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Alpha-2 adrenergic stimulation triggers Achilles tenocyte hypercellularity: comparison between two model systems
Umeå universitet, Medicinska fakulteten, Institutionen för integrativ medicinsk biologi (IMB), Anatomi.ORCID-id: 0000-0002-6091-3982
Umeå universitet, Medicinska fakulteten, Institutionen för integrativ medicinsk biologi (IMB), Anatomi.
Umeå universitet, Medicinska fakulteten, Institutionen för integrativ medicinsk biologi (IMB), Anatomi. Department of Physical Therapy, University of British Columbia and Centre for Hip Health and Mobility, Vancouver Coastal Health and Research Institute, Vancouver, British Columbia, Canada.
Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Idrottsmedicin.
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2013 (Engelska)Ingår i: Scandinavian Journal of Medicine and Science in Sports, ISSN 0905-7188, E-ISSN 1600-0838, Vol. 23, nr 6, s. 687-696Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The histopathology of tendons with painful tendinopathy is often tendinosis, a fibrosis-like condition of unclear pathogenesis characterized by tissue changes including hypercellularity. The primary tendon cells (tenocytes) have been shown to express adrenoreceptors (mainly alpha-2A) as well as markers of catecholamine production, particularly in tendinosis. It is known that adrenergic stimulation can induce proliferation in other cells. The present study investigated the effects of an exogenously administered alpha-2 adrenergic agonist in an established in vivo Achilles tendinosis model (rabbit) and also in an in vitro human tendon cell culture model. The catecholamine producing enzyme tyrosine hydroxylase and the alpha-2A-adrenoreceptor (α(2A) AR) were expressed by tenocytes, and alpha-2 adrenergic stimulation had a proliferative effect on these cells, in both models. The proliferation was inhibited by administration of an α(2A) AR antagonist, and the in vitro model further showed that the proliferative alpha-2A effect was mediated via a mitogenic cell signaling pathway involving phosphorylation of extracellular-signal-regulated kinases 1 and 2. The results indicate that catecholamines produced by tenocytes in tendinosis might contribute to the proliferative nature of the pathology through stimulation of the α(2A) AR, pointing to a novel target for future therapies. The study furthermore shows that animal models are not necessarily required for all aspects of this research.

Ort, förlag, år, upplaga, sidor
John Wiley & Sons, 2013. Vol. 23, nr 6, s. 687-696
Nyckelord [en]
tendinopathy, exercise, cytokines, neurotrophins, alpha(2A) adrenoreceptor, Tendinosis, Achilles tendon
Nationell ämneskategori
Idrottsvetenskap Mikrobiologi inom det medicinska området
Identifikatorer
URN: urn:nbn:se:umu:diva-53462DOI: 10.1111/j.1600-0838.2011.01442.xISI: 000330192000007PubMedID: 22292987OAI: oai:DiVA.org:umu-53462DiVA, id: diva2:512364
Forskningsfinansiär
Vetenskapsrådet, 521-2009-2921Centrum för Idrottsforskning, 54/10, P2011-0170Tillgänglig från: 2012-03-27 Skapad: 2012-03-27 Senast uppdaterad: 2019-02-22Bibliografiskt granskad
Ingår i avhandling
1. Neuropeptide and catecholamine effects on tenocytes in tendinosis development: studies on two model systems with focus on proliferation and apoptosis
Öppna denna publikation i ny flik eller fönster >>Neuropeptide and catecholamine effects on tenocytes in tendinosis development: studies on two model systems with focus on proliferation and apoptosis
2013 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Background: Achilles tendinopathy is a common clinical syndrome of chronic Achilles tendon pain combined with thickening of the tendon and impaired tendon function. Tendinopathy is often, but not always, induced by mechanical overload, and is frequently accompanied by abnormalities at the tissue level, such as hypercellularity and angiogenesis, in which case the condition is called tendinosis. In tendinosis, there are no signs of intratendinous inflammation, but occasionally increased apoptosis is observed. Tendinosis is often hard to treat and its pathogenesis is still not clear. Recently, a new hypothesis has gained support, suggesting a biochemical model based on the presence of a non-neuronal production of classically neuronal signal substances by the primary tendon cells (tenocytes) in tendinosis. The possible functional importance of these signal substances in tendons is unknown and needs to be studied. In particular, the neuropeptide substance P (SP) and catecholamines are of interest in this regard, since these substances have been found to be up-regulated in tendinosis. As both SP and catecholamines are known to exert effects in other tissues resulting in changes similar to those characteristic of tendinosis, it is possible that they have a role in tendinosis development. It is furthermore unknown what elicits the increased intratendinous neuropeptide production in tendinosis, but given that tendon overload is a prominent riskfactor, it is possible that mechanical stimuli are involved.

