An unfolded protein response is the initial cellular response to the expression of mutant matrilin-3 in a mouse model of multiple epiphyseal dysplasia

Abstract

Multiple epiphyseal dysplasia (MED) can result from mutations in matrilin-3, a structural protein of the cartilage extracellular matrix. We have previously shown that in a mouse model of MED the tibia growth plates were normal at birth but developed a progressive dysplasia characterised by the intracellular retention of mutant matrilin-3 and abnormal chondrocyte morphology. By 3 weeks of age, mutant mice displayed a significant decrease in chondrocyte proliferation and dysregulated apoptosis. The aim of this current study was to identify the initial post-natal stages of the disease. We confirmed that the disease phenotype is seen in rib and xiphoid cartilage and, like tibia growth plate cartilage is characterised by the intracellular retention of mutant matrilin-3. Gene expression profiling showed a significant activation of classical unfolded protein response (UPR) genes in mutant chondrocytes at 5 days of age, which was still maintained by 21 days of age. Interestingly, we also noted the upregulation of arginine-rich, mutated in early stage of tumours (ARMET) and cysteine-rich with EGF-like domain protein 2 (CRELD2) are two genes that have only recently been implicated in the UPR. This endoplasmic reticulum (ER) stress and UPR did not lead to increased chondrocyte apoptosis in mutant cartilage by 5 days of age. In an attempt to alleviate ER stress, mutant mice were fed with a chemical chaperone, 4-sodium phenylbutyrate (SPB). SPB at the dosage used had no effect on chaperone expression at 5 days of age but modestly decreased levels of chaperone proteins at 3 weeks. However, this did not lead to increased secretion of mutant matrilin-3 and in the long term did not improve the disease phenotype. We performed similar studies with a mouse model of Schmid metaphyseal chondrodysplasia, but again this treatment did not improve the phenotype.Electronic supplementary materialThe online version of this article (doi:10.1007/s12192-010-0193-y) contains supplementary material, which is available to authorized users.

ER Stress During the Pubertal Growth Spurt Results in Impaired Long-Bone Growth in Chondrocyte-Specific ERp57 Knockout Mice

“…In addition, other skeletal abnormalities, such as pseudoachondrodysplasia (PSACH) or multiple epiphyseal dysplasia (MED) are caused by mutations in cartilage ECM proteins like collagens II, IX, X, and XI, or aggrecan, COMP, and matrilin-3. (26)(27)(28)(29)34,(37)(38)(39)(40)(41)(42)(43) ER stress is thought to constitute the underlying common disease mechanism due to retention of abnormal, improperly folded proteins within the ER. The cells can be rescued after the ER stress-induced unfolded protein response, which arrests the cell cycle, reduces the general protein synthesis, and enhances the production of new chaperones facilitating additional folding processes.…”

“…(44) The expression of calnexin, ERp57, and calreticulin was detected at a level twofold larger than normal in cartilage of mice expressing mutant matrilin-3, which causes ER stress. (28) This suggests that the ERp57-calnexin-calreticulin complex is important for matrilin-3 folding and ameliorating the ER stress. However, if ERp57 is missing in chondrocytes, ER stress cannot improve, efficient folding of glycoproteins is permanently affected, and bone growth is compromised.…”

Biosynthesis and secretion of mouse cysteine‐rich with EGF‐like domains 2

“…Transgenic mice expressing mutant matrilin-3, a structural protein of the cartilage extracellular matrix [41], and INS-1 cells overexpressing mutant insulin 2 (C96Y) derived from the Akita mouse [42] are reported to express higher amounts of CRELD2 mRNA concomitantly with other known ER stress-inducible genes (e.g., GRP78 and GADD153 mRNA). However, Jariwala et al [43] has reported that CRELD2 is one of androgen target genes in prostate cancer cells.…”

Advances in Skeletal Dysplasia Genetics

“…Without proper trafficking of extracellular matrix and cell adhesion components, as well as ligands for critical signaling pathways, the function of the growth plate can be profoundly compromised. Often, the result is profound endoplasmic reticulum stress, which is a common pathogenic mechanism in disorders of the skeleton, including osteogenesis imperfecta (87a, 105a, 116a, 136a). …”