Peritubular Interstitial Cells Research Articles

PDGF-receptor localizes to mesangial, parietal epithelial, and interstitial cells in human and primate kidneys

There is evidence that platelet derived growth factor (PDGF) is a mediator of proliferative changes in renal arteries and mesangium in human disease, in the mesangium in experimental mesangial proliferative glomerulonephritis, and in the interstitium in a rodent model of angiotensin II mediated hypertension. We utilized a monoclonal antibody to the beta-subunit of the PDGF-receptor to localize constitutive expression of this receptor in human and nonhuman primate tissues. Tissues were fixed in cold 2 or 4% paraformaldehyde, and immunohistochemical techniques both at the light microscopic level and immunoelectron microscopy were employed. In the glomerulus, there is widespread expression of this molecule by mesangial cells, and there is frequent expression on the apical and lateral surface of parietal epithelial cells. There is also widespread expression of this molecule by cortical and medullary peritubular interstitial cells, but not by glomerular or peritubular capillary endothelium or other renal parenchymal structures. The identification of receptors capable of binding PDGF B-chain at each of these sites: (1) provides a basis for PDGF mediated mesangial proliferation in human disease; (2) provides a basis for PDGF mediated interstitial cell migration and/or proliferation and/or activation at sites of tubulointerstitial injury; and (3) suggests that glomerular parietal epithelial cells may be responsive to stimulation by PDGF.

Cell-type-specific and hypoxia-inducible expression of the human erythropoietin gene in transgenic mice.

Synthesis of erythropoietin, the primary humoral regulator of erythropoiesis, in liver and kidney is inducible by anemia or hypoxia. Analysis of human erythropoietin gene expression in transgenic mice revealed that sequences located 6-14 kilobases 5' to the gene direct expression to the kidney, whereas sequences within the immediate 3'-flanking region control hepatocyte-specific expression. Human erythropoietin transcription initiation sites were differentially utilized in liver and kidney. Inducible transgene expression was precisely targeted to peritubular interstitial cells in the renal cortex that synthesize endogenous mouse erythropoietin. These studies demonstrate that multiple erythropoietin gene regulatory elements control cell-type-specific expression and inducibility by a fundamental physiologic stimulus, hypoxia.

Editorial: Primary Erythrocytosis in Childhood

Regulation of erythropoiesis to provide the right number of circulating red cells for optimal oxygen transport is a complex process in which the hormone erythropoietin (EPO) plays a central role. Exciting new research is bringing into focus the nature of the biochemical processes that regulate EPO production and the interaction of EPO with target hematopoietic progenitor cells. An oxygen sensor in the adult kidney or fetal liver, thought to be a heme protein,' modulates EPO synthesis so as to maintain normal tissue oxygenation. As reflected in studies of hepatoma cell lines that respond to hypoxia by synthesizing EPO, in the liver the oxygen sensor is found in the same cell that produces EPO so that regulatory signals, which are as yet undefined, may exert their action locally rather than at a distance. In hepatomas, EPO gene expression is regulated at the mRNA transcriptional level and is the consequence of both increased EPO mRNA synthesis and diminished EPO mRNA degradation.* Cis-acting regulatory regions that serve as promotors or enhancers have been identified adjacent to the coding region of the EPO gene3 and the precise way in which these regions, as well as more distant transacting factors, govern EPO gene expression is under active investigation. In situ hybridization studies in the kidney have shown that EPO is produced in tubular epithelial cells or in peritubular interstitial cells.' However, little is known about the renal oxygen sensor, because an in vitro experimental system derived from renal tissue that secretes EPO is not available. EPO stimulates the proliferation and differentiation of erythroid progenitor cells in the fetal liver or postnatal bone marrow. These cells display only sparse numbers of EPO receptors (200-1000 per cell), which exhibit both high- and low-affinity binding of radiolabeled recombinant EPO. The EPO receptor gene has been cloned from murine hematopoietic tissue by D'Andrea et al.4 It consists of 507 amino acids, has a single membrane-spanning domain, and shares considerable homology with several other growth factor receptor proteins (GMCSF, IL-3, IL-4, IL-5, prolactin, and human growth h~rmone).~ Cross-linking studies that use radiolabeled EPO suggest that two EPO receptor proteins (MW 80 kda and 100 kda approximately) are found in erythroid progenitors, implyPediatric Hmiolosy and Oncolosy, B:iii-u, 1991

