The interstitial crystal-nucleating sheet in molluscan Haliotis rufescens shell: A bio-polymeric composite

Multiple Pathways for Pathological Calcification in the Human Body

Biomineralization of skeletal components (e.g., bone and teeth) is generally accepted to occur under strict cellular regulation, leading to mineral-organic composites with hierarchical structures and properties optimized for their designated function. Such cellular regulation includes promoting mineralization at desired sites as well as inhibiting mineralization in soft tissues and other undesirable locations. In contrast, pathological mineralization, with potentially harmful health effects, can occur as a result of tissue or metabolic abnormalities, disease, or implantation of certain biomaterials. This progress report defines mineralization pathway components and identifies the commonalities (and differences) between physiological (e.g., bone remodeling) and pathological calcification formation pathways, based, in part, upon the extent of cellular control within the system. These concepts are discussed in representative examples of calcium phosphate-based pathological mineralization in cancer (breast, thyroid, ovarian, and meningioma) and in cardiovascular disease. In-depth mechanistic understanding of pathological mineralization requires utilizing state-of-the-art materials science imaging and characterization techniques, focusing not only on the final deposits, but also on the earlier stages of crystal nucleation, growth, and aggregation. Such mechanistic understanding will further enable the use of pathological calcifications in diagnosis and prognosis, as well as possibly provide insights into preventative treatments for detrimental mineralization in disease.

Effect of extrapallial protein of Mytilus californianus on the process of in vitro biomineralization of chitosan scaffolds

Biomineralization is the process by which diverse organisms have the capacity to create heterogeneous accumulations, derived from organic and inorganic compounds that induce the process of mineral formation. An example of this can be seen an extrapallial protein (EP) of Mytilus californianus, which is responsible for carrying out the biomineralization process. In order to determine their ability to perform the biomineralization process, EP protein was absorbed and mixed in chitosan scaffolds which were tested in simulated physiological fluid. The materials were analyzed by FTIR spectroscopy, field emission scanning electron microscopy-energy-dispersive electron X-ray spectroscopy andX-ray diffraction. Results confirmed that the EP protein stimulates the rapid growth of biological apatite on the chitosan scaffolds. The mixing method favored more the apatite growth as well as the formation of second nucleation sites than the immersion method.

PFMG1 promotes osteoblast differentiation and prevents osteoporotic bone loss

Nacre is a widely used mineral medicine that has been reported to have beneficial effects in bone remodeling without an increase in inflammation. Water-soluble nacre matrix has been demonstrated to be responsible for the effect, yet core active ingredients are unknown. Pinctada fucata mantle gene 1 (PFMG1) was first discovered in the mantle tissue of Pinctada fucata. The protein has 2 EF-hands, a calcium-binding domain. PFMG1 protein can affect the growth of calcium carbonate crystals in vitro. Here, we demonstrate that PFMG1 affects cell-cycle distribution and promotes preosteoblast proliferation. PFMG1 accelerates preosteoblast differentiation and extracellular matrix mineralization. During the differentiation process, PFMG1 increases the expression level of osteoblastic marker genes and activates the Erk signaling pathway. PFMG1 also accelerates calcium crystal aggregation in culture medium and suppresses osteoclast formation. Moreover, PFMG1 prevents bone loss caused by ovariectomy. RNA sequencing analysis demonstrated that PFMG1 stimulates genes that are associated with tissue development and ossification, which indicated new genes that function in bone remodeling. Our findings demonstrate the therapeutic potential of PFMG1 from nacre as a novel medicine for osteoporosis.-Li, L., Wang, P., Hu, K., Wang, X., Cai, W., Ai, C., Liu, S., Wang, Z. PFMG1 promotes osteoblast differentiation and prevents osteoporotic bone loss.

Ovarian Aging and Osteoporosis

Osteoporosis is the most common bone metabolic disease with a very high morbidity, and women usually got a higher risk of osteoporosis than men. The high incidence rate of osteoporosis in women was mainly caused by (1) women having fewer skeletons and bone mass, (2) pregnancy consuming a large amount of calcium and other nutrients, and most importantly (3) the cease of estrogen secretion by ovaries after menopause. Along with ovarian aging, the follicle pool gradually declines and the oocyte quality reduced, accompanied with decline in serum estrogen. Estrogen deficiency plays an important role in the pathogenesis of postmenopausal osteoporosis; it is mainly a result of the recognition that estrogen regulates bone remodeling by modulating the production of cytokines and growth factors from bone marrow and bone cells. This review will summarize current knowledge concerning ovarian aging and postmenopause osteoporosis and also discuss clinical treatment and new ideas of drug development for osteoporosis.

