P4HB and type 2 diabetes mellitus: A PCA plot bar graph (Fig. 4e) based on the expression levels of MAFA, NKX6.1, CCT4, XBP1 and GRP78, as well as PDIA1 (ESM Fig. 10), shows a clearer division between the three groups, highlighting the progression from NGT to IGT and then type 2 diabetes.