Increased bone mass, altered trabecular architecture and modified growth plate organization in the growing skeleton of SOCS2 deficient mice

Abstract

Suppressor of cytokine signalling-2 (SOCS2) negatively regulates the signal transduction of several cytokines. Socs2(-/-) mice show increased longitudinal skeletal growth associated with deregulated GH/IGF-1 signalling. The present study examined the role of SOCS2 in endochondral ossification and trabecular and cortical bone formation, and investigated whether pro-inflammatory cytokines associated with pediatric chronic inflammatory disorders mediate their effects through SOCS2. Seven-week-old Socs2(-/-) mice were heavier (27%; P < 0.001) and longer (6%; P < 0.001) than wild-type mice. Socs2(-/-) tibiae were longer (8%; P < 0.001) and broader (18%; P < 0.001) than that of wild-type mice, and the Socs2(-/-) mice had wider growth plates (24%; P < 0.001) with wider proliferative and hypertrophic zones (10% (P < 0.05) and 14% (P < 0.001) respectively). Socs2(-/-) mice showed increased total cross-sectional bone area (16%: P < 0.001), coupled to increased total tissue area (17%; P < 0.05) compared to tibia from wild-type mice. Socs2(-/-) mice showed increased percent bone volume (101%; P < 0.001), trabecular number (82%; P < 0.001) and trabecular thickness (11%; P < 0.001), with associated decreases in trabecular separation (19%; P < 0.001). TNFalpha exposure to growth plate chondrocytes for 48 h increased SOCS2 protein expression. Growth of metatarsals from 1-day-old Socs2(-/-) and Socs2(+/+) mice, as well as expression of Aggrecan, Collagen Type II and Collagen Type X, were inhibited by TNFalpha, with no effect of genotype. Our data indicate that physiological levels of SOCS2 negatively regulate bone formation and endochondral growth. Our results further suggest that pro-inflammatory cytokines mediate their inhibitory effects on longitudinal bone growth through a mechanism that is independent of SOCS2.

SOCS2 is the critical regulator of GH action in murine growth plate chondrogenesis

“…(31) Although there was no difference in the number of proliferating cells staining positively for phosphorylated STAT-5 in the SOCS2 À/À growth plates, it was not possible, because of the nonquantitative nature of immunohistochemistry, to estimate levels of activated STAT-5 expression. The presence of STAT-5 phosphorylation in hypertrophic chondrocytes is consistent with the previous observation of GHR expression in these cells of the growth plate.…”

“…The SOCS2 À/À mice were generated as previously described. (31) Tissue processing and staining of tibia…”

“…(28)(29)(30)(31)(32)(33) Epiphyseal chondrocytes express SOCS2, and growth plates from SOCS2 null mice are enlarged with wider proliferative and hypertrophic zones. (31) Because SOCS2 À/À mice do not have increased circulating IGF-1 levels, it is likely that the increased bone growth and observed structural differences within SOCS2…”

“…(31,34,35) The increased body mass and bone growth of SOCS2 null mice are not observed when mutants are mated with mice lacking the STAT-5b gene. (36) This suggests that the SOCS2…”

MOVAS-1 cell line: A new in vitro model of vascular calcification

“…For each sample, total RNA content was assessed by absorbance at 260 nm and purity by A260/A280 ratios. RNA was reverse transcribed and the PCR reaction undertaken as described previously (37,38). For the PCR reaction, primers for 18S rRNA gene (20 cycles) (Ambion, Huntingdon, UK, sequence not disclosed) and SM22α (35 cycles) (Forward 5'TCC AgT CCA CAA ACg ACC AAg C3' , Reverse 5'gAA TTg AgC CAC CTg TTC CAT CTg-3') were used.…”