To further assess the role of Sphk1 during renal fibrosis development, we used PF543, a specific inhibitor of Sphk1 activation, to block Sphk1 endogenous activity in vivo, and found that PF543 treatment led to an evident down-regulation in UUO-induced collagen deposition (Figure 6C) and the expression of α-SMA (Figure 6D) and fibronectin (Figure 6E) in kidney tissues in mice. Here, SPHK1 is linked to renal fibrosis.