RNA sequencing on muscle biopsy from a 5-week bed rest study reveals the effect of exercise and potential interactions with dorsal root ganglion neurons

Sedentary lifestyle, chronic disease, or microgravity can cause muscle deconditioning that then has an impact on other physiological systems. An example is the nervous system, which is adversely affected by decreased physical activity resulting in increased incidence of neurological problems such as chronic pain. We sought to better understand how this might occur by conducting RNA sequencing experiments on muscle biopsies from human volunteers in a 5-week bed-rest study with an exercise intervention arm. We also used a computational method for examining ligand-receptor interactions between muscle and human dorsal root ganglion (DRG) neurons, the latter of which play a key role in nociception and are generators of signals responsible for chronic pain. We identified 1352 differentially expressed genes (DEGs) in bed rest subjects without an exercise intervention but only 132 DEGs in subjects with the intervention. Among 591 upregulated muscle genes in the no intervention arm, 26 of these were ligands that have receptors that are expressed by human DRG neurons. We detected a specific splice variant of one of these ligands, placental growth factor (PGF), in deconditioned muscle that binds to neuropilin 1, a receptor that is highly expressed in DRG neurons and known to promote neuropathic pain. We conclude that exercise intervention protects muscle from deconditioning transcriptomic changes, and prevents changes in the expression of ligands that might sensitize DRG neurons, or act on other cell types throughout the body. Our work creates a set of actionable hypotheses to better understand how deconditioned muscle may influence the function of sensory neurons that innervate the entire body.

Neurobiology of SARS-CoV-2 interactions with the peripheral nervous system: implications for COVID-19 and pain

SARS-CoV-2 is a novel coronavirus that infects cells through the angiotensin-converting enzyme 2 receptor, aided by proteases that prime the spike protein of the virus to enhance cellular entry. Neuropilin 1 and 2 (NRP1 and NRP2) act as additional viral entry factors. SARS-CoV-2 infection causes COVID-19 disease. There is now strong evidence for neurological impacts of COVID-19, with pain as an important symptom, both in the acute phase of the disease and at later stages that are colloquially referred to as "long COVID." In this narrative review, we discuss how COVID-19 may interact with the peripheral nervous system to cause pain in the early and late stages of the disease. We begin with a review of the state of the science on how viruses cause pain through direct and indirect interactions with nociceptors. We then cover what we currently know about how the unique cytokine profiles of moderate and severe COVID-19 may drive plasticity in nociceptors to promote pain and worsen existing pain states. Finally, we review evidence for direct infection of nociceptors by SARS-CoV-2 and the implications of this potential neurotropism. The state of the science points to multiple potential mechanisms through which COVID-19 could induce changes in nociceptor excitability that would be expected to promote pain, induce neuropathies, and worsen existing pain states.

A pharmacological interactome between COVID-19 patient samples and human sensory neurons reveals potential drivers of neurogenic pulmonary dysfunction

The SARS-CoV-2 virus infects cells of the airway and lungs in humans causing the disease COVID-19. This disease is characterized by cough, shortness of breath, and in severe cases causes pneumonia and acute respiratory distress syndrome (ARDS) which can be fatal. Bronchial alveolar lavage fluid (BALF) and plasma from mild and severe cases of COVID-19 have been profiled using protein measurements and bulk and single cell RNA sequencing. Onset of pneumonia and ARDS can be rapid in COVID-19, suggesting a potential neuronal involvement in pathology and mortality. We hypothesized that SARS-CoV-2 infection drives changes in immune cell-derived factors that then interact with receptors expressed by the sensory neuronal innervation of the lung to further promote important aspects of disease severity, including ARDS. We sought to quantify how immune cells might interact with sensory innervation of the lung in COVID-19 using published data from patients, existing RNA sequencing datasets from human dorsal root ganglion neurons and other sources, and a genome-wide ligand-receptor pair database curated for pharmacological interactions relevant for neuro-immune interactions. Our findings reveal a landscape of ligand-receptor interactions in the lung caused by SARS-CoV-2 viral infection and point to potential interventions to reduce the burden of neurogenic inflammation in COVID-19 pulmonary disease. In particular, our work highlights opportunities for clinical trials with existing or under development rheumatoid arthritis and other (e.g. CCL2, CCR5 or EGFR inhibitors) drugs to treat high risk or severe COVID-19 cases.

