TNFα decreases mitochondrial movement in human airway smooth muscle

Alpha-synuclein fine-tunes neuronal response to pro-inflammatory cytokines

Pro-inflammatory cytokines are emerging as neuroinflammatory mediators in Parkinson's disease (PD) due to their ability to act through neuronal cytokine receptors. Critical questions persist regarding the role of cytokines in neuronal dysfunction and their contribution to PD pathology. Specifically, the potential synergy of the hallmark PD protein alpha-synuclein (α-syn) with cytokines is of interest. We therefore investigated the direct impact of pro-inflammatory cytokines on neurons and hypothesized that α-syn pathology exacerbates cytokine-induced neuronal deficits in PD. iPSC-derived cortical neurons (CNs) from healthy controls and patients with α-syn gene locus duplication (SNCA dupl) were stimulated with IL-17A, TNF-α, IFN-γ, or a combination thereof. For rescue experiments, CNs were pre-treated with α-syn anti-oligomerisation compound NPT100-18A prior to IL-17A stimulation. Cytokine receptor expression, microtubule cytoskeleton, axonal transport and neuronal activity were assessed. SNCA dupl CNs displayed an increased IL-17A receptor expression and impaired IL-17A-mediated cytokine receptor regulation. Cytokines exacerbated the altered distribution of tubulin post-translational modifications in SNCA dupl neurites, with SNCA dupl-specific IL-17A effects. Tau pathology in SNCA dupl CNs was also aggravated by IL-17A and cytokine mix. Cytokines slowed down mitochondrial axonal transport, with IL-17A-mediated retrograde slowing in SNCA dupl only. The pre-treatment of SNCA dupl CNs with NPT100-18A prevented the IL-17A-induced functional impairments in axonal transport and neural activity. Our work elucidates the detrimental effects of pro-inflammatory cytokines, particularly IL-17A, on human neuronal structure and function in the context of α-syn pathology, suggesting that cytokine-mediated inflammation represents a second hit to neurons in PD which is amenable to disease modifying therapies that are currently in clinical trials.

Membrane-mediated modulation of mitochondrial physiology by terahertz waves

Extensive studies have demonstrated the diverse impacts of electromagnetic waves at gigahertz and terahertz (THz) frequencies on cytoplasmic membrane properties. However, there is little evidence of these impacts on intracellular membranes, particularly mitochondrial membranes crucial for mitochondrial physiology. In this study, human neuroblast-like cells were exposed to continuous 0.1 THz radiation at an average power density of 33 mW/cm2. The analysis revealed that THz exposure significantly altered the mitochondrial ultrastructure. THz waves enhanced the enzymatic activity of the mitochondrial respiratory chain but disrupted supercomplex assembly, compromising mitochondrial respiration. Molecular dynamics simulations revealed altered rates of change in the quantity of hydrogen bonds and infiltration of water molecules in lipid bilayers containing cardiolipin, indicating the specific behavior of cardiolipin, a signature phospholipid in mitochondria, under THz exposure. These findings suggest that THz radiation can significantly alter mitochondrial membrane properties, impacting mitochondrial physiology through a mechanism related to mitochondrial membrane, and provide deeper insight into the bioeffects of THz radiation.

Heterogeneous distribution of mitochondria and succinate dehydrogenase activity in human airway smooth muscle cells

Succinate dehydrogenase (SDH) is a key mitochondrial enzyme involved in the tricarboxylic acid cycle, where it facilitates the oxidation of succinate to fumarate, and is coupled to the reduction of ubiquinone in the electron transport chain as Complex II. Previously, we developed a confocal-based quantitative histochemical technique to determine the maximum velocity of the SDH reaction (SDHmax) in single cells and observed that SDHmax corresponds with mitochondrial volume density. In addition, mitochondrial volume and motility varied within different compartments of human airway smooth muscle (hASM) cells. Therefore, we hypothesize that the SDH activity varies relative to the intracellular mitochondrial volume within hASM cells. Using 3D confocal imaging of labeled mitochondria and a concentric shell method for analysis, we quantified mitochondrial volume density, mitochondrial complexity index, and SDHmax relative to the distance from the nuclear membrane. The mitochondria within individual hASM cells were more filamentous in the immediate perinuclear region and were more fragmented in the distal parts of the cell. Within each shell, SDHmax also corresponded to mitochondrial volume density, where both peaked in the perinuclear region and decreased in more distal parts of the cell. Additionally, when normalized to mitochondrial volume, SDHmax was lower in the perinuclear region when compared to the distal parts of the cell. In summary, our results demonstrate that SDHmax measures differences in SDH activity within different cellular compartments. Importantly, our data indicate that mitochondria within individual cells are morphologically heterogeneous, and their distribution varies substantially within different cellular compartments, with distinct functional properties.

Mitochondrial regulation of diabetic endothelial dysfunction: Pathophysiological links

Micro- and macrovascular complications frequently occur in patients with diabetes, with endothelial dysfunction playing a key role in the development and progression of the complications. For the early diagnosis and optimal treatment of vascular complications associated with diabetes, it is imperative to comprehend the cellular and molecular mechanisms governing the function of diabetic endothelial cells. Mitochondria function as crucial sensors of environmental and cellular stress regulating endothelial cell viability, structural integrity and function. Impaired mitochondrial quality control mechanisms and mitochondrial dysfunction are the main features of endothelial damage. Hence, targeted mitochondrial therapy is considered promising novel therapeutic options in vascular complications of diabetes. In this review, we focus on the mitochondrial functions in the vascular endothelial cells and the pathophysiological role of mitochondria in diabetic endothelial dysfunction, aiming to provide a reference for related drug development and clinical diagnosis and treatment.

