World of small RNAs: from ribozymes to siRNA and miRNA

Chromosome 1p status in neuroblastoma correlates with higher expression levels of miRNAs targeting neuronal differentiation pathway

Neuroblastoma (NB) is characterized by acquired segmental and numerical chromosome aberrations. Although deletions of distal 1p and 11q are frequent alterations, no candidate tumor suppressor gene residing in these chromosomal sites could be identified so far. In the present study, we detected the genomic imbalances of six neuroblastoma cell lines using the multiplex ligation-dependent probe amplification (MLPA) technique and the microRNA (miRNA) expression profiles of the cell lines by a microarray study. According to MLPA results, we aimed to assess the miRNA expression profiles of the cell lines harboring 11q and 1p deletions. The cell lines with 1p deletions revealed statistically significant higher levels of expression for 29 miRNAs in contrast to the cell lines without 1p deletion in microarray study. We also performed GO enrichment analysis for predicted targets of the differentially expressed miRNAs. According to GO enrichment analysis, miRNAs that showed the high change in expression was associated with neuronal differentiation. We showed that hsa-miR-494, hsa-miR-495, and hsa-miR-543 target most of mRNAs in neuronal differentiation pathway. Although limited to the cell lines, our results highly suggest that NBs with different segmental chromosome abnormalities may have different dysregulated miRNA expression signatures that target the genes involved in neuronal differentiation.

Enhanced osteogenic effect in reduced BMP-2 doses with siNoggin transfected pre-osteoblasts in 3D silk scaffolds

Bone morphogenetic proteins (BMPs), especially BMP-2, are being increasingly used in bone tissue engineering due to its osteo-inductive effects. Although recombinant human BMP-2 (rhBMP-2) was approved by Food and Drug Administration (FDA) to use for bone repair, its high doses cause undesired side effects. In order to reduce the BMP-2 dose for enhanced osteogenic differentiation, in this study we decided to suppress the synthesis of Noggin protein, the primary antagonist of BMP-2, on the MC3T3-E1 cells using Noggin targeted small interfering RNA (siRNA). Unlike other studies, Noggin siRNA (siNoggin) transfected cells were seeded on silk scaffolds, and osteogenic differentiation was investigated for a long-term period (21 days) with MTT, qPCR, SEM/EDS, and histological analysis. Besides, siNoggin transfected MC3T3-E1 cells were evaluated as a new cell source for tissue engineering studies. It was determined that Nog gene expression was suppressed in the siNoggin group and Ocn gene expression increased 5-fold compared to the control group (*p < 0.05). The osteogenic effect of BMP-2 was clearly observed in siNoggin transfected cells. According to the SEM/EDS analysis, the siNoggin group has mineral structures clustered on cells, which contain intense Ca and P elements. Histological staining showed that the siNoggin group has a more intense mineralized area than that of the control group. In conclusion, this study indicated that Noggin silencing by siRNA induces osteogenic differentiation in reduced BMP-2 doses for scaffold-based bone regeneration. This non-gene integration strategy has as a safe therapeutic potential to enhance tissue regeneration.

Design and Characterization of RNA Nanotubes

RNA is a functionally rich and diverse biomaterial responsible for regulating several cellular processes. This functionality has been harnessed to build predominately small nanoscale structures for drug delivery and the treatment of disease. The understanding of design principles to build large RNA structures will allow for further control of stoichiometry and spatial arrangement drugs and ligands. We present the design and characterization of RNA nanotubes that self-assemble from programmable monomers, or tiles, formed by five distinct RNA strands. Tiles include double crossover junctions and assemble via single-stranded sticky-end domains. We find that nanotube formation is dependent on the intertile crossover distance. The average length observed for the annealed RNA nanotubes is ≈1.5 μm, with many nanotubes exceeding 10 μm, enabling the characterization of RNA nanotubes length distribution via fluorescence microscopy. Assembled tubes were observed to be stable for more than 24 h, however post-annealing growth under isothermal conditions does not occur. Nanotubes assemble also from RNA tiles modified to include a single-stranded overhang (toehold), suggesting that it may be possible to decorate these large RNA scaffolds with nanoparticles or other nucleic acid molecules.

