Sequential protooncogene expression in regenerating kidney following acute renal injury

The transcription factor Fosl1 preserves Klotho expression and protects from acute kidney injury

Increased expression of AP-1 transcription factor components has been reported in acute kidney injury (AKI). However, the role of specific components, such as Fosl1, in tubular cells or AKI is unknown. Upstream regulator analysis of murine nephrotoxic AKI transcriptomics identified AP-1 as highly upregulated. Among AP-1 canonical components, Fosl1 was found to be upregulated in two transcriptomics datasets from nephrotoxic murine AKI induced by folic acid or cisplatin and from proximal tubular cells exposed to TWEAK, a cytokine mediator of AKI. Fosl1 was minimally expressed in the kidneys of control uninjured mice. Increased Fosl1 protein was localized to proximal tubular cell nuclei in AKI. In human AKI, FOSL1 was found present in proximal tubular cells in kidney sections and in urine along with increased urinary FOSL1 mRNA. Selective Fosl1 deficiency in proximal tubular cells (Fosl1Δtub) increased the severity of murine cisplatin- or folate-induced AKI as characterized by lower kidney function, more severe kidney inflammation and Klotho downregulation. Indeed, elevated AP-1 activity was observed after cisplatin-induced AKI in Fosl1Δtub mice compared to wild-type mice. More severe Klotho downregulation preceded more severe kidney dysfunction. The Klotho promoter was enriched in Fosl1 binding sites and Fosl1 bound to the Klotho promoter in cisplatin-AKI. In cultured proximal tubular cells, Fosl1 targeting increased the proinflammatory response and downregulated Klotho. In vivo, recombinant Klotho administration protected Fosl1Δtub mice from cisplatin-AKI. Thus, increased proximal tubular Fosl1 expression during AKI is an adaptive response, preserves Klotho, and limits the severity of tubular cell injury and AKI.

Analysis of L-myc gene polymorphism in patients with renal failure outcome to renal transplant

BACKGROUND

Abnormalities of cell numbers and apoptosis have been observed in renal failure. As uncontrolled expression of c-myc is known to induce apoptosis, we thought that polymorphism in the other myc gene, L-myc gene, which is structually similar to c-myc and reported to be expressed in the kidney, may have a role in the induction of apoptosis and thus have role in chronic renal failure. The aim of this study was to investigate the relationship between the distribution of L-myc genotypes and renal failure.

METHODS

In the present study we examined 101 chronic renal failure patients who had either live or cadaveric renal transplants and 105 healthy individuals, for L-myc gene polymorphism by polymerase chain reactions and restriction fragment length polymorphism techniques.

RESULTS

Among our patient group, the distribution of the LL, LS, and SS genotypes was 24% (n=25), 71% (n=71), and 5% (n=5), respectively, versus 41% (n=43), 47% (n=49), and 12% (n=13) in our control group. The distribution of genotypes was significantly different between our patients and the control group (chi2=12.281; P=.002). The frequency of the S allele was significantly higher in the patient group (chi2=6.122; P=.013).

CONCLUSION

Our study showed that having an S allele in the L-myc gene may increase the risk of renal failure.

Ischemic acute renal failure induces the expression of a wide range of nephrogenic proteins

Ischemia-induced acute renal failure (ARF) is a disorder with high morbidity and mortality. ARF is characterized by a regeneration phase, yet its molecular basis is still under study. Changes in gene expression have been reported in ARF, and some of these genes are specific for nephrogenic processes. We tested the hypothesis that the regeneration process developed after ischemia-induced ARF can be characterized by the reexpression of important regulatory proteins of kidney development. The distribution pattern and levels of nephrogenic proteins in rat kidneys after ischemia were studied by immunohistochemistry and immunoblot analysis. Ischemic damage was assessed by conventional morphology, serum creatinine, and the apoptotic markers terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) and caspase 3. The hypoxia levels induced by ischemia were assessed by specific markers: hypoxia induced factor (HIF)-1alpha and 2-pimonidazole. In kidneys with ARF, an important initial damage was observed through periodic acid Schiff staining, by the induction of damage markers alpha-smooth muscle actin (alpha-SMA) and macrophages (ED-1) and by apoptosis induction. In agreement with diminishing renal damage at the initial reparation phase, the expression of the mesenchymal proteins vimentin, neural cell adhesion molecules (Ncam), and the epithelial markers, Pax-2, Noggin, and basic fibroblast growth factor was observed; after, in a second phase, the tubular markers bone morphogen protein 7, Engrailed, and Lim-1, as well as the transcription factors Smad and p-Smad, were observed. Additionally, the endothelial markers VEGF and Tie-2 were induced at the initial and middle stages of regeneration phase, respectively. The expression of these proteins was restricted in time and space, as well as spatially and temporally. Because all of these proteins are important in maintaining a functional kidney, these results suggest that during the regeneration process after induced hypoxia, these nephrogenic proteins can be reexpressed in a similar fashion to that observed during development, thus restoring mature kidney function.

