Induction of unfolded protein response during neuronal induction of rat bone marrow stromal cells and mouse embryonic stem cells

Unraveling the crucial role of UPR pathway in rat brain development

The development of the central nervous system (CNS) is essential for the growth of an organism. The unfolded protein response (UPR) plays an important role in the occurrence and progression of CNS. Hence, to identify the changing pattern of UPR signaling molecules and their related target molecules is extremely important. Immunohistochemical (IHC) analysis was conducted to assess the expression of NeuN, a neuronal marker, within the M1 region of the cerebral cortex of wild-type (WT) rats aged different weeks. The results showed a progressive increase in the expression of NeuN in correlation with the weekly age progression of the rats. Concurrently, in the CA3 region of the hippocampus and the S1Tr area of the cerebral cortex, the levels of UPR key molecules, GRP78 and XBP1s, exhibited an upward trend in accordance with the rats' weekly age. Western blot analysis revealed an inclination toward an increase in the expression of endoplasmic reticulum (ER) stress -associated key molecules, including GRP78, ATF6, XBP1, eIF-2α, CHOP and phosphorylated eIF-2α (p-eIF-2α). Additionally, reverse transcription quantitative polymerase chain reaction (RT-qPCR) demonstrated a positive correlation between the expression of CHOP and the weekly age of the rats. These findings demonstrate that UPR signaling pathway has a certain pattern of change in the development of rat brain, suggesting that the UPR signaling pathway may play an important role in the development of the CNS, and suggesting that an applicability of XBP1s as a therapeutic candidate for childhood autism.

The unfolded protein response machinery in glioblastoma genesis, chemoresistance and as a druggable target

BACKGROUND

The role of the unfolded protein response (UPR) has been progressively unveiled over the last decade and several studies have investigated its implication in glioblastoma (GB) development. The UPR restores cellular homeostasis by triggering the folding and clearance of accumulated misfolded proteins in the ER consecutive to endoplasmic reticulum stress. In case it is overwhelmed, it induces apoptotic cell death. Thus, holding a critical role in cell fate decisions.

METHODS

This article, reviews how the UPR is implicated in cell homeostasis maintenance, then surveils the evidence supporting the UPR involvement in GB genesis, progression, angiogenesis, GB stem cell biology, tumor microenvironment modulation, extracellular matrix remodeling, cell fate decision, invasiveness, and grading. Next, it concurs the evidence showing how the UPR mediates GB chemoresistance-related mechanisms.

RESULTS

The UPR stress sensors IRE1, PERK, and ATF6 with their regulator GRP78 are upregulated in GB compared to lower grade gliomas and normal brain tissue. They are activated in response to oncogenes and are implicated at different stages of GB progression, from its genesis to chemoresistance and relapse. The UPR arms can be effectors of apoptosis as mediators or targets.

CONCLUSION

Recent research has established the role of the UPR in GB pathophysiology and chemoresistance. Targeting its different sensors have shown promising in overcoming GB chomo- and radioresistance and inducing apoptosis.

Understanding the Unfolded Protein Response (UPR) Pathway: Insights into Neuropsychiatric Disorders and Therapeutic Potentials

The Unfolded Protein Response (UPR) serves as a critical cellular mechanism dedicated to maintaining protein homeostasis, primarily within the endoplasmic reticulum (ER). This pathway diligently responds to a variety of intracellular indicators of ER stress with the objective of reinstating balance by diminishing the accumulation of unfolded proteins, amplifying the ER's folding capacity, and eliminating slow-folding proteins. Prolonged ER stress and UPR irregularities have been linked to a range of neuropsychiatric disorders, including major depressive disorder, bipolar disorder, and schizophrenia. This review offers a comprehensive overview of the UPR pathway, delineating its activation mechanisms and its role in the pathophysiology of neuropsychiatric disorders. It highlights the intricate interplay within the UPR and its profound influence on brain function, synaptic perturbations, and neural developmental processes. Additionally, it explores evolving therapeutic strategies targeting the UPR within the context of these disorders, underscoring the necessity for precision and further research to effective treatments. The research findings presented in this work underscore the promising potential of UPR-focused therapeutic approaches to address the complex landscape of neuropsychiatric disorders, giving rise to optimism for improving outcomes for individuals facing these complex conditions.

Patient derived model of UBA5-associated encephalopathy identifies defects in neurodevelopment and highlights potential therapies

UBA5 encodes for the E1 enzyme of the UFMylation cascade, which plays an essential role in ER homeostasis. The clinical phenotypes of UBA5-associated encephalopathy include developmental delays, epilepsy and intellectual disability. To date, there is no humanized neuronal model to study the cellular and molecular consequences of UBA5 pathogenic variants. We developed and characterized patient-derived cortical organoid cultures and identified defects in GABAergic interneuron development. We demonstrated aberrant neuronal firing and microcephaly phenotypes in patient-derived organoids. Mechanistically, we show that ER homeostasis is perturbed along with exacerbated unfolded protein response pathway in cells and organoids expressing UBA5 pathogenic variants. We also assessed two gene expression modalities that augmented UBA5 expression to rescue aberrant molecular and cellular phenotypes. Our study provides a novel humanized model that allows further investigations of UBA5 variants in the brain and highlights novel systemic approaches to alleviate cellular aberrations for this rare, developmental disorder.

Mitochondrial Bcl-xL promotes brain synaptogenesis by controlling non-lethal caspase activation

Non-lethal caspase activation (NLCA) has been linked to neurodevelopmental processes. However, how neurons control NLCA remains elusive. Here, we focused on Bcl-xL, a Bcl-2 homolog regulating caspase activation through the mitochondria. We generated a mouse model, referred to as ER-xL, in which Bcl-xL is absent in the mitochondria, yet present in the endoplasmic reticulum. Unlike bclx knockout mice that died at E13.5, ER-xL mice survived embryonic development but died post-partum because of altered feeding behavior. Enhanced caspase-3 activity was observed in the brain and the spinal cord white matter, but not the gray matter. No increase in cell death was observed in ER-xL cortical neurons, suggesting that the observed caspase-3 activation was apoptosis-independent. ER-xL neurons displayed increased caspase-3 activity in the neurites, resulting in impaired axon arborescence and synaptogenesis. Together, our findings suggest that mitochondrial Bcl-xL finely tunes caspase-3 through Drp-1-dependent mitochondrial fission, which is critical to neural network design.

Cell Rearrangement and Oxidant/Antioxidant Imbalance in Huntington's Disease

Huntington's Disease (HD) is a hereditary neurodegenerative disorder caused by the expansion of a CAG triplet repeat in the HTT gene, resulting in the production of an aberrant huntingtin (Htt) protein. The mutant protein accumulation is responsible for neuronal dysfunction and cell death. This is due to the involvement of oxidative damage, excitotoxicity, inflammation, and mitochondrial impairment. Neurons naturally adapt to bioenergetic alteration and oxidative stress in physiological conditions. However, this dynamic system is compromised when a neurodegenerative disorder occurs, resulting in changes in metabolism, alteration in calcium signaling, and impaired substrates transport. Thus, the aim of this review is to provide an overview of the cell's answer to the stress induced by HD, focusing on the role of oxidative stress and its balance with the antioxidant system.