Circulating cell-free nucleic acids as biomarkers in colorectal cancer screening and diagnosis - an update

Introduction: Screening methods for one of the most frequently diagnosed malignancy, colorectal cancer (CRC), have limitations. Circulating cell-free nucleic acids (cfNA) hold clinical relevance as screening, prognostic and therapy monitoring markers. Area covered: In this review, we summarize potential CRC-specific cfNA biomarkers, the recently developed sample preparation techniques, their applications, and pitfalls. Expert opinion: Automated extraction of cfDNA is highly reproducible, however, cfDNA yield is less compared to manual isolation. Quantitative and highly sensitive detection techniques (e.g. digital PCR, NGS) can be applied to analyze genetic and epigenetic changes. Detection of DNA mutations or methylation in cfDNA and related altered levels of mRNA, miRNA, and lncRNA may improve early cancer recognition, based on specific, CRC-related patterns. Detection of cfDNA mutations (e.g. TP53, KRAS, APC) has limited diagnostic sensitivity (40-60%), however, methylated DNA including SEPT9, SFRP1, SDC2 can be applied with higher sensitivity (up to 90%) for CRC. Circulating miRNAs (e.g. miR-21, miR-92, miR-141) provide comparably high sensitivity for CRC as the circulating tumor cell mRNA markers (e.g. EGFR, CK19, CK20, CEA). Automation of cfNA isolation coupled with quantitative analysis of CRC-related, highly sensitive biomarkers may enhance CRC screening and early detection in the future.

Methods for Using Small Non-Coding RNAs to Improve Recombinant Protein Expression in Mammalian Cells

The ability to produce recombinant proteins by utilizing different “cell factories” revolutionized the biotherapeutic and pharmaceutical industry. Chinese hamster ovary (CHO) cells are the dominant industrial producer, especially for antibodies. Human embryonic kidney cells (HEK), while not being as widely used as CHO cells, are used where CHO cells are unable to meet the needs for expression, such as growth factors. Therefore, improving recombinant protein expression from mammalian cells is a priority, and continuing effort is being devoted to this topic. Non-coding RNAs are RNA segments that are not translated into a protein and often have a regulatory role. Since their discovery, major progress has been made towards understanding their functions. Non-coding RNA has been investigated extensively in relation to disease, especially cancer, and recently they have also been used as a method for engineering cells to improve their protein expression capability. In this review, we provide information about methods used to identify non-coding RNAs with the potential of improving recombinant protein expression in mammalian cell lines.

miR-181a Modulates Chondrocyte Apoptosis by Targeting Glycerol-3-Phosphate Dehydrogenase 1-Like Protein (GPD1L) in Osteoarthritis

BACKGROUND miR-181a is a small non-coding RNA known to be dysregulated in osteoarthritis (OA), but the role of miR-181a in human OA remains unclear. The aim of this study was to identify its function and molecular target in chondrocytes during OA pathogenesis. MATERIAL AND METHODS The function of miR-181a was assessed by gain-of-function studies in human OA chondrocytes. Potential targets of miR-181a were predicted using series of bioinformatics and intersection analysis, then confirmed by luciferase reporter assay. Gene expression was quantified using quantitative reverse transcription PCR (qRT-PCR) assays, and protein production was quantified by Western blot analysis. RESULTS The FITC apoptosis assay results indicated that the upregulation of miR-181a led to an increase of apoptosis rate in chondrocytes. Then bioinformatic analysis identified potential target sites of the miR-181a located in the 3' untranslated region of GPD1L. Dual-luciferase reporter assays results showed that GPD1L is a target gene of miR-181a. Furthermore, Western blot and qRT-PCR analysis demonstrated that miR-181a inhibited GPD1L gene expression. Increased GPD1L and decreased miRNA-181a were observed in tissues from osteoarthritis patients. Moreover, we found a highly negative correlation between miRNA-181a and GPD1L. CONCLUSIONS Our results demonstrated that miR-181a may play an important role in the pathogenesis of OA through targeting GPD1L and regulating chondrocyte apoptosis.

