Temporal patterns of osteoclast formation and activity following withdrawal of RANKL inhibition

Rebound bone loss following denosumab discontinuation is an important clinical challenge. Current treatment strategies to prevent this fail to suppress the rise and overshoot in osteoclast-mediated bone resorption. In this study, we use a murine model of denosumab treatment and discontinuation to show the temporal changes in osteoclast formation and activity during RANKL inhibition and withdrawal. We show that the cellular processes that drive the formation of osteoclasts and subsequent bone resorption following withdrawal of RANKL inhibition precede the rebound bone loss. Furthermore, a rise in serum TRAP and RANKL levels is detected before markers of bone turnover used in current clinical practice. These mechanistic advances may provide insight into a more defined window of opportunity to intervene with sequential therapy following denosumab discontinuation.

Minimally invasive longitudinal intravital imaging of cellular dynamics in intact long bone

Intravital two-photon microscopy enables deep-tissue imaging at high temporospatial resolution in live animals. However, the endosteal bone compartment and underlying bone marrow pose unique challenges to optical imaging as light is absorbed, scattered and dispersed by thick mineralized bone matrix and the adipose-rich bone marrow. Early bone intravital imaging methods exploited gaps in the cranial sutures to bypass the need to penetrate through cortical bone. More recently, investigators have developed invasive methods to thin the cortical bone or implant imaging windows to image cellular dynamics in weight-bearing long bones. Here, we provide a step-by-step procedure for the preparation of animals for minimally invasive, nondestructive, longitudinal intravital imaging of the murine tibia. This method involves the use of mixed bone marrow radiation chimeras to unambiguously double-label osteoclasts and osteomorphs. The tibia is exposed by a simple skin incision and an imaging chamber constructed using thermoconductive T-putty. Imaging sessions up to 12 h long can be repeated over multiple timepoints to provide a longitudinal time window into the endosteal and marrow niches. The approach can be used to investigate cellular dynamics in bone remodeling, cancer cell life cycle and hematopoiesis, as well as long-lived humoral and cellular immunity. The procedure requires an hour to complete and is suitable for users with minimal prior expertise in small animal surgery.

Osteoclasts recycle via osteomorphs during RANKL-stimulated bone resorption

Osteoclasts are large multinucleated bone-resorbing cells formed by the fusion of monocyte/macrophage-derived precursors that are thought to undergo apoptosis once resorption is complete. Here, by intravital imaging, we reveal that RANKL-stimulated osteoclasts have an alternative cell fate in which they fission into daughter cells called osteomorphs. Inhibiting RANKL blocked this cellular recycling and resulted in osteomorph accumulation. Single-cell RNA sequencing showed that osteomorphs are transcriptionally distinct from osteoclasts and macrophages and express a number of non-canonical osteoclast genes that are associated with structural and functional bone phenotypes when deleted in mice. Furthermore, genetic variation in human orthologs of osteomorph genes causes monogenic skeletal disorders and associates with bone mineral density, a polygenetic skeletal trait. Thus, osteoclasts recycle via osteomorphs, a cell type involved in the regulation of bone resorption that may be targeted for the treatment of skeletal diseases.