The hypothesis of this thesis work was that intratendinous production of SP is up-regulated in response to load of Achilles tendons/tenocytes, and thatstimulation of the preferred SP receptor, the neurokinin-1 receptor (NK-1 R), aswell as stimulation of the catecholamine α2 adrenoreceptors, contribute to the hypercellularity seen in tendinosis, via increased proliferation and/or decreased apoptosis, and that SP stimulates tendon angiogenesis. The purpose of the studies was to test this hypothesis. To achieve this, two model systems were used: One in vivo (rabbit Achilles tendon overload model of tendinosis) and one in vitro (human primary Achilles tendon cell culture model).

Results: In the rabbit Achilles tendon tissue, SP and NK-1 R expression was extensive in the blood vessel walls, but also to some extent seen in the tenocytes. Quantification of endogenously produced SP in vivo confirmed intratendinous production of the peptide. The production of SP by human tendon cells in vitro was furthermore demonstrated. The catecholamine synthesizing enzyme tyrosine hydroxylase (TH), as well as the α2A adrenoreceptor (α2A AR), were detected in the tenocytes, both in vivo in the rabbit tissue and in vitro in the human tendon cells. As a response to mechanical loading in the in vivo model, the intratendinous levels of SP increased, and this elevation was found to precede distinct tendinosis changes. The in vitro model demonstrated the same response to load, i.e. an increased SP expression, but in this case also a decrease in the NK-1 R expression. In the in vivo model, exogenously administered SP, as well as clonidine (an α2 AR agonist), accelerated tenocyte hypercellularity, an effect that was not seen when administrating a specific α2A AR antagonist. Exogenous administration of SP also resulted in intratendinous angiogenesis and paratendinous inflammation. In the in vitro model, both SP and clonidine had proliferative effects on the human tenocytes, specifically mediated via NK-1R and α2A AR, respectively; both of which in turn involved activation/phosphorylation of the extracellular signal-regulated kinases 1 and 2 (ERK1/2). Exogenously administered SP, in Anti-Fas induced apoptosis of the tenocytes in vitro, confirmed SP to have an anti-apoptotic effect on these cells. This effect was specifically mediated via NK-1 R and the known anti-apoptotic Akt pathway.

Conclusions: In summary, this thesis concludes that stimulation of NK-1 R and α2A AR on tenocytes, both in vitro and in vivo, mediates significant cell signalling effects leading to processes known to occur in tendinosis, including hypercellularity. The pathological role of the hypercellularity in tendinosis is still unclear, but it is likely to affect collagen metabolism/turnover and arrangement, and thereby indirectly tendon biomechanical function. Additional evidence is here provided showing that SP not only causes tenocyte proliferation, but also contributes to anti-apoptotic events. Furthermore, it was concluded that SP may be involved in the development of tendinosis, since its production is increased in response to load, preceding tendinosis, and since SP accelerates tendinosis changes, through some mechanistic pathways here delineated. These findings suggest that inhibition of SP, and possibly also catecholamines, could be beneficial in the reconstitution/normalization of tendon structure in tendinosis.

Ort, förlag, år, upplaga, sidor
Umeå: Umeå Universitet, 2013. s. 80
Serie
Umeå University medical dissertations, ISSN 0346-6612 ; 1572
Nyckelord
substance P, neurotransmitter, tendinopathy, overuse injury, rabbit, tendon cell, Achilles tendon
Nationell ämneskategori
Cell- och molekylärbiologi
Identifikatorer
urn:nbn:se:umu:diva-70193 (URN)978-91-7459-633-5 (ISBN)978-91-7459-634-2 (ISBN)
Disputation
2013-06-05, sal BiA201, Biologihuset, Umeå universitet, Umeå, 09:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2013-05-15 Skapad: 2013-05-07 Senast uppdaterad: 2019-02-22Bibliografiskt granskad

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