PITTSBURGH — The latest makeover on the Pittsburgh Steelers is accelerating as free agency begins.

The Steelers signed linebacker Arthur Moats to a three-year contract on Monday and released veteran defensive end Brett Keisel as the youth movement that’s been underway for the last several seasons nears completion.

Moats, who turns 27 next weekend, had four sacks in his first season with the Steelers in 2014 after coming over from Buffalo. He added 24 tackles, two forced fumbles and a season-turning fumble recovery at Cincinnati on Dec. 7, feeding a furious rally that helped propel Pittsburgh to a 4-0 season-ending run and the AFC North title.

Moats filled in capably at both inside and outside linebacker last season for the AFC North champions. Pittsburgh is in serious need of help at outside linebacker: James Harrison and Jason Worilds are free agents, leaving Jarvis Jones as the only experienced outside linebacker on the roster when the new league year begins on Tuesday.

Keisel had one year remaining on his contract but his departure was anticipated after the two-time Super Bowl winner tore his triceps in a loss to New Orleans on Nov. 30.

Keisel follows linebacker James Harrison out the door. Harrison came out of a brief retirement to have 5 1-2 sacks last fall. He will remain in training and will explore free agency, but is not expected to return for a third act with the Steelers.