Classical monocytes from older adults maintain capacity for metabolic compensation during glucose deprivation and lipopolysaccharide stimulation

Bioenergetic signatures of neurodevelopmental regression

Background: Studies have linked autism spectrum disorder (ASD) to physiological abnormalities including mitochondrial dysfunction. Mitochondrial dysfunction may be linked to a subset of children with ASD who have neurodevelopmental regression (NDR). We have developed a cell model of ASD which demonstrates a unique mitochondrial profile with mitochondrial respiration higher than normal and sensitive to physiological stress. We have previously shown similar mitochondrial profiles in individuals with ASD and NDR. Methods: Twenty-six ASD individuals without a history of NDR (ASD-NoNDR) and 15 ASD individuals with a history of NDR (ASD-NDR) were recruited from 34 families. From these families, 30 mothers, 17 fathers and 5 typically developing (TD) siblings participated. Mitochondrial respiration was measured in peripheral blood mononuclear cells (PBMCs) with the Seahorse 96 XF Analyzer. PBMCs were exposed to various levels of physiological stress for 1 h prior to the assay using 2,3-dimethoxy-1,4-napthoquinone. Results: ASD-NDR children were found to have higher respiratory rates with mitochondria that were more sensitive to physiological stress as compared to ASD-NoNDR children, similar to our cellular model of NDR. Differences in mitochondrial respiration between ASD-NDR and TD siblings were similar to the differences between ASD-NDR and ASD-NoNDR children. Interesting, parents of children with ASD and NDR demonstrated patterns of mitochondrial respiration similar to their children such that parents of children with ASD and NDR demonstrated elevated respiratory rates with mitochondria that were more sensitive to physiological stress. In addition, sex differences were seen in ASD children and parents. Age effects in parents suggested that mitochondria of older parents were more sensitive to physiological stress. Conclusion: This study provides further evidence that children with ASD and NDR may have a unique type of mitochondrial physiology that may make them susceptible to physiological stressors. Identifying these children early in life before NDR occurs and providing treatment to protect mitochondrial physiology may protect children from experiencing NDR. The fact that parents also demonstrate mitochondrial respiration patterns similar to their children implies that this unique change in mitochondrial physiology may be a heritable factor (genetic or epigenetic), a result of shared environment, or both.

Age-related changes in energy metabolism in peripheral mononuclear blood cells (PBMCs) and the brains of cognitively healthy seniors

Mitochondrial dysfunction is a hallmark of cellular senescence and many age-related neurodegenerative diseases. We therefore investigated the relationship between mitochondrial function in peripheral blood cells and cerebral energy metabolites in young and older sex-matched, physically and mentally healthy volunteers. Cross-sectional observational study involving 65 young (26.0 ± 0.49 years) and 65 older (71.7 ± 0.71 years) women and men recruited. Cognitive health was evaluated using established psychometric methods (MMSE, CERAD). Blood samples were collected and analyzed, and fresh peripheral blood mononuclear cells (PBMCs) were isolated. Mitochondrial respiratory complex activity was measured using a Clarke electrode. Adenosine triphosphate (ATP) and citrate synthase activity (CS) were determined by bioluminescence and photometrically. N-aspartyl-aspartate (tNAA), ATP, creatine (Cr), and phosphocreatine (PCr) were quantified in brains using 1H- and 31P-magnetic resonance spectroscopic imaging (MRSI). Levels of insulin-like growth factor 1 (IGF-1) were determined using a radio-immune assay (RIA). Complex IV activity (CIV) (- 15%) and ATP levels (- 11%) were reduced in PBMCs isolated from older participants. Serum levels of IGF-1 were significantly reduced (- 34%) in older participants. Genes involved in mitochondrial activity, antioxidant mechanisms, and autophagy were unaffected by age. tNAA levels were reduced (- 5%), Cr (+ 11%), and PCr (+ 14%) levels were increased, and ATP levels were unchanged in the brains of older participants. Markers of energy metabolism in blood cells did not significantly correlate with energy metabolites in the brain. Age-related bioenergetic changes were detected in peripheral blood cells and the brains of healthy older people. However, mitochondrial function in peripheral blood cells does not reflect energy related metabolites in the brain. While ATP levels in PBMCs may be be a valid marker for age-related mitochondrial dysfunction in humans, cerebral ATP remained constant.

