Moderate tibial loading and treadmill running, but not overloading, protect adult murine bone from destruction by metastasized breast cancer

Prognostic assessment of osteolytic lesions and mechanical properties of bones bearing breast cancer using neural network and finite element analysis☆

The management of skeletal-related events (SREs), particularly the prevention of pathological fractures, is crucial for cancer patients. Current clinical assessment of fracture risk is mostly based on medical images, but incorporating sequential images in the assessment remains challenging. This study addressed this issue by leveraging a comprehensive dataset consisting of 260 longitudinal micro-computed tomography (μCT) scans acquired in normal and breast cancer bearing mice. A machine learning (ML) model based on a spatial-temporal neural network was built to forecast bone structures from previous μCT scans, which were found to have an overall similarity coefficient (Dice) of 0.814 with ground truths. Despite the predicted lesion volumes (18.5 ​% ​± ​15.3 ​%) being underestimated by ∼21 ​% than the ground truths' (22.1 ​% ​± ​14.8 ​%), the time course of the lesion growth was better represented in the predicted images than the preceding scans (10.8 ​% ​± ​6.5 ​%). Under virtual biomechanical testing using finite element analysis (FEA), the predicted bone structures recapitulated the loading carrying behaviors of the ground truth structures with a positive correlation (y ​= ​0.863x) and a high coefficient of determination (R2 ​= ​0.955). Interestingly, the compliances of the predicted and ground truth structures demonstrated nearly identical linear relationships with the lesion volumes. In summary, we have demonstrated that bone deterioration could be proficiently predicted using machine learning in our preclinical dataset, suggesting the importance of large longitudinal clinical imaging datasets in fracture risk assessment for cancer bone metastasis.

Skeletal response to Yoda1 and whole-body vibration in mice varied with animal age, bone compartment, treatment duration, and radiation exposure

In this study, we investigated the skeletal effects of Yoda1, an agonist of the mechanosensitive Piezo1 channels, and whole-body vibration (WBV), alone and combined, in young mice (8-week-old) and in mature (31- to 36-week-old) mice after radiation exposure. Our goal was to determine whether the two mechanobiology-based interventions, known to induce anabolic response individually in young subjects, could promote the bone health of older subjects undergoing cancer treatments such as radiotherapy. Our hypothesis was that the combination of Yoda1 and WBV could improve young skeletons and protect mature skeletons after radiotherapy better than Yoda1 or WBV alone. Our in vivo experiments demonstrated (1) that Yoda1 (5 mg/kg body weight) alone or combined with WBV (0.3 g, 13 Hz, 30 min/day, 5 days/week, 4 weeks) enhanced bone growth similarly (~2 folds relative to nontreated controls) in young mice; (2) that mature mice were unresponsive to individual interventions but exhibited less polar moment of inertia loss (-56 %) in the tibiae receiving the combination of Yoda1 and WBV (15 min/day) but no radiation exposure; and (3) that the contralateral tibiae receiving fractionated radiation (2 × 8 Gy over three days) did not show different treatment responses in Week 4, while they responded to the combination therapy (increased cortical bone formation) in Week 2. Interestingly, pair comparisons of the irradiated and non-irradiated tibiae of the same animals revealed that radiation exposure resulted in decreased trabecular bone loss regardless of the treatments and increased the percentage of tibiae maintaining better cortical polar moment of inertia and cortical area in the groups receiving Yoda1 or the combination therapy. The complex skeletal responses to Yoda1 and/or WBV were compartment specific (cortical or trabecular bone) and dependent on animal age, radiation exposure, and treatment duration. This study partially supported our original hypothesis, while suggesting the need of finetuning the Yoda1 and WBV regimens and elucidating the underlying mechanisms in order to effectively treat age and radiation induced bone loss.

High-fidelity computational fluid dynamics modeling to simulate perfusion through a bone-mimicking scaffold

Breast cancer cells sense shear stresses in response to interstitial fluid flow in bone and induce specific biological responses. Computational fluid dynamics models have been instrumental in estimating these shear stresses to relate the cell mechanoresponse to exact mechanical signals, better informing experiment design. Most computational models greatly simplify the experimental and cell mechanical environments for ease of computation, but these simplifications may overlook complex cell-substrate mechanical interactions that significantly change shear stresses experienced by cells. In this paper, we construct a high-fidelity model, i.e., a digital twin, of a bone-mimicking scaffold experiencing fluid stresses from a custom perfusion bioreactor by creating a stabilized multi-domain finite element formulation that accounts for physical components of the bioreactor and true flow boundaries. Our goals include determination of a range of applied flow rates that result in physiological wall shear stresses, evaluation of wall shear stress sensitivity to scaffold fabrication, and validation of our bioreactor set-up for applying physiologically-relevant fluid stresses. This work will provide us with a more structured framework to study breast cancer mechanobiology in bone metastasis. Accurate shear stress estimations will allow us to understand how in vitro models of anabolic loading in bone affect the breast cancer cell mechanoresponse.

