Real-time measurement of cellular bioenergetics in fully differentiated human nasal epithelial cells grown at air-liquid-interface

Extracellular glucose triggers metabolic reprogramming of cultured human bronchial epithelial cells and indirect fibroblast activation

Glucose is essential for energy metabolism, and its usage can determine other cellular functions, depending on the cell type. In some pathological conditions, cells are exposed to high concentrations of glucose for extended periods. In this study, we investigated metabolic, oxidative stress, and cellular senescence pathways in human bronchial epithelial cells (HBECs) cultured in media with physiologically low (5 mm) and high (12.5 mm) glucose concentrations. HBECs exposed to 12.5 mm glucose showed increased glucose routing toward the pentose phosphate pathway, lactate synthesis, and glycogen, but not triglyceride synthesis. These metabolic shifts were not associated with changes in cell proliferation rates, oxidative stress, or cellular senescence pathways. Since hyperglycemia is associated with fibrosis in the lung, we asked whether HBECS could activate fibroblasts. Primary human lung fibroblasts cultured in media conditioned by 12.5 mm glucose-exposed HBECs showed a 1.3-fold increase in the gene expression of COL1A1 and COL1A2, along with twofold increased protein levels of smooth muscle cell actin and 2.4-fold of COL1A1. Consistently, HBECs cultured with 12.5 mm glucose secreted proteins associated with inflammation and fibrosis, such as interleukins IL-1β, IL-10, and IL-13, CC chemokine ligands CCL2 and CCL24, and with extracellular matrix remodeling, such as metalloproteinases (MMP)-1, MMP-3, MMP-9, and MMP-13 and tissue inhibitors of MMPs (TIMP)-1 and -2. This study shows that HBECs undergo metabolic reprogramming and increase the secretion of profibrotic mediators following exposure to high concentrations of glucose, and it contributes to the understanding of the metabolic crosstalk of neighboring cells in diabetes-associated pulmonary fibrosis.

Targeting the autophagy-NAD axis protects against cell death in Niemann-Pick type C1 disease models

Impairment of autophagy leads to an accumulation of misfolded proteins and damaged organelles and has been implicated in plethora of human diseases. Loss of autophagy in actively respiring cells has also been shown to trigger metabolic collapse mediated by the depletion of nicotinamide adenine dinucleotide (NAD) pools, resulting in cell death. Here we found that the deficit in the autophagy-NAD axis underpins the loss of viability in cell models of a neurodegenerative lysosomal storage disorder, Niemann-Pick type C1 (NPC1) disease. Defective autophagic flux in NPC1 cells resulted in mitochondrial dysfunction due to impairment of mitophagy, leading to the depletion of both the reduced and oxidised forms of NAD as identified via metabolic profiling. Consequently, exhaustion of the NAD pools triggered mitochondrial depolarisation and apoptotic cell death. Our chemical screening identified two FDA-approved drugs, celecoxib and memantine, as autophagy activators which effectively restored autophagic flux, NAD levels, and cell viability of NPC1 cells. Of biomedical relevance, either pharmacological rescue of the autophagy deficiency or NAD precursor supplementation restored NAD levels and improved the viability of NPC1 patient fibroblasts and induced pluripotent stem cell (iPSC)-derived cortical neurons. Together, our findings identify the autophagy-NAD axis as a mechanism of cell death and a target for therapeutic interventions in NPC1 disease, with a potential relevance to other neurodegenerative disorders.

Autophagy promotes cell survival by maintaining NAD levels

Autophagy is an essential catabolic process that promotes the clearance of surplus or damaged intracellular components. Loss of autophagy in age-related human pathologies contributes to tissue degeneration through a poorly understood mechanism. Here, we identify an evolutionarily conserved role of autophagy from yeast to humans in the preservation of nicotinamide adenine dinucleotide (NAD) levels, which are critical for cell survival. In respiring mouse fibroblasts with autophagy deficiency, loss of mitochondrial quality control was found to trigger hyperactivation of stress responses mediated by NADases of PARP and Sirtuin families. Uncontrolled depletion of the NAD(H) pool by these enzymes ultimately contributed to mitochondrial membrane depolarization and cell death. Pharmacological and genetic interventions targeting several key elements of this cascade improved the survival of autophagy-deficient yeast, mouse fibroblasts, and human neurons. Our study provides a mechanistic link between autophagy and NAD metabolism and identifies targets for interventions in human diseases associated with autophagic, lysosomal, and mitochondrial dysfunction.