Biogenic nanospheres of amorphous carbonated Ca-Mg phosphate within the periostracum of the green mussel Perna viridis

Recently there is increasing evidence that the shell biomineralization proceeds via an amorphous precursor route. Therefore, the search for and investigation of amorphous biominerals in bivalve shells are of great importance and interest. Here, using a scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffractometer (XRD), and Fourier transform infrared spectrometer (FTIR), we investigate the microstructure and mineralogy of the periostracum in Perna viridis. We find that: (1) the periostracum has three layers, of which the inner and outer layer are of proteins, while the middle layer is mineralized with nanospheres of amorphous biominerals; (2) the nanospheres are of amorphous carbonated Ca-Mg phosphate (ACCP), where the CO3(2)(-)/PO4(3)(-) weight ratio is estimated to be ∼0.3, and the Ca/P and Ca/Mg atomic ratio is ∼1.4 and 1.6, respectively; (3) the nanospheres, with a diameter of 43-106nm, are found to assemble into spherules with a diameter of 160-500nm, which are further organized into parallel microlayers separated by the proteins; and (4) the nanospheres are assumed to function as the pH stabilizer to facilitate the shell's initial mineralization. Finally, we expect that these findings will advance our understanding of the shell's biomineralization process.

Mapping nanomechanical properties of freshly grown, native, interlamellar organic sheets on flat pearl nacre

We imaged surfaces of freshly grown flat pearl nacre (Haliotis tuberculata) in different stages of growth in seawater using an atomic force microscope (AFM). Characteristic mineral phases of nacre, such as aragonitic stacks of coins, as well as the associated organic sheets, could be detected. Apart from imaging, the acquisition of force volumes on freshly grown organic surface areas on flat pearl nacre was conducted with the AFM. The evaluation of the force volumes with the Hertz-Sneddon model resulted in Young's moduli in the MPa range. The presented values are considerably smaller than values previously determined from macroscopic tensile tests. This might reflect the anisotropy of the organic nacre layers.

Aragonite-associated biomineralization proteins are disordered and contain interactive motifs

MOTIVATION

The formation of aragonite mineral in the mollusk shell or pearl nacre requires the participation of a diverse set of proteins that form the mineralized extracellular matrix. Although self-assembly processes have been identified for several nacre proteins, these proteins do not contain known globular protein-protein binding domains. Thus, we hypothesize that other sequence features are responsible for nacre matrix protein-protein assembly processes and ultimately aragonite biosynthesis.

RESULTS

Of 39 mollusk aragonite-associated protein sequences, 100% contain at least one region of intrinsic disorder or unfolding, with the highest percentages found in framework and pearl-associated proteins relative to the intracrystalline proteins. In some instances, these intrinsically disordered regions were identified as bind/fold sequences, and a limited number correlate with known biomineral-relevant sequences. Interestingly, 95% of the aragonite-associated protein sequences were found to contain at least one occurrence of amyloid-like or cross-β strand aggregation-prone supersecondary motifs, and this correlates with known aggregation and aragonite formation functions in three experimentally tested protein sequences. Collectively, our findings indicate that aragonite-associated proteins have evolved signature sequence traits of intrinsic disorder and aggregation-prone regions that are important for their role(s) in matrix assembly and mineralization.

The toughening mechanism of nacre and structural materials inspired by nacre

The structure and the toughening mechanism of nacre have been the subject of intensive research over the last 30 years. This interest originates from nacre's excellent combination of strength, stiffness and toughness, despite its high, for a biological material, volume fraction of inorganic phase, typically 95%. Owing to the improvement of nanoscale measurement and observation techniques, significant progress has been made during the last decade in understanding the mechanical properties of nacre. The structure, microscopic deformation behavior and toughening mechanism on the order of nanometers have been investigated, and the importance of hierarchical structure in nacre has been recognized. This research has led to the fabrication of multilayer composites and films inspired by nacre with a layer thickness below 1 μm. Some of these materials reproduce the inorganic/organic interaction and hierarchical structure beyond mere morphology mimicking. In the first part of this review, we focus on the hierarchical architecture, macroscopic and microscopic deformation and fracture behavior, as well as toughening mechanisms in nacre. Then we summarize recent progress in the fabrication of materials inspired by nacre taking into consideration its mechanical properties.