Vitamin K-dependent carboxylation regulates Ca2+ flux and adaptation to metabolic stress in β cells

Pan-PTM profiling identifies post-translational modifications associated with exceptional longevity and preservation of skeletal muscle function in Drosophila

Skeletal muscle weakness is a major component of age-associated frailty, but the underlying mechanisms are not completely understood. Drosophila has emerged as a useful model for studying skeletal muscle aging. In this organism, previous lab-based selection established strains with increased longevity and reduced age-associated muscle functional decline compared to a parental strain. Here, we have applied a computational pipeline (JUMPptm) for retrieving information on 8 post-translational modifications (PTMs) from the skeletal muscle proteomes of 2 long-lived strains and the corresponding parental strain in young and old age. This pan-PTM analysis identified 2470 modified sites (acetylation, carboxylation, deamidation, dihydroxylation, mono-methylation, oxidation, phosphorylation, and ubiquitination) in several classes of proteins, including evolutionarily conserved muscle contractile proteins and metabolic enzymes. PTM consensus sequences further highlight the amino acids that are enriched adjacent to the modified site, thus providing insight into the flanking residues that influence distinct PTMs. Altogether, these analyses identify PTMs associated with muscle functional decline during aging and that may underlie the longevity and negligible functional senescence of lab-evolved Drosophila strains.

Molecular basis of vitamin-K-driven γ-carboxylation at the membrane interface

The γ-carboxylation of glutamate residues enables Ca2+-mediated membrane assembly of protein complexes that support broad physiological functions, including haemostasis, calcium homeostasis, immune response and endocrine regulation1-4. Modulating γ-carboxylation levels provides prevalent treatments for haemorrhagic and thromboembolic diseases5. This unique post-translational modification requires vitamin K hydroquinone (KH2) to drive highly demanding reactions6 catalysed by the membrane-integrated γ-carboxylase (VKGC). Here, to decipher the underlying mechanisms, we determined cryo-electron microscopy structures of human VKGC in unbound form, with KH2 and four haemostatic and non-haemostatic proteins possessing propeptides and glutamate-rich domains in different carboxylation states. VKGC recognizes substrate proteins through knob-and-hole interactions with propeptides, thereby bringing tethered glutamate-containing segments for processive carboxylation within a large chamber that provides steric control. Propeptide binding also triggers a global conformational change to signal VKGC activation. Through sequential deprotonation and KH2 epoxidation, VKGC generates a free hydroxide ion as an exceptionally strong base that is required to deprotonate the γ-carbon of glutamate for CO2 addition. The diffusion of this superbase-protected and guided by a sealed hydrophobic tunnel-elegantly resolves the challenge of coupling KH2 epoxidation to γ-carboxylation across the membrane interface. These structural insights and extensive functional experiments advance membrane enzymology and propel the development of treatments for γ-carboxylation disorders.

Transcriptome Reveals the Promoting Effect of Beta-Sitosterol on the Differentiation of Bovine Preadipocytes

Natural small molecule compounds play crucial roles in regulating fat deposition. Beta-sitosterol exhibits multiple biological activities such as cholesterol reduction and anticancer effects. However, its regulatory mechanism in the differentiation of bovine preadipocytes remains unclear. We identified potential associations of Beta-sitosterol with biological processes such as cholesterol regulation and lipid metabolism through the prediction of its targets. We utilized techniques such as Oil Red O staining, Western blotting, RNA-seq, and others to elucidate the promoting effect of Beta-sitosterol on the differentiation of bovine preadipocytes. Furthermore, reducing the expression of the most downregulated gene among differential expressed genes (DEGs), MGP, promotes the differentiation of bovine preadipocytes. After interfering with MGP, RNA-seq analysis on the sixth day of differentiation revealed that DEGs were most significantly enriched in the PPAR signaling pathway. In this pathway, the expression levels of genes related to adipocyte differentiation, including CD36, RXRα, RXRγ, FABP4, PLIN1, ADIPO, and CAP, were significantly upregulated (P < 0.01). Western blot and ELISA analysis on genes related to the PPAR signaling pathway showed that interfering with MGP increased the expression of proteins such as RXRα, indicating the possible activation of the PPAR signaling pathway. In summary, Beta-sitosterol may promote the differentiation of bovine preadipocytes by reducing the expression of MGP, thereby activating the PPAR signaling pathway.

The Protective Role of Vitamin K in Aging and Age-Related Diseases

Aging is an inevitable aspect of life, but age-related diseases are not an inseparable part of the aging process, and their risk can be reduced through a healthy lifestyle. Vitamin K has a broader impact than just blood clotting, and yet it remains overshadowed by other vitamins and underestimated by both doctors and consumers. Vitamin K (VK) is a multifunctional micronutrient with anti-inflammatory and antioxidant properties, whose deficiency may cause age-related diseases such as cardiovascular diseases, neurodegenerative diseases and osteoporosis. There is a growing body of evidence supporting the role of vitamin K as a protective nutrient in aging and inflammation. This review summarizes the current knowledge regarding the molecular aspects of the protective role of vitamin K in aging and age-related diseases and its clinical implications.

Menaquinone-7 and its therapeutic potential in type 2 diabetes mellitus based on a Zucker diabetic fatty rat model

Background

Type 2 diabetes mellitus (T2DM) is marked by insulin resistance, low grade chronic inflammation, and endothelial dysfunction. Vitamin K2, especially menaquinone-7 (MK-7), might delay T2DM progression and alleviate its consequences. Hence, this study evaluated the effects of MK-7 on serum and urine markers of diabetes in an animal model of T2DM.

