Osteoporosis may complicate iron overload diseases such as genetic hemochromatosis. However, molecular mechanisms involved in the iron-related osteoporosis remains poorly understood. Recent in vitro ...studies support a role of osteoblast impairment in iron-related osteoporosis. Our aim was to analyse the impact of excess iron in Hfe-/- mice on osteoblast activity and on bone microarchitecture. We studied the bone formation rate, a dynamic parameter reflecting osteoblast activity, and the bone phenotype of Hfe-/- male mice, a mouse model of human hemochromatosis, by using histomorphometry. Hfe-/- animals were sacrificed at 6 months and compared to controls. We found that bone contains excess iron associated with increased hepatic iron concentration in Hfe-/- mice. We have shown that animals with iron overload have decreased bone formation rate, suggesting a direct impact of iron excess on active osteoblasts number. For bone mass parameters, we showed that iron deposition was associated with bone loss by producing microarchitectural impairment with a decreased tendency in bone trabecular volume and trabecular number. A disorganization of trabecular network was found with marrow spaces increased, which was confirmed by enhanced trabecular separation and star volume of marrow spaces. These microarchitectural changes led to a loss of connectivity and complexity in the trabecular network, which was confirmed by decreased interconnectivity index and increased Minkowski's fractal dimension. Our results suggest for the first time in a genetic hemochromatosis mouse model, that iron overload decreases bone formation and leads to alterations in bone mass and microarchitecture. These observations support a negative effect of iron on osteoblast recruitment and/or function, which may contribute to iron-related osteoporosis.
Stüve-Wiedemann syndrome (SWS) is characterised by bowing of the lower limbs, respiratory distress and hyperthermia that are often responsible for early death. Survivors develop progressive scoliosis ...and spontaneous fractures. We previously identified
mutations in most SWS cases, but absence of
pathogenic changes in five patients led us to perform exome sequencing and to identify homozygosity for a
mutation in one case p.Ser205Tyrfs*13. The follow-up of this case supported a final diagnosis of osteogenesis imperfecta (OI), based on vertebral collapses and blue sclerae.
This prompted us to screen
in 25 OI patients with no known mutations.We identified a homozygous deleterious variant in
in two affected sibs with typical OI p.His127Arg. Another homozygous variant, p.Asp231Gly, also classed as deleterious, was detected in a patient with type III OI of consanguineous parents using homozygosity mapping and exome sequencing.FAM46A is a member of the superfamily of nucleotidyltransferase fold proteins but its exact function is presently unknown. Nevertheless, there are lines of evidence pointing to a relevant role of FAM46A in bone development. By RT-PCR analysis, we detected specific expression of
in human osteoblasts andinterestingly, a nonsense mutation in
has been recently identified in an ENU-derived (
-ethyl-
-nitrosourea) mouse model characterised by decreased body length, limb, rib, pelvis, and skull deformities and reduced cortical thickness in long bones.
We conclude that
mutations are responsible for a severe form of OI with congenital bowing of the lower limbs and suggest screening this gene in unexplained OI forms.
Summary
In order to understand mechanisms involved in osteoporosis observed during iron overload diseases, we analyzed the impact of iron on a human osteoblast-like cell line. Iron exposure decreases ...osteoblast phenotype.
HHIPL-2
is an iron-modulated gene which could contribute to these alterations. Our results suggest osteoblast impairment in iron-related osteoporosis.
Introduction
Iron overload may cause osteoporosis. An iron-related decrease in osteoblast activity has been suggested.
Methods
We investigated the effect of iron exposure on human osteoblast cells (MG-63) by analyzing the impact of ferric ammonium citrate (FAC) and iron citrate (FeCi) on the expression of genes involved in iron metabolism or associated with osteoblast phenotype. A transcriptomic analysis was performed to identify iron-modulated genes.
Results
FAC and FeCi exposure modulated cellular iron status with a decrease in TFRC mRNA level and an increase in intracellular ferritin level. FAC increased ROS level and caspase 3 activity. Ferroportin, HFE and TFR2 mRNAs were expressed in MG-63 cells under basal conditions. The level of ferroportin mRNA was increased by iron, whereas HFE mRNA level was decreased. The level of mRNA alpha 1 collagen type I chain, osteocalcin and the transcriptional factor RUNX2 were decreased by iron. Transcriptomic analysis revealed that the mRNA level of HedgeHog Interacting Protein Like-2 (
HHIPL-2
) gene, encoding an inhibitor of the hedgehog signaling pathway, was decreased in the presence of FAC. Specific inhibition of
HHIPL-2
expression decreased osteoblast marker mRNA levels. Purmorphamine, hedgehog pathway activator, increased the mRNA level of GLI1, a target gene for the hedgehog pathway, and decreased osteoblast marker levels. GLI1 mRNA level was increased under iron exposure.