Molecular mechanisms of renal tissue repair in survival from acute renal tubule necrosis: role of ERK1/2 pathway

Our earlier studies with S-(1,2-dichlorovinyl)-L-cysteine (DCVC) showed that prior administration of a low priming dose of 15 mg/kg, i.p. to mice, given 72 hours before administration of a normally lethal dose of DCVC (75 mg/kg, i.p.) led to renal tubule necrosis, however sustained renal tubule regeneration was observed and these mice recovered from renal failure and survived. The objective of the present study was to investigate the role of extracellular signal-regulated kinase (ERK) pathway in this autoprotection model. Following the priming dose of DCVC, IL-6 protein and mRNA increased markedly as early as 1 hour after dosing, peaking at 3 hours with a 1.5-fold increase in plasma. Immunocytochemistry on kidney sections using specific antibodies against TGF-alpha, HB-EGF, EGFr, IGF-1Rbeta, Grb-2, and phospho-p44/42 MAP kinase (ERK1/2) revealed a significantly higher staining of these molecules 3 to 72 hours after dosing, indicating up regulation of the ERK pathway. Following a lethal dose of DCVC (75 mg/kg) the early increase in these signaling molecules was not sustained, being markedly reduced 24 and 36 hours after dosing, leading to inhibition of S-phase DNA synthesis, cell division and renal tubule repair. In contrast, prior treatment with a low dose of DCVC, followed by a high dose led to a sustained stimulation of the renal ERK pathway, renal tubule regeneration and recovery from acute renal failure. These results suggest that a sustained activation of the ERK1/2 pathway may be a key factor in enabling a continued renal tubule repair and hence protection from the progressive phase of DCVC-induced acute renal tubular necrosis in the mouse.

Kidney injury molecule-1: a tissue and urinary biomarker for nephrotoxicant-induced renal injury

Nephrotoxicity is a common side effect of therapeutic interventions, environmental insults, and exposure to toxicants in the workplace. Although biomarkers for nephrotoxicity are available, they often lack sensitivity and are not specific as indicators of epithelial cell injury. Kidney injury molecule-1 (Kim-1) is a type 1 membrane protein with extracellular immunoglobulin and mucin domains. The mRNA and protein for Kim-1 are expressed at very low levels in normal rodent kidney, but expression increases dramatically after injury in proximal tubule epithelial cells in postischemic rodent kidney and in humans during ischemic acute renal failure. To evaluate the utility of Kim-1 as a biomarker for other types of renal injury, we analyzed tissue and urinary expression in response to three different types of nephrotoxicants in the rat: S-(1,1,2,2-tetrafluoroethyl)-l-cysteine (TFEC), folic acid, and cisplatin. Marked increases in Kim-1 expression were confirmed by immunoblotting in all three models. The protein was shown to be localized to the proximal tubule epithelial cell by immunofluorescence. Furthermore, Kim-1 protein was detected in urine of toxicant-treated rats. The temporal pattern of expression in response to TFEC is similar to the Kim-1 expression pattern in the postischemic kidney. In folic acid-treated kidneys, Kim-1 is clearly localized to the apical brush border of the well-differentiated proximal tubular epithelial cells. After folic acid treatment, expression of Kim-1 is present in the urine despite no significant increase in serum creatinine. Cisplatin treatment results in early detection of urinary Kim-1 protein and diffuse Kim-1 expression in S3 cells of the proximal tubule. Kim-1 can be detected in the tissue and urine on days 1 and 2 after cisplatin administration, occurring before an increase in serum creatinine. The upregulation of expression of Kim-1 and its presence in the urine in response to exposure to various types of nephrotoxicants suggest that this protein may serve as a general biomarker for tubular injury and repair processes.

Renal ischemia-reperfusion injury in the rat is prevented by a novel immune modulation therapy

BACKGROUND

Vasogen Inc.'s (Mississauga, Ontario, Canada) immune modulation therapy (IMT) is a therapy in which cells from the patient's own blood are modified by ex vivo exposure to specific physicochemical stressors, including oxidation, ultraviolet (UV) light, and an elevated temperature. The therapy has been shown to have a beneficial effect in models of inflammation and vascular diseases. This study tested the hypothesis that IMT can prevent renal ischemia-reperfusion (I/R) injury in rats.

METHODS

Whole blood was collected from syngeneic age-matched donors by cardiac puncture. It was treated with a combination of controlled physiochemical stressors consisting of elevated temperature, a gas mixture of medical oxygen containing ozone, and UV light. The treated blood (150 microL) was injected in the gluteal muscle. Control animals received the same volume of untreated blood or physiological saline. Transient (45 or 60 minutes) left-renal ischemia was produced with simultaneous contralateral nephrectomy in treated and control spontaneously hypertensive rats (SHR). Young and old male and female rats were studied. Plasma creatinine, diuresis, and the survival rates of each group were compared. Renal apoptosis-necrosis was estimated by DNA laddering, histology, and in situ terminal deoxynucleotidyl transferase assay. mRNA levels of several regulators of apoptosis-regeneration were determined in control and postischemic kidneys by Northern blotting.