In vitro cytotoxicity of montelukast in HAPI and SH-SY5Y cells

Montelukast is a cysteinyl leukotriene (CysLT) receptor antagonist with efficacy against a variety of diseases, including asthma and inflammation-related conditions. However, various neuropsychiatric events (NEs) suspected to be related to montelukast have been reported recently, with limited understanding on their association and underlying mechanisms. This study aimed to investigate whether montelukast can induce neuroinflammation and neurotoxicity in microglial HAPI cells and neural SH-SY5Y cells. The present study also compared the effects of montelukast with a 5-lipoxygenase inhibitor (zileuton) and a cyclooxygenase-2 inhibitor (celecoxib) to better understand modulation of related pathways. HAPI or SH-SY5Y cells were treated with the indicated drugs (3.125 μM-100 μM) for 24 h to investigate drug-induced neuroinflammation and neurotoxicity. Montelukast induced cytotoxicity in HAPI cells (50-100 μM), accompanied with caspase-3/7 activation, prostaglandin E₂ (PGE₂) release, and reactive oxygen species (ROS) production. Whilst both montelukast and zileuton down-regulated CysLT release in HAPI cells, zileuton did not significantly affect cell viability or inflammatory and oxidative factors. Celecoxib decreased HAPI cell viability (6.25-100 μM), accompanied with increasing caspase-3/7 activation and ROS production, but in contrast to montelukast increased CysLT release and decreased PGE₂ production. Similar to observations in HAPI cells, both montelukast and celecoxib (50-100 μM) but not zileuton produced toxicity in SH-SY5Y neuroblastoma cells. Similarly, CM from HAPI cells treated with either montelukast or zileuton produced toxicity in SH-SY5Y cells. The results of the current study show the capability of montelukast to directly induce toxicity and inflammation in HAPI cells, possibly through the involvement of PGE₂ and ROS, and toxicity in undifferentiated SH-SY5Y neuroblastoma cells. The current study highlights the importance of consideration between benefit and risk of montelukast usage and provides references for future investigation on decreasing montelukast-related NEs.

A pharmacological interactome between COVID-19 patient samples and human sensory neurons reveals potential drivers of neurogenic pulmonary dysfunction

The SARS-CoV-2 virus infects cells of the airway and lungs in humans causing the disease COVID-19. This disease is characterized by cough, shortness of breath, and in severe cases causes pneumonia and acute respiratory distress syndrome (ARDS) which can be fatal. Bronchial alveolar lavage fluid (BALF) and plasma from mild and severe cases of COVID-19 have been profiled using protein measurements and bulk and single cell RNA sequencing. Onset of pneumonia and ARDS can be rapid in COVID-19, suggesting a potential neuronal involvement in pathology and mortality. We sought to quantify how immune cells might interact with sensory innervation of the lung in COVID-19 using published data from patients, existing RNA sequencing datasets from human dorsal root ganglion neurons and other sources, and a genome-wide ligand-receptor pair database curated for pharmacological interactions relevant for neuro-immune interactions. Our findings reveal a landscape of ligand-receptor interactions in the lung caused by SARS-CoV-2 viral infection and point to potential interventions to reduce the burden of neurogenic inflammation in COVID-19 disease. In particular, our work highlights opportunities for clinical trials with existing or under development rheumatoid arthritis and other (e.g. CCL2, CCR5 or EGFR inhibitors) drugs to treat high risk or severe COVID-19 cases.

