Runx2 Binding Protein and the Regulation of Osteogenesis

One of the key elements of regulating skeletal growth is the Osteoclasts. The Osteoclasts are responsible for initiating the bone remodeling cycle. Blood vessels and nerves are able to penetrate the bone once the chondrocytes die

Osteoporosis develops when the remodeling cycle, which is when the disruption of the bone resorption and bone formation occurs. The imbalance of the remodeling cycle causes osteoporosis. Hormones, cytokines, and paracrine stromal-cell interactions affect the osteoclast’s processes, which includes proliferation, maturation, fusion and activation. The osteoclasts are controlled by the interaction between several interleukins, tumor necrosis factor, transforming growth factor-beta, prostaglandin E2 and hormones. The glucocorticoid-induced osteoporosis is related to increased destruction of osteocytes. Glucocorticoid increase receptor activator of nuclear factor ligand (RANKL) effect and inhibit osteoprotegerin (OPG) production through

Longitudinal bone growth occurs at the epiphyseal plate, which is a thin layer of cartilage between the epiphyseal and metaphyseal bone at the distal ends of the long bones. Bone growth is the result of maturation, growth of chondrocytes, their production of bone matrix, and finally calcification (47). The growth plate is a complex structure consisting of different layers of cells, as shown in figure 3. The most immature cells, the stem cells, are found towards the epiphyseal end of the growth plate in the stem cell zone, or resting zone; the proliferating zone contains more mature chondrocytes and the hypertrophic zone contains the larger chondrocytes. The resting stem cells in the resting zone are recruited, whereupon proliferation and differentiation

Osteoporosis is an age-related disease of the skeletal system characterized by both low bone mass and bone structural degeneration (Nunes, 2011). Understanding osteoporosis is important because it is continues to be overlooked and undertreated, causing high numbers of bone fractures each year –in the elderly, these bone fractures can be debilitating or even life threatening (Eastell, 2009). Osteoporosis manifests when an imbalance between bone resorption and bone rebuilding occurs – this is due to changes in osteoclast and osteoblast activity. I chose this topic because osteoporosis affects millions of people, and research will allow me to better understand this common yet complex, and very perilous bone disease.

The pathophysiology of how strong bone becomes osteoporotic is an interesting process. The body is continuously trying to maintain a sense of homeostasis and keep every cell and organ within the body at a constant state of happiness. During the homeostatic process, cells of bone are continuously undergoing processes of formation and resorption. This all-inclusive progression of building up bone occurs throughout life and is the key in modifying bones during trauma or just natural growth (Van der Kamp, 2012). Bone cells that assist with formation of bone are called osteoclasts, and bone cells that assist with the resorption of bone are called osteoclasts.

Paget’s disease (also known as osteitis deformans) is a chronic disease that affects bone growth, causing bones to become deformed and to be weaker than normal. In normal function, bone is continually being broken down and replaced by new bone, to keep the skeleton strong. In Paget’s disease, the cells called osteoclasts that break down bone, are overactive. This makes the cells that produce new bone, called osteoblasts, to work faster than normal. The resulting new bone is weak and of poor quality. The cause of the disease is unknown, but there is a strong genetic influence. Paget’s disease predominately affects people over the age of 40 years, and can occur asymptomatic. Early diagnosis can be made by X-ray, bone scan, and alkaline phosphatase

Multiple myeloma is a haematological malignancy characterised by the suppression of osteoblastogenesis and the inability to form bone8. The inhibition of the Runt-related transcription factor 2 (Runx2) which is a key transcription factor responsible for osteoblast differentiation is largely implicated in multiple myeloma4. Runx2 stimulates the generation of the bone formation markers alkaline phosphatase (ALP), osteocalcin (OCN) and collagen during early osteoblast differentiation9,10. Transgenic mice without the Runx2 gene exhibit a lack of osteoblast formation causing the arrest of both endochondral and intramembranous ossification11. The upregulation of bone resorption and a decrease in bone mass is a common feature of multiple myeloma, presenting clinically as lytic bone lesions12.

Polymorphisms in the COL1A1gene have been found to alter bone strength by altering binding affinity for the transcription factor Sp1.[23]

Each year in the United States eight to forty children are born with malignant infantile osteopetrosis and one in every two hundred thousand people are affected by the adult form of osteopetrosis. Osteopetrosis is a rare genetic skeletal disorder in which there is an abnormal osteoclastic bone resorption resulting in patients who are more prone to fractures. This disorder “may be inherited as either a dominant or recessive trait and is marked by increased bone density, brittle bones, and, in some cases skeletal abnormalities” (NORD 2014). There are three major types of this condition. They are adult type autosomal dominant, malignant infantile type autosomal recessive, and the last is intermediate mild autosomal recessive.

To begin with, osteopontin (OPN) is a non-collagenous phosphoprotein bone matrix, a homogenous substance in which the cells and fibres of connective tissue are embedded, which is present in numerous cells which includes, epithelial cells, endothelial cells, and vascular smooth muscle cells. OPN is a negatively-charged acidic hydrophilic protein, a protein that has a strong affinity for water, and consists of an approximate number of 300 amino acid remains and can be secreted into all of the fluids in the body. The OPN cDNA from numerous mammalian species, an organism which is classified in the class of mammalia, emits a large degree of homologous

In Identification and Specification of the Mouse Skeletal Stem Cell (Cell, 2015), the Longaker lab explores the differentiation of skeletal stem cells into bone, cartilage, and stromal tissue. Analyzing mRNA present in the cell at different stages of differentiation allowed for determination of the genes that govern which cell type a skeletal stem cell makes. This knowledge was used to shift cell fates from cartilage to bone and vice versa. Additionally, the introduction of BMP2 and VEGF inhibitor allowed for the creation of cartilage in fat tissue. These experiments demonstrate a robust knowledge of the genes that govern the distinct outcomes for differentiated skeletal stem cells. Finally, it was observed that the skeletal stem

Bone development is influenced by a number of factors, including nutrition, hormonal

Osteoblasts are bone forming cells with single nucleus that synthesize bone. Osteoblasts arise from mesenchymal stem cells. Mesenchymal stem cells are mainly found in large numbers in the periosteum, which is fibrous –like layer on outside and surface of bone. Runx2/Cbfa is important regulatory transcription factor required for differentiation of osteoblasts(53). Another important transcription factor required for osteoblastic differentiation is osterix.

Osteoblastogenesis takes place as a result of a number of signalling pathways such as the transforming growth factor-β (TGF-β), Wnt/β-catenin and mitrogen-activated protein kinase (MAPK) signalling. The TGF-β superfamily comprises of the TGF-βs and the bone morphogenetic proteins (BMPs), both of which play critical regulatory roles in bone tissue55,56. TGF-β presents in 3 isoforms namely TGF-β1, TGF-β2 and TGF-β3 with TGF-β1 in particular having a chemotactic effect on osteoblasts in order to promote bone formation55. TGF-β is initially expressed as an inactive complex which is made functional via one of three mechanisms: bond breaking between TGF-β and the latency associated peptide, degradation of the latency associated peptide or conformational change of the latency associated peptide itself55. Post-activation, the TGF-β binds to either type I or type II of the transmembrane serine/threonine receptors57.

The focus of this project hangs on two elements, data from Ethics #16-86 and Ethics # (TBC.) From these two studies, we will cross-correlate the variance of the early Osteoimmunological responses, to the redress of induced defects into the regions identified below.