RESULTS

IMT pretreatment of SHR significantly reduced renal I/R injury compared with equivalent placebo treatments consisting of untreated blood- or saline-injected SHR, as evidenced by a significant increase of the survival rate curves in young and old male SHR, which correlated with 24-hour postischemic diuresis. The increases in plasma creatinine following renal I/R were significantly lower in IMT-treated young male and old female SHR compared with saline or untreated blood-injected controls. Dilution analysis showed that the protective effect of treated blood was lost by dilution. Loss of epithelial cells was reduced in IMT-treated rats, with a significant decline in the peak of apoptosis 12 hours after acute ischemic renal injury. IMT did not modify the pattern of mRNA levels of several genes involved in the inflammation and regeneration processes.

CONCLUSION

Our data demonstrate that IMT prevents the destruction of kidney tissue and the resulting animal death caused by renal I/R injury.

Increased renal expression of monocyte chemoattractant protein-1 and osteopontin in ADPKD in rats

BACKGROUND

Human autosomal-dominant polycystic kidney disease (ADPKD) is variable in the rate of deterioration of renal function, with end-stage renal disease (ESRD) occurring in only approximately 50% of affected individuals. Evidence suggests that interstitial inflammation may be important in the development of ESRD in ADPKD. Han:SPRD rats manifest ADPKD that resembles the human disease. Homozygous cystic (Cy/Cy) rats develop rapidly progressive PKD and die near age 3 weeks. Heterozygous (Cy/+) females develop slowly progressive PKD without evidence of renal dysfunction until the second year of life, whereas heterozygous (Cy/+) males develop more aggressive PKD with renal failure beginning by 8 to 12 weeks of age.

METHODS

To examine the relationship between proinflammatory chemoattractants and the development of interstitial inflammation and ultimately renal failure in ADPKD, we evaluated monocyte chemoattractant protein-1 (MCP-1) and osteopontin mRNAs and proteins in kidneys from Han:SRPD rats.

RESULTS

MCP-1 and osteopontin mRNAs, expressed at low levels in kidneys from normal (+/+) animals at all ages, were markedly elevated in kidneys from 3-week-old Cy/Cy animals. In kidneys from heterozygous (Cy/+) adults of either gender, MCP-1 and osteopontin mRNAs were more abundant than normal; MCP-1 mRNA was more abundant in Cy/+ males than in females. Thus, chemoattractant mRNA expression correlated with the development of renal failure in Cy/Cy and Cy/+ rats. Osteopontin mRNA, localized by in situ hybridization, was moderately expressed in the renal medulla of normal animals; however, this mRNA was expressed at very high levels in the cystic epithelia of Cy/+ and Cy/Cy animals. MCP-1 and osteopontin proteins, localized by immunohistochemistry, were weakly detected in +/+ kidneys but were densely expressed in Cy/Cy and in adult Cy/+ kidneys, primarily over cystic epithelium. Increased expression of chemoattractants was associated with the accumulation of ED-1 positive cells (macrophages) in the interstitium of cystic kidneys.

CONCLUSIONS

We suggest that proinflammatory chemoattractants have a role in the development of interstitial inflammation and renal failure in ADPKD.

Expression of apoptosis regulatory proteins in tubular epithelium stressed in culture or following acute renal failure

BACKGROUND

While tubular cell death is a characteristic of acute renal failure (ARF), the molecular mechanisms that modulate this cell death are unclear. Cell fate in acute renal failure hinges on a balance of survival and mortality factors in a changing environment. We further explored this issue by studying selected cell death-related proteins in experimental renal failure.

METHOD

The expression of genes that promote (c-myc, Bax, BclxS) or protect (Bcl2, BclxL) from cell death was studied by Northern blot, Western blot, and immunohistochemistry in murine kidneys following ARF induced by folic acid or in renal tubular epithelial cells (MCT) stressed in culture.

RESULTS

Renal mRNA levels encoding for c-myc and BclxL were elevated in ARF while the Bcl2/Bax ratio was decreased (Bcl2 decreased and Bax increased; P < 0.05). Protein levels of BclxL increased and Bcl2 protein decreased. Expression of tumor necrosis factor (TNF-alpha), a mediator of ARF, was also increased. Immunohistochemistry further demonstrated that BclxL was increased in some tubuli and absent in others, while Bcl2 expression decreased diffusely. Bax staining was also patchy among tubuli and individual cells in the tubular wall and lumen. As a relative deficit of survival factors is present in ARF, MCT epithelium were deprived of serum survival factors. This resulted in apoptosis, decreased Bcl2/Bax and BclxL/Bax ratios (P < 0.05) and sensitization to TNF-alpha-induced apoptosis (P < 0.05). The latter was prevented by enforced overexpression of BclxL (P < 0.01). TNF-alpha increased the mRNA levels encoding for c-myc and decreased BclxL expression. Neither MCT cells nor the kidney expressed BclxS.

