BMP2 Regulation of CXCL12 Cellular, Temporal, and Spatial Expression is Essential During Fracture Repair.

The cellular and humoral responses that orchestrate fracture healing are still elusive. Here we report that bone morphogenic protein 2 (BMP2)-dependent fracture healing occurs through a tight control of chemokine C-X-C motif-ligand-12 (CXCL12) cellular, spatial, and temporal expression. We found that the fracture repair process elicited an early site-specific response of CXCL12(+)-BMP2(+) endosteal cells and osteocytes that was not present in unfractured bones and gradually decreased as healing progressed. Absence of a full complement of BMP2 in mesenchyme osteoprogenitors (BMP2(cKO/+)) prevented healing and led to a dysregulated temporal and cellular upregulation of CXCL12 expression associated with a deranged angiogenic response. Healing was rescued when BMP2(cKO/+) mice were systemically treated with AMD3100, an antagonist of CXCR4 and agonist for CXCR7 both receptors for CXCL12. We further found that mesenchymal stromal cells (MSCs), capable of delivering BMP2 at the endosteal site, restored fracture healing when transplanted into BMP2(cKO/+) mice by rectifying the CXCL12 expression pattern. Our in vitro studies showed that in isolated endosteal cells, BMP2, while inducing osteoblastic differentiation, stimulated expression of pericyte markers that was coupled with a decrease in CXCL12. Furthermore, in isolated BMP2(cKO/cKO) endosteal cells, high expression levels of CXCL12 inhibited osteoblastic differentiation that was restored by AMD3100 treatment or coculture with BMP2-expressing MSCs that led to an upregulation of pericyte markers while decreasing platelet endothelial cell adhesion molecule (PECAM). Taken together, our studies show that following fracture, a CXCL12(+)-BMP2(+) perivascular cell population is recruited along the endosteum, then a timely increase of BMP2 leads to downregulation of CXCL12 that is essential to determine the fate of the CXCL12(+)-BMP2(+) to osteogenesis while departing their supportive role to angiogenesis. Our findings have far-reaching implications for understanding mechanisms regulating the selective recruitment of distinct cells into the repairing niches and the development of novel pharmacological (by targeting BMP2/CXCL12) and cellular (MSCs, endosteal cells) interventions to promote fracture healing.

PTEN deficiency mediates a reciprocal response to IGFI and mTOR inhibition.

UNLABELLED: Recent evidence implicates the insulin-like growth factor (IGF) pathway in development of Ewing sarcoma, a highly malignant bone and soft-tissue tumor that primarily affects children and young adults. Despite promising results from preclinical studies of therapies that target this pathway, early-phase clinical trials have shown that a significant fraction of patients do not benefit, suggesting that cellular factors determine tumor sensitivity. Using FAIRE-seq, a chromosomal deletion of the PTEN locus in a Ewing sarcoma cell line was identified. In primary tumors, PTEN deficiency was observed in a large subset of cases, although not mediated by large chromosomal deletions. PTEN loss resulted in hyperactivation of the AKT signaling pathway. PTEN rescue led to decreased proliferation, inhibition of colony formation, and increased apoptosis. Strikingly, PTEN loss decreased sensitivity to IGF1R inhibitors but increased responsiveness to temsirolimus, a potent mTOR inhibitor, as marked by induction of autophagy. These results suggest that PTEN is lost in a significant fraction of primary tumors, and this deficiency may have therapeutic consequences by concurrently attenuating responsiveness to IGF1R inhibition while increasing activity of mTOR inhibitors. The identification of PTEN status in the tumors of patients with recurrent disease could help guide the selection of therapies. IMPLICATIONS: PTEN status in Ewing sarcoma affects cellular responses to IGFI and mTOR-directed therapy, thus justifying its consideration as a biomarker in future clinical trials.

Valproic acid reduces the tolerability of temsirolimus in children and adolescents with solid tumors.