Enhanced availability of serotonin increases activation of unfatigued muscle but exacerbates central fatigue during prolonged sustained contractions

KEY POINTS

Animal preparations have revealed that moderate synaptic release of serotonin (5-HT) onto motoneurones enhances motor activity via activation of 5-HT2 receptors, whereas intense release of 5-HT causes spillover of 5-HT to extrasynaptic 5-HT1A receptors on the axon initial segment to reduce motoneurone activity. We explored if increasing extracellular concentrations of endogenously released 5-HT (via the selective serotonin reuptake inhibitor paroxetine) influences the ability to perform unfatigued and fatigued maximal voluntary contractions in humans. Following the ingestion of paroxetine, voluntary muscle activation and torque generation increased during brief unfatigued maximal contractions. In contrast, the ability to generate maximal torque with increased 5-HT availability was compromised under fatigued conditions, which was consistent with paroxetine-induced reductions in motoneurone excitability and voluntary muscle activation. This is the first in vivo human study to provide evidence that 5-HT released onto the motoneurones could play a role in central fatigue.

ABSTRACT

Brief stimulation of the raphe-spinal pathway in the turtle spinal cord releases serotonin (5-HT) onto motoneurones to enhance excitability. However, intense release of 5-HT via prolonged stimulation results in 5-HT spillover to the motoneurone axon initial segment to activate inhibitory 5-HT1A receptors, thus providing a potential spinal mechanism for exercise-induced central fatigue. We examined how increased extracellular concentrations of 5-HT affect the ability to perform brief, as well as sustained, maximal voluntary contractions (MVCs) in humans. Paroxetine was used to enhance 5-HT concentrations by reuptake inhibition, and three studies were performed. Study 1 (n = 14) revealed that 5-HT reuptake inhibition caused an ∼4% increase in elbow flexion MVC. However, when maximal contractions were sustained, time-to-task failure was reduced and self-perceived fatigue was higher with enhanced availability of 5-HT. Study 2 (n = 11) used twitch interpolation to reveal that 5-HT-based changes in motor performance had a neural basis. Enhanced 5-HT availability increased voluntary activation for the unfatigued biceps brachii and decreased voluntary activation of the biceps brachii by 2-5% following repeated maximal elbow flexions. The final study (n = 8) investigated whether altered motoneurone excitability may contribute to 5-HT changes in voluntary activation. F-waves of the abductor digiti minimi (ADM) were unaffected by paroxetine for unfatigued muscle and marginally affected following a brief 2-s MVC. However, F-wave area and persistence were significantly decreased following a prolonged 60-s MVC of the ADM. Overall, high serotonergic drive provides a spinal mechanism by which higher concentrations of 5-HT may contribute to central fatigue.

Folic acid supplementation improves vascular endothelial function, yet not skin blood flow during exercise in the heat, in patients with heart failure

Heart failure (HF) patients are susceptible to heat strain during exercise, secondary to blunted skin blood flow (SkBF) responses, which may be explained by impaired nitric oxide (NO)-dependent vasodilation. Folic acid improves vascular endothelial function and SkBF through NO-dependent mechanisms in healthy older individuals and patients with cardiovascular disease. We examined the effect of folic acid supplementation (5 mg/day for 6 wk) on vascular function [brachial artery flow-mediated dilation (FMD)] and SkBF responses [cutaneous vascular conductance (CVC)] during 60 min of exercise at a fixed metabolic heat production (300 Ẇ_Hprod) in a 30°C environment in 10 patients with HF (New York Heart Association Class I-II) and 10 healthy controls (CON). Serum folic acid concentration increased in HF [preintervention (pre): 1.4 ± 0.2; postintervention (post): 8.9 ± 6.7 ng/ml, P = 0.01] and CON (pre: 1.3 ± 0.6; post: 5.2 ± 4.9 ng/ml, P = 0.03). FMD improved by 2.1 ± 1.3% in HF ( P < 0.01), but no change was observed in CON postintervention ( P = 0.20). During exercise, the external workload performed on the cycle ergometer to attain the fixed level of heat production for exercise was similar between groups (HF: 60 ± 13; CON: 65 ± 20 external workload, P = 0.52). Increases in CVC during exercise were similar in HF (pre: 0.89 ± 0.43; post: 0.83 ± 0.45 au/mmHg, P = 0.80) and CON (pre: 2.01 ± 0.79; post: 2.03 ± 0.72 au/mmHg, P = 0.73), although the values were consistently lower in HF for both pre- and postintervention measurement intervals ( P < 0.05). These findings demonstrate that folic acid improves vascular endothelial function in patients with HF but does not enhance SkBF during exercise at a fixed metabolic heat production in a warm environment.