CONCLUSIONS

A relative deficit of survival factors likely contributes to changes in levels of BclxL and Bax in ARF. These deficits predispose to cell death induced by persistent lethal factors such as TNF-alpha that is increased in ARF and a potential source of increased c-myc, a downstream facilitator of cell death. These findings implicate members of the Bcl2 family of proteins as regulators of tubular cell death in ARF and single them out as potential therapeutic targets.

Protein kinase C isoforms during the development of deciduomata in pregnant rats

In this study, we determined the expression of protein kinase C (PKC) isoforms during pregnancy. At pregnant duration, PKC alpha was down-modulated in the deciduomata but not in the myometrium. Down-modulation was compatible with the increase in cell mitosis, which reached a maximum at 8-9 days. On the other hand, PKC zeta was not down-modulated. It was increased both in the cytosolic and particulate fractions of the deciduomata, and paralleled the frequency of decidual cell mitosis. The other PKC isoform of delta was also increased, but it was associated with the cell regression. Therefore, these findings confirmed that the variable expression of PKC isoforms in decidualizing tissue may be involved in the modulation of decidual cell growth.

Protein kinase C isoforms during the development of deciduomata in pseudopregnant rats

In this study, we determined the expression of protein kinase C (PKC) isoforms during trauma-induced decidualization. The findings revealed that at least five PKC isoforms (alpha, delta, zeta, iota and lambda) were present in both control and decidualized tissues. After trauma-stimulation, PKC alpha was down-modulated in the deciduomata but not in the myometrium. Down-modulation was compatible with the increase in cell mitosis which reached a maximum at 2-3 days. On the other hand, PKC zeta was not down-modulated. It was increased both in the deciduomata and myometrium, and paralleled the frequency of decidual cell mitosis. The PKC isoforms of delta, iota and lambda were also increased, but they were associated with the depression of cell mitosis. Therefore, these findings suggested that the variable expression of PKC isoforms in trauma-induced decidualizing tissue in pseudopregnant rats may be involved in the modulation of decidual cell growth.

The differential induction of two immediate early genes, c-fos and c-jun, after systemic hypovolemic shock/resuscitation in the rat liver and kidney

The aim of this study was to investigate the expression of the immediate early genes (IEGs), c-fos and c-jun, in the rat kidney and liver in two types of hemorrhage shock/resuscitation models. In the first group, hemorrhagic shock was induced by the withdrawal of blood through the carotid artery. A mean arterial blood pressure (MAP) of 40mmHg was maintained for 1h before blood was reperfused. In the second group, the MAP was maintained at the same level for 2h. Animals were resuscitated with Ringer's lactate solution. In the first group, a rapid and transient induction of c-fos and c-jun mRNAs in both the liver and kidney was observed, peaking 0 to 2 h after reperfusion. In the second group, a more protracted pattern of induction was evident in both organs. In both models, the induction of c-fos mRNA was distinctly different in the liver and kidney. These results indicated, first, that with respect to IEG expression, organs respond differently to a systemic shock/resuscitation stimuli, and second, that alterations in the pattern of IEG expression might represent an indication of the degree of organ damage or the repair processes subsequent to hypotension/reperfusion.

The polycystic kidney disease 1 gene product mediates protein kinase C alpha-dependent and c-Jun N-terminal kinase-dependent activation of the transcription factor AP-1

Autosomal dominant polycystic kidney disease (ADPKD) is a common hereditary disorder that accounts for 8-10% of end stage renal disease. PKD1, one of two recently isolated ADPKD gene products, has been implicated in cell-cell and cell-matrix interactions. However, the signaling pathway of PKD1 remains undefined. We found that the C-terminal 226 amino acids of PKD1 transactivate an AP-1 promoter construct in human embryonic kidney cells (293T). PKD1-induced transcription is specific for AP-1; promoter constructs containing cAMP response element-binding protein, c-Fos, c-Myc, or NFkappaB-binding sites are unaffected by PKD1. In vitro kinase assays revealed that PKD1 triggers the activation of c-Jun N-terminal kinase (JNK), but not of mitogen-activated protein kinases p38 or p44. Dominant-negative Rac-1 and Cdc42 mutations abrogated PKD1-mediated JNK and AP-1 activation, suggesting a critical role for small GTP-binding proteins in PKD1-mediated signaling. Several protein kinase C (PKC) inhibitors decreased PKD1-mediated AP-1 activation. Conversely, expression of the C-terminal domain of PKD1 increased PKC activity in 293T cells. A dominant-negative PKC alpha, but not a dominant-negative PKC beta or delta, abrogated PKD1-mediated AP-1 activation. These findings indicate that small GTP-binding proteins and PKC alpha mediate PKD1-induced JNK/AP-1 activation, together comprising a signaling cascade that may regulate renal tubulogenesis.

