SMAD3 and acute kidney injury: We next examined the regulatory role of Smad3 in SARS‐CoV‐2 N protein‐induced AKI by ultrasound‐microbubble‐mediated kidney‐specifically transfecting the SARS‐CoV‐2 N protein expressing plasmids (200 μg/mouse) into the Smad3 wild‐type (WT) or KO mice.