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The rapidly inactivating potassium current (IA ) is important in controlling neuronal action potentials. Altered IA function and K+ channel expression have been found in epilepsy, and activation of the transient receptor potential vanilloid 4 (TRPV4) channel is involved in epilepsy pathogenesis. This study examined whether TRPV4 affects Kv4.2 and K+ channel interacting protein (KCHIP) expression and IA changes following pilocarpine-induced status epilepticus (PISE) in mice. Herein, hippocampal protein levels of Kv4.2 and KCHIP2 increased 3 h-3 d and decreased 7-30 d; that of KCHIP1 increased 3-24 h and decreased 3-30 d post-PISE. The TRPV4 antagonist HC-067047 attenuated the increased protein levels of Kv4.2 and KCHIP2 but not that of KCHIP1 post-PISE. The TRPV4 agonist GSK1016790A increased hippocampal protein levels of Kv4.2 and KCHIP2 but had no effect on KCHIP1 expression. HC-067047 attenuated the increased IA in hippocampal pyramidal neurons 24 h and 3 d post-PISE. GSK1016790A increased IA in hippocampal pyramidal neurons, shifting the voltage-dependent inactivation curve toward depolarization. The GSK1016790A-induced increase of IA was blocked by protein kinase A and calcium/calmodulin-dependent kinase II antagonists but was unaffected by protein kinase C antagonists. We conclude that TRPV4 activation may be responsible for the increases of Kv4.2 and KCHIP2 expression in hippocampi and IA in hippocampal pyramidal neurons in PISE mice, which are likely compensatory measures for hyperexcitability at the early stage of epilepsy.

Activation of transient receptor potential vanilloid 4 (TRPV4) can increase hippocampal neuronal excitability. TRPV4 has been reported to be involved in the pathogenesis of epilepsy. Voltage-gated potassium channels (VGPCs) play an important role in regulating neuronal excitability and abnormal VGPCs expression or function is related to epilepsy. Here, we examined the effect of TRPV4 activation on the delayed rectifier potassium current (IK ) in hippocampal pyramidal neurons and on the Kv subunits expression in male mice. We also explored the role of TRPV4 in changes in Kv subunits expression in male mice following pilocarpine-induced status epilepticus (PISE). Application of TRPV4 agonists, GSK1016790A and 5,6-EET, markedly reduced IK in hippocampal pyramidal neurons and shifted the voltage-dependent inactivation curve to the hyperpolarizing direction. GSK1016790A- and 5,6-EET-induced inhibition of IK was blocked by TRPV4 specific antagonists, HC-067047 and RN1734. GSK1016790A-induced inhibition of IK was markedly attenuated by calcium/calmodulin-dependent kinase II (CaMKII) antagonist. Application of GSK1016790A for up to 1 hr did not change the hippocampal protein levels of Kv1.1, Kv1.2, or Kv2.1. Intracerebroventricular injection of GSK1016790A for 3 d reduced the hippocampal protein levels of Kv1.2 and Kv2.1, leaving that of Kv1.1 unchanged. Kv1.2 and Kv2.1 protein levels as well as IK reduced markedly in hippocampi on day 3 post PISE, which was significantly reversed by HC-067047. We conclude that activation of TRPV4 inhibits IK in hippocampal pyramidal neurons, possibly by activating CaMKII. TRPV4-induced decrease in Kv1.2 and Kv2.1 expression and IK may be involved in the pathological changes following PISE.

Atrial fibrillation (AF) affects >30 million individuals worldwide. However, no genetic mutation from human patients with AF has been linked to inflammation. Here, we show that AF-associated human variant p.Ile138Thr in natriuretic peptide A (NPPA) encoding the atrial natriuretic peptide (ANP) causes inflammation, fibroblast activation, atrial fibrosis, and AF in knock-in (KI) rats. Variant p.Ile138Thr inhibits the interaction between ANP and its receptor natriuretic peptide receptor A and reduces intracellular cGMP levels. RNA sequencing and follow-up analyses showed that mutant ANP (mANP) activates multiple innate immunity pathways, including TNF-α, NF-κB, and IL-1β signaling. mANP induces differentiation of cardiac fibroblasts (CFs) to myofibroblasts and promotes CF proliferation and fibrosis. These results suggest that NPPA variant p.Ile138Thr causes AF by activating TNF-α, NF-κB, and IL-1β signaling, inflammation, and fibrosis. Multiple computational programs suggest that p.Ile138Thr is damaging or deleterious. Based on the 2015 American College of Medical Genetics and Genomics Standards and Guidelines, p.Ile138Thr can be classified as a likely pathogenic variant. Variant p.Ile138Thr was found only in Asian people in the Genome Aggregation Database and Exome Aggregation Consortium database at an averaged frequency of 0.026%. An estimated 1.15 million Asian people carry the variant and might be at risk of AF. The KI rats may provide an inflammation-based, genetic animal model for AF valuable for testing anti-inflammation or other therapies for AF.-Cheng, C., Liu, H., Tan, C., Tong, D., Zhao, Y., Liu, X., Si, W., Wang, L., Liang, L., Li, J., Wang, C., Chen, Q., Du, Y., Wang, Q. K., Ren, X. Mutation in NPPA causes atrial fibrillation by activating inflammation and cardiac fibrosis in a knock-in rat model.