Osteoblast precursors, but not mature osteoblasts, move into developing and fractured bones along with invading blood vessels.

During endochondral bone development, the first osteoblasts differentiate in the perichondrium surrounding avascular cartilaginous rudiments; the source of trabecular osteoblasts inside the later bone is, however, unknown. Here, we generated tamoxifen-inducible transgenic mice bred to Rosa26R-LacZ reporter mice to follow the fates of stage-selective subsets of osteoblast lineage cells. Pulse-chase studies showed that osterix-expressing osteoblast precursors, labeled in the perichondrium prior to vascular invasion of the cartilage, give rise to trabecular osteoblasts, osteocytes, and stromal cells inside the developing bone. Throughout the translocation, some precursors were found to intimately associate with invading blood vessels, in pericyte-like fashion. A similar coinvasion occurs during endochondral healing of bone fractures. In contrast, perichondrial mature osteoblasts did not exhibit perivascular localization and remained in the outer cortex of developing bones. These findings reveal the specific involvement of immature osteoblast precursors in the coupled vascular and osteogenic transformation essential to endochondral bone development and repair.

Conditional mouse osteosarcoma, dependent on p53 loss and potentiated by loss of Rb, mimics the human disease.

Osteosarcoma is the most common primary malignant tumor of bone. Analysis of familial cancer syndromes and sporadic cases has strongly implicated both p53 and pRb in its pathogenesis; however, the relative contribution of these mutations to the initiation of osteosarcoma is unclear. We describe here the generation and characterization of a genetically engineered mouse model in which all animals develop short latency malignant osteosarcoma. The genetically engineered mouse model is based on osteoblast-restricted deletion of p53 and pRb. Osteosarcoma development is dependent on loss of p53 and potentiated by loss of pRb, revealing a dominance of p53 mutation in the development of osteosarcoma. The model reproduces many of the defining features of human osteosarcoma including cytogenetic complexity and comparable gene expression signatures, histology, and metastatic behavior. Using a novel in silico methodology termed cytogenetic region enrichment analysis, we demonstrate high conservation of gene expression changes between murine osteosarcoma and known cytogentically rearranged loci from human osteosarcoma. Due to the strong similarity between murine osteosarcoma and human osteosarcoma in this model, this should provide a valuable platform for addressing the molecular genetics of osteosarcoma and for developing novel therapeutic strategies.

Mitochondrial DNA mutations in oxyphilic and chief cell parathyroid adenomas.

BACKGROUND: The potential pathogenetic significance of mitochondrial DNA (mtDNA) mutations in tumorigenesis is controversial. We hypothesized that benign tumorigenesis of a slowly replicating tissue like the human parathyroid might constitute an especially fertile ground on which a selective advantage conferred by mtDNA mutation could be manifested and might contribute to the oxyphilic phenotype observed in a subset of parathyroid tumors. METHODS: We sought acquired mitochondrial DNA mutations by sequencing the entire 16.6 kb mitochondrial genome of each of thirty sporadic parathyroid adenomas (18 chief cell and 12 oxyphil cell), eight independent, polyclonal, parathyroid primary chief cell hyperplasias plus corresponding normal control samples, five normal parathyroid glands, and one normal thyroid gland. RESULTS: Twenty-seven somatic mutations were identified in 15 of 30 (9 of 12 oxyphil adenomas, 6 of 18 chief cell) parathyroid adenomas studied. No somatic mutations were observed in the hyperplastic parathyroid glands. CONCLUSION: Features of the somatic mutations suggest that they may confer a selective advantage and contribute to the molecular pathogenesis of parathyroid adenomas. Importantly, the statistically significant differences in mutation prevalence in oxyphil vs. chief cell adenomas also suggest that mtDNA mutations may contribute to the oxyphil phenotype.

Continuous activation of G alpha q in osteoblasts results in osteopenia through impaired osteoblast differentiation.

