It's an American colloquialism: shuttered is a form of: shut·ter verb /ˈSHətər/  shuttered, past participle; shuttered, past tense; shuttering, present partici

It's an American colloquialism: shuttered is a form of: shut·ter verb /ˈSHətər/  shuttered, past participle; shuttered, past tense; shuttering, present participle; shutters, 3rd person singular present Close the shutters of (a window or building) - the windows were shuttered against the afternoon heat - barred and shuttered stores Close (a business) - the city was gripped by economic forces that were squeezing its tax base and shuttering its factories