Browsing by Author "Steele, Ashley T."
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Item Craniofacial Morphology of Juvenile Mice with Osteogenesis Imperfecta(2020) Menegaz, Rachel A.; Organ, Jason; Steele, Ashley T.Osteogenesis imperfecta (OI) type III is a severe genetic disorder of type I collagen (Col1) which results in bone fragility, reduced stature, and impaired craniofacial growth. To investigate the mechanisms by which Col1 mutations alter craniofacial growth, we used the homozygous recessive OI murine (OIM) mouse model, which is known to exhibit human-like adult phenotypes but for which the juvenile phenotype is unknown. Weaning OIM and wild type (WT) littermates were µCT scanned at 21 days. Craniofacial landmarks were collected using 3D Slicer software. Interlandmark distances (ILDs) and centroid sizes were calculated using Past 2.17 software. ILDs were scaled against skull/mandible centroid size to remove the effect of overall body size for shape analyses. Mann-Whitney U-tests were used to compare absolute and relative (scaled) ILDs between genotypes. Craniomandibular centroid sizes and absolute linear distances (skull, rostrum, palate, and mandible lengths) demonstrate that OIM mice are smaller overall compared to WT littermates. When scaled to centroid size, juvenile OIM mice have a decrease in midface height, nasal and mandibular diastema length but increased hemimandible length compared to WT mice. For a given skull length, OIM mice have shorter faces in both the anteroposterior and dorsoventral dimensions. The morphometric changes seen in juvenile OIM mice replicate the midfacial hypoplasia seen in human children with OI. This mouse model can be used to investigate the structural changes underlying the human OI phenotype and potential therapeutic interventions. These results can be used to inform future investigations of Col1 in craniofacial development.Item Craniofacial Morphology of Juvenile Mice with Osteogenesis Imperfecta(2020-05) Steele, Ashley T.; Menegaz, Rachel A.; Maddux, Scott D.; Kesterke, Matthew J.Osteogenesis Imperfecta (OI) is a heritable connective tissue disorder affecting the synthesis and structure of type I collagen (Col1) due to autosomal dominant mutations in proa1(I) or proa2(I) collagen genes (COL1A1 and COL1A2). Clinical manifestations of the severe OI type III include bone fragility, reduced physical stature, and midface hypoplasia resulting in a "triangle face" phenotype. Current treatment options have low-success rates and focus primarily on alleviating symptoms through surgical interventions and pharmacologic use of antiresorptive drugs. The homozygous OI murine (OIM-/-) mouse model has a nonlethal, recessively inherited mutation of the COL1A2 gene and exhibits adult cranial and post-cranial phenotypes similar to humans with severe OI type III; however, the juvenile phenotype is unknown. The goals of this study are: (1) to determine if significant differences in craniofacial skeletal shape and size are present at the age of weaning (21 days/4 weeks) in the OIM-/- mice compared to the wild type (WT) and (2) to determine if these differences are still significant when adjusted for the allometric effects of body size. OIM-/- and WT littermates were weaned at 21 days and scanned in-vivo with a Skyscan 1176 micro-CT system. Craniofacial geometric landmarks were collected using 3D Slicer software and were subsequently used to calculate interlandmark distances (ILDs) and centroid sizes. ILDs were scaled against skull/mandible centroid size to account for the effect of overall body size on shape analyses. Mann-Whitney U-tests were used to compare both absolute and relative (scaled) ILDs between the genotypes. Craniomandibular centroid sizes and absolute linear distances (skull, rostrum, palate, and mandible lengths) demonstrate that the OIM-/- mice are smaller overall than their WT littermates. When scaled to centroid size, juvenile OIM-/- mice have a decrease in nasal length, mandibular diastema length, and basicranium but an increase in cranial vaults, midface heights, and both maxillary and mandibular toothrow lengths compared to WT mice. For a given skull length, OIM-/- mice have shorter faces in both the anteroposterior and dorsoventral dimensions. The morphometric changes seen in the juvenile OIM-/- mice replicate the "triangle face" and relative macrocephaly that is commonly seen in human pediatric populations with OI. This suggests that this mouse model can potentially be used to investigate the structural changes underlying the human OI phenotype and for potential therapeutic interventions, such as biomechanical loading, myostatin knock-out, and pharmaceutical therapies. Additionally, the results of this study can be used to inform future investigations of Col1 in craniofacial development. Continuing to evaluate the etiology of this disorder can lead to better treatment options to improve the quality of life for patients with OI, especially pediatric patients.Item Microstructure & Macrostructure Interrelationship in the Growing Hard Palate(2022) Miller, Courtney; Steele, Ashley