Smoking-Associated Exposure of Human Primary Bronchial Epithelial Cells to Aldehydes: Impact on Molecular Mechanisms Controlling Mitochondrial Content and Function

Chronic obstructive pulmonary disease (COPD) is a devastating lung disease primarily caused by exposure to cigarette smoke (CS). During the pyrolysis and combustion of tobacco, reactive aldehydes such as acetaldehyde, acrolein, and formaldehyde are formed, which are known to be involved in respiratory toxicity. Although CS-induced mitochondrial dysfunction has been implicated in the pathophysiology of COPD, the role of aldehydes therein is incompletely understood. To investigate this, we used a physiologically relevant in vitro exposure model of differentiated human primary bronchial epithelial cells (PBEC) exposed to CS (one cigarette) or a mixture of acetaldehyde, acrolein, and formaldehyde (at relevant concentrations of one cigarette) or air, in a continuous flow system using a puff-like exposure protocol. Exposure of PBEC to CS resulted in elevated IL-8 cytokine and mRNA levels, increased abundance of constituents associated with autophagy, decreased protein levels of molecules associated with the mitophagy machinery, and alterations in the abundance of regulators of mitochondrial biogenesis. Furthermore, decreased transcript levels of basal epithelial cell marker KRT5 were reported after CS exposure. Only parts of these changes were replicated in PBEC upon exposure to a combination of acetaldehyde, acrolein, and formaldehyde. More specifically, aldehydes decreased MAP1LC3A mRNA (autophagy) and BNIP3 protein (mitophagy) and increased ESRRA protein (mitochondrial biogenesis). These data suggest that other compounds in addition to aldehydes in CS contribute to CS-induced dysregulation of constituents controlling mitochondrial content and function in airway epithelial cells.

Do compromised mitochondria aggravate severity and fatality by SARS-CoV-2?

At global level, the pandemic coronavirus disease 2019 (COVID-19) is known to be caused by an etiologic agent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Numerous evidence and propositions have emerged on the molecular and cellular attributes that cause COVID-19. Notwithstanding, still several key questions with reference to molecular aspects of severity of infection by SARS-CoV-2 need to be answered. In the same line, the role of healthy mitochondria to maintain intracellular temperature and their association with the severity of SARS-CoV-2 is completely missing. In this direction, preclinical and clinical data on the comorbidities in the case of mitochondrial defective disease and COVID-19 are not available. The authors propose that patients harboring primary mitochondrial disease and secondary mitochondrial dysfunction will display a higher severity and death rate compared to healthy mitochondria harboring patients.

Cellular and systemic energy metabolic dysregulation in asthma development-a hypothesis-generating approach

BACKGROUND

The roles of systemic and airway-specific epithelial energy metabolism in altering the developmental programming of airway epithelial cells (AECs) in early life are poorly understood.

OBJECTIVE

Our aim was to assess carbohydrate metabolism in developing AECs among children with and without wheeze and test the association of infant plasma energy biomarkers with subsequent recurrent wheeze and asthma outcomes.

METHODS

We measured cellular carbohydrate metabolism in live nasal AECs collected at age 2 years from 15 male subjects with and without a history of wheeze and performed a principal component analysis to visually assess clustering of data on AEC metabolism of glycolitic metabolites and simple sugars. Among 237 children with available year 1 plasma samples, we tested the associations of year 1 plasma energy biomarkers and recurrent wheeze and asthma by using generalized estimating equations and logistic regression.

RESULTS

Children with a history of wheeze had lower utilization of glucose in their nasal AECs than did children with no wheeze. Systemically, a higher plasma glucose concentration at year 1 (within the normal range) was associated with decreased odds of asthma at age 5 years (adjusted odds ratio = 0.56; 95% CI = 0.35-0.90). Insulin concentration, glucose-to-insulin ratio, C-peptide concentration, and leptin concentration at year 1 were associated with recurrent wheeze from age 2 years to age 5 years.

CONCLUSION

These results suggest that there is significant energy metabolism dysregulation in early life, which likely affects AEC development. These pertubations of epithelial cell metabolism in infancy may have lasting effects on lung development that could render the airway more susceptible to allergic sensitization.