Adjuvant AS01 activates human monocytes for costimulation and systemic inflammation

BACKGROUND

The adjuvanted recombinant zoster vaccine (RZV) is highly effective even in adults over 80 years old. The high efficacy of RZV is attributed to its highly reactogenic adjuvant, AS01, but limited studies have been done on AS01's activation of human immune cells.

METHODS

We stimulated peripheral blood mononuclear cells (PBMC) with AS01 and used flow cytometry and RNA Sequencing (RNAseq) to analyze the impacts on human primary cells.

RESULTS

We found that incubation of PBMC with AS01 activated monocytes to a greater extent than any other cell population, including dendritic cells. Both classical and non-classical monocytes demonstrated this activation. RNASeq showed that TNF-ɑ and IL1R pathways were highly upregulated in response to AS01 exposure, even in older adults.

CONCLUSIONS

In a PBMC co-culture, AS01 strongly activates human monocytes to upregulate costimulation markers and induce cytokines that mediate systemic inflammation. Understanding AS01's impacts on human cells opens possibilities to further address the reduced vaccine response associated with aging.

Inflammaging and fatty acid oxidation in monocytes and macrophages

Fatty acid oxidation (FAO), primarily known as β-oxidation, plays a crucial role in breaking down fatty acids within mitochondria and peroxisomes to produce cellular energy and preventing metabolic dysfunction. Myeloid cells, including macrophages, microglia, and monocytes, rely on FAO to perform essential cellular functions and uphold tissue homeostasis. As individuals age, these cells show signs of inflammaging, a condition that includes a chronic onset of low-grade inflammation and a decline in metabolic function. These lead to changes in fatty acid metabolism and a decline in FAO pathways. Recent studies have shed light on metabolic shifts occurring in macrophages and monocytes during aging, correlating with an altered tissue environment and the onset of inflammaging. This review aims to provide insights into the connection of inflammatory pathways and altered FAO in macrophages and monocytes from older organisms. We describe a model in which there is an extended activation of receptor for advanced glycation end products, nuclear factor-κB (NF-κB) and the nod-like receptor family pyrin domain containing 3 inflammasome within macrophages and monocytes. This leads to an increased level of glycolysis, and also promotes pro-inflammatory cytokine production and signaling. As a result, FAO-related enzymes such as 5' AMP-activated protein kinase and peroxisome proliferator-activated receptor-α are reduced, adding to the escalation of inflammation, accumulation of lipids, and heightened cellular stress. We examine the existing body of literature focused on changes in FAO signaling within macrophages and monocytes and their contribution to the process of inflammaging.

Aberrant glucose metabolism underlies impaired macrophage differentiation in glycogen storage disease type Ib

Glycogen storage disease type Ib (GSD-Ib) is an autosomal recessive disorder caused by a deficiency in the glucose-6-phosphate (G6P) transporter (G6PT) that is responsible for transporting G6P into the endoplasmic reticulum. GSD-Ib is characterized by disturbances in glucose homeostasis, neutropenia, and neutrophil dysfunction. Although some studies have explored neutrophils abnormalities in GSD-Ib, investigations regarding monocytes/macrophages remain limited so far. In this study, we examined the impact of G6PT deficiency on monocyte-to-macrophage differentiation using bone marrow-derived monocytes from G6pt-/- mice as well as G6PT-deficient human THP-1 monocytes. Our findings revealed that G6PT-deficient monocytes exhibited immature differentiation into macrophages. Notably, the impaired differentiation observed in G6PT-deficient monocytes seemed to be associated with abnormal glucose metabolism, characterized by enhanced glucose consumption through glycolysis, even under quiescent conditions with oxidative phosphorylation. Furthermore, we observed a reduced secretion of inflammatory cytokines in G6PT-deficient THP-1 monocytes during the inflammatory response, despite their elevated glucose consumption. In conclusion, this study sheds light on the significance of G6PT in monocyte-to-macrophage differentiation and underscores its importance in maintaining glucose homeostasis and supporting immune response in GSD-Ib. These findings may contribute to a better understanding of the pathogenesis of GSD-Ib and potentially pave the way for the development of targeted therapeutic interventions.

