Roles of oncogenes and tumor-suppressor genes in osteoclastogenesis (Review).

Osteoporosis is a bone disease that poses a tremendous burden to health care. The receptor activator of nuclear factor-κB (RANK) and its ligand (RANKL) have been a major focus of this research field. RANKL signaling not only activates a variety of downstream signaling pathways required for osteoclast development, but crosstalk with other signaling pathways also adjusts bone homeostasis both in normal physiology and in bone disease. Consequently, novel drugs specifically targeting RANK-RANKL and their signaling pathways in osteoclasts are expected to revolutionize the treatment of various bone diseases such as osteoporosis. Osteoclasts are the exclusive cells involved in bone resorption. Abnormal activation of osteoclasts can lead to reduced bone density, resulting in osteopenia, osteoporosis and other bone disorders. To date, the mechanism of how osteoclast precursors differentiate into mature osteoclasts remains elusive. Cell proliferation and cell death may be key processes in the progression as well as other cell types. Oncogene products and tumor-suppressor molecules play a pivotal role in regulating the processes, which are important in regulating the configuration of bone disorders. Based on the understanding of these processes, promising alternatives to the use of medications against osteoporosis include specific diets with plant-derived supplements to modulate the expression and/or activity of these molecules. In this review, we summarize the progress of research with a focus on the modulatory roles of oncogene products and tumor-suppressor molecules and suggest the scope of further research concerning the prevention of osteoporosis in this field.

PI3K/AKT signaling mediated by G protein­coupled receptors is involved in neurodegenerative Parkinson's disease (Review).

Parkinson's disease (PD) is a common progressive and multifactorial neurodegenerative disease, characterized by the loss of midbrain dopaminergic neurons. Numerous pathological processes including, inflammation, oxidative stress, mitochondrial dysfunction, neurotransmitter imbalance, and apoptosis as well as genetic factors may lead to neuronal degeneration. Motor deficits in PD are due mostly to the progressive loss of nigrostriatal dopaminergic neurons. Neuroprotection of functional neurons is of significance in the treatment of PD. G protein­coupled receptors (GPCRs) have been implicated in the neuroprotection against PD through the survival of dopaminergic neurons. In addition, phosphatidyl­inositol­3­kinase (PI3K)/AKT signaling has also been demonstrated to be neuroprotective. Knowledge of the mechanisms involved in this cellular protection could be critical for developing treatments to prevent this neurodegenerative disorder. In this review, we highlight the protective roles of the PI3K/AKT signaling pathway in the function of representative serotonin GPCRs. Particular attention is given to the molecular mechanisms of this pathway proposed to explain the favorable effects of food ingredients against neurodegenerative disease.

PINK1 signaling in mitochondrial homeostasis and in aging (Review).

Mitochondrial dysfunction is involved in the pathology of Parkinson's disease, an age-associated neurodegenerative disorder. Phosphatase and tensin homolog (PTEN)-induced putative kinase protein 1 (PINK1) is responsible for the most common form of recessive Parkinson's disease. PINK1 is a mitochondrial kinase that is involved in mitrochondrial quality control and promotes cell survival. PINK1 has been shown to protect against neuronal cell death induced by oxidative stress. Accordingly, PINK1 deficiency is associated with mitochondrial dysfunction as well as increased oxidative cellular stress and subsequent neuronal cell death. In addition, several mitochondrial chaperone proteins have been shown to be substrates of the PINK1 kinase. In this review, we discuss recent studies concerning the signaling cascades and molecular mechanisms involved in the process of mitophagy, which is implicated in neurodegeneration and in related aging associated with oxidative stress. Particular attention will be given to the molecular mechanisms proposed to explain the effects of natural compounds and/or food ingredients against oxidative stress. Knowledge of the molecular mechanisms involved in this cellular protection could be critical for developing treatments to prevent and control excessive progression of neurodegenerative disorders.

Effective PI3K modulators for improved therapy against malignant tumors and for neuroprotection of brain damage after tumor therapy (Review).

Due to the key role in various cellular processes including cell proliferation and cell survival on many cell types, dysregulation of the PI3K/AKT pathway represents a crucial step of the pathogenesis in many diseases. Furthermore, the tumor suppressor PTEN negatively regulates the PI3K/AKT pathway through its lipid phosphatase activity, which is recognized as one of the most frequently deleted and/or mutated genes in human cancer. Given the pervasive involvement of this pathway, the development of the molecules that modulate this PI3K/AKT signaling has been initiated in studies which focus on the extensive effective drug discovery. Consequently, the PI3K/AKT pathway appears to be an attractive pharmacological target both for cancer therapy and for neurological protection necessary after the therapy. A better understanding of the molecular relations could reveal new targets for treatment development. We review recent studies on the features of PI3K/AKT and PTEN, and their pleiotropic functions relevant to the signaling pathways involved in cancer progress and in neuronal damage by the therapy.

Roles of PTEN with DNA Repair in Parkinson's Disease.

Oxidative stress is considered to play key roles in aging and pathogenesis of many neurodegenerative diseases such as Parkinson's disease, which could bring DNA damage by cells. The DNA damage may lead to the cell apoptosis, which could contribute to the degeneration of neuronal tissues. Recent evidence suggests that PTEN (phosphatase and tensin homolog on chromosome 10) may be involved in the pathophysiology of the neurodegenerative disorders. Since PTEN expression appears to be one dominant determinant of the neuronal cell death, PTEN should be a potential molecular target of novel therapeutic strategies against Parkinson's disease. In addition, defects in DNA damage response and DNA repair are often associated with modulation of hormone signaling pathways. Especially, many observations imply a role for estrogen in a regulation of the DNA repair action. In the present review, we have attempted to summarize the function of DNA repair molecules at a viewpoint of the PTEN signaling pathway and the hormone related functional modulation of cells, providing a broad interpretation on the molecular mechanisms for treatment of Parkinson's disease. Particular attention will be paid to the mechanisms proposed to explain the health effects of food ingredients against Parkinson's disease related to reduce oxidative stress for an efficient therapeutic intervention.