Modified lipoprotein-induced sFlt1 production in human placental trophoblasts is mediated by protein kinase C

BACKGROUND: Preeclampsia is prevalent in women with diabetes, but the mechanism is unclear. We previously found that oxidized, glycated lipoproteins robustly upregulated soluble fms-like tyrosine kinase-1 (sFlt1), a key mediator of preeclampsia. Here, we determined the role of protein kinase C (PKC) and its subtypes in sFlt1 regulation in placental trophoblasts, and whether this mechanism might mediate the effect of modified lipoproteins.

METHODS: Cultured human HTR8/SVneo and BeWo trophoblasts were treated with the PKC activator phorbol-12-myristate-13-acetate (PMA) for 24h, ± PKC inhibitors GF109203X (general), Ro31-8220 (PKCα-selective), LY333531 (PKCβ-selective) and rottlerin (PKCδ-selective). The effect of 'heavily oxidized, glycated' low-density lipoproteins (HOG-LDL) vs. native LDL (N-LDL), ± high glucose (30 mM), was evaluated in HTR8/SVneo cells. sFlt1 secretion (ELISA), mRNA expression (RT-qPCR), and cellular PKC activity were measured.

RESULTS: PMA stimulated robust sFlt1 release and mRNA expression in both cell lines; these effects were inhibited by GF109203X, Ro31-8220 and LY333531 in a concentration-dependent manner. Rottlerin inhibited sFlt1 in BeWo, but modestly enhanced it in HTR8/SVneo cells. HOG-LDL enhanced PKC activity vs. N-LDL in HTR8/SVneo cells. Also, HOG-LDL, but not high glucose, significantly increased sFlt1 secretion and mRNA expression; this response was inhibited by GF109203X, Ro31-8220 and LY333531 at concentrations comparable to those that blocked PMA induction of sFlt1.

CONCLUSION: Modified lipoproteins upregulate sFlt1 in trophoblasts via a PKC-mediated mechanism, involving at least α and β isoforms. The data suggest potential therapeutic targets to reduce the risk of preeclampsia in women with diabetes.