Effect of Pre-Induced Mesenchymal Stem Cell-Coated Cellulose/Collagen Nanofibrous Nerve Conduit on Regeneration of Transected Facial Nerve

(1) Objective: In order to evaluate the effect of a pre-induced mesenchymal stem cell (MSC)-coated cellulose/collagen nanofibrous nerve conduit on facial nerve regeneration in a rat model both in vitro and in vivo. (2) Methods: After fabrication of the cellulose/collagen nanofibrous conduit, its lumen was coated with either MSCs or pre-induced MSCs. The nerve conduit was then applied to the defective main trunk of the facial nerve. Rats were randomly divided into three treatment groups (n = 10 in each): cellulose/collagen nanofiber (control group), cellulose/collagen nanofiber/MSCs (group I), and cellulose/collagen nanofiber/pre-induced MSCs (group II). (3) Results Fibrillation of the vibrissae of each group was observed, and action potential threshold was compared 8 weeks post-surgery. Histopathological changes were also observed. Groups I and II showed better recovery of vibrissa fibrillation than the control group. (4) Conclusions: Group II, treated with the pre-induced MSC-coated cellulose/collagen nanofibrous nerve conduit, showed the highest degree of recovery based on functional and histological evaluations.

Impact of ER Stress and ER-Mitochondrial Crosstalk in Huntington's Disease

Accumulation of misfolded proteins is a common phenomenon of several neurodegenerative diseases. The misfolding of proteins due to abnormal polyglutamine (PolyQ) expansions are linked to the development of PolyQ diseases including Huntington's disease (HD). Though the genetic basis of PolyQ repeats in HD remains prominent, the primary molecular basis mediated by PolyQ toxicity remains elusive. Accumulation of misfolded proteins in the ER or disruption of ER homeostasis causes ER stress and activates an evolutionarily conserved pathway called Unfolded protein response (UPR). Protein homeostasis disruption at organelle level involving UPR or ER stress response pathways are found to be linked to HD. Due to dynamic intricate connections between ER and mitochondria, proteins at ER-mitochondria contact sites (mitochondria associated ER membranes or MAMs) play a significant role in HD development. The current review aims at highlighting the most updated information about different UPR pathways and their involvement in HD disease progression. Moreover, the role of MAMs in HD progression has also been discussed. In the end, the review has focused on the therapeutic interventions responsible for ameliorating diseased states via modulating either ER stress response proteins or modulating the expression of ER-mitochondrial contact proteins.

The unfolded protein response as regulator of cancer stemness and differentiation: Mechanisms and implications for cancer therapy

The unfolded protein response (UPR) is an adaptive mechanism that regulates protein and cellular homeostasis. Three endoplasmic reticulum (ER) membrane localized stress sensors, IRE1, PERK and ATF6, coordinate the UPR in order to maintain ER proteostasis and cell survival, or induce cell death when homeostasis cannot be restored. However, recent studies have identified alternative functions for the UPR in developmental biology processes and cell fate decisions under both normal and cancerous conditions. In cancer, increasing evidence points towards the involvement of the three UPR sensors in oncogenic reprogramming and the regulation of tumor cells endowed with stem cell properties, named cancer stem cells (CSCs), that are considered to be the most malignant cells in tumors. Here we review the reported roles and underlying molecular mechanisms of the three UPR sensors in regulating stemness and differentiation, particularly in solid tumor cells, processes that have a major impact on tumor aggressiveness. Mainly PERK and IRE1 branches of the UPR were found to regulate CSCs and tumor development and examples are provided for breast cancer, colon cancer and aggressive brain tumors, glioblastoma. Although the underlying mechanisms and interactions between the different UPR branches in regulating stemness in cancer need to be further elucidated, we propose that PERK and IRE1 targeted therapy could inhibit self-renewal of CSCs or induce differentiation that is predicted to have therapeutic benefit. For this, more specific UPR modulators need to be developed with favorable pharmacological properties that together with patient stratification will allow optimal evaluation in clinical studies.

Protein quality control of cell stemness

Protein quality control (PQC) systems play essential roles in the recognition, refolding and clearance of aberrant proteins, thus ensuring cellular protein homeostasis, or proteostasis. Especially, continued proliferation and differentiation of stem cells require a high rate of translation; therefore, accurate PQC systems are essential to maintain stem cell function. Growing evidence suggested crucial roles of PQC systems in regulating the stemness and differentiation of stem cells. This review focuses on current knowledge regarding the components of the proteostasis network in stem cells, and the importance of proteostasis in maintaining stem cell identity and regenerative functions. A complete understanding of this process might uncover potential applications in aging intervention and aging-related diseases.

The Role of Stress Granules in the Neuronal Differentiation of Stem Cells

creativecommons.org/licenses/by-nc-sa/3.0/. Cells assemble stress granules (SGs) to protect their RNAs from exposure to harmful chemical reactions induced by environmental stress. These SGs release RNAs, which resume translation once the stress is relieved. During stem cell differentiation, gene expression is altered to allow cells to adopt various functional and morphological features necessary to differentiate. This process induces stress within a cell, and cells that cannot overcome this stress die. Here, we investigated the role of SGs in the progression of stem cell differentiation. SGs aggregated during the neuronal differentiation of human bone marrow-mesenchymal stem cells, and not in cell lines that could not undergo differentiation. SGs were observed between one and three hours post-induction; RNA translation was restrained at the same time. Immediately after disassembly of SGs, the expression of the neuronal marker neurofilament-M (NFM) gradually increased. Assembled SGs that persisted in cells were exposed to salubrinal, which inhibited the dephosphorylation of eukaryotic translation initiation factor 2 subunit 1 (eIF2α), and in eIF2α/S51D mutant cells. When eIF2α/S51A mutant cells differentiated, SGs were not assembled. In all experiments, the disruption of SGs was accompanied by delayed NF-M expression and the number of neuronally differentiated cells was decreased. Decreased differentiation was accompanied by decreased cell viability, indicating the necessity of SGs for preventing cell death during neuronal differentiation. Collectively, these results demonstrate the essential role of SGs during the neuronal differentiation of stem cells.

Establishment and validation of an endoplasmic reticulum stress reporter to monitor zebrafish ATF6 activity in development and disease

Induction of endoplasmic reticulum (ER) stress is associated with diverse developmental and degenerative diseases. Modified ER homeostasis causes activation of conserved stress pathways at the ER called the unfolded protein response (UPR). ATF6 is a transcription factor activated during ER stress as part of a coordinated UPR. ATF6 resides at the ER and, upon activation, is transported to the Golgi apparatus, where it is cleaved by proteases to create an amino-terminal cytoplasmic fragment (ATF6f). ATF6f translocates to the nucleus to activate transcriptional targets. Here, we describe the establishment and validation of zebrafish reporter lines for ATF6 activity. These transgenic lines are based on a defined and multimerized ATF6 consensus site, which drives either eGFP or destabilized eGFP, enabling dynamic study of ATF6 activity during development and disease. The results show that the reporter is specific for the ATF6 pathway, active during development and induced in disease models known to engage UPR. Specifically, during development, ATF6 activity is highest in the lens, skeletal muscle, fins and gills. The reporter is also activated by common chemical inducers of ER stress, including tunicamycin, thapsigargin and brefeldin A, as well as by heat shock. In models for amyotrophic lateral sclerosis and cone dystrophy, ATF6 reporter expression is induced in spinal cord interneurons or photoreceptors, respectively, suggesting a role for ATF6 response in multiple neurodegenerative diseases. Collectively our results show that these ATF6 reporters can be used to monitor ATF6 activity changes throughout development and in zebrafish models of disease.

This article has an associated First Person interview with the first author of the paper.

