Hibernation: a model of harmony between the intestines and their flora
Does health go out the window in cold weather? This is perhaps the case for some of us in the middle of winter, but not for hibernating animals, whose intestinal defense mechanisms are even strengthened, without harming their bacteria.
A team of American researchers reviewed different studies revealing what takes place in the intestines of animals that shut down over the winter. These include of course the symbolic brown bear, but especially ground squirrels—or Spermophilus— whose name means: “seed-loving” in Greek. Regulated like an August holidaymaker returning from vacation, these rodents hibernate from the end of August until Spring, no matter what happens. But the comparison ends there since these animals endure five to nine months of total fasting.
These months of famine are a real challenge for their intestinal bacteria, whose diversity is thus substantially reduced during hibernation. The bacteria that can manage with the resources at hand are at an advantage, by feeding for example on mucins, sugar-rich fluids which cover the intestinal mucosa. Once this tough period has passed, the entire flora is reconstituted without difficulty when the squirrel resumes its feasting in Spring.
A model of tolerance
Despite this diet and flora upheavals, which would likely destabilize humans, the immune systems of hibernating animals do not turn against their beneficial bacteria. On the contrary, they become more tolerant while becoming stronger via the production of mucus that protects against the invasion of external microbes… feeding their own bacteria in the process.
Helping patients who are fed artificially
The immune system and the microbiota therefore adapt to each other during this period of intense deprivation. Medicine would like to take inspiration from this phenomenon to avoid complications in patients who are in intensive care, undergoing palliative care, suffering from severe bowel diseases, or from the side effects of chemotherapy. They are incapable of receiving nourishment except by infusion of nutrient solutions into the bloodstream (parenteral nutrition), and their weakened microbiota exposes them to inflammation and to infections that are sometimes generalized. Their salvation could therefore come from the study of these small-eared critters, true “sleeping beauties with paws” and whose intestines lie “awake”.
Carey et Assadi-Porter. The Hibernator Microbiome: Host-Bacterial Interactions in an Extreme Nutritional Symbiosis. Annu Rev Nutr 2017, 21;37:477-500.