Gut microbiota and colorectal cancer

Abstract

The gut microbiota is considered as a forgotten organ in human health and disease. It maintains gut homeostasis by various complex mechanisms. However, disruption of the gut microbiota has been confirmed to be related to gastrointestinal diseases such as colorectal cancer, as well as remote organs in many studies. Colorectal cancer is a multi-factorial and multi-stage involved disorder. The role for microorganisms that initiate and facilitate the process of colorectal cancer has become clear. The candidate pathogens have been identified by culture and next sequencing technology. Persuasive models have also been proposed to illustrate the complicated and dynamic time and spatial change in the carcinogenesis. Related key molecules have also been investigated to demonstrate the pathways crucial for the development of colorectal cancer. In addition, risk factors that contribute to the tumorigenesis can also be modulated to decrease the susceptibility for certain population. In addition, the results of basic studies have also translated to clinical application, which displayed a critical value for the diagnosis and therapy of colorectal cancer. In this review, we not only emphasize the exploration of the mechanisms, but also potential clinical practice implication in this microbiota era.

Fig. 1

The interaction between host and commensal microbes in the gut. Under normal conditions, the signals from commensal bacteria could be detected by sensors TLR and NLR. Signals are passed down to trigger the immune system activation and cytokine release to maintain the balance. When the microenvironment changes, the pathogens (Fusobacterium nucleatum, etc.) pass through the inner mucus layer and invade into the stroma by destroying the tight junction and inducing drastic responses

Fig. 2

A variety of factors affect the gut microbiota and host health. The relationship between gut microbiota and host is complicated, with direct and indirect effects. To study the relationship, it is important to take the multi-omics study into consideration both in the host and the microbiota (cohort and cross-section studies). In addition, the model animal and cell studies would provide another aspect of targeting mechanisms. All the factors taken together would contribute a comprehensive understanding of the complicated and sophisticated relationship between gut microbiota and the occurrence and development of colorectal cancer