Conclusion
We showed that in human MG-63 cells, iron exposure impacts iron metabolism and osteoblast gene expression.
HHIPL-2
gene expression modulation may contribute to these alterations. Our results support a role of osteoblast impairment in iron-related osteoporosis.
Summary
Genetic hemochromatosis is a cause of osteoporosis; mechanisms leading to iron-related bone loss are not fully characterized. We assessed the bone phenotype of
HFE
−/−
male mice, a mouse ...model of hemochromatosis. They had a phenotype of osteoporosis with low bone mass and alteration of the bone microarchitecture.
Introduction
Genetic hemochromatosis is a cause of osteoporosis. However, the mechanisms leading to iron-related bone loss are not fully characterized. Recent human data have not supported the hypothesis of hypogonadism involvement. The direct role of iron on bone metabolism has been suggested.
Methods
Our aim was to assess the bone phenotype of
HFE
−/−
male mice, a mouse model of human hemochromatosis, by using microcomputed tomography and histomorphometry.
HFE
−/−
animals were sacrificed at 6 and 12 months and compared to controls.
Results
There was a significant increase in hepatic iron concentration and bone iron content in
HFE
−/−
mice. No detectable Perls’ staining was found in the controls’ trabeculae. Trabecular bone volume (BV/TV) was significantly lower in
HFE
−/−
mice at 6 and 12 months compared to the corresponding wild-type mice: 9.88 ± 0.82% vs 12.82 ± 0.61% (
p
= 0.009) and 7.18 ± 0.68% vs 10.4 ± 0.86% (
p
= 0.015), respectively. In addition, there was an impairment of the bone microarchitecture in
HFE
−/−
mice. Finally, we found a significant increase in the osteoclast number in
HFE
−/−
mice: 382.5 ± 36.75 vs 273.4 ± 20.95 ¢/mm
2
(
p
= 0.004) at 6 months and 363.6 ± 22.35 vs 230.8 ± 18.7 ¢/mm
2
(
p
= 0.001) at 12 months in
HFE
−/−
mice vs controls.
Conclusion
Our data show that
HFE
−/−
male mice develop a phenotype of osteoporosis with low bone mass and alteration of the microarchitecture. They suggest that there is a relationship between bone iron overload and the increase of the osteoclast number in these mice. These findings are in accordance with clinical observations in humans exhibiting genetic hemochromatosis and support a role of excess iron in relation to genetic hemochromatosis in the development of osteoporosis in humans.
ABSTRACT
Cerebro‐costo‐mandibular syndrome (CCMS) is a developmental disorder characterized by the association of Pierre Robin sequence and posterior rib defects. Exome sequencing and Sanger ...sequencing in five unrelated CCMS patients revealed five heterozygous variants in the small nuclear ribonucleoprotein polypeptides B and B1 (SNRPB) gene. This gene includes three transcripts, namely transcripts 1 and 2, encoding components of the core spliceosomal machinery (SmB′ and SmB) and transcript 3 undergoing nonsense‐mediated mRNA decay. All variants were located in the premature termination codon (PTC)‐introducing alternative exon of transcript 3. Quantitative RT‐PCR analysis revealed a significant increase in transcript 3 levels in leukocytes of CCMS individuals compared to controls. We conclude that CCMS is due to heterozygous mutations in SNRPB, enhancing inclusion of a SNRPB PTC‐introducing alternative exon, and show that this developmental disease is caused by defects in the splicing machinery. Our finding confirms the report of SNRPB mutations in CCMS patients by Lynch et al. (2014) and further extends the clinical and molecular observations.
Cerebro‐costo‐mandibular syndrome (CCMS) is a developmental disorder characterized by the association of Pierre Robin sequence and posterior rib defects. We identify heterozygous mutations in the PTC‐introducing exon of SNRPB in five unrelated CCMS cases. SNRPB encodes core spliceosome components: SmB/B', and the mutations appears to promote the alternativ exon, reducing the formation of coding transcrits. CCMS is a novel developmental disease caused by defects in the core splicing machinery.
Ghosal type hematodiaphyseal dysplasia Jeevan, Amrit; Doyard, Mathilde; Kabra, Madhulika ...
Indian pediatrics,
04/2016, Volume:
53, Issue:
4
Journal Article
Peer reviewed
Background
Ghosal Type Hematodiaphyseal Dysplasia is an autosomal recessive disorder characterized by refractory anemia and diaphyseal bone dysplasia.