T.; Organ, Jason; Menegaz, Rachel A.Bone strength is the result of microstructure (bone material properties) and macrostructure (bone size and shape), and deficiencies in either can produce skeletal fragilities with an increased likelihood of injury. The micro- and macro-architecture work together during re/modeling, ensuring that the skeleton is resistant to repetitive loading and preventing fracture. Bone is particularly responsive to loading during the rapid growth occurring in early life. Within the craniofacial complex, the hard palate is a unique structure that undergoes continuous loading due to continuous resting/active tongue pressure and bite forces. Because of this, palatal growth is theorized to drive midfacial growth. The aim of this study is to investigate longitudinal changes in the palate when the relationship between microstructure and macrostructure is perturbed. Here we use the OIM mouse (B6C3FE a/a-Col1a2OIM/J), a strain with a mutation to the structural protein type I collagen, resulting in increased bone fragility and improper biomineralization. We hypothesize that OIM and unaffected wild-type (WT) mice will be most similar in bone micro- and macro-structure in regions of the palate that experience high loading and therefore high rates of bone modeling/remodeling. Mice were micro-CT scanned at two timepoints: week 4 (juvenile) and week 16 (adult). BMD was collected at 3 regions (anterior, mid, and posterior palate). Mann-Whitney U tests were used to compare BMD between genotypes. 28 fixed and 10 sliding landmarks were placed across the palate. Geometric morphologic analyses were conducted to determine variation between genotypes in overall shape and curvature throughout growth. Average BMD decreased along an anteroposterior gradient for all mice. While juvenile OIM mice had lower palate BMD than WT mice at all regions, adult OIM mice had significantly lower BMD at only the anterior and posterior regions but not the midpalate. Procrustes ANOVA revealed significant differences in palatal shape between the genotypes at both the juvenile (p=0.001) and adult (p=0.0015) stages. Principal component analyses revealed that juvenile OIM mice had a shorter anterior palate and broader palate compared to WT mice, while adult OIM mice had a shorter posterior palate than WT mice. OI mice had flatter palatal arches in the coronal plane as juveniles, and in the midsagittal plane as juveniles and adults. Results show significant differences in palatal BMD and morphology between genotypes throughout growth, with fewer significant differences at the adult stage. Increased loading of the anterior palate during incisive gnawing may result in the convergence of bone macrostructure among adult mice, while increased strain at the midpalatal suture may necessitate increased BMD even in the presence of a biomineralization defect. Further research is needed to understand the functional significance of the anteroposterior palatal gradient and its relation to soft tissue attachments, particularly given the difference in oral behaviors between juveniles and adults.Item Neurocranial Growth in the OIM Mouse Model of Osteogenesis Imperfecta(2022) Husain, Tooba S.; Miller, Courtney; Steele, Ashley T.; Gonzales, Lauren; Handler, Emma; Organ, Jason; Menegaz, Rachel A.Osteogenesis imperfecta (OI) is a disorder of type I collagen characterized by abnormal bone formation and weakened bone architecture. Human patients with OI have larger cranial vaults (macrocephaly), altered cranial base morphology including basilar invagination and platybasia (skull base flattening), and midfacial underdevelopment. The neurocranial changes may affect both underlying nervous tissue and growth patterns of the facial skeleton. However, we still do not fully understand how and when these divergent morphologies occur. The aims of this study are: (1) to investigate the integrated development of the skull and the brain in amouse model of OI; and (2) to identify the developmental trajectories of these structures to facilitate future therapeutic interventions. We hypothesize that compared to unaffected mice, mice with OI will have decreased brain volumes due to an overall reduction in cranial size and decreased cranial base angles (CBA) due to platybasia. To test these hypotheses, we used the osteogenesis imperfecta murine (OIM or B6C3FE a/a-Col1a2/J), a model for the severe type III OI in humans, and unaffected wild-type (WT) littermates. Mice were imaged using in vivo micro-computed tomography (micro-CT) at the juvenile (week 4; 10 OIM/14 WT) and adult (week 16; 9OIM/11 WT) stages. All measurements were taken in 3D Slicer software. 