Browsing by Author "Sloan, Kourtney"

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    Characterizing Femoral Structure of the Ts66Yah Mouse Model of Down Syndrome
    (2023-08) Sloan, Kourtney; Roper, Randall J.; Li, Jiliang; McNulty, Margaret A.; Picard, Christine J.
    Down syndrome (DS) is caused by the partial or complete trisomy of human chromosome 21 (Hsa21) and can result in skeletal deficits, including lower bone mineral density (BMD) and increased risk of fracture and osteoporosis or osteopenia earlier than the general population. Mouse models of DS have been developed to understand the genetic mechanisms resulting in these phenotypes, but models differ due to the complex genetic nature of DS and differing genome structures between humans and mice. Ts65Dn mice have been a popular model of DS as they contain ~50% of Hsa21 orthologous genes on a freely segregating minichromosome, but there is speculation that the phenotypes are exaggerated by non-Hsa21 orthologous trisomic genes also present. To address this issue, the Ts66Yah mouse model was developed to remove the non-Hsa21 orthologous trisomic genes. In this study, male and female Ts66Yah mouse femurs were evaluated during bone accrual and peak bone mass to investigate structural differences using micro-computed tomography. Additionally, the role of trisomic Dyrk1a, a Hsa21 gene previously linked to bone deficits in Ts65Dn mice, was evaluated through genetic and pharmacological means in Ts66Yah femurs at postnatal day 36. Ts66Yah mice were found to have little or no trabecular deficits at any age evaluated, but sex-dependent cortical deficits were present at all ages investigated. Reducing Dyrk1a copy number in Ts66Yah mice significantly improved cortical deficits but did not return cortical bone to euploid levels. Pharmacological treatment with DYRK1A inhibitor L21 was confounded by multiple variables, making it difficult to draw conclusions about DYRK1A inhibition in this manner. Overall, these results indicate trabecular deficits associated with Ts65Dn mice may be due to the non-Hsa21 orthologous trisomic genes, and more Hsa21 orthologous trisomic genes are necessary to produce trabecular deficits in DS model mice. As more mouse models of DS are developed, multiple models need to be assessed to accurately define DS-associated phenotypes and test potential treatments.
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    Genetic dissection of triplicated chromosome 21 orthologs yields varying skeletal traits in Down syndrome model mice
    (The Company of Biologists, 2023) Sloan, Kourtney; Thomas, Jared; Blackwell, Matthew; Voisard, Deanna; Lana-Elola, Eva; Watson-Scales, Sheona; Roper, Daniel L.; Wallace, Joseph M.; Fisher, Elizabeth M. C.; Tybulewicz, Victor L. J.; Roper, Randall J.; Biology, School of Science
    Down syndrome (DS) phenotypes result from triplicated genes, but the effects of three copy genes are not well known. A mouse mapping panel genetically dissecting human chromosome 21 (Hsa21) syntenic regions was used to investigate the contributions and interactions of triplicated Hsa21 orthologous genes on mouse chromosome 16 (Mmu16) on skeletal phenotypes. Skeletal structure and mechanical properties were assessed in femurs of male and female Dp9Tyb, Dp2Tyb, Dp3Tyb, Dp4Tyb, Dp5Tyb, Dp6Tyb, Ts1Rhr and Dp1Tyb;Dyrk1a+/+/− mice. Dp1Tyb mice, with the entire Hsa21 homologous region of Mmu16 triplicated, display bone deficits similar to those of humans with DS and served as a baseline for other strains in the panel. Bone phenotypes varied based on triplicated gene content, sex and bone compartment. Three copies of Dyrk1a played a sex-specific, essential role in trabecular deficits and may interact with other genes to influence cortical deficits related to DS. Triplicated genes in Dp9Tyb and Dp2Tyb mice improved some skeletal parameters. As triplicated genes can both improve and worsen bone deficits, it is important to understand the interaction between and molecular mechanisms of skeletal alterations affected by these genes.
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    Increased dosage and treatment time of Epigallocatechin-3-gallate (EGCG) negatively affects skeletal parameters in normal mice and Down syndrome mouse models
    (Public Library of Science, 2022-02-23) Jamal, Raza; LaCombe, Jonathan; Patel, Roshni; Blackwell, Matthew; Thomas, Jared R.; Sloan, Kourtney; Wallace, Joseph M.; Roper, Randall J.; Biology, School of Science
    Bone abnormalities affect all individuals with Down syndrome (DS) and are linked to abnormal expression of DYRK1A, a gene found in three copies in people with DS and Ts65Dn DS model mice. Previous work in Ts65Dn male mice demonstrated that both genetic normalization of Dyrk1a and treatment with ~9 mg/kg/day Epigallocatechin-3-gallate (EGCG), the main polyphenol found in green tea and putative DYRK1A inhibitor, improved some skeletal deficits. Because EGCG treatment improved mostly trabecular skeletal deficits, we hypothesized that increasing EGCG treatment dosage and length of administration would positively affect both trabecular and cortical bone in Ts65Dn mice. Treatment of individuals with DS with green tea extract (GTE) containing EGCG also showed some weight loss in individuals with DS, and we hypothesized that weights would be affected in Ts65Dn mice after EGCG treatment. Treatment with ~20 mg/kg/day EGCG for seven weeks showed no improvements in male Ts65Dn trabecular bone and only limited improvements in cortical measures. Comparing skeletal analyses after ~20mg/kg/day EGCG treatment with previously published treatments with ~9, 50, and 200 mg/kg/day EGCG showed that increased dosage and treatment time increased cortical structural deficits leading to weaker appendicular bones in male mice. Weight was not affected by treatment in mice, except for those given a high dose of EGCG by oral gavage. These data indicate that high doses of EGCG, similar to those reported in some treatment studies of DS and other disorders, may impair long bone structure and strength. Skeletal phenotypes should be monitored when high doses of EGCG are administered therapeutically.
