The microbiota, a partner for health
Five to six hundred different species of bacteria are found in our intestines, and these micro-organisms are ten to a hundred-fold more numerous than the cells of our bodies, reaching a total mass of around a kilogram. The functional potential of these intestinal bacteria is enormous, because the microbiome (all genomes of intestinal bacteria) probably contains 100 times more genes than the human genome. Although this bacterial community usually exerts a positive action on our health, imbalances affecting this ecosystem are associated (without there necessarily being a causal relationship) with certain pathologies such as chronic inflammatory diseases of the intestine (Crohn's disease, etc.) and atopic diseases (food allergies, eczema, asthma). More recently, the intestinal microbiota has been described as a partner in the regulation of body weight.
A proteomic approach
Rather than focusing on identifying a single marker for each pathology, the researchers adopted a non-targeted proteomic approach that enabled the establishment of an expression profile – or identity card – for each disease. They thus compared the metaproteomes (all proteins) of the bacterial communities populating the digestive tracts of healthy subjects and of patients suffering from overweight or Crohn's disease.
Crohn's disease
Crohn's disease remains an enigmatic condition, but one hypothesis concerns the crucial role of the intestinal microbiota in triggering and maintaining inflammation of the digestive tract. Global proteomic analysis of the microbiota in a small number of volunteers (6 healthy subjects and 6 patients) clearly determined a separation between the two groups of subjects, and the selection of 90 spots (out of 2700) specifically associated with the microbiota of patients. This work constitutes the first step in identifying markers that will enable diagnosis, (or even early screening) of this inflammatory disease, before its effects become visible. In the longer term, the therapeutic use of probiotic agents to restore lost functions, or attenuate harmful functions, of the microbiota, could be envisaged.
Obesity
Obesity is a complex condition, for which there are no therapeutic strategies at present that are 100% effective in the long term. For some years, the search for factors other than those normally incriminated (genetics, dietary habits and lifestyle) has highlighted the involvement of the intestinal microbiota, which appears to act on the energy balance. Proteomic analysis, performed in 16 obese or non-obese men, demonstrated some 30 spots of differential expression that could be specific signatures of obesity.
These results, obtained in small samples of the population, suggest that the intestinal metaproteome could be a source of novel biomarkers and/or therapeutic targets. They constitute the first clinical applications of know-how developed by this team of researchers concerning optimisation of the extraction of all soluble proteins expressed by the intestinal microbiota in its digestive environment. Studies will now focus on confirming these results in larger cohorts, and broadening the "observational window" to proteins that are little soluble or present in smaller numbers.
Scientific contact:
Catherine JUSTE
INRA
UR910 Unit for Ecology and Physiology of the Digestive Tract UEPSD
bât 405
INRA 78352 Jouy-en-Josas Cedex ;
Tel: +33(0)1 34 65 24 93 or +33(0)1 34 65 24 87
E-mail : catherine.juste@jouy.inra.fr
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