Respiratory chain inactivation links cartilage-mediated growth retardation to mitochondrial diseases

In childhood skeletal growth is driven by transient expansion of cartilage in the growth plate. Common belief is that energy production in this hypoxic tissue mainly relies on anaerobic glycolysis and not on mitochondrial respiratory chain (RC) activity. However, children with mitochondrial diseases causing RC dysfunction often present with short stature, which indicates that RC activity may be essential for cartilage-mediated skeletal growth. To elucidate the role of the mitochondrial RC in cartilage growth and pathology, we generated mice with impaired RC-function in cartilage. These mice develop normally until birth, but their later growth is retarded. A detailed molecular analysis revealed that metabolic signaling and extracellular matrix formation is disturbed and induces cell death at the cartilage-bone junction to cause a chondrodysplasia-like phenotype. Hence, the results demonstrate the overall importance of the metabolic switch from fetal glycolysis to postnatal RC activation in growth plate cartilage and explain why RC dysfunction can cause short stature in children with mitochondrial disease The RNA from femoral growth plates of 12 days old Cre and CreTW littermate mice or cultured chondrocytes was isolated by phenol-chloroform extraction and RNA integrity was confirmed by microcapillary electrophoresis (2100 Bioanalyzer, Agilent). For microarray analysis, 100ng RNA of growth plate cartilage from four Cre and CreTW mice, respectively, were amplified, labeled and hybridized to a 8x60K whole genome mRNA microarray using the Agilent protocol. Microarrays were scanned (Agilent G2595C scanner), data extracted and analyzed by GeneSpring V14.9 software (Agilent). mRNAs were selected according to their differential expression, to their similar expression levels in all four microarrays of a given genotype and to their statistical significance.