Age-related changes in the calcium homeostasis of adherent neutrophils

Immunosenescence and inflammaging: Mechanisms and role in diseases

Age-related changes initiate a cascade of cellular and molecular alterations that lead to immune system dysfunction or abnormal activation, predisposing individuals to age-related diseases. This phenomenon, commonly referred to as immunosenescence, highlighting aging-associated progressive decline of the immune system. Moreover, mounting evidence suggests that immunosenescence contributes to a related pathological phenomenon known as inflammaging. Inflammaging refers to chronic, low-grade, and systemic inflammation associated with aging, occurring despite the absence of overt stimuli. In the body, inflammation is typically activated in response to overt stimuli such as bacterial/microbial invasion or a pathological state, however, inflammaging occurrence and its underpinning mechanisms seem to be independent and in the absence of such stimuli. Despite recent advancements in molecular characterization and the scrutiny of disease relevance, these two interconnected concepts have remained largely unexplored and unrecognized. In this comprehensive review, we aim to shed light on the mechanistic and cellular aspects of immunosenescence and inflammaging, as well as their pivotal roles in the pathogenesis of aging-related diseases, including cancer, infections, dementia, and neurodegenerative disorders.

ROS production, intracellular HSP70 levels and their relationship in human neutrophils: effects of age

ROS production and intracellular HSP70 levels were measured in human neutrophils for three age groups: young (20-59 years), elders (60-89 years) and nonagenarians (90 years and older). Elders showed higher levels of spontaneous intracellular ROS content compared with young and nonagenarian groups, which had similar intracellular ROS levels. Zymosan-induced (non-spontaneous) extracellular ROS levels were also similar for young and nonagenarians but were lower in elders. However, spontaneous extracellular ROS production increased continuously with age. Correlation analysis revealed positive relationships between HSP70 levels and zymosan-stimulated ROS production in the elder group. This was consistent with a promoting role for HSP70 in ROS-associated neutrophils response to pathogens. No positive correlation between ROS production and intracellular HSP70 levels was found for groups of young people and nonagenarians. In contrast, significant negative correlations of some ROS and HSP70 characteriscics were found for neutrophils from young people and nonagenarians. The observed difference in ROS and HSP70 correlations in elders and nonagenarians might be associated with an increased risk of mortality in older individuals less than 90 years old.

Elevated intracellular calcium in neutrophils in patients with Down syndrome

BACKGROUND

Neutrophils of patients with Down syndrome (DS) are known to have numerous abnormalities associated with diminished resistance to infection. The intracellular calcium (Ca(2+)i) acts as a second messenger and regulates diverse functions in many cell types. The purpose of the present study was to compare the intracellular calcium concentration ([Ca(2+)]i) at baseline and stimulated conditions in DS patients and in normal subjects to investigate [Ca(2+)]i regulation in neutrophils.

METHODS

The study group consisted of 27 subjects with DS (age, 8.6 +/- 4.6 years) and 14 healthy subjects (age, 12.0 +/- 3.9 years). Using a fluorescent probe, fura-2, the baseline levels and changes in [Ca(2+)]i were examined after stimulation of neutrophils with N-formyl-methionyl-leucyl-phenylalanine (fMLP).

RESULTS

At baseline, the [Ca(2+)]i of neutrophils from DS subjects was significantly higher than that of the controls (70.6 +/- 28.0 nmol/L vs 44.4 +/- 16.0 nmol/L, P < 0.01). The absolute [Ca(2+)]i after addition of fMLP in the DS subjects was also significantly higher than that of the control group (250 +/- 91 nmol/L vs 167 +/- 60 nmol/L, respectively: P < 0.01). The neutrophils from the DS subjects had a consistently and significantly prolonged response to fMLP as compared to the neutrophils of control subjects.

CONCLUSIONS

The higher [Ca(2+)]i and the prolonged response of [Ca(2+)]i to fMLP appear to be phenotypic traits of neutrophils in subjects with DS. This suggests intrinsic cellular defects in DS.

