Evidence for specific interaction between matrix vesicle proteins and the connective tissue matrix

Non-viral Gene Delivery Methods for Bone and Joints

Viral carrier transport efficiency of gene delivery is high, depending on the type of vector. However, viral delivery poses significant safety concerns such as inefficient/unpredictable reprogramming outcomes, genomic integration, as well as unwarranted immune responses and toxicity. Thus, non-viral gene delivery methods are more feasible for translation as these allow safer delivery of genes and can modulate gene expression transiently both in vivo, ex vivo, and in vitro. Based on current studies, the efficiency of these technologies appears to be more limited, but they are appealing for clinical translation. This review presents a summary of recent advancements in orthopedics, where primarily bone and joints from the musculoskeletal apparatus were targeted. In connective tissues, which are known to have a poor healing capacity, and have a relatively low cell-density, i.e., articular cartilage, bone, and the intervertebral disk (IVD) several approaches have recently been undertaken. We provide a brief overview of the existing technologies, using nano-spheres/engineered vesicles, lipofection, and in vivo electroporation. Here, delivery for microRNA (miRNA), and silencing RNA (siRNA) and DNA plasmids will be discussed. Recent studies will be summarized that aimed to improve regeneration of these tissues, involving the delivery of bone morphogenic proteins (BMPs), such as BMP2 for improvement of bone healing. For articular cartilage/osteochondral junction, non-viral methods concentrate on targeted delivery to chondrocytes or MSCs for tissue engineering-based approaches. For the IVD, growth factors such as GDF5 or GDF6 or developmental transcription factors such as Brachyury or FOXF1 seem to be of high clinical interest. However, the most efficient method of gene transfer is still elusive, as several preclinical studies have reported many different non-viral methods and clinical translation of these techniques still needs to be validated. Here we discuss the non-viral methods applied for bone and joint and propose methods that can be promising in clinical use.

Extracellular vesicles are integral and functional components of the extracellular matrix

Extracellular vesicles (EV) are small plasma membrane-derived particles released into the extracellular space by virtually all cell types. Recently, EV have received increased interest because of their capability to carry nucleic acids, proteins, lipids and signaling molecules and to transfer their cargo into the target cells. Less attention has been paid to their role in modifying the composition of the extracellular matrix (ECM), either directly or indirectly via regulating the ability of target cells to synthesize or degrade matrix molecules. Based on recent results, EV can be considered one of the structural and functional components of the ECM that participate in matrix organization, regulation of cells within it, and in determining the physical properties of soft connective tissues, bone, cartilage and dentin. This review addresses the relevance of EV as specific modulators of the ECM, such as during the assembly and disassembly of the molecular network, signaling through the ECM and formation of niches suitable for tissue regeneration, inflammation and tumor progression. Finally, we assess the potential of these aspects of EV biology to translational medicine.

Glycation Contributes to Interaction Between Human Bone Alkaline Phosphatase and Collagen Type I

Bone is a biological composite material comprised primarily of collagen type I and mineral crystals of calcium and phosphate in the form of hydroxyapatite (HA), which together provide its mechanical properties. Bone alkaline phosphatase (ALP), produced by osteoblasts, plays a pivotal role in the mineralization process. Affinity contacts between collagen, mainly type II, and the crown domain of various ALP isozymes were reported in a few in vitro studies in the 1980s and 1990s, but have not attracted much attention since, although such interactions may have important implications for the bone mineralization process. The objective of this study was to investigate the binding properties of human collagen type I to human bone ALP, including the two bone ALP isoforms B1 and B2. ALP from human liver, human placenta and E. coli were also studied. A surface plasmon resonance-based analysis, supported by electrophoresis and blotting, showed that bone ALP binds stronger to collagen type I in comparison with ALPs expressed in non-mineralizing tissues. Further, the B2 isoform binds significantly stronger to collagen type I in comparison with the B1 isoform. Human bone and liver ALP (with identical amino acid composition) displayed pronounced differences in binding, revealing that post-translational glycosylation properties govern these interactions to a large extent. In conclusion, this study presents the first evidence that glycosylation differences in human ALPs are of crucial importance for protein-protein interactions with collagen type I, although the presence of the ALP crown domain may also be necessary. Different binding affinities among the bone ALP isoforms may influence the mineral-collagen interface, mineralization kinetics, and degree of bone matrix mineralization, which are important factors determining the material properties of bone.

National Veterans Health Administration inpatient risk stratification models for hospital-acquired acute kidney injury

OBJECTIVE

Hospital-acquired acute kidney injury (HA-AKI) is a potentially preventable cause of morbidity and mortality. Identifying high-risk patients prior to the onset of kidney injury is a key step towards AKI prevention.

