From Leaky Gut to Tissue Microbiota in Metabolic Diseases

Although the gut microbiota has shown its importance in the control of health, recent discoveries have shifted the paradigm to the tissue microbiota. This hypothesis is defined by alive bacteria residing chronically in tissues and or bacterial fragments often characterized by the sequencing of the 16SrRNA gene. The tissue microbiota is specific per tissue and widely spread even in non-pathogenic situations. At the onset of metabolic disease, it is supposed to trigger metabolic inflammation leading to insulin resistance, and adipose cells proliferation, thereby obesity. Many other diseases have been so far characterized by a tissue microbiota, notably hepatic steatosis and fibrosis. Its origin requires an impaired intestinal function meaning a leaky gut. A gut leakiness occurring during diseases will lead to the translocation of specific sets of bacteria or fragments toward tissues. The mechanisms are unknown but could be related to impaired intestinal immune system or defensin production by enterocytes no longer preventing from mucosal bacteria crossing through the epithelial layer and lamina propria. A control of gut leakiness could help prevent the occurrence of chronic inflammatory diseases.