Summary: In this study, we validate transgenic zebrafish generated to specifically report the activity of ATF6, representing a major branch of the endoplasmic reticulum stress pathway with functions in development and disease.

Recent advances in signal integration mechanisms in the unfolded protein response

Since its discovery more than 25 years ago, great progress has been made in our understanding of the unfolded protein response (UPR), a homeostatic mechanism that adjusts endoplasmic reticulum (ER) function to satisfy the physiological demands of the cell. However, if ER homeostasis is unattainable, the UPR switches to drive cell death to remove defective cells in an effort to protect the health of the organism. This functional dichotomy places the UPR at the crossroads of the adaptation versus apoptosis decision. Here, we focus on new developments in UPR signaling mechanisms, in the interconnectivity among the signaling pathways that make up the UPR in higher eukaryotes, and in the coordination between the UPR and other fundamental cellular processes.

Loss of SMPD4 Causes a Developmental Disorder Characterized by Microcephaly and Congenital Arthrogryposis

Sphingomyelinases generate ceramide from sphingomyelin as a second messenger in intracellular signaling pathways involved in cell proliferation, differentiation, or apoptosis. Children from 12 unrelated families presented with microcephaly, simplified gyral pattern of the cortex, hypomyelination, cerebellar hypoplasia, congenital arthrogryposis, and early fetal/postnatal demise. Genomic analysis revealed bi-allelic loss-of-function variants in SMPD4, coding for the neutral sphingomyelinase-3 (nSMase-3/SMPD4). Overexpression of human Myc-tagged SMPD4 showed localization both to the outer nuclear envelope and the ER and additionally revealed interactions with several nuclear pore complex proteins by proteomics analysis. Fibroblasts from affected individuals showed ER cisternae abnormalities, suspected for increased autophagy, and were more susceptible to apoptosis under stress conditions, while treatment with siSMPD4 caused delayed cell cycle progression. Our data show that SMPD4 links homeostasis of membrane sphingolipids to cell fate by regulating the cross-talk between the ER and the outer nuclear envelope, while its loss reveals a pathogenic mechanism in microcephaly.

The Unfolded Protein Response: Detecting and Responding to Fluctuations in the Protein-Folding Capacity of the Endoplasmic Reticulum

Most of the secreted and plasma membrane proteins are synthesized on membrane-bound ribosomes on the endoplasmic reticulum (ER). They require engagement of ER-resident chaperones and foldases that assist in their folding and maturation. Since protein homeostasis in the ER is crucial for cellular function, the protein-folding status in the organelle's lumen is continually surveyed by a network of signaling pathways, collectively called the unfolded protein response (UPR). Protein-folding imbalances, or "ER stress," are detected by highly conserved sensors that adjust the ER's protein-folding capacity according to the physiological needs of the cell. We review recent developments in the field that have provided new insights into the ER stress-sensing mechanisms used by UPR sensors and the mechanisms by which they integrate various cellular inputs to adjust the folding capacity of the organelle to accommodate to fluctuations in ER protein-folding demands.

Unfolded protein response-mediated modulation of mesenchymal stem cells

The endoplasmic reticulum (ER) receives unfolded proteins predestined for the secretory pathway or to be incorporated as transmembrane proteins. The ER has to accommodate the proper folding and glycosylation of these proteins and also to properly incorporate transmembrane proteins. However, under various circumstances, the proteins shuttling through the ER can be misfolded and undergo aggregation, which causes activation of the unfolded protein response (UPR). The UPR is mediated through three primary pathways: activating transcription factor-6, inositol-requiring enzyme-1 (IRE1), and PKR-like endoplasmic reticulum kinase, which up-regulate ER folding chaperones and temporarily suppress protein translation. The UPR can be both cytoprotective and/or cytotoxic depending on the duration of UPR activation and the type of host cell. Proteostasis controls stem cell function, while stress responses affect stem cell identity and differentiation. The present review aimed to explore and discuss the effects of the UPR pathways on mesenchymal stem cells.

The Best for the Most Important: Maintaining a Pristine Proteome in Stem and Progenitor Cells

Pluripotent stem cells give rise to reproductively enabled offsprings by generating progressively lineage-restricted multipotent stem cells that would differentiate into lineage-committed stem and progenitor cells. These lineage-committed stem and progenitor cells give rise to all adult tissues and organs. Adult stem and progenitor cells are generated as part of the developmental program and play critical roles in tissue and organ maintenance and/or regeneration. The ability of pluripotent stem cells to self-renew, maintain pluripotency, and differentiate into a multicellular organism is highly dependent on sensing and integrating extracellular and extraorganismal cues. Proteins perform and integrate almost all cellular functions including signal transduction, regulation of gene expression, metabolism, and cell division and death. Therefore, maintenance of an appropriate mix of correctly folded proteins, a pristine proteome, is essential for proper stem cell function. The stem cells' proteome must be pristine because unfolded, misfolded, or otherwise damaged proteins would interfere with unlimited self-renewal, maintenance of pluripotency, differentiation into downstream lineages, and consequently with the development of properly functioning tissue and organs. Understanding how various stem cells generate and maintain a pristine proteome is therefore essential for exploiting their potential in regenerative medicine and possibly for the discovery of novel approaches for maintaining, propagating, and differentiating pluripotent, multipotent, and adult stem cells as well as induced pluripotent stem cells. In this review, we will summarize cellular networks used by various stem cells for generation and maintenance of a pristine proteome. We will also explore the coordination of these networks with one another and their integration with the gene regulatory and signaling networks.

In vitro culture expansion impairs chondrogenic differentiation and the therapeutic effect of mesenchymal stem cells by regulating the unfolded protein response

In vitro expansion of mesenchymal stem cells (MSCs) has been implicated in loss of multipotency, leading to impaired chondrogenic potential and an eventual therapeutic effect, as reported in our previous study. However, the precise regulatory mechanism is still unclear. Here, we demonstrate that endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) were involved in transformation of MSCs induced by in vitro culture based on the comparative profiling of in vitro cultured bone marrow MSCs at passage 3 (P3 BMSCs) vs. fresh P0 BMSCs by microarray analysis. Indeed, RT-PCR and Western blot analysis showed significantly lower expression levels of three key UPR-related molecules, ATF4, ATF6 and XBP1, in P3 BMSCs than P0 BMSCs. Further, we found that UPR suppression by 4-phenylbutyrate (4-PBA) reduced the chondrogenic potential of P0 BMSCs and further cartilage regeneration. Conversely, UPR induction by tunicamycin (TM) enhanced the chondrogenic differentiation of P3 BMSCs and the therapeutic effect on cartilage repair. Thus, the decline in the chondrogenic potential of stem cells after in vitro culture and expansion may be due to changes in ER stress and the UPR pathway.

ER Proteostasis Control of Neuronal Physiology and Synaptic Function

Neuronal proteostasis is maintained by the dynamic integration of different processes that regulate the synthesis, folding, quality control, and localization of proteins. The endoplasmic reticulum (ER) serves as a fundamental pillar of the proteostasis network, and is emerging as a key compartment to sustain normal brain function. The unfolded protein response (UPR), the main mechanism that copes with ER stress, plays a central role in the quality control of many ion channels and receptors, in addition to crosstalk with signaling pathways that regulate connectivity, synapse formation, and neuronal plasticity. We provide here an overview of recent advances in the involvement of the UPR in maintaining neuronal proteostasis, and discuss its emerging role in brain development, neuronal physiology, and behavior, as well as the implications for neurodegenerative diseases involving cognitive decline.

