The differential crosstalk of the skin-gut microbiome axis as a new emerging actor in systemic sclerosis

Objectives: We characterized the microbiota in systemic sclerosis (SSc), focusing on the skin-oral-gut axis and serum and faecal free fatty acid (FFA) profile. Methods: Twenty-five SSc patients with ACA or anti-Scl70 autoantibodies were enrolled. The microbiota of faecal, saliva and superficial epidermal samples was assessed through next generation-sequencing analysis. Gas chromatography-mass spectroscopy was used to quantity faecal and serum FFAs. Gastrointestinal symptoms were investigated with UCLA GIT-2.0-questionnaire. Results: The ACA+ and anti-Scl70+ groups displayed different cutaneous and faecal microbiota profiles. The classes of cutaneous Sphingobacteria and Alphaproteobacteria, the faecal phylum of Lentisphaerae, the classes of Lentisphaeria and Opitutae, and the genus of NA-Acidaminococcaceae were significantly higher in faecal samples of the ACA+, compared with anti-Scl70+ patients. The cutaneous Sphingobacteria and the faecal Lentisphaerae were significantly correlated (rho = 0.42; p= 0.03). A significant increase in faecal propionic acid was observed in ACA+ patients. Moreover, all faecal medium-chain FFAs and hexanoic acids were significantly higher in ACA+ compared with anti-Scl70+ group (p< 0.05 and p< 0.001, respectively). In the ACA+ group, the analysis of serum FFA levels showed an increasing trend in valeric acid. Conclusions: Different microbiota signatures and FFA profiles were found in the two groups of patients. Despite being in different body districts, the cutaneous Sphingobacteria and faecal Lentisphaerae appear interdependent.