We explored the role of G alpha(q)-mediated signaling on skeletal homeostasis by selectively expressing a constitutively active G alpha(q) (mutation of Q209L) in osteoblasts. Continuous signaling via G alpha(q) in mouse osteoblastic MC3T3-E1 cells impaired differentiation. Mice that expressed the constitutively active G alpha(q) transgene in cells of the osteoblast lineage exhibited severe osteopenia in cortical and trabecular bones. Osteoblast number, bone volume, and trabecular thickness were reduced in transgenic mice, but the osteoclasts were unaffected. Osteoblasts from transgenic mice showed impaired differentiation and matrix formation. In the presence of a protein kinase C inhibitor GF109203X, this impairment was not seen, indicating mediation by the protein kinase C pathway. We propose that continuous activation of the G alpha(q) signal in osteoblasts plays a crucial, previously unrecognized role in bone formation.

A parathyroid myxoadenoma observed grossly.

We are reporting a case of a patient with primary hyperparathyroidism because of an unusual parathyroid adenoma. The tumor had an extensive myxofibrous stroma without an identifiable lipomatous component. Though moderate to extensive myxoid alteration of the stroma has been reported in lipoadenomas, to the best of our knowledge, this is the first parathyroid adenoma in which the myxomatous component was recognized grossly and which lacked a stromal adipose component.

Predictors of an accurate preoperative sestamibi scan for single-gland parathyroid adenomas.

OBJECTIVE: To investigate why some patients with single parathyroid adenomas have negative preoperative sestamibi scans. DESIGN: Retrospective review. SETTING: Tertiary care center. PATIENTS: Twenty-one patients with false-negative (FN) scans were compared with 22 patients with true-positive (TP) scans. All patients had single parathyroid adenomas. INTERVENTIONS: Neck exploration and removal of parathyroid adenomas. MAIN OUTCOME MEASURES: Age; sex; preoperative serum calcium and parathyroid hormone levels; gland weight; location; and pathologic features. RESULTS: There was no significant difference in age or preoperative serum calcium or parathyroid hormone levels. Gland weight was greater in the TP group compared with the FN group (mean +/- SD, 1336 +/- 1603 mg vs 475 +/- 365 mg; P = .04); 13 (62%) of the 21 glands in the FN group were located in the upper position, compared with 6 (27%) of the 22 glands in the TP group (P = .03). Ten of the 22 glands in the TP group consisted predominantly of oxyphil cells, compared with 2 of the 21 glands in the FN group (P = .02). A multivariate logistic regression model yielded the following factors that predicted an accurate scan: higher percentage of oxyphil cells (P = .03), heavier gland (P = .03), female sex (P = .04), and gland location in the lower position (P = .04). CONCLUSIONS: Smaller-volume parathyroid adenomas and those in the upper position are less likely to be localized with sestamibi scans. A TP scan correlates with oxyphil cell predominance, supporting a role for the mitochondrial-rich cell in sestamibi uptake and retention.

Gadofluorine-enhanced magnetic resonance imaging of carotid atherosclerosis in Yucatan miniswine.

OBJECTIVE: The aim of this study was to determine whether gadofluorine, a paramagnetic magnetic resonance imaging (MRI) contrast agent, selectively enhances carotid atherosclerotic plaques in Yucatan miniswine. METHODS: Atherosclerotic plaques were induced in the left carotid arteries (LCA) of Yucatan miniswine (n=3) by balloon denudation and high cholesterol diet. T1-weighted MRI was performed before and 24 hours after gadofluorine injection (at a dose of 100 micromol/kg) to assess the enhancement of the balloon-injured LCA wall relative to healthy, uninjured right carotid artery (RCA) wall. Histopathology was performed to verify the presence and composition of the atherosclerotic plaques imaged with MRI. RESULTS: Gadofluorine was found to enhance LCA atherosclerotic lesions relative to RCA wall by 21% (P<0.025) 24 hours after contrast injection. Enhancement of healthy LCA wall relative to healthy RCA wall was not observed. CONCLUSION: Gadofluorine selectively enhances carotid atherosclerotic plaques in Yucatan miniswine. Gadofluorine appears to be a promising MR contrast agent for detection of atherosclerotic plaques in vivo.

Regional material property alterations in porcine femoral arteries with atheroma development.

