Presence of the neuropeptide Y1 receptor in tenocytes and blood vessel walls in the human Achilles tendon

Abstract

Background: Questions remain concerning the mechanisms of the development of chronic pain and impaired function of tendons (tendinosis). Aspects known to occur are cell proliferation, angiogenesis and altered blood flow regulation. Neuropeptide Y (NPY) is widely distributed in the body and has powerful effects in relation to these processes. NPY has its effects via the G-protein-coupled Y receptors. There is no information concerning the presence or absence of NPY receptors in Achilles tendons or other tendons.

Objective: To clarify the expression patterns of the NPY receptors Y1 and Y2 in normal and tendinosis Achilles tendons of humans.

Methods: Immunohistochemical methods were used. Examination on NPY was carried out in parallel.

Results: The tenocytes showed strong immunoreactions for the Y1 receptor. The immunoreactions were more intense in the tenocytes of tendinosis tendons than in non-tendinosis tendons. The rounded/oval tenocytes typically seen in tendinosis tendons exhibited marked Y1 receptor reactions on their exterior. Pronounced Y1 reactions were seen in the smooth muscle of the arterioles of both tendinosis and non-tendinosis tendons. No reactions for the Y2 receptor were noted. NPY was detected in nerve fascicles and in perivascular innervation.

Conclusions: This study shows that there is a morphological correlate for the occurrence of pronounced NPY effects via the Y1 receptor in both tenocytes, especially for tendinosis tendons, and blood vessel walls in the Achilles tendon. The findings are of particular interest as NPY is known to have proliferative, angiogenic and blood vessel-regulating effects. The effects of targeting the Y1 receptor in tendinosis is an interesting task to be evaluated further.