How Can We Improve Vaccination Response in Old People? Part I: Targeting Immunosenescence of Innate Immunity Cells

Vaccination, being able to prevent millions of cases of infectious diseases around the world every year, is the most effective medical intervention ever introduced. However, immunosenescence makes vaccines less effective in providing protection to older people. Although most studies explain that this is mainly due to the immunosenescence of T and B cells, the immunosenescence of innate immunity can also be a significant contributing factor. Alterations in function, number, subset, and distribution of blood neutrophils, monocytes, and natural killer and dendritic cells are detected in aging, thus potentially reducing the efficacy of vaccines in older individuals. In this paper, we focus on the immunosenescence of the innate blood immune cells. We discuss possible strategies to counteract the immunosenescence of innate immunity in order to improve the response to vaccination. In particular, we focus on advances in understanding the role and the development of new adjuvants, such as TLR agonists, considered a promising strategy to increase vaccination efficiency in older individuals.

Lipopolysaccharide affects energy metabolism and elevates nicotinamide N-methyltransferase level in human aortic endothelial cells (HAEC)

This study aimed to investigate the putative role of nicotinamide N-methyltransferase in the metabolic response of human aortic endothelial cells. This enzyme catalyses S-adenosylmethionine-mediated methylation of nicotinamide to methylnicotinamide. This reaction is accompanied by the reduction of the intracellular nicotinamide and S-adenosylmethionine content. This may affect NAD⁺ synthesis and various processes of methylation, including epigenetic modifications of chromatin. Particularly high activity of nicotinamide N-methyltransferase is detected in liver, many neoplasms as well as in various cells in stressful conditions. The elevated nicotinamide N-methyltransferase content was also found in endothelial cells treated with statins. Although the exogenous methylnicotinamide has been postulated to induce a vasodilatory response, the specific metabolic role of nicotinamide N-methyltransferase in vascular endothelium is still unclear. Treatment of endothelial cells with bacterial lipopolysaccharide evokes several metabolic and functional consequences which built a multifaceted physiological response of endothelium to bacterial infection. Among the spectrum of biochemical changes substantially elevated protein level of nicotinamide N-methyltransferase was particularly intriguing. Here it has been shown that silencing of the nicotinamide N-methyltransferase gene influences several changes which are observed in cells treated with lipopolysaccharide. They include altered energy metabolism and rearrangement of the mitochondrial network. A complete explanation of the mechanisms behind the protective consequences of the nicotinamide N-methyltransferase deficiency in cells treated with lipopolysaccharide needs further investigation.

Metformin Suppresses Monocyte Immunometabolic Activation by SARS-CoV-2 Spike Protein Subunit 1

A hallmark of COVID-19 is a hyperinflammatory state associated with severity. Monocytes undergo metabolic reprogramming and produce inflammatory cytokines when stimulated with SARS-CoV-2. We hypothesized that binding by the viral spike protein mediates this effect, and that drugs which regulate immunometabolism could inhibit the inflammatory response. Monocytes stimulated with recombinant SARS-CoV-2 spike protein subunit 1 showed a dose-dependent increase in glycolytic metabolism associated with production of pro-inflammatory cytokines. This response was dependent on hypoxia-inducible factor-1α, as chetomin inhibited glycolysis and cytokine production. Inhibition of glycolytic metabolism by 2-deoxyglucose (2-DG) or glucose deprivation also inhibited the glycolytic response, and 2-DG strongly suppressed cytokine production. Glucose-deprived monocytes rescued cytokine production by upregulating oxidative phosphorylation, an effect which was not present in 2-DG-treated monocytes due to the known effect of 2-DG on suppressing mitochondrial metabolism. Finally, pre-treatment of monocytes with metformin strongly suppressed spike protein-mediated cytokine production and metabolic reprogramming. Likewise, metformin pre-treatment blocked cytokine induction by SARS-CoV-2 strain WA1/2020 in direct infection experiments. In summary, the SARS-CoV-2 spike protein induces a pro-inflammatory immunometabolic response in monocytes that can be suppressed by metformin, and metformin likewise suppresses inflammatory responses to live SARS-CoV-2. This has potential implications for the treatment of hyperinflammation during COVID-19.

