Nadia Rucci

Clinical, genetic, and cellular analysis of 49 osteopetrotic patients: implications for diagnosis and treatment

Background: Osteopetrosis, a genetic disease characterised by osteoclast failure, is classified into three forms: infantile malignant autosomal recessive osteopetrosis (ARO), intermediate autosomal recessive osteopetrosis (IRO), and autosomal dominant osteopetrosis (ADO). Methods: We studied 49 patients, 21 with ARO, one with IRO, and 27 with type II ADO (ADO II). Results: Most ARO patients bore known or novel (one case) ATP6i (TCIRG1) gene mutations. Six ADO II patients had no mutations in ClCN7, the only so far recognised gene implicated, suggesting involvement of yet unknown genes. Identical ClCN7 mutations produced differing phenotypes with variable degrees of severity. In ADO II, serum tartrate resistant acid phosphatase was always elevated. Bone alkaline phosphatase (BALP) was generally low, but osteocalcin was high, suggesting perturbed osteoblast differentiation or function. In contrast, BALP was high in ARO patients. Elevated osteoclast surface/bone surface was noted in biopsies from most ARO patients. Cases with high osteoclasts also showed increased osteoblast surface/bone surface. ARO osteoclasts were morphologically normal, with unaltered formation rates, intracellular pH handling, and response to acidification. Their resorption activity was greatly reduced, but not abolished. In control osteoclasts, all resorption activity was abolished by combined inhibition of proton pumping and sodium/proton antiport. Conclusions: These findings provide a rationale for novel therapies targeting pH handling mechanisms in osteoclasts and their microenvironment.

Inhibition of Protein Kinase c-Src Reduces the Incidence of Breast Cancer Metastases and Increases Survival in Mice: Implications for Therapy

c-Src is a proto-oncogene, belonging to the nonreceptor protein kinases family, which plays a prominent role in carcinogenesis. In this study, we tested the hypothesis that c-Src could promote breast cancer metastasis acting on several cell types and that pharmacological disruption of its kinase activity could be beneficial for the treatment of metastases. Female BALB/c-nu/nu mice were subjected to intracardiac injection of the human breast cancer cells MDA-MB-231 (MDA-231), which induced prominent bone and visceral metastases. These were pharmacologically reduced by treatment with the c-Src inhibitor [7-{4-[2-(2-methoxy-ethylamino-ethoxy]-phenyl}-5-(3-methoxy-phenyl)-7H-pyrrolo[2,3-d]pyrimidin-4-ylamine] CGP76030 (100 mg/kg/day p.o.), resulting in decreased morbidity and lethality. Metastases were more severe in mice injected with MDA-231 cells stably transfected with wild-type c-Src (MDA-231-SrcWT), whereas transfection in injected cells of a c-Src kinase-dead dominant-negative construct (MDA-231-SrcDN) resulted in reduced morbidity, lethality, and incidence of metastases similar to the mice treated with the inhibitor. An analogous beneficial effect of c-Src inhibition was observed in subcutaneous and intratibial implanted tumors. In vitro, c-Src suppression reduced MDA-231 cell aggressiveness. It also impaired osteoclast bone resorption both directly and by reducing expression by osteoblasts of the osteoclastogenic cytokines interleukin-1β and interleukin-6, whereas parathyroid hormone-related peptide was not implicated. c-Src was also modestly but consistently involved in the enhancement of endothelial cell proliferation in vitro and angiogenesis in vivo. In conclusion, we propose that c-Src disruption affects the metastatic process and thus is a therapeutic target for the treatment of breast cancer.

A Six-Gene Signature Predicting Breast Cancer Lung Metastasis

The lungs are a frequent target of metastatic breast cancer cells, but the underlying molecular mechanisms are unclear. All existing data were obtained either using statistical association between gene expression measurements found in primary tumors and clinical outcome, or using experimentally derived signatures from mouse tumor models. Here, we describe a distinct approach that consists of using tissue surgically resected from lung metastatic lesions and comparing their gene expression profiles with those from nonpulmonary sites, all coming from breast cancer patients. We show that the gene expression profiles of organ-specific metastatic lesions can be used to predict lung metastasis in breast cancer. We identified a set of 21 lung metastasis-associated genes. Using a cohort of 72 lymph node-negative breast cancer patients, we developed a 6-gene prognostic classifier that discriminated breast primary cancers with a significantly higher risk of lung metastasis. We then validated the predictive ability of the 6-gene signature in 3 independent cohorts of breast cancers consisting of a total of 721 patients. Finally, we show that the signature improves risk stratification independently of known standard clinical variables and a previously established lung metastasis signature based on an experimental breast cancer metastasis model.

