The Understanding of the Metazoan Skeletal System, Based on the Initial Discoveries with Siliceous and Calcareous Sponges

[1, 8]-Naphthyridine derivatives as dual inhibitor of alkaline phosphatase and carbonic anhydrase

[1,8]-Naphthyridine derivatives have been reported to possess important biological activities and may serve as attractive pharmacophores in the drug discovery process. [1,8]-Naphthyridine derivatives (1a-1l) were evaluated for inhibitory potential for isozymes of carbonic anhydrase (CA) and alkaline phosphatase (ALP). CAs have been reported to carry out reversible hydration of CO2 into HCO3-, secretion of electrolytes, acid-base regulation, bone resorption, calcification, and biosynthetic reactions. Whereas ALPs hydrolyze monophosphate esters with the release of inorganic phosphate and play an important role in bone mineralization. Both enzymes have been found to be over-expressed and raised functional activities in patients suffering from rheumatoid arthritis. The discovery of dual inhibitors of these enzymes may provide a synergistic effect to cure bone disorders such as rheumatoid arthritis and ankylosing spondylitis. Among the test compounds, the most potent inhibitors for CA-II, CA-IX, and CA-XII were 1e, 1g, and 1a with IC50 values of 0.44 ± 0.19, 0.11 ± 0.03 and 0.32 ± 0.07 µM, respectively. [1,8]-Naphthyridine derivatives (1a-1l) were approximately 4 folds more potent than standard CA inhibitor acetazolamide. While in the case of ALPs, the most potent compounds for b-TNAP and c-IAP were 1b and 1e with IC50 values of 0.122 ± 0.06 and 0.107 ± 0.02 µM, respectively. Thus, synthesized derivatives proved to be 100 to 800 times more potent as compared to standard inhibitors of b-TNAP and c-IAP (Levamisole and L-phenyl alanine, respectively). In addition, selectivity and dual inhibition of [1,8]-Naphthyridine derivatives confer precedence over known inhibitors. Molecular docking and molecular simulation studies were also conducted in the present studies to define the type of interactions between potential inhibitors and enzyme active sites.

Evaluation of Current Studies to Elucidate Processes in Dental Follicle Cells Driving Osteogenic Differentiation

When research on osteogenic differentiation in dental follicle cells (DFCs) began, projects focused on bone morphogenetic protein (BMP) signaling. The BMP pathway induces the transcription factor DLX3, whichh in turn induces the BMP signaling pathway via a positive feedback mechanism. However, this BMP2/DLX3 signaling pathway only seems to support the early phase of osteogenic differentiation, since simultaneous induction of BMP2 or DLX3 does not further promote differentiation. Recent data showed that inhibition of classical protein kinase C (PKCs) supports the mineralization of DFCs and that osteogenic differentiation is sensitive to changes in signaling pathways, such as protein kinase B (PKB), also known as AKT. Small changes in the lipidome seem to confirm the participation of AKT and PKC in osteogenic differentiation. In addition, metabolic processes, such as fatty acid biosynthesis, oxidative phosphorylation, or glycolysis, are essential for the osteogenic differentiation of DFCs. This review article attempts not only to bring the various factors into a coherent picture of osteogenic differentiation in DFCs, but also to relate them to recent developments in other types of osteogenic progenitor cells.

The structural pathology for hypophosphatasia caused by malfunctional tissue non-specific alkaline phosphatase

Hypophosphatasia (HPP) is a metabolic bone disease that manifests as developmental abnormalities in bone and dental tissues. HPP patients exhibit hypo-mineralization and osteopenia due to the deficiency or malfunction of tissue non-specific alkaline phosphatase (TNAP), which catalyzes the hydrolysis of phosphate-containing molecules outside the cells, promoting the deposition of hydroxyapatite in the extracellular matrix. Despite the identification of hundreds of pathogenic TNAP mutations, the detailed molecular pathology of HPP remains unclear. Here, to address this issue, we determine the crystal structures of human TNAP at near-atomic resolution and map the major pathogenic mutations onto the structure. Our study reveals an unexpected octameric architecture for TNAP, which is generated by the tetramerization of dimeric TNAPs, potentially stabilizing the TNAPs in the extracellular environments. Moreover, we use cryo-electron microscopy to demonstrate that the TNAP agonist antibody (JTALP001) forms a stable complex with TNAP by binding to the octameric interface. The administration of JTALP001 enhances osteoblast mineralization and promoted recombinant TNAP-rescued mineralization in TNAP knockout osteoblasts. Our findings elucidate the structural pathology of HPP and highlight the therapeutic potential of the TNAP agonist antibody for osteoblast-associated bone disorders.