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    Sex-specific trisomic Dyrk1a-related skeletal phenotypes during development in a Down syndrome model
    (The Company of Biologists, 2024) LaCombe, Jonathan M.; Sloan, Kourtney; Thomas, Jared R.; Blackwell, Matthew P.; Crawford, Isabella; Bishop, Flannery; Wallace, Joseph M.; Roper, Randall J.; Biology, School of Science
    Skeletal insufficiency affects all individuals with Down syndrome (DS) or trisomy 21 and may alter bone strength throughout development due to a reduced period of bone formation and early attainment of peak bone mass compared to those in typically developing individuals. Appendicular skeletal deficits also appear in males before females with DS. In femurs of male Ts65Dn DS model mice, cortical deficits were pronounced throughout development, but trabecular deficits and Dyrk1a overexpression were transitory until postnatal day (P) 30, when there were persistent trabecular and cortical deficits and Dyrk1a was trending toward overexpression. Correction of DS-related skeletal deficits by a purported DYRK1A inhibitor or through genetic means beginning at P21 was not effective at P30, but germline normalization of Dyrk1a improved male bone structure by P36. Trabecular and cortical deficits in female Ts65Dn mice were evident at P30 but subsided by P36, typifying periodic developmental skeletal normalizations that progressed to more prominent bone deficiencies. Sex-dependent differences in skeletal deficits with a delayed impact of trisomic Dyrk1a are important to find temporally specific treatment periods for bone and other phenotypes associated with trisomy 21.
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    Skeletal Deficits in Male and Female down Syndrome Model Mice Arise Independent of Normalized Dyrk1a Expression in Osteoblasts
    (MDPI, 2021-10-28) Thomas, Jared R.; Sloan, Kourtney; Cave, Kelsey; Wallace, Joseph M.; Roper, Randall J.; Biology, School of Science
    Trisomy 21 (Ts21) causes alterations in skeletal development resulting in decreased bone mass, shortened stature and weaker bones in individuals with Down syndrome (DS). There is a sexual dimorphism in bone mineral density (BMD) deficits associated with DS with males displaying earlier deficits than females. The relationships between causative trisomic genes, cellular mechanisms, and influence of sex in DS skeletal abnormalities remain unknown. One hypothesis is that the low bone turnover phenotype observed in DS results from attenuated osteoblast function, contributing to impaired trabecular architecture, altered cortical geometry, and decreased mineralization. DYRK1A, found in three copies in humans with DS, Ts65Dn, and Dp1Tyb DS model mice, has been implicated in the development of postnatal skeletal phenotypes associated with DS. Reduced copy number of Dyrk1a to euploid levels from conception in an otherwise trisomic Ts65Dn mice resulted in a rescue of appendicular bone deficits, suggesting DYRK1A contributes to skeletal development and homeostasis. We hypothesized that reduction of Dyrk1a copy number in trisomic osteoblasts would improve cellular function and resultant skeletal structural anomalies in trisomic mice. Female mice with a floxed Dyrk1a gene (Ts65Dn,Dyrk1afl/wt) were mated with male Osx-Cre+ (expressed in osteoblasts beginning around E13.5) mice, resulting in reduced Dyrk1a copy number in mature osteoblasts in Ts65Dn,Dyrk1a+/+/Osx-Cre P42 male and female trisomic and euploid mice, compared with littermate controls. Male and female Ts65Dn,Dyrk1a+/+/+ (3 copies of DYRK1A in osteoblasts) and Ts65Dn,Dyrk1a+/+/Osx-Cre (2 copies of Dyrk1a in osteoblasts) displayed similar defects in both trabecular architecture and cortical geometry, with no improvements with reduced Dyrk1a in osteoblasts. This suggests that trisomic DYRK1A does not affect osteoblast function in a cell-autonomous manner at or before P42. Although male Dp1Tyb and Ts65Dn mice exhibit similar skeletal deficits at P42 in both trabecular and cortical bone compartments between euploid and trisomic mice, female Ts65Dn mice exhibit significant cortical and trabecular deficits at P42, in contrast to an absence of genotype effect in female Dp1Tyb mice in trabecular bone. Taken together, these data suggest skeletal deficits in DS mouse models and are sex and age dependent, and influenced by strain effects, but are not solely caused by the overexpression of Dyrk1a in osteoblasts. Identifying molecular and cellular mechanisms, disrupted by gene dosage imbalance, that are involved in the development of skeletal phenotypes associated with DS could help to design therapies to rescue skeletal deficiencies seen in DS.