Molecular mechanisms underlying TNFα-induced mitochondrial fragmentation in human airway smooth muscle cells

Tumor necrosis factor α (TNFα), a proinflammatory cytokine, plays a significant role in mediating the effects of acute inflammation in response to allergens, pollutants, and respiratory infections. Previously, we showed that acute exposure to TNFα induces mitochondrial fragmentation in human airway smooth muscle (hASM) cells, which is associated with increased expression of dynamin-related protein 1 (DRP1). Phosphorylation of DRP1 at serine 616 (pDRP1S616) promotes its translocation and binding to the outer mitochondrial membrane (OMM) and mediates mitochondrial fragmentation. Previously, we reported that TNFα exposure triggers protein unfolding and triggers an endoplasmic reticulum (ER) stress response involving phosphorylation of inositol-requiring enzyme 1α (pIRE1α) at serine 724 (pIRE1αS724) and subsequent splicing of X-box binding protein 1 (XBP1s) in hASM cells. We hypothesize that TNFα-mediated activation of the pIRE1αS724/XBP1s ER stress pathway in hASM cells transcriptionally activates genes that encode kinases responsible for pDRP1S616 phosphorylation. Using 3-D confocal imaging of MitoTracker green-labeled mitochondria, we found that TNFα treatment for 6 h induces mitochondrial fragmentation in hASM cells. We also confirmed that 6 h TNFα treatment activates the pIRE1α/XBP1s ER stress pathway. Using in silico analysis and ChIP assay, we showed that CDK1 and CDK5, kinases involved in the phosphorylation of pDRP1S616, are transcriptionally targeted by XBP1s. TNFα treatment increased the binding affinity of XBP1s on the promoter regions of CDK1 and CDK5, and this was associated with an increase in pDRP1S616 and mitochondria fragmentation. This study reveals a new underlying molecular mechanism for TNFα-induced mitochondrial fragmentation in hASM cells.NEW & NOTEWORTHY Airway inflammation is increasing worldwide. Proinflammatory cytokines mediate an adaptive mechanism to overcome inflammation-induced cellular stress. Previously, we reported that TNFα mediates hASM cellular responses, leading to increased force and ATP consumption associated with increased O2 consumption, and oxidative stress. This study indicates that TNFα induces ER stress, which induces mitochondrial fragmentation via pIRE1αS724/XBP1s mediated CDK1/5 upregulation and pDRP1S616 phosphorylation. Mitochondrial fragmentation may promote hASM mitochondrial biogenesis to maintain healthy mitochondrial pool.

Nicotine affects mitochondrial structure and function in human airway smooth muscle cells

Exposure to cigarette smoke and e-cigarettes, with nicotine as the active constituent, contributes to increased health risks associated with asthma. Nicotine exerts its functional activity via nicotinic acetylcholine receptors (nAChRs), and the alpha7 subtype (α7nAChR) has recently been shown to adversely affect airway dynamics. The mechanisms of α7nAChR action in airways, particularly in the context of airway smooth muscle (ASM), a key cell type in asthma, are still under investigation. Mitochondria have garnered increasing interest for their role in regulating airway tone and adaptations to cellular stress. Here mitochondrial dynamics such as fusion versus fission, and mitochondrial Ca2+ ([Ca2+]m), play an important role in mitochondrial homeostasis. There is currently no information on effects and mechanisms by which nicotine regulates mitochondrial structure and function in ASM in the context of asthma. We hypothesized that nicotine disrupts mitochondrial morphology, fission-fusion balance, and [Ca2+]m regulation, with altered mitochondrial respiration and bioenergetics in the context of asthmatic ASM. Using human ASM (hASM) cells from nonasthmatics, asthmatics, and smokers, we examined the effects of nicotine on mitochondrial dynamics and [Ca2+]m. Fluorescence [Ca2+]m imaging of hASM cells with rhod-2 showed robust responses to 10 μM nicotine, particularly in asthmatics and smokers. In both asthmatics and smokers, nicotine increased the expression of fission proteins while decreasing fusion proteins. Seahorse analysis showed blunted oxidative phosphorylation parameters in response to nicotine in these groups. α7nAChR siRNA blunted nicotine effects, rescuing [Ca2+]m, changes in mitochondrial structural proteins, and mitochondrial dysfunction. These data highlight mitochondria as a target of nicotine effects on ASM, where mitochondrial disruption and impaired buffering could permit downstream effects of nicotine in the context of asthma.NEW & NOTEWORTHY Asthma is a major healthcare burden, which is further exacerbated by smoking. Recognizing the smoking risk of asthma, understanding the effects of nicotine on asthmatic airways becomes critical. Surprisingly, the mechanisms of nicotine action, even in normal and especially asthmatic airways, are understudied. Accordingly, the goal of this research is to investigate how nicotine influences asthmatic airways in terms of mitochondrial structure and function, via the a7nAChR.