Characterization of the osteoblast‐like cell phenotype under microgravity conditions in the NASA‐approved rotating wall vessel bioreactor (RWV)

Weightlessness induces bone loss in humans and animal models. We employed the NASA‐approved Rotating Wall Vessel bioreactor (RWV) to develop osteoblast‐like cell cultures under microgravity and evaluate osteoblast phenotype and cell function. Rat osteoblast‐like cell line (ROS.SMER#14) was grown in the RWV at a calculated gravity of 0.008g. For comparison, aliquots of cells were grown in conventional tissue culture dishes or in Non‐Rotating Wall Vessels (N‐RWV) maintained at unit gravity. In RWV, osteoblasts showed high levels of alkaline phosphatase expression and activity, and elevated expression of osteopontin, osteocalcin, and bone morphogenetic protein 4 (BMP‐4). In contrast, the expression of osteonectin, bone sialoprotein II and BMP‐2 were unaltered compared to cells in conventional culture conditions. These observations are consistent with a marked osteoblast phenotype. However, we observed that in RWV osteoblasts showed reduced proliferation. Furthermore, DNA nucleosome‐size fragmentation was revealed both morphologically, by in situ staining with the Thymine‐Adenine binding dye bis‐benzimide, and electrophoretically, by DNA laddering. Surprisingly, no p53, nor bcl‐2/bax, nor caspase 8 pathways were activated by microgravity, therefore the intracellular cascade leading to programmed cell death remains to be elucidated. Finally, consistent with an osteoclast‐stimulating effect by microgravity, osteoblasts cultured in RWV showed upregulation of interleukin‐6 (IL‐6) mRNA, and IL‐6 proved to be active at stimulating osteoclast formation and resorbing activity in vitro. We conclude that under microgravity, reduced osteoblast life span and enhanced IL‐6 expression may result in inefficient osteoblast‐ and increased osteoclast‐activity, respectively, thus potentially contributing to bone loss in individuals subjected to weightlessness. J. Cell. Biochem. 85: 167–179, 2002.

Kinase-Dependent and -Independent Roles of EphA2 in the Regulation of Prostate Cancer Invasion and Metastasis

Ligand-activated Eph tyrosine kinases regulate cellular repulsion, morphology, adhesion, and motility. EphA2 kinase is frequently up-regulated in several different types of cancers, including prostate, breast, colon, and lung carcinomas, as well as in melanoma. The existing data do not clarify whether EphA2 receptor phosphorylation or its simple overexpression, which likely leads to Eph kinase-independent responses, plays a role in the progression of malignant prostate cancer. In this study, we address the role of EphA2 tyrosine phosphorylation in prostate carcinoma cell adhesion, motility, invasion, and formation of metastases. Tumor cells expressing kinase-deficient EphA2 mutants, as well as an EphA2 variant lacking the cytoplasmic domain, are defective in ephrinA1-mediated cell rounding, retraction fiber formation, de-adhesion from the extracellular matrix, RhoA and Rac1 GTPase regulation, three-dimensional matrix invasion, and in vivo metastasis, suggesting a key role for EphA2 kinase activity. Nevertheless, EphA2 regulation of cell motility and invasion, as well as the formation of bone and visceral tumor colonies, reveals a component of both EphA2 kinase-dependent and -independent features. These results uncover a differential requirement for EphA2 kinase activity in the regulation of prostate carcinoma metastasis outcome, suggesting that although the kinase activity of EphA2 is required for the regulation of cell adhesion and cytoskeletal rearrangement, some distinct kinase-dependent and -independent pathways likely cooperate to drive cancer cell migration, invasion, and metastasis outcome.

Osteoclast receptors and signaling

Osteoclasts are bone-resorbing cells derived from hematopoietic precursors of the monocyte-macrophage lineage. Besides the well known Receptor Activator of Nuclear factor-kappaB (RANK), RANK ligand and osteoprotegerin axis, a variety of factors tightly regulate osteoclast formation, adhesion, polarization, motility, resorbing activity and life span, maintaining bone resorption within physiological ranges. Receptor-mediated osteoclast regulation is rather complex. Nuclear receptors, cell surface receptors, integrin receptors and cell death receptors work together to control osteoclast activity and prevent both reduced or increased bone resorption. Here we will discuss the signal transduction pathways activated by the main osteoclast receptors, integrating their function and mechanisms of action.

Mechanisms inducing low bone density in duchenne muscular dystrophy in mice and humans

Patients affected by Duchenne muscular dystrophy (DMD) and dystrophic MDX mice were investigated in this study for their bone phenotype and systemic regulators of bone turnover. Micro–computed tomographic (µCT) and histomorphometric analyses showed reduced bone mass and higher osteoclast and bone resorption parameters in MDX mice compared with wild‐type mice, whereas osteoblast parameters and mineral apposition rate were lower. In a panel of circulating pro‐osteoclastogenic cytokines evaluated in the MDX sera, interleukin 6 (IL‐6) was increased compared with wild‐type mice. Likewise, DMD patients showed low bone mineral density (BMD) Z‐scores and high bone‐resorption marker and serum IL‐6. Human primary osteoblasts from healthy donors incubated with 10% sera from DMD patients showed decreased nodule mineralization. Many osteogenic genes were downregulated in these cultures, including osterix and osteocalcin, by a mechanism blunted by an IL‐6‐neutralizing antibody. In contrast, the mRNAs of osteoclastogenic cytokines IL6, IL11, inhibin‐βA, and TGFβ2 were increased, although only IL‐6 was found to be high in the circulation. Consistently, enhancement of osteoclastogenesis was noted in cultures of circulating mononuclear precursors from DMD patients or from healthy donors cultured in the presence of DMD sera or IL‐6. Circulating IL‐6 also played a dominant role in osteoclast formation because ex vivo wild‐type calvarial bones cultured with 10% sera of MDX mice showed increase osteoclast and bone‐resorption parameters that were dampen by treatment with an IL‐6 antibody. These results point to IL‐6 as an important mediator of bone loss in DMD and suggest that targeted anti‐IL‐6 therapy may have a positive impact on the bone phenotype in these patients.

