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Published on: January 21, 2015
Spinal Cathepsin S promotes visceral hypersensitivity via FKN/CX3CR1/p38 MAPK signaling pathways
Pei Sun1,2, Wei Lin3, Yuxuan Weng1
1Pain Research Institute, School of Basic Medical Sciences, Fujian Provincial Key Laboratory of Brain Aging and Neurodegenerative Diseases, Fujian Medical University, Fuzhou, China.
Background:
Irritable bowel syndrome (IBS) is one of the typical representatives of chronic functional visceral pain that lacks effective treatment. Recently, attention has been given to the role of microglia in IBS, particularly the activation of spinal microglia and the subsequent release of Cathepsin S (Cat S), a proteolytic enzyme. However, the specific role of spinal Cat S in IBS remains to be elucidated. The purpose of this study is to investigate the mechanisms underlying the regulation of visceral hypersensitivity in IBS-like rats by Cat S.
Methods:
An IBS-like rat model was developed, and visceral sensitivity was tested via the electromyographic (EMG) response to colorectal distention (CRD) and pain threshold. Western blot and immunofluorescence were used to examine the expressions of proteins. The effects of inhibitors or neutralizing antibodies on visceral pain and the downstream molecular expressions were detected. The open-field test was performed to evaluate locomotor activity and anxiety-like behaviors in rats.
Results:
We discovered that spinal Cat S was upregulated and colocalized with microglia in IBS-like rats. Treatment with LY3000328, a selective inhibitor of Cat S, dose-dependently down-regulated EMG amplitude and Fractalkine (FKN) expression, indicating that Cat S regulated visceral hypersensitivity via activating FKN in IBS-like rats. Furthermore, the expressions of FKN, CX3CR1, and p-p38 MAPK were elevated in IBS-like rats whereas inhibition of these molecules could alleviate visceral pain. Moreover, pharmacological inhibitor experiments suggested the activation of CX3CR1 by FKN facilitated p38 MAPK phosphorylation, which in turn promoted Cat S expression in IBS-like rats.
Conclusions:
Neonatal adverse stimulation might enhance the expression of spinal microglial Cat S, thereby activating the FKN/CX3CR1/p38 MAPK pathway and lead to visceral hypersensitivity in IBS-like rats. As a selective inhibitor of Cat S, LY3000328 could become a potential therapeutic option for IBS.
Insights
Spinal Cathepsin S (Cat S) activation in microglia contributes to visceral hypersensitivity in irritable bowel syndrome (IBS)-like rats. Inhibiting Cat S may offer a new therapeutic approach for IBS.
Area of Science:
- Neuroscience
- Gastroenterology
- Immunology
Background:
- Irritable bowel syndrome (IBS) is a chronic functional visceral pain disorder with limited effective treatments.
- Spinal microglia activation and Cathepsin S (Cat S) release are implicated in IBS pathophysiology.
- The precise role of spinal Cat S in IBS-related visceral hypersensitivity requires further investigation.
Purpose of the Study:
- To investigate the role of spinal Cat S in the mechanisms of visceral hypersensitivity in a rat model of IBS.
- To elucidate the molecular pathways regulated by Cat S in the context of IBS-like symptoms.
Main Methods:
- Development of an IBS-like rat model and assessment of visceral sensitivity using electromyography (EMG) during colorectal distention (CRD).
- Analysis of protein expression using Western blot and immunofluorescence.
- Evaluation of the effects of Cat S inhibitors and pathway-specific inhibitors on visceral pain and molecular markers.
- Assessment of behavioral changes, including locomotor activity and anxiety, using the open-field test.
Main Results:
- Spinal Cat S expression was upregulated and colocalized with microglia in IBS-like rats.
- Selective Cat S inhibition (LY3000328) dose-dependently reduced EMG amplitude and Fractalkine (FKN) expression.
- Elevated expressions of FKN, CX3CR1, and phosphorylated p38 mitogen-activated protein kinase (p-p38 MAPK) were observed in IBS-like rats, and their inhibition alleviated visceral pain.
- FKN-induced CX3CR1 activation promoted p38 MAPK phosphorylation, which in turn enhanced Cat S expression, suggesting a positive feedback loop.
Conclusions:
- Neonatal adverse stimulation may increase spinal microglial Cat S, activating the FKN/CX3CR1/p38 MAPK pathway and causing visceral hypersensitivity in IBS-like rats.
- The selective Cat S inhibitor LY3000328 demonstrates potential as a therapeutic agent for IBS by targeting this pathway.
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