A novel mouse model of voluntary stretching and its application in breast cancer research

Background

Stretching exercises such as yoga are recommended for cancer survivors to manage symptoms and promote wellbeing in clinical settings. Although other types of exercise (e.g. running) can reduce the growth of tumors in animal models, the role of stretching on tumor growth remains unclear, and the lack of a preclinical self-stretching model has impeded mechanistic studies on health benefits of stretching. We sought to develop a voluntary stretching animal model to address this research gap and apply it to breast cancer research.

Methods

Using food, water, and enrichment in the home cage as motivators for stretching, a two-week 24/7 behavior monitoring was conducted in a video-based customizable home-cage behavior tracking system, Noldus PhenoTyper, to promote self-stretching in FVB mice. Subsequently, this model was utilized in a comparative study of voluntary stretching and voluntary running on tumor growth and plasma protein profiles in the MET-1 orthotopic mammary tumor FVB mouse model.

Results

The new voluntary stretching model effectively elicited mouse self-stretching in the custom cage setting in the long-term observation and significantly inhibited tumor growth as effectively as voluntary wheel running. Moreover, plasma proteomic analysis demonstrated that voluntary stretch versus voluntary running distinctly impacted systemic protein profiles, possibly linking to different cellular and molecular mechanisms underlying anti-cancer effects and, potentially, exercise-induced benefits in other health conditions.

Conclusion

Our work provides the first preclinical voluntary stretching model, which may be well suited to breast cancer research and a valuable research tool to facilitate investigations of stretching health benefits across various research fields.

Physical activity enhances the effect of immune checkpoint blockade by inhibiting the intratumoral HIF1-α/CEACM1 axis

Immune checkpoint blockade therapy has demonstrated significant therapeutic effects in certain types of cancers. However, there is limited reporting on the influence of physical activity on its efficacy. This study aimed to investigate the impact of physical activity on anti-PDL-1-mediated immune checkpoint therapy and the interplay of immune cells therein. HePa1-6 tumor-bearing mice were treated with anti-PDL-1 in conjunction with physical activity to assess tumor progression. Flow cytometry was utilized to analyze immune cell infiltration and differentiation levels within the tumor. The expression of HIF-a/CEACAM1 within the tumor due to physical activity was evaluated. HePa1-6 cells with high CEACAM1 expression were validated in mice to determine their inhibitory effects on immune cell proliferation and differentiation. A CD3/CEACAM1 chimeric antibody was developed for treating CEACAM1-overexpressing tumors, and flow cytometry was employed to assess T-cell response. Physical activity enhanced the efficacy of anti-PDL1 by suppressing the HIF-a/CEACAM1 axis within the tumor. In vivo experiments revealed that tumors with high CEACAM1 expression decreased infiltration and activation of CD8 + T cells within the tumor, suppressing T cell cytotoxicity without affecting Treg infiltration. In vitro, high CEACAM1 expression impacted the proliferation and activation of CD8 + T cells in a co-culture system. The constructed CD3/CEACAM1 chimeric antibody significantly activated the TCR within CEACAM1-overexpressing tumors and inhibited tumor progression. The findings suggest that physical activity augments the effectiveness of immune checkpoint blockade by inhibiting the intratumoral HIF1-α/CEACM1 axis.

Gut microbial alterations in arginine metabolism determine bone mechanical adaptation

Although mechanical loading is essential for maintaining bone health and combating osteoporosis, its practical application is limited to a large extent by the high variability in bone mechanoresponsiveness. Here, we found that gut microbial depletion promoted a significant reduction in skeletal adaptation to mechanical loading. Among experimental mice, we observed differences between those with high and low responses to exercise with respect to the gut microbial composition, in which the differential abundance of Lachnospiraceae contributed to the differences in bone mechanoresponsiveness. Microbial production of L-citrulline and its conversion into L-arginine were identified as key regulators of bone mechanoadaptation, and administration of these metabolites enhanced bone mechanoresponsiveness in normal, aged, and ovariectomized mice. Mechanistically, L-arginine-mediated enhancement of bone mechanoadaptation was primarily attributable to the activation of a nitric-oxide-calcium positive feedback loop in osteocytes. This study identifies a promising anti-osteoporotic strategy for maximizing mechanical loading-induced skeletal benefits via the microbiota-metabolite axis.