A pediatric study has established a maximum tolerated dose (MTD) for temsirolimus (Tem) of more than 150 mg/m intravenously/week. A phase I trial was conducted to establish the MTD for Tem in combination with valproic acid (VPA) in children and adolescents with refractory solid tumors. The secondary aims included expression of mammalian target of rapamycin (mTOR) markers on archival tumor tissue; Tem pharmacokinetics; assessment of histone acetylation (HA); and tumor response. Patients were treated with VPA (5 mg/kg orally three times daily) with a target serum level of 75-100 mcg/ml. Tem was started at an initial dose of 60 mg/m/week. Pharmacokinetics and HA measurements were performed during weeks 1 and 5. Two of the first three patients experienced dose-limiting toxicity (grade 3 mucositis). Tem at 35 mg/m/week was found to be tolerable. Peak Tem concentrations were higher in all patients compared with those in previously published reports of single agent Tem. Increases in HA are correlated with VPA levels. All tumor samples expressed mTORC1 and mTORC2. An objective response was observed in one patient (melanoma), whereas transient stable disease was observed in four other patients (spinal cord ependymoma, alveolar soft part sarcoma, medullary thyroid carcinoma, and hepatocellular carcinoma). The MTD of Tem when administered with VPA is considerably lower than when used as a single agent, with mucositis the major dose-limiting toxicity. The combination merits further study and may have activity in melanoma. Attention to drug-drug interactions will be important in future multiagent trials including Tem.

Inhibition of IGF-I receptor signaling in combination with rapamycin or temsirolimus increases MYC-N phosphorylation.

BACKGROUND: It has been previously shown that blockade of the type 1 insulin-like growth factor receptor (IGF1R) signaling combined with mTOR inhibition decreased neuroblastoma proliferation in vitro. MYC-N inactivation occurs through phosphorylation by downstream elements of the IGF1R signaling pathway. It was hypothesized that inhibition of IGF1R signaling would increase the inactivation of MYC-N. MATERIALS AND METHODS: BE-2(c) and IMR-32 neuroblastoma cell lines were treated with varying concentrations of alphaIR3, rapamycin and temsirolimus either alone or in combination and the expression of MYC-N and phosphorylated MYC-N proteins were evaluated by Western blotting. The number of apoptotic cells was evaluated through cleaved caspase-3 expression. RESULTS: IGF1R signaling blockade in combination with mTOR inhibition decreased MYC-N protein expression, increased MYC-N phosphorylation and significantly increased cleaved caspase-3 expression in treated cells. CONCLUSION: The combination of rapamycin or temsirolimus with alphaIR3 decreases MYC-N expression, increases MYC-N phosphorylation and induces apoptosis in vitro which may have clinical relevance to children with neuroblastoma.

IGF-I receptor inhibition combined with rapamycin or temsirolimus inhibits neuroblastoma cell growth.

BACKGROUND: Neuroblastoma is the third most common solid tumor in children. Treatment continues to be challenging. The pathogenesis of neuroblastoma has been related to expression of the type 1 insulin-like growth factor receptor (IGF1R) and to transcription factor MYC-N amplification. Previous studies have shown that MYC-N expression is disrupted by blockade of the IGF1R with a specific monoclonal antibody, alphaIR3. Inhibition of IGF1R signaling can be accomplished by other agents, including rapamycin or temsirolimus, which target mTOR (mammalian target of rapamycin). MATERIALS AND METHODS: BE-2(c) and IMR-32 neuroblastoma cell lines were treated with varying concentrations of alphaIR3, rapamycin and temsirolimus alone or in combination and the viable cells were counted. RESULTS: Blockade of IGF1R signaling significantly inhibited cell growth as compared to untreated controls (p < 0.05), and a combination of agents was more effective than each agent alone. CONCLUSION: The combination of rapamycin or temsirolimus with alphaIR3 blocks the IGF1R signaling pathway and has an antiproliferative effect on neuroblastoma cells warranting further investigations using inhibitors of IGF1R signaling as novel combination therapy for neuroblastoma.

Hypercalcemia in children.

Hypercalcemia is an occasional clinical problem in outpatient and in patient pediatrics. If undiagnosed and untreated, it can cause significant sequelae. While the differential diagnosis of hypercalcemia is expansive, the clinician can isolate the cause with their patients if a step-wise approach is taken clinically and biochemically. Here we present the case of an adolescent female with symptomatic hypercalcemia and a family history of hypercalcemia. Next we discuss each cause within the differential diagnosis of hypercalcemia, and provide an algorithm for evaluating patients. We then revisit the case to identify the cause with the proband.

