Dentin Matrix Protein 1 (DMP1): New and Important Roles for Biomineralization and Phosphate Homeostasis

Previously, non-collagenous matrix proteins, such as DMP1, were viewed with little biological interest. The last decade of research has increased our understanding of DMP1, as it is now widely recognized that this protein is expressed in non-mineralized tissues, as well as in cancerous lesions. Protein chemistry studies have shown that the full length of DMP1, as a precursor, is cleaved into two distinct forms: the C-terminal and N-terminal fragments. Functional studies have demonstrated that DMP1 is essential in the maturation of odontoblasts and osteoblasts, as well as in mineralization via local and systemic mechanisms. The identification of DMP1 mutations in humans has led to the discovery of a novel disease: autosomal-recessive hypophosphatemic rickets. Furthermore, the regulation of phosphate homeostasis by DMP1 through FGF23, a newly identified hormone that is released from bone and targeted in the kidneys, sets a new direction for research that associates biomineralization with phosphate regulation.

Post-translational Modifications of SIBLING Proteins and Their Roles in Osteogenesis and Dentinogenesis

The extracellular matrix (ECM) of bone and dentin contains several non-collagenous proteins. One category of non-collagenous protein is termed the SIBLING (Small Integrin-Binding LIgand, N-linked Glycoprotein) family, that includes osteopontin (OPN), bone sialoprotein (BSP), dentin matrix protein 1 (DMP1), dentin sialophosphoprotein (DSPP), and matrix extracellular phosphoglycoprotein (MEPE). These polyanionic SIBLING proteins are believed to play key biological roles in the mineralization of bone and dentin. Although the specific mechanisms involved in controlling bone and dentin formation are still unknown, it is clear that some functions of the SIBLING family members are dependent on the nature and extent of post-translational modifications (PTMs), such as phosphorylation, glycosylation, and proteolytic processing, since these PTMs would have significant effects on their structure. OPN and BSP are present in the ECM of bone and dentin as full-length forms, whereas amino acid sequencing indicates that DMP1 and DSPP exist as proteolytically processed fragments that result from scission of X-Asp bonds. We hypothesized that the processing of DMP1 and DSPP is catalyzed by the PHEX enzyme, since this protein, an endopeptidase that is predominantly expressed in bone and tooth, has a strong preference for cleavage at the NH2-terminus of aspartyl residue. We envision that the proteolytic processing of DMP1 and DSPP may be an activation process that plays a significant, crucial role in osteogenesis and dentinogenesis, and that a failure in this processing would cause defective mineralization in bone and dentin, as observed in X-linked hypophosphatemic rickets.

Visual detection of thrombin using a strip biosensor through aptamer-cleavage reaction with enzyme catalytic amplification

A new class of strip biosensors has been established based on well-distributed thrombin aptamer-linked gold nanoparticle aggregates, which will undergo a cracking reaction when the target recognizes its homologous aptamer. Combining the aptamer-cleavage reaction with the enzyme catalytic amplification system, our proposed lateral flow strip biosensor (LFB) is capable of visually detecting 6.4 pM of thrombin without instrumentation within 12 minutes. Under the optimal conditions, the quantitative detection of thrombin by a portable strip reader exhibited a linear relationship between the peak area and the concentration of thrombin in the range of 6.4 pM-500 nM with a detection limit of 4.9 pM, which is three orders of magnitude lower than that of the aptamer-functionalized gold nanoparticle-based LFB (2.5 nM, Xu et al., Anal. Chem., 2009, 81, 669-675). As the aptamers have no special requirements and the gold nanoparticles can also be replaced by other metallic nanoparticles, this method for strip sensing is expected to be generally applicable in point of care testing, home testing, medical diagnostics, clinical diagnosis, and environmental monitoring.

