Chondrocyte

Chondrocyte
Chondrocytes of hyaline cartilage showing organelles, lacunae and matrix.
Latin	chondrocytus
Code	TH H2.00.03.5.00003

Chondrocytes (from Greek chondros cartilage + kytos cell) are the only cells found in healthy cartilage. They produce and maintain the cartilaginous matrix, which consists mainly of collagen and proteoglycans. Although the word chondroblast is commonly used to describe an immature chondrocyte, the term is imprecise, since the progenitor of chondrocytes (which are mesenchymal stem cells) can differentiate into various cell types, including osteoblasts. How chondrocytes are organized within cartilage depends on the type of cartilage and where they are found in the tissue. ^{[citation needed]}

Differentiation

From least- to terminally-differentiated, the chondrocytic lineage is:

1. Colony-forming unit-fibroblast (CFU-F)
2. Mesenchymal stem cell / marrow stromal cell (MSC)
3. Chondrocyte
4. Hypertrophic chondrocyte

Mesenchymal (mesoderm origin) stem cells (MSC) are undifferentiated, meaning they can differentiate into a variety of generative cells commonly known as osteochondrogenic (or osteogenic, chondrogenic, osteoprogenitor, etc.) cells. When referring to bone, or in this case cartilage, the originally undifferentiated mesenchymal stem cells lose their pluripotency, proliferate and crowd together in a dense aggregate of chondrogenic cells (cartilage) at the location of chondrification. These chondrogenic cells differentiate into so-called chondroblasts, which then synthesize the cartilage extra cellular matrix (ECM), consisting of a ground substance (proteoglycans, glycosaminoglycans for low osmotic potential) and fibers. The chondroblasts trap themselves in small spaces, called lacunae, which are not in contact with the newly created matrix and which contain extracellular fluid. The chondroblast is now a mature chondrocyte that is usually inactive but can still secrete and degrade the matrix, depending on conditions.

BMP4 and FGF2 have been experimentally shown to increase chondrocyte differentiation.^[1]

Chondrocytes undergo terminal differentiation when they become hypertrophic, which happens during endochondral ossification. This last stage is characterized by major phenotypic changes in the cell.

Gallery

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  Chondrocytes in hyaline cartilage

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  Chondrocyte, stained for calcium, showing nucleus (N) and mitochondria (M)

See also

• Endochondral ossification
• Intramembranous ossification

References

1. ↑ Lee, T. J.; Jang, J.; Kang, S.; Jin, M.; Shin, H.; Kim, D. W.; Kim, B. S. (2013). "Enhancement of osteogenic and chondrogenic differentiation of human embryonic stem cells by mesodermal lineage induction with BMP-4 and FGF2 treatment". Biochemical and Biophysical Research Communications 430 (2): 793–797. doi:10.1016/j.bbrc.2012.11.067. PMID 23206696. 

• Dominici M, Hofmann T, Horwitz E (2001). "Bone marrow mesenchymal cells: biological properties and clinical applications". J Biol Regul Homeost Agents 15 (1): 28–37. PMID 11388742. 
• Bianco P, Riminucci M, Gronthos S, Robey P (2001). "Bone marrow stromal stem cells: nature, biology, and potential applications". Stem Cells 19 (3): 180–92. doi:10.1634/stemcells.19-3-180. PMID 11359943. 
• Stem cell information

External links

• BU Histology Learning System: 03317loa
• Chondrocytes at the US National Library of Medicine Medical Subject Headings (MeSH)