Editing Scar (section)

====Myofibroblast====
Mammalian wounds that involve the dermis of the skin heal by repair, not regeneration (except in 1st trimester inter-uterine wounds and in the regeneration of deer antlers). Full-thickness wounds heal by a combination of [[wound contracture]] and edge re-epitheliasation. Partial thickness wounds heal by edge re-epithelialisation and epidermal migration from [[Skin appendage|adnexal]] structures (hair follicles, sweat glands and sebaceous glands). The site of [[keratinocyte]] stem cells remains unknown but stem cells are likely to reside in the [[Stratum basale|basal layer]] of the [[epidermis]] and below the bulge area of hair follicles.

The fibroblast involved in scarring and contraction is the [[myofibroblast]],<ref name="myo201103" /> which is a specialized contractile fibroblast.<ref name="myo2011033" /> These cells express α-smooth muscle actin (α-SMA).<ref name="pmid17586870">{{cite journal |pmid=17586870 |url=https://www.o-wm.com/content/regenerative-healing-fetal-skin-a-review-literature?page=0,11 |year=2007 |last1=Wilgus |first1=T. A. |title=Regenerative healing in fetal skin: A review of the literature |journal=Ostomy/Wound Management |volume=53 |issue=6 |pages=16–31; quiz 32–3 }}</ref> 
The myofibroblasts are absent in the first trimester in the embryonic stage where damage heals scar-free;<ref name=pmid17586870/>  in small incisional or excision wounds less than 2&nbsp;mm that also heal without scarring;<ref name=pmid17586870/> and in adult unwounded tissues where the fibroblast in itself is arrested; however, the myofibroblast is found in massive numbers in adult wound healing which heals with a scar.<ref name=myo2011033/>

The myofibroblasts make up a high proportion of the fibroblasts proliferating in the postembryonic wound at the onset of healing. In the rat model, for instance, myofibroblasts can constitute up to 70% of the fibroblasts,<ref name=myo201103>{{Cite web |author=Linge, Claire (Harrow, GB), Mackie, Ian Paul (Sheffield, GB) | title = Method of preventing or reducing scarring of human skin | quote = myofibroblasts become differentiated from other cells in the wound within a few days after the onset of healing, and in the rat model can reach a peak where about 70% of the fibroblastic cells present are of the myofibroblast phenotype. | publisher = freepatentsonline.com | url = http://www.freepatentsonline.com/y2005/0054608.html| access-date = 26 March 2010}}</ref> and is responsible for fibrosis on tissue.{{needs source|date=October 2024}} Generally, the myofibroblasts disappear from the wound within 30 days,<ref name=myo2011032/> but can remain in pathological cases in [[hypertrophy]], such as keloids.<ref name=myo2011033>{{Cite web |author=Linge, Claire (Harrow, GB), Mackie, Ian Paul (Sheffield, GB) | title = Method of preventing or reducing scarring of human skin| quote = These cells, which differentiate from the unwounded tissue cell type (fibroblasts), are responsible for laying down scar tissue. Indeed, myofibroblasts remain present in hypertrophic scars up to four years after the original wounding event. An in vitro assay was accordingly developed to identify actives which prevent or reduce myofibroblast formation and thus identify actives which are effective in reducing and/or preventing scar tissue formation. | publisher = freepatentsonline.com | url = http://www.freepatentsonline.com/y2005/0054608.html| access-date = 26 March 2010}}</ref><ref name=myo2011032>{{Cite web |author=Linge, Claire (Harrow, GB), Mackie, Ian Paul (Sheffield, GB) | title = Method of preventing or reducing scarring of human skin | quote = the number of myofibroblasts present in the forming scar tissue begins to reduce via apoptosis, until by about 30 days no myofibroblasts are obvious within the scar.| publisher = freepatentsonline.com | url = http://www.freepatentsonline.com/y2005/0054608.html| access-date = 26 March 2010}}</ref> Myofibroblasts have plasticity and in mice can be transformed into fat cells, instead of scar tissue, via the regeneration of hair follicles.<ref name=hairFatMyo>{{cite journal | title = Regeneration of fat cells from myofibroblasts during wound healing | last = Plikus |display-authors=etal | date = 5 January 2017 | journal = Science | pmid=28059714 | doi=10.1126/science.aai8792 | volume=355 | issue = 6326 | pmc=5464786 | pages=748–752| bibcode = 2017Sci...355..748P }}</ref><ref name=MyoFatRegen2017>{{cite journal | title = Repeal and Replace: Adipocyte Regeneration in Wound Repair. | last = Horsley, Watt | date = 6 April 2017 | journal = Cell Stem Cell | pmid=28388424 | doi=10.1016/j.stem.2017.03.015 | volume=20 | issue = 4 | pages=424–426| url = https://kclpure.kcl.ac.uk/portal/en/publications/repeal-and-replace-adipocyte-regeneration-in-wound-repair(bd32d20d-cd1f-4336-a20d-df4f2cda095b).html | type = Submitted manuscript | doi-access = free }}</ref>