AsianScientist (Sep. 4, 2015) – Bacteria can promote symbiosis in the gut by directing selective cargo sorting in intestinal cells known as Paneth cells. These findings, by researchers at the Institute of Biophysics of the Chinese Academy of Sciences, have been published in Nature Immunology.
Humans are ‘super-organisms’ composed of human cells and trillions of bacteria that reside in and on our body. These bacterial guests are commonly referred (to) as commensal bacteria. The mutual beneficial relationship between host and commensal bacteria is referred (to) as symbiosis.
Commensal bacteria are known to be of vital importance to host health, and dysbiosis has been connected to many disorders, including metabolic syndromes, inflammatory bowel disease (IBD) and autism spectrum disorders.
Over 90 percent of commensal bacteria reside in intestinal lumen. Commensal bacteria and host mucosal immunity reciprocally interact and achieve a delicate balance, termed as intestinal homeostasis. Disrupted intestinal homeostasis induces dysbiosis and a range of dysbiosis-associated syndromes.
Paneth cells, secretory epithelial cells at the bottom of small intestinal crypts, play a vital role in maintaining intestinal homeostasis by secreting a range of bactericidal factors into the intestinal lumen. In particular, studies have put Paneth cells at the center stage of pathogenesis of IBD.
The study showed that commensal bacteria could control the secretory mechanism of Paneth cells. Specifically, they found that the commensal bacteria targeted Nod2, a bacteria sensor, to lysozyme-containing vesicles in the cell. This in turn promoted the tagging of other molecules such as LRRK2, a kinase, and Rab2a, a small GTPase, to the lysosomes.
The researchers found that commensal bacteria could then prompt the release of lysozyme into the intestinal lumen to protect the human gut. In the event of the loss of any of the molecules involved, the normal protective secretion is lost, and these cargoes are misdirected to be broken down within the Paneth cells.
This finding advanced our understanding of how the human host cell (Paneth cell) and commensal bacteria in the gut work in concert to promote a healthy gut. It also shed light on the dysfunctions that occur in Paneth cells in IBD, paving a way for better treatment of this disease in future.
The article can be found at: Zhang et al. (2015) Commensal Bacteria Direct Selective Cargo Sorting To Promote Symbiosis.
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Source: Chinese Academy of Sciences; Photo: Ed Uthman/Flickr/CC.
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