ECTS2016 Poster Presentations Chondrocytes and cartilage (14 abstracts)
Desbuquois dysplasia (DBQD) is a rare recessive chondrodysplasia, characterized by growth retardation, multiple dislocations and advanced carpal ossification. Two forms of DBQD have been described on the basis of the presence (type 1) or absence (type 2) of characteristic hand anomalies. DBQD type 1 is caused by mutations in the Calcium-Activated Nucleotidase 1 gene (CANT1), while DBQD type 2 is caused by mutations in the xylosiltransferase 1 gene.
CANT1 is a nucleotidase of the ER/Golgi that hydrolyzes UDP, suggesting its involvement in protein glycosylation; for this reason its role in proteoglycan (PG) metabolism has been hypothesized.
To better characterize CANT1 role in the etiology of DBQD and in PG synthesis, we generated a Cant1 knock out mouse by excision of exon 3 and 4. The KO mouse showed the same growth defects and hand anomalies of patients. To study PG synthesis, rib chondrocytes were metabolically labeled with 35S-sulfate and the amount of newly synthesized PGs was evaluated. KO cells showed reduced PG synthesis compared to wild types both in presence and in absence of β-D-xyloside, an enhancer of glycosaminoglycan (GAG) synthesis. Gel filtration chromatography of GAGs released from newly synthesized PGs after β-elimination demonstrated that the hydrodynamic size of GAG chains was reduced in KO chondrocytes compared to the controls. Ultrastructural analysis of KO and wild type cartilage and cultured chondrocytes by TEM demonstrated the presence of dilated vacuoli containing electrondense proteinaceus material suggesting a role of CANT1 in protein secretion. Pulse-chase labeling of cells with 35S-sulfate demonstrated reduced PG secretion in mutant cells compared to the controls.
In conclusion, we generated and validated a mouse model to study DBQD type 1 and we demonstrated that CANT1 play a role in PG synthesis.
14 May 2016 - 17 May 2016