Journal Staff

BACKGROUND: It has been hypothesised that an upregulation of the neuropeptide substance P (SP) and its preferred receptor, the neurokinin-1 receptor (NK-1 R), is a causative factor in inducing tenocyte hypercellularity, a characteristic of tendinosis, through both proliferative and antiapoptotic stimuli. We have demonstrated earlier that SP stimulates proliferation of human tenocytes in culture. AIM: The aim of this study was to investigate whether SP can mediate an antiapoptotic effect in tumour necrosis factor-α (TNF-α)-induced apoptosis of human tenocytes in vitro. RESULTS: A majority (approximately 75%) of tenocytes in culture were immunopositive for TNF Receptor-1 and TNF Receptor-2. Exposure of the cells to TNF-α significantly decreased cell viability, as shown with crystal violet staining. TNF-α furthermore significantly increased the amount of caspase-10 and caspase-3 mRNA, as well as both BID and cleaved-poly ADP ribosome polymerase (c-PARP) protein. Incubation of SP together with TNF-α resulted in a decreased amount of BID and c-PARP, and in a reduced lactate dehydrogenase release, as compared to incubation with TNF-α alone. The SP effect was blocked with a NK-1 R inhibitor. DISCUSSION: This study shows that SP, through stimulation of the NK-1 R, has the ability to reduce TNF-α-induced apoptosis of human tenocytes. Considering that SP has previously been shown to stimulate tenocyte proliferation, the study confirms SP as a potent regulator of cell-turnover in tendon tissue, capable of stimulating hypercellularity through different mechanisms. This gives further support for the theory that the upregulated amount of SP seen in tendinosis could contribute to hypercellularity

Human tenocytes are stimulated to proliferate by acetylcholine through an EGFR signalling pathway

Studies of human patellar and Achilles tendons have shown that primary tendon fibroblasts (tenocytes) not only have the capacity to produce acetylcholine (ACh) but also express muscarinic ACh receptors (mAChRs) through which ACh can exert its effects. In patients with tendinopathy (chronic tendon pain) with tendinosis, the tendon tissue is characterised by hypercellularity and angiogenesis, both of which might be influenced by ACh. In this study, we have tested the hypothesis that ACh increases the proliferation rate of tenocytes through mAChR stimulation and have examined whether this mechanism operates via the extracellular activation of the epidermal growth factor receptor (EGFR), as shown in other fibroblastic cells. By use of primary human tendon cell cultures, we identified cells expressing vimentin, tenomodulin and scleraxis and found that these cells also contained enzymes related to ACh synthesis and release (choline acetyltransferase and vesicular acetylcholine transporter). The cells furthermore expressed mAChRs of several subtypes. Exogenously administered ACh stimulated proliferation and increased the viability of tenocytes in vitro. When the cells were exposed to atropine (an mAChR antagonist) or the EGFR inhibitor AG1478, the proliferative effect of ACh decreased. Western blot revealed increased phosphorylation, after ACh stimulation, for both EGFR and the extracellular-signal-regulated kinases 1 and 2. Given that tenocytes have been shown to produce ACh and express mAChRs, this study provides evidence of a possible autocrine loop that might contribute to the hypercellularity seen in tendinosis tendon tissue

Substance P Is a Mechanoresponsive, Autocrine Regulator of Human Tenocyte Proliferation

It has been hypothesised that substance P (SP) may be produced by primary fibroblastic tendon cells (tenocytes), and that this production, together with the widespread distribution of the neurokinin-1 receptor (NK-1 R) in tendon tissue, could play an important role in the development of tendinopathy, a condition of chronic tendon pain and thickening. The aim of this study was to examine the possibility of endogenous SP production and the expression of NK-1 R by human tenocytes. Because tendinopathy is related to overload, and because the predominant tissue pathology (tendinosis) underlying early tendinopathy is characterized by tenocyte hypercellularity, the production of SP in response to loading/strain and the effects of exogenously administered SP on tenocyte proliferation were also studied. A cell culture model of primary human tendon cells was used. The vast majority of tendon cells were immunopositive for the tenocyte/fibroblast markers tenomodulin and vimentin, and immunocytochemical counterstaining revealed that positive immunoreactions for SP and NK-1 R were seen in a majority of these cells. Gene expression analyses showed that mechanical loading (strain) of tendon cell cultures using the FlexCell© technique significantly increased the mRNA levels of SP, whereas the expression of NK-1 R mRNA decreased in loaded as compared to unloaded tendon cells. Reduced NK-1 R protein was also observed, using Western blot, after exogenously administered SP at a concentration of 10−7 M. SP exposure furthermore resulted in increased cell metabolism, increased cell viability, and increased cell proliferation, all of which were found to be specifically mediated via the NK-1 R; this in turn involving a common mitogenic cell signalling pathway, namely phosphorylation of ERK1/2. This study indicates that SP, produced by tenocytes in response to mechanical loading, may regulate proliferation through an autocrine loop involving the NK-1 R

