ACTA1 and systemic sclerosis: Nintedanib demonstrates its intracellular inhibition of tyrosine kinases through inhibition of PDGF which consequently impact the normally increasing level of intracellular calcium, prevent the stimulatory effects that PDGF exhibits on myofibroblast differentiation and collagen release, and reduce PDGF-induced transcriptional activity of α-SMA in SSc lung fibroblasts [17].