The effect of O2 tension on pH homeostasis in equine articular chondrocytes.
Abstract: To determine the effects of varying O(2) on pH homeostasis, based on the hypothesis that the function of articular chondrocytes is best understood at realistic O(2) tensions. Methods: Cartilage from equine metacarpophalangeal/tarsophalangeal joints was digested with collagenase to isolate chondrocytes, and then loaded with the pH-sensitive fluorophore 2',7'-bis-2-(carboxyethyl)-5(6)-carboxylfluorescein. The radioisotope(22)Na(+) was used to determine the kinetics of Na(+)/H(+) exchange (NHE) and the activity of the Na(+)/K(+) pump, and ATP levels were assessed with luciferin assays. Levels of reactive oxygen species (ROS) were determined using 2',7'-dichlorofluorescein diacetate. Results: The pH homeostasis was unaffected when comparing tissue maintained at 20% O(2) (the level in water-saturated air at 37 degrees C) with that at 5% O(2) (which approximates the normal level in healthy cartilage); however, an O(2) tension of <5% caused a fall in intracellular pH (pH(i)) and slowed pH(i) recovery following acidification, an effect mediated via inhibition of NHE activity (likely through acid extrusion by NHE isoform 1). The Na(+)/K(+) pump activity and intracellular ATP concentration were unaffected by hypoxia, but the levels of ROS were reduced. Hypoxic inhibition of NHE activity and the reduction in ROS levels were reversed by treatment with H(2)O(2), Co(2+), or antimycin A. Treatment with calyculin A also prevented hypoxic inhibition of NHE activity. Conclusions: The ability of articular chondrocytes to carry out pH homeostasis is compromised when O(2) tensions fall below those normally experienced, via inhibition of NHE. The putative signal is a reduction in levels of ROS derived from mitochondria, acting via altered protein phosphorylation. This effect is relevant to both physiologic and pathologic states of lowered O(2), such as in chronic inflammation.
Publication Date: 2006-11-01 PubMed ID: 17075856DOI: 10.1002/art.22209Google Scholar: Lookup
The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.
This research investigates the impact of different oxygen concentrations on the pH stability of the cells found in horse joints, suggesting that the best understanding of these cells known as articular chondrocytes, comes from examining them in realistic oxygen conditions.
Research Methodology
- The study was carried out using cartilage from the joints of horses, specifically from the metarcarpophalangeal/tarsophalangeal joints. The researchers used collagenase to break down the cartilage to isolate the chondrocytes.
- The chondrocytes were then loaded with a pH-sensitive compound, 2′,7′-bis-2-(carboxyethyl)-5(6)-carboxylfluorescein, which allowed the researchers to measure pH changes by monitoring the fluorescence of the compound.
- The kinetics of Sodium-Hydrogen (Na(+)/H(+)) exchange and the activity of the Sodium-Potassium (Na(+)/K(+)) pump were determined using a Sodium-22 radioisotope.
- The levels of Adenosine triphosphate (ATP), the main source of energy for most cellular processes, were measured using luciferin assays.
- Reactive oxygen species (ROS) levels, which can indicate stress in an organism or cell, were determined using 2′,7′-dichlorofluorescein diacetate.
Research Findings
- The research concluded that pH homeostasis, the balance or equilibrium of the acidity or alkalinity of the cells, remained unaffected when the tissue was maintained at 20% oxygen (the level in water-saturated air at 37 degrees C) or at 5% oxygen (typical level in healthy cartilage).
- When oxygen concentration fell below 5%, an increase in cellular acidity (reduction in intracellular pH) was noticed. This was attributed to an inhibition of Na+/H+ exchange activity, a key mechanism that allows cells to control their pH. Likely the acid extrusion was carried out by the NHE isoform 1.
- Despite the hypoxic conditions, ATP concentrations and Na(+)/K(+) pump activity remained unchanged, however, levels of ROS fell.
- The drop in ROS levels and the inhibition of the Na+/H+ exchange under low-oxygen conditions were reversed when treated with hydrogen peroxide, Cobalt(II) ions, or antimycin A, a known inhibitor of mitochondrial respiration. Calyculin A was also able to prevent the inhibition of the Na(+)/H(+) exchange activity in low oxygen conditions.
Conclusions
- This study demonstrates that a decrease in oxygen levels below those typically experienced can compromise the ability of articular chondrocytes to maintain pH homeostasis, primarily due to inhibition of Na+/H+ exchange.
- The underlying signal appears to be due to a reduction in mitochondrial-reactive oxygen species, mediated via changes in protein phosphorylation.
- The ability of chondrocyte cells to carry out pH homeostasis under conditions of lowered oxygen is relevant in understanding both physiological and pathological states, such as chronic inflammation.
Cite This Article
APA
Milner PI, Fairfax TP, Browning JA, Wilkins RJ, Gibson JS.
(2006).
The effect of O2 tension on pH homeostasis in equine articular chondrocytes.
Arthritis Rheum, 54(11), 3523-3532.
https://doi.org/10.1002/art.22209 Publication
Researcher Affiliations
- University of Cambridge, Cambridge, UK.
