The involvement of osteopontin and its receptors in multiple myeloma cell survival, migration and invasion in the murine 5T33MM model

Mesenchymal Stromal Cells (MSCs): An Ally of B-Cell Acute Lymphoblastic Leukemia (B-ALL) Cells in Disease Maintenance and Progression within the Bone Marrow Hematopoietic Niche

Simple Summary

B-cell acute lymphoblastic leukemia (B-ALL) is the most common pediatric cancer. Even though the cure rate actually exceeds 85%, the prognosis of relapsed/refractory patients is dismal. Recent literature data indicate that the bone marrow (BM) microenvironment could play a crucial role in the onset, maintenance and progression of the disease. In particular, mesenchymal stromal cells (MSCs), which are key components of the BM niche, actively crosstalk with leukemic cells providing crucial signals for their survival and resistance to therapy. We hereby review the main mechanisms exploited by MSCs to nurture and protect B-ALL cells that could become appealing targets for innovative microenvironment remodeling therapies to be coupled with classical leukemia-directed strategies.

Abstract

Mesenchymal stromal cells (MSCs) are structural components of the bone marrow (BM) niche, where they functionally interact with hematopoietic stem cells and more differentiated progenitors, contributing to hematopoiesis regulation. A growing body of evidence is nowadays pointing to a further crucial contribution of MSCs to malignant hematopoiesis. In the context of B-cell acute lymphoblastic leukemia (B-ALL), MSCs can play a pivotal role in the definition of a leukemia-supportive microenvironment, impacting on disease pathogenesis at different steps including onset, maintenance and progression. B-ALL cells hijack the BM microenvironment, including MSCs residing in the BM niche, which in turn shelter leukemic cells and protect them from chemotherapeutic agents through different mechanisms. Evidence is now arising that altered MSCs can become precious allies to leukemic cells by providing nutrients, cytokines, pro-survivals signals and exchanging organelles, as hereafter reviewed. The study of the mechanisms exploited by MSCs to nurture and protect B-ALL blasts can be instrumental in finding new druggable candidates to target the leukemic BM microenvironment. Some of these microenvironment-targeting strategies are already in preclinical or clinical experimentation, and if coupled with leukemia-directed therapies, could represent a valuable option to improve the prognosis of relapsed/refractory patients, whose management represents an unmet medical need.

The antidiabetic drug metformin acts on the bone microenvironment to promote myeloma cell adhesion to preosteoblasts and increase myeloma tumour burden in vivo

Multiple myeloma is a haematological malignancy that is dependent upon interactions within the bone microenvironment to drive tumour growth and osteolytic bone disease. Metformin is an anti-diabetic drug that has attracted attention due to its direct antitumor effects, including anti-myeloma properties. However, the impact of the bone microenvironment on the response to metformin in myeloma is unknown. We have employed in vitro and in vivo models to dissect out the direct effects of metformin in bone and the subsequent indirect myeloma response. We demonstrate how metformin treatment of preosteoblasts increases myeloma cell attachment. Metformin-treated preosteoblasts increased osteopontin (OPN) expression that upon silencing, reduced subsequent myeloma cell adherence. Proliferation markers were reduced in myeloma cells cocultured with metformin-treated preosteoblasts. In vivo, mice were treated with metformin for 4 weeks prior to inoculation of 5TGM1 myeloma cells. Metformin-pretreated mice had an increase in tumour burden, associated with an increase in osteolytic bone lesions and elevated OPN expression in the bone marrow. Collectively, we show that metformin increases OPN expression in preosteoblasts, increasing myeloma cell adherence. In vivo, this translates to an unexpected indirect pro-tumourigenic effect of metformin, highlighting the importance of the interdependence between myeloma cells and cells of the bone microenvironment.

