<qa>  What is metformin used for?There is growing evidence that metformin, a drug widely used for the treatment of type 2 diabetes and polycystic ovary syndrome, may serve as a novel therapy for individuals in the early stages of Autosomal Dominant Polycystic Kidney Disease ADPKD by activating the metabolic sensor AMP-activated protein kinase AMPK. AMPK is activated under conditions of metabolic and other cellular stresses. Through its actions on downstream mediators, AMPK activation during low energy states decreases cellular energy consumption while stimulating energy generating pathways. It has been shown that AMPK phosphorylates and inhibits cystic fibrosis transmembrane conductance regulator CFTR, thus suppressing epithelial fluid and electrolyte secretion. Similarly, AMPK phosphorylates the tuberin protein, leading to indirect inhibition of the mTOR pathway. Thus, AMPK inhibits both CFTR and mTOR, suggesting that targeted activation of this kinase by metformin may provide a therapeutic benefit in ADPKD. It has been shown that metformin treatment of kidney epithelial cells leads to stimulation of AMPK and subsequent inhibition of both mTOR and CFTR activity. It has also been shown that metformin slows cystogenesis in animal models of PKD, supporting the potential of this drug in ADPKD treatment. 