Bone growth factor

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A bone growth factor is a growth factor that stimulates the growth of bone tissue. [1] [2]

Contents

Known bone growth factors include insulin-like growth factor-1 (IGF-1), insulin-like growth factor-2 (IGF-2), transforming growth factor beta (TGF-β), fibroblast growth factors (FGFs), platelet-derived growth factor (PDGF), parathyroid hormone-related peptide (PTHrP), bone morphogenetic proteins (BMPs), and certain members of the growth differentiation factor (GDF) group of proteins. [1] [2] [3]

The ultimate target of bone growth factors are osteoblasts, osteoclasts and fibroblasts. Human fibroblasts and osteoblasts were shown to be capable of producing bone growth factors after stimulation. [4]

Major hormones influencing bone growth and morphology include growth hormone (GH), androgens such as testosterone and dihydrotestosterone, and estrogens such as estradiol. [3] [5]

Types

Transforming growth factor beta

Transforming growth factor beta (TGF-β) is a physiological regulator of osteoblast differentiation, and acts as a central component in the coupling of bone formation and its resorption during bone remodeling. [6]

Bone morphogenetic proteins

Bone morphogenetic proteins (BMPs) are proteins that are made of acidic polypeptides and belongs to the TGF-B family. [7] BMPs promote the regeneration of bone tissue and cartilage. [7] BMP exhibits osteoinductive activity. Osteoinductive activity leads to bone formation, activates mesenchymal cells to transform into osteoblasts which ultimately yield bone formation. BMP targets and binds to mesenchymal cells and activates a transmembrane serine/threonine kinase receptor which will lead to the phosphorylation of molecules called SMADS. SMADS are transcription factors that will induce osteoblast growth. [8]

Platelet derived growth factor

The majority of the substrates of platelet-derived growth factor (PDGF) exhibit similar structures to Src Homology 2 domain. These substrates will bind to the PDGFR receptors which will dimerize and autophosphorylate. This phosphorylation attracted PLC-gamma (induces cell proliferation), Ras (which goes through signaling cascade and acts as a transcription factor), phosphatidylinositol 3-kinase (PI3K) which also promotes a signaling cascade inducing transcription factors, and stress fiber formation, and induces the STAT pathway which activates transcription factors. [9]

Fibroblast growth factor

Platelet-derived growth factors (PDGFs) are polypeptides found in various tissues, including bone, where it was originally postulated that it could act as an autologous regulator of bone remodeling. This protein has been initially isolated in human platelets, and is composed of two different polypeptide chains A and B. The combination of these polypeptides form the homodimeric (AA) or (BB), or heterodimeric (AB) chains of PDGF. [10] Fibroblast growth factor (FGF) signaling cascade is started by the binding of 2 growth factors to the FGFR. Dimerization takes place and initiates the transphosphorylation of each receptor. These phosphorylation sites act as docking sites for proteins so they may induce downstream signaling. These proteins consist of FRS2-alpha and PLC-gamma. FRS2-alpha acts as a scaffold protein to hold GAB1 and GRB2 which then proteins bind to SHP2 and SOS. These several proteins act together to activates the Ras pathway (induces cell proliferation and differentiation) and the PI3K pathway (induces survival and cell fate determination). On the other side of the dimerized receptors, PLC-gamma activates DAG and IP3 which yield PKC and calcium ions. PKC and calcium will ultimately induce morphology, migration, and adhesion. [11]

Insulin-like growth factors

Insulin-like growth factors (IGF) assist bone growth in the body. IGF's are single-chain polypeptides that are similarly structured to insulin. There are 2 IGFs: Insulin-like growth factor 1 (IGF-1), and Insulin-like growth factor 2 (IGF-2). IGF-1 is induced by growth hormone (GH), and targets cartilage, stimulating cell bone cell proliferation. Studies carried out by Yakar S, Rosen CJ have shown in animal models that IGF-1 can enhance longitudinal growth, periosteal circumference, and bone mineral density. [12] IGF-1 is responsible for increasing overall body size, longitudinal bone size, and height, especially during puberty. [3] [5]

Parathyroid hormone-related protein (PTHrP) is important for endochondral bone formation. Martin (2005) found that PTHrP stimulates bone formation by increasing osteoblast differentiation and reducing osteoblast apoptosis. This causes an increase in osteoblasts allowing for new bone cells to be formed. PTHrP also regulates osteoclast formation, further allowing for bone growth. [13]

