La vitamina K è in grado di alterare l'espressione di proteine coinvolte nei processi di calcificazione? Per rispondere a questa domanda sono state fatte prove su cellule umane e su topi. Le analisi hanno riguardato l'espressione dei geni, delle proteine e delle modificazioni post-traduzionali a cui possono andare incontro.
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La vitamina K che ruolo ha?
1. IN VITRO VITAMIN K TREATMENT IS NOT CAPABLE TO RESCUE
UNEFFICIENT MGP-CARBOXYLATION IN PXE FIBROBLASTS
Annovi G., Boraldi F., Quaglino D.
Dept. Biomedical Sciences, University of Modena and Reggio Emilia,
Modena, Italy
Turin, June 21-24, 2011
3. The inappropriate biomineralization occurring in soft tissue is defined as
ectopic calcification
•
•
•
•
•
atherosclerosis
chronic renal disease
diabetes
treatment with anti-coagulant therapy
specific gene defects
5. Ectopic calcification occurence:
1. Circulating nucleational complexes (high Ca / P)
2. Cell death
3. Alteration of NF-kB activity
4. Proteolysis and ECM degradation
5. Presence of “Bone Proteins”
6. Loss of inhibitors
6. Matrix Gla Protein (MGP)
GLA
GLA
GLA
GLA
GLA
a 14-kDa secreted protein
containing 5-glutamic acid
residues that must be γcarboxylated by a vitamin Kdependent γ-carboxylase in
order to acquire calciumbinding properties.
Vit. K1H2
VKOR
MGP
Vit. K1
CO2 + O2
Vitamin K Cycle
Gammacarboxylase
Vit. K1>O
MGP
-COOH
7. Lab Invest. 2010 Jun;90(6):895-905. Epub 2010 Apr 5.
Low serum vitamin K in PXE results in defective carboxylation of mineralization inhibitors
similar to the GGCX mutations in the PXE-like syndrome.
Vanakker OM, Martin L, Schurgers LJ, Quaglino D, Costrop L, Vermeer C, Pasquali-Ronchetti I, Coucke PJ, De Paepe A.
Serum
Gla MGP
%
Serum
Vit K
ng/ml
10. s s
SH SH
Vit. K1H2
e-
MGP
PDI
S S
VKOR
CO2 + O2
PDI
Vitamin K cycle
gamma-carboxylase
SH SH
CALU
CALU
Vit. K1>O
Vit. K1
75
50
PDI
50
37
*
160
80
120
CALU
40
0
C
PXE
MGP
-COOH
11.
12. 1.50
Controllo
Control
Arbitrary unit DH 2
Arbitrary unit DH
2
1.25
PXE
PXE
*
*
1.25
1.00
1.00
$
$
0.75
0.75
0.50
0.50
0.25
0.25
0.00
Control
Control
PXE
PXE
K2 100 µM K2 µM µM K2 1K2 1 µM1 µM K2 0.01 µMK2 0.01 µM
K1 100 µM K1 100 µM K1 1µM
K1
µM K2 1µM K1 0.01 µMK1 0.01 µM
K2 100 100
* p<0.05 PXE vsControl
*p<0.05 PXE vs Control
$ p<0.05 Vitamin K2 PXE vs PXE
Control
PXE
Control
Arbitrary unit H2O2
Arbitrary unit H2O2
1.5
1.0
0.5
0.0
PXE
2.0
2.0
Control
PXE
K1 100 µM K1 100 µM K1 1 µM
K1 1 µM K1 0.01 µMK1 0.01 µM
1.5
1.0
0.5
0.0
Control
PXE
K2 100 µM K2 100 µM K2 1K2 1 µM 1 µM K2 0.01 0.01 µM µM
K2
µM
K2 100 µM
K2 µMK2 0.01
17. Control
PXE
DMF
Days of culture
100µM K1
0,1µM K1
DMF
0,1µM K2
Vitamin K1
100µM K2
Vitamin K2
0.1µM
100µM
0.1µM
100µM
Day 10
Control
0.2 ±0.20
0.4 ±0.25
0.6 ±0.40
0.7 ±0.66
0.8 ±0.48
PXE
0.2 ±0.17
0.4 ±0.40
0.8 ±0.58
0.3 ±0.28
0.4 ±0.24
Control
0.3 ±0.25
1.4 ±0.87
2.6 ±1.39
0.7 ±0.67
2.0 ±0.81 #
PXE
1.2 ±0.56
1.8 ±1.11
4.6 ±2.64
3.4 ±2.57
1.7 ±1.66 #
Control
9.9±3.28
9.4 ±5.01
9.0 ±5.81
26.0 ±7.72
n.d.b)
PXE
14.4 ±4.15
12.0±4.3
11.9±3.86
22.2 ±5.76
n.d. b)
Day 20
Day 30
# morphological
alteration
18. In these work we have demontrated that:
# PXE fibroblasts are able to respond to vitamin K increasing the
efficiency of the carboxylation process.
