Irisin and FGF21 are cold-induced endocrine activators of brown fat function in humans - Lee, P; Linderman, J D; Smith, S; Brychta, R J; Wang, J; Idelson, C; Perron, R M; Werner, C D; Phan, G Q; Kammula, U S; Kebebew, E; Pacak, K; Chen, K Y; Celi, F S (Cell Metab, 2014)