Overexpression of humanKCNA5increasesI_K(V)and enhances apoptosis

Abstract

Apoptotic cell shrinkage, an early hallmark of apoptosis, is regulated by K+ efflux and K+ channel activity. Inhibited apoptosis and downregulated K+ channels in pulmonary artery smooth muscle cells (PASMC) have been implicated in development of pulmonary vascular medial hypertrophy and pulmonary hypertension. The objective of this study was to test the hypothesis that overexpression of KCNA5, which encodes a delayed-rectifier voltage-gated K+ (Kv) channel, increases K+ currents and enhances apoptosis. Transient transfection of KCNA5 caused 25- to 34-fold increase in KCNA5 channel protein level and 24- to 29-fold increase in Kv channel current (I(K(V))) at +60 mV in COS-7 and rat PASMC, respectively. In KCNA5-transfected COS-7 cells, staurosporine (ST)-mediated increases in caspase-3 activity and the percentage of cells undergoing apoptosis were both enhanced, whereas basal apoptosis (without ST stimulation) was unchanged compared with cells transfected with an empty vector. In rat PASMC, however, transfection of KCNA5 alone caused marked increase in basal apoptosis, in addition to enhancing ST-mediated apoptosis. Furthermore, ST-induced apoptotic cell shrinkage was significantly accelerated in COS-7 cells and rat PASMC transfected with KCNA5, and blockade of KCNA5 channels with 4-aminopyridine (4-AP) reduced K+ currents through KCNA5 channels and inhibited ST-induced apoptosis in KCNA5-transfected COS-7 cells. Overexpression of the human KCNA5 gene increases K+ currents (i.e., K+ efflux or loss), accelerates apoptotic volume decrease (AVD), increases caspase-3 activity, and induces apoptosis. Induction of apoptosis in PASMC by KCNA5 gene transfer may serve as an important strategy for preventing the progression of pulmonary vascular wall thickening and for treating patients with idiopathic pulmonary arterial hypertension (IPAH).

Potassium channels in pulmonary arterial hypertension

“…By governing K + movement and intracellular osmolality that drives water flow across cell membrane, K + channels are crucial regulators for cell volume. In PASMCs, increased K + efflux, either by transient transfection of a K V channel or by a K + channel activator, enhances cell death, a conserved mechanism characterised by cell shrinkage, chromatin condensation, nuclear fragmentation and apoptotic body formation [4][5][6]. Conversely, inhibition of K + efflux attenuates PASMC apoptosis [7].…”

Cell shrinkage and monovalent cation fluxes: Role in apoptosis

“…Kv1.2 expression was shown to be elevated in adult rat brain model of cell death following middle cerebral artery occlusion and in SH-SY5Y neuroblastoma cells following hypoxia and glucose deprivation [47]. The overexpression of Kv1.5 potassium channels in COS-7 or pulmonary artery smooth muscle cells (PASMC) resulted in an enhancement of staurosporine-induced apoptosis by accelerating the apoptotic volume decrease and increasing caspase-3 activity [48]. Thus numerous voltage-gated potassium channels have been suggested to play a role in apoptosis.…”

“…A unique feature of these two-pore domain K + channels, suggested to play a role in various apoptotic model systems [48], is their independence from modulation by various intracellular messengers such as calcium, ATP, or arachidonic acid. Additionally, these channels function independent of changes in the transmembrane voltage and the cytoskeleton.…”

Dichloroacetate Inhibits Vascular Remodeling and Increases Voltage-gate K+ Expression in a High-altitude-induced Pulmonary Artery Hypertension Rat Model

“…30) In our study, we also found that apoptosis was increased with the upregulation of Kv1.5 and Kv2.1. Brevnona et al 31) showed that overexpression of the Kv1.5 gene in PASMCs induces apoptosis. Kv2.1 gene transferinduced apoptosis has also been observed in neurons and Chinese hamster ovary cells, which are deficient in functional Kv2.1-encoded K + channels.…”