The GH/IGF-1 axis in a critical period early in life determines cellular DNA repair capacity by altering transcriptional regulation of DNA repair-related genes: implications for the developmental origins of cancer

Abstract

Experimental, clinical, and epidemiological findings support the concept of developmental origins of health and disease (DOHAD), suggesting that early-life hormonal influences during a sensitive period around adolescence have a powerful impact on cancer morbidity later in life. The endocrine changes that occur during puberty are highly conserved across mammalian species and include dramatic increases in circulating GH and IGF-1 levels. Importantly, patients with developmental IGF-1 deficiency due to GH insensitivity (Laron syndrome) do not develop cancer during aging. Rodents with developmental GH/IGF-1 deficiency also exhibit significantly decreased cancer incidence at old age, marked resistance to chemically induced carcinogenesis, and cellular resistance to genotoxic stressors. Early-life treatment of GH/IGF-1-deficient mice and rats with GH reverses the cancer resistance phenotype; however, the underlying molecular mechanisms remain elusive. The present study was designed to test the hypothesis that developmental GH/IGF-1 status impacts cellular DNA repair mechanisms. To achieve that goal, we assessed repair of γ-irradiation-induced DNA damage (single-cell gel electrophoresis/comet assay) and basal and post-irradiation expression of DNA repair-related genes (qPCR) in primary fibroblasts derived from control rats, Lewis dwarf rats (a model of developmental GH/IGF-1 deficiency), and GH-replete dwarf rats (GH administered beginning at 5 weeks of age, for 30 days). We found that developmental GH/IGF-1 deficiency resulted in persisting increases in cellular DNA repair capacity and upregulation of several DNA repair-related genes (e.g., Gadd45a, Bbc3). Peripubertal GH treatment reversed the radiation resistance phenotype. Fibroblasts of GH/IGF-1-deficient Snell dwarf mice also exhibited improved DNA repair capacity, showing that the persisting influence of peripubertal GH/IGF-1 status is not species-dependent. Collectively, GH/IGF-1 levels during a critical period during early life determine cellular DNA repair capacity in rodents, presumably by transcriptional control of genes involved in DNA repair. Because lifestyle factors (e.g., nutrition and childhood obesity) cause huge variation in peripubertal GH/IGF-1 levels in children, further studies are warranted to determine their persisting influence on cellular cancer resistance pathways.

Keywords: Cellular resilience; Endocrine; Growth hormone; Insulin-like growth factor-1; Lifespan, health span; Longevity; Stress resistance.

Fig. 1

Early-life GH/IGF-1 status of donor rats elicits persisting alterations in DNA repair capacity in cultured primary fibroblasts. Fibroblasts were γ-irradiated, and DNA damage was assessed by single-cell electrophoresis (“comet assay”) at different time points post-irradiation. Damaged DNA migrates during electrophoresis from the nucleus toward the anode, forming the shape of a “comet” with a head (cell nucleus with intact DNA) and a tail (relaxed and broken DNA). a Representative images of damaged DNA in irradiated (3 Gy) fibroblasts derived from control rats, Lewis dwarf rats, and Lewis dwarf rats with early-life GH treatment. Median values of tail DNA content in each sample were determined. Note the marked decline in tail DNA content at 20 min post-irradiation due to DNA repair processes. b γ-Irradiated fibroblasts exhibit comparable DNA damage. Shown are γ-irradiation (3 Gy)-induced increases in tail DNA content in fibroblasts derived from control rats, Lewis dwarf rats, and Lewis dwarf rats with peripubertal GH treatment. *p < 0.05 vs respective non-irradiated controls (one-way ANOVA, Tukey’s multiple comparisons). c Fibroblasts derived from control rats Lewis dwarf rats exhibit increased DNA repair capacity, which is prevented by peripubertal GH treatment. For assessment of DNA repair efficiency, the percentage of residual DNA damage was plotted as a function of time post-irradiation. Tail DNA content at each time point is shown. The residual DNA damage at 20 min post-irradiation was the lowest in fibroblasts from untreated Lewis dwarf rats, indicating more efficient DNA repair processes in these cells, which was reversed by peripubertal GH treatment. *p < 0.001 Lewis dwarf vs control; # Lewis dwarf vs Lewis dwarf GH (one-way ANOVA, Tukey’s multiple comparisons); data are mean ± SEM (n = 5–6 for each time-point). The time constant calculated from these plots (τ) is shown next to the legends

Fig. 2

Developmental GH/IGF-1 deficiency in Snell dwarf mice associates with increased DNA repair capacity in cultured primary fibroblasts. a Representative images of damaged DNA in irradiated (3 Gy) fibroblasts derived from control mice and GH/IGF-1-deficient Snell dwarf mice. Note the greater decline in tail DNA content at 20 and 60 min post-irradiation in cells derived from Snell dwarf mice due to improved DNA repair processes. b γ-Irradiated fibroblasts exhibit comparable DNA damage. Shown are increases in tail DNA content induced by increasing doses of γ-irradiation (3 to 9 Gy) in fibroblasts derived from control mice and Snell dwarf mice (n.s.: not significant vs control; t test). c Fibroblasts derived from Snell dwarf mice exhibit increased DNA repair capacity as compared to controls. For assessment of DNA repair efficiency, the percentage of residual DNA damage was plotted as a function of time post-irradiation. Tail DNA content at each time point is shown. The time constant calculated from this plot was shorter, and the residual DNA damage post-irradiation was lower in fibroblasts from Snell dwarf mice as compared to cells derived from control mice, indicating a more efficient DNA repair capacity in these cells. *p < 0.001 Snell dwarf vs control (t test). Data are mean ± SEM (n = 5 for each time-point). d White blood cells derived from mice with adult-onset IGF-1 deficiency (Igf1 ^f/f + TBG-Cre-AAV8) and control mice exhibit comparable DNA repair capacity. Data are mean ± SEM (n = 5 for each time-point)

Fig. 3

qPCR data showing expression of genes involved in regulation of DNA repair pathways, including γ-radiation-induced common stress response genes, in fibroblasts derived from control rats, Lewis dwarf rats, and GH-replete dwarf rats. Expression of target genes was compared under basal conditions and at 2, 4, and 6 h post-irradiation. Data are mean ± SEM (n = 3–6 for each data point). *p < 0.05 Lewis dwarf vs control, #p < 0.05 Lewis dwarf vs Lewis dwarf + GH