Circulating cell-free nucleic acids as biomarkers in colorectal cancer screening and diagnosis

Screening methods for the most frequent diagnosed malignant tumor, colorectal cancer (CRC), have limitations. Circulating cell-free DNA (cfDNA) analysis came into focus as a potential screening test for CRC. Detection of epigenetic and genetic alterations of cfDNA as DNA methylation or DNA mutations and related ribonucleic acids may improve cancer detection based on unique, CRC-specific patterns. In this review the authors summarize the CRC-specific nucleic acid biomarkers measured in peripheral blood and their potential as screening markers. Detection of DNA mutation has inadequate sensitivity; however, methylated DNA can be established with higher sensitivity from CRC plasma samples. The ribonucleic acid based miRNA studies represented higher sensitivity for CRC as compared with mRNA studies. Recently, isolation of cfDNA has become automated, highly reproducible and a high throughput method. With automated possible diagnostic tools, a new approach may be available for CRC screening as liquid biopsy.

Smart functional nucleic acid chimeras: enabling tissue specific RNA targeting therapy

A major obstacle for effective utilization of therapeutic oligonucleotides such as siRNA, antisense, antimiRs etc. is to deliver them specifically to the target tissues. Toward this goal, nucleic acid aptamers are re-emerging as a prominent class of biomolecules capable of delivering target specific therapy and therapeutic monitoring by various molecular imaging modalities. This class of short oligonucleotide ligands with high affinity and specificity are selected from a large nucleic acid pool against a molecular target of choice. Poor cellular uptake of therapeutic oligonucleotides impedes gene-targeting efficacy in vitro and in vivo. In contrast, aptamer-oligonucleotide chimeras have shown the capacity to deliver siRNA, antimiRs, small molecule drugs etc. toward various targets and showed very promising results in various studies on different diseases models. However, to further improve the bio-stability of such chimeric conjugates, it is important to introduce chemically-modified nucleic acid analogs. In this review, we highlight the applications of nucleic acid aptamers for target specific delivery of therapeutic oligonucleotides.

Brain-derived neurotrophic factor is a novel target gene of the has-miR-183/96/182 cluster in retinal pigment epithelial cells following visible light exposure

Light-induced retinal injury is clinically and experimentally well-documented. It may be categorized into three types: Photothermal, photomechanical and photochemical injuries. To date, the variation in the hsa-miR-183/96/182 cluster and its potential target genes in human primary retinal pigment epithelial (RPE) cells, following visible light exposure, has not been reported. In the present study, RPE cells were exposed to 4 h of constant visible light. The expression of the hsa-miR-183/96/182 cluster was determined using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and its potential target genes were investigated. Additionally, hsa-miR-183, hsa-miR-96, hsa-miR-182 and has-miR-183/96/182 mimics were designed and synthesized in vitro, and transfected into the RPE cells. Subsequently, the expression of brain-derived neurotrophic factor (BDNF) mRNA and protein was measured, using RT-qPCR and western blotting, respectively. The regulation of miRNAs to the BDNF gene were then validated using a dual luciferase reporter gene assay system. The expression of hsa-miR-183, hsa-miR-96 and hsa-miR-182 significantly increased in RPE cells following 4 h of visible light exposure, compared with RPE cells that had been exposed to dark conditions (P<0.01). Following RPE cell transfection with mimics, BDNF mRNA and protein expression in the RPE cells was significantly downregulated compared with control RPE cells (P<0.05, P<0.01, respectively). Similarly, the ratio of Renilla luciferase/firefly luciferase significantly decreased in the RPE cells of the mimic + wild type (WT) group compared with cells of the psiCHECK(TM)-2 (a vector lacking the sequence of the BDNF gene), wild type and mimic + mutation groups (P<0.05, P<0.01). The present study suggests that BDNF is a target gene of the has-miR-183-96-182 cluster in RPE cells. The present study suggests an underlying protective mechanism against retinal light injury and may provide a novel target for the prevention and treatment of light-induced retinal injury.

Chromatin, non-coding RNAs, and the expression of HIV

HIV is a chronic viral infection affecting an estimated 34 million people worldwide. Current therapies employ the use of a cocktail of antiretroviral medications to reduce the spread and effects of HIV, however complete eradication from an individual currently remains unattainable. Viral latency and regulation of gene expression is a key consideration when developing effective treatments. While our understanding of these processes remains incomplete new developments suggest that non-coding RNA (ncRNA) mediated regulation may provide an avenue to controlling both viral expression and latency. Here we discuss the importance of known regulatory mechanisms and suggest directions for further study, in particular the use ncRNAs in controlling HIV expression.