Transcriptomic Profiling of MDA-MB-231 Cells Exposed to Boswellia Serrata and 3-O-Acetyl-B-Boswellic Acid; ER/UPR Mediated Programmed Cell Death

BACKGROUND/AIM

Triple-negative breast cancer (TNBC) is characterized by the absence of hormone receptors (estrogen, progesterone and human epidermal growth factor receptor-2) and a relatively poor prognosis due to inefficacy of hormone receptor-based chemotherapies. It is imperative that we continue to explore natural products with potential to impede growth and metastasis of TNBC. In this study, we screened over 1,000 natural products for capacity to induce cell death in TNBC (MDA-MB -231) cells.

MATERIALS AND METHODS

Frankincense (Boswellia serrata extract (BSE)) and 3-O-Acetyl-β-boswellic acid (3-OAβBA) were relatively potent, findings that corroborate the body of existing literature. The effects of BSE and 3-OAβBA on genetic parameters in MDA-MB-231 cells were evaluated by examining whole-transcriptomic influence on mRNAs, long intergenic non-coding RNA transcripts (lincRNA) and non-coding miRNAs.

RESULTS

Bio-statistical analysis demarcates the primary effect of both BSE/3-OAβBA on the up-regulation of PERK (protein kinase RNA-like endoplasmic reticulum kinase)- endoplasmic reticulum (ER)/unfolded protein response (UPR) pathways that are closely tied to activated programmed cell death (APCD). Global profiling confirms concomitant effects of BSE/3-OAβBA on upwardly expressed ER/URP APCD key components PERK (EIF2AK3), XBP1, C/EBP homologous protein transcription factor (CHOP), ATF3 and DDIT3,4/DNA-damage-inducible transcript 3,4 (GADD34). Further, BSE and/or 3-OAβBA significantly down-regulated oncogenes (OG) which, heretofore, lack functional pathway mapping, but are capable of driving epithelial-mesenchymal transition (EMT), cell survival, proliferation, metastasis and drug resistance. Among these are cell migration-inducing protein hyaluronan binding (CEMIP) [-7.22]; transglutaminase 2 [-4.96], SRY box 9 (SOX9) [-4.09], inhibitor of DNA binding 1, dominant negative helix-loop-helix protein (ID1) [-6.56]; and endothelin 1 (EDN1, [-5.06]). Likewise, in the opposite manner, BSE and/or 3-OAβBA induced the robust overexpression of tumor suppressor genes (TSGs), including: glutathione-depleting ChaC glutathione-specific gamma-glutamylcyclotransferase 1 (CHAC1) [+21.67]; the mTOR inhibitors - sestrin 2 (SESN2) [+16.4] Tribbles homolog 3 (TRIB3) [+6.2], homocysteine-inducible, endoplasmic reticulum stress-inducible, ubiquitin-like domain member 1 (HERPUD1) [+12.01]; and cystathionine gamma-lyase (CTH) [+11.12].

CONCLUSION

The anti-cancer effects of the historically used frankincense sap (BSE) appear to involve major impact on the ER/UPR response, concomitant to effecting multiple targets counter to the growth, proliferation and metastasis of TNBC cancer cells. The microarray data are available at Expression Omnibus GEO Series accession number GSE102891.

Cortical progenitor biology: key features mediating proliferation versus differentiation

The cerebral cortex is a highly organized structure whose development depends on diverse progenitor cell types, namely apical radial glia, intermediate progenitors, and basal radial glia cells, which are responsible for the production of the correct neuronal output. In recent years, these progenitor cell types have been deeply studied, particularly basal radial glia and their role in cortical expansion and gyrification. We review here a broad series of factors that regulate progenitor behavior and daughter cell fate. We first describe the different neuronal progenitor types, emphasizing the differences between lissencephalic and gyrencephalic species. We then review key factors shown to influence progenitor proliferation versus differentiation, discussing their roles in progenitor dynamics, neuronal production, and potentially brain size and complexity. Although spindle orientation has been considered a critical factor for mode of division and daughter cell output, we discuss other features that are emerging as crucial for these processes such as organelle and cell cycle dynamics. Additionally, we highlight the importance of adhesion molecules and the polarity complex for correct cortical development. Finally, we briefly discuss studies assessing progenitor multipotency and its possible contribution to the production of specific neuronal populations. This review hence summarizes recent aspects of cortical progenitor cell biology, and pinpoints emerging features critical for their behavior.

A lifetime of stress: ATF6 in development and homeostasis

BACKGROUND

Activating transcription factor 6 (ATF6) is an endoplasmic reticulum (ER)-localised protein and member of the leucine zipper family of transcription factors. Best known for its role in transducing signals linked to stress to the endoplasmic reticulum, the 50 kDa activated form of ATF6 is now emerging as a major regulator of organogenesis and tissue homeostasis. Responsible for the correct folding, secretion and membrane insertion of a third of the proteome in eukaryotic cells, the ER encompasses a dynamic, labyrinthine network of regulators, chaperones, foldases and cofactors. Such structures are crucial to the extensive protein synthesis required to undergo normal development and maintenance of tissue homeostasis. When an additional protein synthesis burden is placed on the ER, ATF6, in tandem with ER stress transducers inositol requiring enzyme 1 (IRE1) and PKR-like endoplasmic reticulum kinase (PERK), slows the pace of protein translation and induces the production of stress-reducing chaperones and foldases.

MAIN TEXT

In the context of development and tissue homeostasis, however, distinct cellular impacts have been attributed to ATF6. Drawing on data published from human, rodent, fish, goat and bovine research, this review first focuses on ATF6-mediated regulation of osteo- and chondrogenesis, ocular development as well as neuro- and myelinogenesis. The purported role of ATF6 in development of the muscular and reproductive systems as well as adipo- and lipogenesis is then described. With relevance to cardiac disease, cancer and brain disorders, the importance of ATF6 in maintaining tissue homeostasis is the subject of the final section.

CONCLUSION

In conclusion, the review encourages further elucidation of ATF6 regulatory operations during organogenesis and tissue homeostasis, to spawn the development of ATF6-targeted therapeutic strategies.

Mechanisms of protein homeostasis (proteostasis) maintain stem cell identity in mammalian pluripotent stem cells

Protein homeostasis, or proteostasis, is essential for cell function, development, and organismal viability. The composition of the proteome is adjusted to the specific requirements of a particular cell type and status. Moreover, multiple metabolic and environmental conditions challenge the integrity of the proteome. To maintain the quality of the proteome, the proteostasis network monitors proteins from their synthesis through their degradation. Whereas somatic stem cells lose their ability to maintain proteostasis with age, immortal pluripotent stem cells exhibit a stringent proteostasis network associated with their biological function and intrinsic characteristics. Moreover, growing evidence indicates that enhanced proteostasis mechanisms play a central role in immortality and cell fate decisions of pluripotent stem cells. Here, we will review new insights into the melding fields of proteostasis and pluripotency and their implications for the understanding of organismal development and survival.

