Collagen (I) homotrimer potentiates the osteogenesis imperfecta (oim) mutant allele and reduces survival in male mice

Water and Collagen: A Mystery Yet to Unfold

Collagen is the most abundant protein in the human body and plays an essential role in determining the mechanical properties of the tissues. Both as a monomeric protein and in fibrous assemblies, collagen interacts with its surrounding molecules, in particular with water. Interestingly, while it is well established that the interaction with water strongly influences the molecular and mechanical properties of collagen and its assemblies, the underlying mechanisms remain largely unknown. Here, we review the research conducted over the past 30 years on the interplay between water and collagen and its relevance for tissue properties. We discuss the water-collagen interaction on relevant time- and length scales, ranging from the vital role of water in stabilizing the characteristic triple helix structure to the negative impact of dehydration on the mechanical properties of tissues. A better understanding of the water-collagen interaction will help to unravel the effect of mutations and defective collagen production in collagen-related diseases and to pinpoint the key design features required to synthesize collagen-based biomimetic tissues with tailored mechanical properties.

Active synthesis of type I collagen homotrimer in Dupuytren's fibrosis is unaffected by anti-TNF-α treatment

Dupuytren's disease is a common fibroproliferative disease of the palmar fascia of the hand, with advanced cases treated surgically. Anti-TNF injection has undergone phase 2 trials and may be effective in slowing early-stage disease progression. Here we sought to determine how new synthesis of type I collagen in Dupuytren's differs from normal palmar fascia samples and to analyze the role of TNF in aberrant collagen synthesis. Model nonfibrotic but fibrous connective tissues were used to analyze active type I collagen protein synthesis in development, aging, and degenerative disease, where it was restricted to early development and ruptured tissue. Dupuytren's tissue was shown to actively synthesize type I collagen, including abnormal type I collagen homotrimer. TNF-α reduced COL1A2 gene expression only in the presence of serum in 2D cell culture and had opposing effects on collagen protein production in the presence or absence of serum. TNF-α had only limited effects in 3D tendon-like constructs. Anti-TNF did not reduce type I collagen synthesis in 3D tendon-like constructs or prevent type I collagen homotrimer synthesis in Dupuytren's tissue. Hence, modulation of the TNF-α pathway in Dupuytren's disease is unlikely to prevent the pathological collagen accumulation that is characteristic of fibrosis.

Cardiac health, type I collagen, and aging in the oim/oim mouse model of osteogenesis imperfecta and a cohort of adults with OI

Osteogenesis imperfecta (OI) is a heritable connective tissue disorder with marked skeletal fragility and increased recognition as a pleiotropic type I collagenopathy. The impact of OI-causing gene variants on cardiac health and lifespan is just beginning to be understood. To begin to investigate cardiac manifestations of OI-causing type I collagen variants, we utilized the osteogenesis imperfecta murine (oim/oim) model to examine survival with increased age, as well as cardiac function and collagen expression at 4 and 18 mo of age. We determined male oim/oim mice had 50% decreased survival by 18 mo of age compared with wild-type (WT) littermates. Cardiac magnetic resonance imaging and echocardiography revealed 18-mo-old male oim/oim mice had increased left ventricular end-diastolic and end-systolic volumes concomitant with decreased function, as well as the presence of aortic stenosis in a subset of 4- and 18-mo-old male oim/oim mice compared with WT littermates. Female oim/oim survival and cardiac function were equivalent to their WT counterparts. Cardiac evaluations of an adult patient cohort with OI corroborated increased incidences of valvular dysfunction in the patient population with OI, with much of the male cohort also presenting with altered left ventricular function. Little is known concerning the impact of OI-causing variants on patient cardiac health and the influence of sex and age. Using an OI mouse model, we determined that 18-mo-old male oim/oim mice have cardiac dysfunction with decreased lifespan, confirming the need for further investigations to understand pleiotropic extraskeletal manifestations and disease progression in osteogenesis imperfecta.NEW & NOTEWORTHY The heritable skeletal dysplasia, osteogenesis imperfecta (OI), recently recognized as a pleiotropic collagenopathy, shows growing evidence of cardiac involvement impacting lifespan. Evaluating cardiac function (magnetic resonance imaging and echocardiography) using an OI mouse model revealed increased left ventricular end-diastolic and end-systolic volumes concomitant with decreased function and reduced survival in 18-mo-old male OI mice. Additional cardiac evaluations of an adult patient cohort with OI corroborated increased incidences of valvular dysfunction in the patient population with OI.