Transgenic expression of dentin phosphoprotein inhibits skeletal development

Dentin sialophosphoprotein (DSPP) is proteolytically processed into an NH₂-terminal fragment called dentin sialoprotein (DSP) and a COOH-terminal fragment known as dentin phosphoprotein (DPP). These two fragments are believed to perform distinct roles in formation of bone and dentin. To investigate the functions of DPP in skeletal development, we generated transgenic mice to overexpress hemagglutinin (HA)-tagged DPP under the control of a 3.6 kb type I collagen (Col1a1) promoter (designated as Col1a1-HA-DPP). The Col1a1-HA-DPP transgenic mice were significantly smaller by weight, had smaller skeletons and shorter long bones than their wild type littermates, as demonstrated by X-ray radiography. They displayed reduced trabecular bone formation and narrower zones of proliferative and hypertrophic chondrocytes in the growth plates of the long bones. Histological analyses showed that the transgenic mice had reduced cell proliferation in the proliferating zone, but lacked obvious defects in the chondrocyte differentiation. In addition, the transgenic mice with a high level of transgene expression developed spontaneous long bone fractures. In conclusion, overexpressing DPP inhibited skeletal development, suggesting that the balanced actions between the NH₂- and COOH-terminal fragments of DSPP may be required for normal skeletal development.

Repair of dentin defects from DSPP knockout mice by PILP mineralization

Dentinogenesis imperfecta type II (DGI-II) lacks intrafibrillar mineral with severe compromise of dentin mechanical properties. A Dspp knockout (Dspp-/-) mouse, with a phenotype similar to that of human DGI-II, was used to determine if poly-L-aspartic acid [poly(ASP)] in the "polymer-induced liquid-precursor" (PILP) system can restore its mechanical properties. Dentin from six-week old Dspp-/- and wild-type mice was treated with CaP solution containing poly(ASP) for up to 14 days. Elastic modulus and hardness before and after treatment were correlated with mineralization from Micro x-ray computed tomography (Micro-XCT). Transmission electron microscopy (TEM)/Selected area electron diffraction (SAED) were used to compare matrix mineralization and crystallography. Mechanical properties of the Dspp-/- dentin were significantly less than wild-type dentin and recovered significantly (P < 0.05) after PILP-treatment, reaching values comparable to wild-type dentin. Micro-XCT showed mineral recovery similar to wild-type dentin after PILP-treatment. TEM/SAED showed repair of patchy mineralization and complete mineralization of defective dentin. This approach may lead to new strategies for hard tissue repair.

Visual multiple recognition of protein biomarkers based on an array of aptamer modified gold nanoparticles in biocomputing to strip biosensor logic operations

We developed a strip biosensors array based on aptamer-modified gold nanoparticles as receptors and combined the protein-aptamer binding reaction with the streptavidin-biotin interaction as well as the sandwich format. We found that a series of protein receptors obtained a distinct response pattern to each target protein. Three proteins have been well distinguished with the naked eyes and a portable reader without mutual interference, accompanying with lower limit of detection and wider linear range. A complete set of four elementary logic gates (AND, OR, INH, and NAND) and eight combinative logic gates (AND-OR; AND-INH; OR-INH; INH-NAND; AND-OR-INH; AND-INH-NAND; OR-INH-NAND; AND-OR-INH-NAND) are thoroughly realized using this array, which could eventually be applicable to the keypad-lock system with enhanced complexity in the near future. Moreover, this array shows excellent linear relationships, anti-interference capability, real human serum samples applicability, long-term storage stability and reproducibility. All indicate that this design has very good prospects for development.

Assessing the safety of outpatient ventral hernia repair: a NSQIP analysis of 7666 patients

PURPOSE

Given the paucity of literature on outpatient ventral hernia repair (VHR), and that assessment of the safety of outpatient surgical procedures is becoming an active area of investigation, we have performed a multi-institutional retrospective analysis benchmarking rates of 30-day complications and readmissions and identifying predictive factors for these outcomes.

METHODS

National surgical quality improvement project data files from 2011 to 2012 were reviewed to collect data on all patients undergoing outpatient VHR during that period. The incidence of 30-day peri-operative complication and unplanned readmission was surveyed. We created a multivariate regression model to identify predictive factors for overall, surgical, and medical complications and unplanned readmissions with proper risk adjustment.

