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Achondroplasia: Development, pathogenesis, and therapy.

ABSTRACT: Autosomal dominant mutations in fibroblast growth factor receptor 3 (FGFR3) cause achondroplasia (Ach), the most common form of dwarfism in humans, and related chondrodysplasia syndromes that include hypochondroplasia (Hch), severe achondroplasia with developmental delay and acanthosis nigricans (SADDAN), and thanatophoric dysplasia (TD). FGFR3 is expressed in chondrocytes and mature osteoblasts where it functions to regulate bone growth. Analysis of the mutations in FGFR3 revealed increased signaling through a combination of mechanisms that include stabilization of the receptor, enhanced dimerization, and enhanced tyrosine kinase activity. Paradoxically, increased FGFR3 signaling profoundly suppresses proliferation and maturation of growth plate chondrocytes resulting in decreased growth plate size, reduced trabecular bone volume, and resulting decreased bone elongation. In this review, we discuss the molecular mechanisms that regulate growth plate chondrocytes, the pathogenesis of Ach, and therapeutic approaches that are being evaluated to improve endochondral bone growth in people with Ach and related conditions. Developmental Dynamics 246:291-309, 2017. © 2016 Wiley Periodicals, Inc.

SUBMITTER: Ornitz DM

PROVIDER: S-EPMC5354942 | biostudies-literature | 2017 Apr

REPOSITORIES: biostudies-literature

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Achondroplasia: Development, pathogenesis, and therapy.

Ornitz David M DM Legeai-Mallet Laurence L

Developmental dynamics : an official publication of the American Association of Anatomists 20170302 4

Autosomal dominant mutations in fibroblast growth factor receptor 3 (FGFR3) cause achondroplasia (Ach), the most common form of dwarfism in humans, and related chondrodysplasia syndromes that include hypochondroplasia (Hch), severe achondroplasia with developmental delay and acanthosis nigricans (SADDAN), and thanatophoric dysplasia (TD). FGFR3 is expressed in chondrocytes and mature osteoblasts where it functions to regulate bone growth. Analysis of the mutations in FGFR3 revealed increased sig ...[more]

PMID: 27987249

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Project description:BackgroundAchondroplasia is a rare genetic disease is characterized by abnormal bone development and early obesity. While the bone aspect of the disease has been thoroughly studied, early obesity affecting approximately 50% of them during childhood has been somewhat neglected. It nevertheless represents a major health problem in these patients, and is associated to life-threatening complications including increasing risk of cardiovascular pathologies. We have thus decided to study obesity in patients and to use the mouse model to evaluate if soluble FGFR3 therapy, an innovative treatment approach for achondroplasia, could also impact the development of this significant complication.Methods and findingsTo achieve this, we have first fully characterized the metabolic deregulations in these patients by conducting a longitudinal retrospective study, in children with achondroplasia Anthropometric, densitometric measures as well as several blood parameters were recorded and compared between three age groups ranging from [0-3], [4-8] and [9-18] years old. Our results show unexpected results with the development of an atypical obesity with preferential fat deposition in the abdomen that is remarkably not associated with classical complications of obesity such as diabetes or hypercholosterolemia. Because it is not associated with diabetes, the atypical obesity has not been studied in the past even though it is recognized as a real problem in these patients. These results were validated in a murine model of achondroplasia (Fgfr3ach/+) where similar visceral adiposity was observed. Unexpected alterations in glucose metabolism were highlighted during high-fat diet. Glucose, insulin or lipid levels remained low, without the development of diabetes. Very interestingly, in achondroplasia mice treated with soluble FGFR3 during the growth period (from D3 to D22), the development of these metabolic deregulations was prevented in adult animals (between 4 and 14 weeks of age). The lean-over-fat tissues ratio was restored and glucose metabolism showed normal levels. Treating Fgfr3ach/+ mice with soluble FGFR3 during the growth period, prevented the development of these metabolic deregulations in adult animals and restored lean-over-fat tissues ratio as well as glucose metabolism in adult animals.ConclusionThis study demonstrate that achondroplasia patients develop an atypical obesity with preferential abdominal obesity not associated with classical complications. These results suggest that achondroplasia induces an uncommon metabolism of energy, directly linked to the FGFR3 mutation. These data strongly suggest that this common complication of achondroplasia should be included in the clinical management of patients. In this context, sFGFR3 proved to be a promising treatment for achondroplasia by normalizing the biology at different levels, not only restoring bone growth but also preventing the atypical visceral obesity and some metabolic deregulations.

