If you want to protect your knees, keep running, and don’t become obese. I’ve looked at several studies about this and I’m far from convinced that running does anything bad to your joints; indeed, I think it may have a bit of a protective effect. You can still have arthritic knees and be a runner, sure, but I don’t think it is more likely just because you run. Over the past 18+ years I’ve worked with countless folks who have had hip and knee replacements, and there’s not been a single runner in the bunch. But the vast majority are over their ideal weight. So I’d keep running, don’t become obese, and try not to tear your ACL or do any other kind of trauma to your knees.
I have bad knees and the more I run the less I hurt. I took some time off to let some shin splints and other stuff get better and now i’m having a hard time getting back in the groove where my knee doesn’t hurt anymore.