The role of CD44 in pathological angiogenesis

Angiogenesis is required for normal development and occurs as a pathological step in a variety of disease settings, such as cancer, ocular diseases, and ischemia. Recent studies have revealed the role of CD44, a widely expressed cell surface adhesion molecule, in promoting pathological angiogenesis and the development of its associated diseases through its regulation of diverse function of endothelial cells, such as proliferation, migration, adhesion, invasion, and communication with the microenvironment. Conversely, the absence of CD44 expression or inhibition of its function impairs pathological angiogenesis and disease progression. Here, we summarize the current understanding of the roles of CD44 in pathological angiogenesis and the underlying cellular and molecular mechanisms.

SPP1 promotes Schwann cell proliferation and survival through PKCα by binding with CD44 and αvβ3 after peripheral nerve injury

BACKGROUND

Schwann cells (SCs) play a crucial role in Wallerian degeneration after peripheral nerve injury. The expression of genes in SCs undergo a series of changes, which greatly affect the proliferation and apoptosis of SCs as well as the fate of peripheral nerve regeneration. However, how do these genes regulate the proliferation and apoptosis of SCs remains unclear.

RESULTS

SPP1 and PKCα were found upregulated after human median peripheral nerve injury, which promoted SCs proliferation and survival. The promoted proliferation and inhibited apoptosis by SPP1 were blocked after the treatment of PKCα antagonist Gö6976. Whereas, the inhibited proliferation and enhanced apoptosis induced by silence of SPP1 could be rescued by the activation of PKCα, which suggested that SPP1 functioned through PKCα. Moreover, both CD44 and αvβ3 were found expressed in SCs and increased after peripheral nerve injury. Silence of CD44 or β3 alleviated the increased proliferation and inhibited apoptosis induced by recombinant osteopontin, suggesting the function of SPP1 on SCs were dependent on CD44 and β3.

CONCLUSION

These results suggested that SPP1 promoted proliferation and inhibited apoptosis of SCs through PKCα signaling pathway by binding with CD44 and αvβ3. This study provides a potential therapeutic target for improving peripheral nerve recovery.

Runx2 Deficiency in Osteoblasts Promotes Myeloma Progression by Altering the Bone Microenvironment at New Bone Sites

Multiple myeloma is a plasma cell malignancy that thrives in the bone marrow (BM), with frequent progression to new local and distant bone sites. Our previous studies demonstrated that multiple myeloma cells at primary sites secrete soluble factors and suppress osteoblastogenesis via the inhibition of Runt-related transcription factor 2 (Runx2) in pre- and immature osteoblasts (OB) in new bone sites, prior to the arrival of metastatic tumor cells. However, it is unknown whether OB-Runx2 suppression in new bone sites feeds back to promote multiple myeloma dissemination to and progression in these areas. Hence, we developed a syngeneic mouse model of multiple myeloma in which Runx2 is specifically deleted in the immature OBs of C57BL6/KaLwRij mice (OB-Runx2-/- mice) to study the effect of OB-Runx2 deficiency on multiple myeloma progression in new bone sites. In vivo studies with this model demonstrated that OB-Runx2 deficiency attracts multiple myeloma cells and promotes multiple myeloma tumor growth in bone. Mechanistic studies further revealed that OB-Runx2 deficiency induces an immunosuppressive microenvironment in BM that is marked by an increase in the concentration and activation of myeloid-derived suppressor cells (MDSC) and the suppression and exhaustion of cytotoxic CD8+ T cells. In contrast, MDSC depletion by either gemcitabine or 5-fluorouracil treatment in OB-Runx2-/- mice prevented these effects and inhibited multiple myeloma tumor growth in BM. These novel discoveries demonstrate that OB-Runx2 deficiency in new bone sites promotes multiple myeloma dissemination and progression by increasing metastatic cytokines and MDSCs in BM and inhibiting BM immunity. Importantly, MDSC depletion can block multiple myeloma progression promoted by OB-Runx2 deficiency.Significance: This study demonstrates that Runx2 deficiency in immature osteoblasts at distant bone sites attracts myeloma cells and allows myeloma progression in new bone sites via OB-secreted metastatic cytokines and MDSC-mediated suppression of bone marrow immunity.

