Chondroblast

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Chondroblast
Diagram of chondroblasts
Details
Identifiers
Latinchondroblastus
THH2.00.03.5.00002
FMA66783
Anatomical terms of microanatomy

Chondroblasts, or

chondrocytes in the growing cartilage matrix. Another name for them is subchondral cortico-spongious progenitors.[1]
They have euchromatic nuclei and stain by basic dyes.

These cells are extremely important in

fibers, until they lie in the matrix lacunae. Once they embed themselves into the cartilage matrix, they grow the cartilage matrix by growing more cartilage extracellular matrix rather than by dividing further.[citation needed
]

Structure

Within adults and developing adults, most chondroblasts are located in the perichondrium. This is a thin layer of connective tissue which protects cartilage and is where chondroblasts help to expand cartilage size whenever prompted to by

]

Matrix formation and composition

The extracellular matrix secreted by chondroblasts is composed of

glycoproteins, water, and a host of macromolecules. Within finished cartilage, collagen fibers compose 10-20% of the volume, water 65-80%, and the proteoglycan-hyaluronic acid aggregates the remaining portion. Due to the proliferative nature of chondroblasts, cells compose a larger portion of the composition than what is normally found within completed cartilage.[3]

Collagen Type II fibers are responsible for giving the future cartilage matrix its

tensile strength. The structure of these fibers, like the majority of collagen fibers, forms a triple helix structure.[3]

Proteoglycans resist the compression generally put upon cartilage and generate the swelling

glycoaminoglycan chains. These chains together are attached to a hyaluronic acid backbone which, in conjunction with the collagen fibrils, create an interstitial intrafibrillar space in which water is held in by the negative charge of the proteoglycans.[4]

Development

As suggested in the name, mesenchymal progenitors originate from the

Signaling, transcription and environmental factors responsible for chondroblast creation

Transcription factors

An important genetic component of this process is Sox9, a HMG box transcription factor, which marks progenitor cells for chondrogenic differentiation. Inactivation of the Sox9 gene will result in the loss of all Cartilage, and thus Chondroblast, formation. This factor is also expressed alongside Sox5 and Sox6.[1]

Runx2 is another important genetic component of Chondroblast formation. It has been found that expressing this gene will result in the suppression of the differentiation of chondroblasts. Expression of this gene will also prompt already formed cartilage to undergo endochondral ossification which will prompt the cartilage to form bone.[citation needed]

It is important to note here that these

environmental factors act upstream in determining what cell type will form out of any particular mesenchymal progenitor cell.[citation needed
]

Wnt/β-catenin signaling

Wnt14 is controlled by Col2a1 and is put through the β-Catenin mediated

Testing of this pathway has indicated that the Wnt/β-Catenin increases

β-Catenin levels before the activation of the Runx2 and Osx transcription factors which seems to suggest that early β-Catenin levels can be a sign of whether an early mesenchymal progenitor cell will progress to a chondrocyte or to an osteoblast.[7]

Retinoic acid

Retinoic acid, part of a family of molecules called

Sox9 expression which is considered a “master switch” for the differentiation of chondroblasts.[8]

Environmental factors

Differentiation of chondroblasts is favored in an environment with high compressive

avascular and thus would be ill-suited to a high oxygen environment.[1]

Function

Chondroblasts appear to migrate to cartilage whenever chondrocytes are destroyed via mechanical force. Remaining chondrocytes divide in order to form more chondroblasts. HMGB-1, a growth factor which promotes chondrocyte division while receptors for advanced glycation products (RAGE) mediated chemotaxis to clean up cell debris resulting from the damage. Chondroblasts then secrete cartilage matrix around themselves in order to reform the lost cartilage tissue.[citation needed]

However, regeneration is still too slow for patient care to effectively rely on this mechanism of repair. Part of this inability to regenerate quickly from injury results from the relative

connective tissues of the human body.[citation needed
]

Pathology

sarcomas have an accompanying osteoblastoma which is similarly benign.[9]

Chondrosarcoma is a more

malignant type of tumor, but most are low grade tumors and often appear in the axial skeletal region. It constitutes 20% of skeletal system tumors in the United States.[10]

See also

References

  1. ^
    S2CID 25710553
    .
  2. . Retrieved 2014-10-22.
  3. ^ .
  4. ^ King, M.W. (2014-02-10). "Glycosaminoglycans". Retrieved 2014-10-22.[unreliable medical source?]
  5. PMID 23206696
    .
  6. .
  7. .
  8. ^ ]
  9. ^ Aufderheide, A.C.; Rodríguez-Martín, C.; Langsjoen, O. (2011). "Chondrosarcoma". The Cambridge encyclopedia of human paleopathology. Cambridge, United Kingdom: Cambridge University Press.
  10. ^ "Epidemiology of Bone Cancer: An Overview".