Introduction We in our research group have previously noticed that the tenocytes of human tendons exhibit reaction for the enzyme choline acetyltransferase (ChAT).^1,4 That was especially the fact for tenocytes of tendinopathic tendons. The findings suggest that the cells can produce the signal substance acetylcholine (ACh). This is in line with findings that there is a non-neuronal cholinergic system in various other tissues, a system which can a number of important effects.³ This means that there in parallel with the classical neuronal cholinergic system is another cholinergic system which does not require presence of nerve structures in the tissue.

It is not known if there is also a potential for ACh degradation in tenocytes nor if the cells express the functionally important ACh-receptor named alpha7nAChR, which is a nicotinic ACh receptor known to be involved in various processes, including reparation processes. An important function for this receptor noted for other tissues is an anti-inflammatory effect.^2,5

Methods Achilles tendon tissue of patients suffering from Achilles tendinopathy (tendinosis) and from healthy individuals were examined. Immunohistochemical and histochemical methods for the detection of the degrading enzyme acetylcholinesterase (AChE) were used as were immunohistochemical methods for the delineation of alpha7nAChR reactions.

Results Alpha7nAChR immunmoreaction was to varying extents noticed for the tenocytes. The reactions were especially noteworthy for the tendon samples of patients suffering from Achilles tendinopathy. Tenocytes were also noted to express reactions for the ACh-degrading enzyme AChE.

Discussion The observations show that tenocytes are not only equipped with a potential for ACh production but also a potential for ACh degradation. Furtermore, tenocytes express the enzyme alpha7nAChR.

The findings of both ChAT and AChE for tenocytes suggest that there is an intricate balance between production and breakdown of ACh in tendon tissue. There is thus a possibility that produced ACh can be readily degradated. This then limits the presumed positive functions of the signal substance. In clinical practice, therefore, medications are used that decrease the amount of ACh in order to lead to an increased ACh effect. That includes medications used in Alzheimer's disease.

The findings of reactions for the alpha7nAChR imply that there is potential effect of ACh via functions on this receptor. This is of interest as the alpha7nAChR is involved in remodulation and anti-inflammatory processes in other tissues. This receptor is actually considered to be the most relevant receptor in bringing about the nowadays known anti-inflammation effect of ACh.

It is suggested that an elevation of alpha7nAChR influence in a situation like arthritis would be very helpful in this situation.

In total, the findings show that there are potentials of production/degradation of ACh in tendon tissue as well a potential of ACh effects via influences on the alpha7nAChR in this tissue. This means that a cholinergic system can be of importance in tendon tissue despite the non-existence of a cholinergic innervation.

References 1 Danielson, et al. Microsc Res Tech. 2006;69:808–819

2 de Jonge, Ulloa. British J Pharmacol. 151: 915–929

3 Kawashima, Fuji. J Pharmacol Sci. 2008;106:167–173

4 Spang, et al. Histol Histopathol. 2013;28: 623–632

5 Tracey. J Clinical Investigation. 2007;117:289–296