Mesenchymal Stromal Cells: Emerging Roles in Bone Metastasis

Bone metastasis is the most advanced stage of many cancers and indicates a poor prognosis for patients due to resistance to anti-tumor therapies. The establishment of metastasis within the bone is a multistep process. To ensure survival within the bone marrow, tumor cells must initially colonize a niche in which they can enter dormancy. Subsequently, reactivation permits the proliferation and growth of the tumor cells, giving rise to a macro-metastasis displayed clinically as a bone metastatic lesion. Here, we review the evidences that suggest mesenchymal stromal cells play an important role in each of these steps throughout the development of bone metastasis. Similarities between the molecular mechanisms implicated in these processes and those involved in the homeostasis of the bone indicate that the metastatic cells may exploit the homeostatic processes to their own advantage. Identifying the molecular interactions between the mesenchymal stromal cells and tumor cells that promote tumor development may offer insight into potential therapeutic targets that could be utilized to treat bone metastasis.

A First Report on [18F]FPRGD2 PET/CT Imaging in Multiple Myeloma

An observational study was set up to assess the feasibility of [¹⁸F]FPRGD₂ PET/CT for imaging patients with multiple myeloma (MM) and to compare its detection rate with low dose CT alone and combined [¹⁸F]NaF/[¹⁸F]FDG PET/CT images. Four patients (2 newly diagnosed patients and 2 with relapsed MM) were included and underwent whole-body PET/CT after injection of [¹⁸F]FPRGD₂. The obtained images were compared with results of low dose CT and already available results of a combined [¹⁸F]NaF/[¹⁸F]FDG PET/CT. In total, 81 focal lesions (FLs) were detected with PET/CT and an underlying bone destruction or fracture was seen in 72 (89%) or 8 (10%) FLs, respectively. Fewer FLs (54%) were detected by [¹⁸F]FPRGD₂ PET/CT compared to low dose CT (98%) or [¹⁸F]NaF/[¹⁸F]FDG PET/CT (70%) and all FLs detected with [¹⁸F]FPRGD₂ PET were associated with an underlying bone lesion. In one newly diagnosed patient, more [¹⁸F]FPRGD₂ positive lesions were seen than [¹⁸F]NaF/[¹⁸F]FDG positive lesions. This study suggests that [¹⁸F]FPRGD₂ PET/CT might be less useful for the detection of myeloma lesions in patients with advanced disease as all FLs with [¹⁸F]FPRGD₂ uptake were already detected with CT alone.

Concurrent Elevations of VEGF, Osteopontin and MCP-1 Serum Levels Are Independent Predictors of Survival in Patients with Diffuse Large B-Cell Lymphoma

BACKGROUND

Diffuse large B-cell lymphomas (DLBCL) are heterogeneous diseases, and the identification of additional DLBCL risk factors is especially important.

METHODS

In this pilot study, we determined pretreatment serum levels of vascular endothelial growth factor (VEGF), osteopontin (OPN) and macrophage chemotactic protein-1 (MCP-1) in 67 newly diagnosed DLBCL patients before treatment with standard chemoimmunotherapy and in 30 healthy persons.

RESULTS

Serum levels of all three cytokines were significantly elevated in untreated patients compared to controls. VEGF and OPN concentrations were higher in patients with advanced Ann Arbor stage, B symptoms, Eastern Cooperative Oncology Group score ≥2, International Prognostic Index (IPI) ≥3 and partial/no remission. A high MCP-1 level was associated with advanced stage, increased IPI and bone marrow infiltration. In univariate analysis, elevated OPN and VEGF, and concurrent elevation of all three biomarkers, were identified as significant predictors of poor survival. Multivariate Cox analysis revealed that elevated OPN combined with elevated VEGF levels was one of the best parameter subsets predicting poorest survival.

CONCLUSION

According to our preliminary results, serum levels of VEGF and OPN before treatment predict response to therapy and survival after chemoimmunotherapy, and may help to further stratify DLBCL patients into risk groups.

