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:It has been reported that various mechanisms such as telomere shortening, histone modification, DNA methylation and miRNA expression affect the proliferation and differentiation of MSCs, resulting in cell senescence (Bonab et al., 2006; Noer et al., 2006; Wagner et al., 2008; Zhang et al., 2008; Bork et al., 2010).
Category: