Modification of Gas6 Protein in the Brain by a Functional Endogenous Tissue Vitamin K Cycle.

The TAM receptor ligand Gas6 is known for regulating inflammatory and immune pathways in various organs including the brain. Gas6 becomes fully functional through the post-translational modification of multiple glutamic acid residues into γ-carboxyglutamic in a vitamin K-dependent manner. However, the significance of this mechanism in the brain is not known. We report here the endogenous expression of multiple components of the vitamin K cycle within the mouse brain at various ages as well as in distinct brain glial cells. The brain expression of all genes was increased in the postnatal ages, mirroring their profiles in the liver. In microglia, the proinflammatory agent lipopolysaccharide caused the downregulation of all key vitamin K cycle genes. A secreted Gas6 protein was detected in the medium of both mouse cerebellar slices and brain glial cell cultures. Furthermore, the endogenous Gas6 γ-carboxylation level was abolished through incubation with the vitamin K antagonist warfarin and could be restored through co-incubation with vitamin K1. Finally, the γ-carboxylation level of the Gas6 protein within the brains of warfarin-treated rats was found to be significantly reduced ex vivo compared to the control brains. In conclusion, we demonstrated for the first time the existence of a functional vitamin K cycle within rodent brains, which regulates the functional modification of endogenous brain Gas6. These results indicate that vitamin K is an important nutrient for the brain. Furthermore, the measurement of vitamin K-dependent Gas6 functionality could be an indicator of homeostatic or disease mechanisms in the brain, such as in neurological disorders where Gas6/TAM signalling is impaired.

Low vitamin K status in adults with cystic fibrosis is associated with reduced body mass index, insulin secretion, and increased pseudomonal colonization.

Patients with cystic fibrosis (CF) are at high risk of fat-soluble vitamin deficiencies, even with supplementation. The contribution of a suboptimal vitamin K status to respiratory and endocrine pathophysiology in CF has been inadequately characterized. This is a cross-sectional study in adult CF patients (≥18 years old) from the Montreal Cystic Fibrosis Cohort. Vitamin K1 (VK1) was measured with high-performance liquid chromatography, using fasted serum samples collected during an oral glucose tolerance test (OGTT: 2 h with plasma glucose and insulin every 30 min) (n = 168). Patients were categorized according to VK1 status (suboptimal defined as <0.30 nmol/L). Suboptimal VK1 levels were observed in 66% of patients. Patients with a suboptimal VK1 status have a higher risk of colonization with Pseudomonas aeruginosa (p = 0.001), have lower body mass index (BMI) (p = 0.003), and were more likely to have exocrine pancreatic insufficiency (p = 0.002). Using an established threshold for VK1, we did show significantly reduced OGTT-derived measures of insulin secretion in patients with a VK1 status below 0.30 nmol/L (first- and second-phase area under the curve (AUC)INS/GLU (p = 0.002 and p = 0.006), AUCINS (p = 0.012) and AUCINS/GLU (p = 0.004)). Subclinical vitamin K deficiency is more common than other fat-soluble vitamin deficiencies in patients with CF. We demonstrate an association between a suboptimal VK1 status and measures of insulin secretion. We highlight the potential associations of mild vitamin K deficiency with pseudomonal colonization and lower BMI, although these need to be validated in prospective studies.

Exploratory analysis of covariation of microbiota-derived vitamin K and cognition in older adults.

BACKGROUND: Vitamin K has multiple important physiological roles, including blood coagulation and beneficial effects on myelin integrity in the brain. Some intestinal microbes possess the genes to produce vitamin K in the form of menaquinone (MK). MK appears in higher concentration in tissues, such as the brain, particularly MK4, than the dietary form of phylloquinone (PK). Lower PK concentrations have been reported in patients with Alzheimer disease while higher serum PK concentrations have been positively associated with verbal episodic memory. Despite knowledge of the importance of vitamin K for various health parameters, few studies have measured MK concentration and biosynthesis by gut commensals. OBJECTIVE: The aim of the current study was to investigate the relation between genes involved in gut-microbiota derived MK, concentrations of MK isoforms, and cognitive function. METHODS: Shotgun metagenomic sequencing of the gut microbiome of 74 elderly individuals with different cognitive ability levels was performed. From this, gene counts for microbial MK biosynthesis were determined. Associations between clusters of individuals, grouped based on a similar presence and prevalence of MK biosynthesis genes, and cognitive ability were investigated. Fecal MK concentrations were quantified by HPLC to investigate correlations with subject clusters. RESULTS: Separation of subject groups defined by banded quantification of the genetic potential of their microbiome to biosynthesize MK was associated with significant differences in cognitive ability [assessed using the Mini-Mental State Examination (MMSE)]. Three MK isoforms were found to be positively associated with MMSE, along with the identification of key components of the MK pathway that drive this association. Although the causality and direction of these associations remain unknown, these findings justify further studies. CONCLUSIONS: This study provides evidence that although total concentrations of MK did not covary with cognition, certain MK isoforms synthesized by the gut microbiome, particularly the longer chains, are positively associated with cognition.

Vitamin K Deficiency Induced by Warfarin Is Associated With Cognitive and Behavioral Perturbations, and Alterations in Brain Sphingolipids in Rats.

Initially discovered for its role in blood coagulation, there is now convincing evidence that vitamin K (VK) has important actions in the nervous system. In brain, VK is present in the form of menaquinone-4 (MK-4), a byproduct of the main dietary source, phylloquinone. It contributes to the biological activation of various proteins (i.e., Gas6), and participates in the synthesis of sphingolipids, a class of lipids widely present in brain cell membranes with important cell signaling functions. In a previous study, we reported that lifetime consumption of a low VK diet resulted in mild cognitive impairment in aged rats, a finding associated with an alteration of the sphingolipid profile. To confirm the role of VK as it relates to sphingolipids, cognition, and behavior outside the context of aging, we conducted a study of acute VK deficiency using a pharmacological model of VK deficiency in brain. In this procedure, rats (8 weeks) are maintained on a ratio of warfarin (a VK antagonist) to VK whereby coagulation is maintained while inducing VK deficiency in extrahepatic tissues. After 10 weeks of treatment, rats who were subjected to the warfarin plus phylloquinone protocol (WVK) exhibited longer latencies in the Morris water maze test as well as lower locomotor activity and exploratory behavior in the open field test, when compared to control rats. The WVK treatment resulted in a dramatic decrease in MK-4 level in all brain regions despite the presence of high local concentrations of phylloquinone, which suggests an inhibition of the biosynthetic MK-4 pathway in the presence of warfarin. Additionally, WVK treatment affected sphingolipid concentrations in key brain regions, notably those of the ganglioside family. Finally, brain MK-4 was correlated with performances in the open field test. This study confirms the modulatory role of VK in cognition and behavior and the implication of sphingolipids, notably those of the ganglioside family.