Second-generation aptamer-conjugated PSMA-targeted delivery system for prostate cancer therapy

Background:

miR-15a and miR-16-1 have been identified as tumor suppressor genes in prostate cancer, but their safe and effective delivery to target cells is key to the successful use of this therapeutic strategy. RNA aptamer A10 has been used as a ligand, targeting prostate cancer cells that express prostate-specific membrane antigen (PSMA). Compared with A10, the binding of the second-generation RNA aptamer, A10-3.2, to PSMA is more efficient.

Methods:

A10-3.2 was investigated as a PSMA-targeting ligand in the design of a polyamidoamine (PAMAM)-based microRNA (miR-15a and miR-16-1) vector to prostate cancer cells. Using polyethyleneglycol (PEG) as a spacer, PAMAM was conjugated to aptamer (PAMAM-PEG-APT) and used as a vehicle for miRNA target delivery.

Results:

Luciferase assays of pGL-3 expression against PC3 (PSMA⁻) and LNCaP (PSMA⁺) cells demonstrated that the transfection efficiency of the synthesized DNA/PAMAM-PEG-APT complex was higher than that of the DNA/PAMAM-PEG complex. In addition, cell viability assays of LNCaP (PSMA⁺) cells showed that, with a N/P ratio of 15:1, the IC₅₀ value of miRNA/PAMAM-PEG-APT was approximately 4.7-fold lower than that of miRNA/PAMAM-PEG.

Conclusion:

This PSMA-targeted system may prove useful in widening the therapeutic window and allow for selective killing of prostate cancer cells.

Selective silencing of DNA topoisomerase IIβ in human mesenchymal stem cells by siRNAs (small interfering RNAs)

hMSCs (human mesenchymal stem cells) express two isoforms of DNA topo II (topoisomerase II). Although both isoforms have the same catalytic activity, they are specialized for different functions in the cell: while topo IIα is essential for chromosome segregation in mitotic cells, topo IIβ is involved in more specific cellular functions. A number of inhibitors are available that inhibit the catalytic activity of both topo II isoforms. However, in order to investigate the isoform-specific inhibition of these two enzymes, it is necessary to use other techniques such as siRNA (small interfering RNA) interference to selectively silence either one of the isoforms individually. Depending on the lipid charge densities and protein varieties of the cell membrane, previous studies have demonstrated that transfection efficiencies of siRNAs to hMSCs are very low. In the study reported here, we demonstrate the use of Lipofectamine RNAiMAX as an efficient transfection reagent to introduce siRNAs into human mesenchymal stem cells with significantly great efficiency to silence topo IIβ selectively. A high level of transfection efficiency (80%) was achieved by using unlabelled topo IIβ-specific siRNA oligos. Specifically, it was confirmed repeatedly that green labelled siRNAs interfere with the transfection of siRNAs. The reagent induced minimal cytotoxicity (3.5–4.5%), and cell viability of the transfected hMSCs decreased 20–30% compared with untreated cells, depending on the concentration of the reagent.

Efficient knockdown of human prnp mRNA expression levels using hybrid hammerhead ribozymes

Prion diseases are invariably fatal infectious diseases of the central nervous system. The prion protein has been identified as the underlying causative agent as PrP knockout mice (prnp(0/0)) are resistant to infection. This suggests that a significant reduction in the expression levels of PrP(c) should interrupt disease progression. Accomplishing this in vivo, upon presentation of symptoms, requires a mechanism that significantly reduces prnp mRNA levels while lacking potential side effects that may be cytotoxic or lethal to the host. Hybrid hammerhead ribozymes (HyHamRzs) include both a helicase recruitment signal and a tRNA(Val) promoter. HyHamRzs offer a means of highly specific and significant mRNA cleavage. In this study, data demonstrate increased activity granted to HamRzs by the addition of the helicase recruitment signal. Results show that three different HyHamRzs, targeting different locations along the full length prnp mRNA, reduced expression levels by greater than 95% relative to the control. It is postulated that HyHamRzs, modified to enhance serum stability and delivered intravenously to neurons by forming a complex with the modified rabies virus G protein (RVG), may offer a potential gene therapy strategy.

Light-activation of gene function in mammalian cells via ribozymes

A ribozyme based gene control element enabled the spatio-temporal regulation of gene function in mammalian cell culture with light.

Are viral-encoded microRNAs mediating latent HIV-1 infection?