Role of the unfolded protein response in the development of central nervous system

The unfolded protein response (UPR) is an intracellular homeostatic signalling pathway that is induced by accumulated misfolded/unfolded proteins in the endoplasmic reticulum (ER). The UPR is closely associated with the development of disease in several tissues, including the central nervous system (CNS), in response to ER stress. More recently, the unique features and importance of the UPR have been revealed in neural stem cells (NSCs) and differentiated CNS cells [neurons and glial cells (astrocytes and oligodendrocytes)]. Although several UPR signalling pathways dynamically change in each CNS cell during brain development, the role of UPR signalling in CNS cells (especially NSCs and glial cells) under pathological or physiological conditions is poorly understood. Here, we discuss and summarize the recent progress in understanding how the UPR regulates the proliferation, differentiation, maturation and viability of CNS cells.

Coordinating Organismal Metabolism During Protein Misfolding in the ER Through the Unfolded Protein Response

The endoplasmic reticulum (ER) is a cellular organelle responsible for folding of secretory and membrane proteins. Perturbance in ER homeostasis caused by various intrinsic/extrinsic stimuli challenges the protein-folding capacity of the ER, leading to an ER dysfunction, called ER stress. Cells have developed a defensive response to adapt and/or survive in the face of ER stress that may be detrimental to cell function and survival. When exposed to ER stress, the cell activates a complex and elaborate signaling network that includes translational modulation and transcriptional induction of genes. In addition to these autonomous responses, recent studies suggest that the stressed tissue secretes peptides or unknown factors that transfer the signal to other cells in the same or different organs, leading the organism as a whole to cope with challenges in a non-autonomous manner. In this review, we discuss the mechanisms by which cells adapt to ER stress challenges autonomously and transfer the stress signal to non-stressed cells in different organs.

Novel KDM1A inhibitors induce differentiation and apoptosis of glioma stem cells via unfolded protein response pathway

Glioma stem cells (GSCs) have a central role in glioblastoma (GBM) development and chemo/radiation resistance, and their elimination is critical for the development of efficient therapeutic strategies. Recently, we showed that lysine demethylase KDM1A is overexpressed in GBM. In the present study, we determined whether KDM1A modulates GSCs stemness and differentiation and tested the utility of two novel KDM1A-specific inhibitors (NCL-1 and NCD-38) to promote differentiation and apoptosis of GSCs. The efficacy of KDM1A targeting drugs was tested on purified GSCs isolated from established and patient-derived GBMs using both in vitro assays and in vivo orthotopic preclinical models. Our results suggested that KDM1A is highly expressed in GSCs and knockdown of KDM1A using shRNA-reduced GSCs stemness and induced the differentiation. Pharmacological inhibition of KDM1A using NCL-1 and NCD-38 significantly reduced the cell viability, neurosphere formation and induced apoptosis of GSCs with little effect on differentiated cells. In preclinical studies using orthotopic models, NCL-1 and NCD-38 significantly reduced GSCs-driven tumor progression and improved mice survival. RNA-sequencing analysis showed that KDM1A inhibitors modulate several pathways related to stemness, differentiation and apoptosis. Mechanistic studies showed that KDM1A inhibitors induce activation of the unfolded protein response (UPR) pathway. These results strongly suggest that selective targeting of KDM1A using NCL-1 and NCD-38 is a promising therapeutic strategy for elimination of GSCs.

New insights into the unfolded protein response in stem cells

The unfolded protein response (UPR) is an evolutionarily conserved adaptive mechanism to increase cell survival under endoplasmic reticulum (ER) stress conditions. The UPR is critical for maintaining cell homeostasis under physiological and pathological conditions. The vital functions of the UPR in development, metabolism and immunity have been demonstrated in several cell types. UPR dysfunction activates a variety of pathologies, including cancer, inflammation, neurodegenerative disease, metabolic disease and immune disease. Stem cells with the special ability to self-renew and differentiate into various somatic cells have been demonstrated to be present in multiple tissues. These cells are involved in development, tissue renewal and certain disease processes. Although the role and regulation of the UPR in somatic cells has been widely reported, the function of the UPR in stem cells is not fully known, and the roles and functions of the UPR are dependent on the stem cell type. Therefore, in this article, the potential significances of the UPR in stem cells, including embryonic stem cells, tissue stem cells, cancer stem cells and induced pluripotent cells, are comprehensively reviewed. This review aims to provide novel insights regarding the mechanisms associated with stem cell differentiation and cancer pathology.

Emerging Roles for the Unfolded Protein Response in the Developing Nervous System

The unfolded protein response (UPR) is a homeostatic signaling pathway triggered by protein misfolding in the endoplasmic reticulum (ER). Beyond its protective role, it plays important functions during normal development in response to elevated demand for protein folding. Several UPR effectors show dynamic temporal and spatial expression patterns that correlate with milestones of the central nervous system (CNS) development. Here, we discuss recent studies suggesting that a dynamic regulation of UPR supports generation, maturation, and maintenance of differentiated neurons in the CNS. We further highlight studies supporting a developmental vulnerability of CNS to UPR dysregulation, which underlies neurodevelopmental disorders. We believe that a better understanding of UPR functions may provide novel opportunities for therapeutic strategies to fight ER/UPR-associated human neurological disorders.

The role of the endoplasmic reticulum stress in stemness, pluripotency and development

The molecular machinery of endoplasmic reticulum (ER) integrates various intracellular and extracellular cues to maintain homeostasis in diverse physiological or pathological scenarios. ER stress and the unfolded protein response (UPR) have been found to mediate molecular and biochemical mechanisms that affect cell proliferation, differentiation, and apoptosis. Although a number of reviews on the ER stress response have been published, comprehensive reviews that broadly summarize ER physiology in the context of pluripotency, embryonic development, and tissue homeostasis are lacking. This review complements the current ER literature and provides a summary of the important findings on the role of the ER stress and UPR in embryonic development and pluripotent stem cells.

Neural stem cell neural differentiation in 3D extracellular matrix and endoplasmic reticulum stress microenvironment

Neural stem cell neural differentiation was protected by nanomatrix and extracellular matrix proteins under the endoplasmic reticulum stress condition.

DOT1L Activity Promotes Proliferation and Protects Cortical Neural Stem Cells from Activation of ATF4-DDIT3-Mediated ER Stress In Vitro

Growing evidence suggests that the lysine methyltransferase DOT1L/KMT4 has important roles in proliferation, survival, and differentiation of stem cells in development and in disease. We investigated the function of DOT1L in neural stem cells (NSCs) of the cerebral cortex. The pharmacological inhibition and shRNA-mediated knockdown of DOT1L impaired proliferation and survival of NSCs. DOT1L inhibition specifically induced genes that are activated during the unfolded protein response (UPR) in the endoplasmic reticulum (ER). Chromatin-immunoprecipitation analyses revealed that two genes encoding for central molecules involved in the ER stress response, Atf4 and Ddit3 (Chop), are marked with H3K79 methylation. Interference with DOT1L activity resulted in transcriptional activation of both genes accompanied by decreased levels of H3K79 dimethylation. Although downstream effectors of the UPR, such as Ppp1r15a/Gadd34, Atf3, and Tnfrsf10b/Dr5 were also transcriptionally activated, this most likely occurred in response to increased ATF4 expression rather than as a direct consequence of altered H3K79 methylation. While stem cells are particularly vulnerable to stress, the UPR and ER stress have not been extensively studied in these cells yet. Since activation of the ER stress program is also implicated in directing stem cells into differentiation or to maintain a proliferative status, the UPR must be tightly regulated. Our and published data suggest that histone modifications, including H3K4me3, H3K14ac, and H3K79me2, are implicated in the control of transcriptional activation of ER stress genes. In this context, the loss of H3K79me2 at the Atf4- and Ddit3-promoters appears to mark a point-of-no-return that activates the death program in NSCs.