Paradoxical effects of the autophagy inhibitor 3-methyladenine on docetaxel-induced toxicity in PC-3 and LNCaP prostate cancer cells

Docetaxel was the first chemotherapeutic agent to increase survival time in patients with androgen-resistant prostate cancer. However, it provides only a modest increase in survival and is associated with significant toxicity. Therefore, there is an urgent need to identify potential adjunct therapies. Given the key role of autophagy in both tumour survival and chemoresistance, the impact of autophagy modulation on docetaxel toxicity was tested in vitro. PC-3 and LNCaP cells were pre-treated with the autophagy inhibitor 3-methyladenine (5 mM) and then exposed to various concentrations (0-100 μM) of docetaxel. Cytoxic effects of docetaxel were measured using resazurin reduction to resorufin, whilst autophagy and apoptosis was measured using monodansylcadaverine, annexin V and caspase-3, respectively. Docetaxel produced significant toxicity in PC-3 cells but was not toxic to LNCaP cells. Pre-treatment with the autophagy inhibitor, 3-methyladenine (5 mM) significantly protected PC-3 cells against docetaxel-induced cytotoxicity, increased autophagosome formation and apoptosis measured using monodansylcadaverine, annexin V and caspase-3 fluorescence, respectively. In contrast, 3-methyladenine was toxic by itself in LNCaP cells and also increased autophagic vesicle formation and apoptosis but did not influence docetaxel toxicity in these cells. These paradoxical effects of 3-methyladenine were largely independent of reactive oxygen species production. We show here that modulation of autophagy may influence docetaxel-induced toxicity in prostate cancer cells and these effects may differ between cell lines.

Molecular mechanisms underlying the effects of statins in the central nervous system

3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, commonly referred to as statins, are widely used in the treatment of dyslipidaemia, in addition to providing primary and secondary prevention against cardiovascular disease and stroke. Statins’ effects on the central nervous system (CNS), particularly on cognition and neurological disorders such as stroke and multiple sclerosis, have received increasing attention in recent years, both within the scientific community and in the media. Current understanding of statins’ effects is limited by a lack of mechanism-based studies, as well as the assumption that all statins have the same pharmacological effect in the central nervous system. This review aims to provide an updated discussion on the molecular mechanisms contributing to statins’ possible effects on cognitive function, neurodegenerative disease, and various neurological disorders such as stroke, epilepsy, depression and CNS cancers. Additionally, the pharmacokinetic differences between statins and how these may result in statin-specific neurological effects are also discussed.

ERK1/2 activation modulates pyocyanin-induced toxicity in A549 respiratory epithelial cells

Pyocyanin (PCN), a virulence factor produced by Pseudomonas aeruginosa, has many damaging effects on mammalian cells. Several lines of evidence suggest that this damage is primarily mediated by its ability to generate oxidative stress. However mechanisms underlying PCN-induced oxidative injury remain unclear. Although oxidative stress and subsequent MAPK signaling has been shown to modulate cell death in other models, its role in PCN-induced cytotoxicity remains unknown. Therefore the aim of this study was to investigate the role of redox-sensitive MAPK in PCN-induced toxicity in A549 cells. Here we show that PCN (50μM) rapidly increased ERK1/2 phosphorylation after 5min. Pre-treatment of A549 cells with the MEK1/2 inhibitor U0126 (10μM) decreased PCN-induced ERK1/2 phosphorylation and protected cells against apoptosis and cell injury suggesting a role for ERK signalling. In contrast, JNK and p38 MAPK phosphorylation remained unchanged following exposure to PCN and pretreatment with either the JNK or p38 MAPK inhibitors (10μM SP600125 and 10μM SB203580, respectively) did not afford protection against PCN toxicity. This would suggest that PCN-induced cytotoxicity appears to occur independently of JNK and p38 MAPK signaling pathways. Finally, although we confirm that oxidative stress contributes to PCN-induced toxicity, our data suggest the contribution of oxidative stress is independent of ERK1/2 signaling. These findings may provide insight for novel targeted therapies to reduce PCN-mediated lung injury in patients with chronic P. aeruginosa respiratory infections.

