Inflammation-associated ectopic mineralization

Ectopic mineralization refers to the deposition of mineralized complexes in the extracellular matrix of soft tissues.Calcific aortic valve disease,vascular calcification,gallstones,kidney stones,and abnormal mineralization in arthritis are common examples of ectopic mineralization.They are debilitating diseases and exhibit excess mortality,disability,and morbidity,which impose on patients with limited social or financial resources.Recent recognition that inflammation plays an important role in ectopic mineralization has attracted the attention of scientists from different research fields.In the present review,we summarize the origin of inflammation in ectopic mineralization and different channels whereby inflammation drives the initiation and progression of ectopic mineralization.The current knowledge of inflammatory milieu in pathological mineralization is reviewed,including how immune cells,pro-inflammatory mediators,and osteogenic signaling pathways induce the osteogenic transition of connective tissue cells,providing nucleating sites and assembly of aberrant minerals.Advances in the understanding of the underlying mechanisms involved in inflammatory-mediated ectopic mineralization enable novel strategies to be developed that may lead to the resolution of these enervating conditions.

Kidney Stones Are Prevalent in Individuals with Pseudoxanthoma Elasticum, a Genetic Ectopic Mineralization Disorder

Objective:Pseudoxanthoma elasticum(PXE)is a rare genetic disorder caused by loss-of-function mutations in the ABCC6 gene.While PXE is characterized by ectopic mineralization of connective tissues clinically affecting the skin,eyes,and cardiovascular system,kidney stones were reported in some individuals with PXE.The aim of this study is to determine whether kidney stones are an incidental finding or a frequent manifestation of PXE.Methods:We first investigated the genetic basis of two siblings diagnosed with PXE.The younger patient presented with recurrent kidney stones since 8 years old.Secondly,to address whether kidney stones are associated with PXE,the prevalence of kidney stones in a survey cohort of 563 respondents with PXE was compared to that of a general U.S.population survey,National Health and Nutrition Examination Survey,with 28,629 participants.Results:Genetic analysis in both patients identified compound heterozygous mutations in ABCC6,c.2787+1G>T,and c.3774_3775insC.The analysis of participants 20 years old and older revealed that 23.4%of PXE patients had previously had a kidney stone,a significant increase compared to 9.2%in the general population(P<0.01).In addition,17.8%of PXE patients reported their first kidney stone episode before age of 18 years old.Conclusions:PXE correlates with an increased risk of developing kidney stones with considerable morbidity and health-care cost.

Atherogenic Diet Accelerates Ectopic Mineralization in a Mouse Model of Pseudoxanthoma Elasticum

Objective:Pseudoxanthoma elasticum(PXE)is a multisystem heritable disorder caused by mutations in the Abcc6 gene.The disease is characterized by ectopic mineralization of the skin,eyes,and arterial blood vessels.Previous studies have suggested that cardiovascular complications in patients with PXE are caused in part by premature atherosclerosis.The aim of this study is to determine the effect of an atherogenic diet on ectopic mineralization.Methods:We used Abcc6^(tm1JfK)mice(Abcc6^(-/-)mice)as an established preclinical model of PXE.The offspring at age of 4 weeks were divided into two groups and fed the standard control laboratory diet(control group)and the atherogenic diet.Serum lipid profiles and bile acids were measured,and steatosis and tissue mineralization were evaluated by histopathologic analysis and chemical calcium quantification assay,respectively.Results:After 50-58 weeks of feeding an atherogenic diet,the concentrations of total cholesterol,low-density lipoprotein/very-low-density lipoprotein cholesterol,and bile acids were significantly higher in the Abcc6^(-/-)mice on the atherogenic diet(180.9±14.8 g/L,145.9±12.9 g/L,and 9.7±1.4μmol/L,respectively)than in Abcc6^(-/-)mice on a control diet(85.2±4.8 g/L,25.1±5.5 g/L,and 3.3±0.5μmol/L,respectively)(P<0.001).Hypercholesterolemia was accompanied by extensive lipid accumulation in the liver and aorta,a characteristic feature of steatosis.The direct calcium assay demonstrated significantly increased mineralization of the muzzle skin containing the dermal sheath of vibrissae(57.2±4.4μmol Ca/gram tissue on the atherogenic diet and 43.9±2.2μmol Ca/gram tissue on control diet;P<0.01),a reproducible biomarker of the ectopic mineralization process in these mice.An increased frequency of mineralization was also observed in the kidneys and eyes of mice on the atherogenic diet(P<0.01).Conclusion:These observations suggest that the atherogenic diet caused hypercholesterolemia and accelerated ectopic mineralization in the Abcc6^(-/-)mice.Our findings have clinical implications for patients with PXE,a currently intractable disorder with considerable morbidity and occasional mortality.

Association Between Dentin Matrix Protein 1 （rs10019009） Polymorphism and Ankylosing Spondylitis in a Chinese Han Population from Shandong Province

Background： Ankylosing spondylitis （AS） is the most common rheumatic condition that is slowly progressive and predominantly affects adolescents. Pathological bone formation associated with AS is an important cause of disability. The aim of the study was to investigate the possible involvement of the genes related to endochondral ossification and ectopia ossification in genetic susceptibility to AS in a Chinese Han population. Methods： Sixty-eight single nucleotide polymorphisms （SNPs） from 13 genes were genotyped in discovery cohorts including 300 AS patients and 180 healthy controls. The rs10019009 in dentin matrix protein 1 （DMP1） gene shown as association with AS after multiple testing corrections in discovery cohorts was replicated in a validation independent cohort of 620 AS patients and 683 healthy controls. The rs 10019009 was assessed with bioin fomlatics including phylogenetic context, F-SNP and FastSNP functional predictions, secondary structure prediction, and molecular modeling. We performed a functional analysis of rs10019009 via reverse transcription-polymerase chain reaction, alkaline phosphatase （ALP） activity in human osteosarcoma U2OS cells. Results： Interestingly, the SNP rs10019009 was associated with AS in both the discovery cohort （P = 0.0012） and validation cohort （P - 0.0349）, as well as overall （P = 0.0004） in genetic case-control association analysis. After a multivariate logistic regression analysis, the effect of this genetic variant was observed to be independent of linkage disequilibrium. Via bioinformatics analysis, it was found that the amino acid change of the rs 10019009 led to changes of SNP function, secondary structure, tertiary confomlation, and splice mode. Finally, functional analysis ofrsl0019009 in U2OS cells demonstrated that the risk T allele of the rsl0019009 increased enzymatic activity of ALP, compared to that of the nonrisk allele （P = 0.0080）. Conclusions： These results suggested that the DMP1 gene seems to be involved in genetic predisposition to AS, which may contribute to the ectopic mineralization or ossification in AS. In addition, DMP1 gene may be a promising intervention target for AS in the future.