Previously, we found that serum PTH and the bone activating transcription factor 4/parathyroid hormone 1 receptor (PTH1R/ATF4) axis, the major pathway responsible for anabolic PTH effect in bone, can inversely affect the bone RANKL/OPG ratio and thus it may regulate bone accrual and strength in young rats with CKD [16]. Here, ATF4 is linked to chronic kidney disease.