Enhanced Autophagy in Polycystic Kidneys of AQP11 Null Mice

Aquaporin-11 (AQP11) is an intracellular water channel expressed at the endoplasmic reticulum (ER) of the kidney proximal tubule. Its gene disruption in mice leads to intracellular vacuole formation at one week old and the subsequent development of polycystic kidneys at three week old. As the damaged proximal tubular cells with intracellular vacuoles later form cysts, autophagy may play a role in their survival. We examined the autophagy activity before and after the development of cysts in AQP11(-/-) kidneys. We first observed an enhanced expression of LC3 gene (Map1lc3b) as well as other autophagy-related genes in AQP11(-/-) mice by quantitative PCR analysis. We then examined the formation of autophagosomes visualized by a green fluorescent fusion protein, GFP–LC3 in its transgenic mice. The expression of GFP-LC3 puncta was increased in the proximal tubule of AQP11(-/-) mice before the cyst formation. Interestingly, they were also observed in the cyst-lining epithelial cell. Further PCR analyses revealed the enhanced expression of apoptosis- and ER stress-related caspase genes before and after the cyst formation suggesting that ER stress may have enhanced autophagy. We conclude that autophagy will play an important role in the development and the survival of the kidney cysts in AQP11(-/-) mice.