Methods

Hetero- (fa/+, control) and homozygous (fa/fa, diabetic) male Zucker diabetic fatty (ZDF) rats were supplemented or not with MK-7 for 12 weeks. After euthanasia, vitamin K1, menaquinone-4 and MK-7 serum concentrations were analyzed via reversed phase high pressure liquid chromatography. Glucose (serum), fructosamine (serum) and creatinine (serum and urine) levels were assessed photometrically, serum cystatin C and urinary total protein were turbidimetrically determined. Serum transforming growth factor beta 1 (TGF-β1) and procollagen type III N-terminal peptide (PIIINP) were quantified with enzyme-linked immunosorbent assay. Urinary marker proteins were analyzed via sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Nephropathy was assessed histologically.

Results

Supplementation led to significantly elevated MK-7 serum levels and a significant reduction of PIIINP serum levels in both hetero- and homozygous ZDF rats. Additionally, not statistically significant reductions of TGF-β1 serum levels, proteinuria as well as the nephropathy score were observed. In vivo body mass, serum fructosamine, glucose, cystatin C and creatinine levels were unaffected.

Conclusion

MK-7 reduced serum markers of fibrosis, histological features of nephropathy and urinary protein excretion, but failed to affect serum markers of T2DM. The therapeutic potential of MK-7 in T2DM and its mode of action should be further investigated in more detail.

Decreased serum levels of 25-OH vitamin D and vitamin K in patients with type 2 diabetes mellitus

Background

Insulin resistance and/or insulin secretion dysfunction are crucial causes of type 2 diabetes mellitus (T2DM). Although some studies have suggested potential roles for vitamins D and K in glucose metabolism and insulin sensitivity, there is limited and inconclusive research on their levels in T2DM patients and their relationship with blood glucose levels and insulin resistance. Additionally, there is a lack of large-scale clinical trials and comprehensive studies investigating the combined effects of vitamins D and K on T2DM.

Methods

A total of 195 participants with newly diagnosed T2DM were included in the research group, while 180 volunteers undergoing physical examinations in our hospital served as the control group. Fasting plasma glucose (FPG) was estimated using the glucose-oxidase technique, and fasting serum insulin (FINS) was evaluated by radioimmunoassay. FPG and FINS were used to calculate the homeostasis model assessment-insulin resistance (HOMA-IR). Serum vitamin D levels were measured using 25-hydroxyvitamin D, and vitamin K levels were evaluated using phylloquinone (VK1) and menaquinone (VK2) via ultra-high performance liquid chromatography and tandem mass spectrometry. Receiver operating characteristic (ROC) analysis was performed to assess the predictive value of these vitamins for T2DM.

Results

Circulating levels of 25-hydroxyvitamin D (25.95 ± 10.42 ng/mL), VK1 (1.24 ± 0.89 ng/mL), and VK2 (0.2 ± 0.21 ng/mL) in T2DM patients were significantly lower than in the control group (37.46 ± 13.95 ng/mL for 25-hydroxyvitamin D, 1.99 ± 1.39 ng/mL for VK1, and 0.33 ± 0.22 ng/mL for VK2; p<0.001 for all comparisons). ROC analysis indicated that 25-hydroxyvitamin D, VK1, and VK2 could predict the occurrence of T2DM, with AUC values of 0.75, 0.69, and 0.71, respectively. In T2DM patients, 25-hydroxyvitamin D levels were positively correlated with VK1 (r=0.43, p<0.001) and VK2 (r=0.40, p<0.001) levels. FPG and HOMA-IR in T2DM patients were negatively correlated with circulating levels of 25-hydroxyvitamin D (r=-0.57, p<0.001), VK1 (r=-0.44, p<0.001), and VK2 (r=-0.36, p<0.001).

Conclusion

Circulating levels of vitamins D and K are lower in T2DM patients and show significant correlations with blood glucose levels and insulin resistance. These findings suggest that measurements of 25-hydroxyvitamin D, VK1, and VK2 could have predictive value for T2DM, highlighting the potential roles of these vitamins in T2DM management.

Vitamin K-dependent carboxylation in β-cells and diabetes

Vitamin K is an essential micronutrient and a cofactor for the enzyme γ-glutamyl carboxylase, which adds a carboxyl group to specific glutamic acid residues in proteins transiting through the secretory pathway. Higher vitamin K intake has been linked to a reduced incidence of type 2 diabetes (T2D) in humans. Preclinical work suggests that this effect depends on the γ-carboxylation of specific proteins in β-cells, including endoplasmic reticulum Gla protein (ERGP), implicated in the control of intracellular Ca2+ levels. In this review we discuss these recent advances linking vitamin K and glucose metabolism, and argue that identification of γ-carboxylated proteins in β-cells is pivotal to better understand how vitamin K protects from T2D and to design targeted therapies for this disease.

Effects of vitamin family members on insulin resistance and diabetes complications

The following letter to the editor highlights the article "Effects of vitamin D supplementation on glucose and lipid metabolism in patients with type 2 diabetes mellitus and risk factors for insulin resistance" in World J Diabetes 2023 Oct 15; 14 (10): 1514-1523. It is necessary to explore the role of vitamin family members in insulin resistance and diabetes complications.