Production of IL-6 and Phagocytosis Are the Most Resilient Immune Functions in Metabolically Compromised Human Monocytes

At sites of inflammation, monocytes carry out specific immune functions while facing challenging metabolic restrictions. Here, we investigated the potential of human monocytes to adapt to conditions of gradually inhibited oxidative phosphorylation (OXPHOS) under glucose free conditions. We used myxothiazol, an inhibitor of mitochondrial respiration, to adjust two different levels of decreased mitochondrial ATP production. At these levels, and compared to uninhibited OXPHOS, we assessed phagocytosis, production of reactive oxygen species (ROS) through NADPH oxidase (NOX), expression of surface activation markers CD16, CD80, CD11b, HLA-DR, and production of the inflammatory cytokines IL-1β, IL-6 and TNF-α in human monocytes. We found phagocytosis and the production of IL-6 to be least sensitive to metabolic restrictions while surface expression of CD11b, HLA-DR, production of TNF-α, IL-1β and production of ROS through NOX were most compromised by inhibition of OXPHOS in the absence of glucose. Our data demonstrate a short-term hierarchy of immune functions in human monocytes, which represents novel knowledge potentially leading to the development of new therapeutics in monocyte-mediated inflammatory diseases.

Resveratrol as an Adjunctive Therapy for Excessive Oxidative Stress in Aging COVID-19 Patients

The coronavirus disease 2019 (COVID-19) pandemic continues to burden healthcare systems worldwide. COVID-19 symptoms are highly heterogeneous, and the patient may be asymptomatic or may present with mild to severe or fatal symptoms. Factors, such as age, sex, and comorbidities, are key determinants of illness severity and progression. Aging is accompanied by multiple deficiencies in interferon production by dendritic cells or macrophages in response to viral infections, resulting in dysregulation of inflammatory immune responses and excess oxidative stress. Age-related dysregulation of immune function may cause a more obvious pathophysiological response to SARS-CoV-2 infection in elderly patients and may accelerate the risk of biological aging, even after recovery. For more favorable treatment outcomes, inhibiting viral replication and dampening inflammatory and oxidative responses before induction of an overt cytokine storm is crucial. Resveratrol is a potent antioxidant with antiviral activity. Herein, we describe the reasons for impaired interferon production, owing to aging, and the impact of aging on innate and adaptive immune responses to infection, which leads to inflammation distress and immunosuppression, thereby causing fulminant disease. Additionally, the molecular mechanism by which resveratrol could reverse a state of excessive basal inflammatory and oxidative stress and low antiviral immunity is discussed.

Glycolysis is integral to histamine-induced endothelial hyperpermeability

Histamine-induced vascular leakage is a core process of allergic pathologies, including anaphylaxis. Here, we show that glycolysis is integral to histamine-induced endothelial barrier disruption and hyperpermeability. Histamine rapidly enhanced glycolysis in endothelial cells via a pathway that involved histamine receptor 1 and phospholipase C beta signaling. Consistently, partial inhibition of glycolysis with 3-(3-pyridinyl)-1-(4-pyridinyl)-2-propen-1-one (3PO) prevented histamine-induced hyperpermeability in human microvascular endothelial cells, by abolishing the histamine-induced actomyosin contraction, focal adherens junction formation, and endothelial barrier disruption. Pharmacologic blockade of glycolysis with 3PO in mice reduced histamine-induced vascular hyperpermeability, prevented vascular leakage in passive cutaneous anaphylaxis and protected from systemic anaphylaxis. In conclusion, we elucidated the role of glycolysis in histamine-induced disruption of endothelial barrier integrity. Our data thereby point to endothelial glycolysis as a novel therapeutic target for human pathologies related to excessive vascular leakage, such as systemic anaphylaxis.

