Tetsuya Takada

Targeting the canonical Wnt/β-catenin pathway in hematological malignancies.

The canonical Wnt/β‐catenin pathway plays an important role in different developmental processes through the regulation of stem cell functions. In the activation of the canonical Wnt/β‐catenin pathway, β‐catenin protein is imported into the nucleus and activates transcription of target genes including cyclin D1 and c‐myc. Aberrant activation of the Wnt/β‐catenin pathway contributes to carcinogenesis and malignant behaviors, and Wnt signaling is essential for the maintenance of cancer stem cells. The canonical Wnt/β‐catenin pathway has been investigated extensively as a target in cancer treatment and several specific inhibitors of this signaling pathway have been identified through high‐throughput screening. In this review, the significance of the canonical Wnt/β‐catenin pathway in hematological carcinogenesis and screening methods for specific inhibitors are discussed.

Microglial Amyloid-β1-40 Phagocytosis Dysfunction Is Caused by High-Mobility Group Box Protein-1: Implications for the Pathological Progression of Alzheimer's Disease

In Alzheimer disease (AD) patient brains, the accumulation of amyloid-β (Aβ) peptides is associated with activated microglia. Aβ is derived from the amyloid precursor protein; two major forms of Aβ, that is, Aβ1-40 (Aβ40) and Aβ1-42 (Aβ42), exist. We previously reported that rat microglia phagocytose Aβ42, and high mobility group box protein 1 (HMGB1), a chromosomal protein, inhibits phagocytosis. In the present study, we investigated the effects of exogenous HMGB1 on rat microglial Aβ40 phagocytosis. In the presence of exogenous HMGB1, Aβ40 markedly increased in microglial cytoplasm, and the reduction of extracellular Aβ40 was inhibited. During this period, HMGB1 was colocalized with Aβ40 in the cytoplasm. Furthermore, exogenous HMGB1 inhibited the degradation of Aβ40 induced by the rat microglial cytosolic fraction. Thus, extracellular HMGB1 may internalize with Aβ40 in the microglial cytoplasm and inhibit Aβ40 degradation by microglia. This may subsequently delay Aβ40 clearance. We further confirmed that in AD brains, the parts of senile plaques surrounded by activated microglia are composed of Aβ40, and extracellular HMGB1 is deposited on these plaques. Taken together, microglial Aβ phagocytosis dysfunction may be caused by HMGB1 that accumulates extracellularly on Aβ plaques, and it may be critically involved in the pathological progression of AD.

Daphnetin inhibits invasion and migration of LM8 murine osteosarcoma cells by decreasing RhoA and Cdc42 expression.

Daphnetin, 7,8-dihydroxycoumarin, present in main constituents of Daphne odora var. marginatai, has multiple pharmacological activities including anti-proliferative effects in cancer cells. In this study, using a Transwell system, we showed that daphnetin inhibited invasion and migration of highly metastatic murine osteosarcoma LM8 cells in a dose-dependent manner. Following treatment by daphnetin, cells that penetrated the Transwell membrane were rounder than non-treated cells. Immunofluorescence analysis revealed that daphnetin decreased the numbers of intracellular stress fibers and filopodia. Moreover, daphnetin treatment dramatically decreased the expression levels of RhoA and Cdc42. In summary, the dihydroxycoumarin derivative daphnetin inhibits the invasion and migration of LM8 cells, and therefore represents a promising agent for use against metastatic cancer.

Inhibition of monocarboxylate transporter 1 suppresses the proliferation of glioblastoma stem cells.

Recent evidence suggests that a minor subset of cancer cells, termed cancer stem cells (CSCs), have self-renewal and tumorigenic potential. Therefore, the characterization of CSCs is important for developing therapeutic strategies against cancer. Cancer cells rely on anaerobic glycolysis to produce ATP even under normoxic conditions, resulting in the generation of excess acidic substances. Cancer cells maintain a weakly alkaline intracellular pH to support functions. Glioblastoma is an aggressive malignancy with a poor 5-year survival rate. Based on the hypothesis that ion transport-related molecules regulate the viability and function of CSCs, we investigated the expression of ion transport-related molecules in glioblastoma CSCs (GSCs). Quantitative RT-PCR analysis showed that monocarboxylate transporter1 (MCT1) were upregulated in GSCs, and inhibition of MCT1 decreased the viability of GSCs compared with that of non-GSCs. Our findings indicate that MCT1 is involved in the maintenance of GSCs and is a promising therapeutic target for glioblastoma.

Preparation and Characterization of Microglia-Like Cells Derived from Rat, Mouse, and Human Bone Marrow Cells for Therapeutic Strategy of Alzheimer's Disease

Dementia-associated neuropsychiatric symptoms, such as depression and apathy, are core features of Alzheimer’s disease (AD). Pathological hallmarks of AD include senile plaques, neurofibrillary tangles (NFTs), and neurodegeneration. Senile plaques are composed of amyloid-β (Aβ) and are surrounded by microglia, an immune effector cells in brains. Studies on responsible genes of familial AD have suggested that Aβ accumulation is a primary event that influences other AD pathologies, and the reduction of brain Aβ has been proposed as a therapeutic target for AD. On the other hand, microglial phagocytosis has been noted as an Aβ clearance system in the brain. In this context, the transplantation of microglia prepared from bone marrow cells may contribute to the clearance of Aβ in vivo brain. As a first step for this cell therapeutic strategy, we examined the preparation of microglia-like cells from mouse, rat, and human bone marrow cells by the treatment with macrophage colony-stimulating factor (M-CSF) and analyzed their phagocytic ability. In the cultivation of bone marrow cells collected from mouse, rat, and human, adherent cells on the culture dish were markedly increased by the treatment with human M-CSF. In addition, the adherent cells from mouse bone marrow cells were more sensitive to human M-CSF than that from rat bone marrow cells and more effectively expressed microglial makers, such as cluster of differentiation (CD) 11b, Iba1, and CD68. Furthermore, we demonstrated that a part of adherent cells derived from mouse and human bone marrow cells have phagocytic abilities of iron particles and Aβ peptides, and the treatment with human M-CSF significantly increased the number of phagocytic cells. Thus, we positively suggest that the microglia-like cells prepared from bone marrow cells by the treatment with human M-CSF could be a source for the cell therapeutic strategy for AD.