Increase of insulin sensitivity and reversal of age-dependent glucose intolerance with inhibition of ASIC3 Shyh-Jer Huang a,b , Wei-Shiung Yang c,d , Yi-Wen Lin b , Hung-Chin Wang b , Chih-Cheng Chen b, * a Graduate Institute of Life Sciences, National Defense Medical Center, Taipei 114, Taiwan b Institute of Biomedical Sciences, Academia Sinica, Nankang, Taipei 115, Taiwan c Graduate Institute of Clinical Medicine, College of Medicine, National Taiwan University, Taipei 100, Taiwan d Department of Internal Medicine, National Taiwan University Hospital, Taipei 100, Taiwan article info Article history: Received 21 April 2008 Available online 6 May 2008 Keywords: ASIC3 APETx2 WAT Glucose tolerance Insulin Aging abstract Glucose tolerance progressively declines with age in humans and is often accompanied by insulin resis- tance and a high prevalence of type 2 diabetes. Little is known about the mechanism underlying the age- related changes in glucose metabolism. Here we reported that acid-sensing ion channel 3 (ASIC3) is func- tionally expressed in adipose cells. ASIC3 / mice were protected against age-dependent glucose intoler- ance with enhanced insulin sensitivity. Acute administration of ASIC3-selective blocker APETx2 improved the glucose control and increased the insulin sensitivity in older (25–27 weeks) ASIC3 +/+ mice. Moreover, the enhanced glucose control in aging ASIC3 / mice was associated with high baseline levels of Akt phos- phorylation and high copy number of mitochondrial DNA in adipose tissues. Taken together, our data suggest that ASIC3 signaling might be involved in the control of age-dependent glucose intolerance and insulin resistance. Ó 2008 Elsevier Inc. All rights reserved. Acid-sensing ion channels (ASICs) mediate inward currents and depolarize cells when the extracellular pH drops [1]. They belong to the epithelial sodium channel/degenerin superfamily, characterized by two membrane-spanning domains with intra- cellular N- and C-termini and a large extracellular loop [2]. There are seven ASIC subunits encoded by five genes, including ASIC1a, ASIC1b, ASIC2a, ASIC2b, ASIC3, ASIC4, and ASIC5 [2,3]. Multiple subunits must assemble to form a functional ion channel [3,4]. Homomeric or heteromeric ASICs perform a variety of sensitivity to extracellular pH drop, ranging from near physiological pH (pH 7.0 for ASIC3) to very acidic status (pH 5.0 for ASIC2a) [5,6]. ASICs express throughout neurons of mammalian central and peripheral nervous systems [1,2]. Thus, the role of ASICs has been implicated in detecting tissue acidosis, ischemia, and modulating synaptic activity [3]. ASIC3 is known as the most sensitive acid-sensing ion channel and dominantly expressed in primary sensory neurons, especially in metaboreceptive sensory neurons or ischemia-sensing neurons [7,8]. ASIC3 channels open when pH drops from 7.4 to 7.0 and lactate can enhance the opening of ASIC3 at near physiological, pH 7.4 [9]. Therefore, these neurons might function as metaboreceptors to sense the anaerobic metabolism of tissues and trigger acid-linked pain sensation in muscle and heart [10–13]. Because lactate does not cause pain in many other tissues (e.g., adipose tissues), ASIC3 may not only be a pain sensor but also be involved in monitoring the metabolic state of tissues. Type 2 diabetes is the most common metabolic disease in aging population worldwide [14]. With physiological aging, resistance to the action of insulin and decline in glucose tolerance develop, resulting in a high prevalence of type 2 diabetes in older people [15–17]. The metabolic disease is closely associated with mito- chondria dysfunction in the elderly [17,18]. Mitochondria dysfunc- tion switches cells to anaerobic glucose metabolism and increases lactate production [19]. The elevated basal level of lactate is consis- tently found in diabetic subjects who also display marked insulin resistance [20]. Therefore, it is tempting to know if the lactate sen- sor, ASIC3, plays a role in control of the age-dependent glucose metabolism. We have previously generated ASIC3 / mice and demonstrated that ASIC3 is mediated high-intensity pain stimuli [12]. In this study, we identified a novel role of ASIC3 in mediating insulin sensitivity in an age-dependent manner. Materials and methods Mice. ASIC3 knockout (ASIC3 / ) mice were generated as previ- ously described [12]. Congenic heterozygous (ASIC3 +/ ) mice were derived from breeding ASIC3 chimera with females of the 129S2/ SvPasCrl wild type (ASIC3 +/+ ). Mice used in this study were off- spring from the congenic ASIC3 +/ mice intercross or breeding with 0006-291X/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2008.04.147 * Corresponding author. Fax: +886 2 2782 9224. E-mail address: chih@ibms.sinica.edu.tw (C.-C. Chen). Biochemical and Biophysical Research Communications 371 (2008) 729–734 Contents lists available at ScienceDirect Biochemical and Biophysical Research Communications journal homepage: www.elsevier.com/locate/ybbrc