Diabetes impairs hematopoietic stem cell mobilization by altering niche function.

Success with transplantation of autologous hematopoietic stem and progenitor cells (HSPCs) in patients depends on adequate collection of these cells after mobilization from the bone marrow niche by the cytokine granulocyte colony-stimulating factor (G-CSF). However, some patients fail to achieve sufficient HSPC mobilization. Retrospective analysis of bone marrow transplant patient records revealed that diabetes correlated with poor mobilization of CD34+ HSPCs. In mouse models of type 1 and type 2 diabetes (streptozotocin-induced and db/db mice, respectively), we found impaired egress of murine HSPCs from the bone marrow after G-CSF treatment. Furthermore, HSPCs were aberrantly localized in the marrow niche of the diabetic mice, and abnormalities in the number and function of sympathetic nerve termini were associated with this mislocalization. Aberrant responses to ß-adrenergic stimulation of the bone marrow included an inability of marrow mesenchymal stem cells expressing the marker nestin to down-modulate the chemokine CXCL12 in response to G-CSF treatment (mesenchymal stem cells are reported to be critical for HSPC mobilization). The HSPC mobilization defect was rescued by direct pharmacological inhibition of the interaction of CXCL12 with its receptor CXCR4 using the drug AMD3100. These data suggest that there are diabetes-induced changes in bone marrow physiology and microanatomy and point to a potential intervention to overcome poor HSPC mobilization in diabetic patients.

Osteogenic differentiation of mesenchymal stem cells in multiple myeloma: identification of potential therapeutic targets.

OBJECTIVE: Osteogenic differentiation of mesenchymal cells toward osteoprogenitor and osteoblastic cells is tightly regulated by several growth and transcription factors at the molecular level. In this article, we focus on the biological mechanisms involved in the osteoblast inhibition induced by myeloma cells. MATERIALS AND METHODS: Current research on the mechanisms regulating myeloma cell and osteoprogenitor cells interactions and on potential therapeutic targets to treat multiple myeloma bone disease is reviewed. RESULTS: Runt-related transcription factor 2 is critically involved in this process along with a large number of nuclear coregulators. Wnt signaling has been recently identified as a critical pathway involved in the regulation of osteoblastogenesis. The impairment of osteogenic differentiation in mesenchymal stem cells occurs in multiple myeloma due to the capacity of malignant plasma cells to suppress the osteogenic differentiation of mesenchymal cells either through the cell contact or the release of soluble factors as interleukin-7, hepatocyte growth factor, interleukin-3, and Wnt inhibitors. CONCLUSION: Runt-related transcription factor 2 and Wnt pathways could be therapeutic targets in the treatment of multiple myeloma bone disease to counterbalance the block of osteogenic differentiation induced by multiple myeloma cells.

The new tumor-suppressor gene inhibitor of growth family member 4 (ING4) regulates the production of proangiogenic molecules by myeloma cells and suppresses hypoxia-inducible factor-1 alpha (HIF-1alpha) activity: involvement in myeloma-induced angiogenesis.

Angiogenesis has a critical role in the pathophysiology of multiple myeloma (MM); however, the molecular mechanisms underlying this process are not completely elucidated. The new tumor-suppressor gene inhibitor of growth family member 4 (ING4) has been recently implicated in solid tumors as a repressor of angiogenesis. In this study, we found that ING4 expression in MM cells was correlated with the expression of the proangiogenic molecules interleukin-8 (IL-8) and osteopontin (OPN). Moreover, we demonstrate that ING4 suppression in MM cells up-regulated IL-8 and OPN, increasing the hypoxia inducible factor-1alpha (HIF-1alpha) activity and its target gene NIP-3 expression in hypoxic condition. In turn, we show that the inhibition of HIF-1alpha by siRNA suppressed IL-8 and OPN production by MM cells under hypoxia. A direct interaction between ING4 and the HIF prolyl hydroxylase 2 (HPH-2) was also demonstrated. Finally, we show that ING4 suppression in MM cells significantly increased vessel formation in vitro, blunted by blocking IL-8 or OPN. These in vitro observations were confirmed in vivo by finding that MM patients with high IL-8 production and microvascular density (MVD) have significantly lower ING4 levels compared with those with low IL-8 and MVD. Our data indicate that ING4 exerts an inhibitory effect on the production of proangiogenic molecules and consequently on MM-induced angiogenesis.

Production of Wnt inhibitors by myeloma cells: potential effects on canonical Wnt pathway in the bone microenvironment.

Osteoblast impairment occurs within multiple myeloma cell infiltration into the bone marrow. Canonical Wnt signaling activation in osteoprogenitor cells is involved in osteoblast formation through the stabilization of dephosphorylated beta-catenin and its nuclear translocation. The effects of multiple myeloma cells on Wnt signaling in human mesenchymal/osteoprogenitor cells are unclear. In 60 multiple myeloma patients checked, we found that among the Wnt inhibitors, Dickkopf-1 and secreted frizzled-related protein-3 were produced by multiple myeloma cells. However, although multiple myeloma cells or multiple myeloma bone marrow plasma affected expression of genes in the canonical Wnt signaling and inhibited beta-catenin stabilization in murine osteoprogenitor cells, they failed to block the canonical Wnt pathway in human mesenchymal or osteoprogenitor cells. Consistently, Wnt3a stimulation in human osteoprogenitor cells did not blunt the inhibitory effect of multiple myeloma cells on osteoblast formation. Consequently, despite the higher Wnt antagonist bone marrow levels in osteolytic multiple myeloma patients compared with nonosteolytic ones, beta-catenin immunostaining was not significantly different. Our results support the link between the production of Wnt antagonists by multiple myeloma cells and the presence of bone lesions in multiple myeloma patients but show that myeloma cells do not inhibit canonical Wnt signaling in human bone microenvironment.

Intravenous neridronate for skeletal damage treatment in patients with multiple myeloma.

Almost 70-80% of the patients with Multiple Myeloma (MM) in advancer phase, of the disease show osteolytic lesions and/or pathologic fractures, with or without secondary osteoporosis. An accelerated osteoclast-mediated bone absorption is believed to be the main cause of bone damage in MM. Osteoclast can be activated by a variety of microenvironmental factors. Bisphosphonates (BF) induce the apoptosis of osteoclasts and inhibit osteoclastogenesis, thus preventing bone absorption. As well as BFs, the so-called second-generation BF (N-BF) may impair the activity of osteoclast. Neridronic acid (NER) is a N-BF molecule officially registered for the treatment of osteogenesis imperfecta. Nevertheless, NER has shown a remarkable efficacy in Paget's disease, postmenopausal osteoporosis and, most recently, in androgen deprivation-treated prostatic carcinoma. The primary endpoint of this study was to evaluate hip and spine Bone Mineral Density (BMD) modifications over the 12-month treatment with NER in a group of patients affected by MM with evidence of initial skeletal damage. Secondary endpoints were (1) changes of calcium and total Alkaline Phosphatase (tAP) plasma levels during treatment with NER and (2) tolerability of 100 mg NER monthly administration for 12 months. These data suggest that NER, if administered at these doses and timing, might allow at least for one year sustained BMD increases in patients. NER has been highly tolerated in this study. The almost complete absence of adverse effects has prompted us to reduce the time of infusions at the end of the study. In conclusion, this study provides the first data on the efficacy and safety of NER in patients with MM-induced bone damage. These initial data encourage wider phase III trials to clearly assess its efficacy in preventing skeletal-related events and its possible anti-neoplastic properties.