Low expression of CD39 and CD73 genes in centenarians compared with octogenarians

Impaired ATP hydrolysis in blood plasma contributes to age-related neutrophil dysfunction

BACKGROUND

The function of polymorphonuclear neutrophils (PMNs) decreases with age, which results in infectious and inflammatory complications in older individuals. The underlying causes are not fully understood. ATP release and autocrine stimulation of purinergic receptors help PMNs combat microbial invaders. Excessive extracellular ATP interferes with these mechanisms and promotes inflammatory PMN responses. Here, we studied whether dysregulated purinergic signaling in PMNs contributes to their dysfunction in older individuals.

RESULTS

Bacterial infection of C57BL/6 mice resulted in exaggerated PMN activation that was significantly greater in old mice (64 weeks) than in young animals (10 weeks). In contrast to young animals, old mice were unable to prevent the systemic spread of bacteria, resulting in lethal sepsis and significantly greater mortality in old mice than in their younger counterparts. We found that the ATP levels in the plasma of mice increased with age and that, along with the extracellular accumulation of ATP, the PMNs of old mice became increasingly primed. Stimulation of the formyl peptide receptors of those primed PMNs triggered inflammatory responses that were significantly more pronounced in old mice than in young animals. However, bacterial phagocytosis and killing by PMNs of old mice were significantly lower than that of young mice. These age-dependent PMN dysfunctions correlated with a decrease in the enzymatic activity of plasma ATPases that convert extracellular ATP to adenosine. ATPases depend on divalent metal ions, including Ca2+, Mg2+, and Zn2+, and we found that depletion of these ions blocked the hydrolysis of ATP and the formation of adenosine in human blood, resulting in ATP accumulation and dysregulation of PMN functions equivalent to those observed in response to aging.

CONCLUSIONS

Our findings suggest that impaired hydrolysis of plasma ATP dysregulates PMN function in older individuals. We conclude that strategies aimed at restoring plasma ATPase activity may offer novel therapeutic opportunities to reduce immune dysfunction, inflammation, and infectious complications in older patients.

Hilaire C, Reddy A, Kim J, Pinsky DJ, Murthy VL, Sutton NR. Circulating Ectonucleotidases Signal Impaired Myocardial Perfusion at Rest and Stress

Background Ectonucleotidases maintain vascular homeostasis by metabolizing extracellular nucleotides, modulating inflammation and thrombosis, and potentially, myocardial flow through adenosine generation. Evidence implicates dysfunction or deficiency of ectonucleotidases CD39 or CD73 in human disease; the utility of measuring levels of circulating ectonucleotidases as plasma biomarkers of coronary artery dysfunction or disease has not been previously reported. Methods and Results A total of 529 individuals undergoing clinically indicated positron emission tomography stress testing between 2015 and 2019 were enrolled in this single-center retrospective analysis. Baseline demographics, clinical data, nuclear stress test, and coronary artery calcium score variables were collected, as well as a blood sample. CD39 and CD73 levels were assessed as binary (detectable, undetectable) or continuous variables using ELISAs. Plasma CD39 was detectable in 24% of White and 8% of Black study participants (P=0.02). Of the clinical history variables examined, ectonucleotidase levels were most strongly associated with underlying liver disease and not other traditional coronary artery disease risk factors. Intriguingly, detection of circulating ectonucleotidase was inversely associated with stress myocardial blood flow (2.3±0.8 mL/min per g versus 2.7 mL/min per g±1.1 for detectable versus undetectable CD39 levels, P<0.001) and global myocardial flow reserve (Pearson correlation between myocardial flow reserve and log(CD73) -0.19, P<0.001). A subanalysis showed these differences held true independent of liver disease. Conclusions Vasodilatory adenosine is the expected product of local ectonucleotidase activity, yet these data support an inverse relationship between plasma ectonucleotidases, stress myocardial blood flow (CD39), and myocardial flow reserve (CD73). These findings support the conclusion that plasma levels of ectonucleotidases, which may be shed from the endothelial surface, contribute to reduced stress myocardial blood flow and myocardial flow reserve.

Peripheral Expression of ADORA2A Is Increased and Is Correlated with Autism Spectrum Disorder Severity in a Sample of Turkish Children

Background

The aim of this study was to evaluate the peripheral expression of ADORA2A (Adenosine A2A receptor gene) in young subjects with autism spectrum disorder compared with healthy controls and its relationship with clinical characteristics.

Method

This study included 93 children and adolescents with a diagnosis of autism spectrum disorder as the study group and 105 healthy age- and gender-matched controls. Blood samples were obtained from all participants, and a real-time quantitative polymerase chain reaction was performed. Parent- and clinician-rated assessment instruments were used to assess and rate the severity of autism spectrum disorder and other emotional/behavioral problems.

Results

The mean age of the study group was 9.06 ± 3.57 and 86% were male (n = 83), whereas the mean age of the control group was 9.22 ± 3.86 and 86.7% were male (n = 91). We have found a higher level of peripheral expression of ADORA2A in children and adolescents with autism spectrum disorder compared with healthy controls (fold change = 1.33, P = .001). We also found a weak negative correlation with autism spectrum disorder severity (r = -0.216; P = .038) and stereotyped behaviors (r = -0.207, P = .046).

Conclusion

ADORA2A genes may have a role in the pathophysiology of autism spectrum disorder. Further studies are needed to evaluate whether peripheral expression of ADORA2A genes may be among the biomarkers for diagnosing or measuring the severity of autism spectrum disorder.

