Mutational and functional analyses of xylosyltransferases and their implication in osteoarthritis.
OBJECTIVE
The hallmark in osteoarthritis (OA) is the loss of proteoglycans (PGs) in articular cartilage (AC). Xylosyltransferase I (XT-I) catalyzes the transfer of xylose to serine residues in the core protein and initiates the biosynthesis of PGs in AC. The XYLT-II gene encodes a highly homologous protein but its biological function is not yet known. Here we investigate for the first time genetic variations in the XYLT-genes and serum XT-I activities and their implication in OA.


METHODS
Denaturing high-performance liquid chromatography (DHPLC) was used for the screening of the XYLT-genes in 49 OA patients. For a detailed characterization of XT-I amino acid exchanges we performed recombinant expression of XT-I mutants in insect cells. Furthermore, the XT activity was measured in the patients' serum.


RESULTS
The variation c.1569C>T (XYLT-II) occurs with a significantly higher frequency in younger OA patients in comparison with the older ones (P<0.001) and the controls (P<0.02). Furthermore, significantly higher serum XT activities were found in patients with a long disease duration of OA (P<0.04). The recombinant XT-I mutants p.P385L and p.I552S had reduced enzymatic activity (85% and 74%) compared with the wildtype (wt).


CONCLUSIONS
Our findings indicate a correlation of the c.1569 T-allele in XYLT-II with an earlier manifestation of OA and that the serum XT activity is a potential biochemical marker for staging and monitoring the progression of AC damage in OA. Comparison of XT-I activity in mutant enzymes in vivo and in vitro revealed that heterozygous mutations are not involved in OA.
Schön
S
S
Institut für Laboratoriums- und Transfusionsmedizin, Herz- und Diabeteszentrum Nordrhein-Westfalen, Universitätsklinik der Ruhr-Universität Bochum, Bad Oeynhausen, Germany.
Huep
G
G
Prante
C
C
Müller
S
S
Christ
R
R
Hagena
F-W
FW
Kuhn
J
J
Kleesiek
K
K
Götting
C
C
D000368:Aged; D000595:Amino Acid Sequence; D004252:DNA Mutational Analysis / Q000379:methods; D005260:Female; D005787:Gene Frequency / Q000235:genetics; D005838:Genotype; D006801:Humans; D008297:Male; D008875:Middle Aged; D009154:Mutation / Q000235:genetics; D010003:Osteoarthritis / Q000097:blood / Q000235:genetics*; D010430:Pentosyltransferases / Q000097:blood / Q000235:genetics*; D010641:Phenotype; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D011994:Recombinant Proteins / Q000235:genetics; D000097608:UDP Xylose-Protein Xylosyltransferase
D010430:Pentosyltransferases; D011994:Recombinant Proteins; D000097608:UDP Xylose-Protein Xylosyltransferase