MATERIALS AND METHODS

A national retrospective cohort of 1,620,898 patient hospitalizations from 116 Veterans Affairs hospitals was assembled from electronic health record (EHR) data collected from 2003 to 2012. HA-AKI was defined at stage 1+, stage 2+, and dialysis. EHR-based predictors were identified through logistic regression, least absolute shrinkage and selection operator (lasso) regression, and random forests, and pair-wise comparisons between each were made. Calibration and discrimination metrics were calculated using 50 bootstrap iterations. In the final models, we report odds ratios, 95% confidence intervals, and importance rankings for predictor variables to evaluate their significance.

RESULTS

The area under the receiver operating characteristic curve (AUC) for the different model outcomes ranged from 0.746 to 0.758 in stage 1+, 0.714 to 0.720 in stage 2+, and 0.823 to 0.825 in dialysis. Logistic regression had the best AUC in stage 1+ and dialysis. Random forests had the best AUC in stage 2+ but the least favorable calibration plots. Multiple risk factors were significant in our models, including some nonsteroidal anti-inflammatory drugs, blood pressure medications, antibiotics, and intravenous fluids given during the first 48 h of admission.

CONCLUSIONS

This study demonstrated that, although all the models tested had good discrimination, performance characteristics varied between methods, and the random forests models did not calibrate as well as the lasso or logistic regression models. In addition, novel modifiable risk factors were explored and found to be significant.

Cellular function and molecular structure of ecto-nucleotidases

Ecto-nucleotidases play a pivotal role in purinergic signal transmission. They hydrolyze extracellular nucleotides and thus can control their availability at purinergic P2 receptors. They generate extracellular nucleosides for cellular reuptake and salvage via nucleoside transporters of the plasma membrane. The extracellular adenosine formed acts as an agonist of purinergic P1 receptors. They also can produce and hydrolyze extracellular inorganic pyrophosphate that is of major relevance in the control of bone mineralization. This review discusses and compares four major groups of ecto-nucleotidases: the ecto-nucleoside triphosphate diphosphohydrolases, ecto-5'-nucleotidase, ecto-nucleotide pyrophosphatase/phosphodiesterases, and alkaline phosphatases. Only recently and based on crystal structures, detailed information regarding the spatial structures and catalytic mechanisms has become available for members of these four ecto-nucleotidase families. This permits detailed predictions of their catalytic mechanisms and a comparison between the individual enzyme groups. The review focuses on the principal biochemical, cell biological, catalytic, and structural properties of the enzymes and provides brief reference to tissue distribution, and physiological and pathophysiological functions.

Proteome analysis of matrix vesicles isolated from femurs of chicken embryo

Matrix vesicles (MVs) are extracellular organelles that initiate mineral formation, accumulating inorganic phosphate (P(i)) and calcium leading to the formation of hydroxyapatite (HA) crystals, the main mineral component of bones. MVs are produced during bone formation, as well as during the endochondral calcification of cartilage. MVs are released into the extracellular matrix from osseous cells such as osteoblasts and hypertrophic chondrocytes. In this report, using 1-D SDS-PAGE, in-gel tryptic digestion and an LC-MS-MS/MS protein identification protocol, we characterized the proteome of MVs isolated from chicken embryo (Gallus gallus) bones and cartilage. We identified 126 gene products, including proteins related to the extracellular matrix and ion transport, as well as enzymes, cytoskeletal, and regulatory proteins. Among the proteins recognized for the first time in MVs were aquaporin 1, annexin A1 (AnxA1), AnxA11, glycoprotein HT7, G(i) protein alpha2, and scavenger receptor type B. The pathways for targeting the identified proteins into MVs and their particular functions in the biomineralization process are discussed. Obtaining a knowledge of the functions and roles of these proteins during embryonic mineralization is a prerequisite for the overall understanding of the initial mineral formation mechanisms.

Rat osseous plate alkaline phosphatase: effect of neutral protease digestion on the hydrolysis of pyrophosphate and nitrophenylphosphate

Collagenase treatment, commonly used to prepare alkaline phosphatase-rich matrix vesicles from epiphyseal cartilage growth plates, seems to affect the integrity of this membrane-bound enzyme. Alkaline phosphatase-rich rat osseous plates were incubated with 1,000 U/mL collagenase for 3 h, at 37 degrees C and after purification on Sepharose 4B, kinetic studies were performed using nitrophenylphosphate and pyrophosphate as substrates. The optimum apparent pH for the hydrolysis of p-nitrophenylphosphate and pyrophosphate increased from 9.4 to 10.25 and from 8.0 to 9.0, respectively, as a consequence ofcollagenase treatment. In the absence of Mg2+ ions, the enzyme hydrolyzed PNPP with KM = 322.5 +/- 15.3 microM and V = 965.2 +/- 45.8 U/mg, while in the presence of 2 mM Mg2+ ions, V increased 66%. Cobalt (K0.5 = 5.3 +/- 0.3 microM) and manganese (K0.5 = 0.72 +/- 0.03 microM) ions stimulated the PNPPase activity of the collagenase-treated enzyme, but with a lower apparent affinity when compared with that of not-treated enzyme. In the absence of Mg2+ ions pyrophosphate was hydrolyzed according to Michaelis-Menten kinetics (KM = 105.1 +/- 6.3 microM and V = 64.9 +/- 3.9 U/mg), but site-site interactions (nH = 1.2) were observed in the presence of 2 mM Mg2+ ions (V = 110.8 +/- 5.5 U/mg; K0.5 = 42.7 +/- 2.0 microM). To our knowledge this is the first report showing significant alterations on phosphohydrolytic activity and metal binding properties of bone alkaline phosphatase due to associated neutral proteases in collagenase preparations often used for the isolation of matrix vesicles.