Chemical Chaperone 4-PBA Mitigates Tumor Necrosis Factor Alpha-Induced Endoplasmic Reticulum Stress in Human Airway Smooth Muscle

Airway inflammation and pro-inflammatory cytokines such as tumor necrosis factor alpha (TNFα) underlie the pathophysiology of respiratory diseases, including asthma. Previously, we showed that TNFα activates the inositol-requiring enzyme 1α (IRE1α)/X-box binding protein 1 spliced (XBP1s) endoplasmic reticulum (ER) stress pathway in human airway smooth muscle (hASM) cells. The ER stress pathway is activated by the accumulation of unfolded proteins in the ER. Accordingly, chemical chaperones such as 4-phenylbutyric acid (4-PBA) may reduce ER stress activation. In the present study, we hypothesized that chemical chaperone 4-PBA mitigates TNFα-induced ER stress in hASM cells. hASM cells were isolated from bronchiolar tissue obtained from five patients with no history of smoking or respiratory diseases. The hASM cells' phenotype was confirmed via the expression of alpha-smooth muscle actin and elongated morphology. hASM cells from the same patient sample were then separated into three 12 h treatment groups: (1) TNFα (20 ng/mL), (2) TNFα + 4-PBA (1 μM, 30 min pretreatment), and (3) untreated control. The expressions of total IRE1α and phosphorylated IRE1α (pIRE1αS724) were determined through Western blotting. The splicing of XBP1 mRNA was analyzed using RT-PCR. We found that TNFα induced an increase in pIRE1αS724 phosphorylation, which was mitigated by treatment with chemical chaperone 4-PBA. We also found that TNFα induced an increase in XBP1s mRNA, which was also mitigated by treatment with chemical chaperone 4-PBA. These results support our hypothesis and indicate that chemical chaperone 4-PBA treatment mitigates TNFα-induced ER stress in hASM cells.

Gaps and Future Directions in Clinical Research on Obesity-Related Asthma

Obesity is a major comorbidity for the development and worsening of asthma. It is associated with increased disease incidence, reduced response to inhaled and systemic steroids, increased asthma exacerbations, and poor disease control. Over the past two decades, we have learned that there are clinical asthma phenotypes associated with obesity, which have unique immune, inflammatory, and metabolic disease mechanisms. The objectives of this review are to provide a brief overview of the associations and gaps between these chronic inflammatory diseases and the role that traditional therapies have on treating patients with obesity-related asthma, and to describe new clinical research of therapeutic developments targeting mechanisms that are more specific to this patient population.

Cell-Based Measurement of Mitochondrial Function in Human Airway Smooth Muscle Cells

Cellular mitochondrial function can be assessed using high-resolution respirometry that measures the O2 consumption rate (OCR) across a number of cells. However, a direct measurement of cellular mitochondrial function provides valuable information and physiological insight. In the present study, we used a quantitative histochemical technique to measure the activity of succinate dehydrogenase (SDH), a key enzyme located in the inner mitochondrial membrane, which participates in both the tricarboxylic acid (TCA) cycle and electron transport chain (ETC) as Complex II. In this study, we determine the maximum velocity of the SDH reaction (SDHmax) in individual human airway smooth muscle (hASM) cells. To measure SDHmax, hASM cells were exposed to a solution containing 80 mM succinate and 1.5 mM nitroblue tetrazolium (NBT, reaction indicator). As the reaction proceeded, the change in optical density (OD) due to the reduction of NBT to its diformazan (peak absorbance wavelength of 570 nm) was measured using a confocal microscope with the pathlength for light absorbance tightly controlled. SDHmax was determined during the linear period of the SDH reaction and expressed as mmol fumarate/liter of cell/min. We determine that this technique is rigorous and reproducible, and reliable for the measurement of mitochondrial function in individual cells.

Size-dependent differences in mitochondrial volume density in phrenic motor neurons

Neuromotor control of diaphragm muscle (DIAm) motor units is dependent on an orderly size-dependent recruitment of phrenic motor neurons (PhMNs). Slow (type S) and fast, fatigue resistant (type FR) DIAm motor units, which are frequently recruited to sustain ventilation, comprise smaller PhMNs that innervate type I and IIa DIAm fibers. More fatigable fast (type FF) motor units, which are infrequently recruited for higher force, expulsive behaviors, comprise larger PhMNs that innervate more type IIx/IIb DIAm fibers. We hypothesize that due to the more frequent activation and thus higher energy demand of type S and FR motor units, the mitochondrial volume density (MVD) of smaller PhMNs is greater compared with larger PhMNs. In eight adult (6 mo old) Fischer 344 rats, PhMNs were identified via intrapleural injection of Alexa488-conjugated cholera toxin B (CTB). Following retrograde CTB labeling, mitochondria in PhMNs were labeled by transdural infusion of MitoTracker Red. PhMNs and mitochondria were imaged using multichannel confocal microscopy using a ×60 oil objective. Following optical sectioning and three-dimensional (3-D) rendering, PhMNs and mitochondria were analyzed volumetrically using Nikon Elements software. Analysis of MVD in somal and dendritic compartments was stratified by PhMN somal surface area. Smaller PhMNs (likely S and FR units) had greater somal MVDs compared with larger PhMNs (likely FF units). By contrast, proximal dendrites or larger PhMNs had higher MVD compared with dendrites of smaller PhMNs. We conclude that more active smaller PhMNs have a higher mitochondrial volume density to support their higher energy demand in sustaining ventilation.NEW & NOTEWORTHY Type S and FR motor units, comprising smaller phrenic motor neurons (PhMNs) are regularly activated to perform indefatigable ventilatory requirements. By contrast, type FF motor units, comprising larger PhMNs, are infrequently activated to perform expulsive straining and airway defense maneuvers. This difference in activation history is mirrored in the mitochondrial volume density (MVD), with smaller PhMNs having higher MVD than larger PhMNs. In proximal dendrites, this trend was reversed, with larger PhMNs having higher MVD than smaller PhMNs, likely due to the maintenance requirements for the larger dendritic arbor of FF PhMNs.

