Deficiency of voltage-gated proton channel Hv1 attenuates streptozotocin-induced β-cell damage

Voltage-Gated Proton Channels in the Tree of Life

With a single gene encoding H_V1 channel, proton channel diversity is particularly low in mammals compared to other members of the superfamily of voltage-gated ion channels. Nonetheless, mammalian H_V1 channels are expressed in many different tissues and cell types where they exert various functions. In the first part of this review, we regard novel aspects of the functional expression of H_V1 channels in mammals by differentially comparing their involvement in (1) close conjunction with the NADPH oxidase complex responsible for the respiratory burst of phagocytes, and (2) in respiratory burst independent functions such as pH homeostasis or acid extrusion. In the second part, we dissect expression of H_V channels within the eukaryotic tree of life, revealing the immense diversity of the channel in other phylae, such as mollusks or dinoflagellates, where several genes encoding H_V channels can be found within a single species. In the last part, a comprehensive overview of the biophysical properties of a set of twenty different H_V channels characterized electrophysiologically, from Mammalia to unicellular protists, is given.

The pH-dependent gating of the human voltage-gated proton channel from computational simulations

Gating of the voltage-gated proton channel H_V1 is strongly controlled by pH. There is evidence that this involves the sidechains of titratable amino acids that change their protonation state with changes of the pH. Despite experimental investigations to identify the amino acids involved in pH sensing only few progress has been made, including one histidine at the cytoplasmic side of the channel that is involved in sensing cellular pH. We have used constant pH molecular dynamics simulations in symmetrical and asymmetrical pH conditions across the membrane to investigate the pH- and ΔpH-dependent gating of the human H_V1 channel. Therefore, the pK_a of every titratable amino acids has been assessed in single simulations. Our simulations captured initial conformational changes between a deactivated and an activated state of the channel induced solely by changes of the pH. The pH-dependent gating is accompanied by an outward displacement of the three S4 voltage sensing arginines that moves the second arginine past the hydrophobic gasket (HG) which separates the inner and outer pores of the channel. H_V1 activation, when outer pH increases, involves amino acids at the extracellular entrance of the channel that extend the network of interactions from the external solution down to the HG. Whereas, amino acids at the cytoplasmic entrance of the channel are involved in activation, when inner pH decreases, and in a network of interactions that extend from the cytoplasm up to the HG.

Inhibitory effects of chondroitin sulfate on alpha-amylase activity: A potential hypoglycemic agent

Inhibiting the activity of the intestinal enzyme α-amylase that catalyzes the degradation of starch into glucose can control blood glucose and provide an essential way for the treatment of Type-II diabetes mellitus (T2DM). Here, we compared the structural information of chondroitin sulfate (CS) from different origins and the effects on activity of α-amylase and blood glucose have been investigated. The inhibitory effects of shark and porcine CSs against α-amylase activity is obvious with IC₅₀ values of 11.97 and 14.42 mg/ml, respectively, but the bovine CS almost no effect. From the data of fluorescence spectroscopic analyses, CSs from shark and pig quench Try fluorescence intensity of the enzyme, whereas bovine CS induces an increase. In vivo, oral administration of shark and porcine CSs efficiently suppresses postprandial blood glucose levels in normal and diabetic mice. Our study found that CSs from different sources showed different biological functions even if both molecular weight and disaccharide subunit composition are almost the same, and demonstrated that the CSs from shark and pig as α-amylase inhibitors could be regarded as a novel functional food ingredient in T2DM management.

Hv1-deficiency protects β cells from glucotoxicity through regulation of NOX4 level

High glucose (HG)-induced oxidative stress contributes to the dysfunction of pancreatic β cells in diabetes. The voltage-gated proton channel Hv1 has been proposed to support reactive oxygen species (ROS) production during respiratory bursts. However, the effect of Hv1 on glucotoxicity in pancreatic β cells is not clear yet. In this study, we examined the protective effects of Hv1-deficiency in HG cultured β cells. Following 48 h of treatment with 30 mM high glucose, Hv1 KO β cells showed higher cell viability, lower cell apoptosis and a more stable insulin gene expression level compared to WT β cells. In both control and HG cultured β cells, deficiency of Hv1 decreased the glucose- and PMA-induced ROS production. Finally, HG incubation led to NOX4 upregulation in WT β cells, which could be inhibited by HV1 deficiency. In conclusion, Hv1-deficiency prevents the HG treatment-induced NOX4 upregulation and protects β cells from glucotoxicity.