Myeloid differentiation architecture of leukocyte transcriptome dynamics in perceived social isolation

Abstract

To define the cellular mechanisms of up-regulated inflammatory gene expression and down-regulated antiviral response in people experiencing perceived social isolation (loneliness), we conducted integrative analyses of leukocyte gene regulation in humans and rhesus macaques. Five longitudinal leukocyte transcriptome surveys in 141 older adults showed up-regulation of the sympathetic nervous system (SNS), monocyte population expansion, and up-regulation of the leukocyte conserved transcriptional response to adversity (CTRA). Mechanistic analyses in a macaque model of perceived social isolation confirmed CTRA activation and identified selective up-regulation of the CD14(++)/CD16(-) classical monocyte transcriptome, functional glucocorticoid desensitization, down-regulation of Type I and II interferons, and impaired response to infection by simian immunodeficiency virus (SIV). These analyses identify neuroendocrine-related alterations in myeloid cell population dynamics as a key mediator of CTRA transcriptome skewing, which may both propagate perceived social isolation and contribute to its associated health risks.

Keywords: health; inflammation; loneliness; social genomics.

Fig. 1.

CTRA gene expression, monocyte prevalence, and neuroendocrine parameters in individuals chronically high in PSI. (A) Differential expression of 53 CTRA indicator transcripts in five yearly longitudinal PBMC samples from individuals chronically high in PSI (n = 36) vs. those intermediate or low in PSI (n = 105). Point estimates and SE come from repeated measures mixed effect linear models (P = 0.024, as in Table 1, row A). (B) Monocyte percentages in two longitudinal whole blood samples from individuals chronically high versus intermediate or low in PSI (association with categorical chronically high PSI, P = 0.052; association with continuously varying PSI as measured by UCLA Loneliness Scale scores, P = 0.012). Boxes, 25th, 50th, and 75th percentiles; whiskers, first and 99th percentiles. (C) CTRA gene expression as a function of monocyte percentage (association, P < 0.001 by repeated measures mixed linear model). (D) PSI-related differences in urinary metabolite concentrations for norepinephrine (association with categorical chronic high PSI, b = 332.1 ± SE 194.7 ng/dL, P = 0.090; association with continuous PSI, b = 23.0 ± 7.4 ng/dL, P = 0.002), epinephrine (categorical, b = 16.0 ± 12.2 ng/dL, P = 0.192; continuous, b = 0.4 ± 0.5 ng/dL, P = 0.401), and cortisol (categorical, b = 197.5 ± 83.6 ng/dL, P = 0.018; continuous, b = 5.4 ± 3.6 ng/dL, P = 0.134).

Fig. 2.

Perceived social isolation, social threat, and SNS activity. (A) Behavioral indicators of preference (gaze frequency and duration) were assessed in 27 adult macaques classified as high PSI (n = 7), intermediate PSI (n = 10), and low PSI (n = 10) as they viewed video presentations of affiliative behavior directed at them by a novel safe juvenile male or risky adult male. Data represent mean ± SE threat discrimination ratios (juvenile target/adult target) on the first day of video exposure (novel social situation) and the third day (habituated) in high-PSI animals vs. intermediate- and low-PSI controls; P values from mixed effects linear model analysis of log-ratios. (B) Average urinary catecholamine metabolite concentrations in 18 adult male macaques classified as high PSI (n = 4) vs. intermediate- (n = 6) or low-PSI (n = 8) controls. Data come from archival analysis of newly derived PSI classifications in a previously published study (21) and represent mean ± SE of up to six assessments over 20 wk; P values indicate group main effect for each metabolite.

Fig. 3.

Differential gene expression, monocyte transcriptome representation, and glucocorticoid regulation in the rhesus macaque model of PSI. (A) Differential expression of 53 CTRA indicator transcripts in PBMC samples from 49 rhesus macaques classified by behavioral observations as low or intermediate PSI (n = 22 and 19, respectively) vs. high PSI (n = 8) as in Fig. 1A (P = 0.017, controlling for age). (B) Transcript origin analyses (12) identifying major leukocyte subset origins of the 229 gene transcripts that showed ≥1.2-fold differential expression in high-PSI vs. intermediate- and low-PSI animals (70 up-regulated transcripts and 159 down-regulated transcripts are listed in Table S1). (C) Transcript origin analyses assessing the extent to which CD14⁺⁺/CD16⁻ classical and CD14⁺/CD16⁺ nonclassical monocyte transcriptomes contributed to differential gene expression. (D) Functional glucocorticoid sensitivity of myeloid lineage immune cells (neutrophils) was assessed using an in vivo hematological redistribution assay that quantified the extent to which circulating neutrophil numbers (normalized to lymphocyte numbers to control for variations in total white blood cell count) varied as a function of endogenous physiological variations in cortisol levels (22, 24). Log-transformed neutrophil/lymphocyte ratios were subject to mixed effect linear model analysis of four repeated measurements collected at 9:00 AM and 3:00 PM on 2 d from low-PSI animals (n = 172 observations on 27 animals, 16 of whom were also resampled 1 y later), intermediate-PSI animals (n = 132 observations on 21 animals, 12 of whom were resampled 1 y later), and high-PSI animals (n = 32 observations on 6 animals, 2 of whom were resampled 1 y later). Average values are displayed in raw ratio units to facilitate interpretation, and lines span the observed range of cortisol values. (E) In vivo transcriptional activity of glucocorticoid receptor (GR) and NF-κB transcription factors as assessed by TELiS bioinformatic analysis (50) of transcription factor-binding motif prevalence in promoter DNA sequences of genes showing ≥1.2-fold differential gene expression in high-PSI animals vs. low- and intermediate-PSI controls.

Fig. 4.

Social threat and monocyte population dynamics. Effect of chronic novelty-related social threat on circulating monocyte populations was assessed in 21 adult male macaques randomized to socialize for 100 min/d on 3–5 d/wk with either a continually varying array of novel social partners (n = 11) or a stable group of social partners (n = 10) (21). Data represent mean ± SE change from presocialization baseline to 5-wk follow-up in total monocytes (A) and classical and nonclassical monocyte subsets (B); P values from mixed effect linear model analysis.

Fig. 5.

IFN gene expression and response to SIV infection in the rhesus macaque model of PSI. (A) mRNA encoding type I (IFNA, IFNB) and type II (IFNG) interferons was assessed in PBMCs from 12 adult male macaques experimentally infected with simian immunodeficiency virus (SIV) (Control 1, 6 low PSI; Control 2, 4 intermediate PSI; PSI model: 2 high PSI) at preinfection baseline, 2 wk postinfection (peak of acute viral replication), and 10 wk postinfection (long-term viral replication set point). Data represent mean ± SE fold-difference from five SIV-uninfected controls; P values contrast high-PSI vs. controls pooling across IFNs. (B) Immunologic response to SIV was assessed by quantifying suppression of SIV gag and env mRNA levels in PBMC from peak viral replication (wk 2 postinfection) to long-term set point (wk 10). Data represent mean ± SE % reduction from wk 2 to wk 10; P value contrasts high-PSI vs. controls pooling across SIV transcripts. Long-term control of viral replication was assessed by plasma SIV viral load (C) and anti-SIV IgG titers (D) at set point (wk 10). Data represent mean ± SE log₁₀ SIV RNA copies per milliliter of plasma or log₂ optical density of IgG ELISA over fourfold plasma dilutions; P values contrast high-PSI vs. controls.