Editing Cartilage (section)

== Structure ==
=== Development ===
{{Main|Chondrogenesis}}

In [[embryogenesis]], the [[skeletal]] system is derived from the [[mesoderm]] germ layer. Chondrification (also known as chondrogenesis) is the process by which cartilage is formed from condensed [[mesenchyme]] tissue, which differentiates into [[chondroblast]]s and begins secreting the molecules ([[aggrecan]] and collagen type&nbsp;II) that form the extracellular matrix. In all vertebrates, cartilage is the main skeletal tissue in early ontogenetic stages;<ref>{{cite journal |last1=Buffrénil |first1=Vivian de |last2=Quilhac |first2=Alexandra |title=An Overview of the Embryonic Development of the Bony Skeleton |journal=Vertebrate Skeletal Histology and Paleohistology |date=2021 |pages=29–38 |doi=10.1201/9781351189590-2 |url=https://www.taylorfrancis.com/chapters/edit/10.1201/9781351189590-2/overview-embryonic-development-bony-skeleton-vivian-de-buffr%C3%A9nil-alexandra-quilhac |publisher=CRC Press|isbn=9781351189590 |s2cid=236422314 |url-access=subscription }}</ref><ref>{{cite journal |last1=Quilhac |first1=Alexandra |title=An Overview of Cartilage Histology |journal=Vertebrate Skeletal Histology and Paleohistology |date=2021 |pages=123–146 |doi=10.1201/9781351189590-7 |url=https://www.taylorfrancis.com/chapters/edit/10.1201/9781351189590-7/overview-cartilage-histology-alexandra-quilhac |publisher=CRC Press|isbn=9781351189590 |s2cid=236413810 |url-access=subscription }}</ref> in osteichthyans, many cartilaginous elements subsequently ossify through [[endochondral]] and perichondral ossification.<ref>{{cite journal |last1=Cervantes-Diaz |first1=Fret |last2=Contreras |first2=Pedro |last3=Marcellini |first3=Sylvain |title=Evolutionary origin of endochondral ossification: the transdifferentiation hypothesis |journal=Development Genes and Evolution |date=March 2017 |volume=227 |issue=2 |pages=121–127 |doi=10.1007/s00427-016-0567-y|pmid=27909803 |s2cid=21024809 }}</ref>

Following the initial chondrification that occurs during embryogenesis, cartilage growth consists mostly of the maturing of immature cartilage to a more mature state. The division of cells within cartilage occurs very slowly, and thus growth in cartilage is usually not based on an increase in size or mass of the cartilage itself.<ref>{{cite journal | vauthors = Asanbaeva A, Masuda K, Thonar EJ, Klisch SM, Sah RL | title = Cartilage growth and remodeling: modulation of balance between proteoglycan and collagen network in vitro with beta-aminopropionitrile | journal = Osteoarthritis and Cartilage | volume = 16 | issue = 1 | pages = 1–11 | date = January 2008 | pmid = 17631390 | doi = 10.1016/j.joca.2007.05.019 | url = https://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=1015&context=meng_fac | doi-access = free }}</ref> It has been identified that non-coding RNAs (e.g. miRNAs and long non-coding RNAs) as the most important epigenetic modulators can affect the chondrogenesis. This also justifies the non-coding RNAs' contribution in various cartilage-dependent pathological conditions such as arthritis, and so on.<ref>{{cite journal | vauthors = Razmara E, Bitaraf A, Yousefi H, Nguyen TH, Garshasbi M, Cho WC, Babashah S | title = Non-Coding RNAs in Cartilage Development: An Updated Review | journal = International Journal of Molecular Sciences | volume = 20 | issue = 18 | pages = 4475 | date = September 2019 | pmid = 31514268 | pmc = 6769748 | doi = 10.3390/ijms20184475 | doi-access = free }}</ref>

=== Articular cartilage ===
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[[File:Cartilage from mouse joint.jpg|thumb|Section from mouse joint showing cartilage (purple)]]

The articular cartilage function is dependent on the molecular composition of the [[extracellular matrix]] (ECM). The ECM consists mainly of [[proteoglycan]] and [[collagen]]s. The main proteoglycan in cartilage is aggrecan, which, as its name suggests, forms large aggregates with [[hyaluronan]] and with itself.<ref name="Chremos2023">{{cite journal | vauthors = Chremos A, Horkay F | title = Coexistence of Crumpling and Flat Sheet Conformations in Two-Dimensional Polymer Networks: An Understanding of Aggrecan Self-Assembly | journal = Physical Review Letters | volume = 131 | pages = 138101  | date = September 2023 | issue = 13 | doi = 10.1103/PhysRevLett.131.138101 | pmid = 37832020 | bibcode = 2023PhRvL.131m8101C | s2cid = 263252529 }}</ref> These aggregates are negatively charged and hold water in the tissue. The collagen, mostly collagen type II, constrains the proteoglycans. The ECM responds to tensile and compressive forces that are experienced by the cartilage.<ref>{{cite journal | vauthors = Asanbaeva A, Tam J, Schumacher BL, Klisch SM, Masuda K, Sah RL | title = Articular cartilage tensile integrity: modulation by matrix depletion is maturation-dependent | journal = Archives of Biochemistry and Biophysics | volume = 474 | issue = 1 | pages = 175–82 | date = June 2008 | pmid = 18394422 | pmc = 2440786 | doi = 10.1016/j.abb.2008.03.012 }}</ref> Cartilage growth thus refers to the matrix deposition, but can also refer to both the growth and remodeling of the extracellular matrix. Due to the great stress on the patellofemoral joint during resisted knee extension, the articular cartilage of the patella is among the thickest in the human body. The ECM of articular cartilage is classified into three regions: the pericellular matrix, the [[territorial matrix]], and the interterritorial matrix.