Matrix Gla protein (MGP) is a vitamin K-dependent γ-carboxylated protein that was initially identified as a physiological inhibitor of ectopic calcification, primarily affecting cartilage and the vascular system. Mutations in the MGP gene were found to be responsible for the Keutel syndrome, a condition characterized by abnormal calcifications in the cartilage, lungs, brain, and vascular system. MGP has been shown to be dysregulated in several tumors, including cervical, ovarian, urogenital, and breast cancers. Using bioinformatic approaches, transcription factor binding sites (TFBSs) containing CpG dinucleotides were identified in the MGP promoter, including those for YY1, GATA1, and C/EBPα. We carried out functional tests using transient transfections with a luciferase reporter assay, primarily for the transcription factors YY1, GATA1, C/EBPα, and RUNX2. By co-transfection analysis, we found that YY1, GATA1, and C/EBPα repressed the MGP promoter. Furthermore, the co-transfection with RUNX2 activated the MGP promoter. In addition, MGP expression is negatively or positively correlated with the studied TFs' expression levels in several cancer types. This study provides novel insights into MGP regulation by demonstrating that YY1, GATA1, and C/EBPα are negative regulators of the MGP promoter, and DNA methylation may influence their activity. The dysregulation of these mechanisms in cancer should be further elucidated.

Calcific deposits in the arterial media have been associated with a number of metabolic and genetic disorders including diabetes, chronic kidney disease and generalized arterial calcification of infancy. The loss of matrix Gla protein (MGP) leads to medial elastic lamina calcification (elastocalcinosis) in both humans and animal models. While MGP-deficient (Mgp-/-) mice have been used as a reliable model to study medial elastocalcinosis, these mice are difficult to maintain because of their fragility. Also, these mice are unsuitable for long-term calcification studies in relation to age and sex as most often they die prematurely. In order to circumvent these problems we generated Mgp-/-;ApoE-FGF23 mice, which in addition to the ablation of Mgp alleles, carries a transgene expressing the phosphaturic hormone FGF23. Increased FGF23 levels in the circulation and ensuing hypophosphatemia in these mice lead to a complete prevention of medial calcification until late adulthood. Interestingly, upon feeding a high phosphorus diet for 10 days, we were able to induce medial calcification in 3-week-old Mgp-/-;ApoE-FGF23 mice. Our mineral analyses showed that the Ca/P% in the calcific deposits in these mice were comparable to that of 5-week-old Mgp-/- mice although the level of crystallinity differed. The aorta explants from Mgp-/-;ApoE-FGF23 mice resulted in elastocalcinosis in the presence of 2 mM phosphate in the culture medium which was completely prevented by pyrophosphate analogue alendronate. Mgp-/-;ApoE-FGF23 mice will be suitable for future in vivo or ex vivo studies examining the effects of age, sex and mineralization inhibitors on medial elastocalcinosis.

Matrix Gla protein (MGP) is a vitamin K-dependent post-translationally modified protein, highly expressed in vascular and cartilaginous tissues. It is a potent inhibitor of extracellular matrix mineralization. Biallelic loss-of-function variants in the MGP gene cause Keutel syndrome, an autosomal recessive disorder characterized by widespread calcification of various cartilaginous tissues and skeletal and vascular anomalies. In this study, we report four individuals from two unrelated families with two heterozygous variants in MGP, both altering the cysteine 19 residue to phenylalanine or tyrosine. These individuals present with a spondyloepiphyseal skeletal dysplasia characterized by short stature with a short trunk, diffuse platyspondyly, midface retrusion, progressive epiphyseal anomalies and brachytelephalangism. We investigated the cellular and molecular effects of one of the heterozygous deleterious variants (C19F) using both cell and genetically modified mouse models. Heterozygous 'knock-in' mice expressing C19F MGP recapitulate most of the skeletal anomalies observed in the affected individuals. Our results suggest that the main underlying mechanism leading to the observed skeletal dysplasia is endoplasmic reticulum stress-induced apoptosis of the growth plate chondrocytes. Overall, our findings support that heterozygous variants in MGP altering the Cys19 residue cause autosomal dominant spondyloepiphyseal dysplasia, a condition distinct from Keutel syndrome both clinically and molecularly.

Matrix Gla protein (MGP) was first identified as a calcification physiological inhibitor and the causal agent of the Keutel syndrome. MGP has been suggested to play a role in development, cell differentiation, and tumorigenesis. This study aimed to compare MGP expression and methylation status in different tumors and adjacent tissues, using The Cancer Genome Atlas (TCGA) data repository. We investigated if changes in MGP mRNA expression were correlated to cancer progression and whether the correlation coefficients could be used for prognosis. Strong correlations were observed between altered MGP levels and disease progression in breast, kidney, liver, and thyroid cancers, suggesting that it could be used to complement current clinical biomarker assays, for early cancer diagnosis. We have also analyzed MGP methylation and identified CpG sites in its promoter and first intron with clear differences in methylation status between healthy and tumoral tissue providing evidence for epigenetic regulation of MGP transcription. Furthermore, we demonstrate that these alterations correlate with the overall survival of the patients suggesting that its assessment can serve as an independent prognostic indicator of patients' survival.