Abaloparatide is more potent than teriparatide in restoring bone mass and strength in type 1 diabetic male mice.

This study investigated the efficacy of the two FDA-approved bone anabolic ligands of the parathyroid hormone receptor 1 (PTH1R), teriparatide or human parathyroid hormone 1-34 (PTH) and abaloparatide (ABL), to restoring skeletal health using a preclinical murine model of streptozotocin-induced T1-DM. Intermittent daily subcutaneous injections of equal molar doses (12 pmoles/g/day) of PTH (50 ng/g/day), ABL (47.5 ng/g/day), or vehicle, were administered for 28 days to 5-month-old C57Bl/6 J male mice with established T1-DM or control (C) mice. ABL was superior to PTH in increasing or restoring bone mass in control or T1-MD mice, respectively, which was associated with superior stimulation of trabecular and periosteal bone formation, upregulation of osteoclastic/osteoblastic gene expression, and increased circulating bone remodeling markers. Only ABL corrected the reduction in ultimate load, which is a measure of bone strength, induced by T1-DM, and it also increased energy to ultimate load. In addition, bones from T1-DM mice treated with PTH or ABL exhibited increased ultimate stress, a material index, compared to T1-DM mice administered with vehicle. And both PTH and ABL prevented the increased expression of the Wnt antagonist Sost/sclerostin displayed by T1-DM mice. Further, PTH and ABL increased to a similar extent the circulating bone resorption marker CTX and the bone formation marker P1NP in T1-DM after 2 weeks of treatment; however, only ABL sustained these increases after 4 weeks of treatment. We conclude that at equal molar doses, ABL is more effective than PTH in increasing bone mass and restoring the cortical and trabecular bone lost with T1-DM, due to higher and longer-lasting increases in bone remodeling.

Notch3 signaling between myeloma cells and osteocytes in the tumor niche promotes tumor growth and bone destruction.

In multiple myeloma (MM), communication via Notch signaling in the tumor niche stimulates tumor progression and bone destruction. We previously showed that osteocytes activate Notch, increase Notch3 expression, and stimulate proliferation in MM cells. We show here that Notch3 inhibition in MM cells reduced MM proliferation, decreased Rankl expression, and abrogated the ability of MM cells to promote osteoclastogenesis. Further, Notch3 inhibition in MM cells partially prevented the Notch activation and increased proliferation induced by osteocytes, demonstrating that Notch3 mediates MM-osteocyte communication. Consistently, pro-proliferative and pro-osteoclastogenic pathways were upregulated in CD138+ cells from newly diagnosed MM patients with high vs. low NOTCH3 expression. These results show that NOTCH3 signaling in MM cells stimulates proliferation and increases their osteoclastogenic potential. In contrast, Notch2 inhibition did not alter MM cell proliferation or communication with osteocytes. Lastly, mice injected with Notch3 knock-down MM cells had a 50% decrease in tumor burden and a 50% reduction in osteolytic lesions than mice bearing control MM cells. Together, these findings identify Notch3 as a mediator of cell communication among MM cells and between MM cells and osteocytes in the MM tumor niche and warrant future studies to exploit Notch3 as a therapeutic target to treat MM.

Targeting Notch Inhibitors to the Myeloma Bone Marrow Niche Decreases Tumor Growth and Bone Destruction without Gut Toxicity.

Systemic inhibition of Notch with γ-secretase inhibitors (GSI) decreases multiple myeloma tumor growth, but the clinical use of GSI is limited due to its severe gastrointestinal toxicity. In this study, we generated a GSI Notch inhibitor specifically directed to the bone (BT-GSI). BT-GSI administration decreased Notch target gene expression in the bone marrow, but it did not alter Notch signaling in intestinal tissue or induce gut toxicity. In mice with established human or murine multiple myeloma, treatment with BT-GSI decreased tumor burden and prevented the progression of multiple myeloma-induced osteolytic disease by inhibiting bone resorption more effectively than unconjugated GSI at equimolar doses. These findings show that BT-GSI has dual anti-myeloma and anti-resorptive properties, supporting the therapeutic approach of bone-targeted Notch inhibition for the treatment of multiple myeloma and associated bone disease. SIGNIFICANCE: Development of a bone-targeted Notch inhibitor reduces multiple myeloma growth and mitigates cancer-induced bone destruction without inducing the gastrointestinal toxicity typically associated with inhibition of Notch.

Skeletal Protection and Promotion of Microbiome Diversity by Dietary Boosting of the Endogenous Antioxidant Response.

