Bone's Response to Mechanical Loading in Aging and Osteoporosis: Molecular Mechanisms.

Mechanotransduction is pivotal in the maintenance of homeostasis in different tissues and involves multiple cell signaling pathways. In bone, mechanical stimuli regulate the balance between bone formation and resorption; osteocytes play a central role in this regulation. Dysfunctions in mechanotransduction signaling or in osteocytes response lead to an imbalance in bone homeostasis. This alteration is very relevant in some conditions such as osteoporosis and aging. Both are characterized by increased bone weakness due to different causes, for example, the increase of osteocyte apoptosis that cause an alteration of fluid space, or the alteration of molecular pathways. There are intertwined yet very different mechanisms involved among the cell-intrinsic effects of aging on bone, the cell-intrinsic and tissue-level effects of estrogen/androgen withdrawal on bone, and the effects of reduced mechanical loading on bone, which are all involved to some degree in how aged bone fails to respond properly to stress/strain compared to younger bone. This review aims at clarifying how the cellular and molecular pathways regulated and induced in bone by mechanical stimulation are altered with aging and in osteoporosis, to highlight new possible targets for antiresorptive or anabolic bone therapeutic approaches.

Biological Rationale for the Use of Vertebral Whole Bone Marrow in Spinal Surgery.

STUDY DESIGN: Laboratory study. OBJECTIVE: Mesenchymal stem cells (MSCs) derived from whole bone marrow aspirate (BMA) and MSCs derived from density-gradient centrifugation were isolated from vertebral bodies and cultured under either hypoxic or normoxic conditions to evaluate their biological characteristics and HOX and TALE signature able to improve spinal surgery procedures. SUMMARY OF BACKGROUND DATA: The use of spinal fusion procedures has increased over the last decades; however, failed fusion still remains an important problem. Clinician and researchers focused their attention on the therapeutic potential of bone marrow MSCs and several methods for their isolation and cultivation have been developed. However, the best source and techniques are still debated. METHODS: MSCs morphology, surface markers, colony-forming-units, and three lineage differentiation through quantitative real-time PCR (qPCR) were evaluated. Additionally, gene expression analysis of HOX and TALE signatures during osteogenic differentiation were analyzed. RESULTS: Our study showed that MSCs derived from whole BMA were successfully isolated and when cultured under hypoxic condition presented greater proliferation, larger colonies, and differentiated onto osteogenic and chondrogenic lineage with greater ability, while adipogenic differentiation was less efficient. Results also revealed that MSCs, differently isolated and cultured, expressed different level of HOX and TALE signatures and that HOXB8 were up-regulated with greater efficiency in MSCs derived from whole BMA under hypoxia. CONCLUSION: Our data indicated that hypoxic preconditioning of MSCs derived from whole BMA exhibited more suitable biological characteristics and different level of HOX and TALE gene activation. We, therefore, concluded that vertebral body MSCs derived from whole BMA may provide alternative sources of MSCs for tissue engineering applications for spine surgery. LEVEL OF EVIDENCE: N/A.

An advanced tri-culture model to evaluate the dynamic interplay among osteoblasts, osteoclasts, and endothelial cells.

The dynamic metabolism and the numerous roles of bone tissue necessitate a suitable in vitro model to represent them. In order to investigate the interaction among the several cell types composing bone microenvironment, we studied a tri-culture model including human osteoblasts (OBs), osteoclasts (OCs), and endothelial cells (HUVEC). While OBs are essential for bone deposition and OCs for bone resorption, the vasculature is necessary to provide growth factors, nutrients, and oxygen in the mature tissue. The results of this study showed a strong mutual influence between OBs, OCs, and HUVEC in term of proliferation, viability, and activity (release of ALP, Coll I, OPG, RANKL, VEGF, CTSK, TGFß, and IL-6). The behavior of the single cultures demonstrated to be different compared to the bi- or tri-cultures and depending on the cell types involved: the coexistence of OBs and OCs stimulated the synthetic activity of both cell types, while the presence of HUVEC induced a stimulating role for OBs but mainly an inhibitory effect for OC. In addition, evidence of the effects of OBs and OCs on HUVEC is highlighted by their morphology: regular and able to "sketch" little vessels in presence of OBs, more disorganized and heterogeneous in presence of OCs. Taken together, these observations well characterize an advanced cellular model to be used as starting point for mimicking bone microenvironment in vivo, thus reducing the use of animals in the preclinical phase and offering a more reliable tool to test new and innovative biomaterials.

