Deficiency of the DSPP-cleaving enzymes meprin α and meprin β does not result in dentin malformation in mice

Ivory poaching and the rapid evolution of tusklessness in African elephants

[Figure: see text].

Manifestation and Mechanisms of Abnormal Mineralization in Teeth

Tooth biomineralization is a dynamic and complicated process influenced by local and systemic factors. Abnormal mineralization in teeth occurs when factors related to physiologic mineralization are altered during tooth formation and after tooth maturation, resulting in microscopic and macroscopic manifestations. The present Review provides timely information on the mechanisms and structural alterations of different forms of pathological tooth mineralization. A comprehensive study of these alterations benefits diagnosis and biomimetic treatment of abnormal mineralization in patients.

[Role of bone morphogenetic protein 1/tolloid proteinase family in the development of teeth and bone]

The bone morphogenetic protein (BMP) 1/tolloid (TLD) proteinase family is a group of important metalloproteinases, which play key roles in the growth and development of tissues and organs via regulating the biosynthetic processing of the extracellular matrix. Clinical reports have revealed that mutations in the genes encoding BMP1/TLD proteinases lead to dentinogenesis imperfecta type Ⅰ, accompanied with osteogenesis imperfecta. Therefore, this proteinase family is essential for the development of hard tissues. In this study, we review the research progress in the function and mechanism of the BMP1/TLD proteinase family in the development of teeth and bone.

Extracellular Matrix Composition and Remodeling: Current Perspectives on Secondary Palate Formation, Cleft Lip/Palate, and Palatal Reconstruction

Craniofacial development comprises a complex process in humans in which failures or disturbances frequently lead to congenital anomalies. Cleft lip with/without palate (CL/P) is a common congenital anomaly that occurs due to variations in craniofacial development genes, and may occur as part of a syndrome, or more commonly in isolated forms (non-syndromic). The etiology of CL/P is multifactorial with genes, environmental factors, and their potential interactions contributing to the condition. Rehabilitation of CL/P patients requires a multidisciplinary team to perform the multiple surgical, dental, and psychological interventions required throughout the patient's life. Despite progress, lip/palatal reconstruction is still a major treatment challenge. Genetic mutations and polymorphisms in several genes, including extracellular matrix (ECM) genes, soluble factors, and enzymes responsible for ECM remodeling (e.g., metalloproteinases), have been suggested to play a role in the etiology of CL/P; hence, these may be considered likely targets for the development of new preventive and/or therapeutic strategies. In this context, investigations are being conducted on new therapeutic approaches based on tissue bioengineering, associating stem cells with biomaterials, signaling molecules, and innovative technologies. In this review, we discuss the role of genes involved in ECM composition and remodeling during secondary palate formation and pathogenesis and genetic etiology of CL/P. We also discuss potential therapeutic approaches using bioactive molecules and principles of tissue bioengineering for state-of-the-art CL/P repair and palatal reconstruction.

Mutant Dentin Sialophosphoprotein Causes Dentinogenesis Imperfecta

Dentin sialophosphoprotein (DSPP) is an extracellular matrix protein highly expressed by odontoblasts in teeth. DSPP mutations in humans may cause dentinogenesis imperfecta (DGI), an autosomal dominant dentin disorder. We recently generated a mouse model (named "Dspp^P19L/+ mice") that expressed a mutant DSPP in which the proline residue at position 19 was replaced by a leucine residue. We found that the Dspp^P19L/+ and Dspp^P19L/P19L mice at a younger age displayed a tooth phenotype resembling human DGI type III characterized by enlarged dental pulp chambers, while the teeth of older Dspp^P19L/+ and Dspp^P19L/P19L mice had smaller dental pulp chambers mimicking DGI type II. The teeth of Dspp^P19L/+ and Dspp^P19L/P19L mice had a narrower pulp chamber roof predentin layer, thinner pulp chamber roof dentin, and thicker pulp chamber floor dentin. In addition, these mice also had increased enamel attrition, accompanied by excessive deposition of peritubular dentin. Immunohistochemistry, in situ hybridization, and real-time polymerase chain reaction analyses showed that the odontoblasts in both Dspp^P19L/+ and Dspp^P19L/P19L mice had reduced DSPP expression, compared to the wild-type mice. We also observed that the levels of DSPP expression were much higher in the roof-forming odontoblasts than in the floor-forming odontoblasts in the wild-type mice and mutant mice. Moreover, immunohistochemistry showed that while the immunostaining signals of dentin sialoprotein (N-terminal fragment of DSPP) were decreased in the dentin matrix, they were remarkably increased in the odontoblasts of the Dspp^P19L/+ and Dspp^P19L/P19L mice. Consistently, our in vitro studies showed that the secretion of the mutant DSPP was impaired and accumulated within endoplasmic reticulum. These findings suggest that the dental phenotypes of the mutant mice were associated with the intracellular retention of the mutant DSPP in the odontoblasts of the DSPP-mutant mice.

Fibrillin microfibrils and proteases, key integrators of fibrotic pathways

Supramolecular networks composed of multi-domain ECM proteins represent intricate cellular microenvironments which are required to balance tissue homeostasis and direct remodeling. Structural deficiency in ECM proteins results in imbalances in ECM-cell communication resulting often times in fibrotic reactions. To understand how individual components of the ECM integrate communication with the cell surface by presenting growth factors or providing fine-tuned biomechanical properties is mandatory for gaining a better understanding of disease mechanisms in the quest for new therapeutic approaches. Here we provide an overview about what we can learn from inherited connective tissue disorders caused primarily by mutations in fibrillin-1 and binding partners as well as by altered ECM processing leading to defined structural changes and similar functional knock-in mouse models. We will utilize this knowledge to propose new molecular hypotheses which should be tested in future studies.

