Biology subjects

Lightfoot, A. P.

Publications and source records attributed to Lightfoot, A. P..

6 recordsLinked to original sources

bioRxiv2026

Many-body quantum percolation sustains ohmic proton flux through the nanoconfined Fo motor

The FoF1-ATP synthase drives cellular bioenergetics by translocating protons across the inner mitochondrial membrane. We recently demonstrated that the lipid cardiolipin acts as a 2D antenna, actively funnelling protons into the nanoconfined Fo motor and enforcing severe "dimensional squeezing". This 1D nanoconfinement forces protons into such close proximity that their hydration shells physically overlap, theoretically generating an infinite classical steric gridlock. Yet, empirical measurements show the Fo motor operates at ~90% efficiency and exhibits barrierless, Ohmic conductance, presenting a biophysical paradox. To resolve this contradiction between classical physics and biological reality, we employed a differentiable inverse-physics framework to blindly deduce the proton wires geometry based solely on macroscopic physiological constraints: ohmic linearity and a 1.7 Deuterium Kinetic Isotope Effect. By substituting classical diffusion frameworks with a Many-Body Overdamped Quantum Langevin Equation (QLE), the optimiser successfully converged. It deduced that physiological flux dictates a steric boundary of 0.137 nm (aligning with the effective crystal radius of oxygen) and a structural confinement scale of 0.974 nm. We demonstrate that when these discovered biological parameters are evaluated under classical, independent-particle assumptions, the 1/r12 steric repulsive forces diverge to infinity, causing a simulation collapse. In contrast, the quantum mechanical nature of the QLE allows protons to exist as spatially spread-out clouds rather than fixed point particles. This enables them to traverse tight steric boundaries via a coordinated chain reaction similar to a frictionless nanoscale Newtons cradle. These findings prove that classical, independent-particle models are incompatible with the spatial confinement of respiratory complexes. We conclude that physiological proton transport through the Fo motor mandates a continuous quantum percolation channel, redefining our theoretical understanding of biological energy transduction. Statement of significanceThe FoF1-ATP synthase sustains cellular life by translocating protons across membranes, driven by its membrane-bound Fo motor. Within this motor, protons navigate a 1-2 nm water wire. Under this extreme biological nanoconfinement, classical physics predicts a structural "traffic jam", i.e., protons should gridlock due to the repulsive overlap of their hydration shells. Yet, the motor operates with highly efficient, ohmic conductance. Using a differentiable inverse-physics framework and the Many-Body Quantum Langevin Equation, we prove classical physics cannot resolve this steric gridlock. Instead, we demonstrate that physiological proton transport inherently mandates many-body quantum percolation. Protons navigate extreme nanoconfinement via spatial quantum delocalisation, establishing that biological energy transduction operates as a nanoscale quantum percolation channel.

biophysics↗

bioRxiv2026

Detrimental effects of advanced glycation end-products (AGEs) on a human neuromuscular junction co-culture model

The neuromuscular junction (NMJ) is a specialised synapse between motor neurons and skeletal muscle, and its progressive deterioration contributes to age-related and metabolic disease-associated declines in muscle function. Advanced glycation end-products (AGEs) accumulate in tissues during ageing, diabetes, and chronic metabolic dysfunction and have been implicated in neuromuscular degeneration, yet their effects on the intact NMJ have not previously been examined in a human model system. This study employed a fully human, serum-free, and neural growth factor-free NMJ co-culture system, combining neural progenitor cells with immortalised human myoblasts derived from an 83-year-old donor, to investigate the effects of AGE exposure on neuromuscular integrity across structural, metabolic, functional, and secretory outcomes. AGE exposure induced significant reductions in motor neuron axonal length, myotube remodelling with centralised nuclear positioning, mitochondrial membrane depolarisation, elevated mitochondrial superoxide production, mitochondrial uncoupling, and reductions in spontaneous contraction intensity and frequency. Neurotrophic and myogenic growth factor signalling was significantly downregulated in AGE-treated co-cultures. These findings identify the NMJ as a sensitive target of glycation stress and establish this fully human co-culture platform as a physiologically relevant model for investigating glycation-related neuromuscular pathology and evaluating candidate therapeutic interventions.

cell biology↗

bioRxiv2024

A combination of major histocompatibility complex (MHC) I overexpression and type I interferon induce mitochondrial dysfunction in human skeletal myoblasts.

The overexpression of major histocompatibility complex (MHC) I on the surface of muscle fibres is a characteristic hallmark of the idiopathic inflammatory myopathies (IIMs), collectively termed myositis. Alongside MHC-I overexpression, sub-types of myositis, display a distinct type I interferon (IFN) signature. This study examined the combinational effects of elevated MHC-I and type I IFNs (IFN/{beta}) on mitochondrial function, as mitochondrial dysfunction is often seen in IIMs. Human skeletal muscle myoblasts were transfected with an MHC-I isoform using the mammalian HLA-A2/Kb vector. Mitochondrial respiration, mitochondrial membrane potential, and reactive oxygen/nitrogen species generation were assessed with or without IFN and IFN{beta}. We show that MHC-I overexpression in human skeletal muscle myoblasts led to decreased basal glycolysis and mitochondrial respiration, cellular spare respiratory capacity, ATP-linked respiration, and an increased proton leak, which were all exaggerated by type I IFNs. Mitochondrial membrane depolarisation was induced by MHC-I overexpression both in absence and presence of type I IFNs. Human myoblasts overexpressing MHC-I showed elevated nitric oxide generation that was abolished when combined with IFN. MHC-I on its own did not result in an increased ROS production, but IFN on their own, or combined with MHC-I overexpression did induce elevated ROS generation. We present new evidence that MHC-I overexpression and type I IFNs aggravate the effects each has on mitochondrial function in human skeletal muscle cells, providing novel insights into their mechanisms of action and suggesting important implications in the further study of myositis pathogenesis.

