It would seem that the thread title can be either the article title and/or anything else the poster desires; specifically, the article title itself should remain intact.
The author writes the article and submits it to the publisher (unless it is self-published). The paper or other publishing source then has someone on staff write the headline. If you are citing an article, you as publisher of your publication can use any headline you want. You can find the same AP article in numerous papers with a wide range of headlines. So I do not believe you would violate any copyright