Acute sleep fragmentation does not alter pro-inflammatory cytokine gene expression in brain or peripheral tissues of leptin-deficient mice

Abstract

Obesity and sleep fragmentation (SF) are often co-occurring pro-inflammatory conditions in patients with obstructive sleep apnea. Leptin is a peptide hormone produced by adipocytes that has anorexigenic effects upon appetite while regulating immunity. The role of leptin in mediating inflammatory responses to SF is incompletely understood. Male C57BL/6j (lean) and ob/ob mice (leptin-deficient mice exhibiting obese phenotype) were subjected to SF or control conditions for 24 h using an automated SF chamber. Trunk blood and tissue samples from the periphery (liver, spleen, fat, and heart) and brain (hypothalamus, prefrontal cortex, and hippocampus) were collected. Quantitative PCR was used to determine relative cytokine gene expression of pro-inflammatory (IL-1β, TNF-α) and anti-inflammatory (TGF-β1) cytokines. Enzyme-linked immunosorbent assay (ELISA) was used to determine serum corticosterone concentration. Ob/ob mice exhibited elevated cytokine gene expression in liver (TNF-α, TGF-β1), heart (TGF-β1), fat (TNF-α), and brain (hippocampus, hypothalamus, prefrontal cortex: IL-1β, TNF-α) compared with wild-type mice. Conversely, leptin deficiency decreased pro-inflammatory cytokine gene expression in heart (IL-1β, TNF-α). SF significantly increased IL-1β and TNF-α gene expression in fat and TGF-β1 expression in spleen relative to controls, but only in wild-type mice. SF increased basal serum corticosterone regardless of genotype. Taken together, these findings suggest that leptin deficiency affects cytokine gene expression differently in the brain compared to peripheral tissues with minimal interaction from acute SF.

Keywords: Corticosterone; IL-1; IL-1β; Inflammation; Leptin; Ob/ob; Sleep fragmentation; Sleep loss; TGF-β1; TNF-α.

Figure 1. Body mass loss in leptin-deficient (OB) and wild-type (lean) mice exposed to SF or control conditions for 24 h.

Data are shown as % change in body mass ± SE for each group. Shared letters indicate no significant difference between groups. The numbers at the base of the column indicate the sample size of each group.

Figure 2. Effects of fragmented sleep, leptin deficiency (OB), and their interaction upon cytokine gene expression in peripheral tissues.

(A) Liver, (B) spleen, (C) epididymal adipose tissue, (D) heart. Data are shown as mean ± SE for each group. Sample size ranged from N = 6–9, as several samples were undetectable by RT-PCR in some tissue samples. *Denotes p < 0.05 relative to non-SF vehicle control. †Denotes p < 0.05 relative to group(s) indicated by horizontal bar(s). ‡Denotes p < 0.05 relative to all other groups.

Figure 3. Effects of fragmented sleep, leptin deficiency (OB), and their interaction upon cytokine gene expression in the brain.

(A) Hippocampus, (B) hypothalamus, and (C) prefrontal cortex. Data are shown as mean ± SE for each group. Sample size ranged from N = 6–9, as several samples were undetectable by RT-PCR in some tissue samples. *Denotes p < 0.05 relative to non-SF vehicle control. †Denotes p < 0.05 relative to group(s) indicated by horizontal bar(s).

Figure 4. Serum corticosterone concentrations after 24 h of sleep fragmentation or control conditions in wild-type (lean) and leptin-deficient (OB) mice.

Data are shown as mean (ng/mL) ± SE for each group. Shared letters indicate there is no significant difference between groups. Numbers at the base of the column indicate sample size.