CXCL12 and acute kidney injury: CXCR4 and CXCR7 expression can differentially modulate the biological activity because of divergent activation pathways.34 In acute renal failure, CXCR7 but not CXCR4 was responsible for the CXCL12-induced renal progenitor cell survival.24 Presently, the exact function of CXCR7 is still controversial.