Overview of positron emission tomography in functional imaging of the lungs for diffuse lung diseases

Positron emission tomography (PET) is a quantitative molecular imaging modality increasingly used to study pulmonary disease processes and drug effects on those processes. The wide range of drugs and other entities that can be radiolabeled to study molecularly targeted processes is a major strength of PET, thus providing a noninvasive approach for obtaining molecular phenotyping information. The use of PET to monitor disease progression and treatment outcomes in DLD has been limited in clinical practice, with most of such applications occurring in the context of research investigations under clinical trials. Given the high costs and failure rates for lung drug development efforts, molecular imaging lung biomarkers are needed not only to aid these efforts but also to improve clinical characterization of these diseases beyond canonical anatomic classifications based on computed tomography. The purpose of this review article is to provide an overview of PET applications in characterizing lung disease, focusing on novel tracers that are in clinical development for DLD molecular phenotyping, and briefly address considerations for accurately quantifying lung PET signals.

Delayed induction of type I and III interferons mediates nasal epithelial cell permissiveness to SARS-CoV-2

The nasal epithelium is a plausible entry point for SARS-CoV-2, a site of pathogenesis and transmission, and may initiate the host response to SARS-CoV-2. Antiviral interferon (IFN) responses are critical to outcome of SARS-CoV-2. Yet little is known about the interaction between SARS-CoV-2 and innate immunity in this tissue. Here we apply single-cell RNA sequencing and proteomics to a primary cell model of human nasal epithelium differentiated at air-liquid interface. SARS-CoV-2 demonstrates widespread tropism for nasal epithelial cell types. The host response is dominated by type I and III IFNs and interferon-stimulated gene products. This response is notably delayed in onset relative to viral gene expression and compared to other respiratory viruses. Nevertheless, once established, the paracrine IFN response begins to impact on SARS-CoV-2 replication. When provided prior to infection, recombinant IFNβ or IFNλ1 induces an efficient antiviral state that potently restricts SARS-CoV-2 viral replication, preserving epithelial barrier integrity. These data imply that the IFN-I/III response to SARS-CoV-2 initiates in the nasal airway and suggest nasal delivery of recombinant IFNs to be a potential chemoprophylactic strategy.

The Role of Mitochondria-Linked Fatty-Acid Uptake-Driven Adipogenesis in Graves Orbitopathy

CONTEXT

Depot-specific expansion of orbital adipose tissue (OAT) in Graves orbitopathy (GO; an autoimmune condition producing proptosis, visual impairment and reduced quality of life) is associated with fatty acid (FA)-uptake-driven adipogenesis in preadipocytes/fibroblasts (PFs).

OBJECTIVE

This work sought a role for mitochondria in OAT adipogenesis in GO.

METHODS

Confluent PFs from healthy OAT (OAT-H), OAT from GO (OAT-GO) and white adipose tissue in culture medium compared with culture medium containing a mixed hormonal cocktail as adipogenic medium (ADM), or culture-medium containing FA-supplementation, oleate:palmitate:linoleate (45:30:25%) with/without different concentration of mitochondrial biosubstrate adenosine 5'-diphosphate/guanosine 5'-diphosphate (ADP/GDP), AICAR (adenosine analogue), or inhibitor oligomycin-A for 17 days. Main outcome measures included oil-red-O staining and foci count of differentiated adipocytes for in vitro adipogenesis, flow cytometry, relative quantitative polymerase chain reaction, MTS-assay/106 cells, total cellular-ATP detection kit, and Seahorse-XFe96-Analyzer for mitochondria and oxidative-phosphorylation (OXPHOS)/glycolysis-ATP production analysis.

RESULTS

During early adipogenesis before adipocyte formation (days 0, 4, and7), we observed OAT-specific cellular ATP production via mitochondrial OXPHOS in PFs both from OAT-H and OAT-GO, and substantially disrupted OXPHOS-ATP/glycolysis-ATP production in PFs from OAT-GO, for example, a 40% reduction in OXPHOS-ATP and trend-increased glycolysis-ATP production on days 4 and 7 compared with day 0, which contrasted with the stable levels in OAT-H. FA supplementation in culture-medium triggered adipogenesis in PFs both from OAT-H and OAT-GO, which was substantially enhanced by 1-mM GDP reaching 7% to 18% of ADM adipogenesis. The FA-uptake-driven adipogenesis was diminished by oligomycin-A but unaffected by treatment with ADP or AICAR. Furthermore, we observed a significant positive correlation between FA-uptake-driven adipogenesis by GDP and the ratios of OXPHOS-ATP/glycolysis-ATP through adipogenesis of PFs from OAT-GO.