The Human Immunodeficiency Virus type 1 (HIV-1), a member of the lentivirus subfamily, infects both dividing and nondividing cells and, following reverse transcription of the viral RNA genome, integrates into the host chromatin where it enters into a latent state. Many of the factors governing viral latency remain unresolved and current antiviral treatment regimens are largely ineffective at eliminating cellular reservoirs of latent virus. The recent identification of microRNA (miRNA) encoding sequences embedded in the HIV-1 genome, and the discovery of functional virus-derived miRNAs, suggests a role for RNA Interference (RNAi) in the regulation of HIV-1 gene expression. Recently, the mammalian RNAi machinery was shown to regulate gene expression epigenetically by transcriptional modulation, providing a direct link between RNAi and a mechanism for inducing latency. Interestingly, both HIV-1 Tat, and the host TAR RNA-binding protein (TRBP), bind to the transactivating response (TAR) RNA of HIV-1 and affect the function of RNAi in human cells. Specifically, TRBP, a cofactor in Tat-TAR interactions, is a vital component of Dicer-mediated dsRNA processing. These novel observations support a central role for HIV-1 and associated host factors in regulating cellular RNAi and viral gene expression through RNA directed processes. Thus, HIV-1 may have evolved mechanisms to exploit the RNAi pathway at both the transcriptional and posttranscriptional level to affect and/or maintain a latent infection.

Assessment of the microRNA system in salt-sensitive hypertension

Most animal microRNAs are imperfectly complementary to their mRNA targets and inhibit protein synthesis through an unknown mechanism. MicroRNAs have been reported to play important roles in a number of biological processes. We assessed the microRNA system in Dahl salt-sensitive rats in order to investigate possible roles of microRNA in salt-sensitive hypertension. We constructed microRNA libraries from the kidneys of Dahl salt-sensitive and Lewis rats taking normal or high-salt diets (4 groups), and identified 91 previously reported and 12 new microRNAs expressed in the kidney. We then used Northern blotting to assess the expression levels of 118 microRNAs in the kidneys and heart ventricles. No significant differences in microRNA expression profiles were observed among the 4 groups. Thus, the microRNA system seemed to be unlikely to contribute to salt-sensitive hypertension in Dahl salt-sensitive rats.

"Genome design" model: evidence from conserved intronic sequence in human-mouse comparison

Introns are shorter in housekeeping genes than in tissue- or development-specific genes. Differing explanations have been offered for this phenomenon: selection for economy (in housekeeping genes), mutation bias or "genomic design." The large-scale implementation in this present paper of a rigorous local sequence alignment algorithm revealed an unprecedented fraction of evolutionarily conserved DNA in human-mouse introns ( approximately 60% of human and approximately 70% of mouse intron length remained after masking for lineage-specific repeats). The length distributions of both conserved and nonconserved regions are very broad but show peaks close to nucleosomal and di-nucleosomal DNA. Both the fraction of conserved sequence and its absolute length were higher in introns of tissue-specific genes than housekeeping genes. This difference remained after control for between-species identity of the conserved fraction, mutation rate, and GC content. In a more direct control, the product of the conserved sequence fraction and the between-species identity of this fraction (which can be considered to be the fraction of conserved nucleotides) was greater in introns of tissue-specific genes than housekeeping genes. Neither the fraction of intron length covered by repeats nor the balance of small insertions and deletions (indels) can explain the greater length of introns in tissue-specific genes. The length of the conserved intronic DNA in a gene is correlated with the number of functional domains in the protein encoded by that gene. These results suggest that the greater length of introns in tissue-specific genes is not due to selection for economy or mutation bias but instead is related to functional complexity (probably mediated by chromatin condensation), and that the evolution of the bulk of noncoding DNA is not completely neutral.

Design of Hammerhead Ribozymes that Cleave Murine Sry mRNA In Vitro and In Vivo

As the first step in investigating the possiblity of applying ribozyme technology to artificial control of the sex ratios at birth in farm animals, where the demand for females exceeds that for males, we designed a hammerhead ribozyme (HHRz) and 2 tRNA(val)-hammerhead ribozyme complexes (tRNARz3 and tRNARz4), and examined their effects upon murine Sry mRNA in vitro and in cells. We demonstrated that HHRz and tRNARz3 could effectively cleave the target Sry mRNA in vitro. For the purpose of experiments in vivo, HHRz was cloned into the highly efficient pUC-CAGGS mammalian expression vector (pCAG/HHRz), and the tRNA ribozyme complexes were cloned into the pol III promoter-driven pPUR-KE vector (pPUR/tRNARz3 and pPUR/tRNARz4); the ribozyme vectors were co-transfected with the target vector (pCAG/Sry). A suppressive action (up to approx. 60%) was confirmed for pCAG/HHRz and pPUR/tRNARz3 upon the transiently expressed exogenously introduced Sry in M15 cultured cells.