Expression of insulin-like growth factor system genes during the early postnatal neurogenesis in the mouse hippocampus.

Insulin-like growth factor-1 (IGF-1) is essential to hippocampal neurogenesis and the neuronal response to hypoxia/ischemia injury. IGF (IGF-1 and -2) signaling is mediated primarily by the type 1 IGF receptor (IGF-1R) and modulated by six high-affinity binding proteins (IGFBP) and the type 2 IGF receptor (IGF-2R), collectively termed IGF system proteins. Defining the precise cells that express each is essential to understanding their roles. With the exception of IGFBP-1, we found that mouse hippocampus expresses mRNA for each of these proteins during the first 2 weeks of postnatal life. Compared to postnatal day 14 (P14), mRNA abundance at P5 was higher for IGF-1, IGFBP-2, -3, and -5 (by 71%, 108%, 100%, and 98%, respectively), lower for IGF-2, IGF-2R, and IGFBP-6 (by 65%, 78%, and 44%, respectively), and unchanged for IGF-1R and IGFBP-4. Using laser capture microdissection (LCM), we found that granule neurons and pyramidal neurons exhibited identical patterns of expression of IGF-1, IGF-1R, IGF-2R, IGFBP-2, and -4, but did not express other IGF system genes. We then compared IGF system expression in mature granule neurons and their progenitors. Progenitors exhibited higher mRNA levels of IGF-1 and IGF-1R (by 130% and 86%, respectively), lower levels of IGF-2R (by 72%), and similar levels of IGFBP-4. Our data support a role for IGF in hippocampal neurogenesis and provide evidence that IGF actions are regulated within a defined in vivo milieu.

A non-transformed oligodendrocyte precursor cell line, OL-1, facilitates studies of insulin-like growth factor-I signaling during oligodendrocyte development.

The process by which oligodendrocyte progenitors differentiate into mature oligodendrocytes is complex and incompletely understood in part because of the paucity of oligodendrocyte precursors cell lines that can be studied in culture. We have developed a non-immortalized rat oligodendrocyte precursor line, called OL-1, which behaves in a fashion consistent with developing oligodendrocytes in vivo. This OL-1 line provides a model for the study of oligodendrocyte development and offers an alternative to the CG-4 cell line. When OL-1 cells are propagated in conditioned growth media, they have morphology consistent with immature oligodendrocytes and exhibit A2B5 antigen positive and myelin basic protein-negative immunoreactivity. Withdrawal of conditioned growth media and culture in serum-free medium results in OL-1 cell maturation, manifested by a shift to myelin basic protein-positive immunoreactivity, A2B5 antigen-negative immunoreactivity, decreased NG2 mRNA expression, increased expression of proteolipid protein mRNA, and increased expression of CNP protein. In addition, the expression of proteolipid protein and its splicing variant DM-20 exhibit a pattern that is similar to brain proteolipid protein expression during development. When OL-1 cells are exposed to Insulin-like growth factor-I, there are significant increases in proteolipid protein mRNA expression (p<0.05), the number of cell processes (p<0.05), and cell number (p<0.05). Treatment with the caspase inhibitors Z-DEVD-FMK and Z-VAD-FMK (inhibitors of caspases 3, 6, 7, 8, 10 and 1, 3, 4, respectively), Insulin-like growth factor-I, or both, results in a similar increase in cell number. Because Insulin-like growth factor-I does not substantially increase the BrdU labeling of OL-1 cells, these data collectively indicate that Insulin-like growth factor-I increases OL-1 cell number predominately by promoting survival, rather than stimulating proliferation. This non-immortalized oligodendrocyte precursor cell line, therefore, exhibits behavior consistent with the in vivo development of oligodendrocytes and provides an excellent model for the study of developing oligodendrocytes.

Human insulin-like growth factor-IA expression in transgenic mice promotes adenomatous hyperplasia but not pulmonary fibrosis.