Thyroid hormone regulates adhesion, migration and matrix metalloproteinase 9 activity via αvβ3 integrin in myeloma cells

Thyroid hormone (3,5,3′-triiodothyronine, T3; L-thyroxine, T4) enhances cancer cell proliferation, invasion and angiogenesis via a discrete receptor located near the RGD recognition site on αvβ3 integrin. Tetraiodothyroacetic acid (tetrac) and its nanoparticulate formulation interfere with binding of T3/T4 to the integrin. This integrin is overexpressed in multiple myeloma (MM) and other cancers. MM cells interact with αvβ3 integrin to support growth and invasion. Matrix metalloproteinases (MMPs) are a family of enzymes active in tissue remodeling and cancer. The association between integrins and MMPs secretion and action is well established. In the current study, we examined the effects of thyroid hormone on myeloma cell adhesion, migration and MMP activity.

We show that T3 and T4 increased myeloma adhesion to fibronectin and induced αvβ3 clustering. In addition, the hormones induced MMP-9 expression and activation via αvβ3 and MAPK induction. Bortezomib, a standard myeloma treatment, caused a decrease in activity/quantity of MMPs and thyroid hormone opposed this effect. RGD peptide and tetrac impaired the production of MMP-9 in cell lines and in primary BM cells from myeloma patients.

In conclusion, thyroid hormone-dependent regulation via αvβ3 of myeloma cell adhesion and MMP-9 production may play a role in myeloma migration and progression.

Osteopontin facilitates ultraviolet B-induced squamous cell carcinoma development

BACKGROUND

Osteopontin (OPN) is a matricellular glycoprotein that is markedly expressed in cutaneous squamous cell carcinomas (cSCCs) and in actinic keratoses implicating its role in photocarcinogenesis.

OBJECTIVE

To determine whether OPN facilitates the development of cSCC and its function.

METHODS

cSCCs development was compared between wild-type (WT) and OPN-null mice subjected to UVB irradiation for 43 weeks. UVB-induced OPN expression was determined by Western blot, immunoprecipitation, ELISA, and semi-quantitative RT-PCR. Epidermal layer and TUNEL analyses assessed if OPN mediates UVB-induced epidermal hyperplasia or suppresses UVB-induced apoptosis of basal keratinocytes, respectively. In vitro experiments determined whether OPN enhances cell survival of UVB-induced apoptosis and its potential mechanisms. Immunohistochemical analyses of epidermis assessed the expression of CD44 and focal adhesion kinase (FAK), molecules that mediate OPN survival function.

RESULTS

Compared to female WT mice, OPN-null mice did not develop cSCCs. UVB irradiation stimulated OPN protein expression in the dorsal skin by 11h and remains high at 24-48h. OPN did not mediate UVB-induced epidermal hyperplasia; instead, it protected basal keratinocytes from undergoing apoptosis upon UVB exposure. Likewise, the addition of OPN suppressed UVB-induced OPN-null cSCC cell apoptosis, the activation of caspase-9 activity, and increased phosphorylation of FAK at Y397. Furthermore, the expression of CD44 and FAK in WT mice epidermis was greater than that of OPN-null mice prior to and during early acute UVB exposure.

CONCLUSION

These data support the hypothesis that chronic UVB-induced OPN expression protects the survival of initiated basal keratinocytes and, consequently, facilitates cSCC develop.

Bone sialoprotein and osteopontin in bone metastasis of osteotropic cancers

The mechanisms underlying malignant cell metastasis to secondary sites such as bone are complex and no doubt multifactorial. Members of the small integrin-binding ligand N-linked glycoproteins (SIBLINGs) family, particularly bone sialoprotein (BSP) and osteopontin (OPN), exhibit multiple activities known to promote malignant cell proliferation, detachment, invasion, and metastasis of several osteotropic cancers. The expression level of BSP and OPN is elevated in a variety of human cancers, particularly those that metastasize preferentially to the skeleton. Recent studies suggest that the "osteomimicry" of malignant cells is not only conferred by transmembrane receptors bound by BSP and OPN, but includes the "switch" in gene expression repertoire typically expressed in cells of skeletal lineage. Understanding the role of BSP and OPN in tumor progression, altered pathophysiology of bone microenvironment, and tumor metastasis to bone will likely result in development of better diagnostic approaches and therapeutic regimens for osteotropic malignant diseases.