Case characteristics
A 3 y 9 mo-old male child ...presented with progressive anemia and bowing of thighs. Child was found to have a previously reported homozygous point mutation c.1238G>A, (p.Arg413Glu) in Exon 16 of
TBXAS1
gene.
Outcome
Low dose steroid therapy resulted in normalization of hemoglobin and prevented further progression of bony changes.
Message
Refractory anemia in association with bony deformities should prompt pediatricians to investigate for inherited bony dysplasia.
Osteoporosis may complicate iron overload diseases such as genetic hemochromatosis. However, molecular mechanisms involved in the iron-related osteoporosis remains poorly understood. Recent in vitro ...studies support a role of osteoblast impairment in iron-related osteoporosis. Our aim was to analyse the impact of excess iron in Hfe-/- mice on osteoblast activity and on bone microarchitecture. We studied the bone formation rate, a dynamic parameter reflecting osteoblast activity, and the bone phenotype of Hfe-/- male mice, a mouse model of human hemochromatosis, by using histomorphometry. Hfe-/- animals were sacrificed at 6 months and compared to controls. We found that bone contains excess iron associated with increased hepatic iron concentration in Hfe-/- mice. We have shown that animals with iron overload have decreased bone formation rate, suggesting a direct impact of iron excess on active osteoblasts number. For bone mass parameters, we showed that iron deposition was associated with bone loss by producing microarchitectural impairment with a decreased tendency in bone trabecular volume and trabecular number. A disorganization of trabecular network was found with marrow spaces increased, which was confirmed by enhanced trabecular separation and star volume of marrow spaces. These microarchitectural changes led to a loss of connectivity and complexity in the trabecular network, which was confirmed by decreased interconnectivity index and increased Minkowski's fractal dimension. Our results suggest for the first time in a genetic hemochromatosis mouse model, that iron overload decreases bone formation and leads to alterations in bone mass and microarchitecture. These observations support a negative effect of iron on osteoblast recruitment and/or function, which may contribute to iron-related osteoporosis.
Métabolisme du fer en 2012 Loréal, Olivier; Ropert, Martine; Doyard, Mathilde ...
Revue francophone des laboratoires,
20/May , Volume:
2012, Issue:
442
Journal Article
Peer reviewed
Le fer intervient dans de nombreuses fonctions biologiques et est donc nécessaire. Cependant, en excès, il est toxique. Le maintien d’un niveau adéquat de fer ainsi que sa bonne répartition dans ...l’organisme et dans les cellules sont possibles grâce à des mécanismes de régulation systémiques et cellulaires. Le contrôle systémique du métabolisme du fer fait intervenir l’hepcidine, peptide secrété par l’hépatocyte, et la ferroportine, protéine membranaire exportant le fer des macrophages et entérocytes vers le plasma. L’hepcidine interagit avec la ferroportine et provoque sa dégradation, contrôlant ainsi le niveau de fer plasmatique. Des niveaux anormaux d’hepcidine sont impliqués dans l’apparition de surcharges ou de carences en fer. La compréhension des mécanismes contrôlant les niveaux d’hepcidine est donc un enjeu majeur. Le contrôle cellulaire du fer fait intervenir le système iron regulatory protein/iron responsive element qui permet d’adapter l’entrée du fer lié à la transferrine dans la cellule et la capacité de stockage cellulaire du fer au niveau de fer intracellulaire, permettant ainsi d’éviter l’apparition de situations délétères pour la cellule. Les nouvelles connaissances acquises sur le métabolisme du fer permettent de mieux comprendre les mécanismes en cause dans les pathologies du métabolisme du fer. De nouvelles stratégies diagnostiques et thérapeutiques, issues de ces connaissances, permettront d’améliorer la prise en charge des patients.
Iron is involved in many biological functions and is therefore required for cell life. However, when present in excess, it is toxic. Maintenance of adequate levels of iron as well as its proper distribution in the body and cells are possible through systemic and cellular mechanisms. Systemic control of iron metabolism involves hepcidin, a peptide secreted by hepatocytes, and ferroportin, the iron exporter from macrophages and enterocytes toward plasma. Hepcidin interacts with ferroportin and causes its degradation, thus controlling the level of plasma iron. Abnormal levels of hepcidin are involved in the onset of iron overload or deficiency. Understanding the mechanisms controlling hepcidin levels is therefore a major issue. Control of cellular iron involves the iron regulatory protein/iron responsive element system that regulates transferrin-iron uptake by cells as well as the iron storage capacity, thus avoiding cell damage. New knowledge on iron metabolism permits a better understanding of the mechanisms involved in iron metabolism disorders. From this knowledge, new diagnostic and therapeutic strategies will improve the patients management.
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