Project description:Our overall goal is to understand how viral envelope proteins mediate membrane fusion and pathogenesis. Membrane fusion is a crucial step in the delivery of the viral genome into the cell resulting in infection. On the other hand, fusion activity of viral envelope glycoproteins expressed in infected cells may cause the demise of uninfected bystander cells by apoptosis. Our general approach is to kinetically resolve steps in the pathway of viral envelope glycoprotein-mediated membrane fusion and to uncover physical parameters underlying those steps using a variety of biochemical, biophysical, virological, and molecular and cell biological techniques. Since HIV fusion involves a complex cascade of interactions of the envelope glycoprotein with two receptors, membrane organization plays an important role and interfering with it may modulate entry. To study this phenomenon, we have either examined cell lines with differential expression of sphingolipids (such as GM3), or altered membrane organization by modifying levels of cholesterol, ceramides, or glycosphingolipids. We show that the localized plasma membrane lipid microenvironment (and not the specific membrane lipids) in the vicinity of CD4 controls receptor mobility and HIV-1 fusion. The complex cascade of conformational changes that must occur to allow virus entry is also a very important target for therapy and vaccine development. We have recently designed and tested peptide analogs composed of chemical spacers and reactive moieties positioned strategically to promote permanent attachment. Using a temperature-arrested state in vitro assay we show evidence for the trapping of a pre-six-helix bundle fusion intermediate by a covalent reaction with the inhibitory reactive peptide. Also, using photo-reactive hydrophobic probes we have found ways to inactivate viral envelope glycoproteins while leaving their overall structures intact. Finally, in order to study the envelope glycoprotein effects on pathogenesis, we have used an in vitro model of co-culture of envelope-expressing cells as effectors and CD4+ T cells as targets. We delineated that apoptosis mediated by envelope glycoprotein in bystander cells correlates with transmembrane subunit (gp41)-induced hemifusion. The apoptotic pathway initiated by this interaction involves caspase-3-dependent mitochondrial depolarization and reactive oxygen species production, which depends on the phenotype of the envelope glycoprotein associated with the virus. Taken as a whole, our studies have many different important implications for antiviral therapies and vaccine development.

Project description:BackgroundAchondroplasia is the most common genetic skeletal disorder causing disproportionate short stature/dwarfism. Common additional features include spinal stenosis, midface retrusion, macrocephaly and a generalized spondylometaphyseal dysplasia which manifest as spinal cord compression, sleep disordered breathing, delayed motor skill acquisition and genu varus with musculoskeletal pain. To better understand the interactions and health outcomes of these potential complications, we embarked on a multi-center, natural history study entitled CLARITY (achondroplasia natural history study). One of the CLARITY objectives was to develop growth curves (length/height, weight, head circumference, weight-for-height) and corresponding reference tables of mean and standard deviations at 1 month increments from birth through 18 years for clinical use and research for achondroplasia patients.MethodsAll available retrospective anthropometry data including length/height, weight and head circumference from achondroplasia patients were collected at 4 US skeletal dysplasia centers (Johns Hopkins University, AI DuPont Hospital for Children, McGovern Medical School University of Texas Health, University of Wisconsin School of Medicine and Public Health). Weight-for-age values beyond 3 SD above the mean were excluded from the weight-for-height and weight-for-age curves to create a stricter tool for weight assessment in this population.ResultsOver 37,000 length/height, weight and head circumference measures from 1374 patients with achondroplasia from birth through 75 years of age were compiled in a REDCap database. Stature and weight data from birth through 18 years of age and head circumference from birth through 5 years of age were utilized to construct new length/height-for-age, weight-for-age, head circumference-for-age and weight-for-height curves.ConclusionAchondroplasia-specific growth curves are essential for clinical care of growing infants and children with this condition. In an effort to provide prescriptive, rather than purely descriptive, references for weight in this population, extreme weight values were omitted from the weight-for-age and weight-for-height curves. This well-phenotyped cohort may be studied with other global achondroplasia populations (e.g. Europe, Argentina, Australia, Japan) to gain further insight into environmental or ethnic influences on growth.

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Achondroplasia: Development, pathogenesis, and therapy.

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Achondroplasia: Development, pathogenesis, and therapy.

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