Adhesion to osteopontin in the bone marrow niche regulates lymphoblastic leukemia cell dormancy

Malignant cells may evade death from cytotoxic agents if they are in a dormant state. The host microenvironment plays important roles in cancer progression, but how niches might control cancer cell dormancy is little understood. Here we show that osteopontin (OPN), an extracellular matrix molecule secreted by osteoblasts, can function to anchor leukemic blasts in anatomic locations supporting tumor dormancy. We demonstrate that acute lymphoblastic leukemia (ALL) cells specifically adhere to OPN in vitro and secrete OPN when localized to the endosteal niche in vivo. Using intravital microscopy to perform imaging studies of the calvarial bone marrow (BM) of xenografted mice, we show that OPN is highly expressed adjacent to dormant tumor cells within the marrow. Inhibition of the OPN-signaling axis significantly increases the leukemic cell Ki-67 proliferative index and leads to a twofold increase in tumor burden in treated mice. Moreover, using cell-cycle-dependent Ara-C chemotherapy to produce minimal residual disease (MRD) in leukemic mice, we show that OPN neutralization synergizes with Ara-C to reduce detectable BM MRD. Taken together, these data suggest that ALL interacts with extracellular OPN within the malignant BM, and that this interaction induces cell cycle exit in leukemic blasts, protecting them from cytotoxic chemotherapy.

Proteins involved in regulating bone invasion in skull base meningiomas

Background

Bone invasive skull base meningiomas are a subset of meningiomas that present a unique clinical challenge due to brain and neural structure involvement and limitations in complete surgical resection, resulting in higher recurrence and need for repeat surgery. To date, the pathogenesis of meningioma bone invasion has not been investigated. We investigated immunoexpression of proteins implicated in bone invasion in other tumor types to establish their involvement in meningioma bone invasion.

Methods

Retrospective review of our database identified bone invasive meningiomas operated on at our institution over the past 20 years. Using high-throughput tissue microarray (TMA), we established the expression profile of osteopontin (OPN), matrix metalloproteinase-2 (MMP2), and integrin beta-1 (ITGB1). Differential expression in tumor cell and vasculature was evaluated and comparisons were made between meningioma anatomical locations.

Results

MMP2, OPN, and ITGB1 immunoreactivity was cytoplasmic in tumor and/or endothelial cells. Noninvasive transbasal meningiomas exhibited higher vascular endothelial cell MMP2 immunoexpression compared to invasive meningiomas. We found higher expression levels of OPN and ITGB1 in bone invasive transbasal compared to noninvasive meningiomas. Strong vascular ITGB1 expression extending from the endothelium through the media and into the adventitia was found in a subset of meningiomas.

Conclusions

We have demonstrated that key proteins are differentially expressed in bone invasive meningiomas and that the anatomical location of bone invasion is a key determinant of expression pattern of MMP1, OPN, and ITGB1. This data provides initial insights into the pathophysiology of bone invasion in meningiomas and identifies factors that can be pursued as potential therapeutic targets.

Biological aspects of angiogenesis in multiple myeloma

Multiple myeloma (MM) is a hematological malignancy characterized by the aberrant expansion of malignant plasma cells within the bone marrow (BM). One of the hallmarks of this disease is the close interaction between myeloma cells and neighboring cells within the BM. Angiogenesis, through the activation of endothelial cells, plays an essential role in MM biology. In the current review, we describe the angiogenesis process in MM by identifying the interacting cells, the pro- and anti-angiogenic cytokines modulated, and the extracellular matrix degrading proteases liable to participate in the pathophysiology. Finally, we highlight the impact of hypoxia (through hypoxia-inducible factor-1) and constitutive activation of nuclear factor-κB in this tumor-induced neo-vascularization.

