Endolysosomal acidification amplifies JNK and IMD/NF-κB signaling and exacerbates oxidative injury in the Drosophila intestine

Abstract

Vacuolar ATPases (V-ATPases) are highly conserved multi-subunit proton pumps that drive the acidification of intracellular vesicles, especially endosomes and lysosomes. Beyond enabling cargo degradation, endolysosomal acidification shapes signal transduction, acting both positively through receptor processing in endosomes and negatively through lysosomal turnover of pathway mediators. Whether endolysosomal acidification shapes the intestinal epithelial response to oxidative injury remains unclear. Here we use Drosophila to define the role of V-ATPases in intestinal injury driven by excessive oxidative stress. Consistent with lysosomal biogenesis programs induced by oxidant in other systems, we find that oxidant exposure increases V-ATPase subunit expression and abundance of acidified vesicles in the midgut. Yet this response is not protective. RNAi depletion of multiple V-ATPase subunits suppresses lethality induced by either hydrogen peroxide or paraquat exposure. These effects map to mature absorptive enterocytes rather than to intestinal progenitors. Enterocyte-specific depletion of Vha44 (subunit C of the V1 domain) preserves intestinal barrier function and suppresses the cell death, JNK pathway activation, and IMD/NF-{kappa}B reporter activity induced by oxidant exposure. Overexpression of the MAP3K Tak1 sensitizes animals to oxidative stress and drives JNK and IMD signaling, both of which require Vha44. Together, these findings identify endolysosomal acidification as an amplifier of pro-apoptotic JNK and IMD/NF-{kappa}B signaling, such that attenuating V-ATPase levels in mature enterocytes protects the intestinal epithelium from excessive oxidant burden.