Expansion of intestinal Prevotella copri correlates with enhanced susceptibility to arthritis

Smoking is now well recognised not only as a risk factor for rheumatoid arthritis (RA), but also as a determinant of disease activity, severity, response to therapy, and possibly mortality. Recent studies have provided significant insights into the molecular and cellular mechanisms which underpin the pathogenesis of smokingrelated RA. These involve release of the enzymes, peptidylarginine deiminases (PADs) 2 and 4 from smoke-activated, resident and infiltrating pulmonary phagocytes. PADs, in turn, mediate the conversion of various endogenous proteins to putative citrullinated autoantigens. In genetically susceptible individuals, these autoantigens trigger the production of anti-citrullinated peptide/protein pathogenic autoantibodies (ACPA), an event which precedes the development of RA. This review is focused primarily on smoking-mediated harmful chronic inflammatory responses, both local and systemic, which promote the formation of ACPA, as well as the possible involvement of other types of outdoor and indoor pollution in the pathogenesis of RA. This is preceded by a brief overview of the evidence implicating smoking as a risk factor for development of ACPA-positive RA.Keywords: Anti-citrullinated peptide/protein antibodies; airway microbiota; atmospheric pollution; heavy metals; peptidylarginine deiminases; smoking cessation strategies. ImplicationsChronic inflammatory mechanisms operative in the lungs of smokers lead to the production of anti-citrullinated protein antibodies which, in turn, drive the development of rheumatoid arthritis. These mechanistic insights not only reinforce the association between smoking and risk for rheumatoid arthritis, but also the necessity to increase the level of awareness in those at highest risk.

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The scientific community has recently come to appreciate that, rather than existing as independent organisms, multicellular hosts and their microbiota comprise a complex evolving superorganism or metaorganism, termed a holobiont. This point of view leads to a re-evaluation of our understanding of different physiological processes and diseases. In this paper we focus on experimental and computational approaches which, when combined in one study, allowed us to dissect mechanisms (traditionally named host-microbiota interactions) regulating holobiont physiology. Specifically, we discuss several approaches for microbiota perturbation, such as use of antibiotics and germ-free animals, including advantages and potential caveats of their usage. We briefly review computational approaches to characterize the microbiota and, more importantly, methods to infer specific components of microbiota (such as microbes or their genes) affecting host functions. One such approach called transkingdom network analysis has been recently developed and applied in our study. 1 Finally, we also discuss common methods used to validate the computational predictions of host-microbiota interactions using in vitro and in vivo experimental systems.