Molecular Mechanism of Vitamin K2 Protection against Amyloid-β-Induced Cytotoxicity

Abstract

The pathological role of vitamin K2 in Alzheimer’s disease (AD) involves a definite link between impaired cognitive functions and decreased serum vitamin K levels. Vitamin K2 supplementation may have a protective effect on AD. However, the mechanism underlying vitamin K2 protection has not been elucidated. With the amyloid-β (Aβ) cascade hypothesis, we constructed a clone containing the C-terminal fragment of amyloid precursor protein (β-CTF/APP), transfected in astroglioma C6 cells and used this cell model (β-CTF/C6) to study the protective effect of vitamin K2 against Aβ cytotoxicity. Both cellular and biochemical assays, including cell viability and reactive oxygen species (ROS), assays assay, and Western blot and caspase activity analyses, were used to characterize and unveil the protective role and mechanism of vitamin K2 protecting against Aβ-induced cytotoxicity. Vitamin K2 treatment dose-dependently decreased the death of neural cells. The protective effect of vitamin K2 could be abolished by adding warfarin, a vitamin K2 antagonist. The addition of vitamin K2 reduced the ROS formation and inhibited the caspase-3 mediated apoptosis induced by Aβ peptides, indicating that the mechanism underlying the vitamin K2 protection is likely against Aβ-mediated apoptosis. Inhibitor assay and Western blot analyses revealed that the possible mechanism of vitamin K2 protection against Aβ-mediated apoptosis might be via regulating phosphatidylinositol 3-kinase (PI3K) associated-signaling pathway and inhibiting caspase-3-mediated apoptosis. Our study demonstrates that vitamin K2 can protect neural cells against Aβ toxicity.

Vitamin K2 Modulates Organelle Damage and Tauopathy Induced by Streptozotocin and Menadione in SH-SY5Y Cells

“…Such a neuroprotective role of vitamin K2 was also observed when differentiated rat pheochromocytoma PC12 cells were pre-treated with vitamin K2 and exposed to Aβ peptide and H 2 O 2 [28]. A similar cytoprotective effect of vitamin K2 was observed in astroglioma C6 cells, where it has been found to protect the C6 cells from Aβ-induced toxicity in a dose-dependent manner [29]. Even it was observed that vitamin K2 reduces the toxic effects of rotenone in SH-SY5Y cells, when BV2 cell conditioned medium (rotenone + MK-4) was added to SH-SY5Y cells, thus protecting from microglia-mediated neuronal cell death [30].…”

“…While post-treatment of vitamin K2 significantly reduced the ROS levels as indicated by the decreased fluorescence intensity of DCFH-DA, suggesting that vitamin K2 protected against streptozotocin-and menadione-induced toxicity by suppressing ROS accumulation. Similarly, vitamin K2 was found to be effective against Aβ [29] and H 2 O 2 [28] induced ROS generation. Increasing evidence reveals that increased ROS production is associated with damage to mitochondrial DNA and a decrease in mitochondrial membrane potential.…”

“…Glycogen synthase kinase 3 (GSK3) also plays an important role in executing ER stress-mediated apoptosis as studied using GSK3 inhibitors in a variety of cell types and ER stress models [29,60]. The phosphotyrosine residue of GSK3 is the "activation loop" of this enzyme (Tyr279 in GSK3α and Tyr216 in GSK3β) and is also linked to activation of MAPK.…”

“…In addition, it was found that lower intake of vitamin K diet was directly associated with cognitive deficits in the aged population [27]. Current studies also showed the antioxidative effect of vitamin K2 on various in vitro models such as differentiated rat pheochromocytoma PC 12 cells [28] and rat astroglia C6 cells by inhibiting the toxicity and oxidative damage induced by Aβ involving various regulatory pathways [29]. Moreover, vitamin K2 was also observed to significantly inhibit the rotenone-induced ROS production, p38 activation and caspase activation in microglial cells [30].…”

Vitamin K2 Holds Promise for Alzheimer’s Prevention and Treatment

“…VK2 also acts as a transcriptional regulator and has antioxidant properties [ 41 , 42 , 43 ]. Unlike VK1, VK2 possesses immunosuppressant effects and inhibits T-cell proliferation [ 44 , 45 , 46 ].…”