Identification of the renal erythropoietin-producing cells using transgenic mice

Abstract

Regulation of erythropoietin production by the kidneys is central to the control of erythropoiesis. Uncertainty about the identity of the renal cells involved has been a major obstacle to understanding this mechanism. We have used sequence from the mouse erythropoietin locus to direct expression of a marker gene, SV40 T antigen, to these cells in transgenic mice. The transgenic constructs contained an oligonucleotide marker (Epo-M) or SV40 sequence (Epo-TAg) in the 5' untranslated region of the mouse erythropoietin gene, flanked on each side by 9 and 7.5 kb of DNA from the mouse erythropoietin locus. Anemia-inducible expression of Epo-M and Epo-TAg was observed in the kidney. In one of thirteen lines, homologous integration of Epo-TAg into the mouse erythropoietin locus occurred. In transgenic mice bearing Epo-TAg at homologous and heterologous insertion sites, renal expression was restricted to a population of cells in the interstitium of the cortex and outer medulla. Immunohistochemical characterization by light and electron microscopy shows that these are the fibroblast-like type I interstitial cells.

Hypoxia and the HIF system in kidney disease

“…When hematocrit is in the normal range, the kidney produces a low level of EPO, with EPO expression limited to a small number of these fibroblasts in the deep cortex and superficial outer medulla [2][3][4]. The increased production of EPO under anemic circumstances involves progressive recruitment of additional interstitial fibroblasts in a pattern that spreads outward from the deep cortex toward the capsule and the inner medulla.…”

Hif-1

“…Intriguing is that individual fibroblasts seem to be recruited in an all-or-none manner (91). At maximal stimulation, it seems that almost all of the fibroblasts of the cortex and the outer medulla activate expression of the EPO (82).…”

“…One reason for this is no renal fibroblast cell line that expresses the EPO gene has yet been generated. When hematocrit is in the normal range, the kidney produces a low level of EPO, with EPO expression limited to a small number of interstitial fibroblasts in the deep cortex and superficial outer medulla (82,91,92). Anemia results in a dramatic increase in EPO production, resulting in a rise in up to 3 orders of magnitude in the circulating level.…”

Abnormal erythropoietin (Epo) gene expression in the murine erythroleukemia IW32 cells results from a rearrangement between the G-protein β2 subunit gene and the Epo gene

“…This latter observation could suggest the putative existence of another exon located 5' to the published Epo gene structure. Many studies focused on the mechanisms regulating Epo gene expression have shown that the cis-acting sequences involved in hepatic and renal expression of Epo were di erent (Semenza et al, 1990(Semenza et al, , 1991Maxwell et al, 1993); moreover, Epo expression has also been detected in the brain (Masuda et al, 1994;Digicaylioglu et al, 1995). Speci®c expression in di erent tissues could involve alternative promoters of the same gene, as it was described for the porphobilinogen deaminase (Chre tien et al, 1988), pyruvate kinase (Noguchi et al, 1987), (Max-Audit et al, 1993) and choline acetyl transferase genes (Chireux et al, 1995).…”