title: A reduction in intestinal cell pHi due to loss of the Caenorhabditis elegans Na+/H+ exchanger NHX-2 increases life span.
abstract: Na+/H+ exchangers are involved in cell volume regulation, fluid secretion and absorption, and pH homeostasis. NHX-2 is a Caenorhabditis elegans Na+/H+ exchanger expressed exclusively at the apical membrane of intestinal epithelial cells. The inactivation of various intestinal nutrient transport proteins has been shown previously to influence aging via metabolic potential and a mechanism resembling caloric restriction. We report here a functional coupling of NHX-2 activity with nutrient uptake that results in long lived worms. Gene inactivation of nhx-2 by RNAi led to a loss of fat stores in the intestine and a 40% increase in longevity. The NHX-2 protein was coincidentally expressed with OPT-2, an oligopeptide transporter that is driven by a transmembrane proton gradient and that is also known to be involved in fat accumulation. Gene inactivation of opt-2 led to a phenotype resembling that of nhx-2, although not as severe. In order to explore this potential functional interaction, we combined RNA interference with a genetically encoded, fluorescence-based reagent to measure intestinal intracellular pH (pHi) in live worms under physiological conditions. Our results suggest first that OPT-2 is the main dipeptide uptake pathway in the nematode intestine, and second that dipeptide uptake results in intestinal cell acidification, and finally that recovery following dipeptide-induced acidification is normally a function of NHX-2. The loss of NHX-2 protein results in decreased steady-state intestinal cell pHi, and we hypothesize that this change perturbs proton-coupled nutrient uptake processes such as performed by OPT-2. Our data demonstrate a functional role for a Na+/H+ exchanger in nutrient absorption in vivo and lays the groundwork for examining integrated acid-base physiology in a non-mammalian model organism.
authors.affiliation: Gastroenterology Unit, Department of Medicine, University of Rochester Medical Center, Rochester, New York 14642, USA. keith_nehrke@urmc.rochester.edu
authors.forename: Keith
authors.initials: K
authors.lastname: Nehrke
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000502:physiology; D000136:Acid-Base Equilibrium; D000375:Aging; D000818:Animals; D017173:Caenorhabditis elegans / Q000502:physiology*; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000502:physiology*; D004151:Dipeptides / Q000378:metabolism; D005456:Fluorescent Dyes; D015870:Gene Expression; D020868:Gene Silencing; D049452:Green Fluorescent Proteins; D006863:Hydrogen-Ion Concentration; D007202:Indicators and Reagents; D007408:Intestinal Absorption; D007422:Intestines / Q000737:chemistry; D007700:Kinetics; D008136:Longevity; D008164:Luminescent Proteins / Q000235:genetics; D018613:Microscopy, Confocal; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000502:physiology*
chemical_list: D018528:ATP-Binding Cassette Transporters; D029742:Caenorhabditis elegans Proteins; D004151:Dipeptides; D005456:Fluorescent Dyes; D007202:Indicators and Reagents; D008164:Luminescent Proteins; C480043:NHX-2 protein, C elegans; D017923:Sodium-Hydrogen Exchangers; C113070:pept-1 protein, C elegans; D049452:Green Fluorescent Proteins