MeSH Terms
- Adenosine Triphosphate / metabolism
- Animals
- Cartilage, Articular / cytology
- Cell Hypoxia / physiology
- Chondrocytes / drug effects
- Chondrocytes / metabolism
- Enzyme Inhibitors / pharmacology
- Homeostasis / drug effects
- Homeostasis / physiology
- Horses
- Hydrogen-Ion Concentration
- Marine Toxins
- Oxazoles / pharmacology
- Oxygen / metabolism
- Oxygen / pharmacology
- Phosphoprotein Phosphatases / antagonists & inhibitors
- Phosphoprotein Phosphatases / metabolism
- Phosphorylation
- Reactive Oxygen Species / metabolism
- Sodium-Hydrogen Exchangers / metabolism
- Sodium-Potassium-Exchanging ATPase / metabolism
Citations
This article has been cited 16 times.- Ji ML, Jiang H, Li Z, Geng R, Hu JZ, Lin YC, Lu J. Sirt6 attenuates chondrocyte senescence and osteoarthritis progression.. Nat Commun 2022 Dec 10;13(1):7658.
- Deng Z, Li Y, Liu H, Xiao S, Li L, Tian J, Cheng C, Zhang G, Zhang F. The role of sirtuin 1 and its activator, resveratrol in osteoarthritis.. Biosci Rep 2019 May 31;39(5).
- Zhang X, Yang Y, Li X, Zhang H, Gang Y, Bai L. Alterations of autophagy in knee cartilage by treatment with treadmill exercise in a rat osteoarthritis model.. Int J Mol Med 2019 Jan;43(1):336-344.
- Liu Z, Hu X, Man Z, Zhang J, Jiang Y, Ao Y. A novel rabbit model of early osteoarthritis exhibits gradual cartilage degeneration after medial collateral ligament transection outside the joint capsule.. Sci Rep 2016 Oct 19;6:34423.
- Cheng C, Zhang FJ, Tian J, Tu M, Xiong YL, Luo W, Li YS, Song BB, Gao SG, Lei GH. Osteopontin inhibits HIF-2α mRNA expression in osteoarthritic chondrocytes.. Exp Ther Med 2015 Jun;9(6):2415-2419.
- Collins JA, Moots RJ, Clegg PD, Milner PI. Resveratrol and N-acetylcysteine influence redox balance in equine articular chondrocytes under acidic and very low oxygen conditions.. Free Radic Biol Med 2015 Sep;86:57-64.
- Cillero-Pastor B, Rego-Pérez I, Oreiro N, Fernandez-Lopez C, Blanco FJ. Mitochondrial respiratory chain dysfunction modulates metalloproteases -1, -3 and -13 in human normal chondrocytes in culture.. BMC Musculoskelet Disord 2013 Aug 9;14:235.
- Collins JA, Moots RJ, Winstanley R, Clegg PD, Milner PI. Oxygen and pH-sensitivity of human osteoarthritic chondrocytes in 3-D alginate bead culture system.. Osteoarthritis Cartilage 2013 Nov;21(11):1790-8.
- Yodmuang S, Gadjanski I, Chao PH, Vunjak-Novakovic G. Transient hypoxia improves matrix properties in tissue engineered cartilage.. J Orthop Res 2013 Apr;31(4):544-53.
- Hübner S, Efthymiadis A. Recent progress in histochemistry and cell biology.. Histochem Cell Biol 2012 Apr;137(4):403-57.
- Schultz M, Jin W, Waheed A, Moed BR, Sly W, Zhang Z. Expression profile of carbonic anhydrases in articular cartilage.. Histochem Cell Biol 2011 Aug;136(2):145-51.
- Fermor B, Gurumurthy A, Diekman BO. Hypoxia, RONS and energy metabolism in articular cartilage.. Osteoarthritis Cartilage 2010 Sep;18(9):1167-73.
- White R, Gibson JS. The effect of oxygen tension on calcium homeostasis in bovine articular chondrocytes.. J Orthop Surg Res 2010 Apr 26;5:27.
- Thoms BL, Murphy CL. Inhibition of hypoxia-inducible factor-targeting prolyl hydroxylase domain-containing protein 2 (PHD2) enhances matrix synthesis by human chondrocytes.. J Biol Chem 2010 Jul 2;285(27):20472-80.
- Gibson JS, McCartney D, Sumpter J, Fairfax TP, Milner PI, Edwards HL, Wilkins RJ. Rapid effects of hypoxia on H+ homeostasis in articular chondrocytes.. Pflugers Arch 2009 Oct;458(6):1085-92.
- Gibson JS, Milner PI, White R, Fairfax TP, Wilkins RJ. Oxygen and reactive oxygen species in articular cartilage: modulators of ionic homeostasis.. Pflugers Arch 2008 Jan;455(4):563-73.
Use Nutrition Calculator
Check if your horse's diet meets their nutrition requirements with our easy-to-use tool Check your horse's diet with our easy-to-use tool
Talk to a Nutritionist
Discuss your horse's feeding plan with our experts over a free phone consultation Discuss your horse's diet over a phone consultation
Submit Diet Evaluation
Get a customized feeding plan for your horse formulated by our equine nutritionists Get a custom feeding plan formulated by our nutritionists
