Bone Abstracts

Transforming growth factor (TGF)-β1 is the most abundant growth factor in human bone. Several polymorphisms have been described in the TGF-β1 gene (TGFB1). We have previously shown that individuals with the CC genotype of the T²⁹C polymorphism have higher bone mass at the femoral neck. The T²⁹C polymorphism causes a change from leucine to proline at codon 10, which is located in the hydrophobic α-helical part of the signal peptide. A proline at this position would be expected to disrupt the α-helical structure, thereby altering the ability of the signal peptide to direct protein transport across the endoplasmic reticulum.

To examine whether the T²⁹C polymorphism affects TGF-β1 secretion in osteoblast like cell lines, we transfected the osteosarcoma cell line; U2OS and SaOS-2 with TGF-β1 expression plasmids containing different T²⁹C genotypes. pcDNA3.1-TGF-β1-10L and pcDNA3.1-TGF-β1-10P were generated from cDNA encoding TGF-β1 WT and variant amplified from RNA isolated from primary human osteoblasts and the mammalian expression vector pcDNA3.1+. The two cell lines were transfected with the TGF-β1 expression plasmids using Fugene. The influence of the T²⁹C polymorphism on TGF-β1 levels in peripheral serum and bone marrow serum was examined in 185 young healthy individuals. TGF-β1 in supernatants, marrow and peripheral plasma was determined by ELISA. The study was approved by the local ethical committee.

The secretion of the variant protein was increased by 14±6% (P=0.02, n=27) compared to the WT in U2OS cells and by 80±7% (P<0.001, n=27) in SaOS-2 cells. In contrast, healthy, young individuals homozygous for the variant C allele had reduced TGF-β1 levels compared to carriers of the normal allele; 16.8±6.6 ng/ml vs 19.5±6.0 ng/ml, P=0.02 in serum and 14.0±4.3 ng/ml vs 15.9±4.6 ng/ml, P=0.04 in bone marrow serum.

In conclusion, we found that the T²⁹C polymorphism was associated with TGF-β1 secretion in vitro and in vivo.