Inhibition of Protein Kinase c-Src as a Therapeutic Approach for Cancer and Bone Metastases

c-Src is a proto-oncogene involved in the genesis of and invasion by many cancers. This non-receptor tyrosine kinase also plays a crucial role in bone homeostasis, since inhibition or deletion of c-Src impairs the function of osteoclasts, the bone resorbing cells. It is thus conceivable that c-Src could be a suitable target for the pharmacological treatment of cancers, skeletal metastases and diseases of bone loss, such as osteoporosis. The pyrrolo-pyrimidines CGP77675 and CGP76030 proved to be effective in preventing bone loss in animal models, while the effect of AZD0530, a dually active inhibitor of c-Src and Bcr-ABL, on bone resorption, has been tested in a Phase I clinical trials with promising results. As far as the metastatic bone disease is concerned, c-Src inhibitors could potentially have inhibitory effects both on osteoclasts and on tumour cells, and could disrupt the vicious circle established between these cell types in the bone microenvironment. In accord with this idea, CGP76030 is able to reduce the incidence of osteolytic lesions and of visceral metastases, and to suppress morbidity and lethality in a bone metastasis mouse model without obvious adverse effects. The purine-based c-Src inhibitor AP23451 and the dual c-Src/Abl inhibitors AP22408 and AP23236 proved efficacious in reducing bone metastases in preclinical studies. These results open a new avenue for the development of innovative therapies for the treatment of bone metastatic disease.

Osteoblast and osteocyte: games without frontiers.

The portrait of osteoblasts and osteocytes has been subjected to a revision, since a large body of evidence is attributing these cells amazing roles both inside and outside the bone. The osteoblast, long confined to its bone building function, is actually a very eclectic cell, actively regulating osteoclast formation and function as well as hematopoietic stem cells homeostasis. It is also an endocrine cell, affecting energy metabolism, male fertility and cognition through the release of osteocalcin, a perfect definition-fitting hormone in its uncarboxylated state. As for the osteocytes, many evidence shows that they do not merely represent the final destination of the osteoblasts, but they are instead very active cells that, besides a mechanosensorial function, actively contribute to the bone remodelling by regulating bone formation and resorption. The regulation is exerted by the production of sclerostin (SOST), which in turn inhibits osteoblast differentiation by blocking Wnt/beta-catenin pathway. At the same time, osteocytes influence bone resorption both indirectly, by producing RANKL, which stimulates osteoclastogenesis, and directly by means of a local osteolysis, which is observed especially under pathological conditions. The great versatility of both these cells reflects the complexity of the bone tissue, which has not only a structural role, but influences and is influenced by different organs, taking part in homeostatic and adaptive responses affecting the whole organism.

Modeled microgravity stimulates osteoclastogenesis and bone resorption by increasing osteoblast RANKL/OPG ratio

Mechanical unloading causes detrimental effects on the skeleton, but the underlying mechanisms are still unclear. We investigated the effect of microgravity on osteoblast ability to regulate osteoclastogenesis. Mouse osteoblast primary cultures were grown for 24 h at unit gravity or under simulated microgravity, using the NASA‐developed Rotating Wall Vessel bioreactor. Conditioned media (CM) from osteoblasts subjected to microgravity increased osteoclastogenesis and bone resorption in mouse bone marrow cultures. In these osteoblasts, the RANKL/OPG ratio was higher relative to 1g. Consistently, treatment with high concentrations of OPG‐inhibited osteoclastogenesis and bone resorption in the presence of CM arising from osteoblasts cultured under microgravity. Microgravity failed to affect osteoblast differentiation and function in the time frame of the experiment, as we found no effect on alkaline phosphatase mRNA and activity, nor on Runx2, osteocalcin, osteopontin, and collagen1A2 mRNA expression. In contrast, microgravity induced a time dependent increase of ERK‐1/2 phosphorylation, while phospho‐p38 and phospho‐JNK remained unchanged. Apoptosis, revealed by bis‐benzimide staining, was similar among the various gravity conditions, while it was increased under microgravity after treatment with the MEK‐1/2 inhibitor, PD98059, suggesting a protection role by ERK‐1/2 against cell death. In conclusion, microgravity is capable to indirectly stimulate osteoclast formation and activity by regulating osteoblast secretion of crucial regulatory factors such as RANKL and OPG. We hypothesize that this mechanism could contribute to bone loss in individuals subjected to weightlessness and other unloading conditions. J. Cell. Biochem. 100: 464–473, 2007.