Mitochondrial adaptations to inactivity in diaphragm muscle fibers

Type I and IIa diaphragm muscle (DIAm) fibers comprise slow and fast fatigue-resistant motor units that are recruited to accomplish breathing and thus have a high duty cycle. In contrast, type IIx/IIb fibers comprise more fatigable fast motor units that are infrequently recruited for airway protective and straining behaviors. We hypothesize that mitochondrial structure and function in type I and IIa DIAm fibers adapt in response to inactivity imposed by spinal cord hemisection at C₂ (C₂SH). At 14 days after C₂SH, the effect of inactivity on mitochondrial structure and function was assessed in DIAm fibers. Mitochondria in DIAm fibers were labeled using MitoTracker Green (Thermo Fisher Scientific), imaged in three-dimensions (3-D) by fluorescence confocal microscopy, and images were analyzed for mitochondrial volume density (MVD) and complexity. DIAm homogenate from either side was assessed for PGC1α, Parkin, MFN2, and DRP1 using Western blot. In alternate serial sections of the same DIAm fibers, the maximum velocity of the succinate dehydrogenase reaction (SDH_max) was determined using a quantitative histochemical technique. In all groups and both sides of the DIAm, type I and IIa DIAm fibers exhibited higher MVD, with more filamentous mitochondria and had higher SDH_max normalized to both fiber volume and mitochondrial volume compared with type IIx/IIb Diam fibers. In the inactive right side of the DIAm, mitochondria became fragmented and MVD decreased in all fiber types compared with the intact side and sham controls, consistent with the observed reduction in PGC1α and increased Parkin and DRP1 expression. In the inactive side of the DIAm, the reduction in SDH_max was found only for type I and IIa fibers. These results show that there are intrinsic fiber-type-dependent differences in the structure and function of mitochondria in DIAm fibers. Following C₂SH-induced inactivity, mitochondrial structure (MVD and fragmentation) and function (SDH_max) were altered, indicating that inactivity influences all DIAm fiber types, but inactivity disproportionately affected SDH_max in the more intrinsically active type I and IIa fibers.NEW & NOTEWORTHY Two weeks of diaphragm (DIAm) inactivity imposed by C2SH caused reduced mitochondrial volume density, mitochondrial fragmentation, and a concomitant reduction of SDH_max in type I and IIa DIAm fibers on the lesioned side. Type I and IIa DIAm fibers were far more sensitive to inactivation than type IIx/IIb fibers, which exhibited little pathology. Our results indicate that mitochondria in DIAm fibers are plastic in response to varying levels of activity.

Chronic cerebral aspects of long COVID, post-stroke syndromes and similar states share their pathogenesis and perispinal etanercept treatment logic

The chronic neurological aspects of traumatic brain injury, post-stroke syndromes, long COVID-19, persistent Lyme disease, and influenza encephalopathy having close pathophysiological parallels that warrant being investigated in an integrated manner. A mechanism, common to all, for this persistence of the range of symptoms common to these conditions is described. While TNF maintains cerebral homeostasis, its excessive production through either pathogen-associated molecular patterns or damage-associated molecular patterns activity associates with the persistence of the symptoms common across both infectious and non-infectious conditions. The case is made that this shared chronicity arises from a positive feedback loop causing the persistence of the activation of microglia by the TNF that these cells generate. Lowering this excess TNF is the logical way to reducing this persistent, TNF-maintained, microglial activation. While too large to negotiate the blood-brain barrier effectively, the specific anti-TNF biological, etanercept, shows promise when administered by the perispinal route, which allows it to bypass this obstruction.

Mitochondrial morphology and function varies across diaphragm muscle fiber types

In diaphragm muscle (DIAm), type I and IIa fibers are recruited to accomplish breathing, while type IIx/IIb fibers are recruited only during expulsive/straining behaviors. Thus, type I and IIa DIAm fibers are much more active (duty cycle of ∼40 %) than type IIx/IIb fibers (duty cycle of <1%), which we hypothesized underlies intrinsic differences in mitochondrial structure and function. MitoTracker Green labeled mitochondria were imaged in 3-D using confocal microscopy. Mitochondrial volume density (MVD, per muscle fiber volume) was higher, and mitochondria were more filamentous in type I and IIa DIAm compared to type IIx/IIb fibers. The maximum velocity of the succinate dehydrogenase reaction (SDH_max), measured using a quantitative histochemical technique was found to be higher in type I and IIa DIAm fibers compared to type IIx/IIb fibers with and without normalizing for MVD. These results are consistent with fiber type differences in the intrinsic structural and functional properties of DIAm fibers and closely match differences in energetic demands.

Mitochondria in Focus: From Function to Therapeutic Strategies in Chronic Lung Diseases

Mitochondria are essential organelles for cell metabolism, growth, and function. Mitochondria in lung cells have important roles in regulating surfactant production, mucociliary function, mucus secretion, senescence, immunologic defense, and regeneration. Disruption in mitochondrial physiology can be the central point in several pathophysiologic pathways of chronic lung diseases such as chronic obstructive pulmonary disease, idiopathic pulmonary fibrosis, and asthma. In this review, we summarize how mitochondria morphology, dynamics, redox signaling, mitophagy, and interaction with the endoplasmic reticulum are involved in chronic lung diseases and highlight strategies focused on mitochondrial therapy (mito-therapy) that could be tested as a potential therapeutic target for lung diseases.