Inorganic phosphate in growing calcium carbonate abalone shell suggests a shared mineral ancestral precursor

The presence of phosphate from different origins (inorganic, bioorganic) is found more and more in calcium carbonate-based biominerals. Phosphate is often described as being responsible for the stabilization of the transient amorphous calcium carbonate phase. In order to specify the composition of the mineral phase deposited at the onset of carbonated shell formation, the present study investigates, down to the nanoscale, the growing shell from the European abalone Haliotis tuberculata, using a combination of solid state nuclear magnetic resonance, scanning transmission electron microscope and spatially-resolved electron energy loss spectroscopy techniques. We show the co-occurrence of inorganic phosphate with calcium and carbonate throughout the early stages of abalone shell formation. One possible hypothesis is that this first-formed mixed mineral phase represents the vestige of a shared ancestral mineral precursor that appeared early during Evolution. In addition, our findings strengthen the idea that the final crystalline phase (calcium carbonate or phosphate) depends strongly on the nature of the mineral-associated proteins in vivo.

Phosphate involvement in calcium carbonate biominerals raises questions on biomineralisation pathways. Here, the authors explore the presence of phosphate in the growing shell of the European abalone and suggest a shared mixed mineral ancestral precursor with final crystal phase being selected by mineral-associated proteins.

Aerophobin-1 from the Marine Sponge Aplysina aerophoba Modulates Osteogenesis in Zebrafish Larvae

Longer life expectancy has led to an increase in efforts directed to the discovery of new healing agents for disorders related to aging, such as bone diseases. Harboring an incredible variety of bioactive metabolites, marine organisms are standing out as fruitful sources also in this therapeutic field. On the other hand, the in vivo zebrafish model has proven to be an excellent low-cost screening platform for the fast identification of molecules able to regulate bone development. By using zebrafish larvae as a mineralization model, we have thus evaluated the effects of the crude acetonic extract from the marine sponge Aplysina aerophoba and its bromotyrosine components on bone development. Obtained results led to the selection of aerophobin-1 (1) as a promising candidate for applications in regenerative medicine, paving the way for the development of a novel therapeutic option in osteoporosis treatment.

Osteodystrophies of jaws

Bone is a dense, semi rigid, porous, calcified connective tissue forming the major portion of the skeleton of most vertebrates. It consists of a dense organic matrix and an inorganic mineral component. Bone remodelling is a complex process by which old bone is continuously replaced by new tissue, which requires interaction between different cell phenotypes and is regulated by a variety of biochemical and mechanical factors. In a homeostatic equilibrium, the process of resorption and formation are balanced so that old bone is continuously replaced by new tissue and it adapts to mechanical load and strain. Several local and systematic factors which cause disturbances in bone resorption and deposition leads to abnormal or defective development of bone commonly termed as osteodystrophy - A defective ossification of bone usually is associated with disturbed calcium and phosphorus metabolism. The better understanding of molecular cellular biology and pathogenic mechanism aids to define the abnormalities in osteoblastic and osteoclastic lineages and to develop new therapeutic approaches.

Destabilised human transthyretin shapes the morphology of calcium carbonate crystals

Human transthyretin (TTR) is a homotetramer that transports thyroid hormones and retinol in the serum and cerebrospinal fluid. TTR is also an intracellular protein found in tissues such as those in the brain, eye and pancreas. TTR is a nutrition marker, reflecting the health of the organism, and TTR levels are linked to the normal and diseased states of the body. The switch from a protective to a pathological role is attributed to the destabilisation of the TTR structure, which leads to tetramer dissociation and amyloid formation. Native and destabilised TTR have been associated with osteoarthritis and bone density in humans. Moreover, TTR is present in eggshell mammillary cones; therefore, we verified the putative TTR engagement in the process of mineral formation. Using an in vitro assay, we found that TTR affected calcium carbonate crystal growth and morphology, producing asymmetric crystals with a complex nanocrystalline composition. The crystals possessed rounded edges and corners and irregular etch pits, suggesting the selective inhibition of crystal growth and/or dissolution imposed by TTR. The occurrence of many porosities, fibrillary inclusions and amorphous precipitates suggested that destabilisation of the TTR structure is an important factor involved in the mineralisation process. Crystals grown in the presence of TTR exhibited the characteristic features of crystals controlled by biomineralisation-active proteins, suggesting novel functions of TTR in the mineral formation process.

Amorphous polyphosphate, a smart bioinspired nano-/bio-material for bone and cartilage regeneration: towards a new paradigm in tissue engineering

Physiological amorphous polyphosphate nano/micro-particles, injectable and implantable, attract and stimulate MSCs into implants for tissue regeneration.