Abstract 5225: Coronary Vasospasm Induced in Transgenic Mice With Variant Phospholipase C-δ1 (R257H)
We previously showed that the activity of phospholipase C (PLC)- δ1, a key enzyme for Ca2+ signaling in the coronary artery, was enhanced by 3 times in patients with coronary spastic angina (CSA) compared with control subjects, and it was positively correlated with coronary vasomotility. We further showed that structural mutation at 864G-A variant with the amino acid replacement of arginine 257 by histidine (R257H), was present in 10% of CSA patients and was related to enhanced PLC-δ1 activity. However, no evidence was documented whether this variant directly and causatively contributes to the enhanced coronary vasomotility. We therefore examined the direct role of structural mutant PLC-δ1 in the genesis of coronary spasm by generating the R257H variant PLC-δ1 overexpressing transgenic (TG) mice. In TG mice, the introduced gene of human R257H variant PLC-δ1 was expressed in overall vessels including the coronary arteries, and upregulated by 2 times compared with wild type (WT) littermate mice. Baseline blood pressure, heart rate, and body weight were similar between 20-week-old TG and WT mice. Ergonovine at 15, 50, and 80 mg/kg was injected through the carotid vein additively, and ECG was monitored continuously. The incidence of ST segment transient elevation was higher in TG mice than in WT after injection of ergonovine at 15 mg/kg (6/18 in TG vs 1/22 in WT, P<0.05), 50 mg/kg (18/18 in TG vs 3/22 in WT, P<0.01), and 80 mg/kg (18/18 in TG vs 11/22 in WT, P<0.01). Concomitantly with the ST segment elevation, AV block or sinus bradycardia was observed. To further examine the morphological changes in the coronary artery, the microvascular filling technique was used in mice untreated with ergonovine. In TG mice, the decrease in coronary arteriole diameter at baseline was documented in the widespread area, although no change was found in WT mice. These suggest that overexpression of R257H variant PLC-δ1 in the coronary artery causes coronary spasm at baseline and after ergonovine. The variant of PLC-δ1 appears to be a therapeutic target for coronary spasm in CSA patients.