DNA Methylation-Based Age Prediction and Telomere Length Reveal an Accelerated Aging in Induced Sputum Cells Compared to Blood Leukocytes: A Pilot Study in COPD Patients

Abstract

Aging is the predominant risk factor for most degenerative diseases, including chronic obstructive pulmonary disease (COPD). This process is however very heterogeneous. Defining the biological aging of individual tissues may contribute to better assess this risky process. In this study, we examined the biological age of induced sputum (IS) cells, and peripheral blood leukocytes in the same subject, and compared these to assess whether biological aging of blood leukocytes mirrors that of IS cells. Biological aging was assessed in 18 COPD patients (72.4 ± 7.7 years; 50% males). We explored mitotic and non-mitotic aging pathways, using telomere length (TL) and DNA methylation-based age prediction (DNAmAge) and age acceleration (AgeAcc) (i.e., difference between DNAmAge and chronological age). Data on demographics, life style and occupational exposure, lung function, and clinical and blood parameters were collected. DNAmAge (67.4 ± 5.80 vs. 61.6 ± 5.40 years; p = 0.0003), AgeAcc (-4.5 ± 5.02 vs. -10.8 ± 3.50 years; p = 0.0003), and TL attrition (1.05 ± 0.35 vs. 1.48 ± 0.21 T/S; p = 0.0341) are higher in IS cells than in blood leukocytes in the same patients. Blood leukocytes DNAmAge (r = 0.927245; p = 0.0026) and AgeAcc (r = 0.916445; p = 0.0037), but not TL, highly correlate with that of IS cells. Multiple regression analysis shows that both blood leukocytes DNAmAge and AgeAcc decrease (i.e., younger) in patients with FEV1% enhancement (p = 0.0254 and p = 0.0296) and combined inhaled corticosteroid (ICS) therapy (p = 0.0494 and p = 0.0553). In conclusion, new findings from our work reveal a differential aging in the context of COPD, by a direct quantitative comparison of cell aging in the airway with that in the more accessible peripheral blood leukocytes, providing additional knowledge which could offer a potential translation into the disease management.

Keywords: DNA methylation age; age acceleration; chronic obstructive pulmonary disease; induced sputum; lung aging; telomere length.

Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Copyright © 2021 Campisi, Liviero, Maestrelli, Guarnieri and Pavanello.

Figures

Figure 1

DNAmAge and AgeAcc of the induced sputum cells and blood leukocytes in COPD patients. In (A), box plots show levels of DNAmAge in induced sputum cells (n = 7) and in paired blood leukocytes of the same COPD patient (n = 7), and in blood leukocyte samples of all COPD patients (n = 16). In box plots, the boundary of the box closest to the x-axis indicates the 25th percentile, the line within the box marks the mean, and the boundary of the box farthest from the x-axis indicates the 75th percentile. Whiskers (error bars) above and below the box indicate the 95 and 5th percentiles. The horizontal bar with asterisk indicates the significant comparison between induced sputum cells (n = 7) and paired blood leukocytes DNAmAge of the same patient (n = 7) (*Paired t-test: mean 67.4 ± 5.80 years vs. mean 61.6 ± 5.40 years; p = 0.0003). In contrast, the comparison between the DNAmAge of the induced sputum cells (n = 7) and all blood leukocytes (n = 16) is not significant (Mann–Whitney U-test: mean 67.4 ± 5.80 years vs. mean 63.3 ± 5.60 years; p = 0.1589). In (B), box plots show levels of AgeAcc in induced sputum cells (n = 7) and in paired blood leukocytes of the same COPD patient (n = 7), and in blood leukocytes samples of all COPD patients (n = 16). In box plots, the boundary of the box closest to the x-axis indicates the 25th percentile, the line within the box marks the mean, and the boundary of the box farthest from the x-axis indicates the 75th percentile. Whiskers (error bars) above and below the box indicate the 95th and 5th percentiles. The horizontal bar with an asterisk indicates the significant comparison between induced sputum cells (n = 7) and paired blood leukocytes AgeAcc of the same patient (*Paired t-test (n = 7): mean −4.5 ± 5.02 years vs. mean −10.8 ± 3.50 years; p = 0.0003]. The upper longer horizontal bar with two asterisks indicates the significant comparison between AgeAcc of the induced sputum cells (n = 7) and blood leukocytes in all patients (n = 16) (**Mann–Whitney U-test: mean −4.5 ± 5.02 years vs. mean −10.3 ± 3.63 years; p = 0.0156].

Figure 2

TL of the induced sputum cells and blood leukocytes in COPD patients. Box plots show levels of TL in induced sputum cells (n = 8) and in paired blood leukocytes of the same patient (n = 8), and blood leukocyte samples of all patients (n = 18). In box plots, the boundary of the box closest to the x-axis indicates the 25th percentile, the line within the box marks the mean, and the boundary of the box farthest from the x-axis indicates the 75th percentile. Whiskers (error bars) above and below the box indicate the 95 and 5th percentiles. The horizontal bar with one asterisk indicates the significant comparison between induced sputum cells (n = 8) and paired blood leukocyte TL of the same patient (n = 8) (*Paired t-test: mean 1.05 ± 0.35 T/S vs. mean 1.48 ± 0.21 T/S; p = 0.0341). The upper longer horizontal bar with two asterisks indicates the significant comparison between TL of the induced sputum cells (n = 8) and blood leukocytes in all patients (n = 18) (**MannWhitney U-test: mean 1.05 ± 0.35 T/S vs. mean 1.47 ± 0.26 T/S; p = 0.0133).

Figure 3

Correlation curves between blood leukocytes DNAmAge (A) or AgeAcc (B) and chronological age of n = 16 COPD patients. In (A), a simple linear regression plot shows the correlation between blood leukocyte DNAmAge and chronological age [correlation coefficient (r) = 0.836142; two-sided p < 0.0001], while in (B), simple linear regression linear regression plot showing the correlation between blood leukocyte AgeAcc and chronological age [correlation coefficient (r) = −0.53542; two-sided p = 0.0326]. Mean, standard error (SE), and 95% coefficient intervals (CI) are represented as green, pink, and black lines, respectively.

Figure 4

Correlation curves between blood leukocytes and induced sputum cells DNAmAge (A) or AgeAcc (B) of n = 7 COPD patients. In (A), a simple linear regression plot shows the correlation between blood leukocytes and induced sputum cell DNAmAge [correlation coefficient (r) = 0.927245; two-sided p = 0.0026], whereas in (B), a simple linear regression plot shows the correlation between blood leukocytes and induced sputum cells AgeAcc [correlation coefficient (r) = 0.916445; two-sided p = 0.0037]. Mean, standard error (SE), and 95% coefficient intervals (CI) are represented as green, pink, and black lines, respectively.