Effect of osmotic stress on the expression of TRPV4 and BKCa channels and possible interaction with ERK1/2 and p38 in cultured equine chondrocytes.
Abstract: The metabolic activity of articular chondrocytes is influenced by osmotic alterations that occur in articular cartilage secondary to mechanical load. The mechanisms that sense and transduce mechanical signals from cell swelling and initiate volume regulation are poorly understood. The purpose of this study was to investigate how the expression of two putative osmolyte channels [transient receptor potential vanilloid 4 (TRPV4) and large-conductance Ca(2+)-activated K(+) (BKCa)] in chondrocytes is modulated in different osmotic conditions and to examine a potential role for MAPKs in this process. Isolated equine articular chondrocytes were subjected to anisosmotic conditions, and TRPV4 and BKCa channel expression and ERK1/2 and p38 MAPK protein phosphorylation were investigated using Western blotting. Results indicate that the TRPV4 channel contributes to the early stages of hypo-osmotic stress, while the BKCa channel is involved in responding to elevated intracellular Ca(2+) and mediating regulatory volume decrease. ERK1/2 is phosphorylated by hypo-osmotic stress (P < 0.001), and p38 MAPK is phosphorylated by hyperosmotic stress (P < 0.001). In addition, this study demonstrates the importance of endogenous ERK1/2 phosphorylation in TRPV4 channel expression, where blocking ERK1/2 by a specific inhibitor (PD98059) prevented increased levels of the TRPV4 channel in cells exposed to hypo-osmotic stress and decreased TRPV4 channel expression to below control levels in iso-osmotic conditions (P < 0.001).
Copyright © 2014 the American Physiological Society.
Publication Date: 2014-03-26 PubMed ID: 24671100DOI: 10.1152/ajpcell.00287.2013Google Scholar: Lookup
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Summary
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The research investigates the effects of varied osmotic conditions on certain ion channels in cartilage cells, and explores how changes in these conditions may potentially signal volume regulation – responses essential for the functioning of these cells under physical stress.
Understanding the Research
In order to understand this study, it is important to breakdown its key components:
- Articular chondrocytes are the only cells found in articular cartilage—the tissue responsible for smooth movement between joints. These cells maintain the cartilage’s structure and respond to its environment, which often involves alternating periods of loading and unloading that cause fluctuations in osmotic pressure.
- Ion channels TRPV4 and BKCa play a crucial role in maintaining cellular volume and function under such varied osmotic conditions.
- ERK1/2 and p38 MAPK are signaling molecules (MAPK protoins) that facilitate communication within cells, playing a critical role in converting external stimuli into a wide range of cellular responses.
Purpose and Methodology of the Study
The purpose of this study was to understand the relationships between osmotic stress—caused by the loading and unloading of joint pressure—ion channels, and signaling proteins within articular chondrocytes. The researchers isolated these cells from horses and subjected the cells to various osmotic conditions. Using a technique called Western blotting, they then investigated changes in the expression of TRPV4 and BKCa channels and the phosphorylation of ERK1/2 and p38 MAPK proteins.
Findings
The researchers found that:
- Expression of the TRPV4 ion channel is associated with the early stages of hypo-osmotic stress, a condition of lower osmotic pressure.
- The BKCa ion channel is activated in response to increased intracellular calcium levels, and helps regulate cell volume.
- ERK1/2 is phosphorylated under hypo-osmotic stress, while p38 MAPK is phosphorylated under hyperosmotic stress—conditions of higher osmotic pressure.
- When ERK1/2 phosphorylation is inhibited, the TRPV4 channel levels drop below average under iso-osmotic conditions, indicating ERK1/2’s role in the expression of this ion channel.
The results suggest these ion channels and signaling molecules interact complexly and significantly in response to different osmotic conditions in joint cartilage, highlighting potential pathways for maintaining joint health and potential areas for therapeutic intervention.
Cite This Article
APA
Hdud IM, Mobasheri A, Loughna PT.
(2014).
Effect of osmotic stress on the expression of TRPV4 and BKCa channels and possible interaction with ERK1/2 and p38 in cultured equine chondrocytes.
Am J Physiol Cell Physiol, 306(11), C1050-C1057.
https://doi.org/10.1152/ajpcell.00287.2013 Publication
Researcher Affiliations
- School of Veterinary Medicine and Science, Faculty of Medicine and Health Sciences, The University of Nottingham, Sutton Bonington Campus, Leicestershire, United Kingdom;
- School of Veterinary Medicine and Science, Faculty of Medicine and Health Sciences, The University of Nottingham, Sutton Bonington Campus, Leicestershire, United Kingdom; Medical Research Council-Arthritis Research UK Centre for Musculoskeletal Ageing Research, Nottingham, United Kingdom; Arthritis Research UK Centre for Sport, Exercise and Osteoarthritis, Arthritis Research UK Pain Centre, Queen's Medical Centre, Nottingham, United Kingdom; and Center of Excellence in Genomic Medicine Research (CEGMR), King Fahd Medical Research Center (KFMRC), King AbdulAziz University, Jeddah, Kingdom of Saudi Arabia.
- School of Veterinary Medicine and Science, Faculty of Medicine and Health Sciences, The University of Nottingham, Sutton Bonington Campus, Leicestershire, United Kingdom; Medical Research Council-Arthritis Research UK Centre for Musculoskeletal Ageing Research, Nottingham, United Kingdom; paul.loughna@nottingham.ac.uk.
MeSH Terms
- Animals
- Calcium / metabolism
- Cell Size / drug effects
- Cells, Cultured
- Chondrocytes / drug effects
- Chondrocytes / metabolism
- Enzyme Inhibitors / pharmacology
- Female
- Gene Expression Regulation
- Horses
- Large-Conductance Calcium-Activated Potassium Channel alpha Subunits / biosynthesis
- MAP Kinase Signaling System / drug effects
- MAP Kinase Signaling System / physiology
- Male
- Osmotic Pressure / drug effects
- Osmotic Pressure / physiology
- Protein Binding / physiology
- TRPV Cation Channels / biosynthesis
- p38 Mitogen-Activated Protein Kinases / metabolism
Citations
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