KCNH6 is essential for insulin secretion by regulating intracellular ER Ca2+ store.

Appropriate Ca2+ concentration in the endoplasmic reticulum (ER), modulating cytosolic Ca2+ signal, serves significant roles in physiological function of pancreatic ß cells. To maintaining ER homeostasis, Ca2+ movement across the ER membrane is always accompanied by a simultaneous K+ flux in the opposite direction. KCNH6 was proven to modulate insulin secretion by controlling plasma membrane action potential duration and intracellular Ca2+ influx. Meanwhile, the specific function of KCNH6 in pancreatic ß-cells remains unclear. In this study, we found that KCNH6 exhibited mainly ER localization and Kcnh6 ß-cell-specific knockout (ßKO) mice suffered from abnormal glucose tolerance and impaired insulin secretion in adulthood. ER Ca2+ store was overloaded in islets of ßKO mice, which contributed to ER stress and ER stress-induced apoptosis in ß cells. Next, we verified that ethanol treatment induced increases in ER Ca2+ store and apoptosis in pancreatic ß cells, whereas adenovirus-mediated KCNH6 overexpression in islets attenuated ethanol-induced ER stress and apoptosis. In addition, tail-vein injections of KCNH6 lentivirus rescued KCNH6 expression in ßKO mice, restored ER Ca2+ overload and attenuated ER stress in ß cells, which further confirms that KCNH6 protects islets from ER stress and apoptosis. These data suggest that KCNH6 on the ER membrane may help to stabilize intracellular ER Ca2+ stores and protect ß cells from ER stress and apoptosis. In conclusion, our study reveals the protective potential of KCNH6-targeting drugs in ER stress-induced diabetes.

High bicarbonate concentration increases glucose-induced insulin secretion in pancreatic ß-cells.

Low serum bicarbonate is closely related to type 2 diabetes mellitus. However, the precise role of bicarbonate on glucose homeostasis and insulin secretion remains unknown. In this study, we investigated the effects of bicarbonate concentration on pancreatic ß-cells. It was observed that the high bicarbonate concentration of the cell culture medium significantly increased the glucose-induced insulin secretion (GSIS) levels in mouse islets, MIN6, and the INS-1E ß cells. MIN6 cells presented an impaired GSIS; the cells produced a lower bicarbonate concentration when co-cultured with Capan-1 than when with CFPAC-1. NBCe1, a major bicarbonate transporter was observed to block the increasing insulin secretions, which were promoted by a high concentration of bicarbonate. In addition, higher extracellular bicarbonate concentration significantly increased the intracellular cAMP level, pHi, and calcium concentration with a 16.7 mM of glucose stimulation. Further study demonstrated that a low concentration of extracellular bicarbonate significantly impaired the functioning of pancreatic ß cells by reducing coupling Ca2+ influx, whose process may be modulated by NBCe1. Taken together, our results conclude that bicarbonate may serve as a novel target in diabetes prevention-related research.

Effect of KCNH6 on Hepatic Endoplasmic Reticulum Stress and Glucose Metabolism.

Adult patients with a dysfunctional ether-a-go-go 2 (hERG2) protein, which is encoded by the KCNH6 gene, present with hyperinsulinemia and hyperglycemia. However, the mechanism of KCNH6 in glucose metabolism disorders has not been clearly defined. It has been proposed that sustained endoplasmic reticulum (ER) stress is closely concerned with hepatic insulin resistance and inflammation. Here, we demonstrate that Kcnh6 knockout (KO) mice had impaired glucose tolerance and increased levels of hepatic apoptosis, in addition to displaying an increased insulin resistance that was mediated by high ER stress levels. By contrast, overexpression of KCNH6 in primary hepatocytes led to a decrease in ER stress and apoptosis induced by thapsigargin. Similarly, induction of Kcnh6 by tail vein injection into KO mice improved glucose tolerance by reducing ER stress and apoptosis. Furthermore, we show that KCNH6 alleviated hepatic ER stress, apoptosis, and inflammation via the NFκB-IκB kinase (IKK) pathway both in vitro and in vivo. In summary, our study provides new insights into the causes of ER stress and subsequent induction of primary hepatocytes apoptosis.

All-potassium channel CRISPR screening reveals a lysine-specific pathway of insulin secretion.

OBJECTIVE: Genome-scale CRISPR-Cas9 knockout coupled with single-cell RNA sequencing (scRNA-seq) has been used to identify function-related genes. However, this method may knock out too many genes, leading to low efficiency in finding genes of interest. Insulin secretion is controlled by several electrophysiological events, including fluxes of KATP depolarization and K+ repolarization. It is well known that glucose stimulates insulin secretion from pancreatic ß-cells, mainly via the KATP depolarization channel, but whether other nutrients directly regulate the repolarization K+ channel to promote insulin secretion is unknown. METHODS: We used a system involving CRISPR-Cas9-mediated knockout of all 83 K+ channels and scRNA-seq in a pancreatic ß cell line to identify genes associated with insulin secretion. RESULTS: The expression levels of insulin genes were significantly increased after all-K+ channel knockout. Furthermore, Kcnb1 and Kcnh6 were the two most important repolarization K+ channels for the increase in high-glucose-dependent insulin secretion that occurred upon application of specific inhibitors of the channels. Kcnh6 currents, but not Kcnb1 currents, were reduced by one of the amino acids, lysine, in both transfected cells, primary cells and mice with ß-cell-specific deletion of Kcnh6. CONCLUSIONS: Our function-related CRISPR screen with scRNA-seq identifies Kcnh6 as a lysine-specific channel.

KCNH6 Enhanced Hepatic Glucose Metabolism through Mitochondrial Ca2+ Regulation and Oxidative Stress Inhibition.

KCNH6 has been proven to affect glucose metabolism and insulin secretion both in humans and mice. Further study revealed that Kcnh6 knockout (KO) mice showed impaired glucose tolerance. However, the precise function of KCNH6 in the liver remains unknown. Mitochondria have been suggested to maintain intracellular Ca2+ homeostasis; ROS generation and defective mitochondria can cause glucose metabolism disorders, including type 2 diabetes (T2D). Here, we found that Kcnh6 attenuated glucose metabolism disorders by decreasing PEPCK and G6pase abundance and induced Glut2 and IRS2 expression. Overexpression of Kcnh6 increased hepatic glucose uptake and glycogen synthesis. Kcnh6 attenuated intracellular and mitochondrial calcium levels in primary hepatocytes and reduced intracellular ROS and mitochondrial superoxide production. Kcnh6 suppressed oxidative stress by inhibiting mitochondrial pathway activation and NADPH oxidase expression. Experiments demonstrated that Kcnh6 expression improved hepatic glucose metabolism disorder through the c-Jun N-terminal kinase and p38MAPK signaling pathways. These results were confirmed by experiments evaluating the extent to which forced Kcnh6 expression rescued metabolic disorder in KO mice. In conclusion, KCNH6 enhanced hepatic glucose metabolism by regulating mitochondrial Ca2+ levels and inhibiting oxidative stress. As liver glucose metabolism is key to T2D, understanding KCNH6 functions may provide new insights into the causes of diabetes.