Hormones

Estrogens cause the hips to widen and become rounded during puberty in females, and androgens cause the shoulders to broaden in males. [14] [15] [16] Estrogens mediate epiphyseal closure in both males and females. [3] [5] Other hormones implicated in control of bone growth include thyroid hormone, parathyroid hormone, [17] calcitonin, [18] glucocorticoids such as cortisol, and vitamin D (calcitriol). [5] According to menoPAUSE, a blog from University of Rochester, estrogen causes females to have their fat distributed in their breasts, thighs, and along their pelvic area, implying that the fat can be used as an energy source for future pregnancies. For men, androgens (such as testosterone) increases male's muscle-to-fat ratio.Woods J. "What does Estrogen Have to Do with Belly Fat?".

Clinical significance

Potential treatment for osteoporosis

Osteoporosis is a bone disease where bone mass is less than the average and can increase fractures. Some causes that lead to osteoporosis is how old you are, and decreasing amount of estrogen, which is why it mainly occurs in older women (however it can also impact men as well). [19]

During a recent study performed at Children's Medical Center Research Institute at UT Southwestern, Bone Growth Factor Osteolectin (Clec11a) has also shown regenerative properties. Ovaries were removed from mice to simulate osteoporosis of post menopausal women. Results were based on daily injections of Osteolectin to determine the effects. This research showed an increase in bone volume of mice with bone loss after their ovaries were removed. [20]

To be more specific, in order to help people with osteoporosis, medication is used along with treating bone fractures. Clec11a is a glycoprotein that bone marrow expresses which Elifesciences states. [21]

Tendon treatment

Several studies have shown a correlation between the administration of bone growth factors and the amelioration of the tendon-to-bone healing. The focus of these studies was primarily on the anterior cruciate ligament (ACL) located in the knee, due to the high volume of incidences[ spelling? ] of injuries sustained by athletes. [22] The University of Dammam, King Fahd Hospital in Saudi Arabia was able to show that the addition of SHMSP bone growth factor via powder facilitated the process of tendon-graft healing in rabbits. Comparison of this SHMSP test group to the control group illustrated a higher level of formation and organization within the knee.   [22]

The Hospital for Special Surgery in New York conducted a similar study, in which a collagen sponge containing bone protein was implanted in the ACL of rabbits. In this case, the bone protein isolated from bovine femurs contained several bone morphogenetic proteins, which are part of an important signaling system that aides in the structure of bones. [23] As with the application of SHMSP, the inclusion of bone protein in the collagen sponge was seen to improve the healing process, when compared to control groups with the sponge alone or no sponge. [23]

In a separate study also implemented by the Hospital for Special Surgery as well as the University of California, treatment of the anterior cruciate ligament utilized the recombinant human bone morphogenic protein rhBMP-2 in two phases. [24] In phase one, the dosages of noggin, a regulator protein, as well as rhBMP-2 were properly calibrated, and in phase two these proteins carried on synthetic calcium phosphate matrix (CPM) were then injected into the ACL region. The results of this procedure also demonstrated an improvement in the collagen fiber formation between the tendon and the bone. [24] Hence, all three treatments were seen to improve the efficacy of tendon-to-bone healing via the different bone growth factors: SHMSP, bone protein, and rhBMP-2.

Related Research Articles

<span class="mw-page-title-main">Bone</span> Rigid organs that constitute part of the endoskeleton of vertebrates

A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, and enable mobility. Bones come in a variety of shapes and sizes and have complex internal and external structures. They are lightweight yet strong and hard and serve multiple functions.

A growth factor is a naturally occurring substance capable of stimulating cell proliferation, wound healing, and occasionally cellular differentiation. Usually it is a secreted protein or a steroid hormone. Growth factors are important for regulating a variety of cellular processes.

<span class="mw-page-title-main">Mammary gland</span> Exocrine gland in humans and other mammals

A mammary gland is an exocrine gland in humans and other mammals that produces milk to feed young offspring. Mammals get their name from the Latin word mamma, "breast". The mammary glands are arranged in organs such as the breasts in primates, the udder in ruminants, and the dugs of other animals. Lactorrhea, the occasional production of milk by the glands, can occur in any mammal, but in most mammals, lactation, the production of enough milk for nursing, occurs only in phenotypic females who have gestated in recent months or years. It is directed by hormonal guidance from sex steroids. In a few mammalian species, male lactation can occur. With humans, male lactation can occur only under specific circumstances.

