Injuries have forced the Steelers to lean fairly heavily on younger defensive linemen, perhaps giving a glimpse into Pittsburgh's future up front. DE Aaron Smith, 35, was placed on injury reserve on Oct. 22 with a neck injury, and with injuries limiting him to just 15 games the last three seasons, his future is uncertain. Third-year pro Ziggy Hood, who replaced Smith in the lineup, has pass-rush ability but is still regarded as a work in progress, the way we hear it. At 24, Hood is the youngest starter on defense. The Steelers' 2011 first-round pick, Cameron Heyward, who is regarded has having prototypical size and strength for an end in a 3-4 scheme, is only 22. He has appeared in every game as a reserve. At nose tackle, injuries to veterans Casey Hampton and Chris Hoke have led to more playing time for 25-year-old Steve McLendon, who is vying to continue being a contributor in the middle now and in the future.