JAK2 and hydrops fetalis: Interestingly, the JAK2/STAT3 pathway could be slightly activated as a compensatory mechanism upon HF status, and transfection with Ad-S1R could further increase phosphorylation of JAK2 and STAT3, followed by an upregulation of p-VEGFR2 and VEGF expression, all the effects of which, however, were counteracted by AG490.