Furthermore, the NPC-enriched disc fibrocytes express HTRA1 and ANGPTL4. HTRA1 is a proteolytic enzyme for degrading the matrix either on its own64 or by upregulating ADAMTS526 or matrix metalloproteinases, whereas expression of ANGPTL4 is positively associated with IDD severity.27 Notably, our data suggest that ANGPTL4 is a major mediator of the intercellular communication between the disc fibrocytes and the CyclingNP, RegNP and FibroNP subpopulations. This evidence concerns the gene ANGPTL4 and intervertebral disk degenerative disorder.