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Volume 3, Issue 2, pp. 29 - 69, February 2019

Issue cover
Cover: This month in Cell Stress: Myeloid-derived suppressor cells in therapeutic control of glioblastoma. Image depicts glioblastoma multiforme - magnetic resonance imaging (T1 axial) with contrast agent. Credit: Hellerhoff CC BY 3.0 license, from Wikimedia Commons. Image modified by Cell Stress. The cover is published under the CC BY 3.0 license. Enlarge issue cover

Viewpoint

Could de-stressing the brain be the solution for long-term weight loss?

Florian Seyfried and Mohammed K. Hankir

page 29-37 | 10.15698/cst2019.02.174 | Full text | PDF | Abstract

The obese brain is stressed and inflamed. This is mainly at the level of neurons and glial cells in the hypothalamus: a brain region where the adipokine leptin acts to control feeding and body weight. Relieving hypothalamic neuronal endoplasmic reticulum (ER) stress with the natural small molecule drugs celastrol or withaferin-A reverses the leptin resistance commensurate with obesity, producing a degree of weight loss found only with bariatric surgery. Here, recent evidence from rodent models of vertical sleeve gastrectomy (VSG) is brought to the fore which suggests that this particular bariatric surgical procedure may work in a similar fashion to celastrol and withaferin-A alongside remedying hypothalamic inflammation and gliosis. Thus, restoring and preserving healthy hypothalamic neuronal and glial cell function, be it by pharmacological or surgical means, ensures a negative energy balance in an environment constructed to promote a one – possibly through re-establishing communication between adipose tissue and the brain.

Reviews

R-loops: formation, function, and relevance to cell stress

David F Allison and Gang Greg Wang

page 38-47 | 10.15698/cst2019.02.175 | Full text | PDF | Abstract

Exposure of genomic, single-stranded DNA (ssDNA) during transcription and replication creates opportunities for the formation of inappropriate secondary structures. Cells manage this exposure by using topoisomerases and helicases to reduce the inherent topological stress that arises from unwinding the double helix and by coating ssDNA with protective protein complexes. Interestingly, specific DNA-RNA hybrids, known as R-loops, form during transcription and exist in homeostasis throughout the genomes of prokaryotes and eukaryotes. These hybrids nucleate from guanine rich clusters in the template strand and extend across GC rich spans of transcribed genes. In vivo regulatory functions have evolved from R-loops, including regulation of gene expression and telomere lengthening. However, they also exist as a form of stress, particularly when replication forks collide with the transcription machinery. New methodologies and models are being developed to delineate the biology of R-loops, including those related to cell stress-based diseases like cancer. As accumulation of R-loops is associated with disease, targeting molecular pathways that regulate their formation or removal could provide new avenues for therapeutic intervention. This review covers recent understandings of the molecular basis for R-loop formation, removal, and biological outcomes in the context of cellular stress.

Metabolic and functional reprogramming of myeloid-derived suppressor cells and their therapeutic control in glioblastoma

Woong-Jai Won, Jessy S. Deshane, Jianmei W. Leavenworth, Claudia R. Oliva and Corinne E. Griguer

page 48-65 | 10.15698/cst2019.02.176 | Full text | PDF | Abstract

Glioblastoma, also known as glioblastoma multiforme, is the most common and deadliest form of high-grade malignant brain tumors with limited available treatments. Within the glioblastoma tumor microenvironment (TME), tumor cells, stromal cells, and infiltrating immune cells continuously interact and exchange signals through various secreted factors including cytokines, chemokines, growth factors, and metabolites. Simultaneously, they dynamically reprogram their metabolism according to environmental energy demands such as hypoxia and neo-vascularization. Such metabolic reprogramming can determine fates and functions of tumor cells as well as immune cells. Ultimately, glioma cells in the TME transform immune cells to suppress anti-tumor immune cells such as T, natural killer (NK) cells, and dendritic cells (DC), and evade immune surveillance, and even to promote angiogenesis and tumor metastasis. Glioma-associated microglia/macrophages (GAMM) and myeloid-derived suppressor cells (MDSC) are most abundantly recruited and expanded myeloid lineage cells in glioblastoma TME and mainly lead to immunosuppression. In this review, of myeloid cells we will focus on MDSC as an important driver to induce immunosuppression in glioblastoma. Here, we review current literature on immunosuppressive functions and metabolic reprogramming of MDSCs in glioblastoma and discuss their metabolic pathways as potential therapeutic targets to improve current incurable glioblastoma treatment.

Microreviews

Development of novel methods that monitor necroptosis and the release of DAMPs at the single cell resolution

Hiroyasu Nakano, Shin Murai, Yoshifumi Yamaguchi, Yoshitaka Shirasaki, Osamu Nakabayashi and Soh Yamazaki

page 66-69 | 10.15698/cst2019.02.177 | Full text | PDF | Abstract

Necroptosis is a regulated form of necrosis that depends on receptor-interacting protein kinase (RIPK)3 and mixed lineage kinase domain-like protein (MLKL). While danger-associated molecular pattern (DAMP)s are released from dead cells and involved in various pathological conditions, the mechanisms underlying regulation of the release of DAMPs are not fully understood. Apoptosis and pyroptosis can be detected by several types of sensors such as Forster resonance energy transfer (FRET) biosensors, termed SCAT1 (a sensor for caspase 1 activation based on FRET) and SCAT3, respectively. These sensors have provided better understanding of pyroptosis and apoptosis in vitro and in vivo. However, there have been no biosensors to monitor necroptosis. Development of a FRET biosensor that monitors necroptosis and generation of transgenic mice expressing such FRET biosensor might be useful to understand the mechanisms underlying the execution of necroptosis and also the consequences of necroptosis in vivo. In our recent study (Nat Commun, 9(1):4457), we developed a FRET biosensor for necroptosis, termed SMART (a sensor for MLKL activation by RIPK3 based on FRET). SMART is composed of a fragment of MLKL and monitors necroptosis, but not apoptosis or necrosis. Moreover, we recently developed a platform called Live-Cell Imaging for Secretion activity (LCI-S) to monitor protein secretion at the single cell level. This platform has enabled us to monitor the release of HMGB1 (High Mobility Group Box 1), one of the DAMPs, at the single cell level and reveals two different modes of the release of HMGB1 from necroptotic cells.

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