The Warburg Effect Occurs Rapidly in Stimulated Human Adult but Not Umbilical Cord Blood Derived Macrophages

The Warburg effect, defined as increased glycolysis and decreased oxidative phosphorylation, occurs in murine macrophages following LPS stimulation and is required for activation. There are differences between human and murine macrophage metabolic responses to stimulation, with peak metabolite concentrations occurring earlier in humans than mice. Complex changes occur in the human immune system with age, resulting in the very young and the very old being more susceptible to infections. Anti-bacterial immune responses in umbilical cord immune cells are considered deficient but there is a paucity of data on the role that metabolism plays. We hypothesized that metabolic responses in human macrophages occur early during activation. In addition, we hypothesized that umbilical cord derived macrophages have an altered immunometabolic response compared with adult macrophages. We demonstrate that adult and cord blood monocyte derived macrophages (MDM) immediately increase glycolysis in response to stimulation with LPS or Mycobacterium tuberculosis (Mtb), however only adult MDM decrease oxidative phosphorylation. At 24 hours post stimulation, glycolysis remains elevated in both adult and cord blood MDM, oxidative phosphorylation remains unchanged in the cord blood MDM and has normalized in the adult MDM stimulated with Mtb. However, LPS stimulated adult MDM have increased oxidative phosphorylation at 24 hours, illustrating differences in metabolic responses to different stimuli, time-dependent variation in responses and differences in macrophage metabolism in adults compared with umbilical cord blood. We compared the phenotype and function of macrophages derived from adult or cord blood. Cord blood MDM secreted less TNF following Mtb stimulation and more IL-6 following LPS stimulation compared with adult MDM. Our findings demonstrate that whilst cord blood MDM exhibit an immediate increase in glycolytic flux in response to stimulation, similar to adult MDM, cord blood MDM do not concomitantly decrease oxygen consumption. This indicates that adult macrophages shift to Warburg metabolism immediately after stimulation, but cord blood macrophages do not. Understanding the differences in the metabolic profiles of macrophages over a human lifetime will enable the translation of immunometabolism into effective immuno-supportive therapies that could potentially be targeted at vulnerable populations, such as the very old and the very young.

Growth differentiation factor-15 is associated with age-related monocyte dysfunction

OBJECTIVE

Age-associated decreases in immune functions are precipitated by a variety of mechanisms and affect nearly every immune cell subset. In myeloid cells, aging reduces numbers of phagocytes and impairs their functional abilities, including antigen presentation, phagocytosis, and bacterial clearance. Recently, we described an aging effect on several functions in monocytes, including impaired mitochondrial function and reduced inflammatory cytokine gene expression during stimulation with lipopolysaccharide. We hypothesized that circulating factors altered by the aging process underly these changes. Growth differentiation factor-15 (GDF-15) is a distant member of the transforming growth factor-β superfamily that has known anti-inflammatory effects in macrophages and has been shown to be highly differentially expressed during aging.

METHODS

We used biobanked plasma samples to assay circulating GDF-15 levels in subjects from our previous studies and examined correlations between GDF-15 and monocyte function.

RESULTS

Monocyte interleukin-6 production due to lipopolysaccharide stimulation was negatively correlated to plasma GDF-15. Additionally, GDF-15 was positively correlated to circulating CD16 + monocyte proportions and negatively correlated to monocyte mitochondrial respiratory capacity.

CONCLUSIONS

These results suggest that GDF-15 is a potential circulating factor affecting a variety of monocyte functions and promoting monocyte immunosenescence and thus may be an attractive candidate for therapeutic intervention to ameliorate this.

Exercise immunology: Future directions

Several decades of research in the area of exercise immunology have shown that the immune system is highly responsive to acute and chronic exercise training. Moderate exercise bouts enhance immunosurveillance and when repeated over time mediate multiple health benefits. Most of the studies prior to 2010 relied on a few targeted outcomes related to immune function. During the past decade, technologic advances have created opportunities for a multi-omics and systems biology approach to exercise immunology. This article provides an overview of metabolomics, lipidomics, and proteomics as they pertain to exercise immunology, with a focus on immunometabolism. This review also summarizes how the composition and diversity of the gut microbiota can be influenced by exercise, with applications to human health and immunity. Exercise-induced improvements in immune function may play a critical role in countering immunosenescence and the development of chronic diseases, and emerging omics technologies will more clearly define the underlying mechanisms. This review summarizes what is currently known regarding a multi-omics approach to exercise immunology and provides future directions for investigators.

