u-0126 and Noonan-Syndrome

Growth retardation is a constant feature of Noonan syndrome (NS) but its physiopathology remains poorly understood. We previously reported that hyperactive NS-causing SHP2 mutants impair the systemic production of insulin-like growth factor 1 (IGF1) through hyperactivation of the RAS/extracellular signal-regulated kinases (ERK) signalling pathway. Besides endocrine defects, a direct effect of these mutants on growth plate has not been explored, although recent studies have revealed an important physiological role for SHP2 in endochondral bone growth. We demonstrated that growth plate length was reduced in NS mice, mostly due to a shortening of the hypertrophic zone and to a lesser extent of the proliferating zone. These histological features were correlated with decreased expression of early chondrocyte differentiation markers, and with reduced alkaline phosphatase staining and activity, in NS murine primary chondrocytes. Although IGF1 treatment improved growth of NS mice, it did not fully reverse growth plate abnormalities, notably the decreased hypertrophic zone. In contrast, we documented a role of RAS/ERK hyperactivation at the growth plate level since 1) NS-causing SHP2 mutants enhance RAS/ERK activation in chondrocytes in vivo (NS mice) and in vitro (ATDC5 cells) and 2) inhibition of RAS/ERK hyperactivation by U0126 treatment alleviated growth plate abnormalities and enhanced chondrocyte differentiation. Similar effects were obtained by chronic treatment of NS mice with statins. In conclusion, we demonstrated that hyperactive NS-causing SHP2 mutants impair chondrocyte differentiation during endochondral bone growth through a local hyperactivation of the RAS/ERK signalling pathway, and that statin treatment may be a possible therapeutic approach in NS.

Topics: Animals; Butadienes; Cell Differentiation; Cell Proliferation; Chondrocytes; Disease Models, Animal; Growth Plate; Humans; Insulin-Like Growth Factor I; MAP Kinase Signaling System; Nitriles; Noonan Syndrome; Protein Tyrosine Phosphatase, Non-Receptor Type 11

A gain of function mutation in SHP2, a protein phosphatase encoded by PTPN11, causes Noonan syndrome (NS), which is characterized in part by developmental deficits in both the cardiac and skull fields. Previously, we found that expression of the mutated protein SHP2 Q79R in the heart led to a phenotypic presentation that mimicked some aspects of NS and that this was dependent upon activation of the ERK1/2 pathway. To understand the role that ERK1/2 signaling plays in skull development through signaling in the neural crest, we explored the consequences of Q79R expression in neural crest cells, which contribute to a subset of the bony and cartilaginous structures of the skull. Hyperactivation of ERK1/2 led to craniofacial defects that included smaller skull lengths, greater inner canthal distances, and taller frontal bone heights. In proportion to the smaller skull length, mandibular bone length was also reduced. Inhibition of ERK1/2 hyperactivity as a result of Q79R expression was achieved by injection of the MAPK/ERK kinase inhibitor U0126 during pregnancy. The drug effectively decreased the severity of the craniofacial defects and restored normal skull shape and fontanelle closure. X-ray computer-assisted microtomography analysis of the head confirmed that decreasing ERK1/2 activity led to an abrogation of the craniofacial deficits and brain shape changes that presented in the mice. These data show that normal ERK1/2 signaling in the neural crest is imperative for normal craniofacial development and offer insight into how the heart and craniofacial developmental fields might be affected in some congenital syndromic presentations.

Topics: Animals; Butadienes; Craniofacial Abnormalities; Enzyme Inhibitors; Female; Mice; Mice, Transgenic; Mitogen-Activated Protein Kinase 3; Neural Crest; Nitriles; Noonan Syndrome; Pregnancy; Protein Tyrosine Phosphatase, Non-Receptor Type 11; Signal Transduction; X-Ray Microtomography