Aberrant Exon 8/8a Splicing by Downregulated PTBP (Polypyrimidine Tract-Binding Protein) 1 Increases Ca V 1.2 Dihydropyridine Resistance to Attenuate Vasodilation

Abstract

Objective: Calcium channel blockers, such as dihydropyridines, are commonly used to inhibit enhanced activity of vascular Ca V 1.2 channels in hypertension. However, patients who are insensitive to such treatments develop calcium channel blocker-resistant hypertension. The function of Ca V 1.2 channel is diversified by alternative splicing, and the splicing factor PTBP (polypyrimidine tract-binding protein) 1 influences the utilization of mutually exclusive exon 8/8a of the Ca V 1.2 channel during neuronal development. Nevertheless, whether and how PTBP1 makes a role in the calcium channel blocker sensitivity of vascular Ca V 1.2 channels, and calcium channel blocker-induced vasodilation remains unknown. Approach and Results: We detected high expression of PTBP1 and, inversely, low expression of exon 8a in Ca V 1.2 channels (Ca V 1.2 E8a ) in rat arteries. In contrast, the opposite expression patterns were observed in brain and heart tissues. In comparison to normotensive rats, the expressions of PTBP1 and Ca V 1.2 E8a channels were dysregulated in mesenteric arteries of hypertensive rats. Notably, PTBP1 expression was significantly downregulated, and Ca V 1.2 E8a channels were aberrantly increased in dihydropyridine-resistant arteries compared with dihydropyridine-sensitive arteries of rats and human. In rat vascular smooth muscle cells, PTBP1 knockdown resulted in shifting of Ca V 1.2 exon 8 to 8a. Using patch-clamp recordings, we demonstrated a concomitant reduction of sensitivity of Ca V 1.2 channels to nifedipine, due to the higher expression of Ca V 1.2 E8a isoform. In vascular myography experiments, small interfering RNA-mediated knockdown of PTBP1 attenuated nifedipine-induced vasodilation of rat mesenteric arteries. Conclusions: PTBP1 finely modulates the sensitivities of Ca V 1.2 channels to dihydropyridine by shifting the utilization of exon 8/8a and resulting in changes of responses in dihydropyridine-induced vasodilation.