A mechanobiological model of bone metastasis reveals that mechanical stimulation inhibits the pro-osteolytic effects of breast cancer cells

Bone is highly susceptible to cancer metastasis, and both tumor and bone cells enable tumor invasion through a "vicious cycle" of biochemical signaling. Tumor metastasis into bone also alters biophysical cues to both tumor and bone cells, which are highly sensitive to their mechanical environment. However, the mechanobiological feedback between these cells that perpetuate this cycle has not been studied. Here, we develop highly advanced in vitro and computational models to provide an advanced understanding of how tumor growth is regulated by the synergistic influence of tumor-bone cell signaling and mechanobiological cues. In particular, we develop a multicellular healthy and metastatic bone model that can account for physiological mechanical signals within a custom bioreactor. These models successfully recapitulated mineralization, mechanobiological responses, osteolysis, and metastatic activity. Ultimately, we demonstrate that mechanical stimulus provided protective effects against tumor-induced osteolysis, confirming the importance of mechanobiological factors in bone metastasis development.

Mechanically stimulated osteocytes maintain tumor dormancy in bone metastasis of non-small cell lung cancer by releasing small extracellular vesicles

Although preclinical and clinical studies have shown that exercise can inhibit bone metastasis progression, the mechanism remains poorly understood. Here, we found that non-small cell lung cancer (NSCLC) cells adjacent to bone tissue had a much lower proliferative capacity than the surrounding tumor cells in patients and mice. Subsequently, it was demonstrated that osteocytes, sensing mechanical stimulation generated by exercise, inhibit NSCLC cell proliferation and sustain the dormancy thereof by releasing small extracellular vesicles with tumor suppressor micro-RNAs, such as miR-99b-3p. Furthermore, we evaluated the effects of mechanical loading and treadmill exercise on the bone metastasis progression of NSCLC in mice. As expected, mechanical loading of the tibia inhibited the bone metastasis progression of NSCLC. Notably, bone metastasis progression of NSCLC was inhibited by moderate exercise, and combinations with zoledronic acid had additive effects. Moreover, exercise preconditioning effectively suppressed bone metastasis progression. This study significantly advances the understanding of the mechanism underlying exercise-afforded protection against bone metastasis progression.

Role of the osteocyte in bone metastasis - The importance of networking

Metastatic bone disease is a complex condition resulting from the migration and colonization of cancer cells from their primary site to the bone microenvironment, where they typically develop a metastatic niche. Osteocytes, the most abundant cells in bone tissue and the master regulators of bone remodelling, are increasingly thought to play a crucial role in this process through intricate interactions with cancer cells. This review covers the recent progress made in exploring the multifaceted interactions between osteocytes and cancer cells in the metastatic microenvironment, highlighting the importance of signalling networks in bone metastases. Though these interactions are particularly complex, the renewed focus of researchers on osteocytes within the last 5 years has uncovered multiple new potential molecular mechanisms underlying osteocyte-mediated regulation of cancer cell survival, proliferation, and invasion. A number of key papers will be discussed in detail, emphasizing the significance of signalling pathways and molecular crosstalk, and exploring potential therapeutic strategies targeting osteocyte-cancer cell interactions to improve patient treatment and outcomes.

Exercise improves cognitive dysfunction and neuroinflammation in mice through Histone H3 lactylation in microglia

BACKGROUND

Exercise is postulated to be a promising non-pharmacological intervention for the improvement of neurodegenerative disease pathology. However, the mechanism of beneficial effects of exercise on the brain remains to be further explored. In this study, we investigated the effect of an exercise-induced metabolite, lactate, on the microglia phenotype and its association with learning and memory.

RESULTS

Microglia were hyperactivated in the brains of AlCl3/D-gal-treated mice, which was associated with cognitive decline. Running exercise ameliorated the hyperactivation and increased the anti-inflammatory/reparative phenotype of microglia and improved cognition. Mice were injected intraperitoneally with sodium lactate (NaLA) had similar beneficial effects as that of exercise training. Exogenous NaLA addition to cultured BV2 cells promoted their transition from a pro-inflammatory to a reparative phenotype.

CONCLUSION

The elevated lactate acted as an "accelerator" of the endogenous "lactate timer" in microglia promoting this transition of microglia polarization balance through lactylation. These findings demonstrate that exercise-induced lactate accelerates the phenotypic transition of microglia, which plays a key role in reducing neuroinflammation and improving cognitive function.

