Keeping minus sign in first position in URL

My WP website is displaying YT videos using the YT video ID as title of the posts, each post is dedicated to one video. So, sometimes, a YT video ID start with a minus sign. For example: -Y5jk8_ghP5 (this is a fictive ID).

The problem is that WP (this is a formatting.php effect I guess) deletes this minus sign, even I try to modify the URL. The minus sign is always present in the name of the post, in the posts lists created by WP, but not in the URL. So the URL:

mywebsite.com/Y5jk8_ghP5

is corresponding to a post named -Y5jk8_ghP5

If I try to manually add the minus sign in the address bar of my browser (mywebsite.com/-Y5jk8_ghP5) this works too.

So, what I would like is to modify formatting.php file to keep minus sign in URL. Can any body help?