Inhibitors of cyclic nucleotide phosphodiesterase isozymes block renal tubular cell proliferation induced by folic acid

In previous studies we observed that inhibition of cyclic 3',5'-nucleotide phosphodiesterase (PDE) isozymes, namely isozyme PDE3, suppresses proliferation of rat renal glomerular mesangial cells in vitro and in vivo. To determine whether activation of the cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA) signaling pathway coupled to specific PDE isozymes modulates accelerated proliferation of renal epithelial cells, we investigated the effect of selective PDE isozyme inhibition on renal epithelial cell proliferation induced in rats by injection of folic acid (FA). In extracts from suspensions of renal cortical tubules, cAMP was metabolized predominantly by isozyme PDE4; activity of PDE3 was about three times lower. The increase in proliferative activity of renal cortical tissue from FA-injected rats, evaluated by immunostaining with Mib-1 antibody, was limited to tubular epithelial cells. Administration of the PDE3 inhibitors cilostazol or cilostamide together with the PDE4 inhibitor rolipram blocked mitogenic synthesis of DNA, as determined by (3H)-thymidine incorporation into renal cortical DNA, in FA-treated rats. FA injection caused an increase of more than 10-fold in proliferating cell nuclear antigen (PCNA) in renal cortical tissue; administration of the potent PDE3 inhibitor lixazinone or, to a lesser degree, cilostazol suppressed these high PCNA levels, whereas rolipram alone had no effect. The results indicate that FA-stimulated in vivo proliferation of renal tubular epithelial cells is down-regulated by activation of a cAMP-PKA signaling pathway linked to PDE3 isozymes. These observations are consistent with the notion that negative crosstalk between cAMP signaling and mitogen-stimulated signaling pathways regulates mitogenesis of renal cells of different terminal differentiation, including tubular epithelial cells.

Growth characteristics of cells cultured from two murine models of polycystic kidney disease

Polycystic kidney disease (PKD) is characterized by multiple renal cysts that are lined by epithelium and filled with fluid. PKD may result from one of a number of factors, either inherited or environmental. In this study, we have compared two mouse models in which PKD results from a genetic cause. In the C57BL/6J-cpk model, the mutated gene is unknown. In the other model, an SV40 large T antigen transgene causes renal cysts. We examined cultured cells from the kidneys of these mouse models, comparing growth characteristics. Although several features of PKD lead one to expect that the epithelial cells lining the cysts would have an increased rate of proliferation in culture, we found that they did not. The implications of these findings are discussed.

DNA synthesis is dissociated from the immediate-early gene response in the post-ischemic kidney

The response of the kidney to ischemic injury includes increased DNA synthesis, which is preceded by rapid and brief expression of the c-fos proto-oncogene. While the timing of these two events would suggest that c-Fos participates in an immediate-early gene program leading to proliferation, no direct test of this hypothesis exists. The purpose of these studies was (1) to determine whether c-fos is expressed as part of a typical immediate-early (IE) gene response, which would require co-expression of c-jun and sensitivity to cycloheximide, and (2) to determine whether the cells expressing c-Fos are the same as those undergoing DNA synthesis. Northern analysis was performed on renal mRNA at different times following release of a 50 minute period of renal hilar clamping. c-jun and c-fos mRNA were rapidly and briefly expressed following renal ischemia and their expression was superinduced by cycloheximide in a manner typical of an immediate-early gene response. 3H-thymidine autoradiography performed on semi-thin sections from intravascularly perfusion fixed kidneys 24 hours following induction of ischemia showed labeled nuclei in cells lining the damaged proximal tubules of the outer stripe of the outer medulla, as well as proximal tubules in the cortex and interstitial cells throughout the kidney. However, immunohistochemical localization of c-Fos and c-Jun protein occurred predominantly in nuclei of the thick ascending limb, distal tubule and collecting duct cells. The studies demonstrate that c-fos and c-jun are expressed following renal ischemia as a typical immediate-early gene response, but they are expressed in cells that do not enter the cell cycle. The failure of the cells to enter the cell cycle may depend on the co-expression of jun-B and jun-D, which suppress the mitogenic activity of c-Jun in other cells. The data suggest that the IE response following renal ischemia is part of the stress response, which is antiproliferative rather than proliferative. The role of the stress response during renal ischemia and the fate of the cells undergoing it are unknown.