Osteocytes: New Kids on the Block for Cancer in Bone Therapy

The tumor microenvironment plays a central role in the onset and progression of cancer in the bone. Cancer cells, either from tumors originating in the bone or from metastatic cancer cells from other body systems, are located in specialized niches where they interact with different cells of the bone marrow. These interactions transform the bone into an ideal niche for cancer cell migration, proliferation, and survival and cause an imbalance in bone homeostasis that severely affects the integrity of the skeleton. During the last decade, preclinical studies have identified new cellular mechanisms responsible for the dependency between cancer cells and bone cells. In this review, we focus on osteocytes, long-lived cells residing in the mineral matrix that have recently been identified as key players in the spread of cancer in bone. We highlight the most recent discoveries on how osteocytes support tumor growth and promote bone disease. Additionally, we discuss how the reciprocal crosstalk between osteocytes and cancer cells provides the opportunity to develop new therapeutic strategies to treat cancer in the bone.

Microfluidic Co-culture Platforms for Studying Osteocyte Regulation of Other Cell Types under Dynamic Mechanical Stimulation

PURPOSE OF REVIEW

Osteocytes are the most abundant cell type in bone. These unique cells act primarily as mechanosensors and play crucial roles in the functional adaptation of bone tissue. This review aims to summarize the recent microfluidic studies on mechanically stimulated osteocytes in regulating other cell types.

RECENT FINDINGS

Microfluidics is a powerful technology that has been widely employed in recent years. With the advantages of microfluidic platforms, researchers can mimic multicellular environments and integrate dynamic systems to study osteocyte regulation under mechanical stimulation. Microfluidic platforms have been developed to investigate mechanically stimulated osteocytes in the direct regulation of multiple cell types, including osteoclasts, osteoblasts, and cancer cells, and in the indirect regulation of cancer cells via endothelial cells. Overall, these microfluidic studies foster the development of treatment approaches targeting osteocytes under mechanical stimulation.

Effects of Whole-Body Vibration on Breast Cancer Bone Metastasis and Vascularization in Mice

We evaluated whether whole-body vibration (WBV) prevented bone loss induced by breast cancer (BC) metastasis and the involvement of bone marrow vasculature. One day after orthotopic transplantation of mammary 4T1 tumor cells, 8-week-old BALB/c mice were subjected to 0.3 g/90 Hz vertical vibration for 20 min/day for 5 days/week (BC-WBV) or sham-handled (BC-Sham) over 3 weeks. Age-matched intact mice (Intact) were also sham-handled. Both tibiae were harvested from BC-WBV (n = 7), BC-Sham (n = 9), and Intact (n = 5) mice for bone structure imaging by synchrotron radiation-based computed tomography (SRCT) and hematoxylin and eosin staining, whereas right tibiae were harvested from other BC-WBV and BC-Sham (n = 6 each) mice for vascular imaging by SRCT. Tumor cells were similarly widespread in the marrow in BC-WBV and BC-Sham mice. In BC-Sham mice, cortical bone volume, trabecular volume fraction, trabecular thickness, trabecular number density, and bone mineral density were smaller, and marrow volume and trabecular separation were larger than in Intact mice. However, although trabecular thickness was smaller in BC-WBV than Intact mice, the others did not differ between the two groups. Serum osteocalcin tended to be higher in BC-WBV than BC-Sham mice. Compared with BC-Sham mice, BC-WBV mice had a smaller vessel diameter, a trend of a larger vessel number density, and smaller vessel diameter heterogeneity. In conclusion, WBV mitigates bone loss in BC bone metastasis, which may be partly due to increased bone anabolism. The alteration of marrow vasculature appears to be favorable for anti-tumor drug delivery. Further studies are needed to clarify the multiple actions of WBV on bone, tumor, and marrow vasculature and how they contribute to bone protection in BC metastasis.

Yoda1 Enhanced Low-Magnitude High-Frequency Vibration on Osteocytes in Regulation of MDA-MB-231 Breast Cancer Cell Migration