cell biology↗

bioRxiv2022

Major Histocompatibility Complex (MHC) I-induced Endoplasmic Reticulum (ER) Stress mediates the secretion of pro-inflammatory muscle-derived cytokines

Major histocompatibility complex (MHC) I is an important component of intracellular antigen presentation. However, improper expression of MHC I upon the cell surface has been associated with several autoimmune diseases. Myositis is a rare acquired autoimmune diseases which targets skeletal muscle, and MHC I overexpression on the surface of muscle fibres and immune cell infiltration are clinical hallmarks. MHC I overexpression may have an important pathogenic role, mediated by the activation of the endoplasmic reticulum (ER) stress response. Given the evidence that muscle is a diverse source of cytokines, we aimed to investigate whether MHC I overexpression can modify the profile of muscle-derived cytokines and what role the ER stress pathway may play. Using C2C12 myoblasts we overexpressed MHC I with a H-2kb vector in the presence or absence of salubrinal an ER stress pathway modifying compound. MHC I overexpression induced ER stress pathway activation and elevated cytokine gene expression. MHC I overexpression caused significant release of cytokines and chemokines, which was attenuated in the presence of salubrinal. Conditioned media from MHC I overexpressing cells induced in vitro T-cell chemotaxis, atrophy of healthy myotubes and modified mitochondrial function, features which were attenuated in the presence of salubrinal. Collectively, these data suggest that MHC I overexpression can induce pro-inflammatory cytokine/chemokine release from C2C12 myoblasts, a process which appears to be mediated in-part by the ER stress pathway.

cell biology↗

bioRxiv2020

Eukarion-134 attenuates endoplasmic reticulum stress-induced mitochondrial dysfunction in human skeletal muscle cells

ABSTRACTMaladaptive endoplasmic reticulum (ER) stress is associated with modified reactive oxygen species (ROS) generation, altered mitochondrial bioenergetics, and oxidative damage; and is postulated as a potential mechanism involved in the underlying muscle weakness experienced by patients with myositis, an acquired autoimmune neuromuscular disease. In this study, we investigate the impact of ROS generation in an in vitro model of ER stress in skeletal muscle, using the ER stress inducer tunicamycin (24 hours) in presence or absence of a superoxide dismutase/catalase mimetic Eukarion (EUK)-134. ER stress activation, ROS generation, mitochondrial function, biogenesis, morphology and dynamics (fusion/fission) were examined. Tunicamycin induced maladaptive ER stress, validated by stimulation of GRP94, GRP78, CHOP, XBP-1, ERDJ4, and GADD34, which were mostly mitigated by EUK-134 at transcriptional level. ER stress triggered mitochondrial unfolded protein response and promoted mitochondrial dysfunction, described by substantial loss of mitochondrial membrane potential, as well as reduction of respiratory control ratio, reserve capacity, phosphorylating respiration, and coupling efficiency, which was ameliorated by EUK-134. ROS-mediated biogenesis and fusion of mitochondria was evident in presence of tunicamycin, which however, had high propensity of fragmentation, accompanied by upregulated mRNA levels of fission-related markers. Increased cellular ROS generation oxidative stress was observed in response to ER stress that was ameliorated in the presence of EUK-134, even though no changes in mitochondrial superoxide were noticeable. These findings suggest that targeting ROS generation using the superoxide dismutase/catalase mimetic EUK-134 can amend aspects of ER stress-induced changes in mitochondrial dynamics and function. Overall, this study suggests that in instances of chronic ER stress, such as in myositis, quenching ROS generation may be a promising therapy for muscle weakness and dysfunction.Competing Interest StatementThe authors have declared no competing interest.View Full Text

physiology↗

bioRxiv2018

17-(Allylamino)-17demethoxygeldanamycin reduces Endoplasmic Reticulum (ER) stress-induced mitochondrial dysfunction in C2C12 myotubes

In patients with myositis, persistent skeletal muscle weakness in the absence of significant inflammatory cell infiltrates is a well-recognised, but poorly understood, cause of morbidity. This has led researchers to investigate cellular mechanisms independent of immune cells, which may contribute to this underlying muscle weakness. Chronic ER stress pathway activation is evident in the muscle of myositis patients, and is now a potential mediator of muscle weakness in the absence of inflammation. Abnormal ER stress pathway activation is associated with mitochondrial dysfunction, resulting in bioenergetic deficits and reactive oxygen species (ROS) generation, which in this context may potentially damage muscle proteins and thus impair contractile performance. This study examined whether treatment with the HSP90 inhibitor 17-N-allylamino-17-demethoxygeldanamycin (17AAG) could mitigate these ER stress-induced changes. C2C12 myotubes were treated with the ER stress-inducing compound Tunicamycin, in the presence or absence of 17AAG. Myotubes were examined for changes relating to ER stress pathway activation, mitochondrial function, markers of oxidative damage and in myotubular dimensions. ER stress pathway activation caused mitochondrial dysfunction, as evidenced by reduced oxygen consumption and ATP generation and by increased gene expression levels of the bio-energetic regulator, uncoupling protein 3 (UCP-3), the latter indicative of electron transport chain uncoupling. ER stress pathway activation also caused increased gene expression of superoxide dismutase (SOD) 2 and peroxiredoxin (PRDX) 3, elevated H2O2 levels, and reduced total thiol pool levels and a significant diminution of myotubular dimensions. Exposure to 17AAG ameliorated these ER stress-induced changes. These findings, which suggest that 17AAG can reduce ER stress-induced mitochondrial dysfunction, oxidative damage and myotubular atrophy, have potential implications in the context of human myositis.

cell biology↗