Complementary expression of IGF-II and IGFBP-5 during anterior pituitary development

The specification of the five individual hormone-secreting cell types in the anterior pituitary requires a series of sequential cell fate decisions. We have immortalized cells at several stages along this pathway of pituitary differentiation. Here, we present analysis of differences in gene expression between an anterior pituitary precursor cell line, alphaT1-1, and an immature gonadotrope cell line, alphaT3-1, identified by using cDNA subtraction. Messenger RNA expression of members of the insulin-like growth factor signaling system, IGF-II and IGFBP-5, was found in the alphaT1-1 precursor cell line, but not in the more differentiated cell line, alphaT3-1. This inferred stage specificity was confirmed in the mouse embryo by using in situ hybridization on embryonic days e10.5 through e18.5. Expression of IGF-II and IGFBP-5 mRNAs was both temporally and spatially regulated during pituitary development. IGF-II was highly expressed in the epithelium surrounding Rathke's pouch at e10.5, while IGFBP-5 expression was restricted to the adjacent oral epithelium. At e11.5 (represented by alphaT1-1), IGF-II was expressed throughout the pouch, but was coexpressed with IGFBP-5 and alpha-subunit in the ventral portion of the pouch epithelium. On e12.5, the two mRNAs were expressed in opposing dorsoventral (IGF-II) and ventrodorsal (IGFBP-5) patterns, with IGF-II excluded from the rostral, alpha-subunit-expressing region. A decrease of both mRNAs was observed at e14.5 (equivalent to alphaT3-1), with IGF-II levels low and IGFBP-5 concentrated in the anterior pituitary rostral tip. These findings suggest that the timing of IGF-II expression and regulation of its accessibility by IGFBP-5 may play a role in anterior pituitary differentiation, survival, and/or proliferation.     

Increased Serum Hepcidin Levels in Subjects with the Metabolic Syndrome: A Population Study

The recent discovery of hepcidin, the key iron regulatory hormone, has changed our view of iron metabolism, which in turn is long known to be linked with insulin resistant states, including type 2 diabetes mellitus and the Metabolic Syndrome (MetS). Serum ferritin levels are often elevated in MetS (Dysmetabolic hyperferritinemia - DHF), and are sometimes associated with a true mild-to-moderate hepatic iron overload (dysmetabolic iron overload syndrome - DIOS). However, the pathophysiological link between iron and MetS remains unclear. This study was aimed to investigate, for the first time, the relationship between MetS and hepcidin at population level. We measured serum hepcidin levels by Mass Spectrometry in 1,391 subjects from the Val Borbera population, and evaluated their relationship with classical MetS features. Hepcidin levels increased significantly and linearly with increasing number of MetS features, paralleling the trend of serum ferritin. In multivariate models adjusted for relevant variables including age, C-Reactive Protein, and the HFE C282Y mutation, ferritin was the only significant independent predictor of hepcidin in males, while in females MetS was also independently associated with hepcidin. Overall, these data indicate that the fundamental iron regulatory feedback is preserved in MetS, i.e. that hepcidin tends to progressively increase in response to the increase of iron stores. Due to recently discovered pleiotropic effects of hepcidin, this may worsen insulin resistance and contribute to the cardiovascular complications of MetS.     

Inhibition of the MET Receptor Tyrosine Kinase as a Novel Therapeutic Strategy in Medulloblastoma

Medulloblastoma is the most common pediatric posterior fossa malignancy, with a 5-year overall survival of only 60% and many survivors experiencing treatment-related morbidity secondary to current therapeutic regimens. With an improved understanding of the molecular basis for this disease, the opportunity to develop novel treatments with more tolerable toxicity profiles that target key molecular pathways, now exists. Recently, the hepatocyte growth factor (HGF)/MET signaling pathway has been implicated in medulloblastoma pathogenesis. Several therapeutic strategies targeting this pathway exist, including small molecule inhibitor therapy against the MET receptor tyrosine kinase. We examined the in vitro efficacy of targeting the MET receptor using the highly specific small molecule inhibitor PHA665752 as a novel treatment strategy in medulloblastoma. MET inhibition using PHA665752 was effective at reducing the proliferative capacity of the D283, ONS76, and MED8A medulloblastoma cell lines as assessed by MTS assay. Furthermore, PHA665752 treatment reduced D283 and ONS76 cell motility and impaired the growth of D283 cells in soft agar. Pretreatment of D283, ONS76, and MED8A cells with PHA665752 blocked exogenous recombinant human HGF-induced up-regulation of the downstream RAS/mitogen-activated protein kinase signaling pathway in D283, ONS76 and MED8A cell lines. Similarly, PHA665752 prevented HGF-induced phosphatidylinositol 3-kinase/AKT signaling in ONS76 and MED8A cells. These results highlight the efficacy of targeting the MET receptor tyrosine kinase therapeutically in medulloblastoma and provide support for further preclinical testing of small molecule inhibitors targeting the MET receptor in medulloblastoma.