FN1 and systemic sclerosis: To examine the contribution of cognate IGF-II receptors to IGF-II-mediated fibrosis, siRNA knockdown and pharmacological inhibition were utilized in NL and SSc fibroblasts, since SSc fibroblasts showed a more pronounced induction of fibronectin and collagen expression with IGF-II stimulation than IPF fibroblasts (S1 Fig).