Enamel and dental anomalies in latent-transforming growth factor beta-binding protein 3 mutant mice

Dental characteristics of patients with four different types of skeletal dysplasias

OBJECTIVE

Skeletal dysplasia (SD) comprises more than 450 separate disorders. We hypothesized that their dental features would be distinctive and investigated the tooth characteristics of four patients with different SDs.

MATERIAL AND METHODS

Four SD patients with molecularly confirmed diagnoses, Pt-1 acromicric dysplasia, Pt-2 hypophosphatasia and hypochondroplasia, Pt-3 cleidocranial dysplasia, and Pt-4 achondroplasia, were recruited. A tooth from each patient was evaluated for mineral density (micro-computerized tomography), surface roughness (surface profilometer), microhardness, mineral contents (energy-dispersive X-ray), and ultrastructure (scanning electron microscopy and histology), and compared with three tooth-type matched controls.

RESULTS

Pt-1 and Pt-3 had several unerupted teeth. Pt-2 had an intact-root-exfoliated tooth at 2 years old. The lingual surfaces of the patients' teeth were significantly smoother, while their buccal surfaces were rougher, than controls, except for Pt-1's buccal surface. The patients' teeth exhibited deep grooves around the enamel prisms and rough intertubular dentin. Pt-3 demonstrated a flat dentinoenamel junction and Pt-2 had an enlarged pulp, barely detectable cementum layer, and ill-defined cemento-dentinal junction. Reduced microhardnesses in enamel, dentin, and both layers were observed in Pt-3, Pt-4, and Pt-1, respectively. Pt-1 showed reduced Ca/P ratio in dentin, while both enamel and dentin of Pt-2 and Pt-3 showed reduced Ca/P ratio.

CONCLUSION

Each SD has distinctive dental characteristics with changes in surface roughness, ultrastructure, and mineral composition of dental hard tissues.

CLINICAL RELEVANCE

In this era of precision dentistry, identifying the specific potential dental problems for each patient with SD would help personalize dental management guidelines.

Expanding genotypic and phenotypic spectrums of LTBP3 variants in dental anomalies and short stature syndrome

Mutations in LTBP3 are associated with Dental Anomalies and Short Stature syndrome (DASS; MIM 601216), which is characterized by hypoplastic type amelogenesis imperfecta, hypodontia, underdeveloped maxilla, short stature, brachyolmia, aneurysm and dissection of the thoracic aorta. Here we report a novel (p.Arg545ProfsTer22) and a recurrent (c.3107-2A > G) LTBP3 variants, in a Turkish family affected with DASS. The proband, who carried compound heterozygous variant c.3107-2A > G, p.Arg545ProfsTer22, was most severely affected with DASS. The proband's father, who carried the heterozygous variant c.3107-2A > G had short stature and prognathic mandible. The mother and brother of the proband carried the heterozygous variant p.Arg545ProfsTer22, but only the mother showed any DASS characteristics. The c.3107-2A > G and the p.Arg545ProfsTer22 variants are expected to result in abnormal LTPB3 protein, failure of TGFβ-LAP-LTBP3 complex formation, and subsequent disruption of TGFβ secretion and activation. This is the first report of heterozygous carriers of LTBP3 variants showing phenotypes. The new findings of DASS found in this family include taurodontism, single-rooted molars, abnormal dentin, calcified dental pulp blood vessels, prognathic mandible, failure of mandibular tooth eruption, interatrial septal aneurysm, secundum atrial septal defect, tricuspid valve prolapse, and a recurrent glenohumeral joint dislocation.

DNA methylation in childhood dental caries and hypomineralization

OBJECTIVES

Epigenetic modulation of gene expression may be important in dental conditions, including dental caries and enamel hypomineralisation. The aims of this study were to assess associations between DNA methylation in cord blood leucocytes at birth, and caries experience and enamel hypomineralisation at six years of age.