There is an unmet need for interventions with better compliance that prevent the adverse effects of sex steroid deficiency on the musculoskeletal system. We identified a blueberry cultivar (Montgomerym [Mont]) that added to the diet protects female mice from musculoskeletal loss and body weight changes induced by ovariectomy. Mont, but not other blueberries, increased the endogenous antioxidant response by bypassing the traditional antioxidant transcription factor Nrf2 and without activating estrogen receptor canonical signaling. Remarkably, Mont did not protect the male skeleton from androgen-induced bone loss. Moreover, Mont increased the variety of bacterial communities in the gut microbiome (α-diversity) more in female than in male mice; shifted the phylogenetic relatedness of bacterial communities (ß-diversity) further in females than males; and increased the prevalence of the taxon Ruminococcus1 in females but not males. Therefore, this nonpharmacologic intervention (i) protects from estrogen but not androgen deficiency; (ii) preserves bone, skeletal muscle, and body composition; (iii) elicits antioxidant defense responses independently of classical antioxidant/estrogenic signaling; and (iv) increases gut microbiome diversity toward a healthier signature. These findings highlight the impact of nutrition on musculoskeletal and gut microbiome homeostasis and support the precision medicine principle of tailoring dietary interventions to patient individualities, like sex. © 2020 American Society for Bone and Mineral Research (ASBMR).

Protection From Glucocorticoid-Induced Osteoporosis by Anti-Catabolic Signaling in the Absence of Sost/Sclerostin.

Excess of glucocorticoids, either due to disease or iatrogenic, increases bone resorption and decreases bone formation and is a leading cause of osteoporosis and bone fractures worldwide. Improved therapeutic strategies are sorely needed. We investigated whether activating Wnt/ß-catenin signaling protects against the skeletal actions of glucocorticoids, using female mice lacking the Wnt/ß-catenin antagonist and bone formation inhibitor Sost. Glucocorticoids decreased the mass, deteriorated the microarchitecture, and reduced the structural and material strength of bone in wild-type (WT), but not in Sost-/- mice. The high bone mass exhibited by Sost-/- mice is due to increased bone formation with unchanged resorption. However, unexpectedly, preservation of bone mass and strength in Sost-/- mice was due to prevention of glucocorticoid-induced bone resorption and not to restoration of bone formation. In WT mice, glucocorticoids increased the expression of Sost and the number of sclerostin-positive osteocytes, and altered the molecular signature of the Wnt/ß-catenin pathway by decreasing the expression of genes associated with both anti-catabolism, including osteoprotegerin (OPG), and anabolism/survival, such as cyclin D1. In contrast in Sost-/- mice, glucocorticoids did not decrease OPG but still reduced cyclin D1. Thus, in the context of glucocorticoid excess, activation of Wnt/ß-catenin signaling by Sost/sclerostin deficiency sustains bone integrity by opposing bone catabolism despite markedly reduced bone formation and increased apoptosis. This crosstalk between glucocorticoids and Wnt/ß-catenin signaling could be exploited therapeutically to halt resorption and bone loss induced by glucocorticoids and to inhibit the exaggerated bone formation in diseases of unwanted hyperactivation of Wnt/ß-catenin signaling. © 2016 American Society for Bone and Mineral Research.

Bidirectional Notch Signaling and Osteocyte-Derived Factors in the Bone Marrow Microenvironment Promote Tumor Cell Proliferation and Bone Destruction in Multiple Myeloma.

In multiple myeloma, an overabundance of monoclonal plasma cells in the bone marrow induces localized osteolytic lesions that rarely heal due to increased bone resorption and suppressed bone formation. Matrix-embedded osteocytes comprise more than 95% of bone cells and are major regulators of osteoclast and osteoblast activity, but their contribution to multiple myeloma growth and bone disease is unknown. Here, we report that osteocytes in a mouse model of human MM physically interact with multiple myeloma cells in vivo, undergo caspase-3-dependent apoptosis, and express higher RANKL (TNFSF11) and sclerostin levels than osteocytes in control mice. Mechanistic studies revealed that osteocyte apoptosis was initiated by multiple myeloma cell-mediated activation of Notch signaling and was further amplified by multiple myeloma cell-secreted TNF. The induction of apoptosis increased osteocytic Rankl expression, the osteocytic Rankl/Opg (TNFRSF11B) ratio, and the ability of osteocytes to attract osteoclast precursors to induce local bone resorption. Furthermore, osteocytes in contact with multiple myeloma cells expressed high levels of Sost/sclerostin, leading to a reduction in Wnt signaling and subsequent inhibition of osteoblast differentiation. Importantly, direct contact between osteocytes and multiple myeloma cells reciprocally activated Notch signaling and increased Notch receptor expression, particularly Notch3 and 4, stimulating multiple myeloma cell growth. These studies reveal a previously unknown role for bidirectional Notch signaling that enhances MM growth and bone disease, suggesting that targeting osteocyte-multiple myeloma cell interactions through specific Notch receptor blockade may represent a promising treatment strategy in multiple myeloma.