Cell cultures

Normal human dermal fibroblasts (NHDFs) obtained from a pool of adult donors (Sigma-Aldrich, St. Louis, MO, USA; 106-05A) were cultured in DMEM with 10% foetal bovine serum (FBS). SSc fibroblasts at early cell culture passages (2–3; SSc1 and SSc2) already present in our cell repository were used in this study as senescence controls. SSc had been previously isolated from affected dorsal skin of the hands, as previously described [28], after approval of the local ethics committee of Azienda Ospedaliero–Universitaria Careggi di Firenze. All patients provided written informed consent (see Supplementary Data S1, available at Rheumatology online, for details).