Abstract IA015: Niche-dependent control of tumor cell dormancy

Dormancy is an elusive and deadly component of cancers. Rare, therapy resistant cells lay dormant for decades and when reactivated cause disease progression and relapse. Eradicating dormant cancer cells is key to curing cancers yet is an unrealized goal. The skeleton remains a common location for dissemination and dormancy, yet our understanding of the cellular and molecular pathways that control dormant cancer cells in the the skeleton is limited. We hypothesized that dormant cancer cells occupy a common niche in the skeleton and this supports long-term dormancy. To test this we developed technology to identify and analyse dormant cancers cells from different cancer types and the compartment in the skeleton in which they reside. Membrane label retention was able to distinguish dormant cancer cells from reactivated cancer cells. Intravital imaging showed that dormant cancer cells were found associated with endosteal bone surface suggesting that different cancers may occupy a common niche. Single cell RNA sequencing of dormant cancer cells showed they expressed a distinct gene signature that was enriched for myeloid genes. Single cell RNA sequencing of >130,000 cells isolated from the endosteal bone compartment and the bone marrow identified 32 distinct cell clusters. Detailed transcriptional analysis facilitated construction of a map of all of the cell types/states present in the endosteal bone compartment. In silico ligand/receptor interaction mapping enabled identification of the cell types and the molecular pathways that may mediate dormant cell niche formation in vivo. Non-haemopoietic cells, particularly cells of the osteoblast lineage and endothelia cells were the most enriched for dormant cell binding partners. This was common across three different dormant tumor types. Detailed analysis of cells of the osteoblast lineage showed greatest enrichment for binding partners in LeprHigh/Cxcl12High mesenchymal cells. Further analysis of the molecular pathways that can interact with binding partners identified a number of potential molecular regulators of dormancy. For example, Gas6, which is expressed by LeprHigh/Cxcl12High mesenchymal cells, has the binding partners Axl expressed by dormant myeloma cells, Mertk in dormant breast cancer cells and Mertk and Tyro3 in dormant prostate cancer. Treatment of mice bearing myeloma cells with small molecule inhibitors of Axl reduced dormant cells and increased tumor burden suggesting the Axl/Gas6 interaction is functional important in controlling dormancy. Together these data show that single cell sequencing can be used to define the cells and molecular pathways that facilitate dormant cancer cell niche formation in the skeleton. This approach suggests that that cancer cell specific molecules interact with common molecules in the endosteal niche, including LeprHigh/Cxcl12High mesenchymal cells, to switch on common molecular pathways to control dormancy.

Citation Format: Peter Croucher, Weng Hua Khoo, Ryan Chai, Alex Corr, James Smith, Qihao Ren, Paul Baldock, Michelle McDonald, Sheila Stewart, Tri G. Phan. Niche-dependent control of tumor cell dormancy [abstract]. In: Proceedings of the AACR Virtual Special Conference on the Evolving Tumor Microenvironment in Cancer Progression: Mechanisms and Emerging Therapeutic Opportunities; in association with the Tumor Microenvironment (TME) Working Group; 2021 Jan 11-12. Philadelphia (PA): AACR; Cancer Res 2021;81(5 Suppl):Abstract nr IA015.

Isometric Finger Pose Recognition with Sparse Channel SpatioTemporal EMG Imaging

High fidelity myoelectric control of prostheses and orthoses isparamount to restoring lost function to amputees and neuro-muscular disease sufferers. In this study we prove that patio-temporal imaging can be used to allow convolutional neural networks to classify sparse channel EMG samples from a consumer-grade device with over 94 % accuracy. 10,572 images are generated from 960 samples of simple and complex isometric finger poses recorded from 4 fully intact subjects. Real-time classification of 12 poses is achieved with a 250ms continuous overlapping window.

Wnt activation protects against neomycin-induced hair cell damage in the mouse cochlea

Recent studies have reported the role of Wnt/β-catenin signaling in hair cell (HC) development, regeneration, and differentiation in the mouse cochlea; however, the role of Wnt/β-catenin signaling in HC protection remains unknown. In this study, we took advantage of transgenic mice to specifically knockout or overactivate the canonical Wnt signaling mediator β-catenin in HCs, which allowed us to investigate the role of Wnt/β-catenin signaling in protecting HCs against neomycin-induced damage. We first showed that loss of β-catenin in HCs made them more vulnerable to neomycin-induced injury, while constitutive activation of β-catenin in HCs reduced HC loss both in vivo and in vitro. We then showed that loss of β-catenin in HCs increased caspase-mediated apoptosis induced by neomycin injury, while β-catenin overexpression inhibited caspase-mediated apoptosis. Finally, we demonstrated that loss of β-catenin in HCs led to increased expression of forkhead box O3 transcription factor (Foxo3) and Bim along with decreased expression of antioxidant enzymes; thus, there were increased levels of reactive oxygen species (ROS) after neomycin treatment that might be responsible for the increased aminoglycoside sensitivity of HCs. In contrast, β-catenin overexpression reduced Foxo3 and Bim expression and ROS levels, suggesting that β-catenin is protective against neomycin-induced HC loss. Our findings demonstrate that Wnt/β-catenin signaling has an important role in protecting HCs against neomycin-induced HC loss and thus might be a new therapeutic target for the prevention of HC death.

