Topical Area: Vitamins and Minerals
There is now convincing evidence that vitamin K (VK) has important actions in the nervous system and cognition. Two VK-dependent proteins are closely linked to the brain namely Gas6 and protein S (PS). Functionally, both proteins are ligands for receptors of tyrosine kinases Tyro3, Axl, and Mer. In vitro, Gas6 and PS have been shown to possess pro-survival activity towards neurons and glia through stimulation of the extracellular signal-regulated (ERK) and serine-threonine (Akt) kinases pathways. In a previous study, targeted depletion of VK in brain induced by warfarin (W) treatment, a VK antagonist, resulted in cognitive and behavioral impairment. In the present study, we aimed to characterize the role of Gas6 and PS and their signaling pathways in W-treated rats fed or not with supplemental menaquinone-4 (MK-4), the principal K vitamer in brain.
Male Wistar rats (n=5-7/gp) were randomly allocated to a AIN-93 based diet containing 750 mcg phylloquinone (K1)/kg/d supplemented with 100 mg MK-4/kg/d (MK-4) or not (N). After one week, rats were administered 14 mg W/kg/d (in drinking water) and subcutaneous K1 (94 mg/kg), 3X/wk, for 9 wks. [Subcutaneous K1 treatment is required to maintain the coagulation function]. A control gp (C) treated with normal water and injected with saline was also included. Gas6, PS, pAkt, pERK as well as brain-derived neurotrophic factor (BDNF) and microglial CD11b/c protein, were assessed in hippocampus (HPP), frontal cortex (FC) and striatum (STR), three regions involved in cognition, by immunoblotting. Group difference were tested by one-way ANOVA.
Impact of W treatment was particularly marked in HPP, rats from N group showing decreased Gas6, PS and ERK activity as well as decreased BDNF expression, compared to C gp. Further, rats from N group presented increased expression of CD11bc, a marker of inflammation (all p < 0.05). Supplementing the diet with MK-4 normalized PS activity and BDNF and CD11bc expression in HPP, Gas6 and pERK in CF, and pAkt in STR (all p < 0.05).
Results indicate that W treatment as used in the present study alters Gas6 and PS activity and their downstream signaling pathways, and stimulates microglial activity. Supplementing the diet with large amounts of MK-4 normalized much of the phenotype.
Funding Sources :
Study funded by CIHR.