The effects of substance P and acetylcholine on human tenocyte proliferation converge mechanistically via TGF-β1

Abstract

Previous in vitro studies on human tendon cells (tenocytes) have demonstrated that the exogenous administration of substance P (SP) and acetylcholine (ACh) independently result in tenocyte proliferation, which is a prominent feature of tendinosis. Interestingly, the possible link between SP and ACh has not yet been explored in human tenocytes. Recent studies in other cell types demonstrate that both SP and ACh independently upregulate TGF-β1 expression via their respective receptors, the neurokinin 1 receptor (NK-1R) and muscarinic ACh receptors (mAChRs). Furthermore, TGF-β1 has been shown to downregulate NK-1R expression in human keratocytes. The aim of this study was to examine if TGF-β1 is the intermediary player involved in mediating the proliferative pathway shared by SP and ACh in human tenocytes. The results showed that exogenous administration of SP and ACh both caused significant upregulation of TGF-β1 at the mRNA and protein levels. Exposing cells to TGF-β1 resulted in increased cell viability of tenocytes, which was blocked in the presence of the TGFβRI/II kinase inhibitor. In addition, the proliferative effects of SP and ACh on tenocytes were reduced by the TGFβRI/II kinase inhibitor; this supports the hypothesis that the proliferative effects of these signal substances are mediated via the TGF-β axis. Furthermore, exogenous TGF-β1 downregulated NK-1R and mAChRs expression at both the mRNA and protein levels, and these effects were negated by simultaneous exposure to the TGFβRI/II kinase inhibitor, suggesting a negative feedback loop. In conclusion, the results indicate that TGF-β1 is the intermediary player through which the proliferative actions of both SP and ACh converge mechanistically.

Sustained Exposure of Substance P Causes Tendinopathy

“…Using in vitro and in vivo experiments, we tested our hypothesis that the duration of SP exposure determines its effect on the tendons. While brief exposure to SP is closely related to tendon healing, repetitive long-term exposure is strongly linked to the development of tendinopathy [ 22 , 23 ]. Our quantification using different histological factors and analysis of varying tendon strengths after injection of SP revealed that SP is a cause of tendinopathy.…”

Risk Factors for Shoulder Stiffness: Current Concepts

“…Lastly, an increase in substance P has been reported in SS: this may represent an early element of the fibrotic cascade, since substance P upregulates TGF-β and promotes neo-angiogenesis, fibroblasts proliferation, and contraction, without directly altering ECM synthesis. 12 A myofibroblast-mast cell-neuropeptide axis has been described, in which the interaction of substance P with the resident mast cells in the cellular microenvironment is involved in fibrosis progression. 13 …”

Biological Amnion Prevents Flexor Tendon Adhesion in Zone II: A Controlled, Multicentre Clinical Trial

“…As early as in 1913, stem used the amniotic membrane for skin burn and ulcer wound transplantation. Subsequently, the amniotic membrane was used in ophthalmology, neurosurgery, and gynaecology as a dressing [17–19]. Studies have found that human amniotic membrane cells present the characteristics of embryonic stem cells and are also differentiated into three different types of embryonic cells; amniotic membrane cells show low immunogenicity and immunosuppressive effects and do not induce rejection or tumorigenicity after transplantation.…”