Reduced mtDNA copy number increases the sensitivity of tumor cells to chemotherapeutic drugs

Many cancer drugs are toxic to cells by activating apoptotic pathways. Previous studies have shown that mitochondria have key roles in apoptosis in mammalian cells, but the role of mitochondrial DNA (mtDNA) copy number variation in the pathogenesis of tumor cell apoptosis remains largely unknown. We used the HEp-2, HNE2, and A549 tumor cell lines to explore the relationship between mtDNA copy number variation and cell apoptosis. We first induced apoptosis in three tumor cell lines and one normal adult human skin fibroblast cell line (HSF) with cisplatin (DDP) or doxorubicin (DOX) treatment and found that the mtDNA copy number significantly increased in apoptotic tumor cells, but not in HSF cells. We then downregulated the mtDNA copy number by transfection with shRNA-TFAM plasmids or treatment with ethidium bromide and found that the sensitivity of tumor cells to DDP or DOX was significantly increased. Furthermore, we observed that levels of reactive oxygen species (ROS) increased significantly in tumor cells with lower mtDNA copy numbers, and this might be related to a low level of antioxidant gene expression. Finally, we rescued the increase of ROS in tumor cells with lipoic acid or N-acetyl-L-cysteine and found that the apoptosis rate decreased. Our studies suggest that the increase of mtDNA copy number is a self-protective mechanism of tumor cells to prevent apoptosis and that reduced mtDNA copy number increases ROS levels in tumor cells, increases the tumor cells' sensitivity to chemotherapeutic drugs, and increases the rate of apoptosis. This research provides evidence that mtDNA copy number variation might be a promising new therapeutic target for the clinical treatment of tumors.

Bmi1 regulates auditory hair cell survival by maintaining redox balance

Reactive oxygen species (ROS) accumulation are involved in noise- and ototoxic drug-induced hair cell loss, which is the major cause of hearing loss. Bmi1 is a member of the Polycomb protein family and has been reported to regulate mitochondrial function and ROS level in thymocytes and neurons. In this study, we reported the expression of Bmi1 in mouse cochlea and investigated the role of Bmi1 in hair cell survival. Bmi1 expressed in hair cells and supporting cells in mouse cochlea. Bmi1^−/− mice displayed severe hearing loss and patched outer hair cell loss from postnatal day 22. Ototoxic drug-induced hair cells loss dramatically increased in Bmi1^−/− mice compared with that in wild-type controls both in vivo and in vitro, indicating Bmi1^−/− hair cells were significantly more sensitive to ototoxic drug-induced damage. Cleaved caspase-3 and TUNEL staining demonstrated that apoptosis was involved in the increased hair cell loss of Bmi1^−/− mice. Aminophenyl fluorescein and MitoSOX Red staining showed the level of free radicals and mitochondrial ROS increased in Bmi1^−/− hair cells due to the aggravated disequilibrium of antioxidant–prooxidant balance. Furthermore, the antioxidant N-acetylcysteine rescued Bmi1^−/− hair cells from neomycin injury both in vitro and in vivo, suggesting that ROS accumulation was mainly responsible for the increased aminoglycosides sensitivity in Bmi1^−/− hair cells. Our findings demonstrate that Bmi1 has an important role in hair cell survival by controlling redox balance and ROS level, thus suggesting that Bmi1 may work as a new therapeutic target for the prevention of hair cell death.

Immunohistochemical study of monocyte chemoattractant protein-1 in the pancreas of NOD mice following cyclophosphamide administration and during spontaneous diabetes

In type 1 diabetes mellitus (T1DM), the processes which control the recruitment of immune cells into pancreatic islets are poorly defined. Complex interactions involving adhesion molecules, chemokines and chemokine receptors may facilitate this process. The chemokine, monocyte chemoattractant protein-1 (MCP-1), previously shown to be important in leukocyte trafficking in other disease systems, may be a key participant in the early influx of blood-borne immune cells into islets during T1DM. In the non-obese diabetic (NOD) mouse, the expression of MCP-1 protein has not been demonstrated. We employed dual-label immunohistochemistry to examine the intra-islet expression, distribution and cellular source of MCP-1 in the NOD mouse following cyclophosphamide administration. NOD mice were treated with cyclophosphamide at day 72-73 and MCP-1 expression studied at days 0, 4, 7, 11 and 14 after treatment and comparisons were made between age-matched NOD mice treated with diluent and non-diabetes-prone CD-1 mice. Pancreatic expression of MCP-1 was also examined in NOD mice at various stages of spontaneous diabetes. In the cyclophosphamide group at day 0, MCP-1 immunolabelling was present in selective peri-islet macrophages but declined at day 4. It increased slightly at day 7 but was more marked from day 11, irrespective of diabetes development. The pattern of MCP-1 expression in macrophages was different over time in both the cyclophosphamide and control groups. In the cyclophosphamide group, there was a change over time with an increase at day 11. In the control group, there was little evidence of change over time. There was no significant difference in the mean percentage of MCP-1 positive macrophages between the cyclophosphamide-treated diabetic and non-diabetic mice. During spontaneous diabetes in the NOD mouse, only a few peri-islet MCP-1 cells appeared at day 45. These became more numerous from day 65 but were absent at diabetes onset. We speculate that a proportion of early islet-infiltrating macrophages which express MCP-1 may attract additional lymphocytes and macrophages into the early inflamed islets and intensify the process of insulitis.