Polycystic kidney disease: etiology, pathogenesis, and treatment

Once viewed as hopelessly incurable disorders and the dustbin for careers in academic medicine, the polycystic kidney diseases have emerged as prime targets of pathophysiologic study and palliative and definitive treatment in the era of molecular medicine. Polycystic kidney disease (PKD) may be hereditary or acquired. The major inherited types are autosomal dominant (AD) and autosomal recessive (AR). ADPKD is caused by at least two (and possibly three) genes located on separate chromosomes, while ADPKD-1 is due to a 14 kb transcript in a duplicated region on the short arm of chromosome 16 very near the alpha-globin gene cluster and the gene for one form of tuberous sclerosis. ADPKD-2 has been assigned to the long arm of chromosome 4. ARPKD is due to a mutated gene on both copies of the long arm of chromosome 6. Cysts originate in renal tubules. Proliferation of tubule epithelial cells modulated by endocrine, paracrine, and autocrine factors is a major element in the pathogenesis of renal cystic diseases. In addition, fluid that is abnormally accumulated within the cysts is derived from glomerular filtrate and, to a greater extent, by transepithelial fluid secretion. Abnormal synthesis and degradation of matrix components associated with interstitial inflammation are additional features in the pathogenesis of renal cystic diseases. The ADPKD genotypes are characterized by bilateral kidney cysts, hypertension, hematuria, renal infection, stones, and renal insufficiency. ADPKD is a systemic disorder; cysts appear with decreasing frequency in the kidneys, liver, pancreas, brain, spleen, ovaries, and testis. Cardiac valvular disorders, abdominal and inguinal hernias, and aneurysms of cerebral and coronary arteries and aorta are also associated with ADPKD. Treatment is supportive: dietary regulation of salt and protein intake, control of hypertension and renal stones, and dialysis and transplantation at the end stage. ARPKD is a relatively rare disease that causes clinical symptoms at birth, with significant mortality in the first month of life. The cysts develop primarily in the collecting ducts because of a failure in the maturation process. Early complications include Potter's syndrome; excessive size of the kidneys, causing respiratory dysfunction; hypertension; and renal insufficiency. Hepatic fibrosis is an associated extrarenal problem that results in significant morbidity in young children and adolescents. Treatment includes supportive care, dialysis, and renal transplantation. Acquired cysts (solitary/simple) are commonplace in older persons. Multiple cysts may be seen in association with potassium deficiency, congenital disorders, metabolic diseases, and toxic renal injury.(ABSTRACT TRUNCATED AT 400 WORDS)

Calcium oxalate crystal interaction with renal tubular epithelium, mechanism of crystal adhesion and its impact on stone development

The interaction between renal epithelial cells and calcium oxalate (CaOx) crystals and/or oxalate ions plays a critical role in the formation of urinary stones. Epithelial cells respond to hyperoxaluria and the presence of CaOx crystals in the kidneys by increased enzymuria and internalization of the crystals. Crystal cell interaction results in movement of crystals from the luminal to the basolateral side between the cells and the basement membrane. Once beneath the epithelium, crystals adhere to the basement membrane and become anchored inside the kidneys. Crystals anchored to basement membrane of the peripheral collecting duct aggregate with other crystals and move through an eroding epithelium to the papillary surface, furnishing an encrustation platform or a nidus for future development of a kidney stone. Thus interaction between renal epithelial cells and CaOx crystals and/or oxalate ions is an essential element in the development of urinary stone disease.

Cellular biology of tubulointerstitial growth

The study of tubular growth has certainly become more complex since Pierre-Rayers's time and is progressing toward a molecular dissection of regulatory events. Understanding the mechanisms of tubular growth is important, because these cells represent the bulk of the nephron, and there is convincing evidence of a link between tubular hypertrophy and the progression of renal disease with irreversible tubulointerstitial fibrosis as an end point. Two tubular growth responses can be distinguished: hypertrophy and hyperplasia. These fundamentally different patterns of growth indicate that diverse molecular mechanisms may be involved in inducing distinct growth responses. It is likely that cytokines and polypeptide growth factors play a role in tubular hypertrophy and hyperplasia. Probably, a combination of growth factors including inhibitory polypeptides like TGF beta, rather than a single factor, is necessary for differentiated tubular growth responses. Such factors bind to their receptors, and signals are transduced to the nucleus by various second messengers involving protein kinases, cyclic nucleotides, Ca++, and inositolphosphates. The phosphorylation of nuclear trans-acting factors resulting in an expression of immediate early genes may be the common pathway of many of these mediators. Finally, whether the cell is to proliferate or to remain in the G1-phase of the cell cycle is determined by the very complex cascade phosphorylation of kinases and their associations with different cyclins. How the induction of immediate early genes is linked to events of the cell cycle is currently incompletely understood. Negative regulation of growth through protein growth suppressors like the retinoblastoma gene product or the expression of special genes only during cell rest may be mandatory for the fine tuning of tubular growth.

Expression of the helix-loop-helix protein, Id, during branching morphogenesis in the kidney

Id, a member of the helix-loop-helix protein family, is an inhibitor of transcriptional activation by basic-helix-loop-helix proteins. In the developing mouse kidney, Id mRNA was observed as early as 12.5 days post-coitum (dpc) specifically in the condensed mesenchyme surrounding the ureteric buds by in situ hybridization. At 14.5 dpc, Id mRNA was localized to the collecting tubules and developing glomeruli while the surrounding mesenchyme lacked Id hybridization. From birth to day 10 postnatal, Id mRNA is localized to the collecting tubules, immature glomeruli and renal pelvis. In the adult kidney, Id mRNA was detectable by Northern blot analysis but no cell type-specific localization was noted by in situ hybridization. These results indicate a role for HLH-bHLH proteins in the differentiation of the epithelial structures of the kidney.

