Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Thus, in HEK293 cells, FGF23 and FGF2 activate distinct FGFR adaptor proteins, which could explain their differential downstream signaling in cardiac myocytes (Faul et al., 2011).
Category: