Osteoclast

osteoclastsodontoclastanti-osteoclastogenicosteoblastsosteoclast cellosteoclasticosteoclastic bone resorptionosteoclastogenesis
An osteoclast is a type of bone cell that breaks down bone tissue.wikipedia
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Bone

cortical bonebone tissuecancellous bone
An osteoclast is a type of bone cell that breaks down bone tissue. This function is critical in the maintenance, repair, and remodelling of bones of the vertebral skeleton.
Osteoblasts and osteocytes are involved in the formation and mineralization of bone; osteoclasts are involved in the resorption of bone tissue.

Bone resorption

resorptionresorbedresorption of bone
The osteoclast disassembles and digests the composite of hydrated protein and mineral at a molecular level by secreting acid and a collagenase, a process known as bone resorption.
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.

Osteocyte

osteocytesbone cellbone cells
An osteoclast is a type of bone cell that breaks down bone tissue.
They destroy bone through a rapid, transient (relative to osteoclasts) mechanism called osteocytic osteolysis.

Bone remodeling

bone metabolismremodelingbone turnover
This function is critical in the maintenance, repair, and remodelling of bones of the vertebral skeleton.
Two main types of cells are responsible for bone metabolism: osteoblasts (which secrete new bone), and osteoclasts (which break bone down).

Cathepsin K

CTSKK
This permits characterization of osteoclasts by their staining for high expression of tartrate resistant acid phosphatase (TRAP) and cathepsin K.
This protein, which is a member of the peptidase C1 protein family, is expressed predominantly in osteoclasts.

Deciduous teeth

deciduousmilk teethbaby teeth
An odontoclast (/odon·to·clast/; o-don´to-klast) is an osteoclast associated with absorption of the roots of deciduous teeth.
The erupting permanent teeth cause root resorption, where the permanent teeth push on the roots of the primary teeth, causing the roots to be dissolved by odontoclasts (as well as surrounding alveolar bone by osteoclasts) and become absorbed by the forming permanent teeth.

Macrophage

macrophagesM2 macrophagesTissue macrophages
When osteoclast-inducing cytokines are used to convert macrophages to osteoclasts, very large cells that may reach 100 µm in diameter occur.

Tartrate-resistant acid phosphatase

ACP5tartrate resistant acid phosphataseTRAP-positive
This permits characterization of osteoclasts by their staining for high expression of tartrate resistant acid phosphatase (TRAP) and cathepsin K.
Under normal circumstances, TRAP is highly expressed by osteoclasts, activated macrophages, neurons, and by the porcine endometrium during pregnancy.

Osteopetrosis

Albers-Schonberg diseaseAlbers-Schönberg diseaseAlbers–Schonberg disease
RANKL knockout mice exhibit a phenotype of osteopetrosis and defects of tooth eruption, along with an absence or deficiency of osteoclasts.
The cause of the disease is understood to be malfunctioning osteoclasts, and its inability to resorb bone.

Multinucleate

multinucleatedmultinucleated cellsmultinucleated cell
An osteoclast is a large multinucleated cell and human osteoclasts on bone typically have five nuclei and are 150–200 µm in diameter.
Osteoclasts are multinuclear cells which are found commonly in the human body that aid in the maintenance and repair of the bones by secreting acid that dissolves bone matter.

Osteoblast

osteoblastsosteogenesisosteoblastic
Three theories were dominant: from 1949 to 1970 the connective tissue origin was popular, which stated that osteoclasts and osteoblasts are of the same lineage, and osteoblasts fuse together to form osteoclasts.
Bone is a dynamic tissue that is constantly being reshaped by osteoblasts, which produce and secrete matrix proteins and transport mineral into the matrix, and osteoclasts, which break down the tissues.

RANK

TNFRSF11ACD265osteoclastogenesis
RANKL activates NF-κβ (nuclear factor-κβ) and NFATc1 (nuclear factor of activated t cells, cytoplasmic, calcineurin-dependent 1) through RANK.
RANK is the receptor for RANK-Ligand (RANKL) and part of the RANK/RANKL/OPG signaling pathway that regulates osteoclast differentiation and activation.