Evaluation of RNA from human trabecular bone and identification of stable reference genes.

The isolation of good quality RNA from tissues is an essential prerequisite for gene expression analysis to study pathophysiological processes. This study evaluated the RNA isolated from human trabecular bone and defined a set of stable reference genes. After pulverization, RNA was extracted with a phenol/chloroform method and then purified using silica columns. The A260/280 ratio, A260/230 ratio, RIN, and ribosomal ratio were measured to evaluate RNA quality and integrity. Moreover, the expression of six candidates was analyzed by qPCR and different algorithms were applied to assess reference gene stability. A good purity and quality of RNA was achieved according to A260/280 and A260/230 ratios, and RIN values. TBP, YWHAZ, and PGK1 were the most stable reference genes that should be used for gene expression analysis. In summary, the method proposed is suitable for gene expression evaluation in human bone and a set of reliable reference genes has been identified.

A Human 3D In Vitro Model to Assess the Relationship Between Osteoporosis and Dissemination to Bone of Breast Cancer Tumor Cells.

Despite consistent improvements in diagnostic and therapeutic strategies for breast cancer, up to 40% of patients will develop bone metastases. To reduce the morbidity and complications related with bone metastases, it is imperative to reduce their etiological factors. Osteoporosis, being characterized by a sudden estrogen deficiency, may provide a favorable condition for bone metastasis. This work, using a humanized 3D in vitro model, aims at evaluating the relationship between osteoporosis and breast cancer-derived bone metastases. Bone tissue discarded from total hip replacement surgery of healthy and osteoporotic patients was cultured in a rolling apparatus system in hypoxic environment. Protein levels (i.e., vascular endothelial growth factor (VEGF), VEGF receptor 1, VEGF receptor 2, interleukin (IL)-6, IL-1ß, IL-8 IL-10, tumor necrosis factor α (TNF-α), osteoprotegerin (OPG), receptor activator for nuclear factor KB ligand (RANKL)) and histological and immunohistochemical (i.e., cytokeratin 8 and 18) analyses showed a noticeable specificity of breast cancer cells for the colonization of osteoporotic bone. These data are the first to demonstrate that using humanized 3D in vitro systems, which individually model the pre- and postmenopausal bone microenvironment, it is possible to recognize major differences in tumor growth and colonization between healthy and osteoporotic status. Thus, this system might help to develop a shared system between basic and clinical sciences where a personalized diagnosis is associated to a therapeutic strategy designed for a single patient: a model able to achieve a translational research approach in the clinical setting, which may lead to the application and dissemination of personalized medicine. J. Cell. Physiol. 232: 1826-1834, 2017. © 2016 Wiley Periodicals, Inc.

Increased Chondrogenic Potential of Mesenchymal Cells From Adipose Tissue Versus Bone Marrow-Derived Cells in Osteoarthritic In Vitro Models.

Primarily, to compare the behavior of human mesenchymal stem cells (MSCs) derived from bone marrow (hBMSCs) and adipose tissue (hADSCs) in an osteoarthritic (OA) microenvironment; secondly, to investigate the reaction of these cell types in two alternative in vitro culture systems, obtained by using TNFα and/or IL1ß as inflammation mediators, or by using synovial fluid harvested by OA patients (OSF) to simulate the complex inflamed knee microenvironment. 3D micromass cultures of hBMSCs or hADSCs were grown in chondrogenic medium (CTR), in the presence of TNFα and/or IL1ß, or synovial fluid from OA patients. After 1 month of culture, the chondrogenic differentiation of micromasses was evaluated by gene expression, matrix composition, and organization. Both hMSCs types formed mature micromasses in CTR, but a better response of hADSCs to the inflammatory environment was documented by micromass area and Bern score evaluations. The addition of OSF elicited a milder reaction than with TNFα and/or IL1ß by both cell types, probably due to the presence of both catabolic and protective factors. In particular, SOX9 and ACAN gene expression and GAG synthesis were more abundant in hADSCs than hBMSCs when cultured in OSF. The expression of MMP1 was increased for both hMSCs in inflammatory conditions, but in particular by hBMSCs. hADSCs showed an increased chondrogenic potential in inflammatory culture systems, suggesting a better response of hADSCs in the OA environment, thus underlining the importance of appropriate in vitro models to study MSCs and potential advantages of using these cells for future clinical applications. J. Cell. Physiol. 232: 1478-1488, 2017. © 2016 Wiley Periodicals, Inc.

