Experimental nephrology最新文献

Transforming growth factors beta (TGF-betas) are peptides involved in autocrine and paracrine control of cell growth and differentiation. In the kidneys, TGF-beta(2) has been shown to localize specifically in renin-producing cells in various conditions stimulating the renin response. To test in vivo the functional role of TGF-beta(2), the renin response was investigated in mice heterozygous for a null mutation of the TGF-beta(2) gene, which had a twofold reduction in the amount of TGF-beta(2) mRNA. Although the increase in plasma renin concentration triggered by dehydration was not different from wild-type mice, renal renin mRNA and protein levels were higher in mutant mice under hydrated or dehydrated conditions. These data suggest that TGF-beta(2) exerts an inhibitory effect on renin synthesis and release from the juxtaglomerular apparatuses.

Scientific analyses fortified by interpretations of immunodeficiency diseases as 'experiments of nature' have revealed the specific immune systems to be comprised of T cells subserving cell-mediated immunities plus B cells and plasma cells which produce and secrete antibodies. These two separate cellular systems regularly interact with each other to produce a coordinated defense which permits mammals to live within a sea of microorganisms that threaten the integrity and the survival of individuals. We have shown that bone marrow transplantation (BMT) can be used as a form of cellular engineering to construct or reconstruct the immune systems and cure otherwise fatal severe combined immunodeficiency. When severe aplastic anemia complicated the first BMT which was performed to cure a fatal severe combined immunodeficiency, a second BMT cured for the first time a complicating severe aplastic anemia. Subsequently, BMT has been used effectively to treat some 75 otherwise fatal diseases such as resistant leukemias, lymphomas, inborn errors of metabolism, and genetic anomalies of the hematopoietic development such as sickle cell anemia, thalassemia, congenital neutropenias, and many other diseases. More recently, we have employed BMT in mice both to cure and cause autoimmunities, and, together, these experiments showed that autoimmunities actually reside in the hematopoietic stem cells. We have also found that mixed BMT or mixed hematopoietic stem cell transplantation (HSCT) can be used to prevent and cure the most complex autoimmunities such as those occurring in BXSB mice and in (NZW x BXSB)F1 W/BF1 mice. Untreated, the former develop fulminating lethal glomerulonephritis plus numerous humoral autoimmunities. Mice of the (W/B)F1 strain develop autoimmune thrombocytopenic purpura, coronary vascular disease with myocardial infarction, glomerulonephritis, and numerous autoantibodies. All of these abnormalities are prevented or cured by mixed syngeneic (autoimmune) plus allogeneic (normal healthy) BMT or mixed peripheral blood HSCT. Thus, the most complex autoimmune diseases can be prevented or cured in experimental animals by mixed syngeneic plus allogeneic BMT or HSCT which produce stable mixed chimerism as a form of cellular engineering.

Renal tubular epithelial cells (RTC) form a barrier between the host and ascending microbes in upper urinary tract infection. Previous studies have shown the ability of the kidney to produce defensins--antimicrobial peptides that play a pivotal role in unspecific host defense. To further clarify the role of renal epithelium for direct antibacterial activity we investigated the expression, regulation and production of antimicrobial peptides by cultured human RTC. Cell culture supernatants of RTC exert strong bactericidal activity against Escherichia coli and Klebsiella pneumoniae, two of the most important pathogens in urinary tract infections. The antimicrobial effect depends on salt concentration, a typical feature of human defensins. RT-PCR of RNA from cultured proximal and distal RTC showed constitutive expression of human beta-defensin 1 (hbd-1) and human beta-defensin 2 (hbd-2) whereas only hbd-1 expression could be detected in RNA preparation from renal biopsy material. Hbd-2 expression of RTC was induced by inflammatory processes as shown by semiquantitative competitive RT-PCR. Coincubation of the cultured cells with IL-1alpha or E. coli promote the strongest hbd-2 induction whereas TNF-alpha and LPS lead to a weaker or no (IL-6) hbd-2 induction. This is the first evidence that human RTC are able to produce antibacterial substances in a biologically relevant amount and that beta-defensins are candidate proteins responsible for this effect.

