Gut microbiome is dispensable for normal respiratory function and respiratory chemoreflex
Authors: Lusk Savannah , Ray Russell 
Published: May 2024

Increasing evidence indicates that gut microbiota can influence changes in respiratory homeostasis. Alterations to the gut microbiome have been hypothesized to play roles in autoimmune diseases, social behavioral deficits, and metabolic diseases such as diabetes and cardiovascular disease. We therefore aimed to determine if a model of gut dysbiosis, the absence of a gut microbiome, would result in alterations to respiratory homeostasis. After 5 days of habituation inside the Gnotobiotic animal facility, we assayed 8-week-old C57Bl/6J germ-free (GF, n=24) and specific-pathogen-free (SPF, n=24) control mice under normoxic (21% O2,79% N2) conditions, followed by a hypercapnic challenge (5% CO2, 21% O2, 74% N2) and hypoxic challenge (10% O2, 90% N2). Importantly, this germfree model does not involve treatment with high-dose antibiotics, which have been implicated in neurotoxic sequela. Whole-body flow through plethysmography was used to monitor respiratory function and metabolic demand in conscious and unrestrained animals. Recordings were interrogated using our newly published open-source software, Breathe Easy, for breath cycle duration, respiratory rate (Vf), tidal volume (VT), minute ventilation (VE), oxygen consumption (VO2), and minute ventilation normalized by oxygen consumption (VE/VO2) during room air, initial hypoxic and hypercapnic exposures, and steady-state hypoxic and hypercapnic respiratory responses. A linear mixed effects model with a Tukey post-hoc test was performed to test for significant differences wherein respiratory outcomes were dependent variables, and strain and sex were independent variables. In male mice, there was a significant decrease in breath cycle duration during room air in GF compared to SPF controls. We also saw a significant decrease in ventilatory equivalents of oxygen in the initial hypoxic response in GF mice compared to SPF controls in males, but not in the steady-state of hypoxic exposure. Finally, we note a significant increase in oxygen consumption in females during room air measurements. Of note, female mice showed significant irregularity in all respiratory parameters except oxygen consumption whereas males only showed significant irregularity in breath cycle duration during hypoxic steady-state and the hypercapnic steady-state, and tidal volume in the initial hypoxic response. While there are significant changes, it remains to be determined what the underlying mechanisms are and how they may play a contributory role in pathophysiologies co-morbid with gut microbiome dysregulation. Taken together, these results suggest that the gut microbiome is largely dispensable for normal respiratory function and respiratory chemoreflexes in adult mice and that the lack of a gut microbiome, a model of gut dysbiosis, does not result in broad significant changes in respiratory homeostasis. NIH: 1F32HL160073-01A1, R01HL130249 44617-S4. BCM McNair Scholar Program, March of Dimes Basil O'Connor Research Award, Parker B. Francis Fellowship, CJ Foundation for SIDS. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.