Akt-mediated anti-apoptotic effects of substance P in Anti-Fas-induced apoptosis of human tenocytes

Substance P (SP) and its receptor, the neurokinin-1 receptor (NK-1 R), are expressed by human tenocytes, and they are both up-regulated incases of tendinosis, a condition associated with excessive apoptosis. It is known that SP can phosphorylate/activate the protein kinase Akt,which has anti-apoptotic effects. This mechanism has not been studied for tenocytes. The aims of this study were to investigate if Anti-Fastreatment is a good apoptosis model for human tenocytes in vitro, if SP protects from Anti-Fas-induced apoptosis, and by which mechanismsSP mediates an anti-apoptotic response. Anti-Fas treatment resulted in a time- and dose-dependent release of lactate dehydrogenase (LDH), i.e.induction of cell death, and SP dose-dependently reduced the Anti-Fas-induced cell death through a NK-1 R specific pathway. The same trendwas seen for the TUNEL assay, i.e. SP reduced Anti-Fas-induced apoptosis via NK-1 R. In addition, it was shown that SP reduces Anti-Fas-induced decrease in cell viability as shown with crystal violet assay. Protein analysis using Western blot confirmed that Anti-Fas inducescleavage/activation of caspase-3 and cleavage of PARP; both of which were inhibited by SP via NK-1 R. Finally, SP treatment resulted in phosphorylation/activation of Akt as shown with Western blot, and it was confirmed that the anti-apoptotic effect of SP was, at least partly, inducedthrough the Akt-dependent pathway. In conclusion, we show that SP reduces Anti-Fas-induced apoptosis in human tenocytes and that this antiapoptoticeffect of SP is mediated through NK-1 R and Akt-specific pathways

Acetylcholine enhances keratocyte proliferation through muscarinic receptor activation.

Acetylcholine (ACh), a classical neurotransmitter, has been shown to be present in various non-neuronal cells, including cells of the eye, such as corneal epithelium and endothelium, and to have widespread physiological effects such as cytoskeleton reorganization, cellular proliferation, differentiation, and apoptosis. The aim of this study was to investigate the effect of ACh on corneal keratocyte proliferation, and the underlying mechanisms, in order to explore its possible effect in corneal wound healing. Primary culture of human keratocytes was established from donated corneas. Cell viability and fraction of proliferating cells were detected by MTS assay and BrdU incorporation ELISA, respectively. Expression of proliferative markers, PCNA and Ki-67, was detected by western blot and immunocytochemistry. Activation of the MAPK/Erk signaling pathway and its involvement in ACh-enhanced proliferation was determined by western blot analysis, MTS, and BrdU ELISA. We found that ACh enhanced keratocyte proliferation even at low concentrations. Stimulation of proliferation was mediated through activation of muscarinic ACh receptors (mAChRs). Western blot analysis revealed that ACh stimulation of keratocytes upregulated the expression of PCNA and Ki-67, and Ki-67 immunocytochemistry showed that ACh-treated cells were in an active phase of the cell cycle. ACh activated MAPK signaling, and this step was crucial for the ACh-enhanced proliferation, as inhibition of the MAPK pathway resulted in ACh having no proliferative effect. In conclusion, ACh enhances keratocyte proliferation and might thus play a role in proper corneal wound healing

Antiapoptotic Effect of Acetylcholine in Fas-Induced Apoptosis in Human Keratocytes

PURPOSE. To investigate the possible antiapoptotic effect of acetylcholine (ACh) in Fas-mediated apoptosis of primary human keratocytes in vitro, and to explore the underlying mechanism. METHODS. Primary human keratocytes were isolated from healthy corneas. Fas ligand (FasL) was used to induce apoptosis in keratocytes. Cell death was assessed by ELISA. Activity of caspase-3, -7, -8, and -9 was measured with luminescent caspase activity assays. Expression of nuclear factor-kappa B (NF-kappa B) gene was assessed with RT-quantitative (q)PCR. Cytochrome c release apoptosis assay kit was used to extract mitochondria and cytosol. Cytochrome c release, cleavage of Bid, and expression of B-cell lymphoma 2 (Bcl-2) were determined by Western blot. RESULTS. Cell death ELISA revealed that ACh is able to reduce Fas-induced apoptosis in keratocytes. Analysis of the activity of effector caspases-3 and -7 showed that ACh, when added to Fas-treated cells, decreases the activation of both these enzymes. The activity of initiator caspases -8 and -9 also decreased when ACh was added to Fas-treated cells. This antiapoptotic effect of ACh was dependent on ACh concentration and activation of muscarinic ACh receptors. Analysis of the antiapoptotic mechanisms triggered by ACh showed that ACh downregulates expression of FasL-induced NF-kappa B RNA expression, upregulates expression of antiapoptotic protein Bcl-2, downregulates expression of proapoptotic protein Bad, reduces cytochrome c release, and prevents proapoptotic Bid protein cleavage. CONCLUSIONS. Acetylcholine has an antiapoptotic effect in a Fas-apoptosis model of human primary keratocytes in vitro. It is therefore possible that ACh may play a role in corneal wound healing, by modulating its initiation phase

