Manipulation of Gut Microbiota during Critical Windows of Development and its Effects on Immune System Function Later in Life

Abstract

The potential long-term complications of gut microbiota perturbation during critical developmental periods of early life and puberty are a growing concern. Exposure to immune stressors such as antibiotics or lipopolysaccharides (LPS) in these periods disturbs the gut microbial balance and increases the risk of immunological disorders later in life. Probiotics and prebiotics can counteract inflammation and microbiota perturbation induced by antibiotic or LPS exposure. However, the underlying mechanisms remain inadequately explored. We postulated that exposure to LPS/antibiotic during puberty or early life negatively affects immune system homeostasis later in life while probiotic/prebiotic intake mitigates immune system disturbance related to LPS/antibiotic-induced inflammation and dysbiosis through modulating signaling pathways and epigenetic mechanisms, including miRNAs and DNA methylation. Therefore, this thesis aims to understand better the mechanisms underlying the protective effects of biotics intake against lasting immune deregulation associated with exposure to immune stressors during the developmental stages of life. The objectives of this project are: 1. To study the immunomodulatory properties of probiotic SV-53, viable and heat-inactivated forms, and prebiotic PCA, by assessing cytokines, miRNAs, and DNA methylation of genes related to the pro-inflammatory cytokine IL-17 signaling at the gut level. 2. To study if probiotic/prebiotic intake counteracts long-term immune system deregulation induced by inflammation and dysbiosis during puberty, through assessing cytokines, signaling pathways, miRNAs, and DNA methylation of genes related to the pro-inflammatory cytokine IL-17 pathway at the gut level. 3. To study if prebiotic intake counteracts early life antibiotic induced-dysbiosis and its long-term adverse effects on immune system homeostasis by assessing cytokines and miRNAs related to inflammatory pathways, including NF-κB and STAT3 at the gut level. We used pre-clinical models involving Balb/c mice, exposing them to a single dose of LPS at puberty or to low-dose penicillin early in life by feeding dams with the antibiotic during the last week of gestation until weaning of pups. The role of probiotic/prebiotic intake in preventing and correcting long-term consequences of LPS or antibiotic was assessed by exploring the gut microbiota using fecal samples, as well as immune signaling, miRNA expressions, and DNA methylation in the ileum samples. Results of these studies revealed the ability of probiotic SV-53 to improve gut immunity by increasing IgA levels and reducing inflammatory cytokines and miRNAs, such as IL-17A, IL-6, IL-23, miR-223, and miR-425, as well as epigenetic regulation of genes related to IL-17 signaling, including Il6, Il17rc, Il9, Il11, Akt1, Ikbkg, Sgk1, Cblb, and Smad4. In addition, probiotic and prebiotic intake alleviated immune system dysfunction induced by pubertal LPS by modulating IL-17A, IL-17F, IL-6, IL-1β, STAT3, FOXO1, miR-145, and DNA methylation of genes related to IL-17 signaling, including Lpb, Rorc, Runx1, Il17ra, Rac1, Ccl5, and Il10. Finally, maternal prebiotic intake could mitigate enduring immune dysfunction related to early-life antibiotic-induced dysbiosis in offspring by diminishing gut microbiota disturbances, reducing NF-κB levels, and inhibiting antibiotic-induced alterations in gut miRNAs, including miR-145. These findings highlight the importance of dietary intervention as an effective approach to influence immune system programming during critical developmental stages and mitigate health issues stemming from early-life dysbiosis later in life.