Leukemia inhibitory factor is involved in tubular regeneration after experimental acute renal failure.

Leukemia inhibitory factor (LIF) is known to play a crucial role in the conversion of mesenchyme into epithelium during nephrogenesis. This study was carried out to test the hypothesis that LIF and LIF receptor (LIFR) are involved in the renal epithelial regeneration after acute renal failure. First, the authors investigated the spatiotemporal expression of LIF and LIFR in fetal and adult rat kidney. In developing kidney, LIF was expressed in the ureteric buds and LIFR was located in nephrogenic mesenchyme and the ureteric buds; in adult kidney, LIF and LIFR expression was confined to the collect- ing ducts. Next, the authors examined the expression of LIF and LIFR during the recovery phase after ischemia-reperfusion injury. Real-time PCR analysis revealed that LIF mRNA ex- pression was significantly increased from day 1 to day 7 after reperfusion and that LIFR mRNA was upregulated from day 4 to day 14. Histologic analysis demonstrated that the increased expression of LIF mRNA and protein was most marked in the outer medulla, especially in the S3 segment of the proximal tubules. To elucidate the mitogenic role of LIF in the regen- eration process, cultured rat renal epithelial (NRK 52E) cells were subjected to ATP depletion (an in vitro model of acute renal failure), and LIF expression was found to be enhanced during recovery after ATP depletion. Blockade of endogenous LIF with a neutralizing antibody significantly reduced the cell number and DNA synthesis during the recovery period. These results suggest that LIF participates in the regeneration process after tubular injury. The mammalian kidney is susceptible to injury by ischemia and nephrotoxins, and recovery of normal renal function re- quires regeneration of damaged tubular epithelium. The pro- cess of regeneration after renal injury is characterized by a sequence of events that includes epithelial cell spreading, mi- gration to cover exposed areas of the basement membrane, cell dedifferentiation and proliferation to restore cell number, and then differentiation (1,2). In many respects this nephrogenic repair process resembles the growth and maturation of nephrons during kidney development (3,4). Several genes crit- ical for kidney development have been shown to be upregu- lated in the regeneration process after injury and participate in the regeneration. Pax-2 (5), Wnt-4 (6), and activin-A (7) have been shown to be re-expressed in the regenerating tubules after injury (8 -11). These findings support the hypothesis that a cascade of developmental gene pathways is reactivated during tissue regeneration. Leukemia inhibitory factor (LIF), a member of the interleu- kin-6 (IL-6) family, is a multifunctional cytokine originally identified as a proliferation inhibitor and differentiation in- ducer of mouse myeloid leukemia cell line M1 (12,13). LIF is synthesized by a variety of cells, including renal epithelial cells (14), and, functionally, it has been implicated in a number of processes including development, hematopoiesis, inflamma- tion, and regeneration after injury (15). LIF has been shown to play a pivotal role in kidney development. It is secreted by ureteric buds and induces conversion of mesenchyme into epithelium (16). The importance of LIF in nephrogenesis prompted us to test the hypothesis that LIF participates in renal epithelial tubular regeneration. In this study, we first investigated the expression of LIF and LIF receptor (LIFR) in ischemia/reperfusion-in- jured kidney and in normal fetal and adult rat kidney; we then used an in vitro ischemia model (ATP depletion method) to investigate the mitogenic effect of LIF on kidney epithelial cells (NRK 52E) during the regenerative process. The results showed that LIF is transiently increased in regenerating tubular cells during the recovery phase both in vivo and in vitro and that LIF contributes to renal epithelial regeneration.