Molecular mechanisms of oxidative stress in asthma

The lungs are exposed to reactive oxygen species oxygen (ROS) produced as a result of inhalation of oxygen, as well as smoke and other air pollutants. Cell metabolism and the NADPH oxidases (Nox) generate low levels of intracellular ROS that act as signal transduction mediators by inducing oxidative modifications of histones, enzymes and transcription factors. Redox signalling is also regulated by localised production and sensing of ROS in mitochondria, the endoplasmic reticulum (ER) and inside the nucleus. Intracellular ROS are maintained at low levels through the action of a battery of enzymatic and non-enzymatic antioxidants. Asthma is a heterogeneous airway inflammatory disease with different immune endotypes; these include atopic or non-atopic Th2 type immune response associated with eosinophilia, or a non-Th2 response associated with neutrophilia. Airway remodelling and hyperresponsiveness accompany the inflammatory response in asthma. Over-production of ROS resulting from infiltrating immune cells, particularly eosinophils and neutrophils, and a concomitant impairment of antioxidant responses lead to development of oxidative stress in asthma. Oxidative stress is augmented in severe asthma and during exacerbations, as well as by air pollution and obesity, and causes oxidative damage of tissues promoting airway inflammation and hyperresponsiveness. Furthermore, deregulated Nox activity, mitochondrial dysfunction, ER stress and/or oxidative DNA damage, resulting from exposure to irritants, inflammatory mediators or obesity, may lead to redox-dependent changes in cell signalling. ROS play a central role in airway epithelium-mediated sensing, development of innate and adaptive immune responses, and airway remodelling and hyperresponsiveness. Nonetheless, antioxidant compounds have proven clinically ineffective as therapeutic agents for asthma, partly due to issues with stability and in vivo metabolism of these compounds. The compartmentalised nature of ROS production and sensing, and the role of ROS in homeostatic responses and in the action of corticosteroids and β2-adrenergic receptor agonists, adds another layer of complexity to antioxidant therapy development. Nox inhibitors and mitochondrial-targeted antioxidants are in clinical development for a number of diseases but they have not yet been investigated in asthma. A better understanding of the complex role of ROS in the pathogenesis of asthma will highlight new opportunities for more targeted and effective redox therapies.

Mitochondrial Fragmentation and Dysfunction in Type IIx/IIb Diaphragm Muscle Fibers in 24-Month Old Fischer 344 Rats

Sarcopenia is characterized by muscle fiber atrophy and weakness, which may be associated with mitochondrial fragmentation and dysfunction. Mitochondrial remodeling and biogenesis in muscle fibers occurs in response to exercise and increased muscle activity. However, the adaptability mitochondria may decrease with age. The diaphragm muscle (DIAm) sustains breathing, via recruitment of fatigue-resistant type I and IIa fibers. More fatigable, type IIx/IIb DIAm fibers are infrequently recruited during airway protective and expulsive behaviors. DIAm sarcopenia is restricted to the atrophy of type IIx/IIb fibers, which impairs higher force airway protective and expulsive behaviors. The aerobic capacity to generate ATP within muscle fibers depends on the volume and intrinsic respiratory capacity of mitochondria. In the present study, mitochondria in type-identified DIAm fibers were labeled using MitoTracker Green and imaged in 3-D using confocal microscopy. Mitochondrial volume density was higher in type I and IIa DIAm fibers compared with type IIx/IIb fibers. Mitochondrial volume density did not change with age in type I and IIa fibers but was reduced in type IIx/IIb fibers in 24-month rats. Furthermore, mitochondria were more fragmented in type IIx/IIb compared with type I and IIa fibers, and worsened in 24-month rats. The maximum respiratory capacity of mitochondria in DIAm fibers was determined using a quantitative histochemical technique to measure the maximum velocity of the succinate dehydrogenase reaction (SDH _max ). SDH _max per fiber volume was higher in type I and IIa DIAm fibers and did not change with age. In contrast, SDH _max per fiber volume decreased with age in type IIx/IIb DIAm fibers. There were two distinct clusters for SDH _max per fiber volume and mitochondrial volume density, one comprising type I and IIa fibers and the second comprising type IIx/IIb fibers. The separation of these clusters increased with aging. There was also a clear relation between SDH _max per mitochondrial volume and the extent of mitochondrial fragmentation. The results show that DIAm sarcopenia is restricted to type IIx/IIb DIAm fibers and related to reduced mitochondrial volume, mitochondrial fragmentation and reduced SDH _max per fiber volume.

Metabolomics in asthma: A platform for discovery

Asthma, characterized by airway hyperresponsiveness, inflammation and remodeling, is a chronic airway disease with complex etiology. Severe asthma is characterized by frequent exacerbations and poor therapeutic response to conventional asthma therapy. A clear understanding of cellular and molecular mechanisms of asthma is critical for the discovery of novel targets for optimal therapeutic control of asthma. Metabolomics is emerging as a powerful tool to elucidate novel disease mechanisms in a variety of diseases. In this review, we summarize the current status of knowledge in asthma metabolomics at systemic and cellular levels. The findings demonstrate that various metabolic pathways, related to energy metabolism, macromolecular biosynthesis and redox signaling, are differentially modulated in asthma. Airway smooth muscle cell plays pivotal roles in asthma by contributing to airway hyperreactivity, inflammatory mediator release and remodeling. We posit that metabolomic profiling of airway structural cells, including airway smooth muscle cells, will shed light on molecular mechanisms of asthma and airway hyperresponsiveness and help identify novel therapeutic targets.

The Impact of Endoplasmic Reticulum-Associated Protein Modifications, Folding and Degradation on Lung Structure and Function

The accumulation of unfolded/misfolded proteins in the endoplasmic reticulum (ER) causes ER stress and induces the unfolded protein response (UPR) and other mechanisms to restore ER homeostasis, including translational shutdown, increased targeting of mRNAs for degradation by the IRE1-dependent decay pathway, selective translation of proteins that contribute to the protein folding capacity of the ER, and activation of the ER-associated degradation machinery. When ER stress is excessive or prolonged and these mechanisms fail to restore proteostasis, the UPR triggers the cell to undergo apoptosis. This review also examines the overlooked role of post-translational modifications and their roles in protein processing and effects on ER stress and the UPR. Finally, these effects are examined in the context of lung structure, function, and disease.

