ATF4 and Hyperglycemia: The results showed that metformin significantly reduced the expression of ERS-associated proteins, such as PERK, ATF4, and CHOP (Figure 5A), in hyperglycaemic osteoblasts; downregulating PPARγ levels enhanced the effect of metformin on PERK, CHOP and ATF4 in the context of hyperglycemia (Figure 5B).