Activation of NF-κB signaling via cytosolic mitochondrial RNA sensing in kerotocytes with mitochondrial DNA common deletion

Scar formation as a result of corneal wound healing is a leading cause of blindness. It is a challenge to understand why scar formation is more likely to occur in the central part of the cornea as compared to the peripheral part. The purpose of this study was to unravel the underlying mechanisms. We applied RNA-seq to uncover the differences of expression profile in keratocytes in the central/peripheral part of the cornea. The relative quantity of mitochondrial RNA was measured by multiplex qPCR. The characterization of mitochondrial RNA in the cytoplasm was confirmed by immunofluoresence microscope and biochemical approach. Gene expression was analyzed by western blot and RT qPCR. We demonstrate that the occurrence of mitochondrial DNA common deletion is greater in keratocytes from the central cornea as compared to those of the peripheral part. The keratocytes with CD have elevated oxidative stress levels, which leads to the leakage of mitochondrial double-stranded RNA into the cytoplasm. The cytoplasmic mitochondrial double-stranded RNA is sensed by MDA5, which induces NF-κB activation. The NF-κB activation thereafter induces fibrosis-like extracellular matrix expressions and IL-8 mRNA transcription. These results provide a novel explanation of the different clinical outcome in different regions of the cornea during wound healing

The tenocyte phenotype of human primary tendon cells in vitro is reduced by glucocorticoids

Background: The use of corticosteroids (e.g., dexamethasone) as treatment for tendinopathy has recently been questioned as higher risks for ruptures have been observed clinically. In vitro studies have reported that dexamethasone exposed tendon cells, tenocytes, show reduced cell viability and collagen production. Little is known about the effect of dexamethasone on the characteristics of tenocytes. Furthermore, there are uncertainties about the existence of apoptosis and if the reduction of collagen affects all collagen subtypes. Methods: We evaluated these aspects by exposing primary tendon cells to dexamethasone (Dex) in concentrations ranging from 1 to 1000 nM. Gene expression of the specific tenocyte markers scleraxis (Scx) and tenomodulin (Tnmd) and markers for other mesenchymal lineages, such as bone (Alpl, Ocn), cartilage (Acan, Sox9) and fat (Cebpα, Pparg) was measured via qPCR. Cell viability and proliferation was calculated using a MTS Assay. Cell death was measured by LDH assay and cleaved caspase-3 using Western Blot. Gene expression of collagen subtypes Col1, Col3 and Col14 was analyzed using qPCR. Results: Stimulation with Dex decreased cell viability and LDH levels. Dex also induced a significant reduction of Scx gene expression and a marked loss of fibroblast like cell shape. The mRNA for all examined collagen subtypes was found to be down-regulated. Among non-tendinous genes only Pparg was significantly increased, whereas Acan, Alpl and Sox9 were reduced. Conclusions: These results indicate a Dex induced phenotype drift of the tenocytes by reducing scleraxis expression. Reduction of several collagen subtypes, but not cell death, seems to be a feature of Dex induced tissue degeneration

Acetylcholine enhances keratocyte proliferation through muscarinic receptor activation.

Acetylcholine (ACh), a classical neurotransmitter, has been shown to be present in various non-neuronal cells, including cells of the eye, such as corneal epithelium and endothelium, and to have widespread physiological effects such as cytoskeleton reorganization, cellular proliferation, differentiation, and apoptosis. The aim of this study was to investigate the effect of ACh on corneal keratocyte proliferation, and the underlying mechanisms, in order to explore its possible effect in corneal wound healing. Primary culture of human keratocytes was established from donated corneas. Cell viability and fraction of proliferating cells were detected by MTS assay and BrdU incorporation ELISA, respectively. Expression of proliferative markers, PCNA and Ki-67, was detected by western blot and immunocytochemistry. Activation of the MAPK/Erk signaling pathway and its involvement in ACh-enhanced proliferation was determined by western blot analysis, MTS, and BrdU ELISA. We found that ACh enhanced keratocyte proliferation even at low concentrations. Stimulation of proliferation was mediated through activation of muscarinic ACh receptors (mAChRs). Western blot analysis revealed that ACh stimulation of keratocytes upregulated the expression of PCNA and Ki-67, and Ki-67 immunocytochemistry showed that ACh-treated cells were in an active phase of the cell cycle. ACh activated MAPK signaling, and this step was crucial for the ACh-enhanced proliferation, as inhibition of the MAPK pathway resulted in ACh having no proliferative effect. In conclusion, ACh enhances keratocyte proliferation and might thus play a role in proper corneal wound healing