Paradoxical Role of 3-Methyladenine in Pyocyanin-Induced Toxicity in 1321N1 Astrocytoma and SH-SY5Y Neuroblastoma Cells

The role of autophagy in pyocyanin (PCN)-induced toxicity in the central nervous system (CNS) remains unclear, with only evidence from our group identifying it as a mechanism underlying toxicity in 1321N1 astrocytoma cells. Therefore, the aim of this study was to further examine the role of autophagy in PCN-induced toxicity in the CNS. To achieve this, we exposed 1321N1 astrocytoma and SH-SY5Y neuroblastoma cells to PCN (0-100 μmol/L) and tested the contribution of autophagy by measuring the impact of the autophagy inhibitor 3-methyladenine (3-MA) using a series of biochemical and molecular markers. Pretreatment of 1321N1 astrocytoma cells with 3-MA (5 mmol/L) decreased the PCN-induced acidic vesicular organelle and autophagosome formation as measured using acridine orange and green fluorescent protein-LC3 -LC3 fluorescence, respectively. Furthermore, 3-MA (5 mmol/L) significantly protected 1321N1 astrocytoma cells against PCN-induced toxicity. In contrast pretreatment with 3-MA (5 mmol/L) increased PCN-induced toxicity in SH-SY5Y neuroblastoma cells. Given the influence of autophagy in inflammatory responses, we investigated whether the observed effects in this study involved inflammatory mediators. The PCN (100 μmol/L) significantly increased the production of interleukin-8 (IL-8), prostaglandin E2 (PGE2), and leukotriene B4 (LTB4) in both cell lines. Consistent with its paradoxical role in modulating PCN-induced toxicity, 3-MA (5 mmol/L) significantly reduced the PCN-induced production of IL-8, PGE2, and LTB4 in 1321N1 astrocytoma cells but augmented their production in SH-SY5Y neuroblastoma cells. In conclusion, we show here for the first time the paradoxical role of autophagy in mediating PCN-induced toxicity in 1321N1 astrocytoma and SH-SY5Y neuroblastoma cells and provide novel evidence that these actions may be mediated by effects on IL-8, PGE2, and LTB4 production.

Effects of Pseudomonas aeruginosa virulence factor pyocyanin on human urothelial cell function and viability

PURPOSE

We determined the effects of Pseudomonas aeruginosa virulence factor pyocyanin on human urothelial cell viability and function in vitro.

MATERIALS AND METHODS

RT4 urothelial cells were treated with pyocyanin (1 to 100 μM) for 24 hours. After exposure the treatment effects were measured according to certain end points, including changes in urothelial cell viability, reactive oxygen species formation, caspase-3 activity, basal and stimulated adenosine triphosphate release, SA-β-gal activity and detection of acidic vesicular organelles.

RESULTS

The 24-hour pyocyanin treatment resulted in a concentration dependent decrease in cell viability at concentrations of 25 μM or greater, and increases in reactive oxygen species formation and caspase-3 activity at 25 μM or greater. Basal adenosine triphosphate release was significantly decreased at all tested pyocyanin concentrations while stimulated adenosine triphosphate release was significantly inhibited at pyocyanin concentrations of 12.5 μM or greater with no significant stimulated release at 100 μM. Pyocyanin treated RT4 cells showed morphological characteristics associated with cellular senescence, including SA-β-gal expression. This effect was not evident at 100 μM pyocyanin and may have been due to apoptotic cell death, as indicated by increased caspase-3 activity. An increase in acridine orange stained vesicular-like organelles was observed in RT4 urothelial cells after pyocyanin treatment.

CONCLUSIONS

Exposure to pyocyanin alters urothelial cell viability, reactive oxygen species production and caspase-3 activity. Treatment also results in cellular senescence, which may affect the ability of urothelium to repair during infection. The virulence factor depressed stimulated adenosine triphosphate release, which to our knowledge is a novel finding with implications for awareness of bladder filling in patients with P. aeruginosa urinary tract infection.