Insulin-like growth factor-I (IGF-I) has been implicated in postnatal alveolar development, pulmonary fibrosis, and non-small cell lung cancer. To further investigate the role of IGF-I, we created a line of transgenic mice in which alveolar type II epithelial cells express human IGF-IA under the control of the surfactant protein C promoter. We determined the effect of pulmonary overexpression of human IGF-IA on 1) pulmonary inflammation and fibrosis in response to intratracheal instillation of bleomycin, 2) premalignant pulmonary adenomatous hyperplasia, and 3) adenoma formation. Transgenic expression of human IGF-IA had no effect on baseline gross lung pathology, cellularity of bronchoalveolar lavage, or total lung collagen content. In addition, there were no significant differences between transgenic mice and nontransgenic littermate controls in the development of pulmonary inflammation or pulmonary fibrosis in response to intratracheal bleomycin instillation. However, pulmonary expression of human IGF-IA in older mice (>12 mo) significantly increased the incidence of premalignant adenomatous hyperplastic lesions compared with littermate controls without affecting adenoma formation. These findings suggest that increased expression of human IGF-IA in alveolar air spaces does not affect the development of pulmonary fibrosis but promotes premalignant changes in the alveolar epithelium.

Novel mutation in the SLC19A2 gene in an African-American female with thiamine-responsive megaloblastic anemia syndrome.

Thiamine-responsive megaloblastic anemia (TRMA) syndrome is an autosomal recessive disorder characterized by diabetes mellitus (DM), progressive sensorineural deafness, and thiamine-responsive anemia. Mutations in the SLC19A2 gene encoding a high-affinity thiamine transporter protein THTR-1 are responsible for the clinical features associated with TRMA syndrome. We report an African-American female with TRMA-syndrome associated with thyroid disease and retinitis pigmentosa caused by a novel mutation in the SLC19A2 gene. The patient presented at 12 months of age with paroxysmal atrial tachycardia and hepatosplenomegaly. One month later, she developed DM requiring intermittent insulin therapy. At 2-1/2 years of age, profound sensorineural hearing loss was discovered. By 4 years of age, daily insulin therapy (0.5 U/kg/day) was instituted and her insulin requirement gradually increased to 1.0 U/kg/day by 9 years of age. She developed optic atrophy, retinitis pigmentosa, and visual impairment by 12 years of age with severe restriction of peripheral vision by 16 years. At age 19, a thiamine-responsive normocytic anemia was discovered. She was diagnosed with autoimmune thyroiditis at 20 years and she experienced a psychotic episode associated with a mood disorder at age 21. With oral thiamine therapy, her insulin requirement decreased by 30% over a 20 month period. Molecular analysis revealed that the patient is homozygous for a missense mutation (C152T) in exon 1 of the SLC19A2 gene.

Dexamethasone changes the composition of insulin-like growth factor binding proteins in the newborn mouse ileum.

BACKGROUND: Early postnatal glucocorticoid exposure accelerates the maturation of the bowel mucosa but results in bowel wall thinning in the newborn mouse ileum and increases the risk of focal ileal perforation in extremely premature infants. We have previously demonstrated a redistribution of insulin-like growth factor-I (IGF-I) from the submucosa in control animals to the distal villi of those treated with early postnatal dexamethasone, implicating IGF-I as an important mediator of dexamethasone's capacity to alter tissue growth. To investigate the possibility that IGF binding proteins (IGFBPs) might contribute to this process, we characterized the localization and abundance of IGFBP peptides and mRNAs in the same model. METHODS: Newborn mice received daily intraperitoneal injections of dexamethasone (l microg/g) or phosphate-buffered saline and then were euthanized on day 3 of life. Their ileums were harvested and prepared for microscopy. Tissue sections of ileum from both treatment conditions were processed in parallel for immunolocalization of each of the six IGFBP peptides and for in situ hybridization of each of the six IGFBP transcripts. RESULTS: Transcripts for IGFBP-1, -2, and -3 were highly abundant and ubiquitous the ileal mucosa, whereas transcripts for IGFBP-4, -5, and -6 were less abundant in epithelial cells. There were no differences in abundance between control and dexamethasone-treated ileum with regard to mRNA localization or abundance for IGFBP-1, -2, -3, and -6. In contrast, mRNA transcripts for IGFBP-4 and -5 were modestly increased with dexamethasone treatment (although only IGFBP-4 was significant). Strikingly different patterns of IGFBP immunolocalization were observed between control and dexamethasone-treated animals. IGFBP-1, -2, -3, and -5 were not detected in control ileum, whereas IGFBP-4 and -6 were both present in the mucosa. In contrast, dexamethasone treatment resulted in dramatic mucosal increases in IGFBP-2, -3, -4, and -5, paralleling the changing distribution of IGF-I that we previously reported. CONCLUSION: Taken together, these findings further implicate the IGF system as an important participant in dexamethasone-induced maturation in the newborn mouse ileum.