We have developed a novel methodology that permits assessment of regional vascular mechanical property alterations in the presence of atheroma in vivo employing a Yucatan miniswine model with induced lesions. Femoral arteries were imaged with intravascular ultrasound. Image data were segmented and, following three-dimensional reconstruction, underwent finite element and sensitivity analysis with optimization to identify regions with altered vascular mechanical properties. All regions were compared to histological analysis. In 12 animals with 8 weeks of endothelial cell denudation and high cholesterol diet (induced atherosclerosis), the elastic modulus initially decreased with early lesion development and then increased with increasing fibrosis-(elastic modulus-all values x10(4)Pa-mean+/-SEM) histologically normal (non-denuded control segment) elements 9.73+/-0.01, fatty elements 9.53+/-0.01, fibrofatty elements 9.41+/-0.03, and fibrous elements 9.68+/-0.02 (all p<0.001 vs. normal elements). Wall thickness, however, increased with atheroma formation. These data demonstrate decreasing vascular material properties with early lesions, followed by an increase as lesions progress. This methodology permits determination of areas with early atheroma development, follow atheroma progression, and potentially evaluate interventions aimed at decreasing atheroma load and normalizing vascular material properties.

Porcine carotid arterial material property alterations with induced atheroma: an in vivo study.

OBJECTIVE: A novel methodology has been developed to evaluate regional alterations in arterial wall material properties with induced atheroma in an animal model. METHODS: Atheromatous lesions (fatty, fibro-fatty, and fibrous) were induced in the carotid arteries of a Yucatan miniswine model by endothelial cell denudation and high cholesterol diet. The images at base line and 8 weeks after denudation were obtained using intravascular ultrasound (IVUS) imaging along with hemodynamic data. Finite element analysis (FEA) along with optimization was employed to assess regional alterations in elastic modulus in the presence of atheroma confirmed by histology. RESULTS: In animals with 8 weeks of induced atherosclerosis, the elastic modulus increased-(elastic modulus-all values x 10(4) Pa, mean+/-S.D.) normal elements (9.34+/-0.36) compared to abnormal elements (9.52+/-0.36) (p<0.05 versus normal elements). Wall thickness increased with atheroma formation. These data demonstrate stiffening vascular wall elastic modulus with lesion progression. This is different from the behavior of femoral arteries, where the elastic modulus decreases with early stages of atheroma development followed by an increase as lesions progress. CONCLUSIONS: This methodology permits determination of areas with early atheroma development, follow atheroma progression, and potentially evaluate interventions aimed at decreasing atheroma load and normalizing vascular material properties.

Weight of normal parathyroid glands in patients with parathyroid adenomas.

Although the size and weight of a parathyroid gland are frequently the only intraoperative determinants of abnormality, these parameters have not been examined in living patients with primary hyperparathyroidism (PHP). The records of 240 patients who underwent parathyroidectomy according to standard surgical practice by a single surgeon were reviewed to identify those who were euparathyroid after in toto removal of a histologically confirmed normal gland and a histologically confirmed adenoma. The 25 (86%) females and 4 (14%) males who met the study criteria had a mean age of 60 yr (range, 33-82 yr). The mean PTH level was 130.1 pg/ml (range, 58-278) before parathyroidectomy and 32.4 pg/ml (range, 1-68) after parathyroidectomy. The mean calcium level was 11.1 mg/dl (range, 10-14) before and 8.7 mg/dl (range, 8-10) after parathyroidectomy. Thirty-four intact normal glands were removed and available for analysis. Their mean weight was 62.4 +/- 31.6 mg (range, 18-161 mg), and 15 (44%) weighed 60 mg or more. The mean weight of the adenomas was 553.7 +/- 520.5 mg (range, 66-2536). Adenomas were clearly distinguished from normal glands by cellularity, stromal fat, and intracellular fat in chief cells. The weight of normal parathyroid glands removed at surgery in patients with PHP may be greater than that reported in autopsy studies. Therefore, certain histological features are a better measure than weight in determining whether a gland is normal, and intraoperative identification of slightly enlarged glands should not lead to immediate subtotal parathyroidectomy.