MAPK3 and chronic kidney disease: As shown in Figure 7A, after induction of renal injury, the down-regulated protein expression levels of p-ERK1/2 and p-SGK1, and the up-regulated protein expression levels of NHERF-1 and NaPi-2a in the kidneys of the CKD–MBD model rats were detected significantly, compared to those of the Sham group rats.