A multifunctional envelope-type nano device for novel gene delivery of siRNA plasmids

A multifunctional envelope-type nano device (MEND) for use in the delivery of siRNA expression plasmids is described. The plasmid DNA encoding anti-luciferase short interfering RNA (siRNA) was condensed by poly-L-lysine (PLL) and packaged into the MEND. The silencing effect of the MEND(PLL) showed a 96% inhibition of luciferase activities in a co-transfection study. The silencing effect was maintained at more than 60%, even under the 100-fold diluted conditions. In the luciferase transformed cells, however, the MEND(PLL) showed no significant silencing effect (10%), indicating heterogeneity in transfection by the MEND(PLL). To solve this problem, the DNA condensing agents were optimized by comparing PLL, stearyl octaarginine (STR-R8) and protamine (Prot). No difference in silencing effect (95-97%) was found among these MENDs in a co-transfection study. However, the MEND(Prot) showed a 70% silencing effect in the transformed cells. These results suggest that the MEND(Prot) has less heterogeneity in transfection, while the MEND(PLL) and the MEND(STR-R8) have large heterogeneities. These results demonstrate that MEND(Prot) is a promising gene delivery system for siRNA expression plasmids with less heterogeneity associated with the transfection.

Imminent approaches towards molecular interventions in ageing

Ageing is an innate feature of living organisms. Sensational progress in its molecular understanding in the last decade has culminated into a highly complex picture. Emerging from this complexity are the distinctive roles of some of the tumor suppressor pathways including p53 and pRB in maintenance of senescence phenotype, and telomere maintaining pathways in its escape. We discuss here the current scenario of molecular ageing and the use of modern approaches for its intervention in culture system, at least. Many of the tools we describe here are the newly emergent functional RNA tools that are proved to be fruitful in decoding the human genome. These post-genomic technologies will help us in the discovery of gene targets for interventions aiming to improve the quality at later years of life beyond their mere algebraic extension.

Generation of an shRNAi expression library against the whole human transcripts

RNA interference is a phenomenon in which expression of an individual gene can be specifically silenced by introducing a double-stranded RNA, homologous to the gene, and is receiving attention as a powerful tool for reverse genetics in the post-genome era. Throughout our current research to generate an siRNA expression library for the whole human genome, we face many technical difficulties. We present here the strategies for overcoming some of the difficulties, including the development of genetically stable and highly active siRNA expression vectors, the selection procedure of the favorable target sites, and the efficient and low cost procedure for constructing an siRNA expression library. Furthermore, we demonstrate that the screening using the constructed siRNA-expression library indeed works, by evaluating siRNA-expression library against apoptosis-related genes.

An RNA-dependent protein kinase is involved in tunicamycin-induced apoptosis and Alzheimer's disease

Various types of stress, such as disruption of calcium homeostasis, inhibition of protein glycosylation and reduction of disulfide bonds, result in accumulation of misfolded proteins in the endoplasmic reticulum (ER). The initial cellular response involves removal of such proteins by the ER, but excessive and/or long-term stress results in apoptosis. In this study, we used a randomized ribozyme library and ER stress-mediated apoptosis (tunicamycin-induced apoptosis) in SK-N-SH human neuroblastoma cells as a selective phenotype to identify factors involved in this process. We identified a double-stranded RNA-dependent protein kinase (PKR) as one of the participants in this process. The level of nuclear PKR was elevated, but the level of cytoplasmic PKR barely changed in tunicamycin-treated SK-N-SH cells. Furthermore, tunicamycin also raised levels of phosphorylated PKR in the nucleus. We also detected the accumulation of phosphorylated PKR in the nuclei of autopsied brain tissues in Alzheimer's disease. Thus, PKR might play a role in ER stress-induced apoptosis and in Alzheimer's disease.