Expression of CYP 4A ω-hydroxylase and formation of 20-hydroxyeicosatetreanoic acid (20-HETE) in cultured rat brain astrocytes

Abstract

Astrocytes secrete vasodilator and vasoconstrictor factors via end feet processes, altering blood flow to meet neuronal metabolic demand. Compared to what is known about the ability of astrocytes to release factors that dilate local cerebral vasculature, very little is known regarding the source and identity of astrocyte derived constricting factors. The present study investigated if astrocytes express CYP 4A ω-hydroxylase and metabolize arachidonic acid (AA) to 20-hydroxyeicotetraenoic acid (20-HETE) that regulates KCa channel activity in astrocytes and cerebral arterial myocyte contractility. Here we report that cultured astrocytes express CYP 4A2/3 ω-hydroxylase mRNA and CYP 4A protein and produce 20-HETE and the CYP epoxygenase metabolites epoxyeicosatrienoic acids (EETs) when incubated with AA. The production of 20-HETE and EETs was enhanced following stimulation of metabotropic glutamate receptors (mGluR) on the astrocytes. Exogenous application of 20-HETE attenuated, whereas inhibition of 20-HETE production with HET-0016 increased the open state probabilities (NPo) of 71 pS and 161 pS KCa single-channel currents recorded from astrocytes. Exposure of isolated cerebral arterial myocytes to conditioned media from cultured astrocytes caused shortening of the length of freshly isolated cerebral arterial myocytes that was not evident following inhibition of astrocyte 20-HETE synthesis and action. These findings suggest that astrocytes not only release vasodilator EETs in response to mGluR stimulation but also synthetize and release the cerebral arterial myocyte constrictor 20-HETE that also functions as an endogenous inhibitor of the activity of two types of KCa channel currents found in astrocytes.

Hyperbaric oxygenation and 20‐hydroxyeicosatetreanoic acid inhibition reduce stroke volume in female diabetic Sprague–Dawley rats

“…20‐Hydroxyeicosatetreanoic acid (20‐HETE), a cytochrome P450 (CYP) enzyme metabolite of arachidonic acid and a very potent vasoconstrictor produced in cerebral arterioles and brain tissue (Gebremedhin et al . ), is a well‐described mediator of neural tissue damage in stroke (Dunn et al . ).…”

Cytochrome P450 eicosanoids in cerebrovascular function and disease

“…All of these cells types therefore have the necessary machinery to produce 19- and 20-HETE (Alonso-Galicia et al, 1999; Bylund et al, 2002; Al-Anizy et al, 2006; Gebremedhin et al, 1998; 2000; 2016; Carver et al, 2014, Dunn et al, 2008; Zhu et al, 2015; Zhang et al, 2017c). 20-HETE, but not 19-HETE have been detected in vascular smooth muscle cells, and more recently astrocytes and neurons (Gebremedhin et al, 1998; 2008; 2016; Zhang et al, 2017c). 20-HETE has also been reported to be produced in cerebral microvessels and arteries, although the specific cell type was not identified (Gebremedhin et al, 1998; Dunn et al, 2008).…”

“…When incubated with AA astrocytes produce 20-HETE, which is released into culture medium, this is also enhanced upon stimulation of mGluRs. Application of exogenous 20-HETE attenuates, while pharmacological inhibition of 20-HETE synthesis using HET0016 increases, the open state probabilities of calcium-dependent potassium channel (K Ca ; 71 pS and 161 pS) single-channel ion currents (Gebremedhin et al, 2016). Upon glutamatergic stimulation astrocytes are therefore able to release both EETs and HETEs into the perivascular space, which have opposing roles on K Ca channels and cerebrovascular function under physiological and pathophysiological conditions.…”

Cerebral Autoregulation in Hypertension and Ischemic Stroke: A Mini Review

“…In the Central Nervous System (CNS), 20-HETE is produced primarily in the VSMCs, neurons, and astrocytes [62][63][64]. It is a potent vasoconstrictor that potentiates the response to angiotensin II and endothelin and ATP, as well as vascular hypertrophy, endothelial dysfunction, angiogenesis, inflammation, apoptosis and platelet aggregation [18][19][20].…”