The Effects of Diet and Altered Expression of the Keap1/CncC Pathway on Secretion of Organic Toxins by Malpighian Tubules of Drosophila melanogaster

Abstract

The Keap1-Nrf2 pathway is a major upstream regulator of xenobiotic detoxification. In Drosophila, directed activation of the protein complex of Keap1 and CncC (the homolog of human Nrf2) in principal and stellate cells of the Malpighian (renal) tubules confers resistance to lethal doses of the pesticide malathion, which is metabolized into organic anions. Dietary exposure to organic anions such as salicylate (10 mM) causes increases in fluid secretion rate and salicylate flux across Malpighian (renal) tubules. Here we used salicylate-selective microelectrodes and Ramsay assays to determine the role of Keap1/CncC in regulating these responses. Fluid secretion rate and salicylate flux across tubules isolated from adults with directed activation of Keap1/CncC in the principal cells are comparable to the values from salicylate-fed controls. Fluid secretion rate, concentration of salicylate in the secreted fluid and salicylate flux did not differ significantly between tubules isolated from adults with directed activation of Keap1/CncC in the principal cells reared on a diet containing salicylate and those reared on control media, indicating that the detoxification pathway was activated regardless of the presence of dietary salicylate. This is in contrast to the significant increase in fluid secretion rate and salicylate flux between tubules isolated from salicylate-fed adults and adults reared on a control diet with directed activation of Keap1/CncC in the stellate cells, supporting previous studies that demonstrated the inability of stellate cells to transport organic anions. Taken together, these results suggest a role for Keap1/CncC in upregulating fluid secretion in response to the presence of dietary organic anions.