Clinical and endocrine correlates of circulating sclerostin levels in patients with type 1 diabetes mellitus.

AIM: Type 1 diabetes mellitus (T1DM) increases fragility fractures due to low bone mass, micro-architectural alterations and decreased bone formation. Sclerostin is expressed by osteocytes and inhibits osteoblastic bone formation. We evaluated serum sclerostin levels in T1DM and their association with bone mineral density (BMD), bone turnover, glycaemic control and physical activity. PATIENTS AND METHODS: In a cross-sectional study, 128 men and premenopausal women with long-standing T1DM (mean age 43·4 ± 8·8 years, diabetes duration 22·4 ± 9·5 years) and 77 age-, BMI (Body Mass Index) and gender-matched healthy individuals were evaluated. RESULTS: Serum sclerostin levels were higher in T1DM compared with controls, irrespective of gender (male 0·55 ± 0·17 vs 0·49 ± 0·12 ng/ml, P = 0·046; female 0·52 ± 0·19 ng/ml vs 0·43 ± 0·12 ng/ml, P = 0·012). Partial correlation analysis adjusted for age and gender revealed a positive correlation between serum sclerostin levels and BMD at lumbar spine and femoral neck in T1DM and between BMD at lumbar spine, femoral neck and total hip in controls. Bone turnover markers, parathyroid hormone, calcium and vitamin D did not correlate with serum sclerostin levels in T1DM or controls. Physical activity was not associated with serum sclerostin levels. A multivariate analysis revealed that only the interaction of T1DM and age affects serum sclerostin levels but not T1DM alone. The influence of age on serum sclerostin levels was more pronounced in T1DM compared with controls. CONCLUSIONS: Sclerostin serum levels were increased in patients with T1DM, and the positive correlation of age with serum sclerostin levels was stronger in T1DM. There was no effect of serum sclerostin levels on markers of bone metabolism and they do not explain the detrimental effects of T1DM on BMD.

Multiple effects of ephrin-A5 on cortical neurons are mediated by SRC family kinases.

The Eph receptor tyrosine kinases and their membrane-bound ligands, the ephrins, are involved in a variety of developmental processes such as axonal guidance, cell migration, cell adhesion, proliferation, and differentiation. In addition to repulsive effects, ephrins can also induce attractive responses. Up to now, little was known about the underlying signaling mechanisms that regulate attractive versus repulsive effects. In this study, we show that ephrin-A5 enhances the motility of cortical neurons that is dependent on the activity of Src-family kinases (SFKs). Ephrin-A5 further changes the adhesive properties of neurons by inducing the formation of cell aggregates. Using the stripe assay, we found that the motogenic effect of ephrin-A5 is the result of repulsive ephrin-A interactions. Blocking SFK function leads to a conversion of repulsion into adhesion, suggesting that SFKs can act as a biological switch for the response of EphA receptors. Finally, we discovered a ligand-induced release of membrane particles containing EphA receptors, suggesting membrane ripping as a novel mechanism to overcome the "ephrin paradox" of repulsion after high-affinity receptor-ligand binding.