International Union of Basic and Clinical Pharmacology. CXII: Adenosine Receptors: A Further Update

Our previous International Union of Basic and Clinical Pharmacology report on the nomenclature and classification of adenosine receptors (2011) contained a number of emerging developments with respect to this G protein-coupled receptor subfamily, including protein structure, protein oligomerization, protein diversity, and allosteric modulation by small molecules. Since then, a wealth of new data and results has been added, allowing us to explore novel concepts such as target binding kinetics and biased signaling of adenosine receptors, to examine a multitude of receptor structures and novel ligands, to gauge new pharmacology, and to evaluate clinical trials with adenosine receptor ligands. This review should therefore be considered a further update of our previous reports from 2001 and 2011. SIGNIFICANCE STATEMENT: Adenosine receptors (ARs) are of continuing interest for future treatment of chronic and acute disease conditions, including inflammatory diseases, neurodegenerative afflictions, and cancer. The design of AR agonists ("biased" or not) and antagonists is largely structure based now, thanks to the tremendous progress in AR structural biology. The A2A- and A2BAR appear to modulate the immune response in tumor biology. Many clinical trials for this indication are ongoing, whereas an A2AAR antagonist (istradefylline) has been approved as an anti-Parkinson agent.

The elegant complexity of mammalian ecto-5'-nucleotidase (CD73)

Purinergic signaling is a fundamental mechanism used by all cells to control their internal activities and interact with the environment. A key component of the purinergic system, the enzyme ecto-5'-nucleotidase (CD73) catalyzes the last step in the extracellular metabolism of ATP to form adenosine. Efforts to harness the therapeutic potential of endogenous adenosine in cancer have culminated in the ongoing clinical development of multiple CD73-targeting antibodies and small-molecule inhibitors. However, recent studies are painting an increasingly complex picture of CD73 mRNA and protein regulation and function in cellular homeostasis, physiological adaptation, and disease development. This review discusses the latest conceptual and methodological advances that are helping to unravel the complexity of this important enzyme that was identified nearly 90 years ago.

Calorie restriction slows age-related microbiota changes in an Alzheimer's disease model in female mice

Alzheimer's disease (AD) affects an estimated 5.8 million Americans, and advanced age is the greatest risk factor. AD patients have altered intestinal microbiota. Accordingly, depleting intestinal microbiota in AD animal models reduces amyloid-beta (Aβ) plaque deposition. Age-related changes in the microbiota contribute to immunologic and physiologic decline. Translationally relevant dietary manipulations may be an effective approach to slow microbiota changes during aging. We previously showed that calorie restriction (CR) reduced brain Aβ deposition in the well-established Tg2576 mouse model of AD. Presently, we investigated whether CR alters the microbiome during aging. We found that female Tg2576 mice have more substantial age-related microbiome changes compared to wildtype (WT) mice, including an increase in Bacteroides, which were normalized by CR. Specific gut microbiota changes were linked to Aβ levels, with greater effects in females than in males. In the gut, Tg2576 female mice had an enhanced intestinal inflammatory transcriptional profile, which was reversed by CR. Furthermore, we demonstrate that Bacteroides colonization exacerbates Aβ deposition, which may be a mechanism whereby the gut impacts AD pathogenesis. These results suggest that long-term CR may alter the gut environment and prevent the expansion of microbes that contribute to age-related cognitive decline.

Contribution of adenosine and ATP to the carotid body chemosensory activity in ageing

KEY POINTS

Adenosine and ATP are excitatory neurotransmitters involved in the carotid body (CB) response to hypoxia. During ageing the CB exhibits a decline in its functionality, demonstrated by decreased hypoxic responses. In aged rats (20-24 months old) there is a decrease in: basal and hypoxic release of adenosine and ATP from the CB; expression of adenosine and ATP receptors in the petrosal ganglion; carotid sinus nerve (CSN) activity in response to hypoxia; and ventilatory responses to ischaemic hypoxia. There is also an increase in SNAP25, ENT1 and CD73 expression. It is concluded that, although CSN activity and ventilatory responses to hypoxia decrease with age, adjustments in purinergic metabolism in the CB in aged animals are present aiming to maintain the contribution of adenosine and ATP. The possible significance of the findings in the context of ageing and in CB-associated pathologies is considered.

ABSTRACT

During ageing the carotid body (CB) exhibits a decline in its functionality. Here we investigated the effect of ageing on functional CB characteristics as well as the contribution of adenosine and ATP to CB chemosensory activity. Experiments were performed in 3-month-old and 20- to 24-month-old male Wistar rats. Ageing decreased: the number of tyrosine hydroxylase immune-positive cells, but not type II cells or nestin-positive cells in the CB; the expression of P2X₂ and A_2A receptors in the petrosal ganglion; and the basal and hypoxic release of adenosine and ATP from the CB. Ageing increased ecto-nucleotidase (CD73) immune-positive cells and the expression of synaptosome associated protein 25 (SNAP25) and equilibrative nucleoside transporter 1 (ENT1) in the CB. Additionally, ageing did not modify basal carotid sinus nerve (CSN) activity or the activity in response to hypercapnia, but decreased CSN activity in hypoxia. The contribution of adenosine and ATP to stimuli-evoked CSN chemosensory activity in aged animals followed the same pattern of 3-month-old animals. Bilateral common carotid occlusions during 5, 10 and 15 s increased ventilation proportionally to the duration of ischaemia, an effect decreased by ageing. ATP contributed around 50% to ischaemic-ventilatory responses in young and aged rats; the contribution of adenosine was dependent on the intensity of ischaemia, being maximal in ischaemias of 5 s (50%) and much smaller in 15 s ischaemias. Our results demonstrate that both ATP and adenosine contribute to CB chemosensory activity in ageing. Though CB responses to hypoxia, but not to hypercapnia, decrease with age, the relative contribution of both ATP and adenosine for CB activity is maintained.