The unfolded protein response in retinal vascular diseases: implications and therapeutic potential beyond protein folding

Angiogenesis is a complex, step-wise process of new vessel formation that is involved in both normal embryonic development as well as postnatal pathological processes, such as cancer, cardiovascular disease, and diabetes. Aberrant blood vessel growth, also known as neovascularization, in the retina and the choroid is a major cause of vision loss in severe eye diseases, such as diabetic retinopathy, age-related macular degeneration, retinopathy of prematurity, and central and branch retinal vein occlusion. Yet, retinal neovascularization is causally and dynamically associated with vasodegeneration, ischemia, and vascular remodeling in retinal tissues. Understanding the mechanisms of retinal neovascularization is an urgent unmet need for developing new treatments for these devastating diseases. Accumulating evidence suggests a vital role for the unfolded protein response (UPR) in regulation of angiogenesis, in part through coordinating the secretion of pro-angiogenic growth factors, such as VEGF, and modulating endothelial cell survival and activity. Herein, we summarize current research in the context of endoplasmic reticulum (ER) stress and UPR signaling in retinal angiogenesis and vascular remodeling, highlighting potential implications of targeting these stress response pathways in the prevention and treatment of retinal vascular diseases that result in visual deficits and blindness.

Automated method for the rapid and precise estimation of adherent cell culture characteristics from phase contrast microscopy images

The quantitative determination of key adherent cell culture characteristics such as confluency, morphology, and cell density is necessary for the evaluation of experimental outcomes and to provide a suitable basis for the establishment of robust cell culture protocols. Automated processing of images acquired using phase contrast microscopy (PCM), an imaging modality widely used for the visual inspection of adherent cell cultures, could enable the non-invasive determination of these characteristics. We present an image-processing approach that accurately detects cellular objects in PCM images through a combination of local contrast thresholding and post hoc correction of halo artifacts. The method was thoroughly validated using a variety of cell lines, microscope models and imaging conditions, demonstrating consistently high segmentation performance in all cases and very short processing times (<1 s per 1,208 × 960 pixels image). Based on the high segmentation performance, it was possible to precisely determine culture confluency, cell density, and the morphology of cellular objects, demonstrating the wide applicability of our algorithm for typical microscopy image processing pipelines. Furthermore, PCM image segmentation was used to facilitate the interpretation and analysis of fluorescence microscopy data, enabling the determination of temporal and spatial expression patterns of a fluorescent reporter. We created a software toolbox (PHANTAST) that bundles all the algorithms and provides an easy to use graphical user interface. Source-code for MATLAB and ImageJ is freely available under a permissive open-source license. Biotechnol. Bioeng. 2014;111: 504–517. © 2013 Wiley Periodicals, Inc.

An indole derivative protects against acetaminophen-induced liver injury by directly binding to N-acetyl-p-benzoquinone imine in mice

AIMS

Acetaminophen (APAP)-induced liver injury is mainly due to the excessive formation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) through the formation of a reactive intermediate, N-acetyl-p-benzoquinone imine (NAPQI), in both humans and rodents. Here, we show that the indole-derived synthetic compound has a protective effect against APAP-induced liver injury in C57Bl/6 mice model.

RESULTS

NecroX-7 decreased tert-butylhydroperoxide (t-BHP)- and APAP-induced cell death and ROS/RNS formation in HepG2 human hepatocarcinoma and primary mouse hepatocytes. In mice, NecroX-7 decreased APAP-induced phosphorylation of c-Jun N-terminal kinase (JNK) and 3-nitrotyrosine (3-NT) formation, and also protected mice from APAP-induced liver injury and lethality by binding directly to NAPQI. The binding of NecroX-7 to NAPQI did not require any of cofactors or proteins. NecroX-7 could only scavenge NAPQI when hepatocellular GSH levels were very low.

INNOVATION

NecroX-7 is an indole-derived potent antioxidant molecule, which can be bound to some types of radicals and especially NAPQI. It is well known that the NAPQI is a major intermediate of APAP, which causes necrosis of hepatocytes in rodents and humans. Thus, blocking NAPQI formation or eliminating NAPQI are novel strategies for the treatment or prevention of APAP-induced liver injury instead of GSH replenishment.

CONCLUSION

Our data suggest that the indole-derivative, NecroX-7, directly binds to NAPQI when hepatic GSH levels are very low and the NAPQI-NecroX-7 complex is secreted to the blood from the liver. NecroX-7 shows more preventive and similar therapeutic effects against APAP-induced liver injury when compared to the effect of N-acetylcysteine in C57Bl/6 mice.

Mechanical strain downregulates C/EBPβ in MSC and decreases endoplasmic reticulum stress

Exercise prevents marrow mesenchymal stem cell (MSC) adipogenesis, reversing trends that accompany aging and osteoporosis. Mechanical input, the in-vitro analogue to exercise, limits PPARγ expression and adipogenesis in MSC. We considered whether C/EBPβ might be mechanoresponsive as it is upstream to PPARγ, and also is known to upregulate endoplasmic reticulum (ER) stress. MSC (C3H10T1/2 pluripotent cells as well as mouse marrow-derived MSC) were cultured in adipogenic media and a daily mechanical strain regimen was applied. We demonstrate herein that mechanical strain represses C/EBPβ mRNA (0.6-fold ±0.07, p<0.05) and protein (0.4-fold ±0.1, p<0.01) in MSC. SiRNA silencing of β-catenin prevented mechanical repression of C/EBPβ. C/EBPβ overexpression did not override strain's inhibition of adipogenesis, which suggests that mechanical control of C/EBPβ is not the primary site at which adipogenesis is regulated. Mechanical inhibition of C/EBPβ, however, might be critical for further processes that regulate MSC health. Indeed, overexpression of C/EBPβ in MSC induced ER stress evidenced by a dose-dependent increase in the pro-apoptotic CHOP (protein 4-fold ±0.5, p<0.05) and a threshold reduction in the chaperone BiP (protein 0.6-fold ±0.1, p = 0.2; mRNA 0.3-fold ±0.1, p<0.01). ChIP-seq demonstrated a significant association between C/EBPβ and both CHOP and BiP genes. The strain regimen, in addition to decreasing C/EBPβ mRNA (0.5-fold ±0.09, p<0.05), expanded ER capacity as measured by an increase in BiP mRNA (2-fold ±0.2, p<0.05) and protein. Finally, ER stress induced by tunicamycin was ameliorated by mechanical strain as demonstrated by decreased C/EBPβ, increased BiP and decreased CHOP protein expression. Thus, C/EBPβ is a mechanically responsive transcription factor and its repression should counter increases in marrow fat as well as improve skeletal resistance to ER stress.