METHOD

The study sample was from a birth cohort study of twins. Dental examinations at six years identified the presence/absence of (i) 'any caries' (untreated and treated caries), (ii) 'advanced caries' (untreated, advanced caries and/or past treatment) and (iii) hypomineralised second primary molars (HSPM). Genome-wide analysis of DNA methylation was performed on cord blood of 27 twin pairs (14 dizygotic and 13 monozygotic) using the Illumina Infinium MethylationEPIC BeadChip array. Differentially methylated CpGs (DMCpGs) and regions (DMRs) associated with each dental outcome were investigated, while accounting for the relatedness of twins. Results with a false discovery rate <0.05 were treated as statistically significant.

RESULTS

19 children had 'any caries', 15 had 'advanced' caries, and 18 had HSPM. No DMCpGs were associated with 'any caries', 16 and 19 DMCpGs were associated with 'advanced caries' and HSPM, respectively. DMRs were identified in association with all three outcomes. Genes implicated by these analyses included PBX1, ACAT2, LTBP3 and DDR1 which have been linked with dental tissue development in genetic studies.

CONCLUSION

This exploratory study identified differential methylation in several genes at birth associated with dental caries and HSPM at six years. Further research may provide valuable insights into aetiology of dental disease and/or reveal novel molecular-based approaches for early risk stratification.

CLINICAL SIGNIFICANCE

Epigenetic differences at birth are likely to be associated with dental health at six years and may be valuable biomarkers of early influences on dental health.

LTBP4 in Health and Disease

Latent transforming growth factor β (TGFβ)-binding protein (LTBP) 4, a member of the LTBP family, shows structural homology with fibrillins. Both these protein types are characterized by calcium-binding epidermal growth factor-like repeats interspersed with 8-cysteine domains. Based on its domain composition and distribution, LTBP4 is thought to adopt an extended structure, facilitating the linear deposition of tropoelastin onto microfibrils. In humans, mutations in LTBP4 result in autosomal recessive cutis laxa type 1C, characterized by redundant skin, pulmonary emphysema, and valvular heart disease. LTBP4 is an essential regulator of TGFβ signaling and is related to development, immunity, injury repair, and diseases, playing a central role in regulating inflammation, fibrosis, and cancer progression. In this review, we focus on medical disorders or diseases that may be manipulated by LTBP4 in order to enhance the understanding of this protein.

Thoracic aortic aneurysm gene dictionary

Thoracic aortic aneurysm is typically clinically silent, with a natural history of progressive enlargement until a potentially lethal complication such as rupture or dissection occurs. Underlying genetic predisposition strongly influences the risk of thoracic aortic aneurysm and dissection. Familial cases are more virulent, have a higher rate of aneurysm growth, and occur earlier in life. To date, over 30 genes have been associated with syndromic and non-syndromic thoracic aortic aneurysm and dissection. The causative genes and their specific variants help to predict the disease phenotype, including age at presentation, risk of dissection at small aortic sizes, and risk of other cardiovascular and systemic manifestations. This genetic "dictionary" is already a clinical reality, allowing us to personalize care based on specific causative mutations for a substantial proportion of these patients. Widespread genetic sequencing of thoracic aortic aneurysm and dissection patients has been and continues to be crucial to the rapid expansion of this dictionary and ultimately, the delivery of truly personalized care to every patient.

TGF-β1 - A truly transforming growth factor in fibrosis and immunity

'Jack of all trades, master of everything' is a fair label for transforming growth factor β1 (TGF-β) - a cytokine that controls our life at many levels. In the adult organism, TGF-β1 is critical for the development and maturation of immune cells, maintains immune tolerance and homeostasis, and regulates various aspects of immune responses. Following acute tissue damages, TGF-β1 becomes a master regulator of the healing process with impacts on about every cell type involved. Divergence from the tight control of TGF-β1 actions, for instance caused by chronic injury, severe trauma, or infection can tip the balance from regulated physiological to excessive pathological repair. This condition of fibrosis is characterized by accumulation and stiffening of collagenous scar tissue which impairs organ functions to the point of failure. Fibrosis and dysregulated immune responses are also a feature of cancer, in which tumor cells escape immune control partly by manipulating TGF-β1 regulation and where immune cells are excluded from the tumor by fibrotic matrix created during the stroma 'healing' response. Despite the obvious potential of TGF-β-signalling therapies, globally targeting TGF-β1 receptor, downstream pathways, or the active growth factor have proven to be extremely difficult if not impossible in systemic treatment regimes. However, TGF-β1 binding to cell receptors requires prior activation from latent complexes that are extracellularly presented on the surface of immune cells or within the extracellular matrix. These different locations have led to some divergence in the field which is often either seen from the perspective of an immunologists or a fibrosis/matrix researcher. Despite these human boundaries, there is considerable overlap between immune and tissue repair cells with respect to latent TGF-β1 presentation and activation. Moreover, the mechanisms and proteins employed by different cells and spatiotemporal control of latent TGF-β1 activation provide specificity that is amenable to drug development. This review aims at synthesizing the knowledge on TGF-β1 extracellular activation in the immune system and in fibrosis to further stimulate cross talk between the two research communities in solving the TGF-β conundrum.