Quantifying mitochondrial volume density in phrenic motor neurons

BACKGROUND

Previous assessments of mitochondrial volume density within motor neurons used electron microscopy (EM) to image mitochondria. However, adequate identification and sampling of motor neurons within a particular motor neuron pool is largely precluded using EM. Here, we present an alternative method for determining mitochondrial volume density in identified motor neurons within the phrenic motor neuron (PhMN) pool, with greatly increased sampling.

NEW METHOD

This novel method for assessing mitochondrial volume density in PhMNs uses a combination of intrapleural injection of Alexa 488-conjugated cholera toxin B (CTB) to retrogradely label PhMNs, followed by intrathecal application of MitoTracker Red to label mitochondria. This technique was validated by comparison to 3D EM determination of mitochondrial volume density as a "gold standard".

RESULTS

A mean mitochondrial volume density of ∼11 % was observed across PhMNs using the new MitoTracker Red method. This compared favourably with mitochondrial volume density (∼11 %) measurements using EM.

COMPARISON WITH EXISTING METHOD

The range, mean and variance of mitochondrial volume density estimates in PhMNs were not different between EM and fluorescent imaging techniques.

CONCLUSIONS

Fluorescent imaging may be used to estimate mitochondrial volume density in a large sample of motor neurons, with results similar to EM, although EM did distinguish finer mitochondrion morphology compared to MitoTracker fluorescence. Compared to EM methods, the assessment of a larger sample size and unambiguous identification of motor neurons belonging to a specific motor neuron pool represent major advantages over previous methods.

TNFα induces mitochondrial fragmentation and biogenesis in human airway smooth muscle

In human airway smooth muscle (hASM), mitochondrial volume density is greater in asthmatic patients compared with normal controls. There is also an increase in mitochondrial fragmentation in hASM of moderate asthmatics associated with an increase in dynamin-related protein 1 (Drp1) and a decrease in mitofusin 2 (Mfn2) expression, mitochondrial fission, and fusion proteins, respectively. Proinflammatory cytokines such TNFα contribute to hASM hyperreactivity and cell proliferation associated with asthma. However, the involvement of proinflammatory cytokines in mitochondrial remodeling is not clearly established. In nonasthmatic hASM cells, mitochondria were labeled using MitoTracker Red and imaged in three dimensions using a confocal microscope. After 24-h TNFα exposure, mitochondria in hASM cells were more fragmented, evidenced by decreased form factor and aspect ratio and increased sphericity. Associated with increased mitochondrial fragmentation, Drp1 expression increased while Mfn2 expression was reduced. TNFα also increased mitochondrial biogenesis in hASM cells reflected by increased peroxisome proliferator-activated receptor-γ coactivator 1α expression and increased mitochondrial DNA copy number. Associated with mitochondrial biogenesis, TNFα exposure also increased mitochondrial volume density and porin expression, resulting in an increase in maximum O2 consumption rate. However, when normalized for mitochondrial volume density, O2 consumption rate per mitochondrion was reduced by TNFα exposure. Associated with mitochondrial fragmentation and biogenesis, TNFα also increased hASM cell proliferation, an effect mimicked by siRNA knockdown of Mfn2 expression and mitigated by Mfn2 overexpression. The results of this study support our hypothesis that in hASM cells exposed to TNFα mitochondria are more fragmented, with an increase in mitochondrial biogenesis and mitochondrial volume density resulting in reduced O2 consumption rate per mitochondrion.

Inflammation-Induced Protein Unfolding in Airway Smooth Muscle Triggers a Homeostatic Response in Mitochondria

The effects of airway inflammation on airway smooth muscle (ASM) are mediated by pro-inflammatory cytokines such as tumor necrosis factor alpha (TNFα). In this review article, we will provide a unifying hypothesis for a homeostatic response to airway inflammation that mitigates oxidative stress and thereby provides resilience to ASM. Previous studies have shown that acute exposure to TNFα increases ASM force generation in response to muscarinic stimulation (hyper-reactivity) resulting in increased ATP consumption and increased tension cost. To meet this increased energetic demand, mitochondrial O₂ consumption and oxidative phosphorylation increases but at the cost of increased reactive oxygen species (ROS) production (oxidative stress). TNFα-induced oxidative stress results in the accumulation of unfolded proteins in the endoplasmic reticulum (ER) and mitochondria of ASM. In the ER, TNFα selectively phosphorylates inositol-requiring enzyme 1 alpha (pIRE1α) triggering downstream splicing of the transcription factor X-box binding protein 1 (XBP1s); thus, activating the pIRE1α/XBP1s ER stress pathway. Protein unfolding in mitochondria also triggers an unfolded protein response (^mtUPR). In our conceptual framework, we hypothesize that activation of these pathways is homeostatically directed towards mitochondrial remodeling via an increase in peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC1α) expression, which in turn triggers: (1) mitochondrial fragmentation (increased dynamin-related protein-1 (Drp1) and reduced mitofusin-2 (Mfn2) expression) and mitophagy (activation of the Phosphatase and tensin homolog (PTEN)-induced putative kinase 1 (PINK1)/Parkin mitophagy pathway) to improve mitochondrial quality; (2) reduced Mfn2 also results in a disruption of mitochondrial tethering to the ER and reduced mitochondrial Ca²⁺ influx; and (3) mitochondrial biogenesis and increased mitochondrial volume density. The homeostatic remodeling of mitochondria results in more efficient O₂ consumption and oxidative phosphorylation and reduced ROS formation by individual mitochondrion, while still meeting the increased ATP demand. Thus, the energetic load of hyper-reactivity is shared across the mitochondrial pool within ASM cells.