Low-magnitude (≤1 g) high-frequency (≥30 Hz) (LMHF) vibration has been shown to enhance bone mineral density. However, its regulation in breast cancer bone metastasis remains controversial for breast cancer patients and elder populations. Yoda1, an activator of the mechanosensitive Piezo1 channel, could potentially intensify the effect of LMHF vibration by enhancing the mechanoresponse of osteocytes, the major mechanosensory bone cells with high expression of Piezo1. In this study, we treated osteocytes with mono- (Yoda1 only or vibration only) or combined treatment (Yoda1 and LMHF vibration) and examined the further regulation of osteoclasts and breast cancer cells through the conditioned medium. Moreover, we studied the effects of combined treatment on breast cancer cells in regulation of osteocytes. Combined treatment on osteocytes showed beneficial effects, including increasing the nuclear translocation of Yes-associated protein (YAP) in osteocytes (488.0%, p < 0.0001), suppressing osteoclastogenesis (34.3%, p = 0.004), and further reducing migration of MDA-MB-231 (15.1%, p = 0.02) but not Py8119 breast cancer cells (4.2%, p = 0.66). Finally, MDA-MB-231 breast cancer cells subjected to the combined treatment decreased the percentage of apoptotic osteocytes (34.5%, p = 0.04) but did not affect the intracellular calcium influx. This study showed the potential of stimulating Piezo1 in enhancing the mechanoresponse of osteocytes to LMHF vibration and further suppressing breast cancer migration via osteoclasts.

Breast Cancer Induced Bone Osteolysis Prediction Using Temporal Variational Autoencoders

Objective and Impact Statement. We adopt a deep learning model for bone osteolysis prediction on computed tomography (CT) images of murine breast cancer bone metastases. Given the bone CT scans at previous time steps, the model incorporates the bone-cancer interactions learned from the sequential images and generates future CT images. Its ability of predicting the development of bone lesions in cancer-invading bones can assist in assessing the risk of impending fractures and choosing proper treatments in breast cancer bone metastasis. Introduction. Breast cancer often metastasizes to bone, causes osteolytic lesions, and results in skeletal-related events (SREs) including severe pain and even fatal fractures. Although current imaging techniques can detect macroscopic bone lesions, predicting the occurrence and progression of bone lesions remains a challenge. Methods. We adopt a temporal variational autoencoder (T-VAE) model that utilizes a combination of variational autoencoders and long short-term memory networks to predict bone lesion emergence on our micro-CT dataset containing sequential images of murine tibiae. Given the CT scans of murine tibiae at early weeks, our model can learn the distribution of their future states from data. Results. We test our model against other deep learning-based prediction models on the bone lesion progression prediction task. Our model produces much more accurate predictions than existing models under various evaluation metrics. Conclusion. We develop a deep learning framework that can accurately predict and visualize the progression of osteolytic bone lesions. It will assist in planning and evaluating treatment strategies to prevent SREs in breast cancer patients.

Osteocytes and Cancer

PURPOSE OF REVIEW

While the function of osteocytes under physiologic conditions is well defined, their role and involvement in cancer disease remains relatively unexplored, especially in a context of non-bone metastatic cancer. This review will focus on describing the more advanced knowledge regarding the interactions between osteocytes and cancer.

RECENT FINDINGS

We will discuss the involvement of osteocytes in the onset and progression of osteosarcoma, with the common bone cancers, as well as the interaction that is established between osteocytes and multiple myeloma. Mechanisms responsible for cancer dissemination to bone, as frequently occur with advanced breast and prostate cancers, will be reviewed. While a role for osteocytes in the stimulation and proliferation of cancer cells has been reported, protective effects of osteocytes against bone colonization have been described as well, thus increasing ambiguity regarding the role of osteocytes in cancer progression and dissemination. Lastly, supporting the idea that skeletal defects can occur also in the absence of direct cancer dissemination or osteolytic lesions directly adjacent to the bone, our recent findings will be presented showing that in the absence of bone metastases, the bone microenvironment and, particularly, osteocytes, can manifest a clear and dramatic response to the distant, non-metastatic tumor. Our observations support new studies to clarify whether treatments designed to preserve the osteocytes can be combined with traditional anticancer therapies, even when bone is not directly affected by tumor growth.

Mechanobiology of Bone Metastatic Cancer

PURPOSE OF REVIEW

In this review, we provide an overview of what is currently known about the impacts of mechanical stimuli on metastatic tumor-induced bone disease (TIBD). Further, we focus on the role of the osteocyte, the skeleton's primary mechanosensory cell, which is central to the skeleton's mechanoresponse, sensing and integrating local mechanical stimuli, and then controlling the downstream remodeling balance as appropriate.

RECENT FINDINGS

Exercise and controlled mechanical loading have anabolic effects on bone tissue in models of bone metastasis. They also have anti-tumorigenic properties, in part due to offsetting the vicious cycle of osteolytic bone loss as well as regulating inflammatory signals. The impacts of metastatic cancer on the mechanosensory function of osteocytes remains unclear. Increased mechanical stimuli are a potential method for mitigating TIBD.