Diadenosine polyphosphates release by human corneal epithelium.
Gonzalo Carracedo1, Ana Guzman-Aranguez, Patricia Loma
1Department of Optics II (Optometry and Vision), Faculty of Optics and Optometry, Universidad Complutense de Madrid, Madrid, Spain. gonzalocarracedo@gmail.com
Experimental Eye Research
|June 25, 2013
Summary
Mechanical stress on the eye releases diadenosine polyphosphates (Ap4A and Ap5A) from corneal cells. This finding explains the origin of these compounds crucial for ocular surface health.
Area of Science:
- Ocular Surface Biochemistry
- Cellular Physiology
- Molecular Biology
Background:
- Diadenosine polyphosphates (Ap4A, Ap5A) are found in human tears, but their source and release mechanisms are unclear.
- These dinucleotides play roles in ocular surface biochemistry and physiology.
Purpose of the Study:
- To investigate if shear stress stimulates the release of Ap4A and Ap5A from human corneal epithelial cells.
- To elucidate the origin of Ap4A and Ap5A in human tears.
Main Methods:
- In vitro studies using stratified human corneal epithelial cells subjected to mechanical shear stress.
- In vivo experiments measuring tear concentrations of Ap4A and Ap5A in individuals with increased blinking frequency.
- Lactate dehydrogenase assays to rule out cell lysis as the cause of dinucleotide release.
Main Results:
- In vitro: Shear stress significantly increased Ap4A and Ap5A concentrations in corneal cells (e.g., Ap4A from 3.18 to 12.01 nM).
- In vitro: No significant lactate dehydrogenase activity increase indicated no cell lysis.
- In vivo: Increased blinking frequency led to substantial increases in tear Ap4A (up to 75-fold) and Ap5A (up to 125-fold).
Conclusions:
- Mechanical shear stress is a key stimulus for releasing Ap4A and Ap5A from human corneal epithelium.
- This study clarifies the origin of these dinucleotides, essential for ocular surface function.
More Related Videos
10:46Mechanical Stimulation-induced Calcium Wave Propagation in Cell Monolayers: The Example of Bovine Corneal Endothelial Cells
Published on: July 16, 2013
06:29Effect of Artificial Tear Formulations on the Metabolic Activity of Human Corneal Epithelial Cells after Exposure to Desiccation
Published on: May 2, 2020
Related Concept Videos
01:27Transducer Mechanism: Enzyme-Linked Receptors
Enzyme-linked receptors are cell-surface receptors acting as an enzyme or associating with an enzyme intracellularly. They make excellent drug targets. Drugs can bind to the extracellular ligand-binding domain or directly affect their enzymatic domain and alter their activity.
Major types that are helpful drug targets include:
Major types that are helpful drug targets include:
01:31ATP Energy Storage and Release
ATP is a highly unstable molecule. Unless quickly used to perform work, ATP spontaneously dissociates into ADP and inorganic phosphate (Pi), and the free energy released during this process is lost as heat. The energy released by ATP hydrolysis is used to perform work inside the cell and depends on a strategy called energy coupling. Cells couple the exergonic reaction of ATP hydrolysis with endergonic reactions, allowing them to proceed.
One example of energy coupling using ATP involves a...
One example of energy coupling using ATP involves a...
01:11IP3/DAG Signaling Pathway
Membrane lipids such as phosphatidylinositol (PI) are precursors for several membrane-bound and soluble second messengers. Specific kinases phosphorylate PI and produce phosphorylated inositol phospholipids. One such inositol phospholipids are the phosphatidylinositol-4,5 bisphosphate [PI(4,5)P2], present in the inner half of the lipid bilayer. Upon ligand binding, GPCR stimulates Gq proteins to turn on phospholipase Cꞵ. Activated phospholipase Cꞵ cleaves PI(4,5)P2 and produces two-second...
01:09GPCRs Regulate Adenylyl Cylase Activity
Some GPCRs transmit signals through adenylyl cyclase (AC), a transmembrane enzyme. AC helps synthesize second messenger cyclic adenosine monophosphate (cAMP). AC catalyzes cyclization reaction and converts ATP to cAMP by releasing a pyrophosphate. The pyrophosphate is further hydrolyzed to phosphate by the enzyme pyrophosphatase, which drives cAMP synthesis to completion. However, cAMP is rapidly degraded to 5′ AMP by the enzymes phosphodiesterase (PDE), preventing overstimulation of cells.
Two...
Two...
01:25cAMP-dependent Protein Kinase Pathways
Cyclic Adenosine Monophosphate (cAMP) is an essential second messenger that activates protein kinase A (PKA) and regulates various biological processes. A single epinephrine molecule binds to GPCR and activates several heterotrimeric G proteins, each stimulating multiple adenylyl cyclase, amplifying the signal, and synthesizing large numbers of cAMP molecules. Small changes in cAMP concentration affect PKA activity. The binding of four cAMP molecules induces a conformational change in PKA,...
01:08Hydrolysis of ATP
The bonds of adenosine triphosphate (ATP) can be broken through the addition of water, releasing one or two phosphate groups in an exergonic process called hydrolysis. This reaction liberates the energy in the bonds for use in the cell—for instance, to synthesize proteins from amino acids.
If one phosphate group is removed, a molecule of ADP—adenosine diphosphate—remains, along with inorganic phosphate. ADP can be further hydrolyzed to AMP—adenosine monophosphate—by the removal of a second...
If one phosphate group is removed, a molecule of ADP—adenosine diphosphate—remains, along with inorganic phosphate. ADP can be further hydrolyzed to AMP—adenosine monophosphate—by the removal of a second...