Long-term effects of early-life gut microbiota perturbations on pancreatic islet development

  • Author / Creator
    Sosa Alvarado, Carla
  • Impaired secretion of insulin from pancreatic beta-cells, along with loss of cell mass, is one of the hallmarks of the pathogenesis of type 2 diabetes, a metabolic disorder characterized by chronic hyperglycemia. In humans, beta-cells’ ability to secrete insulin in response to glucose is acquired in the first year of life and is considered as a critical window for beta-cell mass expansion and maturation. However, early exposure to environmental and metabolic stressors could impair the acquisition of beta-cell functional maturation and increase the susceptibility to develop diabetes.
    Along with genetic factors, lifestyle and diet, the gut microbiota has been considered as an environmental factor that plays an important role in the etiology of diabetes. Children treated with more than one course of antibiotic during the first 2 years of life have a higher risk of childhood overweight, which is a risk for developing diabetes. Moreover, previous work by our laboratory found that antibiotic-induced gut microbiota perturbations altered pancreatic islet function and morphology in weaning piglets after antibiotic withdrawal, with impaired glucose tolerance later in life.
    Therefore, the first aim of this thesis is to examine earlier, neonatal pancreatic islet functional maturation during antibiotic administration in the piglet model with the hypothesis that antibiotic administration will change the composition of the gut microbiota, leading to alterations in microbial metabolites that will be associated with impaired beta-cell functional maturation.
    We examined the gut microbiota composition and pancreatic islet function and growth from neonatal piglets exposed to antibiotics. Compared with controls (CON), antibiotic-treated (ANTI) postnatal day (PND)7 pigs had elevated transcripts of proteins involved in GLP-1 synthesis or signaling in islets (p<0.05) coinciding with a pattern of higher plasma GLP-1 (p=0.11), which were not detected by PND14. mRNA levels of Tnf (p<0.05) a pro-inflammatory cytokine, and Npg1 (p<0.05), a cathelicidin, were also transiently increased in pancreas of PND7 ANTI pigs’ concomitant with 10-fold higher culturable intestinal coliforms (p<0.05). Antibiotic-induced changes in ileal microbial composition at PND7 included relative increases in genera Escherichia, Coprococcus, Ruminococcus, Dehalobacterium, and Oscillospira, which were normalized after antibiotic withdrawal. In ANTI islets at PND14, the expression of key regulators Pdx1, Igf2 and Tcf7l2 was down-regulated, preceding a 40% reduction of beta-cell area (p<0.01) and insulin content/islet at PND49 (p<0.05). At PND49, a 2-fold elevated non-fasted plasma insulin concentration (p=0.07) was observed in ANTI compared with CON.
    In conclusion, antibiotic treatment of neonatal piglets elicits gut microbial changes accompanied by phasic alterations in key regulatory genes in pancreatic islets at PND7 and 14. By PND49, reduced beta-cell area and islet insulin content were accompanied by elevated non-fasted insulin despite normoglycemia, indicative of islet stress.
    The second aim was to study whether elevated gut Escherichia coli in combination with antibiotics contributed to altered glucose tolerance in adulthood. We used C57BL/6 black mice exposed to oral doses of amoxicillin during the first 14 days of life in the absence or presence of Escherichia coli in the gut, and then weaned onto a high-fat diet. We observed an increase in body weight in Escherichia coli mice at PND14. Combined exposure to Escherichia coli and early-life antibiotic treatment caused worsened glucose tolerance at age 7 weeks, consistent with insulin secretion dysfunction and/or insulin resistance.
    Together, this work confirms that gut microbiota perturbations elicit long-term effects on beta-cell function and glucose homeostasis. Possible mechanistic explanations are likely related to alterations in the temporal programming of transcription factors important for controlling beta-cell mass and function.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.