ShcA promotes chondrocyte hypertrophic commitment and osteoarthritis in mice through RunX2 nuclear translocation and YAP1 inactivation.

OBJECTIVE: Chondrocyte hypertrophic differentiation, a key process in endochondral ossification, is also a feature of osteoarthritis leading to cartilage destruction. Here we investigated the role of the adaptor protein Src homology and Collagen A (ShcA) in chondrocyte differentiation and osteoarthritis. METHODS: Mice ablated for ShcA in osteochondroprogenitor cells were generated by crossing mice carrying the Twist2-Cre transgene with ShcAflox/flox mice. Their phenotype (n = 5 to 14 mice per group) was characterized using histology, immuno-histology and western-blot. To identify the signaling mechanisms involved, in vitro experiments were conducted on wild type and ShcA deficient chondrocytes (isolated from n = 4 to 7 littermates) and the chondroprogenitor cell line ATDC5 (n = 4 independent experiments) using western-blot, cell fractionation and confocal microscopy. RESULTS: Deletion of ShcA decreases the hypertrophic zone of the growth plate (median between group difference -11.37% [95% confidence interval -17.34 to -8.654]), alters the endochondral ossification process, and leads to dwarfism (3 months old male mice nose-to-anus length -1.48 cm [-1.860 to -1.190]). ShcA promotes ERK1/2 activation, nuclear translocation of RunX2, the master transcription factor for chondrocyte hypertrophy, while maintaining the Runx2 inhibitor, YAP1, in its cytosolic inactive form. This leads to hypertrophic commitment and expression of markers of hypertrophy, such as Collagen X. In addition, loss of ShcA protects from age-related osteoarthritis development in mice (2 years old mice OARSI score -6.67 [-14.25 to -4.000]). CONCLUSION: This study reveals ShcA as a new player in the control of chondrocyte hypertrophic differentiation and its deletion slows down osteoarthritis development.

Mutants of Escherichia coli K12 with defects in anaerobic pyruvate metabolism.

A strain of Escherichia coli with a mutation in the ana gene was shown to lack acetaldehyde dehydrogenase and alcohol dehydrogenase. The requirement of this strain for an external oxidant to grow anaerobically on glucose shows that the reduction of acetyl-CoA is the principal means of reoxidation of NADH produced during glycolysis in E. coli. Further mutants derived from the ana strain were shown to be affected in the enzymes involved in the fermentation of pyruvate (pyruvate formate-lyase, phosphotransacetylase, acetate kinase). A gene controlling acetate kinase (ackB) activity has been located at 39 min on the chromosomal map. Evidence is presented that anaerobic nitrite reduction with pyruvate involves at least the dehydrogenase subunit of the pyruvate dehydrogenase complex.

Nitrite reduction in Escherichia coli: genetic analysis of nir mutants.

Five mutants of Escherichia coli impaired on nitrite reduction were studied. All have lost NADH-nitrite reductase activity but have retained the capacity to synthesize all or part of their cytochrome c552. Three genes, nir C, nir D, and nir E were mapped at 26, 72.5 and 49.5 min, respectively. Another gene, nir F was tentatively localized around 52 min.

Laboratoire de Chimie Bactérienne C.N.R.S., Marsielle, France.

Mutants of E. coli, completely devoid of nitrite reductase activity with glucose or formate as donor were studied. Biochemical analysis indicates that they are simultaneously affected in nitrate reductase, nitrite reductase, fumarate reductase and hydrogenase activities as well as in cytochrome C552 biosynthesis. The use of an antiserum specific for nitrate reductase shows that the nitrate reductase protein is probably missing. A single mutation is responsible for this phenotype: the gene affected, nir R, is located close to tyr R i.e. at 29 min on the chromosomal map.