Browsing by Author "Kroon, Tori"

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    Global Deletion of Sost Increases Intervertebral Disc Hydration But May Trigger Chondrogenesis
    (2020-05) Kroon, Tori; Holguin, Nilsson; Wallace, Joseph; Wagner, Diane
    Intervertebral discs (IVD) degenerate earlier than many other musculoskeletal tissues and will continue to degenerate with aging. IVD degeneration affects up to 80 percent of the adult population and is a major contributing factor to low back pain. Anti-sclerostin antibody is an FDA-approved treatment for osteoporosis in postmenopausal women at high-risk for fracture and, as a systemic stimulant of the Wnt/LRP5/β-Catenin signaling pathway, may impact the IVD. Stabilization of β-Catenin in the IVD increases Wnt signaling and is anabolic to the extracellular matrix (ECM), while deletion of β-catenin or LRP5 decreases Wnt signaling and is catabolic to the ECM. Here, we hypothesized that a reduction of Sost would stimulate ECM anabolism. Lumbar and caudal (tail) IVD and vertebrae of Sost KO and WT (wildtype) mice (n=8 each) were harvested at 16 weeks of age and tested by MRI, histology, immunohistochemistry, Western Blot, qPCR, and microCT. Compared to WT, Sost KO reduced sclerostin protein and Sost gene expression. Next, Sost KO increased the hydration of the IVD and the proteoglycan stain in the nucleus pulposus and decreased the expression of genes associated with IVD degeneration, e.g., heat shock proteins. However, deletion of Sost was compensated by less unphosphorylated (active) β-Catenin protein in the cell nucleus, upregulation of Wnt signaling inhibitors Dkk1 and sFRP4, and catabolic ECM gene expression. Consequently, notochordal and early chondrocyte-like cells (CLCs) were replaced by mature CLCs. Overall, Sost deletion increased hydration and proteoglycan protein content, but activated a compensatory suppression of Wnt signaling that may trigger chondrogenesis and may potentially be iatrogenic to the IVD in the long-term.
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    Suppression of sost/sclerostin and dikkopf-1 augment intervertebral disc structure in mice
    (Wiley, 2022) Kroon, Tori; Bhadouria, Neharika; Niziolek, Paul; Edwards, Daniel; Clinkenbeard, Erica L.; Robling, Alexander; Holguin, Nilsson; Biomedical Engineering, School of Engineering and Technology
    Intervertebral disc (IVD) degeneration is a leading cause of low back pain, characterized by accelerated extracellular matrix breakdown and IVD height loss but there is no approved pharmacological therapeutic. Deletion of Wnt ligand competitor Lrp5 induces IVD degeneration, suggesting that Wnt signaling is essential for IVD homeostasis. Therefore, the IVD may respond to neutralization of Wnt ligand competitors sost(gene)/sclerostin(protein) and/or dikkopf-1 (dkk1). Anti-sclerostin antibody (scl-Ab) is an FDA-approved bone therapeutic that activates Wnt signaling. We (1) determined if pharmacological neutralization of sclerostin, dkk1 or their combination would stimulate Wnt signaling and augment IVD structure and (2) determined the prolonged adaptation of the IVD to global, persistent deletion of sost. Nine-week-old C57Bl/6J female mice (n = 6-7/grp) were subcutaneously injected 2x/wk for 5.5 wk with scl-Ab (25 mg/kg), dkk1-Ab (25 mg/kg), 3:1 scl-Ab/dkk1-Ab (18.75:6.25 mg/kg) or vehicle (veh). Separately, IVD of sost KO and wildtype (WT) mice (n = 8/grp) were harvested at 16 weeks of age. First, compared to vehicle, injection of scl-Ab, dkk1-Ab and 3:1 scl-Ab/dkk1-Ab similarly increased lumbar IVD height and β-catenin gene expression. Despite these similarities, only injection of scl-Ab alone strengthened IVD mechanical properties and decreased heat shock protein gene expressions. Genetically and compared to WT, sost KO enlarged IVD height, increased proteoglycan staining and imbibed IVD hydration. Notably, persistent deletion of sost was compensated by upregulation of dkk1, which consequently reduced the cell nuclear fraction for Wnt signaling co-transcription factor β-catenin in the IVD. Lastly, RNA-sequencing pathway analysis confirmed the compensatory suppression of Wnt signaling and revealed a reduction of cellular stress-related pathways. Together, suppression of sost/sclerostin or dkk1 each augmented IVD structure by stimulating Wnt signaling, but scl-Ab outperformed dkk1-Ab in strengthening the IVD. Ultimately, postmenopausal women prescribed scl-Ab injections to prevent vertebral fracture may also benefit from a restoration of IVD height and health.