Current Molecular Medicine - Volume 15, Issue 10, 2015

Citrate is one of the major substrates for intracellular metabolism. The extracellular level of citrate is stable in blood but varies locally, with slightly increased levels in brain and high levels in prostate. Recent metabolomics research suggests that citrate level is a potential harbinger of different pathophysiological states; its decrease has been correlated with male infertility, brain diseases and metastatic cancer. In this review we discuss the role of citrate as an energy substrate for sperm. We also review the function of citrate released by astrocytes in the normal operation of neurons, and consequently we suggest a potential role of neuronal plasma membrane citrate transporters in mental disorders. Finally, we review recent relevant publications studying blood, urine and tissue citrate levels in cancer patients and hypothesize that extracellular citrate supports cancer cell metabolism critical for metastasis. Despite the importance of extracellular citrate in physiological and pathophysiological processes, surprisingly little is known about citrate synthesis in specialized cells, or about citrate transporters controlling citrate movement across various membranes. Determination of the molecular origin of citrate transporters in astrocytes, sperm and cancer cells could offer novel therapeutic targets and the possibility to pharmacologically regulate citrate release and uptake for preventing male infertility, treating mental diseases and targeting cancer.

Metastasis, the main cause of mortality in cancer patients, is a complex process consisting of several sequential, interlinked, and highly-selective steps. Fibroblast growth factor-inducible 14 (Fn14) is one member of the tumor necrosis factor receptor family, which is influential in controlling cell division, life, and death. The role of Fn14 in tumor metastasis regulation is slowly being unraveled, including roles in the regulation of the epithelial-mesenchymal transition, angiogenesis, cytoskeleton modulation, extracellular matrix degradation and inflammation. This review will focus on recent studies that demonstrate the involvement of Fn14 in tumor progression and will briefly describe various pathways of Fn14-regulated metastasis. Finally, future prospects will be discussed for the potential role of Fn14 as a predictive marker and therapeutic agent for tumor metastasis suppression.

Atherosclerosis and its complications represent the leading death cause worldwide, despite many therapeutic developments. Atherosclerosis is a complex, multistage disease whereby perturbed lipid metabolism leads to cholesterol accumulation into the vascular walls and plaque formation. Generation of apoE-/- and LDLR-/- atherosclerosis mouse models opened the avenue for investigating the mechanisms of action for specific molecules. We focus herein on the involvement of non-lipoprotein receptors in atherogenesis, as revealed by their total or site-specific ablation in the aforementioned murine models. The receptors reviewed span a broad range, from molecules related to lipid metabolism (adiponectin receptors) to molecules whose connection with atherogenesis is less obvious (cannabinoid receptors). We also outline cross-transplantation studies which allowed uncoupling the lipid modulating effects from the inflammatory ones. For certain receptors, since knockouts were unavailable, pharmacological data are presented instead. We emphasize the contribution of the receptors to the pathology, based on functional criteria, such as oxidative stress, immune response, inflammation, angiogenesis. Controversial aspects regarding the pro- or anti- atherogenic activity of some receptors are highlighted. We assume these discrepancies are due to the experimental setup, animal models used, tissue-specific action, various isoforms analyzed, divergent signaling or cross-talk between metabolic and immune pathways. Understanding the influences of cellular receptors in the progression of atherosclerosis allows their modulation towards an antiatherogenic phenotype. The experimental studies in animal models were in some cases successfully extrapolated to humans leading to atheroma reduction, and we expect this to occur even to a greater extent, based on the newest achievements.

Ectonucleotide pyrophosphatase/phosphodiesterase 2 (ENPP2) also known as Autotaxin, is a secreted lysophospholipase D, which hydrolyzes lysophosphatidylcholine (LPC) into Lysophosphatidic acid (LPA). LPA is the bioactive product of ENPP2 enzyme, which induces diverse signalling pathways via six LPA-G-protein coupled receptors (GPCRs). ENPP2 is an essential protein for normal development and its altered expression is associated with various human diseases. Cellular ENPP2 silencing results in lethality at the embryonic stage in mice. Initially, it is identified as an autocrine factor in melanoma cells. Different research groups are currently exploring to understand the multifaceted role of ENPP2 in various processes such as embryonic and neural development, migration, invasion, differentiation, proliferation, angiogenesis, and survival. Altered expression of ENPP2 is also associated with various diseases like inflammation, cancer, fibrosis, rheumatoid arthritis and neural defects. In this article, we have summarized structural aspects of ENPP2 and biochemical functions associated with its diverse cellular roles in various human diseases including cancer and Alzheimer’s disease (AD). In addition, keeping in view and advocating findings, a note on various phytochemicals and synthetic inhibitors, which are currently explored as therapeutic agents targeting functions of ENPP2 for the treatment of various human diseases is also presented.

The protein serine/threonine phosphatases-1 and -2A are major cellular phosphatases, playing a fundamental role in organisms from prokaryotes to eukaryotes. They contribute to 90% dephosphorylation in eukaryote proteins. In the eye, both phosphatases are highly expressed and display important functions in regulating normal eye development. Moreover, they are implicated in pathogenesis through modulation of stress-induced apoptosis. Here we review the recent progresses on these aspects.

