Coronary endothelial catecholaminergic machinery in myocardial ischaemia-reperfusion injury and metabolic stress.

Abstract

BACKGROUND: Catecholamine-mediated regulation of the coronary vasculature has traditionally been attributed to neuronal and endocrine sources. Emerging evidence suggests that endothelial cells may express components involved in catecholamine biosynthesis, although their presence and regulation within the coronary endothelium remain incompletely characterised. We investigated the expression of catecholamine biosynthetic enzymes and vesicular monoamine transporters in cardiac endothelial cells and their regulation following myocardial ischaemia-reperfusion (I/R) injury. We further examined the effects of pharmacological TH inhibition on endothelial metabolic activity and stress-associated signalling. METHODS: The expression of tyrosine hydroxylase (TH), aromatic L-amino acid decarboxylase (AADC), dopamine β-hydroxylase (DBH), and the vesicular monoamine transporters VMAT1 and VMAT2 was examined in coronary endothelial cells from sham-operated and I/R rat hearts using immunohistochemistry and immunofluorescence. TH expression was additionally examined in hTERT-immortalised human endothelial cells (TeloHAECs). The effects of pharmacological TH inhibition with metyrosine were assessed under basal and H₂O₂-induced oxidative stress conditions using MTT reduction and an analysis of LKB1-mTORC1-associated signalling. RESULTS: TH and AADC immunoreactivity was detected within coronary endothelial cells and was significantly increased following myocardial I/R injury, as demonstrated by increased immunoreactivity scores and proportions of positively stained endothelial cells. VMAT2 immunoreactivity was also detected within the vascular endothelium and increased following I/R, whereas DBH immunoreactivity was sparse and VMAT1 was not detected. A TH-immunoreactive protein was detected in TeloHAECs. Pharmacological TH inhibition reduced cellular metabolic activity under basal conditions (~33% versus control; p < 0.0001) and was associated with a further reduction during oxidative stress (~17% versus H₂O₂ alone; p < 0.05). TH inhibition was also associated with increased LKB1 and ACC phosphorylation and reduced phosphorylation of mTOR, S6 ribosomal protein and 4E-BP1, consistent with a metabolic stress-associated signalling profile. CONCLUSIONS: These findings identify a previously underappreciated catecholamine-related molecular machinery within the coronary endothelium, comprising proteins involved in catecholamine biosynthesis and vesicular monoamine transport. The increased endothelial expression of TH, AADC and VMAT2 following myocardial I/R injury indicates that this machinery is dynamically regulated in response to myocardial stress, while pharmacological TH inhibition links TH activity with endothelial metabolic and stress-associated signalling. Together, these findings expand the current understanding of coronary endothelial biology and identify endothelial catecholamine-related pathways as a potential component of the vascular response to myocardial ischaemia-reperfusion injury.

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