Phenotypic and biochemical consequences of collagen X mutations in mice and humans

Skeletal biology has entered an exciting period with the technological advances in murine transgenesis and human genetics. This review focuses on how these two approaches are being used to address the role of collagen X, the major extracellular matrix component of the focal zone of endochondral ossification, the hypertrophic cartilage zone. The hypothesized role of this unique collagen in skeletal morphogenesis and the phenotypic and biochemical consequences resulting from the disruption of its function are discussed. Specifically, data from three murine models, including transgenic mice with a dominant interference phenotype for collagen X, and two sets of mice with an inactivated collagen X gene through gene targeting and homologous recombination, as well as the human disorder of Schmid metaphyseal chondrodysplasia resulting from mutations in collagen X, are summarized and compared. Several inconsistencies and unresolved issues regarding the murine and human phenotypes and the function of collagen X are discussed.

Different responses of bone alkaline phosphatase isoforms during recombinant insulin-like growth factor-I (IGF-I) and during growth hormone therapy in adults with growth hormone deficiency

We studied serum bone alkaline phosphatase (ALP) isoforms and other markers of bone turnover in growth hormone-deficient (GHD) adults (n = 22). The patients were followed during 1 week of insulin-like growth factor-I (IGF-I) administration, 40 micrograms/kg of body weight/day (n = 6), and during 24 months of growth hormone (GH) therapy, 0.125 IU/kg of body weight/week for the first month, and then 0.250 IU/kg of body weight/week (n = 20). Six ALP isoforms were separated and quantified by high-performance liquid chromatography: one bone/intestinal, two bone (B1, B22), and three liver ALP isoforms. At baseline, the mean levels of B1, B22, and osteocalcin were higher in GHD adults than in healthy adults. After 2 week of IGF-I administration and 1 month of GH therapy, only B1 was decreased. We suggest that the initial decrease of B1 during GH therapy could be an effect of endocrine IGF-I action mediated by GH. After 3 months of GH therapy, both B1 and B2 increased as compared with placebo. Osteocalcin, carboxy-terminal propeptide of type I procollagen (PICP), cross-linked carboxy-terminal telopeptide of type I collagen (ICTP), and urinary pyridinoline cross-links/creatinine ratio increased during GH therapy. PICP increased significantly before bone ALP and osteocalcin, indicating early stimulation of type I collagen synthesis as previously demonstrated by in vitro models. Different responses of the bone ALP isoforms during IGF-I and during GH therapy suggest different regulations in vivo.

Stress-relaxation of fibroblasts in collagen matrices triggers ectocytosis of plasma membrane vesicles containing actin, annexins II and VI, and beta 1 integrin receptors

To learn about the effects of tension on fibroblast function, we have been studying initial cellular responses to stress-relaxation. Human foreskin fibroblasts were cultured in anchored collagen matrices for 2 days, during which time mechanical stress developed. Subsequently, the matrices were dislodged; thereby allowing stress to dissipate. Within 5 min after initiating stress-relaxation, fibroblasts retracted their pseudopodia. At this time, we observed the disappearance of cellular stress fibers and the formation of actin clusters along the cell margins. The actin was found to be located inside 200 nm diameter vesicles that were budding from the cell surface. Vesicles isolated from the matrix after stress-relaxation contained prominent 24 kDa, 36 kDa (doublet), 45 kDa, and 135 kDa polypeptides. The 45 kDa polypeptide was the major component in the Triton-insoluble vesicle fraction and appeared to be actin. The 36 kDa (doublet) polypeptide, which was found predominantly in the Triton-soluble vesicle fraction, was identified as annexin II. Vesicles also contained annexin VI and beta 1 integrin receptors but not tubulin, vimentin, vinculin or annexin I. The results suggest that stress-relaxation of fibroblasts induces a novel ectocytotic process involving transient budding of intact, plasma membrane vesicles from the cell cortex. On the basis of their morphological and biochemical features, these vesicles may be analogous to the ‘matrix vesicles’ released by chondrocytes and could play a role in extracellular matrix remodeling after wound contraction.