Expression and distribution of grp-78/bip in mineralizing tissues and mesenchymal cells

Role of DMP1-mediated GRP78 activation in osteoimmunomodulation of periodontal ligament stem cells

The oral microbiome dysbiosis that causes periodontal disease leads to disruption of various signaling pathways that can result in alveolar bone degradation and subsequent tooth loss. Previous studies have demonstrated the potential of stem cell-based therapies in regeneration of the lost periodontium for the preservation of natural dentition. Periodontal ligament stem cells (PDLSCs) have osteoblast differentiation potential and their proximity to bone makes them an ideal candidate for regenerative therapies. Dentin matrix protein 1 (DMP1), a non-collagenous extracellular matrix protein, is integral to mineralized tissue formation due to its dual roles as an extracellular mediator of hydroxyapatite deposition and intracellular regulator of osteoblastogenesis. Heat shock protein 5A (GRP78) is a master regulator of the endoplasmic reticulum stress response and previous studies in our laboratory have also demonstrated its function as a membrane receptor for DMP1. Bulk RNA sequencing analysis of PDLSCs and PDLSCs overexpressing GRP78 (PDLSCs GRP78) with or without treatment with DMP1 was conducted to evaluate alterations to the differentially expressed gene profiles. This study aims to elucidate pathways in PDLSCs that are altered upon treatment with DMP1 to further characterize its relationship with GRP78 and cell stress signaling cascades. Pathway enrichment analysis of each transcriptomic profile demonstrated enrichment of osteogenic and immune response pathways upon DMP1 stimulation. Results from this study indicate a novel role for DMP1 and GRP78 in modulating immune signaling cascades in PDLSCs.

Heat Shock Proteins in Tooth Development and Injury Repair

Heat shock proteins (HSPs) are a class of molecular chaperones with expression increased in response to heat or other stresses. HSPs regulate cell homeostasis by modulating the folding and maturation of intracellular proteins. Tooth development is a complex process that involves many cell activities. During tooth preparation or trauma, teeth can be damaged. The damaged teeth start their repair process by remineralizing and regenerating tissue. During tooth development and injury repair, different HSPs have different expression patterns and play a special role in odontoblast differentiation and ameloblast secretion by mediating signaling pathways or participating in protein transport. This review explores the expression patterns and potential mechanisms of HSPs, particularly HSP25, HSP60 and HSP70, in tooth development and injury repair.

ER stress-related protein, CHOP, may serve as a biomarker of mechanical asphyxia: a primary study

The precise authentication of death from mechanical asphyxia (DMA) has been a complex problem in forensic medicine. Besides the traditional methods that concern the superficial characterization of the body, researchers are now paying more attention to the biomarkers that may help the identification of DMA. It has been reported that the extremely hypoxic environment created by DMA can cause the specific expression of mitochondria-related protein, which may sever as the biomarkers of DMA authentication. Since endoplasmic reticulum stress (ER stress) has been found to be related to the dysfunction of mitochondria, it is promising to look for the biomarkers of DMA among ER stress-related proteins. In this article, animal and cell experiments were conducted to examine how ER-mitochondria interaction may be influenced in the hypoxic condition caused by DMA primarily. Human samples were then used to verify the possible biomarkers of DMA. We found that ER stress-related protein CHOP was significantly up-regulated within a short-term postmortem interval (PMI) in brain tissue of DMA samples, which may interact with a series of ER stress- and mitochondria-related protein, leading to the apoptosis of the cells. It was also verified in human samples that the expression level of CHOP can sever as a potential biomarker of DMA within a specific PMI.

Biomineralization of Enamel and Dentin Mediated by Matrix Proteins

Biomineralization of enamel, dentin, and bone involves the deposition of apatite mineral crystals within an organic matrix. Bone and teeth are classic examples of biomaterials with unique biomechanical properties that are crucial to their function. The collagen-based apatite mineralization and the important function of noncollagenous proteins are similar in dentin and bone; however, enamel is formed in a unique amelogenin-containing protein matrix. While the structure and organic composition of enamel are different from those of dentin and bone, the principal molecular mechanisms of protein-protein interactions, protein self-assembly, and control of crystallization events by the organic matrix are common among these apatite-containing tissues. This review briefly summarizes enamel and dentin matrix components and their interactions with other extracellular matrix components and calcium ions in mediating the mineralization process. We highlight the crystallization events that are controlled by the protein matrix and their interactions in the extracellular matrix during enamel and dentin biomineralization. Strategies for peptide-inspired biomimetic growth of tooth enamel and bioinspired mineralization of collagen to stimulate repair of demineralized dentin and bone tissue engineering are also addressed.