RESULTS

30-day complication and readmission rates in outpatient VHR were acceptably low. 3% of the queried outpatients experienced an overall complication, 2.1% a surgical complication, and 1.1% a medical complication. 3.3% of all patients were readmitted within 30 days. Upon multivariate analysis, predictors of overall complications included age, BMI, history of Chronic Obstructive Pulmonary Disease (COPD), and total operation time, predictors of surgical complications included age, BMI, total operation time, predictors of medical complications included total operation time, and predictors of unplanned readmissions included history of COPD, bleeding disorder, American Society of Anesthesiologists Class 3, 4, or 5, total operation time, and use of the laparoscopic technique.

CONCLUSION

We have demonstrated that the risk of peri-operative morbidity in VHR as granularly defined in our study is low in the outpatient setting. Identification of predictive factors will be important to patient risk stratification.

An in situ hybridization study of perlecan, DMP1, and MEPE in developing condylar cartilage of the fetal mouse mandible and limb bud cartilage

The main purpose of this in situ hybridization study was to investigate mRNA expression of three bone/cartilage matrix components (perlecan, DMP1, and MEPE) in developing primary (tibial) and secondary (condylar) cartilage. Perlecan mRNA expression was first detected in newly formed chondrocytes in tibial cartilage at E13.0, but this expression decreased in hypertrophic chondrocytes at E14.0. In contrast, at E15.0, perlecan mRNA was first detected in the newly formed chondrocytes of condylar cartilage; these chondrocytes had characteristics of hypertrophic chondrocytes, which confirmed the previous observation that progenitor cells of developing secondary cartilage rapidly differentiate into hypertrophic chondrocytes. DMP1 mRNA was detected in many chondrocytes within the lower hypertrophic cell zone in tibial cartilage at E14.0. In contrast, DMP1 mRNA expression was only transiently detected in a few chondrocytes of condylar cartilage at E15.0. Thus, DMP1 may be less important in the developing condylar cartilage than in the tibial cartilage. Another purpose of this study was to test the hypothesis that MEPE may be a useful marker molecule for cartilage. MEPE mRNA was not detected in any chondrocytes in either tibial or condylar cartilage; however, MEPE immunoreactivity was detected throughout the cartilage matrix. Western immunoblot analysis demonstrated that MEPE antibody recognized two bands, one of 67 kDa and another of 59 kDa, in cartilage-derived samples. Thus MEPE protein may gradually accumulate in the cartilage, even though mRNA expression levels were below the limits of detection of in situ hybridization. Ultimately, we could not designate MEPE as a marker molecule for cartilage, and would modify our original hypothesis.

Anti-CII antibody as a novel indicator to assess disease activity in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic autoimmune disorder that affects a variety of organ systems. Anti-dsDNA Abs and complement factors have been used as indicators of lupus activity for more than 50 years. A novel indicator of activation in SLE is reported in this paper. Anti-collagen type II (CII) Ab was obviously elevated in patients with SLE compared to those patients with ankylosing spondylitis (AS) and healthy controls (HCs). Anti-CII-Ab-positive patients with SLE showed significantly higher levels of serum IgG and higher titers of ANA but lower levels of C3 and C4 than controls. A positive correlation was demonstrated between anti-CII Ab and serum IgG in SLE patients (r = 0.50, p < 0.0001). The negative correlations of anti-CII Ab with C3 and C4 were observed in SLE patients (r = -0.36, p = 0.0013; r = -0.37, p = 0.0006, respectively). The reduced anti-CII Ab level was accompanied by decreased level of serum IgG and increased levels of C3 and C4 after regular treatment. Therefore, anti-CII Ab could be a novel indicator for monitoring activity of SLE.

