Lipid phosphate phosphatase inhibitors locally amplify lysophosphatidic acid LPA1 receptor signalling in rat brain cryosections without affecting global LPA degradation.
BACKGROUND
Lysophosphatidic acid (LPA) is a signalling phospholipid with multiple biological functions, mainly mediated through specific G protein-coupled receptors. Aberrant LPA signalling is being increasingly implicated in the pathology of common human diseases, such as arteriosclerosis and cancer. The lifetime of the signalling pool of LPA is controlled by the equilibrium between synthesizing and degradative enzymatic activity. In the current study, we have characterized these enzymatic pathways in rat brain by pharmacologically manipulating the enzymatic machinery required for LPA degradation.


RESULTS
In rat brain cryosections, the lifetime of bioactive LPA was found to be controlled by Mg2+-independent, N-ethylmaleimide-insensitive phosphatase activity, attributed to lipid phosphate phosphatases (LPPs). Pharmacological inhibition of this LPP activity amplified LPA1 receptor signalling, as revealed using functional autoradiography. Although two LPP inhibitors, sodium orthovanadate and propranolol, locally amplified receptor responses, they did not affect global brain LPA phosphatase activity (also attributed to Mg2+-independent, N-ethylmaleimide-insensitive phosphatases), as confirmed by Pi determination and by LC/MS/MS. Interestingly, the phosphate analog, aluminium fluoride (AlFx-) not only irreversibly inhibited LPP activity thereby potentiating LPA1 receptor responses, but also totally prevented LPA degradation, however this latter effect was not essential in order to observe AlFx--dependent potentiation of receptor signalling.


CONCLUSIONS
We conclude that vanadate- and propranolol-sensitive LPP activity locally guards the signalling pool of LPA whereas the majority of brain LPA phosphatase activity is attributed to LPP-like enzymatic activity which, like LPP activity, is sensitive to AlFx- but resistant to the LPP inhibitors, vanadate and propranolol.
School of Pharmacy, University of Eastern Finland, P,O, Box 1627, 70211, Kuopio, Finland. Niina.Aaltonen@uef.fi
Niina
N
Aaltonen
Marko
M
Lehtonen
Katri
K
Varonen
Gemma Arrufat
GA
Goterris
Jarmo T
JT
Laitinen
D017607:Aluminum Compounds / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005459:Fluorides / Q000494:pharmacology; D066298:In Vitro Techniques; D008246:Lysophospholipids / Q000378:metabolism; D008297:Male; D010711:Phosphatidate Phosphatase / Q000037:antagonists & inhibitors; D011433:Propranolol / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D049368:Receptors, Lysophosphatidic Acid / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D014638:Vanadates / Q000494:pharmacology*
D017607:Aluminum Compounds; D004791:Enzyme Inhibitors; D008246:Lysophospholipids; D049368:Receptors, Lysophosphatidic Acid; D014638:Vanadates; D011433:Propranolol; C112948:lipid phosphate phosphatase; D010711:Phosphatidate Phosphatase; C032881:lysophosphatidic acid; D005459:Fluorides; C032311:aluminum fluoride