Elsevier

Neurobiology of Aging

Volume 21, Issue 5, 1 September 2000, Pages 661-670
Neurobiology of Aging

Age-related changes of apoptotic cell death in human lymphocytes

https://doi.org/10.1016/S0197-4580(00)00171-8Get rights and content

Abstract

Apoptosis seems to be involved in immunosenescence associated with aging. Moreover, in lymphocytes (PBL) of patients with Alzheimer’s disease, an increased susceptibility to the apoptotic pathway has been described possibly due to impaired protection of oxidative stress. Accordingly, it seemed to be of particular interest to investigate the contribution of normal aging to the susceptibility from human lymphocytes to programmed cell death. We could show that PBL from elderly individuals (>60 years) accumulate apoptosing cells to a significant higher extent in spontaneous and activation-induced cell death compared to younger controls (<35 years). Treatment with the oxidative stressor 2-deoxy-d-ribose or with agonistic-CD95-antibody pronounced this effect even more implicating a higher sensitivity to reactive oxygen species and a higher functional CD95 expression, respectively. In addition, expression of the activation markers HLA-DR and CD95 was significantly increased in CD3+-cells of aged subjects, while expression of CD25 did not seem to be affected by age. Expression of Bcl-2 was increased in aging and correlated with the number of apoptotic cells.

Introduction

Programmed cell death (PCD) or apoptosis is of particular interest in aging, as it is thought to play an important role in various age-related degenerative diseases. Apoptosis of white blood cells could be one reason for the decrease of the total number of leukocytes and the decrease of the immune response with aging related to cancer, infections, and autoimmune disorders [3]. Several changes in lymphocytes have been observed related to aging: diminished synthesis of growth and survive factors [46], [51], impaired intracellular calcium regulation [18], different surface molecule expression [43], and defects of signal transduction [36]. Some of these pathological changes are additionally altered in patients with Alzheimer’s disease (AD), but are not present in vascular dementia [13], [14], [15], [17]. In order to differentiate common and divergent mechanisms of an enhanced susceptibility of lymphocytes to apoptosis in aging and sporadic AD, we investigated in detail the molecular basis of enhanced apoptosis in aged human lymphocytes.

Oxidative stress increases with aging and leads to enhanced cellular damage (e.g. lipidperoxidation, protein oxidation, DNA damage (for review see ref. [10]). In addition, reactive oxygen species (ROS) can trigger cells to undergo programmed cell death and can act as second messenger by influencing transcription factors like NF-κB and AP-1. Increased oxidative stress and decreased ability to cope with ROS could amplify apoptotic cell death in aging lymphocytes. Bcl-2 acts in an antioxidative and antiapoptotic way and can interfere with the apoptotic pathway [7], [47].

One of the best known and characterized surface receptors related to PCD in lymphocytes is Apo1/Fas (CD95), a member of the tumor necrosis factor (TNF) superfamily. Stimulation of this receptor by binding to its physiological ligand (Fas-L) or an agonistic anti-Fas antibody leads to apoptosis via a distinct pathway [26]. In addition, activated lymphocytes express the α-chain of the IL2-receptor (CD25) and the MHC class-II related molecule HLA-DR. Lymphocytes bearing these surface molecules or activation markers [4] show enhanced sensitivity to apoptosis upon stimulation of these receptors. Accumulation of chronically activated lymphocytes seems to be one reason for the higher susceptibility to apoptotic cell death probably leading to a lowered leukocyte number in aged individuals. In the present study, we evaluated the basal, spontaneous, activation-, and agent-induced apoptosis and ROS of native and activated peripheral human lymphocytes. In addition, basal expression of activation markers (CD25, CD95, and HLA-DR) and Bcl-2 was determined.

Section snippets

Subjects

Blood samples were taken from n = 85 healthy subjects (55 women and 30 men) between 15 and 93 years. There were 20 women and 12 men in the aged group (n = 32; aged over 60 years, mean age 73.8 ± 8.3 years) and 25 women and 9 men in the group of young controls (n = 34; age under 35 years, mean age 26.4 ± 5.1 years). The remainders were part of the intermediate ages shown in Fig. 3, Fig. 4, Fig. 6. Subjects with psychiatric and neurodegenerative disorders or acute infections were excluded. In

Basal and spontaneous apoptosis are increased in lymphocytes of elderly subjects

Using PI staining, we quantified sub-G1-DNA content in lymphocytes from healthy elderly and young controls. Fig. 1 shows the histogram plots of PI-stained lymphocytes of two representative subjects. Student’s t-test revealed that the percentage of basal apoptotic nuclei in freshly isolated lymphocytes was significantly elevated in aged subjects compared to young controls (means ± SEM: old, 1.35 ± 0.20% versus young, 0.84 ± 0.11%; ∗, P < 0.05; Fig. 2 a). In addition, we found a significantly

Discussion

Previous results of our group reported an increased content of basal and dRib-induced apoptotic cells in PBMC from patients with Alzheimer’s disease relative to age-matched controls [13], [40]. This effect is probably not related to the physiological process of immunosenescence. In addition, apoptosis is a hallmark in brains derived from Alzheimer’s patients, possibly associated with states of increased oxidative stress [8], [45], [49], [52]. Similar alterations could also be detected in

Acknowledgements

This work was supported by grants from the Alzheimer Forschung Frankfurt and Fonds der chemischen Industrie.

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