Exploring the gut microbiota and its potential as a biomarker in gliomas.

Gut microbiome alterations are associated with various cancers including brain tumours such as glioma and glioblastoma. The gut communicates with the brain via a bidirectional pathway known as the gut-brain axis (GBA) which is essential for maintaining homeostasis. The gut microbiota produces many metabolites including short chain fatty acids (SCFAs) and essential amino acids such as glutamate, glutamine, arginine and tryptophan. Through the modulation of these metabolites the gut microbiome is able to regulate several functions of brain cells, immune cells and tumour cells including DNA methylation, mitochondrial function, the aryl hydrocarbon receptor (AhR), T-cell proliferation, autophagy and even apoptosis. Here, we summarise current findings on gut microbiome with respect to brain cancers, an area of research that is widely overlooked. Several studies investigated the relationship between gut microbiota and brain tumours. However, it remains unclear whether the gut microbiome variation is a cause or product of cancer. Subsequently, a biomarker panel was constructed for use as a predictive, prognostic and diagnostic tool with respect to multiple cancers including glioma and glioblastoma multiforme (GBM). This review further presents the intratumoural microbiome, a fascinating microenvironment within the tumour as a possible treatment target that can be manipulated to maximise effectiveness of treatment via personalised therapy. Studies utilising the microbiome as a biomarker and therapeutic strategy are necessary to accurately assess the effectiveness of the gut microbiome as a clinical tool with respect to brain cancers.

A chronic moderate methionine administration induced hyperhomocysteinemia associated with cardiovascular disease phenotype in the sand rat Psammomys obesus.

INTRODUCTION: Cardiovascular diseases were defined as coronary artery, cerebrovascular, or peripheral arterial disease. Hyperhomocysteinemia (Hhcy) is an independent risk factor of cardiovascular diseases, including atherosclerosis. Our previous studies demonstrated the involvement of Hhcy in cardiovascular remodeling in the sand rat Psammomys obesus. MATERIAL AND METHODS: An experimental Hhcy was induced, in the sand rat Psammomys obesus, by a daily intraperitoneal injection of 70 mg/kg of methionine for a total duration of 6 months. The impact of Hhcy on the cellular and matrix structures of the heart, aorta and liver was analyzed using histological techniques. Additionally we treatedprimary cultures of aortic smooth muscle cells (SMCs) with high concentration of methionine to investigate the effects of methionine at the cellular level. RESULTS: A moderate Hhcy induced a significant increase in the extracellular matrix components particularly collagens which accumulated in the interstitial and perivascular spaces in the studied organs indicating a developing fibrosis. A liver steatosis was also observed following methionine treatment. Further analysis of the aorta showed that Hhcy also induced vascular alterations including SMCs reorientation and proliferation associated with aneurysm formation. CONCLUSIONS: Our results show for the first time that Hhcy can induce a cardiovascular and liver diseases phenotype in Psammomys obesus, a species previously shown to be a good model for the studies of diabetes and other metabolism-related pathologies.

AßPP-induced UPR Transcriptomic Signature of Glial Cells to Oxidative Stress as an Adaptive Mechanism to Preserve Cell Function and Survival.

BACKGROUND: Alzheimer's disease (AD) and age-related macular degeneration (AMD) present similarities, particularly with respect to oxidative stress, including production of 4-Hydroxy-2- nonenal (HNE). AMD has been named the AD in the eye. The Müller cells (MC) function as a principal glia of the retina and maintain water/potassium, glutamate homeostasis and redox status. Any MC dysfunction results in retinal neurodegeneration. OBJECTIVES: We investigated the effects of HNE in human MC. RESULTS: HNE induced an increase of the reactive oxygen species associated with mitochondrial dysfunction and apoptosis. HNE induced endoplasmic reticulum (ER) stress (upregulation of GRP78/Bip, and the proapoptotic factor, CHOP). HNE also impaired expression of genes controlling potassium homeostasis (KCNJ10), glutamate detoxification (GS), and the visual cycle (RLBP1). MC adaptive response to HNE included upregulation of amyloid-ß protein precursor (AßPP). To determine the role of AßPP, we overexpressed AßPP in MC. Overexpression of AßPP induced strong antioxidant and anti-ER stress (PERK downregulation and GADD34 upregulation) responses accompanied by activation of the prosurvival branch of the unfolded protein response. It was also associated with upregulation of major genes involved in MC-controlled retinal homeostasis (KCNJ10, GS, and RLBP1) and protection against HNE-induced apoptosis. Therefore, AßPP is an ER and oxidative stress responsive molecule, and is able to stimulate the transcription of major genes involved in MC functions impaired by HNE. CONCLUSION: Our study suggests that targeting oxidative and ER stress might be a potential therapeutic strategy against glia impairment in AMD and AD, in light of the common features between the two pathologies.

The ciliary marginal zone of the zebrafish retina: clonal and time-lapse analysis of a continuously growing tissue.

Clonal analysis is helping us understand the dynamics of cell replacement in homeostatic adult tissues (Simons and Clevers, 2011). Such an analysis, however, has not yet been achieved for continuously growing adult tissues, but is essential if we wish to understand the architecture of adult organs. The retinas of lower vertebrates grow throughout life from retinal stem cells (RSCs) and retinal progenitor cells (RPCs) at the rim of the retina, called the ciliary marginal zone (CMZ). Here, we show that RSCs reside in a niche at the extreme periphery of the CMZ and divide asymmetrically along a radial (peripheral to central) axis, leaving one daughter in the peripheral RSC niche and the other more central where it becomes an RPC. We also show that RPCs of the CMZ have clonal sizes and compositions that are statistically similar to progenitor cells of the embryonic retina and fit the same stochastic model of proliferation. These results link embryonic and postembryonic cell behaviour, and help to explain the constancy of tissue architecture that has been generated over a lifetime.

