Lunasin functionally enhances LDL uptake via inhibiting PCSK9 and enhancing LDLR expression in vitro and in vivo

Abstract

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a serine protease which regulates serum low-density lipoprotein cholesterol (LDL-C) levels by promoting the degradation of the hepatic low-density lipoprotein receptor (LDLR), and has become an attractive therapeutic target for cholesterol lowering intervention. Lunasin, a 43-amino acid polypeptide initially isolated from soybean, has been previously proven to possess cholesterol lowering activity. Here we identified the down-regulation of PCSK9 expression by lunasin as one new mechanism that increased cell-surface LDLR level and enhanced LDL uptake in vitro and in vivo. Treatment of HepG2 cells with lunasin inhibited the expression of PCSK9 at mRNA and protein levels in a dose-and-time dependent manner via down-regulating hepatocyte nuclear factor-1α (HNF-1α), thereby contributing to increasing LDLR level and functionally enhancing LDL uptake. ApoE−/− mice receiving lunasin administration by intraperitoneal injection at doses of 0.125∼0.5 μmol/kg·day for 4 weeks had significantly lower PCSK9 and higher LDLR levels in hepatic tissue, as well as remarkably reduced total-cholesterol (T-CHO) and LDL-C in blood as compared to mice in vehicle control group. Furthermore, we identified that LDLR expression was up-regulated by lunasin via PI3K/Akt-mediated activation of SREBP-2 in HepG2 cells. Taken together, our findings suggest that lunasin inhibits PCSK9 expression by down-regulating HNF-1α and enhances LDLR expression via PI3K/Akt-mediated activation of SREBP-2 pathway, thereby functionally enhances LDL uptake in HepG2 cells and in ApoE−/− mice.

Proteolysis of the low density lipoprotein receptor by bone morphogenetic protein-1 regulates cellular cholesterol uptake

“…The presence of the 120 kDa CTF at the cell surface, as evidenced by its ability to be surface biotinylated, is consistent with this assumption. Although pharmacological inhibition or genetic knockdown of BMP1 almost totally inhibited LDLR cleavage, LDLR cell surface expression and LDL uptake were only increased by ~20% suggesting tight regulation of the amount of receptor expressed at the cell surface as observed in previous studies 26,27 .…”

Beneficial Effects of Soybean-Derived Bioactive Peptides

“…Lunasin downregulated the expression of genes associated with proprotein convertase subtilisin/kexin type 9 (PCSK9) and upregulated the expression of LDL receptor (LDLR) at the transcriptional and translational levels in HepG2 cells [66]. In ApoE−/− mice, lunasin administration by intraperitoneal injection decreased total cholesterol and LDL-cholesterol levels in the serum by downregulating the expression of PCSK9 and increasing the expression of LDLR and sterol regulatory element-binding protein 2 (SREBP-2) [66]. Soybean glycinin-derived peptides, such as IAVPGEVA, IAVPTGVA, and LPYP, activated the LDLR/SREBP2 pathway in HepG2 cells in vitro, but not in vivo, suggesting that the peptides directly regulate cholesterol metabolism [81].…”

Lunasin Improves the LDL-C Lowering Efficacy of Simvastatin via Inhibiting PCSK9 Expression in Hepatocytes and ApoE−/− Mice

“…We have previously revealed that lunasin treatment effectively inhibited PCSK9 expression and remarkably elevated LDLR level in hepatocytes and mice [20]; thus, we were prompted to explore whether combination therapy with simvastatin and lunasin could enhance the LDL-C lowering efficacy of simvastatin. In liver tissue, PCSK9 synthesis is largely controlled at the gene transcriptional level by HNF1; there are two members of the HNF1 family, HNF1α and HNF1β.…”

“…Lunasin, a 43-amino acid polypeptide with a molecular weight of ~5 kDa, which was initially identified from soybean [16], has been previously proven to possess various pharmacological activities against cancer [17], inflammation [18], and CVD [19]. Interestingly, we previously revealed that lunasin can functionally enhance LDL uptake in hepatocytes via both inhibiting PCSK9 expression and enhancing LDLR level, thereby remarkably reducing total cholesterol (TC) and LDL-C in blood as compared to vehicle control [20]. Thus, in this study, we investigated whether simvastatin combined with lunasin could improve the cholesterol lowering efficacy of simvastatin.…”