title: Further proof of the existence of a non-neuronal cholinergic system in the human Achilles tendon: Presence of the AChRα7 receptor in tendon cells and cells in the peritendinous tissue.
abstract: Human tendon cells have the capacity for acetylcholine (ACh) production. It is not known if the tendon cells also have the potential for ACh breakdown, nor if they show expression of the nicotinic acetylcholine receptor AChRα7 (α7nAChR). Therefore, tendon tissue specimens from patients with midportion Achilles tendinopathy/tendinosis and from normal midportion Achilles tendons were examined. Reaction for the degradative enzyme acetylcholinesterase (AChE) was found in some tenocytes in only a few tendinopathy tendons, and was never found in those of control tendons. Tenocytes displayed more regularly α7nAChR immunoreactivity. However, there was a marked heterogeneity in the degree of this reaction within and between the specimens. α7nAChR immunoreactivity was especially pronounced for tenocytes showing an oval/widened appearance. There was a tendency that the magnitude of α7nAChR immunoreactivity was higher in tendinopathy tendons as compared to control tendons. A stronger α7nAChR immunoreactivity than seen for tenocytes was observed for the cells in the peritendinous tissue. It is likely that the α7nAChR may be an important part of an auto-and paracrine loop of non-neuronal ACh that is released from the tendon cells. The effects may be related to proliferative and blood vessel regulatory functions as well as features related to collagen deposition. ACh can furthermore be of importance in leading to anti-inflammatory effects in the peritendinous tissue, a tissue nowadays considered to be of great relevance for the tendinopathy process. Overall, the findings show that tendon tissue, a tissue known to be devoid of cholinergic innervation, is a tissue in which there is a marked non-neuronal cholinergic system.
authors.affiliation: Department of Integrative Medical Biology, Anatomy Section, Umeå University, Umeå, Sweden. Electronic address: sture.forsgren@umu.se.
authors.forename: Sture
authors.initials: S
authors.lastname: Forsgren
authors.affiliation: Department of Community Medicine and Rehabilitation, Section for Sports Medicine, Umeå University, Umeå, Sweden.
authors.forename: Håkan
authors.initials: H
authors.lastname: Alfredson
authors.affiliation: Department of Integrative Medical Biology, Anatomy Section, Umeå University, Umeå, Sweden; Department of Surgical and Perioperative Science, Section for Hand and Plastic Surgery, Umeå University, Umeå, Sweden.
authors.forename: Gustav
authors.initials: G
authors.lastname: Andersson
mesh_terms: D000125:Achilles Tendon / Q000166:cytology*; D000328:Adult; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D008297:Male; D008875:Middle Aged; D064569:alpha7 Nicotinic Acetylcholine Receptor / Q000235:genetics / Q000276:immunology / Q000378:metabolism*
chemical_list: D064569:alpha7 Nicotinic Acetylcholine Receptor
keywords: Achilles; Cholinergic; Nicotinic; Tendons; Tenocytes