Endoplasmic Reticulum Stress Mediates Vascular Smooth Muscle Cell Calcification via Increased Release of Grp78 (Glucose-Regulated Protein, 78 kDa)-Loaded Extracellular Vesicles

OBJECTIVE

Vascular calcification is common among aging populations and mediated by vascular smooth muscle cells (VSMCs). The endoplasmic reticulum (ER) is involved in protein folding and ER stress has been implicated in bone mineralization. The role of ER stress in VSMC-mediated calcification is less clear. Approach and Results: mRNA expression of the ER stress markers PERK (PKR (protein kinase RNA)-like ER kinase), ATF (activating transcription factor) 4, ATF6, and Grp78 (glucose-regulated protein, 78 kDa) was detectable in human vessels with levels of PERK decreased in calcified plaques compared to healthy vessels. Protein deposition of Grp78/Grp94 was increased in the matrix of calcified arteries. Induction of ER stress accelerated human primary VSMC-mediated calcification, elevated expression of some osteogenic markers (Runx2 [RUNX family transcription factor 2], OSX [Osterix], ALP [alkaline phosphatse], BSP [bone sialoprotein], and OPG [osteoprotegerin]), and decreased expression of SMC markers. ER stress potentiated extracellular vesicle (EV) release via SMPD3 (sphingomyelin phosphodiesterase 3). EVs from ER stress-treated VSMCs showed increased Grp78 levels and calcification. Electron microscopy confirmed the presence of Grp78/Grp94 in EVs. siRNA (short interfering RNA) knock-down of Grp78 decreased calcification. Warfarin-induced Grp78 and ATF4 expression in rat aortas and VSMCs and increased calcification in an ER stress-dependent manner via increased EV release.

CONCLUSIONS

ER stress induces vascular calcification by increasing release of Grp78-loaded EVs. Our results reveal a novel mechanism of action of warfarin, involving increased EV release via the PERK-ATF4 pathway, contributing to calcification. This study is the first to show that warfarin induces ER stress and to link ER stress to cargo loading of EVs.

Activation of the EIF2α/ATF4 and ATF6 Pathways in DU-145 Cells by Boric Acid at the Concentration Reported in Men at the US Mean Boron Intake

Fruits, nuts, legumes, and vegetables are rich sources of boron (B), an essential plant nutrient with chemopreventive properties. Blood boric acid (BA) levels reflect recent B intake, and men at the US mean intake have a reported non-fasting level of 10 μM. Treatment of DU-145 prostate cancer cells with physiological concentrations of BA inhibits cell proliferation without causing apoptosis and activates eukaryotic initiation factor 2 (eIF2α). EIF2α induces cell differentiation and protects cells by redirecting gene expression to manage endoplasmic reticulum stress. Our objective was to determine the temporal expression of endoplasmic reticulum (ER) stress-activated genes in DU-145 prostate cells treated with 10 μM BA. Immunoblots showed post-treatment increases in eIF2α protein at 30 min and ATF4 and ATF6 proteins at 1 h and 30 min, respectively. The increase in ATF4 was accompanied by an increase in the expression of its downstream genes growth arrest and DNA damage-induced protein 34 (GADD34) and homocysteine-induced ER protein (Herp), but a decrease in GADD153/CCAAT/enhancer-binding protein homologous protein (CHOP), a pro-apoptotic gene. The increase in ATF6 was accompanied by an increase in expression of its downstream genes GRP78/BiP, calreticulin, Grp94, and EDEM. BA did not activate IRE1 or induce cleavage of XBP1 mRNA, a target of IRE1. Low boron status has been associated with increased cancer risk, low bone mineralization, and retinal degeneration. ATF4 and BiP/GRP78 function in osteogenesis and bone remodeling, calreticulin is required for tumor suppressor p53 function and mineralization of teeth, and BiP/GRP78 and EDEM prevent the aggregation of misfolded opsins which leads to retinal degeneration. The identification of BA-activated genes that regulate its phenotypic effects provides a molecular underpinning for boron nutrition and biology.

Induction of apoptosis by hypertension via endoplasmic reticulum stress

BACKGROUND/AIMS

Endoplasmic reticulum (ER) stress is one of the intrinsic apoptosis pathways, and cardiac apoptosis can occur in cardiovascular diseases, such as hypertension. However, the mechanisms by which ER stress leads to apoptosis remain enigmatic, particularly in the progression from cardiac hypertrophy to diastolic heart failure due to hypertension.

METHODS

We used spontaneously hypertensive rats (SHRs) to investigate possible signalling pathways for ER stress.

RESULTS

We found that cardiac protein and mRNA levels of glucoseregulated protein 78 were up-regulated. In addition, the CHOP- and caspase-12-dependent pathways, but not that of JNK, were activated in the SHR rats.

CONCLUSIONS

These results suggest that ER stress can contribute to myocardial apoptosis during hypertensive disease.

Biomimetic extracellular matrix mediated somatic stem cell differentiation: applications in dental pulp tissue regeneration

Dental caries is one of the most widely prevalent infectious diseases in the world. It affects more than half of the world's population. The current treatment for necrotic dental pulp tissue arising from dental caries is root canal therapy. This treatment results in loss of tooth sensitivity and vitality making it prone for secondary infections. Over the past decade, several tissue-engineering approaches have attempted regeneration of the dental pulp tissue. Although several studies have highlighted the potential of dental stem cells, none have transitioned into a clinical setting owing to limited availability of dental stem cells and the need for growth factor delivery systems. Our strategy is to utilize the intact ECM of pulp cells to drive lineage specific differentiation of bone marrow derived mesenchymal stem cells. From a clinical perspective, pulp ECM scaffolds can be generated using cell lines and patient specific somatic stem cells can be used for regeneration. Our published results have shown the feasibility of using pulp ECM scaffolds for odontogenic differentiation of non-dental mesenchymal cells. This focused review discusses the issues surrounding dental pulp tissue regeneration and the potential of our strategy to overcome these issues.

