Michael J. Fox Shows Off 'Back to the Future' Marty McFly Shoes (Video)

He also talks to David Letterman about Charlie Sheen, who replaced him on Spin City.
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Michael J. Fox showed off the Nike Air Mags -- the shoes his character Marty McFly wears in Back to the Future 2 -- on the Late Show With David Letterman Thursday night.

STORY: First Pair of Back to the Future Marty McFly Nike Shoes Sell for $37,500

Nike is releasing 1,500 pairs of the shoes on eBay, with proceeds to benefit the Michael J. Fox Foundation for Parkinson's Research. A pair was auctioned off in L.A. Thursday night for $37,500.

"This brings together three populations of major Joneses," Fox told Letterman, "the sneakerheads, the Back to the Future people, who, believe me, are out of their minds… in a good way! Thank God for them. And the people in the Parkinson's community who have an interest in research."

STORY: Marty McFly Nike Shoes Ignite Strong Fan Response

Fox then also confirmed that the co-founder of Google, Sergey Brin, was going to match up to $50 million of the proceeds raised through 2012 for research.

Fox also discussed Charlie Sheen, who replaced him on Spin City.

PHOTOS: Charlie Sheen's Colorful Career

"He worked and I got paid," he joked. "He was great and I feel bad for all his troubles now."

When Letterman quipped that Sheen was "all out there winning," Fox agreed: "That's a straightforward argument to me. He's winning, and that's fine, and I have no judgment about that… I wish Charlie all the best, and I wish Ashton all the best.

He then joked: "Show business. We're all here because we're not all there."