title: The role of CD40 and CD40L in bone mineral density and in osteoporosis risk: A genetic and functional study.
abstract: Compelling data are revealing that the CD40/CD40L system is involved in bone metabolism. Furthermore, we have previously demonstrated that polymorphisms in both genes are associated with bone phenotypes. The aim of this study is to further characterize this association and to identify the causal functional mechanism. We conducted an association study of BMD with 15 SNPs in CD40/CD40L genes in a population of 779 women. In addition, we assessed the functionality of this association through the study of the allele-dependent expression of CD40 and CD40L in peripheral blood leukocytes (PBLs) and in human osteoblasts (OBs) obtained from bone explants by qPCR and by sequencing. When an allelic imbalance (AI) was detected, studies on allele-dependent in vitro transcription rate and on CpG methylation in the gene promoter were also performed. Our results confirm the genetic association between SNP rs116535 (T>C) of CD40L gene with LS-BMD. Regarding CD40 gene, two SNPs showed nominal P-values<0.05 for FN- and LS-BMD (Z-scores), although the association was not significant after correcting for multiple testing. Homozygous TT women for SNP rs1883832 (C>T) of CD40 gene showed a trend to have lower levels of OPG (Q-value=0.059), especially when women of BMD-quartile ends were selected (P<0.05). Regarding functionality, we detected an AI for rs1883832 with the C allele the most expressed in OBs and in PBLs. Since the rs116535 of CD40L gene did not show AI, it was not further analyzed. Finally, we described a differential methylation of CpGs in the CD40 promoter among women of high in comparison to low BMD. Our results suggest that the CD40/CD40L system plays a role in regulating BMD. Effectively, our data suggest that a decreased production of OPG could be the cause of the lower BMD observed in TT women for rs1883832 of the CD40 gene and that the degree of methylation of CpGs in the CD40 promoter could contribute to the acquisition of BMD. One possibility that deserves further study is whether the degree of methylation of the CD40 gene affects the level of CD40 expression and, consequently, the level of OPG.
authors.affiliation: Research Foundation, Institute of Health Research INCLIVA, 46010 Valencia, Spain.
authors.forename: Layla
authors.initials: L
authors.lastname: Panach
authors.affiliation: Research Foundation, Institute of Health Research INCLIVA, 46010 Valencia, Spain.
authors.forename: Begoña
authors.initials: B
authors.lastname: Pineda
authors.affiliation: Orthopedic Surgery and Traumatology, Clinic Hospital, Institute of Health Research INCLIVA, 46010 Valencia, Spain.
authors.forename: Damián
authors.initials: D
authors.lastname: Mifsut
authors.affiliation: Department of Functional Biology and Physical Anthropology, University of Valencia, 46100 Burjassot, Spain.
authors.forename: Juan J
authors.initials: JJ
authors.lastname: Tarín
authors.affiliation: Department of Pediatrics, Obstetrics and Gynecology, University of Valencia, 46010 Valencia, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Cano
authors.affiliation: Research Foundation, Institute of Health Research INCLIVA, 46010 Valencia, Spain; Department of Genetics, University of Valencia, 46100 Burjassot, Spain. Electronic address: migarpe@uv.es.
authors.forename: Miguel Ángel
authors.initials: MÁ
authors.lastname: García-Pérez
mesh_terms: D000483:Alleles; D015519:Bone Density / Q000235:genetics*; D001842:Bone and Bones / Q000473:pathology; D019013:CD40 Antigens / Q000235:genetics*; D023201:CD40 Ligand / Q000235:genetics*; D015331:Cohort Studies; D018899:CpG Islands / Q000235:genetics; D019175:DNA Methylation / Q000235:genetics; D005260:Female; D017930:Genes, Reporter; D056726:Genetic Association Studies; D020022:Genetic Predisposition to Disease; D006801:Humans; D040582:Inheritance Patterns / Q000235:genetics; D008875:Middle Aged; D008957:Models, Genetic; D010024:Osteoporosis / Q000097:blood / Q000453:epidemiology / Q000235:genetics* / Q000503:physiopathology*; D053244:Osteoprotegerin / Q000378:metabolism; D010641:Phenotype; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D012307:Risk Factors; D013030:Spain; D014158:Transcription, Genetic
chemical_list: D019013:CD40 Antigens; D053244:Osteoprotegerin; D023201:CD40 Ligand
keywords: Association study; CD40/CD40L genes; Functional genetics; Osteoimmunology; Osteoporosis