Genes Associated with Thoracic Aortic Aneurysm and Dissection: 2019 Update and Clinical Implications

Thoracic aortic aneurysm is a typically silent disease characterized by a lethal natural history. Since the discovery of the familial nature of thoracic aortic aneurysm and dissection (TAAD) almost 2 decades ago, our understanding of the genetics of this disorder has undergone a transformative amplification. To date, at least 37 TAAD-causing genes have been identified and an estimated 30% of the patients with familial nonsyndromic TAAD harbor a pathogenic mutation in one of these genes. In this review, we present our yearly update summarizing the genes associated with TAAD and the ensuing clinical implications for surgical intervention. Molecular genetics will continue to bolster this burgeoning catalog of culprit genes, enabling the provision of personalized aortic care.

Genotypic Categorization of Loeys-Dietz Syndrome Based on 24 Novel Families and Literature Data

Loeys-Dietz syndrome (LDS) is a connective tissue disorder first described in 2005 featuring aortic/arterial aneurysms, dissections, and tortuosity associated with craniofacial, osteoarticular, musculoskeletal, and cutaneous manifestations. Heterozygous mutations in 6 genes (TGFBR1/2, TGFB2/3, SMAD2/3), encoding components of the TGF-β pathway, cause LDS. Such genetic heterogeneity mirrors broad phenotypic variability with significant differences, especially in terms of the age of onset, penetrance, and severity of life-threatening vascular manifestations and multiorgan involvement, indicating the need to obtain genotype-to-phenotype correlations for personalized management and counseling. Herein, we report on a cohort of 34 LDS patients from 24 families all receiving a molecular diagnosis. Fifteen variants were novel, affecting the TGFBR1 (6), TGFBR2 (6), SMAD3 (2), and TGFB2 (1) genes. Clinical features were scored for each distinct gene and matched with literature data to strengthen genotype-phenotype correlations such as more severe vascular manifestations in TGFBR1/2-related LDS. Additional features included spontaneous pneumothorax in SMAD3-related LDS and cervical spine instability in TGFB2-related LDS. Our study broadens the clinical and molecular spectrum of LDS and indicates that a phenotypic continuum emerges as more patients are described, although genotype-phenotype correlations may still contribute to clinical management.

Fibrillin microfibrils and elastic fibre proteins: Functional interactions and extracellular regulation of growth factors

Fibrillin microfibrils are extensible polymers that endow connective tissues with long-range elasticity and have widespread distributions in both elastic and non-elastic tissues. They act as a template for elastin deposition during elastic fibre formation and are essential for maintaining the integrity of tissues such as blood vessels, lung, skin and ocular ligaments. A reduction in fibrillin is seen in tissues in vascular ageing, chronic obstructive pulmonary disease, skin ageing and UV induced skin damage, and age-related vision deterioration. Most mutations in fibrillin cause Marfan syndrome, a genetic disease characterised by overgrowth of the long bones and other skeletal abnormalities with cardiovascular and eye defects. However, mutations in fibrillin and fibrillin-binding proteins can also cause short-stature pathologies. All of these diseases have been linked to dysregulated growth factor signalling which forms a major functional role for fibrillin.

