Gene Knockout of NHX-3 in the Soil Nematode Caenorhabditis elegans Leads to Broad-Spectrum Compensatory Regulation of Na /H Exchangers, Antiporters, and the V-Type H -ATPase

Na+/H+ exchangers are directly involved in a variety of an animal's essential physiological processes such as ionoregulation, acid-base regulation, nitrogenous waste excretion, and nutrient absorption. While nine NHX isoforms have been identified in Caenorhabditis elegans, the physiological importance of each isoform is not understood. The current study aimed to further our knowledge of NHX-3 which has previously been suggested to be involved in the movement of ammonia and acid-base equivalents across the nematode's hypodermis. Although NHX-3 knockout mutant nematodes exported H+ and imported Na+ at slower rates than wild-type nematodes, attempts to inhibit the NHX activity of mutant nematodes using amiloride and EIPA caused an unexpected increase in hypodermal H+ export and did not impact Na+ fluxes suggesting that the different H+ and Na+ transport profiles of the nematodes are likely due to compensatory changes in the mutants in response to the NHX-3 knockout, rather than the loss of NHX-3's physiological function. Significant changes in the mRNA expression of 7 other NHX isoforms, 2 Na+/H+ antiporter isoforms, and the V-type H+-ATPase were detected between wild-type and mutant nematodes. Furthermore, mutant nematodes possessed significantly reduced rates of cytochrome C oxidase activity and ammonia excretion rates, indicating the knockout of NHX-3 induced fundamental changes in metabolism that could impact the nematode's need to eliminate metabolic end-products like H+ and ammonia that relate to NHX transport. While C. elegans is a popular genetic model with cheap and accessible commercial mutants, our findings suggest caution in interpretation of results in studies using mutants to study physiological traits and the biological significance of specific transporters.