CONCLUSION

Our study confirmed that FA uptake can drive OAT adipogenesis and revealed a fundamental role for mitochondria-OXPHOS in GO development, which provides potential for therapeutic interventions.

PGC-1α mediates a metabolic host defense response in human airway epithelium during rhinovirus infections

Human rhinoviruses (HRV) are common cold viruses associated with exacerbations of lower airways diseases. Although viral induced epithelial damage mediates inflammation, the molecular mechanisms responsible for airway epithelial damage and dysfunction remain undefined. Using experimental HRV infection studies in highly differentiated human bronchial epithelial cells grown at air-liquid interface (ALI), we examine the links between viral host defense, cellular metabolism, and epithelial barrier function. We observe that early HRV-C15 infection induces a transitory barrier-protective metabolic state characterized by glycolysis that ultimately becomes exhausted as the infection progresses and leads to cellular damage. Pharmacological promotion of glycolysis induces ROS-dependent upregulation of the mitochondrial metabolic regulator, peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α), thereby restoring epithelial barrier function, improving viral defense, and attenuating disease pathology. Therefore, PGC-1α regulates a metabolic pathway essential to host defense that can be therapeutically targeted to rescue airway epithelial barrier dysfunction and potentially prevent severe respiratory complications or secondary bacterial infections.

Epithelial host defense to rhinovirus infections is enhanced by targeting the mitochondrial metabolic regulator, PGC-1a. Using metabolomics and proteomics, Michi et al show that human airway epithelial cells mount a barrier-protective early glycolysis-shift in response to rhinovirus, and that by targeting PGC-1a early in infection, epithelial barrier function, viral defense and pathology are improved.

Prematurity alters the progenitor cell program of the upper respiratory tract of neonates

The impact of prematurity on human development and neonatal diseases, such as bronchopulmonary dysplasia, has been widely reported. However, little is known about the effects of prematurity on the programs of stem cell self-renewal and differentiation of the upper respiratory epithelium, which is key for adaptation to neonatal life. We developed a minimally invasive methodology for isolation of neonatal basal cells from nasopharyngeal (NP) aspirates and performed functional analysis in organotypic cultures to address this issue. We show that preterm NP progenitors have a markedly distinct molecular signature of abnormal proliferation and mitochondria quality control compared to term progenitors. Preterm progenitors had lower oxygen consumption at baseline and were unable to ramp up consumption to the levels of term cells when challenged. Although they formed a mucociliary epithelium, ciliary function tended to decline in premature cells as they differentiated, compared to term cells. Together, these differences suggested increased sensitivity of preterm progenitors to environmental stressors under non-homeostatic conditions.

A toolbox for studying respiratory viral infections using air-liquid interface cultures of human airway epithelial cells

Submerged cultures of primary human airway epithelial cells or human airway epithelial cell lines have been a mainstay of airway epithelial biology research for decades due to their robust in vitro proliferative capacity, relatively low maintenance culture conditions, and clinically translatable results to nasal or bronchial brushings. With the development and improvement of air-liquid interface (ALI) cultures of human airway epithelial cells, such cultures have been considered superior to immortalized cell lines and primary cell monolayers, as such cultures effectively recapitulate in vivo epithelial architecture and cell types. Although ALI culture growth protocols are well-established and widely available, many researchers have avoided their use, as ALI cultures not only take longer to grow but also present technical challenges and limitations that make in vitro intracellular and structural assays taxing. Challenges arise relating to their complex structure, requirements for air exposure, the constraints of transwell growth apparatus, and interference in assays caused by mucus secretion. Although few publications briefly describe technical adaptations for some assays, there is still considerable trial and error required for researchers to establish consistent and reliable assay adaptations, often becoming a deterrent for pursuing mechanistic investigation. We have created a user-friendly toolbox detailing comprehensive protocols for numerous techniques and assay adaptations, particularly focusing on respiratory virus infections. By expanding the repertoire of ALI culture-adapted in vitro assays, we hope to facilitate the widespread adoption of this valuable culture system for mechanistic investigations of respiratory viral infections or other epithelial-pathogen models.