RANKL

TNFSF11RANKL inhibitorRANK ligand
Osteoclast formation requires the presence of RANKL (receptor activator of nuclear factor κβ ligand) and M-CSF (Macrophage colony-stimulating factor).
This surface-bound molecule (also known as CD254), found on osteoblasts, serves to activate osteoclasts, which are critically involved in bone resorption.

Podosome

podosomes
Sealing zones are bounded by belts of specialized adhesion structures called podosomes.
Many different specialized cells exhibit these dynamic structures such as invasive cancer cells, osteoclasts, vascular smooth muscle cells, endothelial cells, and certain immune cells like macrophages and dendritic cells.

Acid phosphatase

acid phosphatasesacidic phosphatase
These vacuoles include lysosomes filled with acid phosphatase.
Tartrate-resistant acid phosphatase may be used as a biochemical marker of osteoclast function during the process of bone resorption.

Macrophage colony-stimulating factor

M-CSFCSF1colony stimulating factor 1
Osteoclast formation requires the presence of RANKL (receptor activator of nuclear factor κβ ligand) and M-CSF (Macrophage colony-stimulating factor).
M-CSF released by osteoblasts (as a result of endocrine stimulation by parathyroid hormone) exerts paracrine effects on osteoclasts.

Cathepsin

cathepsinscathepsin bcathepsin d
In addition, several hydrolytic enzymes, such as members of the cathepsin and matrix metalloprotease (MMP) groups, are released to digest the organic components of the matrix.
There are, however, exceptions such as cathepsin K, which works extracellularly after secretion by osteoclasts in bone resorption.

V-ATPase

vacuolar ATPaseV-type ATPaseV-type proton ATPase
Hydrogen ions are pumped against a high concentration gradient by proton pumps, specifically a unique vacuolar-ATPase.
V-ATPases are also found in the plasma membranes of a wide variety of cells such as intercalated cells of the kidney, osteoclasts (bone resorbing cells), macrophages, neutrophils, sperm, midgut cells of insects, and certain tumor cells.

Osteopontin

SPP1Secreted phosphoprotein 1
Attachment to the bone matrix is facilitated by integrin receptors, such as αvβ3, via the specific amino acid motif Arg-Gly-Asp in bone matrix proteins, such as osteopontin.
Specifically, research suggests it plays a role in anchoring osteoclasts to the mineral matrix of bones.

Parathyroid hormone

PTHParathormoneparathyroid hyperplasia
Osteoclasts are regulated by several hormones, including parathyroid hormone (PTH) from the parathyroid gland, calcitonin from the thyroid gland, and growth factor interleukin 6 (IL-6).
PTH indirectly stimulates osteoclast activity within the bone matrix (osteon), in an effort to release more ionic calcium (Ca 2+ ) into the blood to elevate a low serum calcium level.

Interleukin 6

IL-6interleukin-6IL6
This last hormone, IL-6, is one of the factors in the disease osteoporosis, which is an imbalance between bone resorption and bone formation.
In addition, osteoblasts secrete IL-6 to stimulate osteoclast formation.

Transcytosis

transcytose
In addition, it permits the vesicular transcytosis of the mineral and degraded collagen from the ruffled border to the free membrane of the cell, and its release into the extracellular compartment.
Blood capillaries are a well-known site for transcytosis, though it occurs in other cells, including neurons, osteoclasts and M cells of the intestine.

Bisphosphonate

bisphosphonatesdiphosphonateaminobisphosphonates
Giant osteoclasts can occur in some diseases, including Paget's disease of bone and bisphosphonate toxicity.
Bone tissue undergoes constant remodeling and is kept in balance (homeostasis) by osteoblasts creating bone and osteoclasts destroying bone.

Feline odontoclastic resorptive lesion

In cats, abnormal odontoclast activity can cause feline odontoclastic resorptive lesions, necessitating extraction of the affected teeth.
Feline Tooth Resorption (TR) is a syndrome in cats characterized by resorption of the tooth by odontoclasts, cells similar to osteoclasts.

Osteoporosis

bone lossosteoporoticpostmenopausal osteoporosis
This last hormone, IL-6, is one of the factors in the disease osteoporosis, which is an imbalance between bone resorption and bone formation. This enzyme has been targeted in the prevention of osteoporosis.
Osteoclasts are assisted by transcription factor PU.1 to degrade the bone matrix, while osteoblasts rebuild the bone matrix.