# vitamin K2 reduce the expression of MGP mRNA and protein.
#vitamin k have negligible effects on MGP carboxylation
#vitamin k are not able to counteract the in vitro mineralization
process.
° mice data
°in vivo data
Editor's Notes
Vitamin K is a group of fat soluble vitamins that, in their reduced form, are needed for the posttranslational modification of a number of proteins involved in blood coagulation as well as in the mineralization process.
Development of ectopic calcifications is responsible for clinical complications occurring during atherosclerosis, chronic renal diseases, diabetes and upon treatments with warfarin, or as the result of specific gene defects.
Manca l'occhio
pseudoxanthoma elasticum (PXE), a rare genetic disorder associated to mutations in the ABCC6 gene, and characterized by the progressive mineralization of elastic fibers (Le Saux 2000). Clinical manifestations mainly affect skin with laxity and formation of xantomatous papule; eyes, with angioid streaks and retinal haemorrhages leading to central vision loss; and the cardiovascular system with premature intermittent claudication and higher frequency of angina and myocardial infarction
Ectopic calcification may occur (1) when the systemic concentrations of calcium
and phosphate in extracellular fluid exceed the saturation point (metastatic
calcification); (2) as a consequence of the replacement or transition of injured,
degenerated, and necrotic tissue by mineral depositions (dystrophic calcification);
or (3) by means of the transdifferentiation of mesenchymal cells into bone tissue
(ectopic calcification) (
Matrix Gla Protein (MGP) is an important local inhibitor of cartilage, arterial
and soft tissues calcification (Ketteler M. et al., 2005). Several in vitro and in vivo
studies have shown that MGP is expressed by many peripheral cell types,
including fibroblasts and smooth muscle cells (Fraser J.D. and Price P.A., 1988;
Shanahan C.M. et al., 1993).
MGP is a small ECM protein that contains nine γ- carboxyglutamic acid residues, five of which are posttranslationally modified, resulting from vitamin K-dependent carboxylation of the protein in the endoplasmic reticulum (Price P.A. et al., 1983; Price P.A. and Williamson M.K., 1985).
MGP γ- carboxylation is performed by the vitamin K-dependent enzyme, γ-carboxylase and this modification appears to be important in its function: conditions causing a
relative deficiency of functional vitamin K may increase vascular calcification
because of incomplete γ-carboxylation and reduced function of MGP (Jie K.S. et
al., 1995)The case of mutations in the MGP gene that, due to the production of
nonfunctional or absent MGP, is associated to abnormal cartilage and arterial mineralization,
. Moreover, lack of function due to insufficient γ-carboxylation or to reduced levels of vitamin K rather than the amount of MGP, is the factor that increases the risk of calcification and is inversely
correlated with the severity of coronary artery calcification (Jono S. et al., 2004).
Reduced levels of vitamin K and the consequent reduction of carboxylated-Matrix Gla
Protein (Gla-MGP) have been demonstrated by Vanakker and coworker in serum of pseudoxanthoma elasticum (PXE) patients
In this paper we have demonstrated that PXE fibroblasts exhibited an insufficient vitamin-K-dependent carboxylation of MGP
Moreover, we have recently reported that fibroblasts, isolated from PXE patients and cultured in vitro, have an altered protein profile
And in particular, PXE firolasts have dispalyed a down-regulation of protein disulfide isomerase (PDI) and an up- regulation of calumenin (CALU), two proteins of the endoplasmic reticulum that are involved in vitamin K cycle, by assuring the appropriate reduced environment, necessary for regenerating the vitamin in its active form, and by inhibiting the γ-carboxylase activity, respectively
Taken together these evidences, it could be conceivable that vitamin K supplementation might be capable to counteract the abnormal expression of proteins involved in vitamin K cycle and in MGP carboxylation in PXE fibroblasts.
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