<span class="mw-page-title-main">Osteoblast</span> Cells secreting extracellular matrix

Osteoblasts are cells with a single nucleus that synthesize bone. However, in the process of bone formation, osteoblasts function in groups of connected cells. Individual cells cannot make bone. A group of organized osteoblasts together with the bone made by a unit of cells is usually called the osteon.

<span class="mw-page-title-main">Parathyroid hormone-related protein</span> Mammalian protein

Parathyroid hormone-related protein (PTHrP) is a proteinaceous hormone and a member of the parathyroid hormone family secreted by mesenchymal stem cells. It is occasionally secreted by cancer cells. However, it also has normal functions in bone, teeth, vascular tissues and other tissues.

<span class="mw-page-title-main">Paracrine signaling</span> Form of localized cell signaling

In cellular biology, paracrine signaling is a form of cell signaling, a type of cellular communication in which a cell produces a signal to induce changes in nearby cells, altering the behaviour of those cells. Signaling molecules known as paracrine factors diffuse over a relatively short distance, as opposed to cell signaling by endocrine factors, hormones which travel considerably longer distances via the circulatory system; juxtacrine interactions; and autocrine signaling. Cells that produce paracrine factors secrete them into the immediate extracellular environment. Factors then travel to nearby cells in which the gradient of factor received determines the outcome. However, the exact distance that paracrine factors can travel is not certain.

<span class="mw-page-title-main">Platelet-derived growth factor</span> Signaling glycoprotein regulating cell proliferation

Platelet-derived growth factor (PDGF) is one among numerous growth factors that regulate cell growth and division. In particular, PDGF plays a significant role in blood vessel formation, the growth of blood vessels from already-existing blood vessel tissue, mitogenesis, i.e. proliferation, of mesenchymal cells such as fibroblasts, osteoblasts, tenocytes, vascular smooth muscle cells and mesenchymal stem cells as well as chemotaxis, the directed migration, of mesenchymal cells. Platelet-derived growth factor is a dimeric glycoprotein that can be composed of two A subunits (PDGF-AA), two B subunits (PDGF-BB), or one of each (PDGF-AB).

<span class="mw-page-title-main">Osteoprotegerin</span> Mammalian protein found in Homo sapiens

Osteoprotegerin (OPG), also known as osteoclastogenesis inhibitory factor (OCIF) or tumour necrosis factor receptor superfamily member 11B (TNFRSF11B), is a cytokine receptor of the tumour necrosis factor (TNF) receptor superfamily encoded by the TNFRSF11B gene.

<span class="mw-page-title-main">Osteocyte</span> Mature osteoblasts which helps in communication between cells and also in molecular synthesis

An osteocyte, an oblate shaped type of bone cell with dendritic processes, is the most commonly found cell in mature bone. It can live as long as the organism itself. The adult human body has about 42 billion of them. Osteocytes do not divide and have an average half life of 25 years. They are derived from osteoprogenitor cells, some of which differentiate into active osteoblasts. Osteoblasts/osteocytes develop in mesenchyme.

Transforming growth factor is used to describe two classes of polypeptide growth factors, TGFα and TGFβ.

<span class="mw-page-title-main">Basic fibroblast growth factor</span> Growth factor and signaling protein otherwise known as FGF2

Fibroblast growth factor 2, also known as basic fibroblast growth factor (bFGF) and FGF-β, is a growth factor and signaling protein encoded by the FGF2 gene. It binds to and exerts effects via specific fibroblast growth factor receptor (FGFR) proteins, themselves a family of closely related molecules. Fibroblast growth factor protein was first purified in 1975; soon thereafter three variants were isolated: 'basic FGF' (FGF2); Heparin-binding growth factor-2; and Endothelial cell growth factor-2. Gene sequencing revealed that this group is the same FGF2 protein and is a member of a family of FGF proteins.

