Effect of doxycycline on the gut microbiome and neuroinflammation

Abstract: Many mouse models of neurological disease use the tetracycline transactivator (tTA) system to control transgene expression by oral treatment with the broad-spectrum antibiotic doxycycline. Antibiotic treatment used for transgene control might have undesirable systemic effects, including the potential to affect immune responses in the brain via changes in the gut microbiome. Recent work has shown that an antibiotic cocktail to perturb the gut microbiome can suppress microglial reactivity to brain amyloidosis in transgenic mouse models of Alzheimer's disease based on controlled overexpression of the amyloid precursor protein (APP). Here we assessed the impact of chronic low dose doxycycline on gut microbiome diversity and neuroimmune response to systemic LPS challenge in a tTA-regulated model of Alzheimer's amyloidosis. We show that doxycycline decreased microbiome diversity in both APP transgenic and wild-type mice and that these changes persisted long after drug withdrawal. Despite this change in microbiome composition, dox treatment had minimal effect on transcriptional signatures in the brain, both at baseline and following acute LPS challenge. Our findings suggest that central neuroinflammatory responses may be less affected by dox at doses needed for transgene control than by antibiotic cocktail at doses used for microbiome manipulation. Twenty-three RNA samples (extracted from brain cortex) were analyzed. There are 4 experimental groups: Untreated (n=8), Dox (n=4), LPS (n=5), and Dox+LPS (n=6). Untreated mice were never exposed to doxycycline. Dox mice received oral doxycycline treatment in chow (100mg/kg) from neonatal day P3 until 6 weeks of age, followed by 6 weeks of doxycycline washout. LPS mice never received dox treatment and were administered 1 IP LPS injection (2mg/kg) 18 hours before harvest. Dox+LPS mice received oral doxycycline treatment in chow from neonatal day P3 until 6 weeks of age, followed by 6 weeks of doxycycline washout, and then they were administered 1 IP LPS injection (2mg/kg) 18 hours before harvest.