Homogentisate 1,2 dioxygenase is expressed in human osteoarticular cells: implications in alkaptonuria.

Alkaptonuria (AKU) results from defective homogentisate1,2-dioxygenase (HGD), causing degenerative arthropathy. The deposition of ochronotic pigment in joints is so far attributed to homogentisic acid produced by the liver, circulating in the blood and accumulating locally. Human normal and AKU osteoarticular cells were tested for HGD gene expression by RT-PCR, mono- and 2D-Western blotting. HGD gene expression was revealed in chondrocytes, synoviocytes, osteoblasts. Furthermore, HGD expression was confirmed by Western blotting, that also revealed the presence of five enzymatic molecular species. Our findings indicate that AKU osteoarticular cells produce the ochronotic pigment in loco and this may strongly contribute to induction of ochronotic arthropathy.