Multifunctional ECM proteins in bone and teeth

The extracellular matrix (ECM) of all tissues and organs is a highly organized and complex structure unique to the specific organ type. The ECM contains structural and functional proteins that define cellular function, organization, behavior and ultimately organ characteristics and function. The ECM was initially thought to contain only a specific set of secretory proteins. However, our group and several other groups have shown that the ECM contains functional proteins that have been previously defined as solely intracellular. In the present review, we have focused on the ECM of mineralized tissues namely bone and dentin. We provide here, a brief review of some non-classical ECM proteins that have been shown to possess both intra and extracellular roles in the formation of these mineralized matrices.

Identification of novel amelogenin-binding proteins by proteomics analysis

Emdogain (enamel matrix derivative, EMD) is well recognized in periodontology. It is used in periodontal surgery to regenerate cementum, periodontal ligament, and alveolar bone. However, the precise molecular mechanisms underlying periodontal regeneration are still unclear. In this study, we investigated the proteins bound to amelogenin, which are suggested to play a pivotal role in promoting periodontal tissue regeneration. To identify new molecules that interact with amelogenin and are involved in osteoblast activation, we employed coupling affinity chromatography with proteomic analysis in fractionated SaOS-2 osteoblastic cell lysate. In SaOS-2 cells, many of the amelogenin-interacting proteins in the cytoplasm were mainly cytoskeletal proteins and several chaperone molecules of heat shock protein 70 (HSP70) family. On the other hand, the proteomic profiles of amelogenin-interacting proteins in the membrane fraction of the cell extracts were quite different from those of the cytosolic-fraction. They were mainly endoplasmic reticulum (ER)-associated proteins, with lesser quantities of mitochondrial proteins and nucleoprotein. Among the identified amelogenin-interacting proteins, we validated the biological interaction of amelogenin with glucose-regulated protein 78 (Grp78/Bip), which was identified in both cytosolic and membrane-enriched fractions. Confocal co-localization experiment strongly suggested that Grp78/Bip could be an amelogenin receptor candidate. Further biological evaluations were examined by Grp78/Bip knockdown analysis with and without amelogenin. Within the limits of the present study, the interaction of amelogenin with Grp78/Bip contributed to cell proliferation, rather than correlate with the osteogenic differentiation in SaOS-2 cells. Although the biological significance of other interactions are not yet explored, these findings suggest that the differential effects of amelogenin-derived osteoblast activation could be of potential clinical significance for understanding the cellular and molecular bases of amelogenin-induced periodontal tissue regeneration.

Odontogenic induction of dental stem cells by extracellular matrix-inspired three-dimensional scaffold

Currently, root canal therapy is the only clinical treatment available to treat damaged or necrotic dental pulp tissue arising from caries. This treatment results in the loss of tooth vitality. Somatic dental stem cell-based tissue engineering approaches can alleviate this problem by preserving tooth vitality. Dental stem cells are multipotent and under appropriate conditions could be used for dental pulp tissue engineering. Successful use of these cells in pulp repair requires a combination of growth factors and appropriate scaffolds to induce cell differentiation. In this study, we demonstrate the odontogenic differentiation of human dental pulp stem cells (DPSCs) and the human periodontal ligament stem cells when cultured on a decellularized 3D extracellular matrix (ECM) scaffold without the need for exogenous addition of growth factors. Subcutaneous implantation of the ECM scaffolds containing DPSCs showed the formation of dental pulp-like tissue with cells expressing dentin sialoprotein (DSP) and dentin phosphophoryn (DPP). Additionally, we also show that the ECM scaffold can be exploited as a tool to study the extracellular function of multifunctional proteins. These promising results demonstrate the feasibility of developing these biomimetic scaffolds for treatment of dental caries.

The Histochemistry and Cell Biology compendium: a review of 2012

The year 2012 was another exciting year for Histochemistry and Cell Biology. Innovations in immunohistochemical techniques and microscopy-based imaging have provided the means for advances in the field of cell biology. Over 130 manuscripts were published in the journal during 2012, representing methodological advancements, pathobiology of disease, and cell and tissue biology. This annual review of the manuscripts published in the previous year in Histochemistry and Cell Biology serves as an abbreviated reference for the readership to quickly peruse and discern trends in the field over the past year. The review has been broadly divided into multiple sections encompassing topics such as method advancements, subcellular components, extracellular matrix, and organ systems. We hope that the creation of this subdivision will serve to guide the reader to a specific topic of interest, while simultaneously providing a concise and easily accessible encapsulation of other topics in the broad area of Histochemistry and Cell Biology.