A new Col1a1 conditional knock-in mouse model to study osteogenesis imperfecta

Osteogenesis imperfecta (OI) constitutes a family of bone fragility disorders characterized by both genetic and clinical heterogeneity. Several different mouse models reproduce the classic features of OI, and the most commonly studied carry either a spontaneous or genetically induced pathogenic variant in the Col1a1 or Col1a2 gene. When OI is caused by primary alterations of type I collagen, it represents a systemic connective tissue disease that, in addition to the skeleton, also affects several extra-skeletal tissues and organs, such as skin, teeth, lung, heart, and others, where the altered type I collagen is also expressed. Currently, existing mouse models harbor a disease-causing genetic variant in all tissues and do not allow assessing the primary vs secondary consequences of the mutation on a specific organ/system. Here, we describe the generation of the first conditional knock-in allele for Col1a1 that can express a severe OI-causing glycine substitution (p.Gly1146Arg) in the triple helical region of α1(I) but only after Cre-driven recombination in the tissue of choice. We called this new dominant allele Col1a1G1146R-Floxed/+ and introduced it into the murine model. We describe its validation by crossing mice carrying this allele with EIIA-Cre expressing mice and showing that offspring with the recombined allele reproduce the classic features of a severe form of OI. The new mouse model will be useful to study the tissue-specific impact of this severe mutation on organs, such as the lung, the heart, and others.

Extra-Skeletal Manifestations in Osteogenesis Imperfecta Mouse Models

Osteogenesis imperfecta (OI) is a rare heritable connective tissue disorder of skeletal fragility with an incidence of roughly 1:15,000. Approximately 85% of the pathogenic variants responsible for OI are in the type I collagen genes, COL1A1 and COL1A2, with the remaining pathogenic OI variants spanning at least 20 additional genetic loci that often involve type I collagen post-translational modification, folding, and intracellular transport as well as matrix incorporation and mineralization. In addition to being the most abundant collagen in the body, type I collagen is an important structural and extracellular matrix signaling molecule in multiple organ systems and tissues. Thus, OI disease-causing variants result not only in skeletal fragility, decreased bone mineral density (BMD), kyphoscoliosis, and short stature, but can also result in hearing loss, dentinogenesis imperfecta, blue gray sclera, cardiopulmonary abnormalities, and muscle weakness. The extensive genetic and clinical heterogeneity in OI has necessitated the generation of multiple mouse models, the growing awareness of non-skeletal organ and tissue involvement, and OI being more broadly recognized as a type I collagenopathy.This has driven the investigation of mutation-specific skeletal and extra-skeletal manifestations and broadened the search of potential mechanistic therapeutic strategies. The purpose of this review is to outline several of the extra-skeletal manifestations that have recently been characterized through the use of genetically and phenotypically heterogeneous mouse models of osteogenesis imperfecta, demonstrating the significant potential impact of OI disease-causing variants as a collagenopathy (affecting multiple organ systems and tissues), and its implications to overall health.

Galunisertib downregulates mutant type I collagen expression and promotes MSCs osteogenesis in pediatric osteogenesis imperfecta

Qualitative alterations in type I collagen due to pathogenic variants in the COL1A1 or COL1A2 genes, result in moderate and severe Osteogenesis Imperfecta (OI), a rare disease characterized by bone fragility. The TGF-β signaling pathway is overactive in OI patients and certain OI mouse models, and inhibition of TGF-β through anti-TGF-β monoclonal antibody therapy in phase I clinical trials in OI adults is rendering encouraging results. However, the impact of TGF-β inhibition on osteogenic differentiation of mesenchymal stem cells from OI patients (OI-MSCs) is unknown. The following study demonstrates that pediatric skeletal OI-MSCs have imbalanced osteogenesis favoring the osteogenic commitment. Galunisertib, a small molecule inhibitor (SMI) that targets the TGF-β receptor I (TβRI), favored the final osteogenic maturation of OI-MSCs. Mechanistically, galunisertib downregulated type I collagen expression in OI-MSCs, with greater impact on mutant type I collagen, and concomitantly, modulated the expression of unfolded protein response (UPR) and autophagy markers. In vivo, galunisertib improved trabecular bone parameters only in female oim/oim mice. These results further suggest that type I collagen is a tunable target within the bone ECM that deserves investigation and that the SMI, galunisertib, is a promising new candidate for the anti-TGF-β targeting for the treatment of OI.

Supporting the translation of multiscale research in rare disease

Summary: In anticipation of our upcoming Special Issue, ‘Translating Multiscale Research in Rare Disease’, we celebrate the strides taken in rare disease research that are improving patient diagnosis, prognosis and treatment.

Murine Animal Models in Osteogenesis Imperfecta: The Quest for Improving the Quality of Life

Osteogenesis imperfecta is a rare genetic disorder characterized by bone fragility, due to alterations in the type I collagen molecule. It is a very heterogeneous disease, both genetically and phenotypically, with a high variability of clinical phenotypes, ranging from mild to severe forms, the most extreme cases being perinatal lethal. There is no curative treatment for OI, and so great efforts are being made in order to develop effective therapies. In these attempts, the in vivo preclinical studies are of paramount importance; therefore, serious analysis is required to choose the right murine OI model able to emulate as closely as possible the disease of the target OI population. In this review, we summarize the features of OI murine models that have been used for preclinical studies until today, together with recently developed new murine models. The bone parameters that are usually evaluated in order to determine the relevance of new developing therapies are exposed, and finally, current and innovative therapeutic strategies attempts considered in murine OI models, along with their mechanism of action, are reviewed. This review aims to summarize the in vivo studies developed in murine models available in the field of OI to date, in order to help the scientific community choose the most accurate OI murine model when developing new therapeutic strategies capable of improving the quality of life.