Mitochondrial dysfunction in lung ageing and disease

Mitochondrial biology has seen a surge in popularity in the past 5 years, with the emergence of numerous new avenues of exciting mitochondria-related research including immunometabolism, mitochondrial transplantation and mitochondria-microbe biology. Since the early 1960s mitochondrial dysfunction has been observed in cells of the lung in individuals and in experimental models of chronic and acute respiratory diseases. However, it is only in the past decade with the emergence of more sophisticated tools and methodologies that we are beginning to understand how this enigmatic organelle regulates cellular homeostasis and contributes to disease processes in the lung. In this review, we highlight the diverse role of mitochondria in individual lung cell populations and what happens when these essential organelles become dysfunctional with ageing and in acute and chronic lung disease. Although much remains to be uncovered, we also discuss potential targeted therapeutics for mitochondrial dysfunction in the ageing and diseased lung.

Endoplasmic Reticulum Stress and Mitochondrial Function in Airway Smooth Muscle

Inflammatory airway diseases such as asthma affect more than 300 million people world-wide. Inflammation triggers pathophysiology via such as tumor necrosis factor α (TNFα) and interleukins (e.g., IL-13). Hypercontraction of airway smooth muscle (ASM) and ASM cell proliferation are major contributors to the exaggerated airway narrowing that occurs during agonist stimulation. An emergent theme in this context is the role of inflammation-induced endoplasmic reticulum (ER) stress and altered mitochondrial function including an increase in the formation of reactive oxygen species (ROS). This may establish a vicious cycle as excess ROS generation leads to further ER stress. Yet, it is unclear whether inflammation-induced ROS is the major mechanism leading to ER stress or the consequence of ER stress. In various diseases, inflammation leads to an increase in mitochondrial fission (fragmentation), associated with reduced levels of mitochondrial fusion proteins, such as mitofusin 2 (Mfn2). Mitochondrial fragmentation may be a homeostatic response since it is generally coupled with mitochondrial biogenesis and mitochondrial volume density thereby reducing demand on individual mitochondrion. ER stress is triggered by the accumulation of unfolded proteins, which induces a homeostatic response to alter protein balance via effects on protein synthesis and degradation. In addition, the ER stress response promotes protein folding via increased expression of molecular chaperone proteins. Reduced Mfn2 and altered mitochondrial dynamics may not only be downstream to ER stress but also upstream such that a reduction in Mfn2 triggers further ER stress. In this review, we summarize the current understanding of the link between inflammation-induced ER stress and mitochondrial function and the role played in the pathophysiology of inflammatory airway diseases.

TNFα selectively activates the IRE1α/XBP1 endoplasmic reticulum stress pathway in human airway smooth muscle cells

Airway inflammation is a key aspect of diseases such as asthma. Proinflammatory cytokines such as TNFα mediate the inflammatory response. In various diseases, inflammation leads to endoplasmic reticulum (ER) stress, the accumulation of unfolded proteins, which triggers homeostatic responses to restore normal cellular function. We hypothesized that TNFα triggers ER stress through an increase in reactive oxygen species generation in human airway smooth muscle (hASM) with a downstream effect on mitofusin 2 (Mfn2). In hASM cells isolated from lung specimens incidental to patient surgery, dose- and time-dependent effects of TNFα exposure were assessed. Exposure of hASM to tunicamycin was used as a positive control. Tempol (500 μM) was used as superoxide scavenger. Activation of three ER stress pathways were evaluated by Western blotting: 1) autophosphorylation of inositol-requiring enzyme1 (IRE1α) leading to splicing of X-box binding protein 1 (XBP1); 2) autophosphorylation of protein kinase RNA-like endoplasmic reticulum kinase (PERK) leading to phosphorylation of eukaryotic initiation factor 2α; and 3) translocation and cleavage of activating transcription factor 6 (ATF6). We found that exposure of hASM cells to tunicamycin activated all three ER stress pathways. In contrast, TNFα selectively activated the IRE1α/XBP1 pathway in a dose- and time-dependent fashion. Our results indicate that TNFα does not activate the PERK and ATF6 pathways. Exposure of hASM cells to TNFα also decreased Mfn2 protein expression. Concurrent exposure to TNFα and tempol reversed the effect of TNFα on IRE1α phosphorylation and Mfn2 protein expression. Selective activation of the IRE1α/XBP1 pathway in hASM cells after exposure to TNFα may reflect a unique homeostatic role of this pathway in the inflammatory response of hASM cells.

Mitochondrial regulation of airway smooth muscle functions in health and pulmonary diseases

Mitochondria are important for airway smooth muscle physiology due to their diverse yet interconnected roles in calcium handling, redox regulation, and cellular bioenergetics. Increasing evidence indicates that mitochondria dysfunction is intimately associated with airway diseases such as asthma, IPF and COPD. In these pathological conditions, increased mitochondrial ROS, altered bioenergetics profiles, and calcium mishandling contribute collectively to changes in cellular signaling, gene expression, and ultimately changes in airway smooth muscle contractile/proliferative properties. Therefore, understanding the basic features of airway smooth muscle mitochondria and their functional contribution to airway biology and pathology are key to developing novel therapeutics for airway diseases. This review summarizes the recent findings of airway smooth muscle mitochondria focusing on calcium homeostasis and redox regulation, two key determinants of physiological and pathological functions of airway smooth muscle.

