Epithelial membrane protein 1 inhibits human spinal chondrocyte differentiation

The molecular mechanisms underlying human spinal chondrocyte differentiation remain unclear. We recently demonstrated that epithelial membrane protein 1 (EMP1) is highly expressed in degenerative intervertebral discs. EMP1 is involved in the differentiation of multiple cell types, including progenitor/pre-B cells, neurons, and podocytes. Therefore, we hypothesize that EMP1 may participate in the differentiation of spinal chondrocytes. We cultured chondrocytes from human nucleus pulposus. Through lentivirus-mediated knockdown and overexpression of EMP1, we find that EMP1 promotes cell proliferation and survival, alters cell morphology and cell cycle, reduces cell condensation, and inhibits cell hypertrophy and the expression of chondrocyte maturation markers such as collagen X, aggrecan, sex-determining region Y (SRY)-box 9, and runt-related transcription factor 2. We also show that EMP1 is not expressed in the ossification center of vertebrae but is highly expressed in the nucleus pulposus and growth plate, where chondrocytes are immature and endochondral ossification has not occurred. These results suggest that EMP1 inhibits human spinal chondrocyte differentiation.