SIRT4 and endothelial dysfunction: Finally, i-PCSK9 enhanced the ability of i-miR-15b to restore the SIRT4 protein levels (p < 0.05 versus i-miR-15b + LPS) (Fig. 7E), indicating the pivotal role of the miR-15b-5p–SIRT4 axis in endothelial dysfunction under sepsis.