In vivo imaging tools for functional assessment of biomaterials implanted bone regeneration

AUTHORS

Subhasis Roy, Prasenjit Mukherjee, Samit Kumar Nandi

ABSTRACT

Since the discovery of X-rays and its first use in imaging of a hand, bone tissue has been the chapter of interest in medical imaging. However, X-ray imaging poses limitations nowadays owing to the augmented complexity of implant scaffolds as well as with the advances in bone engineering. As a result, advanced follow-up imaging techniques are of paramount necessity for effective postoperative characterization. Moreover, it is also needed to search for non-invasive, high-sensitivity, and high-resolution structural, functional, and molecular imaging techniques such as acoustic, optical, magnetic, X-Ray, electron, ultrasound, and nuclear imaging, etc. as an alternative to normally used X-ray computed tomography. Further, enthusiastic preclinical scanners have turned out to be accessible, with sensitivity and resolution even superior to clinical scanners, as a consequence helping a rapid transformation from preclinical to clinical applications. Besides, recently, bone-specific probes and contrast agents are developing for better imaging tools in bone-tissue engineering applications. This review highlights such emerging preclinical imaging tools, each with its individual potencies and flaws, either used only or in combination. In particular, multimodal imaging will significantly add to improve the present understanding in the characterization of bone regenerative processes.

Conditional Loss of Ikkα in Sp7/osterix+ Cells Has No Effect on Bone, but Leads to Cell Autonomous, Age-related Loss of Peripheral Fat

AUTHORS

Jennifer L Davis, Nitin K Pokhrel, Linda Cox, Roberta Faccio, Deborah J Veis

ABSTRACT

NF-κB has been reported to both promote and inhibit bone formation. To further explore its role in osteolineage cells, we conditionally deleted IKKα, an upstream kinase required for non-canonical NF-κB activation, using Sp7/Osterix (Osx)-Cre. Surprisingly, we found no effect on either cancellous or cortical bone, even following mechanical loading. However, we noted that IKKα conditional knockout (cKO) mice began to lose body weight after 6 months of age with severe reductions in fat mass in geriatric animals. Low levels of recombination at the IKKα locus were detected in fat pads isolated from 15 month old cKO mice. To determine if these effects were mediated by unexpected deletion of IKKα in peripheral adipocytes, we looked for Osx-Cre-mediated recombination in fat using reporter mice, which showed increasing degrees of reporter activation in adipocytes with age up to 18 months. Since Osx-Cre-driven recombination in peripheral adipocytes increases over time, we conclude that loss of fat in aged cKO mice is most likely caused by progressive deficits of IKKα in adipocytes. To further explore the effect of IKKα loss on fat metabolism, we challenged mice with a high fat diet at 2 months of age, finding that cKO mice gained less weight and showed improved glucose metabolism, compared to littermate controls. Thus, Osx-Cre mediated recombination beyond bone, including within adipocytes, should be considered as a possible explanation for extraskeletal phenotypes, especially in aging and metabolic studies.

Hedgehog signaling controls bone homeostasis by regulating osteogenic/adipogenic fate of skeletal stem/progenitor cells in mice

AUTHORS

Liwei Zhang, Xuejie Fu, Li Ni, Cunchang Liu, Yixin Zheng, Hongji You, Meng Li, Chunmei Xiu, Lei Zhang, Tingting Gong, Na Luo, Zunyi Zhang, Guangxu He, Shijun Hu, Huilin Yang, Di Chen, Jianquan Chen

ABSTRACT

Skeletal stem/progenitor cells (SSPCs) can differentiate into osteogenic or adipogenic lineage. The mechanism governing lineage allocation of SSPCs is still not completely understood. Hedgehog (Hh) signaling plays an essential role in specifying osteogenic fate of mesenchymal progenitors during embryogenesis. However, it is still unclear whether Hh signaling is required for lineage allocation of SSPCs in postnatal skeleton, and whether its dysregulation is related to age-related osteoporosis. Here, we demonstrated that Hh signaling was activated in metaphyseal SSPCs during osteogenic differentiation in the adult skeleton, and its activity decreased with aging. Inactivation of Hh signaling by genetic ablation of Smo, a key molecule in Hh signaling, in Osx-Cre-targeted SSPCs and hypertrophic chondrocytes led to decreased bone formation and increased bone marrow adiposity, two key pathological features of age-related osteoporosis. Moreover, we found that the bone-fat imbalance phenotype caused by Smo deletion mainly resulted from aberrant allocation of SSPCs toward adipogenic lineage at the expense of osteogenic differentiation, but not due to accelerated transdifferentiation of chondrocytes into adipocytes. Mechanistically, we found that Hh signaling regulated osteoblast versus adipocyte fate of SSPCs partly through upregulating Wnt signaling. Thus, our results indicate that Hh signaling regulates bone homeostasis and age-related osteoporosis by acting as a critical switch of cell fate decisions of Osx-Cre-targeted SSPCs in mice and suggest that Hh signaling may serve as a potential therapeutic target for the treatment of osteoporosis and other metabolic bone diseases.