Circulating osteopontin: a dual marker of bone destruction and angiogenesis in patients with multiple myeloma

The matrix protein osteopontin has been shown to be a marker of osteoclastic activity in multiple myeloma patients, as well as a regulator of angiogenesis. We measured serum levels of osteopontin in 50 untreated multiple myeloma patients (in 25, also after treatment) and examined the relation to markers of osteolytic and angiogenic activity. The median (range) of serum osteopontin was 85 (5-232) in the patient group vs. 36 (2-190) ng/ml in the control group. Serum osteopontin levels were significantly higher in patients with advanced stage or grade of myeloma disease. All patients with serum osteopontin levels >100 ng/ml had advanced stage (II or III) or high grade bone disease, whereas stage I or low grade patients had serum osteopontin levels <100ng/ml. Serum osteopontin levels significantly decreased after treatment. There was a positive correlation of osteopontin with the bone turnover marker N-terminal propeptide of procollagen type I (NTx) and the angiogenic markers vascular endothelial growth factor (VEGF) and bone marrow microvessel density (r: 0.35, 0.47 and 0.30 respectively, p < 0.05). These results support osteopontin as a dual marker of bone destruction and angiogenic activity in myeloma patients. Osteopontin represents a useful biomarker for monitoring myeloma disease activity.

RARalpha2 expression is associated with disease progression and plays a crucial role in efficacy of ATRA treatment in myeloma

Specific genetic alterations in multiple myeloma (MM) may cause more aggressive diseases. Paired gene array analysis on 51 samples showed that retinoic acid (RA) receptor alpha (RARalpha) expression significantly increased at relapse compared with diagnosis. RARalpha encodes 2 major isoforms: RARalpha1 and RARalpha2. In this study, we examined the function of RARalpha2 in MM. Reverse transcription-polymerase chain reaction (RT-PCR) revealed ubiquitous RARalpha1 expression in MM cells, but RARalpha2 was expressed in 26 (32%) of 80 newly diagnosed patients and 10 (28%) of 36 MM cell lines. Patients with RARalpha2 expression had a significantly shorter overall survival on identical treatments. The presence of RARalpha2 remained significant on multivariate analysis. Knockdown of RARalpha2 but not RARalpha1 induced significant MM cell death and growth inhibition, and overexpressing RARalpha2 activated STAT3 and mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) signaling pathways. Interestingly, all-trans retinoic acid (ATRA) treatment induced potent cell death and growth inhibition in RARalpha2(+) but not RARalpha2(-) MM cells; overexpressing RARalpha2 in RARalpha2-deficient MM cells restored sensitivity to ATRA. Furthermore, ATRA treatment significantly inhibited the growth of RARalpha2-overexpressing MM tumors in severe combined immunodeficiency (SCID) mouse model. These findings provide a rationale for RA-based therapy in aggressive RARalpha2(+) MM.

Inhibitor of DASH proteases affects expression of adhesion molecules in osteoclasts and reduces myeloma growth and bone disease

Dipeptidyl peptidase (DPP) IV activity and/or structure homologues (DASH) are serine proteases implicated in tumourigenesis. We previously found that a DASH protease, fibroblast activation protein (FAP), was involved in osteoclast-induced myeloma growth. Here we further demonstrated expression of various adhesion molecules in osteoclasts cultured alone or cocultured with myeloma cells, and tested the effects of DASH inhibitor, PT-100, on myeloma cell growth, bone disease, osteoclast differentiation and activity, and expression of adhesion molecules in osteoclasts. PT-100 had no direct effects on viability of myeloma cells or mature osteoclasts, but significantly reduced survival of myeloma cells cocultured with osteoclasts. Real-time PCR array for 85 adhesion molecules revealed upregulation of 17 genes in osteoclasts after coculture with myeloma cells. Treatment of myeloma/osteoclast cocultures with PT-100 significantly downregulated 18 of 85 tested genes in osteoclasts, some of which are known to play roles in tumourigenesis and osteoclastogenesis. PT-100 also inhibited osteoclast differentiation and subsequent pit formation. Resorption activity of mature osteoclasts and differentiation of osteoblasts were not affected by PT-100. In primary myelomatous severe combined immunodeficient (SCID)-hu mice PT-100 reduced osteoclast activity, bone resorption and tumour burden. These data demonstrated that DASH proteases are involved in myeloma bone disease and tumour growth.