Retinoic acid attenuates O2-induced inhibition of lung septation.

Exposure of the newborn lung to hyperoxia is associated with impaired alveolar development. In newborn rats exposed to hyperoxia and studied at day 14 of life, retinoic acid (RA) treatment improved survival and increased lung collagen but did not improve alveolar development. To determine whether RA treatment during exposure to hyperoxia results in late improvement in alveolarization, we treated newborn rats with RA and hyperoxia from day 3 to day 14 and then weaned O2 to room air by day 20, and studied the animals on day 42. O2-exposed animals had larger mean lung volumes, larger alveoli, and decreased gas-exchange tissue relative to air-exposed animals, whereas RA-treated O2-exposed animals were not statistically different from air-exposed controls. Relative to control animals, elastin staining at day 14 was decreased in hyperoxia-exposed lung independent of RA treatment, and, at day 42, elastin staining was similar in all treatment groups. At day 14, elastin gene expression was similar in all treatment groups, whereas at day 42 lung previously exposed to hyperoxia showed increased elastin signal independent of RA treatment. These results indicate that RA treatment during hyperoxia exposure promotes septal formation without evidence of effects on elastin gene expression after 4 wk of recovery.

Pro- and anti-inflammatory cytokines regulate insulin-like growth factor binding protein production by fetal rat lung fibroblasts.

The inflammatory response of the lung to noxious factors contributes to the pathogenesis of chronic lung injury. Inflammatory mediators regulate the insulin-like growth factor (IGF) system, a key modulator of lung fibroblast proliferation. The activity of IGFs is regulated by IGF-binding proteins (IGFBPs) secreted by lung cells. To investigate the regulation of lung fibroblast IGFBPs by cytokines, we exposed 19-d fetal rat lung fibroblasts to various pro- and anti-inflammatory mediators. IGFBP abundance in conditioned medium (CM) was measured by ligand blot and RNA transcript abundance by RNase protection assays. Fetal rat lung fibroblasts exposed to interleukin (IL)-1beta or tumor necrosis factor (TNF)-alpha for 48 h demonstrated increased abundance of CM IGFBP-3 (5.9- and 4.7-fold increases for IL-1beta and TNF-alpha, respectively) and IGFBP-4 (5.7- and 7.4-fold increases for IL-1beta and TNF-alpha, respectively) that was accompanied by a small increase in IGFBP-4 mRNA and a larger increase in IGFBP-3 mRNA abundance. IGFBP-4 specific proteolysis was examined in CM collected from fetal rat lung fibroblasts after incubation with serum-free medium (SFM), IL-1beta, or TNF-alpha for 48 h. Cell-free aliquots of SFM-CM incubated at 37C for 24 h showed a 65% decrease in IGFBP-4 abundance that was inhibited by 1,10-phenanthroline. In contrast, CM from cells exposed to IL-1beta or TNF-alpha incubated at 37 degrees C for 24 h did not show a significant decrease in IGFBP-4 abundance unless IGF-I was present during the cell-free incubation. Addition of IGFBP-3 to aliquots of SFM-CM reversed the IGF-I-mediated acceleration of IGFBP-4 proteolysis. Similarly, addition of IGFBP-3 to cells in culture increased the accumulation of CM IGFBP-4. These results demonstrate that cytokines regulate IGFBP production and clearance by fetal lung cells and suggest a mechanism by which cytokines regulate cell proliferation following lung injury.