Similar to the work being performed through the American Gut Project to elucidate relationships between human diseases and the gastrointestinal microbiota, efforts are being made to explore health status and the gut microbiota of man’s best friend, the dog. Many people do not realize that dogs naturally develop many of the same diseases that people do, including inflammatory bowel disease (IBD), which is a major focus of researchers in the Gastrointestinal Laboratory in the Small Animal Clinical Sciences department at Texas A&M University. The GI Lab receives samples from all over the United States and beyond, often through collaborations with veterinary researchers throughout the world. These samples come from client-owned patients, and unlike rodent models of human disease, these pets share environmental exposures with their owners, from the water they drink to the air they breathe, often even sleeping in the same bed.
Among aspects studied by the Knight lab, dog ownership was shown to influence the human microbiome. Simply being a dog owner alters the microbiome compared to people who do not own dogs, and within households that have a dog, a greater degree of similarity was observed between human members of the household. But rather than focusing on the human microbiome, what about the dog’s microbiome?
By employing some of the same molecular tools used in the American Gut Project, we see both similarities and differences across host species. From an evolutionary perspective, this makes sense. As diverse as the class Mammalia is, each species has developed a blueprint that is compatible with life in its normal environment, efficiently filling a niche with the assistance of the microbiota that co-evolved with them. In veterinary species, as in humans, we are still learning and trying to understand the wide range of functions and influences that are credited to the microbiota.
My personal favorite tool for exploring these functional effects is metabolomics, which is broadly analyzing a sample (serum, urine, feces, saliva, tears, tissue homogenates, etc.) for the metabolites it contains. Interestingly, some of the metabolites found in feces are thought to be produced exclusively by the microbiota, some only by the host, and still others that may be produced by either. A given metabolite might be produced by many different bacterial groups, and the metabolic activity of the bacteria might depend upon available substrates or interactions with other bacteria in the environment. In other words, the metabolome and microbiome are intensely interdependent, yet also can change independently to an extent. This greatly complicates interpretation of the etiology of differences of biochemical composition between fecal samples of healthy and diseased dogs. However, becoming aware of disease-associated alterations in metabolite profiles might help guide us towards therapeutic strategies, or finding non-invasive biomarkers for gastrointestinal disease, even if we don’t completely understand the underlying mechanism driving the change.
While the microbiome and metabolome of the dog are certainly not the same as those of the human, ultimately they are far more similar than different. Extrapolations across host species about characteristics of health versus disease may require caution, but the “rules” that govern host-microbiota interactions are likely more universal. Thus the work being done by the American Gut Project is an asset to our understanding of any mammalian gut microbiome.