A tubing hanger assembly which includes: a body which comprises an annular outer surface (132, 134); a lockdown feature which is located on the body; a load nut which is threadedly connected to the body, the load nut comprising a downward facing load shoulder; and characterized by: a piston assembly which includes: an elongated cylinder which is positioned circumferentially around the outer surface of the body axially adjacent the load nut, the cylinder comprising a first cylinder end which is connected to the body and an open second cylinder end; an elongated piston which is slidably received in the cylinder, the piston comprising a first piston end which is oriented toward the first cylinder end and a second piston end which is configured to extend through the second cylinder end and engage the load nut such that extension of the piston causes the load nut to rotate relative to the body; and a seal which is positioned between the piston and the cylinder to thereby define a piston chamber between the first cylinder end and the first piston end, the piston chamber being connectable to a source of fluid pressure; wherein in operation of the piston assembly, the piston rotates the load nut to thereby move the load nut axially relative to the body; whereby an axial distance between the load shoulder and the lockdown feature is adjustable. a body which comprises an annular outer surface (132, 134); a lockdown feature which is located on the body; a load nut which is threadedly connected to the body, the load nut comprising a downward facing load shoulder; and characterized by: a piston assembly which includes: an elongated cylinder which is positioned circumferentially around the outer surface of the body axially adjacent the load nut, the cylinder comprising a first cylinder end which is connected to the body and an open second cylinder end; an elongated piston which is slidably received in the cylinder, the piston comprising a first piston end which is oriented toward the first cylinder end and a second piston end which is configured to extend through the second cylinder end and engage the load nut such that extension of the piston causes the load nut to rotate relative to the body; and a seal which is positioned between the piston and the cylinder to thereby define a piston chamber between the first cylinder end and the first piston end, the piston chamber being connectable to a source of fluid pressure; wherein in operation of the piston assembly, the piston rotates the load nut to thereby move the load nut axially relative to the body; whereby an axial distance between the load shoulder and the lockdown feature is adjustable. a piston assembly which includes: an elongated cylinder which is positioned circumferentially around the outer surface of the body axially adjacent the load nut, the cylinder comprising a first cylinder end which is connected to the body and an open second cylinder end; an elongated piston which is slidably received in the cylinder, the piston comprising a first piston end which is oriented toward the first cylinder end and a second piston end which is configured to extend through the second cylinder end and engage the load nut such that extension of the piston causes the load nut to rotate relative to the body; and a seal which is positioned between the piston and the cylinder to thereby define a piston chamber between the first cylinder end and the first piston end, the piston chamber being connectable to a source of fluid pressure; an elongated cylinder which is positioned circumferentially around the outer surface of the body axially adjacent the load nut, the cylinder comprising a first cylinder end which is connected to the body and an open second cylinder end; an elongated piston which is slidably received in the cylinder, the piston comprising a first piston end which is oriented toward the first cylinder end and a second piston end which is configured to extend through the second cylinder end and engage the load nut such that extension of the piston causes the load nut to rotate relative to the body; and a seal which is positioned between the piston and the cylinder to thereby define a piston chamber between the first cylinder end and the first piston end, the piston chamber being connectable to a source of fluid pressure; wherein in operation of the piston assembly, the piston rotates the load nut to thereby move the load nut axially relative to the body; whereby an axial distance between the load shoulder and the lockdown feature is adjustable.