Abstract
Phospholipase C (PLC) comprises a superfamily of enzymes that play a key role in a wide array of intracellular signalling pathways, including protein kinase C and intracellular calcium. Thirteen different mammalian PLC isoforms have been identified and classified into 6 families (PLC-β, γ, δ, ε, ζ and η) based on their biochemical properties. Although the expression of PLC isoforms is tissue-specific, concomitant expression of different PLC has been reported, suggesting that PLC family is involved in multiple cellular functions. Despite their critical role, the PLC isoforms expressed in native endothelial cells (ECs) remains undetermined. A conventional PCR approach was initially used to elucidate the mRNA expression pattern of PLC isoforms in 3 distinct murine vascular beds: mesenteric (MA), pulmonary (PA) and middle cerebral arteries (MCA). mRNA encoding for most PLC isoforms was detected in MA, MCA and PA with the exception of η2 and β2 (only expressed in PA), δ4 (only expressed in MCA), η1 (expressed in all but MA) and ζ (not detected in any vascular beds tested). The endothelial-specific PLC expression was then sought in freshly isolated ECs. Interestingly, the PLC expression profile appears to differ across the investigated arterial beds. While mRNA for 8 of the 13 PLC isoforms was detected in ECs from MA, two additional PLC isoforms were detected in ECs from PA and MCA. Co-expression of multiple PLC isoforms in ECs suggests an elaborate network of signalling pathways: PLC isoforms may contribute to the complexity or diversity of signalling by their selective localization in cellular microdomains. However in situ immunofluorescence revealed a homogeneous distribution for all PLC isoforms probed (β3, γ2 and δ1) in intact endothelium. Although PLC isoforms play a crucial role in endothelial signal transduction, subcellular localization alone does not appear to be sufficient to determine the role of PLC in the signalling microdomains found in the native endothelium.
Highlights
Vascular endothelium, a thin-cell monolayer lining blood vessels walls, is ideally positioned to detect and transduce biochemical and physical information
Expression of phospholipases C (PLC) isoforms was initially determined in freshly isolated arteries from 3 different vascular beds: mesenteric arteries (MA), PA and middle cerebral arteries (MCA) (Figs 1–4, panels A)
While mRNA for 8 of the 13 PLC isoforms were detected in MA, were found in MCA and in PA
Summary
A thin-cell monolayer lining blood vessels walls, is ideally positioned to detect and transduce biochemical and physical information. PLC can regulate several cellular functions through DAG production, via activation of protein kinase C [3] and through modulation of PIP2 levels [4]. PLCβ isoforms are activated by Gα and Gβ/γ subunits of heterotrimeric G proteins whereas PLCγ isoforms are activated by tyrosine kinase receptors and PLCε can be activated by both [5]. The absence of PLCβ2 expression leads to decreased intracellular calcium release and superoxide production in neutrophils [10]. These studies strengthened the notion that each PLC isoform has a specific and complementary role in physiology
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