EphrinB2 Signalling in Osteoblast Differentiation, Bone Formation and Endochondral Ossification

A Brief Review of Bone Cell Function and Importance

This review focuses on understanding the macroscopic and microscopic characteristics of bone tissue and reviews current knowledge of its physiology. It explores how these features intricately collaborate to maintain the balance between osteoblast-mediated bone formation and osteoclast-mediated bone resorption, which plays a pivotal role in shaping not only our physical framework but also overall health. In this work, a comprehensive exploration of microscopic and macroscopic features of bone tissue is presented.

Assembling the Puzzle Pieces. Insights for in Vitro Bone Remodeling

As a highly dynamic organ, bone changes during throughout a person's life. This process is referred to as 'bone remodeling' and it involves two stages - a well-balanced osteoclastic bone resorption and an osteoblastic bone formation. Under normal physiological conditions bone remodeling is highly regulated that ensures tight coupling between bone formation and resorption, and its disruption results in a bone metabolic disorder, most commonly osteoporosis. Though osteoporosis is one of the most prevalent skeletal ailments that affect women and men aged over 40 of all races and ethnicities, currently there are few, if any safe and effective therapeutic interventions available. Developing state-of-the-art cellular systems for bone remodeling and osteoporosis can provide important insights into the cellular and molecular mechanisms involved in skeletal homeostasis and advise better therapies for patients. This review describes osteoblastogenesis and osteoclastogenesis as two vital processes for producing mature, active bone cells in the context of interactions between cells and the bone matrix. In addition, it considers current approaches in bone tissue engineering, pointing out cell sources, core factors and matrices used in scientific practice for modeling bone diseases and testing drugs. Finally, it focuses on the challenges that bone regenerative medicine is currently facing.

Cellular Processes by Which Osteoblasts and Osteocytes Control Bone Mineral Deposition and Maturation Revealed by Stage-Specific EphrinB2 Knockdown

PURPOSE OF REVIEW

We outline the diverse processes contributing to bone mineralization and bone matrix maturation by describing two mouse models with bone strength defects caused by restricted deletion of the receptor tyrosine kinase ligand EphrinB2.

RECENT FINDINGS

Stage-specific EphrinB2 deletion differs in its effects on skeletal strength. Early-stage deletion in osteoblasts leads to osteoblast apoptosis, delayed initiation of mineralization, and increased bone flexibility. Deletion later in the lineage targeted to osteocytes leads to a brittle bone phenotype and increased osteocyte autophagy. In these latter mice, although mineralization is initiated normally, all processes involved in matrix maturation, including mineral accrual, carbonate substitution, and collagen compaction, progress more rapidly. Osteoblasts and osteocytes control the many processes involved in bone mineralization; defining the contributing signaling activities may lead to new ways to understand and treat human skeletal fragilities.

Microengineered platforms for co-cultured mesenchymal stem cells towards vascularized bone tissue engineering

Bone defects are common disease requiring thorough treatments since the bone is a complex vascularized tissue that is composed of multiple cell types embedded within an intricate extracellular matrix (ECM). For past decades, tissue engineering using cells, proteins, and scaffolds has been suggested as one of the promising approaches for effective bone regeneration. Recently, many researchers have been interested in designing effective platform for tissue regeneration by orchestrating factors involved in microenvironment around tissues. Among factors affecting bone formation, vascularization during bone development and after minor insults via endochondral and intramembranous ossification is especially critical for the long-term support for functional bone. In order to create vascularized bone constructs, the interactions between human mesenchymal stem cells (MSCs) and endothelial cells (ECs) have been investigated using both direct and indirect co-culture studies. Recently, various culture methods including micropatterning techniques, three dimensional scaffolds, and microfluidics have been developed to create micro-engineered platforms that mimic the nature of vascularized bone formation, leading to the creation of functional bone structures. This review focuses on MSCs co-cultured with endothelial cells and microengineered platforms to determine the underlying interplay between co-cultured MSCs and vascularized bone constructs, which is ultimately necessary for adequate regeneration of bone defects.