegenerative disease, cardiomyopathy is the leading cause of mortality. Cardiac manifestations of FA span from concentric hypertrophic cardiomyopathy with preserved systolic function and impaired diastolic relaxation, resembling heart failure with preserved ejection fraction (HFpEF), to systolic heart failure with reduced ejection fraction (HFrEF). The molecular mechanisms driving progression towards these cardiac phenotypes remain poorly understood. We examined mitochondrial content, dynamics and mitophagy in two FA mouse models: cardiac/skeletal muscle-specific MCK-Cre FXN knockout (FXN-cKO) mice, which develop HFrEF, and inducible FXN knockdown (FXNKD) mice, which develop HFpEF-like cardiomyopathy. FXN-cKO hearts exhibited increased mitochondrial transcription factor A expression, an elevated mitochondrial-to-nuclear DNA ratio and greater mitochondrial density by electron microscopy, consistent with enhanced mitochondrial biogenesis. In contrast, FXNKD hearts showed no changes in mitochondrial content or biogenesis markers. Mitochondrial dynamics were markedly altered in FXN-cKO hearts, with reduced mitofusin-2 and increased FIS1 expression, accompanied by smaller, fragmented mitochondria. FXNKD hearts exhibited preserved fission, modestly increased fusion and mild mitochondrial enlargement. Markers of mitophagy were increased in FXN-cKO hearts, but a reduced LC3-II/I ratio suggested impaired autophagosome maturation and defective mitochondrial clearance. No changes in mitophagy were observed in FXNKD hearts. These findings demonstrate that FA-associated HFrEF is characterized by increased mitochondrial biogenesis coupled with impaired mitochondrial quality control and fragmentation, whereas FA-associated HFpEF-like phenotype shows preserved mitochondrial architecture and turnover. Mitochondrial remodelling programmes may underlie divergent cardiac phenotypes in FA and represent therapeutic targets for disease modification. KEY POINTS: Friedreich's ataxia (FA) cardiomyopathy develops as heart failure with reduced ejection fraction (HFrEF) or heart failure with preserved ejection fraction (HFpEF)-like disease, but mechanisms leading to different cardiac phenotypes are unclear. We compared mitochondrial remodelling in FA mouse models with divergent cardiac phenotypes. Frataxin knockout (FXN-cKO) mice with HFrEF phenotype showed increased mitochondrial biogenesis, fragmentation and impaired mitochondrial quality control. FXN knockdown (FXNKD) mice with HFpEF-like phenotype showed largely preserved mitochondrial structure and turnover. Distinct mitochondrial adaptations may drive phenotype-specific cardiac outcomes in FA.