Small integrin-binding ligand N-linked glycoproteins (SIBLINGs): multifunctional proteins in cancer

Numerous components and pathways are involved in the complex interplay between cancer cells and their environment. The family of glycophosphoproteins comprising osteopontin, bone sialoprotein, dentin matrix protein 1, dentin sialophosphoprotein and matrix extracellular phosphoglycoprotein - small integrin-binding ligand N-linked glycoproteins (SIBLINGs) - are emerging as important players in many stages of cancer progression. From their detection in various human cancers to the demonstration of their key functional roles during malignant transformation, invasion and metastasis, the SIBLINGs are proteins with potential as diagnostic and prognostic tools, as well as new therapeutic targets.

Osteopontin-deficient mice exhibit less inflammation, greater tissue damage, and impaired locomotor recovery from spinal cord injury compared with wild-type controls

Osteopontin (OPN) is expressed in many tissues during inflammatory responses. After spinal cord injury, microglia expresses OPN at the site of injury during the early to subacute stages. However, the function of OPN in spinal cord injury is not well understood. This study examines the responses of OPN knock-out (KO) and wild-type (WT) mice to spinal cord contusion injury. KO and WT mice were injured with a modified New York University impactor. Weights of 10 or 5.6 g were dropped 6.25 mm onto the T13 spinal cord under isoflurane anesthesia. At 24 h, homogenized spinal cords were analyzed for total potassium concentration to estimate lesion volumes. Expression of apoptotic genes, proinflammatory cytokines, and nerve growth factors was measured by reverse transcription (RT)-PCR and Western blot. In a series of animals, locomotor recovery was assessed with the Basso mouse scale (BMS) for 6 weeks, and histological analyses was performed to determine tissue preservation. Lesion volume showed no significant differences between KO and WT mice at 24 h. RT-PCR indicated that KO mice had significantly less Bcl-2, tumor necrosis factor-alpha, interleukin-1beta, and interleukin-6 mRNA compared with WT controls. Western blot also showed that KO had significantly less Bcl-2 7 d after spinal cord injury. KO mice had significantly worse BMS locomotor scores than WT at 6 weeks. KO mice also had a significantly reduced area of spared white matter and fewer neuronal-specific nuclear protein-positive neurons in the spinal cord surrounding the impact site. This result supports a potential neuroprotective role for OPN in the inflammatory response to spinal cord injury.

Papilloma development is delayed in osteopontin-null mice: implicating an antiapoptosis role for osteopontin

Osteopontin is a secreted, adhesive glycoprotein, whose expression is markedly elevated in several types of cancer and premalignant lesions, implicating its association with carcinogenesis. To test the hypothesis that induced osteopontin is involved in tumor promotion in vivo, osteopontin-null and wild-type (WT) mice were subjected to a two-stage skin chemical carcinogenesis protocol. Mice were initiated with 7,12-dimethylbenz(a)anthracene (DMBA) applied on to the dorsal skin followed by twice weekly application of 12-O-tetradecanoylphorbol-13-acetate (TPA) for 27 weeks. Osteopontin-null mice showed a marked decrease both in tumor/papilloma incidence and multiplicity compared with WT mice. Osteopontin is minimally expressed in normal epidermis, but on treatment with TPA its expression is highly induced. To determine the possible mechanism(s) by which osteopontin regulates tumor development, we examined cell proliferation and cell survival. Epidermis from osteopontin-null and WT mice treated with TPA thrice or with DMBA followed by TPA for 11 weeks showed a similar increase in epidermal hyperplasia, suggesting that osteopontin does not mediate TPA-induced cell proliferation. Bromodeoxyuridine staining of papillomas and adjacent epidermis showed no difference in cell proliferation between groups. However, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling analyses indicated a greater number of apoptotic cells in DMBA-treated skin and papillomas from osteopontin-null versus WT mice. These studies are the first to show that induction of the matricellular protein osteopontin facilitates DMBA/TPA-induced cutaneous carcinogenesis most likely through prevention of apoptosis.