Severe COVID-19 and aging: are monocytes the key?

The ongoing pandemic severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) causes a disproportionate number of severe cases and deaths in older adults. Severe SARS-CoV-2-associated disease (coronavirus disease 2019 (COVID-19)) was declared a pandemic by the World Health Organization in March 2020 and is characterized by cytokine storm, acute respiratory distress syndrome, and in some cases by systemic inflammation-related pathology. Currently, our knowledge of the determinants of severe COVID-19 is primarily observational. Here, I review emerging evidence to argue that monocytes, a circulating innate immune cell, are principal players in cytokine storm and associated pathologies in COVID-19. I also describe changes in monocyte function and phenotype that are characteristic of both aging and severe COVID-19, which suggests a potential mechanism underlying increased morbidity and mortality due to SARS-CoV-2 infection in older adults. The innate immune system is therefore a potentially important target for therapeutic treatment of COVID-19, but experimental studies are needed, and SARS-CoV-2 presents unique challenges for pre-clinical and mechanistic studies in vivo. The immediate establishment of colonies of SARS-CoV-2-susceptible animal models for aging studies, as well as strong collaborative efforts in the geroscience community, will be required in order to develop the therapies needed to combat severe COVID-19 in older adult populations.

Macrophage Immunometabolism and Inflammaging: Roles of Mitochondrial Dysfunction, Cellular Senescence, CD38, and NAD

Aging is a complex process that involves dysfunction on multiple levels, all of which seem to converge on inflammation. Macrophages are intimately involved in initiating and resolving inflammation, and their dysregulation with age is a primary contributor to inflammaging—a state of chronic, low-grade inflammation that develops during aging. Among the age-related changes that occur to macrophages are a heightened state of basal inflammation and diminished or hyperactive inflammatory responses, which seem to be driven by metabolic-dependent epigenetic changes. In this review article we provide a brief overview of mitochondrial functions and age-related changes that occur to macrophages, with an emphasis on how the inflammaging environment, senescence, and NAD decline can affect their metabolism, promote dysregulation, and contribute to inflammaging and age-related pathologies.

Fanning the Flames of Inflammaging: Impact of Monocyte Metabolic Reprogramming

Monocytes are circulating innate immune cells that are functionally dysregulated during aging. However, while metabolic regulation of innate immune cell function is now well-established, only a handful of studies have examined this in the context of aging. In a recent article published in Aging Cell, Saare et al. observe comprehensive metabolic reprogramming of otherwise unstimulated monocytes isolated from older adults. These cells display increased glucose uptake and dysregulation of mitochondrial function, concomitant with activation of signaling pathways contributing to increased inflammation. These findings suggest a mechanism whereby metabolic reprogramming in aged monocytes contributes to chronic low-grade inflammation and open new avenues of investigation into the biological underpinning of inflammaging.

Classical monocytes from older adults maintain capacity for metabolic compensation during glucose deprivation and lipopolysaccharide stimulation

Inflammaging is the chronic low-grade inflammation that occurs with age that contributes to the pathology of age-related diseases. Monocytes are innate immune cells that become dysregulated with age and which can contribute to inflammaging. Metabolism plays a key role in determining immune cell functions, with anti-inflammatory cells primarily relying on fatty acid oxidation and pro-inflammatory cells primarily relying on glycolysis. It was recently shown that lipopolysaccharide (LPS)-stimulated monocytes can compensate for a lack of glucose by utilizing fatty acid oxidation. Given that mitochondrial function decreases with age, we hypothesized that classical monocytes taken from aged individuals would have an impaired ability to upregulate oxidative metabolism along with impaired effector functions. Aging did not impair LPS-induced oxygen consumption rate during glucose deprivation as measured on a Seahorse XFp system. Additionally, aged classical monocytes maintained inflammatory gene expression responses and phagocytic capacity during LPS stimulation in the absence of glucose. In conclusion, aged classical monocytes maintain effector and metabolic functions during glucose deprivation, at least in an ex vivo context.