Erythropoietin

The remarkable capacity of the bone marrow to compensate for blood loss and for reduced atmospheric oxygen tension has been found to be mediated by a renal hormone, named erythropoietin. It is produced by peritubular interstitial cells in response to renal hypoxia, but molecular engineering has permitted large scale production of an identical recombinant erythropoietin in vitro. When used as a replacement hormone in patients with impaired endogenous production it has been found to be capable of improving or eliminating the anemia of chronic kidney disease and the anemia of prematurity. In the future it may also be used as a pharmacologic agent and possibly be able to control the anemia of patients with bone marrow failure and make them transfusion-independent.

Erythropoietin: Biology and Clinical Use

Red cell production in vertebrates is controlled by a glycoprotein hormone known as erythropoietin (Ep), which is produced by the kidney in response to hypoxia and acts on the marrow to selectively stimulate erythropoiesis. The gene for Ep has recently been cloned, and highly pure recombinant human Ep (rHuEp) is now available in considerable quantity. This has led to a better understanding of many aspects of Ep biology and to clinical trials in humans. The amino acid sequence of Ep is now completely known, and the protein portion of the natural hormone and the recombinant product are identical. Both the natural hormone and rHuEp produced in Chinese hamster ovary cells are heavily glycosylated in a very similar manner. This glycosylation is not necessary for in vitro activity but is required for activity in vivo. Radioimmunoassays (RIAs), which use labeled rHuEp, have been developed and are sufficiently sensitive to measure normal plasma levels. However, since Ep exists in plasma in several forms that vary in their immunologic and biologic activities, the ability of a RIA to provide information on the pathogenesis of clinical disease may be limited and should be referenced to the polycythemic mouse assay. The kidney's role in the production of Ep has been greatly clarified. Studies using probes to Ep mRNA have shown that Ep is primarily made in the kidney and secreted as the intact hormone. Moreover, renal secretion appears to be regulated by the rate of synthesis of the hormone, which in turn is dependent on the rate of synthesis of Ep mRNA. The cells that produce Ep have been identified as peritubular interstitial cells that may be endothelial in origin. The initiating mechanism for hormone production appears primarily to involve recruitment of additional cells rather than increased production by individual cells. Ep primarily acts on the marrow to stimulate the growth and maturation of early cells in the erythroid lineage that are known as the burst-forming unit-erythroid (BFU-E) and colony-forming unit-erythroid (CFU-E). The BFU-E is a very early cell closely related to the pluripotent stem cell, while the CFU-E is a later cell close to the first recognizable erythroblast.(ABSTRACT TRUNCATED AT 400 WORDS)

The antibody from an infertile woman that induces sperm agglutination interacts with rat testicular cells and sperm.

The serum obtained from an infertile woman induced a specific head-to-head agglutination of human and rat sperm. The immunoglobulin G (IgG) fraction of the serum was obtained and found to interact with the proteins of rat sperm in testis and epididymis. Using an indirect immunofluorescent method with rat sperm from vas deferens, we determined that the antibody recognized the protein on the convex and concave regions of the acrosome and over the entire tail. However, with testicular spermatozoa, the antibody recognized only the distal end of the tails. In paraffin sections of adult rat testis, sperm tails located at the luminal region of the seminiferous tubules stained intensely. Weak but significant staining also occurred on late spermatids. In the epididymal sections, staining was restricted to spermatozoa in the lumen. On the other hand, sections of testes from 25-day-old rats containing spermatogonia and early spermatocytes had a completely negative reaction. Testicular somatic cells, including Sertoli cells, peritubular myoid cells and interstitial cells, did not stain. To identify the testicular protein interacting with the antibody, adult rat testis proteins were prepared and analyzed by a sodium dodecyl sulfate-polyacrylamide gel electrophoretic (SDS-PAGE) immunoblot technique. The antibody interacted with a protein with an estimated molecular weight of 82,000 in the testicular homogenate and particulate fraction, whereas the reaction was considerably weaker with the testicular cytosol fraction.