Modification of immunoreactive EGF and EGF receptor after acute tubular necrosis induced by tobramycin or cisplatin

Acute tubular necrosis induced by aminoglycoside antibiotics and various other nephrotoxins is followed by a regenerative process which leads to the restoration of damaged tubules. Several lines of evidence indicate that tubular regeneration is mediated by polypeptide growth factors such as epidermal growth factor (EGF). Previous studies devoted to cisplatin nephrotoxicity have shown that this agent causes tubular cystic degeneration possibly related to an impairment of renal tissue repair. Thus, we examined on a comparative basis the time course of the regenerative response subsequent to tubular damage induced by tobramycin or cisplatin, particular attention being paid to renal EGF and its receptor. Female Sprague-Dawley rats (160-180 g body weight) were treated during 4 consecutive days with daily doses of 200 mg/kg tobramycin i.p. (BID) or 2 mg/kg cisplatin (once a day). Sham-treated rats were given 0.9% NaCl i.p. following the same protocol. Groups of experimental animals (n = 5-10) were terminated at increasing time intervals (1, 4, 7, 14, 21, 60 days) after cessation of treatment. One hour prior to sacrifice, each individual received i.p. 200 mg/kg 5-bromo-2'-deoxyuridine (BrdU) for the immunohistochemical demonstration of cell proliferation. Blood was collected at the time of sacrifice in order to assess glomerular filtration rate by measuring serum creatinine and BUN levels. Kidneys were analyzed with respect to total EGF determined by RIA in renal tissue homogenates, and soluble EGF was assayed in extracts prepared by centrifugation. Renal tissue was processed for the immunohistochemical detection of S-phase cells, of EGF, of EGF receptors, and of the intermediate filament vimentin, the latter being used as a marker of epithelium dedifferentiation. In absence of nephrotoxic alterations, EGF was immunolocalized in distal tubules, whereas EGF receptor immunostaining was seen in proximal tubules cells. Vimentin immunostaining was confined to glomeruli and blood vessels. Tobramycin and cisplatin caused acute tubular necrosis in proximal convoluted tubules and proximal straight tubules, respectively. Tissue damage was accompanied by renal dysfunction reflected by an elevation of serum creatinine and BUN levels. Tubular necrosis was followed by a proliferative response indicative of tubular regeneration. Regenerative hyperplasia was associated with a reduction of total immunoreactive EGF due to a decrease of tissue-bound proEGF. Tubules undergoing regenerative repair were characterized by a disappearance of EGF receptors and the presence of immunoreactive vimentin. In tobramycin-treated rats, renal dysfunction lasted for 4-7 days and was fully reversible, as indicated by the return of serum markers to normal values.

Enhanced expression of the protooncogenes c-myc and c-fos in normal and malignant renal growth

The protooncogenes c-myc and c-fos play an important role in growth and differentiation of renal tissue. They are highly expressed during embryogenesis in the mitotically active tubule epithelium, while in terminally differentiated tubule cells of the kidney the expression is completely shut off. Furthermore, induction of cell proliferation in cultured renal cells by addition of growth factors is preceded by enhanced expression of c-myc and c-fos. Increased expression of these protooncogenes is also obtained by treatment of kidney cells in culture with the potent nephrocarcinogen N-dimethylnitrosamine and also with the nephrotoxin and possibly nephrocarcinogen S-(1,2-dichlorovinyl)-L-cysteine. Finally, the expression of c-myc and c-fos is induced after unilateral nephrectomy during compensatory renal growth in the remaining kidney and also during regenerative cell proliferation after in vivo application of the strong nephrotoxins folic acid and mercury chloride.

Autosomal-dominant polycystic kidney disease in the rat

Kaspareit-Rittinghausen described a rodent model of inherited polycystic kidney disease (PKD), the Han:SPRD rat [1, 2], in which heterozygotes develop renal cysts and renal failure (in males) over several months, whereas homozygous animals develop rapidly progressive renal enlargement that leads to death in a few weeks. In this study, we examined selected elements of the pathogenesis of this disease in heterozygotes and homozygotes from birth to advanced disease. Heterozygous male rats developed slowly progressive renal cystic disease with interstitial fibrosis and azotemia seen by six months of age. Female heterozygotes developed slowly progressive renal cystic disease, but did not develop interstitial fibrosis or azotemia. Epithelial cells lining cyst cavities showed various degrees of morphologic immaturity. Cyst walls also developed basement membrane thickening, especially in areas of cellular immaturity, suggesting an interrelationship between this basement membrane thickening and cellular dedifferentiation. Thickened basement membranes were associated with increased immunoreactivity for type IV collagen, laminin, and fibronectin. Homozygous rats developed massive renal enlargement, marked azotemia, and died near three weeks of age. Renal c-myc proto-oncogene expression was elevated in homozygous cystic infants and in adult heterozygotes. In situ hybridization showed high levels of c-myc mRNA in cyst epithelia, suggesting abnormal regulation of cellular proliferation in the cells lining cysts, as seen in other models of PKD. The Han:SPRD rat is the only well-documented animal model of inherited PKD with an autosomal-dominant inheritance pattern and appears to have several features which resemble human ADPKD.

