Delayed-onset progressive pseudorheumatoid dysplasia with secondary synovial chondromatosis

CCN6 influences transcription and controls mitochondrial mass and muscle organization

Mutations in Cellular Communication Network Factor 6 (CCN6) are linked to the debilitating musculoskeletal disease Progressive Pseudo Rheumatoid Dysplasia (PPRD), which disrupts mobility. Yet, much remains unknown about CCN6 function at the molecular level. In this study, we revealed a new function of CCN6 in transcriptional regulation. We demonstrated that CCN6 localizes to chromatin and associates with RNA Polymerase II in human chondrocyte lines. Using zebrafish as a model organism we validated the nuclear presence of CCN6 and its association with RNA Polymerase II in different developmental stages from 10 hpf embryo to adult fish muscle. In concurrence with these findings, we confirmed the requirement of CCN6 in the transcription of several genes encoding mitochondrial electron transport complex proteins in the zebrafish, both in the embryonic stages and in the adult muscle. Reduction in the expression of these genes upon morpholino-mediated knockdown of CCN6 protein expression led to reduced mitochondrial mass, which correlated with defective myotome organization during zebrafish muscle development. Overall, this study suggests that the developmental musculoskeletal abnormalities linked with PPRD could be contributed at least partly by impaired expression of genes encoding mitochondrial electron transport complexes due to defects in CCN6 associated transcriptional regulation.

Ccn6 Is Required for Mitochondrial Integrity and Skeletal Muscle Function in Zebrafish

Mutations in the CCN6 (WISP3) gene are linked with a debilitating musculoskeletal disorder, termed progressive pseudorheumatoid dysplasia (PPRD). Yet, the functional significance of CCN6 in the musculoskeletal system remains unclear. Using zebrafish as a model organism, we demonstrated that zebrafish Ccn6 is present partly as a component of mitochondrial respiratory complexes in the skeletal muscle of zebrafish. Morpholino-mediated depletion of Ccn6 in the skeletal muscle leads to a significant reduction in mitochondrial respiratory complex assembly and activity, which correlates with loss of muscle mitochondrial abundance. These mitochondrial deficiencies are associated with notable architectural and functional anomalies in the zebrafish muscle. Taken together, our results indicate that Ccn6-mediated regulation of mitochondrial respiratory complex assembly/activity and mitochondrial integrity is important for the maintenance of skeletal muscle structure and function in zebrafish. Furthermore, this study suggests that defects related to mitochondrial respiratory complex assembly/activity and integrity could be an underlying cause of muscle weakness and a failed musculoskeletal system in PPRD.