ARTS PARTY: Pierre Sarkozy, the son of French President Nicolas Sarkozy, commanded the dancefloor at Les Arts Decoratifs in Paris on Wednesday night as guest DJ for Reebok’s party celebrating the inauguration of the exhibition, “An Ideal History of Contemporary Fashion, Vol. 2.” Among guests, an intrepid Helena Christensen, who had spent the day shooting her second Reebok campaign, was back from a trip to Nepal where she was raising awareness for climate change. “I have been in sneakers all day, I didn’t think they would go with this outfit,” she giggled, pointing to her vertiginous black heels. Meanwhile, Marie-Ange Casta revealed she is working on a jewelry line for French brand Maty, due to launch in February. The burgeoning model, who has also just wrapped filming “Mineurs 27,” with Gilles Lellouche, is the face of the brand’s current campaign.