ATF4 and cyclic hematopoiesis: Wei et al. (2012) found that Ihh overexpression is involved in CH hypertrophy and accelerates the progression of OA, and treating CHs with the inhibitor of Ihh can decrease the transcription levels of MMP13 and Col-X. During the ossification of mouse CHs, ATF4 is confirmed to transcriptionally regulate Ihh expression by binding to its promoter (Wang et al., 2009).