These results suggested that cyst fluid TNFα might act through PI3K-Akt mediated activation of mTOR to increase the levels of Id2 to regulate cyst lining epithelial cell proliferation during cyst development, which might be one of the reasons that rapamycin could inhibit cyst lining epithelial cell proliferation in Pkd1 knockout mouse models [38]. Here, ID2 is linked to cyst.