An in vitro 3D bone metastasis model by using a human bone tissue culture and human sex-related cancer cells.

One of the main limitations, when studying cancer-bone metastasis, is the complex nature of the native bone environment and the lack of reliable, simple, inexpensive models that closely mimic the biological processes occurring in patients and allowing the correct translation of results. To enhance the understanding of the mechanisms underlying human bone metastases and in order to find new therapies, we developed an in vitro three-dimensional (3D) cancer-bone metastasis model by culturing human breast or prostate cancer cells with human bone tissue isolated from female and male patients, respectively. Bone tissue discarded from total hip replacement surgery was cultured in a rolling apparatus system in a normoxic or hypoxic environment. Gene expression profile, protein levels, histological, immunohistochemical and four-dimensional (4D) micro-CT analyses showed a noticeable specificity of breast and prostate cancer cells for bone colonization and ingrowth, thus highlighting the species-specific and sex-specific osteotropism and the need to widen the current knowledge on cancer-bone metastasis spread in human bone tissues. The results of this study support the application of this model in preclinical studies on bone metastases and also follow the 3R principles, the guiding principles, aimed at replacing/reducing/refining (3R) animal use and their suffering for scientific purposes.

Novel therapeutic targets in osteoarthritis: Narrative review on knock-out genes involved in disease development in mouse animal models.

Osteoarthritis (OA) can affect every joint, especially the knee. Given the complexity of this pathology, OA is difficult to treat with current therapies, which only relieve pain and inflammation and are not capable of restoring tissues once OA has started. Currently, researchers focus on finding a therapeutic strategy that may help to arrest disease progression. The present narrative review gives an overview of the genes involved in the development and progression of OA, assessing in vivo studies performed in knock-out mice affected by OA, to suggest new therapeutic strategies. The article search was performed on the PubMed database and www.webofknowledge.com website with the following keywords: "knee osteoarthritis" AND "knockout mice". The included studies were in English and published from 2005 to 2015. Additional papers were found within the references of the selected articles. In the 55 analyzed in vivo studies, genes mainly affected chondrocyte homeostasis, inflammatory processes, extracellular matrix and the relationship between obesity and OA. Genes are defined as inducing, preventing and not influencing OA. This review shows that joint homeostasis depends on a variety of genetic factors, and preventing or restoring the loss of a gene encoding for protective proteins, or inhibiting the expression of proteins that induce OA, might be a potential therapeutic approach. However, conclusions cannot be drawn because of the wide variability concerning the technique used for OA induction, the role of the genes, the method for tissue evaluations and the lack of assessments of all joint tissues.

Photobiomodulation with low-level diode laser promotes osteoblast migration in an in vitro micro wound model.

Laser photobiomodulation can improve bone healing, but well-defined treatment parameters are lacking. Saos-2 human osteoblast-like cells were subjected to an in vitro scratch-wound healing assay and irradiated by a 915-nm gallium-aluminum-arsenide diode laser for 0, 48, 96, and 144 s using doses of, respectively, 0, 5, 10, and 15 J/cm(2) . Wound area was measured after 4, 24, 48, and 72 h. Cell viability, DNA content, gene expression, and release of bone-related proteins were evaluated after 24, 48, and 72 h. Laser significantly improved wound healing compared with nonirradiated controls. Cells treated with laser doses of 5 and 10 J/cm(2) reached wound closure after 72 h, followed by 15 J/cm(2) after 96 h. With the cell proliferation inhibitor Mitomycin C, the doses of 10 and 15 J/cm(2) maintained an improved wound healing compared with controls. Laser increased collagen type 1 gene expression with higher doses inducing a longer-lasting effect, whereas transforming growth factor-beta 1 showed comparable or decreased levels in irradiated versus nonirradiated groups, with no effect on protein release. This study demonstrated that laser photobiomodulation at 915 nm promoted wound healing mainly through stimulation of cell migration and collagen deposition by osteoblasts.