82 cranial landmarks were used to calculate centroid size, an estimate of overall head size. The segmentations tool was used to create virtual endocasts as a proxy for brain volume. The angle tool was used to measure CBA in the midsagittal plane using threelandmarks: foramen cecum, midsphenoidal synchondrosis, and basion. Mann-Whitney U tests were used to compare centroid sizes, brain volumes, and CBA between the genotypes. Both juvenile (p=0.008) and adult (p=0.003) OIM mice were found to have absolutely smaller brains than WT mice. However, OIM mice also have significantly smaller cranial centroid sizes compared to WT mice (p=0.003, p< 0.001). When scaled to cranial size, juvenile mice had relatively larger brain volumes (p=0.016) butadult OIM relative brain volumes were not significantly different from WT. No significant difference was seen in CBA at the juvenile (p=0.065) or adult (p=0.171) stages, however a trend was observed for decreased CBA at the adult stage. These results suggest that neurocranial dysmorphologies in OI may be more severe at earlier stages of postnatal development. Previous analyses of these mice have documented relative skeletal macrocephaly in both juvenile and adults, however here we document an increase in relative endocranial volume only at the juvenile stage. A reduction in CBA during growth, possibly due to platybasia, may underlie this decoupling between external and internal cranial morphology. Future work will investigate the effect of CBA on facial growth and midfacial underdevelopment in these mice. A better understanding of the integration and growth trajectory of the neurocranium is foundational for formulating treatments to manage basicranial instabilities in patients with OI. Support or Funding Information Funding was provided by an Indiana University Collaborative Research Grant, Ralph W. and Grace Showalter Trust, and a UNTHSC Physiology & Anatomy SEED Grant.Item Postweaning Craniofacial Growth in the OIM Mouse Model of Osteogenesis Imperfecta(2022) Steele, Ashley T.; Mitchell, D. Rex; Organ, Jason; Menegaz, Rachel A.Osteogenesis imperfecta (OI) type III is a severe genetic disorder of type I collagen (Col1) resulting in bone fragility, reduced stature, and impaired craniofacial growth resulting in midface hypoplasia, dental malocclusions, and macrocephaly. While the adult OI murine (OIM) mouse model exhibits craniofacial phenotypes similar to patients with OI, little is known about the developmental trajectories of these phenotypes. To investigate the mechanisms by which Col1 mutations alter postnatal craniofacial growth, we analyzed the phenotype of the OIM mouse from the age of weaning until adulthood (skeletal maturity). OIM and wild-type (WT) littermates were scanned in-vivo with a Skyscan 1176 micro-CT system at 4 weeks (weaning) and 16 weeks (adulthood). 3D landmarks were collected using 3D Slicer software. Centroid size (a proxy for craniomandibular size) was compared using Mann-Whitney U tests. Morphological analysis for shape variation, including Generalized Procrustes analysis (GPA) and principal component analyses (PCA), were performed using the "geomorph" package in R. Procrustes ANOVAs were used to test for significant differences in craniomandibular shape between the genotypes. Morphological disparity was estimated as the Procrustes variance and statistically compared using the morphol.disparity function in R. Craniomandibular centroid sizes were significantly smaller in the OIM mice than the WT mice at both weeks 4 and 16 (p< 0.010). When the effects of size were accounted for by the GPA, significant shape differences were present (p< 0.002) throughout growth. For their size, both juvenile and adult OIM mice had shortened midfaces and increased cranial vault dimensions (relative macrocephaly) compared to WT littermates. Morphological differences were seen around the rostrum, temporal crests, and zygomatic arches. Marked vertical expansion of the neurocranium at the sagittal and coronal sutures presented with a concomitant basicranial shortening in the juvenile OIM mice only. Compared to WT, both juvenile and adult OIM mice had mandibles that were longitudinally shortened and mediolaterally wide. Morphological differences were seen around the incisal ramus and angular process at both ages, and in the coronoid process of adult OIM mice. Significantly different (p=0.001) morphological disparity between the genotypes existed only at the juvenile stage, demonstrating an overall decrease in variance throughout postnatal development period. This suggests that mice with greater variances in cranial shape experienced higher rates of attrition. This is potentially related to increased craniofacial fracture rates seen in the OIM mice. These results suggest that while the OIM craniofacial phenotype differs significantly from the WT throughout postweaning growth, functional constraints (such as feeding performance) may limit the degree of potential phenotypic divergence. Furthermore, while previous work in human patients with OI has linked the development of macrocephaly to basicranial shortening during early skull development, our results provide limited support for this hypothesis due to the absence of basicranial changes in adult OIM mice. Future investigations will examine perinatal and pre-weaning growth in the OIM mouse model to better understand the development of these craniofacial dysmorphologies, and to identify optimal growth windows during which interventions might recover bone quality and growth trajectories in patients with OI.