Enamel and dental anomalies in latent-transforming growth factor beta-binding protein 3 mutant mice

Latent‐transforming growth factor beta‐binding protein 3 (LTBP‐3) is important for craniofacial morphogenesis and hard tissue mineralization, as it is essential for activation of transforming growth factor‐β (TGF‐β). To investigate the role of LTBP‐3 in tooth formation we performed micro‐computed tomography (micro‐CT), histology, and scanning electron microscopy analyses of adult Ltbp3‐/‐ mice. The Ltbp3‐/‐ mutants presented with unique craniofacial malformations and reductions in enamel formation that began at the matrix formation stage. Organization of maturation‐stage ameloblasts was severely disrupted. The lateral side of the incisor was affected most. Reduced enamel mineralization, modification of the enamel prism pattern, and enamel nodules were observed throughout the incisors, as revealed by scanning electron microscopy. Molar roots had internal irregular bulbous‐like formations. The cementum thickness was reduced, and microscopic dentinal tubules showed minor nanostructural changes. Thus, LTBP‐3 is required for ameloblast differentiation and for the formation of decussating enamel prisms, to prevent enamel nodule formation, and for proper root morphogenesis. Also, and consistent with the role of TGF‐β signaling during mineralization, almost all craniofacial bone components were affected in Ltbp3‐/‐ mice, especially those involving the upper jaw and snout. This mouse model demonstrates phenotypic overlap with Verloes Bourguignon syndrome, also caused by mutation of LTBP3, which is hallmarked by craniofacial anomalies and amelogenesis imperfecta phenotypes.

LTBP3 Pathogenic Variants Predispose Individuals to Thoracic Aortic Aneurysms and Dissections

The major diseases affecting the thoracic aorta are aneurysms and acute dissections, and pathogenic variants in 11 genes are confirmed to lead to heritable thoracic aortic disease. However, many families in which multiple members have thoracic aortic disease do not have alterations in the known aortopathy genes. Genes highly expressed in the aorta were assessed for rare variants in exome sequencing data from such families, and compound rare heterozygous variants (p.Pro45Argfs^∗25 and p.Glu750^∗) in LTBP3 were identified in affected members of one family. A homozygous variant (p.Asn678_Gly681delinsThrCys) that introduces an additional cysteine into an epidermal growth factor (EGF)-like domain in the corresponding protein, latent TGF-β binding protein (LTBP-3), was identified in a second family. Individuals with compound heterozygous or homozygous variants in these families have aneurysms and dissections of the thoracic aorta, as well as aneurysms of the abdominal aorta and other arteries, along with dental abnormalities and short stature. Heterozygous carriers of the p.Asn678_Gly681delinsThrCys variant have later onset of thoracic aortic disease, as well as dental abnormalities. In these families, LTBP3 variants segregated with thoracic aortic disease with a combined LOD score of 3.9. Additionally, heterozygous rare LTBP3 variants were found in individuals with early onset of acute aortic dissections, and some of these variants disrupted LTBP-3 levels or EGF-like domains. When compared to wild-type mice, Ltbp3^-/- mice have enlarged aortic roots and ascending aortas. In summary, homozygous LTBP3 pathogenic variants predispose individuals to thoracic aortic aneurysms and dissections, along with the previously described skeletal and dental abnormalities.

LTBPs in biology and medicine: LTBP diseases

The latent transforming growth factor (TGF) β binding proteins (LTBP) are crucial mediators of TGFβ function, as they control growth factor secretion, matrix deposition, presentation and activation. Deficiencies in specific LTBP isoforms yield discrete phenotypes representing defects in bone, lung and cardiovascular development mediated by loss of TGFβ signaling. Additional phenotypes represent loss of unique TGFβ-independent features of LTBP effects on elastogenesis and microfibril assembly. Thus, the LTBPs act as sensors for the regulation of both growth factor activity and matrix function.

Evidence-Based Advances in Rodent Medicine

The number of exotic companion pet rodents seen in veterinary practices is growing very rapidly. According to the American Veterinary Medical Association's surveys, more than 2,093,000 pet rodents were kept in US households in 2007 and in 2012 it was more than 2,349,000 animals. This article summarizes the most important evidence-based knowledge in exotic pet rodents (diagnostics of the hyperadrenocorticism in guinea pigs, pituitary tumors in rats, urolithiasis in guinea pigs, use of itopride as prokinetics, use of deslorelin acetate in rodents, cause of dental disease, and prevention of mammary gland tumors in rats).