Impact of parathyroidectomy on neutrophil cytosolic calcium in chronic kidney disease patients: a prospective parallel group trial

OBJECTIVES

Polymorphonuclear leucocytes (PMNs) of chronic kidney disease (CKD) patients display elevated basal cytosolic calcium concentrations (iCa(2+)). As parathyroid hormone is considered to substantially contribute to the inappropriate cellular entry of calcium in uraemia, we hypothesized that parathyroidectomy lowers PMN iCa(2+).

DESIGN AND SETTING

Prospective parallel group trial at a tertiary care centre. SUBJECTS, INTERVENTION AND MAIN OUTCOME MEASURES: Two patient cohorts (cohort 1: 14 CKD patients; cohort 2: 14 renal transplant recipients) underwent parathyroidectomy for uncontrolled secondary hyperparathyroidism. We assessed PMN iCa(2+) (primary objective) spectrofluorimetrically 1 day before and 20 days after intervention (secondary objective: PMN glucose uptake). Data were compared with those of 16 matched maintenance haemodialysis patients (cohort 3), and to 15 healthy subjects (cohort 4), by generalized estimating equations.

RESULTS

PMN iCa(2+) of cohort 1 decreased over time and was significantly higher than that of cohort 3 before but not after parathyroidectomy [mean difference before/after parathyroidectomy: 19.1 nmol L(-1) (95% confidence interval: 9.4-22.4), P =0.0003/-3.2 (-20.9-14.5), P = 0.71]. PMN iCa(2+) of cohort 2 decreased over time, but we found no significant difference in comparison with cohort 3 [mean difference before/after parathyroidectomy: 6.5 nmol L(-1) (-9.4-22.4), P = 0.4/-15.8 (-43.6-12.0), P = 0.25]. PMN iCa(2+) of all CKD patients was substantially higher in comparison with that of healthy subjects [cohort 4 vs. 3: -35.3 (-48.9-21.6), P < 0.001]. PMN glucose uptake increased significantly in both interventional cohorts in comparison with cohort 3.

CONCLUSIONS

Parathyroidectomy lowers, but does not normalize PMN iCa(2+) of CKD patients. Further variables, possibly uraemic retention solutes, control both PMN iCa(2+) and functional responses.

Signal transduction and functional changes in neutrophils with aging

It is well known that the immune response decreases during aging, leading to a higher susceptibility to infections, cancers and autoimmune disorders. Most widely studied have been alterations in the adaptive immune response. Recently, the role of the innate immune response as a first-line defence against bacterial invasion and as a modulator of the adaptive immune response has become more widely recognized. One of the most important cell components of the innate response is neutrophils and it is therefore important to elucidate their function during aging. With aging there is an alteration of the receptor-driven functions of human neutrophils, such as superoxide anion production, chemotaxis and apoptosis. One of the alterations underlying these functional changes is a decrease in signalling elicited by specific receptors. Alterations were also found in the neutrophil membrane lipid rafts. These alterations in neutrophil functions and signal transduction that occur during aging might contribute to the significant increase in infections in old age.

Neutrophil immunity of the elderly

Due to age-related changes of the immune system, elderly people are more susceptible to microbial infections than the young. Most research concerning immune senescence has been done on T and B cells, yet the first cells to migrate into microbe-infected tissue are neutrophils, which phagocytose and kill the pathogens. Long regarded as mere phagocytes, the neutrophils' importance for the immune response has been recognized in current publications, which acknowledge them an active participation in the cytokine network. Similarities in the symptoms of patients with genetical neutrophil deficiencies and those of the elderly indicate a leading role of neutrophils in the effects of immune senescence. While the number of circulating neutrophils remains unaltered in the elderly compared with young controls, phagocytosis and intracellular killing have been reported impaired. Oddly enough, the results for various stimuli differed: while some showed a decrease in neutrophil activation, the response to others remained unaltered. More research needs to be done on this, preferably using preparations of high purity to exclude monocytic interventions. Elucidation of immune deficiencies caused by neutrophil senescence can be an important contribution to a healthier elderly population.