Calcium activated nucleotidase 1 (CANT1) is critical for glycosaminoglycan biosynthesis in cartilage and endochondral ossification

Abstract

Desbuquois dysplasia type 1 (DBQD1) is a chondrodysplasia caused by mutations in CANT1 gene encoding an ER/Golgi calcium activated nucleotidase 1 that hydrolyses UDP. Here, using Cant1 knock-in and knock-out mice recapitulating DBQD1 phenotype, we report that CANT1 plays a crucial role in cartilage proteoglycan synthesis and in endochondral ossification. Specifically, the glycosaminoglycan synthesis was decreased in chondrocytes from Cant1 knock-out mice and their hydrodynamic size was reduced, whilst the sulfation was increased and the overall proteoglycan secretion was delayed. Interestingly, knock-out chondrocytes had dilated ER cisternae suggesting delayed protein secretion and cellular stress; however, no canonical ER stress response was detected using microarray analysis, Xbp1 splicing and protein levels of BiP and ATF4. The observed proteoglycan defects caused deregulated chondrocyte proliferation and maturation in the growth plate resulting in the reduced skeletal growth. In conclusion, the pathogenic mechanism of DBQD1 comprises deregulated chondrocyte performance due to defective intracellular proteoglycan synthesis and altered proteoglycan properties in the extracellular matrix.

Bone and connective tissue disorders caused by defects in glycosaminoglycan biosynthesis: a panoramic view

“…In skin fibroblasts from patients with DBQD1, ER enlargement with retention of proteinaceous material has been observed . The same findings have been reported in cartilage from a Cant1 knock‐out mouse; however, ER enlargement does not trigger ER stress and conventional unfolded protein response (UPR) despite reduced PG secretion . Lastly, confocal microscopy in skin fibroblasts from patients with mutations in SLC10A7 has demonstrated enlargement of the Golgi due to post‐Golgi transport defects through the secretory pathway .…”

“…Besides altered sulfation in disorders linked to proteins and enzymes involved in the sulfate activation pathway, CS sulfation imbalance with an increased percentage of nonsulfated disaccharide has been reported in the limb of the Chsy1 knock‐out mouse . Altered CS sulfation has also been detected in chondrocyte cultures and in cartilage of the Cant1 knock‐out mouse . Moreover, in cartilage explants from mouse models of DBQD1 and Schneckenbecken dysplasia CS chains with reduced length have been detected .…”

“…Altered CS sulfation has also been detected in chondrocyte cultures and in cartilage of the Cant1 knock‐out mouse . Moreover, in cartilage explants from mouse models of DBQD1 and Schneckenbecken dysplasia CS chains with reduced length have been detected .…”

CANT1 deficiency in a mouse model of Desbuquois dysplasia impairs glycosaminoglycan synthesis and chondrocyte differentiation in growth plate cartilage

“…Meanwhile, CANT1 is a nucleotidase that preferentially hydrolyzes UDP to UMP and phosphate [16–18]. CANT1 has also been predicted to be involved in GAG synthesis, and the recent study using genetically modified mice has confirmed the prediction [6–8,19].…”

“…Paganini and colleagues generated two mouse strains by an ES cell‐based method: a Cant1 knockout (KO) and a Cant1 knock‐in harboring DD type 1 causative p.R302H missense mutation [19]. Both strains present skeletal dysplasia phenotypes similar to DD type 1.…”