Distinct effects of inflammation on gliosis, osmohomeostasis, and vascular integrity during amyloid beta-induced retinal degeneration.

In normal retinas, amyloid-ß (Aß) accumulates in the subretinal space, at the interface of the retinal pigment epithelium, and the photoreceptor outer segments. However, the molecular and cellular effects of subretinal Aß remain inadequately elucidated. We previously showed that subretinal injection of Aß(1-42) induces retinal inflammation, followed by photoreceptor cell death. The retinal Müller glial (RMG) cells, which are the principal retinal glial cells, are metabolically coupled to photoreceptors. Their role in the maintenance of retinal water/potassium and glutamate homeostasis makes them important players in photoreceptor survival. This study investigated the effects of subretinal Aß(1-42) on RMG cells and of Aß(1-42)-induced inflammation on retinal homeostasis. RMG cell gliosis (upregulation of GFAP, vimentin, and nestin) on day 1 postinjection and a proinflammatory phenotype were the first signs of retinal alteration induced by Aß(1-42). On day 3, we detected modifications in the protein expression patterns of cyclooxygenase 2 (COX-2), glutamine synthetase (GS), Kir4.1 [the inwardly rectifying potassium (Kir) channel], and aquaporin (AQP)-4 water channels in RMG cells and of the photoreceptor-associated AQP-1. The integrity of the blood-retina barrier was compromised and retinal edema developed. Aß(1-42) induced endoplasmic reticulum stress associated with sustained upregulation of the proapoptotic factors of the unfolded protein response and persistent photoreceptor apoptosis. Indomethacin treatment decreased inflammation and reversed the Aß(1-42)-induced gliosis and modifications in the expression patterns of COX-2, Kir4.1, and AQP-1, but not of AQP-4 or GS. Nor did it improve edema. Our study pinpoints the adaptive response to Aß of specific RMG cell functions.

CCR2/CCL2-mediated inflammation protects photoreceptor cells from amyloid-ß-induced apoptosis.

Age-related macular degeneration is characterized by the formation of drusen containing amyloid-ß (Aß) and the degeneration of photoreceptors. To explore the largely unknown role of Aß in the retina, we investigated the effects on photoreceptors of the oligomeric form of Aß(1-42). Subretinal injection of the Aß peptide induced misplaced expression of recoverin and synaptophysin in the photoreceptors, oxidative stress in their inner and outer segments, and finally apoptosis. Aß did not induce cell death in purified photoreceptor cell cultures, but did so in retinal cell cultures, thereby suggesting that the cellular environment plays a role in Aß-induced photoreceptor apoptosis. Subretinal injection of Aß was followed by activation and migration of microglial cells and then by photoreceptor apoptosis. Microglial cells phagocytosed rhodopsin-containing debris and Aß in the subretinal space. Quantitative RT-PCR allowed us to identify a specific gene expression profile associated with the Aß-induced progression of retinal degeneration and consistent with oxidative stress, inflammation, and an apoptotic program. The gene most highly upregulated in Aß-injected retinas was that for the chemokine CCL2, and its absence or that of its cognate receptor CCR2 greatly reduced migration of activated microglial cells to the site of retinal injury and profoundly worsened photoreceptor degeneration and disorganization of the retinal pigment epithelium in Aß-injected retinas. Our study pinpoints the roles of Aß and of CCL2/CCR2 axis-dependent inflammation in photoreceptor apoptosis.

Amyloid-beta(1-42) alters structure and function of retinal pigmented epithelial cells.

Age-related macular degeneration (AMD) is characterized by the formation of drusen, extracellular deposits associated with atrophy of the retinal pigmented epithelium (RPE), disturbance of the transepithelial barrier and photoreceptor death. Amyloid-beta (Abeta) is present in drusen but its role during AMD remains unknown. This study investigated the in vitro and in vivo effects of the oligomeric form of Abeta(1-42) - OAbeta(1-42) - on RPE and found that it reduced mitochondrial redox potential and increased the production of reactive oxygen species, but did not induce apoptosis in RPE cell cultures. It also disorganized the actin cytoskeleton and halved occludin expression, markedly decreasing attachment capacity and abolishing the selectivity of RPE cell transepithelial permeability. Antioxidant pretreatment partially reversed the effects of OAbeta(1-42) on mitochondrial redox potential and transepithelial permeability. Subretinally injected OAbeta(1-42) induced pigmentation loss and RPE hypertrophy but not RPE cell apoptosis in C57BL/6 J mice. Rapid OAbeta(1-42)-induced disorganization of cytoskeletal actin filaments was accompanied by decreased RPE expression of the tight junction proteins occludin and zonula occludens-1 and of the visual cycle proteins cellular retinaldehyde-binding protein and RPE65. The number of photoreceptors decreased by half within a few days. Our study pinpoints the role of Abeta in RPE alterations and dysfunctions leading to retinal degeneration and suggests that targeting Abeta may help develop selective methods for treating diseases involving retinal degeneration, such as AMD.