[The effects of levothyroxine replacement therapy on bone and mineral metabolism in patients with hypothyroidism]

OBJECTIVE

To investigate the effects of short-term thyroid hormone replacement therapy on bone and mineral metabolism in patients with hypothyroidism.

METHODS

Enzyme linked immunosorbent assay (ELISA) was used to measure urinary deoxypyridinoline (DPD) and radioimmunoassay (RIA) to measure serum calcitonin (CT), parathyroid hormone (PTH-M), bone GLA protein (BGP), free T(3) (FT(3)), free T(4) (FT(4)) and thyroid-stimulating hormone (TSH) in 29 patients with hypothyroidism before and after treatment with levothyroxine for (11.5 +/- 2.5) months. Dual energy X-ray absorptiometry was used to measure bone mineral density (BMD) of their spine (L(2 - 4)) and femur neck, trochanter and Ward's triangle. The results were compared with those in 37 healthy controls.

RESULTS

In hypothyroidism patients before treatment, serum BGP level was significantly lower (P < 0.05) than but urinary DPD was similar with those of control. BMD was significantly lower in postmenopausal patients (P < 0.01 - 0.001) than that in control group, but there was no change in premenopausal patients. After replacement therapy serum BGP and urinary DPD elevated significantly (P < 0.05), whereas BMD decreased slightly both in the premenopausal and postmenopausal patients when compared with that before treatment, with no statistical significance (P > 0.05). BMD decreased by 0.7% and 1.7% - 5.1% in premenopausal and postmenopausal patients respectively, but there was no significant difference between these two groups (P > 0.05). FT(3) was positively correlated with BGP. FT(4) and FT(3) were positively correlated with DPD. BMD of femur neck and trochanter sites was negatively correlated with FT(4).

CONCLUSION

Short-term physiological dose levothyroxine replacement therapy causes increase of bone turnover and leads to bone mass loss to various extent on hypothyroidism patients.

[Changes of bone and mineral metabolism in patients with hyperthyroidism before and after treatment]

OBJECTIVE

To investigate the changes of bone and mineral metabolism in patients with hyperthyroidism before and after treatment.

METHODS

Enzyme linked immunosorbent assay was used to measure bone-specific alkaline phosphatase (BAP) and deoxypyridinoline (DPD); radioimmunoassay to to measure serum calcitonin (CT), parathyroid hormone (PTH-M), bone GLA protein (BGP) and other markers related to bone metabolism; dual energy X-ray absorptiometry to measure bone mineral density (BMD) of spine(L2-4) and femur(Neck, Troch, Ward's) in 45 patients with hyperthyroidism before and after treatment and 58 healthy volunteers.

RESULTS

The urinary DPD level was elevated by 527% in patients with hyperthyroidism before treatment. Compared to controls the serum ALP, BAP, BGP elevated by 62%, 146%, 87% (P < 0.001), BMD decreased to various extent, and women L2-4, Ward's were marked (P < 0.05). The results after treatment and before treatment showed that urinary DPD decreased by 79%; serum ALP, BAP, BGP decreased by 19.5%, 24.7%, 27.5% respectively (P < 0.001, 0.05, 0.05, > 0.05). All sites BMD increased, and women Troch sites were marked (P < 0.05). The correlation analysis showed that the urinary DPD was positively correlated with serum BGP(r = 0.349 P < 0.05). FT4 was positively correlated with BAP, ALP and DPD respectively) (r = 0.353, P < 0.05, r = 0.294 P = 0.05, r = 0.426 P < 0.01).

CONCLUSION

Hyperthyroidism bone disease is caused by excessive serum thyroid hormone that speeds up bone turnover and marked bone absorption compared to bone formation.