Interaction of Complement Defence Collagens C1q and Mannose-Binding Lectin with BMP-1/Tolloid-like Proteinases

The defence collagens C1q and mannose-binding lectin (MBL) are immune recognition proteins that associate with the serine proteinases C1r/C1s and MBL-associated serine proteases (MASPs) to trigger activation of complement, a major innate immune system. Bone morphogenetic protein-1 (BMP-1)/tolloid-like proteinases (BTPs) are metalloproteinases with major roles in extracellular matrix assembly and growth factor signalling. Despite their different functions, C1r/C1s/MASPs and BTPs share structural similarities, including a specific CUB-EGF-CUB domain arrangement found only in these enzymes that mediates interactions with collagen-like proteins, suggesting a possible functional relationship. Here we investigated the potential interactions between the defence collagens C1q and MBL and the BTPs BMP-1 and mammalian tolloid-like-1 (mTLL-1). C1q and MBL bound to immobilized BMP-1 and mTLL-1 with nanomolar affinities. These interactions involved the collagen-like regions of the defence collagens and were inhibited by pre-incubation of C1q or MBL with their cognate complement proteinases. Soluble BMP-1 and mTLL-1 did not inhibit complement activation and the defence collagens were neither substrates nor inhibitors of BMP-1. Finally, C1q co-localized with BMP-1 in skin biopsies following melanoma excision and from patients with recessive dystrophic epidermolysis bullosa. The observed interactions provide support for a functional link between complement and BTPs during inflammation and tissue repair.

The Human Odontoblast Cell Layer and Dental Pulp Proteomes and N-Terminomes

The proteome and N-terminome of the human odontoblast cell layer were identified for the first time by shotgun proteomic and terminal amine isotopic labeling of substrates (TAILS) N-terminomic analyses, respectively, and compared with that of human dental pulp stroma from 26 third molar teeth. After reverse-phase liquid chromatography-tandem mass spectrometry, >170,000 spectra from the shotgun and TAILS analyses were matched by 4 search engines to 4,888 and 12,063 peptides in the odontoblast cell layer and pulp stroma, respectively. Within these peptide groups, 1,543 and 5,841 protein N-termini, as well as 895 and 2,423 unique proteins, were identified with a false discovery rate of ≤1%. Thus, the human dental pulp proteome was expanded by 974 proteins not previously identified among the 4,123 proteins in our 2015 dental pulp study. Further, 222 proteins of the odontoblast cell layer were not found in the pulp stroma, suggesting many of these proteins are synthesized only by odontoblasts. When comparing the proteomes of older and younger donors, differences were more apparent in the odontoblast cell layer than in the dental pulp stroma. In the odontoblast cell layer proteome, we found proteomic evidence for dentin sialophosphoprotein, which is cleaved into dentin sialoprotein and dentin phosphoprotein. By exploring the proteome of the odontoblast cell layer and expanding the known dental pulp proteome, we found distinct proteome differences compared with each other and with dentin. Moreover, between 61% and 66% of proteins also occurred as proteoforms commencing with a neo-N-terminus not annotated in UniProt. Hence, TAILS increased proteome coverage and revealed considerable proteolytic processing, by identifying stable proteoforms in these dynamic dental tissues. All mass spectrometry raw data have been deposited to ProteomeXchange with the identifier <PXD006557>, with the accompanying metadata at Mendeley Data ( https://data.mendeley.com/datasets/b57zfh6wmy/1 ).

Meprin metalloproteases: Molecular regulation and function in inflammation and fibrosis

The zinc-endopeptidases meprin α and meprin β are extracellular proteases involved in connective tissue homeostasis, intestinal barrier function and immunological processes. Meprins are unique among other extracellular proteases with regard to cleavage specificity and structure. Meprin α and meprin β have a strong preference for negatively charged amino acids around the scissile bond, reflected by cleavage sites identified in procollagen I, the amyloid precursor protein (APP) and the interleukin-6 receptor (IL-6R). In this review we report on recent findings that summarize the complex molecular regulation of meprins, particular folding, activation and shedding. Dysregulation of meprin α and meprin β is often associated with pathological conditions such as neurodegeneration, inflammatory bowel disease and fibrosis. Based on mouse models and patient data we suggest meprins as possible key regulators in the onset and progression of fibrotic disorders, leading to severe diseases such as pulmonary hypertension. This article is part of a Special Issue entitled: Proteolysis as a Regulatory Event in Pathophysiology edited by Stefan Rose-John.

Meprin β and BMP-1 are differentially regulated by CaCl2

The two metalloproteases meprin β and bone morphogenetic protein 1 (BMP-1) are both members of the astacin protease family. They share specificity for negatively charged residues around the scissile bond and they are expressed in overlapping compartments of the human body. One important proteolytic substrate they share is pro-collagen I. Ablation of one of the two proteases however leads to different collagen I associated phenotypes in vivo. Over the last years calcium emerged as a regulator for the proteolytic activity of both enzymes. For meprin β a reduction and for BMP-1 an increase in activity was reported under increasing calcium concentrations. Here we revisit different compartments that rely on pro-collagen I maturation and explore the crystal structure of both proteases to highlight possible calcium binding sites. With this we aim to emphasize a to date underestimated regulator that influences both proteases.