Apoptosis induced by adenosine involves endoplasmic reticulum stress in EC109 cells

Apoptosis plays a critical role in the development and homeostasis of multicellular organisms, and endoplasmic reticulum stress (ERS) is one of the intrinsic apoptosis pathways. Previous studies have shown that adenosine induces apoptosis in several cancer cell lines. However, the molecular mechanism remains poorly understood. In this study, we explored whether adenosine triggers apoptosis of EC109 esophageal carcinoma (EC) cells by ERS. The MTT assay was used to determine cell proliferation; cell cycle detection (FCM) and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay were performed to determine cell apoptosis. The subcellular distribution and expression of the ERS-related proteins GRP78, cleaved caspase-3, cleaved caspase-4, CHOP and NF-κB p65 were detected by western blot techniques. NF-κB activation was measured by electrophoretic mobility shift assay (EMSA). The MTT assay demonstrated that adenosine inhibited EC109 cell proliferation in a dose- and time-dependent manner. FCM and TUNEL assay verified that adenosine caused an apoptotic peak in cell cycle arrest and a higher percentage of apoptotic cells. Western blot analysis confirmed that the expression of GRP78, cleaved caspase-4, CHOP, NF-κB p65 and cleaved caspase-3 were upregulated in a dose-dependent manner after adenosine treatment. EMSA revealed that adenosine activated NF-κB p65. This is the first demonstration that adenosine inhibits cell proliferation, increases GRP78 and NF-κB p65 expression and induces apoptosis by CHOP and caspase-4 pathways. The ERS pathway is involved in adenosine-induced apoptosis in EC109 cells.

ER stress response during the differentiation of H9 cells induced by retinoic acid

Endoplasmic reticulum (ER) stress occurs during early embryonic development. The aim of this study is to determine whether ER stress occurs during human embryonic stem cell differentiation induced by retinoic acid (RA). H9 human embryonic stem cells were subjected to RA treatment for up to 29days to induce differentiation. HEK293 cells were treated with RA as a control. The results demonstrate that several ER stress-responsive genes are differentially regulated in H9 and HEK293 cells in response to 5days of RA treatment. GRP78/Bip was upregulated in H9 cells but downregulated in HEK293 cells. eIF2α was downregulated in H9 cells but not in HEK293 cells. Phosphorylation of eIF2α was downregulated in H9 cells but upregulated in HEK293 cells. XBP-1 was downregulated immediately after RA treatment in H9 cells, but its downregulation was much slower in HEK293 cells. Additionally, two ER-resident E3 ubiquitin ligases, gp78 and Hrd1, were both upregulated in H9 cells following 5 days of exposure to RA. Moreover, the protein Bcl2 was undetectable in H9 cells and H9-derived cells but was expressed in HEK293 cells, and it expression in the two types of cells was unaltered by RA treatment. In H9 cells treated with RA for 29 days, GRP78/Bip, XBP-1 and Bcl2 were all upregulated. These results suggest that ER stress is involved in H9 cell differentiation induced by RA.

Role of glucose-regulated Protein 78 in embryonic development and neurological disorders

Glucose-regulated protein 78 (GRP78) is an important chaperone protein that is predominantly expressed in the endoplasmic reticulum. The multifunctional roles of GRP78 in protein folding, endoplasmic reticulum calcium binding, cytoprotection, and anti-apoptosis, as well as its function as a receptor on the cell surface, disclose its major involvement in physiological and numerous pathological conditions. Recent advances in mouse models targeting GRP78 allele have revealed the essential roles of GRP78 in development and neurological disorders, as well as accurate neural migration and neuroprotection. This review of correlation between GRP78 and embryogenesis and neurological disorders provides further directions for investigation, as well as potential therapeutics for clinical use.

Involvement of endoplasmic reticulum stress in myofibroblastic differentiation of lung fibroblasts

Stress that impairs endoplasmic reticulum (ER) function leads to an accumulation of unfolded or misfolded proteins in the ER (ER stress) and triggers the unfolded protein response (UPR). Recent studies suggest that ER stress is involved in idiopathic pulmonary fibrosis (IPF). The present study was undertaken to determine the role of ER stress on myofibroblastic differentiation of fibroblasts. Fibroblasts in fibroblastic foci of IPF showed immunoreactivity for GRP78. To determine the role of ER stress on α-smooth muscle actin (α-SMA) and collagen type I expression in fibroblasts, mouse and human lung fibroblasts were treated with TGF-β1, and expression of ER stress-related proteins, α-SMA, and collagen type I was analyzed by Western blotting. TGF-β1 significantly increased expression of GRP78, XBP-1, and ATF6α, which was accompanied by increases in α-SMA and collagen type I expression in mouse and human fibroblasts. A chemical chaperone, 4-PBA, suppressed TGF-β1-induced UPR and α-SMA and collagen type I induction. We also showed that TGF-β1-induced UPR was mediated through the reactive oxygen species generation. Our study provides the first evidence implicating the UPR in myofibroblastic differentiation during fibrosis. These findings of the role of ER stress and chemical chaperones in pulmonary fibrosis may improve our understanding of the pathogenesis of IPF.

Ethanol induces endoplasmic reticulum stress in the developing brain

BACKGROUND

Ethanol exposure during brain development causes profound damages to the central nervous system (CNS). The underlying cellular/molecular mechanisms remain unclear. The endoplasmic reticulum (ER) is involved in posttranslational protein processing and transport. The accumulation of unfolded or misfolded proteins in the ER lumen triggers ER stress, which is characterized by translational attenuation, synthesis of ER chaperone proteins, and activation of transcription factors. Sustained ER stress ultimately leads to cell death. ER stress is implicated in various neurodegenerative processes.

METHODS

Using a third trimester equivalent mouse model of ethanol exposure, we tested the hypothesis that ethanol induces ER stress in the developing brain. Seven-day-old C57BL/6 mice were acutely exposed to ethanol by subcutaneous injection and the expression of ER stress-inducible proteins (ERSIPs) and signaling pathways associated with ER stress were examined.

RESULTS

Ethanol exposure significantly increased the expression of ERSIPs and activated signaling pathways associated with ER stress; these include ATF6, CHOP/GADD153, GRP78, and mesencephalic astrocyte-derived neurotrophic factor as well as the phosphorylation of IRE1α, eIF2α, PERK, and PKR. The ethanol-induced increase in ERSIPs occurred within 4 hours of ethanol injection, and levels of some ERSIPs remained elevated after 24 hours of ethanol exposure. Ethanol-induced increase in phosphorylated eIF2α, caspase-12, and CHOP was distributed in neurons of specific areas of the cerebral cortex, hippocampus, and thalamus.

CONCLUSIONS

Our finding indicates that ethanol induces ER stress in immature neurons, providing novel insight into ethanol's detrimental effect on the developing CNS.

Baicalein protects HT22 murine hippocampal neuronal cells against endoplasmic reticulum stress-induced apoptosis through inhibition of reactive oxygen species production and CHOP induction

Baicalein is one of the major flavonoids in Scutellaria baicalensis Georgi and possesses various effects, including cytoprotection and anti-inflammation. Because endoplasmic reticulum (ER) stress has been implicated in neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and cerebral ischemia, we investigated the effects of baicalein on apoptotic death of HT22 mouse hippocampal neuronal cells induced by thapsigargin (TG) and brefeldin A (BFA), two representative ER stress inducers. Apoptosis, reactive oxygen species (ROS) production, and mitochondrial membrane potential (MMP) were measured by flow cytometry. Expression level and phosphorylation status of ER stress-associated proteins and activation and cleavage of apoptosis-associated proteins were analyzed by Western blot. Baicalein reduced TG- and BFA-induced apoptosis of HT22 cells and activation and cleavage of apoptosis-associated proteins, such as caspase-12 and -3 and poly(ADP-ribose) polymerase. Baicalein also reduced the TG- and BFA-induced expression of ER stress-associated proteins, including C/EBP homologous protein (CHOP) and glucose-regulated protein 78, the cleavage of X-box binding protein-1 and activating transcription factor 6α, and the phosphorylation of eukaryotic initiation factor-2α and mitogen-activated protein kinases, such as p38, JNK, and ERK. Knock-down of CHOP expression by siRNA transfection and specific inhibitors of p38 (SB203580), JNK (SP600125), and ERK (PD98059) as well as anti-oxidant (N-acetylcysteine) reduced TG- or BFA-induced cell death. Baicalein also reduced TG- and BFA-induced ROS accumulation and MMP reduction. Taken together, these results suggest that baicalein could protect HT22 neuronal cells against ER stress-induced apoptosis by reducing CHOP induction as well as ROS accumulation and mitochondrial damage.

