GNC has filed for bankruptcy and will close up to 1,200 stores.The 85-year-old vitamin and dietary supplement company has been saddled with nearly a billion dollars of debt.GNC has faced declining sales at its brick-and-mortar locations since before the pandemic.However, GNC said that stay-at-home orders during the COVID-19 pandemic had a "dramatic negative impact" on its business.GNC will continue operating, but after closing 20% of its retail stores, it will become a smaller company.The company hopes to emerge from bankruptcy in the fall..