Homeobox (HOX) transcript antisense RNA (HOTAIR), a long nuclear-retained noncoding RNA (lncRNA), is overexpressed in a variety of human cancers. Increasing evidence shows that HOTAIR plays a vital role in cancer initiation and progression by affecting cell cycle progress, apoptosis and invasion. However, whether HOTAIR serves as a target of therapeutic potential and the underlying mechanism in head and neck squamous cell carcinoma (HNSCC) is still unclear. Thus, we employed a HOTAIR specific siRNA to deplete its expression in two human HNSCC cell lines, Tca8113 and Tscca. The flow cytometry (FCM) analysis showed that HOTAIR depletion induced tumor cell apoptosis in vitro. JC-1 probe examination showed that the mitochondrial membrane potential was changed significantly by HOTAIR blockage. Mitochondrial calcium uptake 1(MICU1) dependent cell death was induced by HOTAIR depletion. Protein expression analysis indicated that mitochondrial related cell death pathway (Bcl-2, BAX, Caspase-3, Cleaved Caspase-3, Cytochrome c) involved in HOTAIR dependent apoptosis process. Moreover, a Tscca derived xenograft tumor model was employed to further validate that injection of HOTAIR siRNA inhibited tumor growth. In summary, we suggested that HOTAIR inhibition could be developed as a new therapeutic in HNSCC treatments.

Burkholderia pseudomallei is the causative agent of melioidosis and represents a potential bioterrorism threat. In this study, the transcriptomic responses of B. pseudomallei infection of a human macrophage cell model were investigated using whole-genome microarrays. Gene expression profiles were compared between infected THP-1 human monocytic leukemia cells with or without treatment with Daboia russelli russelli daboiatoxin (DRRDbTx) or ceftazidime (antibiotic control). Microarray analyses of infected and treated cells revealed differential upregulation of various inflammatory genes such as interleukin-1 (IL-1), IL-6, tumor necrosis factor-alpha (TNF-α), cyclooxygenase (COX-2), vascular endothelial growth factor (VEGF), chemokine C-X-C motif ligand 4 (CXCL4), transcription factor p65 (NF-kB); and several genes involved in immune and stress responses, cell cycle, and lipid metabolism. Moreover, following DRR-DbTx treatment of infected cells, there was enhanced expression of the tolllike receptor 2 (TLR-2) mediated signaling pathway involved in recognition and initiation of acute inflammatory responses. Importantly, we observed that highly inflammatory cytokine gene responses were similar in infected cells exposed to DRR-DbTx or ceftazidime after 24 h. Additionally, there were increased transcripts associated with cell death by caspase activation that can promote host tissue injury. In summary, the transcriptional responses during B. pseudomallei infection of macrophages highlight a broad range of innate immune mechanisms that are activated within 24 h post-infection. These data provide insights into the transcriptomic kinetics following DRR-DbTx treatment of human macrophages infected with B. pseudomallei.

Lipodystrophy is a common complication in HIV-infected patients taking highly active antiretroviral therapy. Its early diagnosis is crucial for timely modification of antiretroviral therapy. We hypothesize that mitochondrial DNA in plasma may be a potential marker of LD in HIV-infected individuals. In this study, we compared plasma mitochondrial DNA levels in HIV-infected individuals and non-HIV-infected individuals to investigate its potential diagnostic value. Total plasma DNA was extracted from 67 HIV-infected patients at baseline and 12, 24 and 30 months after initiating antiretroviral therapy. Real-time quantitative PCR was used to determine the mitochondrial DNA levels in plasma. Lipodystrophy was defined by the physician-assessed presence of lipoatrophy or lipohypertrophy in one or more body regions. The mitochondrial DNA levels in plasma were significantly higher at baseline in HIV-infected individuals than in non-HIV-infected individuals (p<0.05). At month 30, 33 out of 67 patients (49.2%) showed at least one sign of lipodystrophy. The mean plasma mitochondrial DNA levels in lipodystrophy patients were significantly higher compared to those without lipodystrophy at month 24 (p<0.001). The receiver operating curve analysis demonstrated that using plasma mitochondrial DNA level (with cut-off value >5.09 log10 copies/ml) as a molecular marker allowed identification of patients with lipodystrophy with a sensitivity of 64.2% and a specificity of 73.0%. Our data suggest that mitochondrial DNA levels may help to guide therapy selection with regards to HIV lipodystrophy risk.

Alzheimer’s disease (AD) is a neurodegenerative disorder which mainly affects elderly population. MicroRNAs (miRNA) are small RNA molecules that fine-tune gene expression at posttranscriptional level and exert important functions in AD. MicroRNA-124 (miR-124) is a kind of miRNA abundantly expressed in the central nervous system. It is highly conserved from Caenorhabditis elegans to humans. However, its function in AD is still elusive. In this study, we found miR-124 was significantly down-regulated in AD flies. miR-124 mutant flies showed impaired climbing ability and shortened lifespan. In contrast, miR-124 expression rescued locomotive defects of AD flies. Using microarray analysis to test gene expression profiles of miR-124 mutant flies, we found that Notch signaling pathway was potentially targeted by miR-124. Further experiments showed that miR-124 regulated Notch ligand Delta expression by acting on specific site of Delta 3'UTR. In addition, reduced Delta expression by RNA interference extended lifespan and ameliorated learning defects of AD Drosophila. Notch inhibitor DAPT could also alleviate AD phenotypes, which confirmed our findings. In conclusion, our study indicates that miR-124 plays neuroprotective roles in AD Drosophila by targeting Delta in Notch signaling pathway, which helps further our understanding of miRNAs in the molecular pathology of AD.

Aberrant activation of Wnt/β-catenin signaling pathway is commonly associated to cancer development. However, molecular mechanisms controlling Wnt/β-catenin signaling pathway have been clarified only in part. Here, we show that β-catenin is differently modulated in patients with multiple sclerosis (MS), displaying that different pharmacological treatments used for clinical MS management cause different nuclear expression levels of β-catenin. Proteins extracted by peripheral blood mononuclear cells were assessed to evaluate the western blot expression levels of β-catenin. Analyzing our results, we realized that β-catenin is totally inhibited by Natalizumab and could have a role in MS management. This could offer new promising studies focused on the possible therapeutic control of β-catenin translocation.