Erythropoietin (EPO) in the renal cortex is synthesized by fibroblast-like cells that are in direct contact with capillaries and adjacent tubular cells. Prompted by this anatomical relationship, we asked whether renal cells express EPO receptors (EPORs) through which EPO could act as a renotropic cytokine. We found that all regions of human, rat and mouse kidney, mesangial and proximal and distal tubular cells express authentic EPORs. Similar EPOR expression was detected in kidney cancer cells, and in cyst epithelia from polycystic kidneys. In vitro, EPO stimulated mitogenesis in all normal and malignant cells, and cell survival and motogenesis in injured tubular cells. Since the normal kidney is essentially unresponsive to EPO, we hypothesized that EPO's cytokine effects in the kidney are revealed when tubular cells are induced to proliferate by a prior insult, as occurs in acute renal failure. Accordingly, we found that EPO treatment of rats with 'ischemic' acute renal failure afforded renoprotection and accelerated functional recovery.

Angiogenesis plays a key role in a broad array of physiologic and pathologic processes. Two major systems--coagulation and fibrinolysis--maintaining hemostasis, have recently been implicated in angiogenesis. Generation of mice deficient in components of coagulation and plasminogen systems has provided an extraordinary opportunity to define the role of each of these systems in vivo and to elucidate molecular mechanisms involved in angiogenesis. It appears that several factors of the coagulation system, such as the tissue factor, the factor V and the thrombin receptor, play an important role in embryonic vessel formation, most probably in the formation of the primitive vascular wall. In addition, the plasminogen system appears to play a significant role in angiogenesis in adulthood, regulating the migration of endothelial and smooth muscle cells, the degradation of the extracellular matrix and activity of the metalloproteinase system. These new revelations open a possibility for future therapeutic strategies to specifically control angiogenesis in different pathological processes where abnormalities of tissue vascularization are pathogenetically prominent.

As the only ex utero mechanism for the removal of nitrogenous waste, the mammalian kidney achieves some 50-fold increase in urine production during the perinatal period when the placental circulation becomes no longer available as a functional dialyzer. This urine is efficiently removed from the kidney by the renal pelvis, a smooth muscle structure unique to mammals, which develops during the perinatal period. We found that mutant mice completely devoid of angiotensinogen or its type 1 receptor, as well as wild-type neonates given an ACE inhibitor, fail to develop a renal pelvis or a ureteral peristaltic movement. These structural and functional defects in the urinary tract are followed by severe obstructive injury of the renal parenchyma. The ability of angiotensin to directly induce the pelvis is demonstrated in an organ culture system, in which treatment with angiotensin induces the characteristic smooth muscle layer in the wild type, but not in homozygous null mutants. Upregulation of both renal angiotensin content and type 1 receptor at the renal hilum are also demonstrated in the wild type during the transition from intra- to extra-uterine life. By inducing the timely development of the renal pelvis, angiotensin thus facilitates the removal from the renal parenchyma of the urine that promptly increases at birth, thereby effectively preventing a buildup of intrarenal pressure and a consequent development of dysmorphic kidney.

The present paper reports the glomerular and renal individual glycosaminoglycan levels in an experimental model of chronic renal failure (CRF) that was induced in Wistar rats by five-sixths mass ablation. Glycemia, body weight, blood systolic pressure and urinary excretions of creatinine, albumin and glycosaminoglycans were measured for 12 weeks. At the end of the experiment, the weight and the glycosaminoglycan composition of the kidneys were determined. In control rats, heparan sulfate was the main glycosaminoglycan found both in whole kidney and isolated glomeruli, with trace amounts of dermatan sulfate. Isolated glomeruli presented higher heparan sulfate concentrations than whole kidney (expressed as mg/g dry weight). In CRF rats, albuminuria appeared from the 2 week on, and dermatan sulfate and chondroitin sulfate contents of the kidney increased, whereas heparan sulfate levels remained unaltered. Changes in urine glycosaminoglycans (heparan sulfate, chondroitin sulfate and dermatan sulfate) were not statistically significant. The increase in glomerular dermatan sulfate and chondroitin sulfate observed in this experimental model could be related to the mechanisms involved in the glomerulosclerosis and proteinuria that occur in CRF.