<span class="mw-page-title-main">Bone resorption</span> Medical condition

Bone resorption is resorption of bone tissue, that is, the process by which osteoclasts break down the tissue in bones and release the minerals, resulting in a transfer of calcium from bone tissue to the blood.

<span class="mw-page-title-main">Sclerostin</span> Protein-coding gene in the species Homo sapiens

Sclerostin is a protein that in humans is encoded by the SOST gene. It is a secreted glycoprotein with a C-terminal cysteine knot-like (CTCK) domain and sequence similarity to the DAN family of bone morphogenetic protein (BMP) antagonists. Sclerostin is produced primarily by the osteocyte but is also expressed in other tissues, and has anti-anabolic effects on bone formation.

<span class="mw-page-title-main">Bone morphogenetic protein 2</span> Protein-coding gene in the species Homo sapiens

Bone morphogenetic protein 2 or BMP-2 belongs to the TGF-β superfamily of proteins.

<span class="mw-page-title-main">Bone morphogenetic protein 4</span> Human protein and coding gene

Bone morphogenetic protein 4 is a protein that in humans is encoded by BMP4 gene. BMP4 is found on chromosome 14q22-q23.

<span class="mw-page-title-main">Bone morphogenetic protein 6</span> Protein-coding gene in the species Homo sapiens

Bone morphogenetic protein 6 is a protein that in humans is encoded by the BMP6 gene.

<span class="mw-page-title-main">BMPR1A</span> Bone morphogenetic protein receptor

The bone morphogenetic protein receptor, type IA also known as BMPR1A is a protein which in humans is encoded by the BMPR1A gene. BMPR1A has also been designated as CD292.

<span class="mw-page-title-main">GDF2</span> Protein-coding gene in the species Homo sapiens

Growth differentiation factor 2 (GDF2) also known as bone morphogenetic protein (BMP)-9 is a protein that in humans is encoded by the GDF2 gene. GDF2 belongs to the transforming growth factor beta superfamily.

<span class="mw-page-title-main">Adipogenesis</span>

Adipogenesis is the formation of adipocytes from stem cells. It involves 2 phases, determination, and terminal differentiation. Determination is mesenchymal stem cells committing to the adipocyte precursor cells, also known as preadipocytes which lose the potential to differentiate to other types of cells such as chondrocytes, myocytes, and osteoblasts. Terminal differentiation is that preadipocytes differentiate into mature adipocytes. Adipocytes can arise either from preadipocytes resident in adipose tissue, or from bone-marrow derived progenitor cells that migrate to adipose tissue.

The human skeletal system is a complex organ in constant equilibrium with the rest of the body. In addition to support and structure of the body, bone is the major reservoir for many minerals and compounds essential for maintaining a healthy pH balance. The deterioration of the body with age renders the elderly particularly susceptible to and affected by poor bone health. Illnesses like osteoporosis, characterized by weakening of the bone's structural matrix, increases the risk of hip-fractures and other life-changing secondary symptoms. In 2010, over 258,000 people aged 65 and older were admitted to the hospital for hip fractures. Incidence of hip fractures is expected to rise by 12% in America, with a projected 289,000 admissions in the year 2030. Other sources estimate up to 1.5 million Americans will have an osteoporotic-related fracture each year. The cost of treating these people is also enormous, in 1991 Medicare spent an estimated $2.9 billion for treatment and out-patient care of hip fractures, this number can only be expected to rise.

References

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  20. ↑ "Scientists discover new bone-forming growth factor that reverses osteoporosis in mice". ScienceDaily. Retrieved 2019-12-05.
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  23. 1 2 Anderson K, Seneviratne AM, Izawa K, Atkinson BL, Potter HG, Rodeo SA (2001–2011). "Augmentation of tendon healing in an intraarticular bone tunnel with use of a bone growth factor". The American Journal of Sports Medicine. 29 (6): 689–98. doi:10.1177/03635465010290060301. PMID   11734478. S2CID   9946916.
  24. 1 2 Ma CB, Kawamura S, Deng XH, Ying L, Schneidkraut J, Hays P, Rodeo SA (April 2007). "Bone morphogenetic proteins-signaling plays a role in tendon-to-bone healing: a study of rhBMP-2 and noggin". The American Journal of Sports Medicine. 35 (4): 597–604. doi:10.1177/0363546506296312. PMID   17218656. S2CID   22750694.
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