Dpp10 - A New Putative Regulatory ß-subunit Of Ito In Failing And Non-failing Human Heart

Background: Recently we reported that the dipeptidyl-aminopeptidase-like protein DPP6 serves as a regulatory ß-subunit for cardiac Kv4.3 channels. DPP6 is up-regulated in human failing hearts in which Kv4.3 and the ß-subunit KChIP2 are down-regulated. Here, we provide evidence for the presence of a new member of this protein family, i.e. DPP10, in failing and non-failing human hearts and investigate the role of this putative ß-subunit in regulating transient outward current. Methods: mRNA was extracted from samples of 5 failing and 5 non-failing human hearts and quantified by realtime PCR. Functional interaction of DPP10 and Kv4.3 was studied in co-expression experiments (Chinese hamster ovary CHO cells) with standard voltage clamp techniques. Results: Expression level of DPP10 was 85±13 fg/ng in failing and 33±6 fg/ng total RNA in non-failing hearts (P<0.01), amounting to a 2.6fold reduction. In comparison, DPP6 was up-regulated 1.3fold (P<0.001). After co-expression of Kv4.3 and DPP10 in CHO cells, channel complexes were verified in the plasma membrane by immunostaining, suggesting proper trafficking as with co-expression of Kv4.3 and KChIP2. Expression of Kv4.3 alone failed to yield Ito current, but robust Ito amplitudes were measured after co-expression of Kv4.3 and DPP10, DDP6, or KChIP2. Compared with the conventional co-expression combination of Kv4.3 and KChIP2, kinetics of Ito inactivation were accelerated in Kv4.3 plus DPP10 channels ({tau}fast: 56± 3 ms and 5.9±0.4 ms, respectively; P<0.01), however, recovery from inactivation was not affected ({tau}rec: 53± 7 ms vs. 58±13 ms). Co-expression of Kv4.3 with KChIP2 plus DPP10 maintained rapid inactivation of Ito ({tau}fast 8±1ms), but enhanced recovery kinetics ({tau}rec: 13±2 ms, P<0.001). The role of glycosylation for channel kinetics was studied with the glycosylation inhibitor tunicamicin (10 µg/ml; 24h). In the presence of tunicamicin, Ito inactivation and recovery were slowed ({tau}fast 51± 4 ms and {tau}rec: 42±3 ms), suggesting importance of glycosylation for channel function. Kinetics were similarly slowed when extracellular domain of DDP10 was deleted ({tau}fast: 48±5 ms, {tau}rec: 30± 4 ms). Conclusion: DPP10, like DPP6 and KChIP2, contributes to regulation of Ito in normal and diseased human hearts.