Neurokinin 1 receptor promotes rat airway smooth muscle cell migration in asthmatic airway remodelling by enhancing tubulin expression

Background

Airway remodelling is a major contributor to hyper-responsiveness leading to chronic asthma; however, the underlying mechanisms remain unclear. This study aimed to investigate the effects of a neurokinin 1 receptor (NK1R) antagonist (WIN62577) on the migration of airway smooth muscle cells (ASMCs) and the expression of NK1R and alpha-tubulin in airway remodelling using young rats with asthma.

Methods

Sprague-Dawley rats were randomly divided into a control group and airway remodelling group. Rats in the model group were stimulated with ovalbumin for 8 weeks. Primary ASMCs were cultured and purified from all rats, and then treated with different doses of WIN62577. The expression of NK1R and α-tubulin in ASMCs was assessed using immunofluorescence, real-time quantitative polymerase chain reaction, and western blotting. Changes in ASMC migration were detected by a transwell chamber assay.

Results

The transwell assay showed that the number of migrating ASMCs in the asthmatic airway remodelling group was significantly greater than that in the control group (P<0.01), which was inhibited by WIN62577 in a dose-dependent manner, with peak inhibition detected at 10^-8 mol/L. The mRNA and protein expression levels of NK1R and α-tubulin were significantly higher in the asthmatic airway remodelling group than in the control group (P<0.05 and P<0.01, respectively), and were significantly decreased after treatment with WIN62577 (P<0.01 and P<0.05, respectively).

Conclusions

NK1R antagonists may suppress ASMC migration in a rat model of airway remodelling by inhibiting tubulin expression, indicating a new potential target for the treatment and control of chronic asthma.

Mitochondrial dysfunction and pulmonary hypertension: cause, effect, or both

Pulmonary hypertension describes a heterogeneous disease defined by increased pulmonary artery pressures, and progressive increase in pulmonary vascular resistance due to pathologic remodeling of the pulmonary vasculature involving pulmonary endothelial cells, pericytes, and smooth muscle cells. This process occurs under various conditions, and although these populations vary, the clinical manifestations are the same: progressive dyspnea, increases in right ventricular (RV) afterload and dysfunction, RV-pulmonary artery uncoupling, and right-sided heart failure with systemic circulatory collapse. The overall estimated 5-yr survival rate is 72% in highly functioning patients, and as low as 28% for those presenting with advanced symptoms. Metabolic theories have been suggested as underlying the pathogenesis of pulmonary hypertension with growing evidence of the role of mitochondrial dysfunction involving the major proteins of the electron transport chain, redox-related enzymes, regulators of the proton gradient and calcium homeostasis, regulators of apoptosis, and mitophagy. There remain more studies needed to characterize mitochondrial dysfunction leading to impaired vascular relaxation, increase proliferation, and failure of regulatory mechanisms. The effects on endothelial cells and resulting interactions with their microenvironment remain uncharted territory for future discovery. Additionally, on the basis of observations that the "plexigenic lesions" of pulmonary hypertension resemble the unregulated proliferation of tumor cells, similarities between cancer pathobiology and pulmonary hypertension have been drawn, suggesting interactions between mitochondria and angiogenesis. Recently, mitochondria targeting has become feasible, which may yield new therapeutic strategies. We present a state-of-the-art review of the role of mitochondria in both the pathobiology of pulmonary hypertension and potential therapeutic targets in pulmonary vascular processes.

Regulating effect of glycyrrhetinic acid on bronchial asthma smooth muscle proliferation and apoptosis as well as inflammatory factor expression through ERK1/2 signaling pathway

OBJECTIVE

To study the influence of glycyrrhetinic acid (GA) on bronchial asthma (BA) smooth muscle proliferation and apoptosis as well as inflammatory factor expression and its molecular mechanism.

METHODS

Male SD guinea pigs were selected and made into asthma models, bronchial asthma smooth muscle cells were cultured and divided into BA group, GA group and GA + LM group that were treated with serum-free RPMI1640 culture medium, serum-free RPMI1640 culture medium containing 50 ng/mL glycyrrhetinic acid, serum-free RPMI1640 culture medium containing 50 ng/mL glycyrrhetinic acid and 100 ng/mL LM22B-10 respectively; normal guinea pigs were collected and bronchial smooth muscle cells were cultured as control group. The cell proliferation activity as well as the expression of proliferation and apoptosis genes, inflammatory factors and p-ERK1/2 was determined.

RESULTS

Proliferation activity value and mRNA expression of Bcl-2, TNF-α, IL-4, IL-6, YKL-40, protein expression of p-ERK1/2 of airway smooth muscle cell in BA group were significantly higher than those of control group while mRNA expression levels of Bax, caspase-9 as well as caspase-3 were significantly lower than that of control group (P < 0.05); proliferation activity value and mRNA expression of Bcl-2, TNF-α, IL-4, IL-6, YKL-40, protein expression of p-ERK1/2 of airway smooth muscle cell in GA group were significantly lower than those of BA group (P < 0.05) while the mRNA expression levels of Bax, caspase-9 as well as caspase-3 were significantly higher than those of BA group (P < 0.05); proliferation activity value and mRNA expression of Bcl-2, TNF-α, IL-4, IL-6, YKL-40 of airway smooth muscle cell in GA + LM group were significantly higher than those of GA group (P < 0.05) while mRNA expression levels of Bax, caspase-9 as well as caspase-3 were significantly lower that of GA group (P < 0.05).

CONCLUSION

GA can inhibit the proliferation of bronchial smooth muscle cells and reduce the expression of inflammatory factors by inhibiting the phosphorylation of ERK1/2.