Ischemia/reperfusion injury increases the expression of bioactive heparin-binding epidermal growth factor-like growth factor (HB-EGF) in the rat kidney, suggesting that oxidant stress or cell injury related to oxidant stress might affect HB-EGF expression in the injured renal parenchyma. We utilized a nontransformed rat renal epithelial cell line (NRK-52E cells) to investigate whether reactive oxygen species induced transcriptional activation of HB-EGF mRNA. Hypoxia/reoxygenation increased HB-EGF expression in NRK-52E cells, and at concentrations that induced sublethal cell injury, hydrogen peroxide (H(2)O(2)) increased HB-EGF mRNA expression 4.7-fold. The free radical scavengers, dimethylthiourea and N-acetylcysteine inhibited HB-EGF mRNA induction. In contrast, another free radical scavenger, pyrrolidine thiocarbamate (PDTC), augmented H(2)O(2)-mediated HB-EGF expression. Since PDTC has been reported to augment AP-1-mediated transcriptional activation, we utilized an electrophoretic mobility shift assay to confirm that H(2)O(2) administration to NRK-52E cells did increase nuclear extract DNA-binding activity to a consensus AP-1 sequence. Using a CAT reporter assay coupled to the proximal 2,000 bp of the human HB-EGF 5'-untranslated region, we determined that H(2)O(2) administration increased CAT activity 5.5-fold. Truncation or deletion mutations of a putative AP-1-binding site reduced the H(2)O(2)-stimulated activity by >60%, and there was increased DNA binding of nuclear extracts from H(2)O(2)-treated cells to a 24-bp oligonucleotide containing this putative AP-1 site. Anti-fos and jun antibodies inhibited this binding, and there was no binding to an oligonucleotide in which the putative AP-1 site was mutated. The site of the residual activation was found to exist in the most proximal 5'-untranslated region (-121 to +60), which contains two putative SP1 sites. Timing and localization of AP-1-binding activity from nuclear extracts from the post-ischemic tissue correlated with HB-EGF mRNA expression. Therefore, in renal epithelial cells, oxidant stress increases HB-EGF expression, which appears to be mediated in part by an increase in AP-1 binding. This activation may play an important role in the induction of HB-EGF mRNA in response to tissue injury and may regulate early stages of recovery following ischemic damage.

Genetic animal models are central to ongoing efforts to elucidate the pathophysiology and genetic basis of hypertension. The rat is the leading species in experimental hypertension. Several rat models of hypertension are available for research, including inbred strains, congenic lines, transgenic animals and recombinant inbred strains. Each of these models has been designed to express different phenotypes, including spontaneous hypertension, salt sensitivity, stress sensitivity and susceptibility to end-organ damage. All these models have been extremely useful in the search for the physiological mechanisms that underlie hypertension, but some of them have been specifically designed for detecting the hypertension genes. This latter task is extremely complex in spontaneous hypertension, but genetic animal models may simplify the task by enabling to focus on specific phenotypes. Despite intensive efforts over nearly 3 decades, the genetic basis of hypertension has not been unveiled so far in the rat or in other species. Recent dense mapping of the rat genome, the development of new strategies and technologies in molecular genetics including differential gene expression, expressed sequence tags and DNA biochips render hope that the formidable task of identification of new candidate genes in hypertension will move another major step forward. Once these genes are identified, their function and role in hypertension will have to be determined, utilizing functional genomic strategies and bioinformatics. Finally, the findings in genetic animal models of hypertension will have to be extrapolated to humans by homology and syntenic mapping strategies.

Background: The fourth complex of the mitochondrial respiratory chain, cytochrome-c oxidase (CytC) consists of thirteen both mitochondrially and nuclearly encoded subunits, which are differently regulated in proteinuric kidneys. The effect of mitochondrial involvement on proteinuria is not known.

Methods: We set up an in vitro kidney perfusion model to study the direct effect of inhibitors of the mitochondrial respiratory chain, rotenone and antimycin A, on the glomerular filtration barrier by using immunohistochemistry and Northern blotting and quantitating the resulting proteinuria.

Results: Rapid onset of proteinuria and characteristic changes in CytC subunits were seen in the perfused kidneys. Urinary protein excretion increased significantly in the rotenone- and antimycin-A-treated groups during perfusion. Downregulation of CytC subunits I and IV was similarly found in the groups treated with rotenone and antimycin A, while increases in the lipid peroxidation (LPO) products malondialdehyde and 4-hydroxynonenal which reflect mitochondrial damage, were observed.

Conclusions: These data show rapid changes in mitochondrial proteins and induction of proteinuria in response to exposure to mitochondrial inhibitors. Together with the concomitant increase in local LPO products, these results suggest that continuous maintenance of a proper energy balance is important to maintain the glomerular filtration barrier.