Neurobiological effects of a probiotic-supplemented diet in chronically stressed male Long-Evans rats: Evidence of enhanced resilience

AUTHORS

Nick R. Natale, Molly Kent, Nathan Fox, Dylan Vavra, Kelly Lambert

ABSTRACT

Probiotics that regulate the microbiome-gut-brain axis and provide mental health benefits to the host are referred to as psychobiotics. Preclinical studies have demonstrated psychobiotic effects on early life stress-induced anxiety- and depression-related behavior in rodents; however, the specific mechanisms remain ill-defined. In the current study, we investigated the effects of probiotic supplementation on neurobiological responses to chronic stress in adult male Long-Evans rats. Twenty-four rats were randomly assigned to probiotic (PB) or vehicle control (VEH) groups, then to either chronic unpredictable stress (CUS) or no-stress control (CON) conditions within each group (n = 6/subgroup). We hypothesized that PB supplementation would reduce markers of anxiety and enhance emotional resilience, especially in the CUS animals. In the cognitive uncertainty task, a nonsignificant trend was observed indicating that the PB-supplemented animals spent more time oriented toward the food reward than VEH animals. In the open-field task, CUS-PB animals spent more time in the center of the arena than CUS-VEH animals, an effect not observed between the two CON groups. In the swim task, the PB animals, regardless of stress assignment, exhibited increased floating, suggesting a conserved response in a challenging context. Focusing on the endocrine measures, higher dehydroepiandrosterone (DHEA)-to-corticosterone fecal metabolite ratios, a correlate of emotional resilience, were observed in PB animals. Further, PB animals exhibited reduced microglia immunoreactivity in the basolateral amygdala, possibly indicating a neuroprotective effect of PB supplements in this rodent model. These results provide evidence that PB supplementation interacts with stress exposure to influence adaptive responses associated with endocrine, neural, and behavioral indices of anxiety.

Preliminary study on the osseointegration effects of contactless automated implant cavity preparation via femtosecond laser ablation

AUTHORS

Shanshan Liang, Jianqiao Zheng, and Fusong Yuan

ABSTRACT

Microrobots were used to control the femtosecond laser ablation of bone tissues to prepare implant cavities for dental implant surgery. The method was optimized through depth-of-cut experiments of ex vivo rabbit femurs, and the optimized method was used to prepare implant cavities on the left femurs of eight live rabbits. A power of 10 W and a scanning rate of 4000 mm/s were found to be optimal. After seven days of osteoinduction, the expression of collagen type I was significantly higher in the experimental group than in the control group (manually drilled implant cavities). The bone–implant contacts of the experimental group at 4 and 8 weeks were 9.65% and 23.08%, respectively.

Fibroblast Growth Factor Receptor 1 Drives the Metastatic Progression of Prostate Cancer

AUTHORS

Estefania Labanca, Jun Yang, Peter D.A. Shepherd, Xinhai Wan, Michael W. Starbuck, Leah D. Guerra, Nicolas Anselmino, Juan A. Bizzotto, Jiabin Dong, Arul M. Chinnaiyan, Murali K. Ravoori, Vikas Kundra, Bradley M. Broom, Paul G. Corn, Patricia Troncoso, Geraldine Gueron, Christopher J. Logothethis, Nora M. Navone

ABSTRACT

Background

No curative therapy is currently available for metastatic prostate cancer (PCa). The diverse mechanisms of progression include fibroblast growth factor (FGF) axis activation.

Objective

To investigate the molecular and clinical implications of fibroblast growth factor receptor 1 (FGFR1) and its isoforms (α/β) in the pathogenesis of PCa bone metastases.

Design, setting, and participants

In silico, in vitro, and in vivo preclinical approaches were used. RNA-sequencing and immunohistochemical (IHC) studies in human samples were conducted.

Outcome measurements and statistical analysis

In mice, bone metastases (chi-square/Fisher’s test) and survival (Mantel-Cox) were assessed. In human samples, FGFR1 and ladinin 1 (LAD1) analysis associated with PCa progression were evaluated (IHC studies, Fisher’s test).

Results and limitations

FGFR1 isoform expression varied among PCa subtypes. Intracardiac injection of mice with FGFR1-expressing PC3 cells reduced mouse survival (α, p < 0.0001; β, p = 0.032) and increased the incidence of bone metastases (α, p < 0.0001; β, p = 0.02). Accordingly, IHC studies of human castration-resistant PCa (CRPC) bone metastases revealed significant enrichment of FGFR1 expression compared with treatment-naïve, nonmetastatic primary tumors (p = 0.0007). Expression of anchoring filament protein LAD1 increased in FGFR1-expressing PC3 cells and was enriched in human CRPC bone metastases (p = 0.005).

Conclusions

FGFR1 expression induces bone metastases experimentally and is significantly enriched in human CRPC bone metastases, supporting its prometastatic effect in PCa. LAD1 expression, found in the prometastatic PCa cells expressing FGFR1, was also enriched in CRPC bone metastases. Our studies support and provide a roadmap for the development of FGFR blockade for advanced PCa.

Patient summary

We studied the role of fibroblast growth factor receptor 1 (FGFR1) in prostate cancer (PCa) progression. We found that PCa cells with high FGFR1 expression increase metastases and that FGFR1 expression is increased in human PCa bone metastases, and identified genes that could participate in the metastases induced by FGFR1. These studies will help pinpoint PCa patients who use fibroblast growth factor to progress and will benefit by the inhibition of this pathway.