Autophagy is a tightly regulated process involving the degradation of the cellular components through the lysosomal machinery which helps cells to maintain a balance between production and degradation during development and growth, while acting as a survival pathway during starvation, stress, and bacterial infections (1). Vibrio cholerae infects and kills C. elegans via cholerae toxin and toxin-co-regulated pili independent manner. V. cholerae hemolysin (VCC), which is a pore forming toxin, is required for the lethality, growth retardation and intestinal cell vacuolation during the infection (2). VCC induced vacuoles found to be co-localized with LC3 (mammalian homolog of
lgg-1) punctuate, a feature indicative of autophagosome formation, in cultured cells (3). To characterize the large intestinal vacuoles induced by the VCC in C. elegans, we have analyzed the autophagosome distribution in C. elegans intestine exposed to WT and hlyA deletion mutant strains of V. cholerae, using
lgg-1::GFP marker. Exposure of C. elegans to WT V. cholerae led to increased levels of
lgg-1::GFP expression with increased number of dots in some of the intestinal cells, in comparison with intestines of worms exposed to hlyA deletion mutant strains. Accumulation of autophagosomes may reflect the induction of autophagy or reduced turnover of autophagosomes in blocked autophagy conditions. To differentiate between these two outcomes we genetically blocked the autophagy pathway using
unc-51/
atg-1 mutants. Inactivation of autophagy pathway using
unc-51(
e369) mutants led to a decrease in the formation of
lgg-1::GFP punctuate, during V. cholerae infection, suggesting an induction rather than a blockage in intestinal autophagy (4). Intestinal autophagy activity was observed in a single cell or a group of intestinal cells while other parts of the intestine looked unaffected. We found that same intestinal cells showing induced autophagy upon V.cholerae infection also contain large vacuoles, and autophagosomes are located in close proximity of these vacuoles. To address the question of whether large intestinal vacuoles are autophagolysosome related, we used
lmp-1::GFP (lysosome-associated membrane protein-1) marker, and found that
lmp-1::GFP is expressed in the membranes of the large vacuoles. Altogether our data suggest that V. cholerae induces autophagy response in C. elegans intestine via VCC and large intestinal vacuoles observed during infection are originated from autophagolysosomes. 1) Jia K. et al. PNAS, 106 (2009) 14564-14569 2) Cinar et al. PLoS ONE, 2010, 5(7):
e11558. doi:10.1371/journal.pone.0011558 3) Gutierrez MG. et al. PNAS, 104 (2007) 1829-1834 4) Cinar HN. et al. Ag. meta. pathogenesis in C. elegans Meeting 2010.