In vivo cellular adaptation to ER stress: survival strategies with double-edged consequences

Disturbances to the balance of protein synthesis, folding and secretion in the endoplasmic reticulum (ER) induce stress and thereby the ER stress signaling (ERSS) response, which alleviates this stress. In this Commentary, we review the emerging idea that ER stress caused by abnormal physiological conditions and/or mutations in genes that encode client proteins of the ER is a key factor underlying different developmental processes and the pathology of diverse diseases, including diabetes, neurodegeneration and skeletal dysplasias. Recent studies in mouse models indicate that the effect of ERSS in vivo and the nature of the cellular strategies induced to ameliorate pathological ER stress are crucial factors in determining cell fate and clinical disease features. Importantly, ERSS can affect cellular proliferation and the differentiation program; cells that survive the stress can become 'reprogrammed' or dysfunctional. These cell-autonomous adaptation strategies can generate a spectrum of context-dependent cellular consequences, ranging from recovery to death. Secondary effects can include altered cell-extracellular-matrix interactions and non-cell-autonomous alteration of paracrine signaling, which contribute to the final phenotypic outcome. Recent reports showing that ER stress can be alleviated by chemical compounds suggest the potential for novel therapeutic approaches.

Neurogenic transdifferentiation of human adipose-derived stem cells? A critical protocol reevaluation with special emphasis on cell proliferation and cell cycle alterations

Adipose-derived stem cells (ASCs) are reported to display multilineage differentiation potential, including neuroectodermal pathways. The aim of the present study was to critically re-evaluate the potential neurogenic (trans-)differentiation capacity of ASCs using a neurogenic induction protocol based on the combination of isobutylmethylxanthine (IBMX), indomethacin and insulin. ASCs isolated from lipo-aspirate samples of five healthy female donors were characterized and potential neurogenic (trans-)differentiation was assessed by means of immunohistochemistry and gene expression analyses. Cell proliferation and cell cycle alterations were studied, and the expression of CREB/ATF transcription factors was analyzed. ASCs expressed CD59, CD90 and CD105, and were tested negative for CD34 and CD45. Under neurogenic induction, ASCs adopted a characteristic morphology comparable to neur(on)al progenitors and expressed musashi1, β-III-tubulin and nestin. Gene expression analyses revealed an increased expression of β-III-tubulin, GFAP, vimentin and BDNF, as well as SOX4 in induced ASCs. Cell proliferation was significantly reduced under neurogenic induction; cell cycle analyses showed a G2-cell cycle arrest accompanied by differential expression of key regulators of cell cycle progression. Differential expression of CREB/ATF transcription factors could be observed on neurogenic induction, pointing to a decisive role of the cAMP-CREB/ATF system. Our findings may point to a potential neurogenic (trans-)differentiation of ASCs into early neur(on)al progenitors, but do not present definite evidence for it. Especially, the adoption of a neural progenitor cell-like morphology must not automatically be misinterpreted as a specific characteristic of a respective (trans-)differentiation process, as this may as well be caused by alterations of cell cycle progression.

The Unfolded Protein Response, Degradation from Endoplasmic Reticulum and Cancer

The endoplasmic reticulum (ER) is an essential organelle involved in many cellular functions including protein folding and secretion, lipid biosynthesis and calcium homeostasis. Proteins destined for the cell surface or for secretion are made in the ER, where they are folded and assembled into multi-subunit complexes. The ER plays a vital role in cellular protein quality control by extracting and degrading proteins that are not correctly folded or assembled into native complexes. This process, known as ER-associated degradation (ERAD), ensures that only properly folded and assembled proteins are transported to their final destinations. Besides its role in protein folding and transport in the secretory pathway, the ER regulates the biosynthesis of cholesterol and other membrane lipids. ERAD is an important means to ensure that levels of the responsible enzymes are appropriately maintained. The ER is also a major organelle for oxygen and nutrient sensing as cells adapt to their microenvironment. Stresses that disrupt ER function leads to accumulation of unfolded proteins in the ER, a condition known as ER stress. Cells adapt to ER stress by activating an integrated signal transduction pathway called the unfolded protein response (UPR) (1). The UPR represents a survival response by the cells to restore ER homeostasis. If ER stress persists, cells activate mechanisms that result in cell death. Chronic ER stress is increasingly being recognized as a factor in many human diseases such as diabetes, neurodegenerative disorders and cancer. In this review we discuss the roles of the UPR and ERAD in cancer and suggest directions for future research.

Induction of the unfolded protein response and cell death pathway in Alzheimer's disease, but not in aged Tg2576 mice

The endoplasmic reticulum (ER) stress results from disrupted protein folding triggered by protein mutation or oxidation, reduced proteasome activity, and altered Ca2+ homeostasis. ER stress is accompanied by activation of the unfolded protein response (UPR) and cell death pathway. We examined if the UPR and cell death pathway would be activated in Alzheimer's disease (AD). RT-PCR experiments revealed increased splicing of X-box binding protein-1 (XBP-1), an UPR transcription factor, in AD compared with age-matched control. Among target genes of XBP-1, expression of protein disulfide isomerase (PDI), but not glucose-regulated protein 78 (GRP78), was increased in AD, suggesting disturbed activation of the UPR in AD. C/EBP homologous protein (CHOP), caspase-3, caspase-4, and caspase-12, downstream mediators of cell death pathway, were activated in AD. Neither the UPR nor cell death pathway was induced in aged Tg2576 mice, a transgenic mouse model of Alzheimer's disease that reveals both plaque pathology and some cognitive deficits. The present study suggests that disturbed induction of the UPR and activation of the pro-apoptotic proteins contribute to neuropathological process in AD irrespective of amyloid beta and senile plaque.

Transgenic mouse and cell culture models demonstrate a lack of mechanistic connection between endoplasmic reticulum stress and tau dysfunction

In vivo aggregation of tau protein is a hallmark of many neurodegenerative disorders, including Alzheimer's disease (AD). Recent evidence has also demonstrated activation of the unfolded protein response (UPR), a cellular response to endoplasmic reticulum (ER) stress, in AD, although the role of the UPR in disease pathogenesis is not known. Here, three model systems were used to determine whether a direct mechanistic link could be demonstrated between tau aggregation and the UPR. The first model system used was SH-SY5Y cells, a neuronal cultured cell line that endogenously expresses tau. In this system, the UPR was activated using chemical stressors, tunicamycin and thapsigargin, but no changes in tau expression levels, solubility, or phosphorylation were observed. In the second model system, wild-type 4R tau and P301L tau, a variant with increased aggregation propensity, were heterologously overexpressed in HEK 293 cells. This overexpression did not activate the UPR. The last model system examined here was the PS19 transgenic mouse model. Although PS19 mice, which express the P301S variant of tau, display severe neurodegeneration and formation of tau aggregates, brain tissue samples did not show any activation of the UPR. Taken together, the results from these three model systems suggest that a direct mechanistic link does not exist between tau aggregation and the UPR.