Biology subjects

Longo, S.

Publications and source records attributed to Longo, S..

3 recordsLinked to original sources

bioRxiv2026

Spinal Noradrenergic Overdrive Promotes Reversible Motor Unit Aging and Sarcopenia

Background Sarcopenia is characterized by progressive loss of skeletal muscle mass, strength, and physical function with aging. Motor unit degeneration is a major contributor, but the mechanisms driving age-related deterioration of motor neurons, neuromuscular junctions (NMJs), and muscle fibers remain incompletely understood. Norepinephrine (NE) regulates spinal motor neuron excitability, but its role in motor unit aging has not been established. Methods Whole-cell patch-clamp electrophysiology, optogenetics, fast-scan cyclic voltammetry, microdialysis, high-performance liquid chromatography, western blotting, and chemogenetics were used in mice aged 1-25 months. Motor neuron intrinsic properties were examined in 135 lumbar motor neurons from 81 mice. NE release dynamics, tissue content, and expression of the NE transporter (NET) and 2A-adrenergic autoreceptor were assessed in adult and aged mice. Descending spinally projecting noradrenergic neurons were selectively inhibited in aged mice using a retrograde chemogenetic approach. Results Aging produced progressive motor neuron hyperexcitability characterized by membrane depolarization, increased input resistance, elevated firing frequency, and altered action potential threshold (all P < 0.005). Optogenetically evoked endogenous NE increased motor neuron excitability by reducing action potential latency (P = 0.0001) and decreasing rheobase (P = 0.0028); these effects were prevented by 1-adrenergic receptor blockade (P = 0.0313). Aging enhanced stimulus-evoked spinal NE release, with greater responses at 20 Hz (P = 0.0223), 30 Hz (P = 0.0022), and 40 Hz (P < 0.0001). NE release elicited by stimulation of locus coeruleus and A5 noradrenergic inputs was also increased in aged mice (P = 0.0349 and P = 0.0016, respectively). Basal extracellular NE concentrations were unchanged, whereas spinal cord NE content increased (P = 0.0403). Aging reduced 2A-adrenergic receptor (P = 0.0009) and NET expression (P = 0.0046). Chemogenetic suppression of descending noradrenergic neurons in aged mice increased hindlimb muscle mass (P = 0.0111-0.0344), muscle fiber cross-sectional area (P = 0.0078-0.0467), NMJ innervation (P = 0.0210), and motor neuron soma size (P = 0.0353). Conclusions Aging promotes spinal noradrenergic overdrive characterized by increased NE storage, enhanced activity-dependent NE release, and impaired autoregulatory control. Excessive noradrenergic signaling contributes to motor neuron hyperexcitability and motor unit deterioration. Suppression of descending noradrenergic activity reverses structural features of motor neuron, NMJ, and skeletal muscle aging, identifying spinal noradrenergic signaling as a potential therapeutic target for sarcopenia.

neuroscience↗

bioRxiv2025

LAM/TREM2+ macrophages release extracellular vesicles and extracellular lipid droplets which modulate the phenotype of recipient macrophages and homeostasis of skeletal muscle cells

The polarization of tissue-resident macrophages is influenced by a variety of signals from the immune system and the local tissue environment, including nutrition. Although it is known that the quality and quantity of ingested lipids have a significant effect on the lipid composition of extracellular vesicles and their fate, it is unknown how the nutritional environment modifies the release and the function of macrophage-derived EVs. In this study, we used a combination of palmitate and oleate (1:2, FFA) to generate lipid-associated TREM2-expressing macrophages (LAM/TREM2+) in vitro. Using various electron microscopy techniques (TEM, SEM, CryoEM) and fluorophores, we found that FFA overload not only induces lipid storage in LAM/TREM2+ macrophages, but also alters their morphology and reduces the diversity and the number of the lipid-derived structures they release. In addition, LAM/TREM2+ macrophages accumulated lipid droplets (LDs) below the plasma membrane and we discovered for the first time that they export and disseminate full LDs into their environment, in addition to extracellular vesicles, by using a cellular pathway associated to CD81. The use of 14C-palmitate confirmed the presence of 14C-triacylglycerols in the large extracellular vesicle pellet. LAM/TREM2+ macrophage-derived EVs induced TREM2 and Il-10 expression in recipient M0 macrophages. These data provide potential insights into how dietary factors and metabolic perturbations can shape the functions of macrophage-derived EVs in the context of metabolic diseases such as diabetes and obesity. In addition, LAM/TREM2+ macrophage-derived EVs modulated insulin-sensitivity, mitochondrial oxidative capacity, lipid profiles and the expressions of genes encoding extracellular matrix components in recipient skeletal muscle cells. Although previously postulated but never demonstrated, these data also highlight the LAM/TREM2+ macrophage-derived EVs as important players in SkM tissue renewal and metabolic homeostasis.

cell biology↗

bioRxiv2023

M1-derived extracellular vesicles polarize recipient macrophages into M2 and alter skeletal muscle homeostasis in a hyper-glucose environment

BackgroundMacrophages release not only cytokines but also extracellular vesicles (EVs). EVs are small lipid-derived vesicles with virus-like properties transferring lipids, RNA and proteins between cells. Until now, the consequences of macrophage plasticity on the release and the composition of EVs have been poorly explored. In this study, we determined the impact of high-glucose (HG) concentrations on macrophage metabolism, and characterized their derived EV subpopulations. Finally, we determined whether HG-treated macrophage-derived EVs participate in immune responses and in metabolic alterations of skeletal muscle cells. MethodsTHP1-macrophages (M0) were treated with 15mM (MG15) or 30mM (MG30) glucose. M1 or M2 canonical markers, pro- and anti-inflammatory cytokines and lactate production were evaluated. Macrophage-derived EVs were characterized by TEM, flow cytometry, and 1H-Nuclear magnetic resonance spectroscopy for lipid composition. M0 macrophages or C2C12 muscle cells were used as recipients of MG15 and MG30-derived EVs. The lipid profiles of recipient cells were determined, as well as protein and mRNA levels of relevant genes for macrophage polarization or muscle metabolism. ResultsM0 released 2 populations of small and large EVs (sEVs, lEVs) with specific lipid profiles. Proportionally to the glucose concentration, glucose-treatment induced glycolysis in M0 macrophages which consequently shifted into a pro-inflammatory M1 phenotype, containing increased triacylglycerol and cholesterol content. Glucose also affected macrophage sphingolipid and phospholipid compositions. The lipid profile differences between sEVs and lEVs were abolished and represented the lipid profile alterations of MG15 and MG30 macrophages. Both sEVs and lEVs from M15 and M30 macrophages polarized M0 into anti-inflammatory M2, with increased contents of triacylglycerol and cholesterol. MG15 lEVs and sEVs induced insulin-induced AKT hyper-phosphorylation and accumulation of triacylglycerol in muscle cells, a state observed in pre-diabetes. Conversely, MG30 lEVs and sEVs induced insulin resistance in myotubes. ConclusionsAs inflammation involves first M1 macrophages, then the activation of M2 macrophages to attenuate inflammation, this study demonstrates that the dialog between macrophages through the EV route is an intrinsic part of the inflammatory response. In a hyperglycemic context, EV macrophages could participate in the development of muscle insulin-resistance and chronic inflammation.

cell biology↗