Dspp-independent Effects of Transgenic Trps1 Overexpression on Dentin Formation

The Trps1 transcription factor is highly expressed in dental mesenchyme and preodontoblasts, while in mature, secretory odontoblasts, it is expressed at low levels. Previously, we have shown that high Trps1 levels in mature odontoblasts impair their function in vitro and in vivo. Col1a1-Trps1 transgenic (Trps1-Tg) mice demonstrate defective dentin secretion and mineralization, which are associated with significantly decreased Dspp expression due to direct repression of the Dspp gene by Trps1. Here, by crossing Trps1-Tg and Col1a1-Dspp transgenic (Dspp-Tg) mice, we generated Col1a1-Trps1;Col1a1-Dspp double transgenic (double-Tg) mice in which Dspp was restored in odontoblasts overexpressing Trps1. Comparative micro-computed tomography analyses revealed partial correction of the dentin volume and no improvement of dentin mineralization in double transgenic mice in comparison with Trps1-Tg and wild-type (WT) mice. In addition, dentin of double-Tg mice has an irregular mineralization pattern characteristic for dentin in hypophosphatemic rickets. Consistent with this phenotype, decreased levels of Phex, Vdr, and Fam20c proteins are detected in both Trps1-Tg and double-Tg odontoblasts in comparison with WT and Dspp-Tg odontoblasts. This suggests that the Dspp-independent dentin mineralization defects in Trps1-Tg mice are a result of downregulation of a group of proteins critical for mineral deposition within the dentin matrix. In summary, by demonstrating that Trps1 functions as a repressor of later stages of dentinogenesis, we provide functional significance of the dynamic Trps1 expression pattern during dentinogenesis.

Identification and characterisation of tobacco microRNA transcriptome using high-throughput sequencing

MicroRNAs (miRNAs) are post-transcriptional regulators that are involved in numerous biological processes in plants. In this study, we investigate miRNAs in Honghua Dajinyuan, an agronomically important species of tobacco in China. Here, we report a comprehensive analysis of miRNA expression profiles in the leaf, stem and root using a high-throughput sequencing approach. A total of 165 miRNAs, representing 55 conserved families, and 50 novel miRNAs, representing 19 families, were identified in three libraries. In addition, 12 miRNAs were randomly selected from a differentially expressed conserved miRNA family in three libraries with expression alterations and subjected to qRT-PCR validation. Of these, the expression level of nta-miR167d is highly enriched in the leaf tissue. In addition, the expression level of nta-miR319a is prominently enriched in the stem, while nta-miR160c is highly enriched in the root. Moreover, the target prediction showed that most of the targets coded for transcription factors that are involved in cellular and metabolic processes. GO analysis showed that most of the targets were involved in organelle function, served binding functions, and take part in cellular and metabolic processes. This study helps shed new light on understanding the role of miRNAs in different parts of the tobacco plant and adds a significant number of novel miRNAs to the tobacco miRNA transcriptome.

Relationship between clinicopathological features and HIF-2α in gastric adenocarcinoma

Hypoxia influences tumor growth by inducing angiogenesis and genetic alterations. Hypoxia-inducible factor-2α (HIF-2α) plays an essential role in oxygen homeostasis. Expression of HIF-2α-inducible genes is associated with tumor progression. In this study, we investigated this correlation immunohistochemically and using quantitative reverse transcription-polymerase chain reaction to examine various clinical and pathological features in 55 specimens of gastric cancer and 40 specimens of normal gastric tissue. The HIF-2α mRNA expression level and protein expression were significantly higher in gastric cancer tissue samples than in adjacent tissue samples. The positive rates of HIF-2α, matrix metalloprotease-9 (MMP-9), and vascular endothelial growth factor (VEGF) protein were 63.6% (35/55), 80.0% (44/55), and 65.5% (36/55) in gastric cancer tissue specimens, respectively. These values were significantly higher than those in normal gastric tissue samples (P = 0.001, P = 0.000, and P = 0.007, respectively). HIF-2α and MMP-9 were significantly correlated with primary tumor size (P = 0.0065 and P = 0.036, respectively) and invasion depth (P = 0.012 and P = 0.008, respectively). HIF-2α and VEGF were significantly correlated with lymph node involvement (P = 0.030 and P = 0.016, respectively). Expression of HIF-2α was positively correlated with the expression of VEGF and MMP-9 (P = 0.036 and P = 0.000, respectively). These results suggest that HIF-2α is involved in gastric carcinogenesis and disease progression and is a potential therapeutic target for gastric carcinoma.

A double-enhanced strip biosensor for the rapid and ultrasensitive detection of protein biomarkers

A LFB based on AuNP aggregation and HRP-assisted dual-class signal amplification and the specific biotin–streptavidin recognition reaction.