Induction of immediate early and stress genes in rat proximal tubule epithelium following injury: the significance of cytosolic ionized calcium

This study was designed to investigate the influence of intracellular ionized calcium ([Ca2+]i) on the induction of c-fos, c-jun, c-myc, and hsp70 genes after oxidant stress induced by xanthine/xanthine oxidase (X/XOD) treatment or after heat shock using primary cultures of rat proximal tubule epithelium (PTE). X/XOD (500 microM/25 mU/mL) induced all of these genes; ionomycin also resulted in similar kinetics of induction of all genes. The expression of both c-fos following X/XOD treatment and hsp70 following heat shock was markedly decreased through chelation of [Ca2+]i by Quin 2/AM. The c-fos expression following X/XOD treatment was partly reduced by a protein kinase C inhibitor, staurosporine (ST), and markedly inhibited by another protein kinase inhibitor, 2-aminopurine (2AP), while both ST and 2AP markedly reduced hsp70 expression. The ADP-ribosylation transferase inhibitor 3-aminobenzamide had no effect on either c-fos or hsp70 expression. These results suggest that cell injuries leading to increased [Ca2+]i in PTE result in induction of c-fos, c-jun, c-myc, and hsp70; and that the activation of c-fos and hsp70 genes may be regulated by [Ca2+]i and [Ca2+]i-dependent protein kinases.

The nephrotoxin dichlorovinylcysteine induces expression of the protooncogenes c-fos and c-myc in LLC-PK1 cells--a comparative investigation with growth factors and 12-O-tetradecanoylphorbolacetate

Previous studies in kidney cells showed that S-(1,2-dichlorovinyl)-L-cysteine (DCVC) induces both direct DNA damage and DNA double-strand breaks by activation of Ca(2+)-dependent endonucleases. The objective of this study was to investigate the effects of DCVC on the expression of the protooncogenes c-fos and c-myc in cultured kidney cells (LLC-PK1). Supplementation of the incubation medium with 10% FCS after 24 hr incubation in 0.2% FCS resulted in a clear, but comparatively weak induction of the expression of c-fos and c-myc in LLC-PK1 cells. Addition of 500 microns DCVC to the high serum incubation medium induced a further three-fold increase of the transcript levels. A similar increase in the absolute amount of c-fos mRNA was induced by a mixture of growth factors (epidermal growth factor/insulin/transferrin) and of c-myc mRNA with 12-O-tetradecanoylphorbolacetate. However, the kinetics of gene expression were different. In the presence of DCVC the expression of c-fos and c-myc increased continuously in a time-dependent manner during the entire incubation period. In contrast, with growth factors and 12-O-tetradecanoyl-phorbolacetate the maximum transcript levels were detected after 0.5 hr (c-fos) and 1 hr (c-myc), respectively; thereafter, a slight decrease was observed up to the end of the incubation time.

Polycystic kidney disease: primary extracellular matrix abnormality or defective cellular differentiation?

Polycystic kidney disease (PKD) is inherited as a dominant or recessive trait or can be provoked by environmental factors. The disease is characterized by the growth of large epithelial-lined cysts derived from the nephrons and collecting ducts of affected kidneys. Cysts are thought to initiate as small dilations in renal tubules, which then expand into fluid-filled cavities of relatively large size. Cyst formation appears to involve increased cell proliferation, reversal of tubular epithelial polarity, and epithelial fluid secretion. In addition, a number of pronounced extracellular matrix changes have been found in the cystic kidneys of several animal models and in human autosomal dominant PKD. These abnormalities include thickened, laminated basement membrane, increased expression of alpha 1 type IV collagen and laminins B1 and B2, and changes in heparan sulfate proteoglycan and fibronectin. Some of these changes can also be seen in vitro, reflecting intrinsic abnormalities, and may be associated with abnormal tubular morphogenesis early in cyst formation as well as later in cyst expansion. We have been investigating gene expression in the C57BL/6J-cpk mouse, which has an autosomal recessive form of PKD, to determine the genetic basis of the abnormal tubule cell growth and morphology manifested during cyst formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Autosomal dominant polycystic kidney disease--in vitro culture of cyst-lining epithelial cells

The major form of autosomal dominant polycystic kidney disease (ADPKD) in humans is linked to the PKD1 gene on chromosome 16p. The identity of the gene and the underlying pathogenetic mechanisms are not yet defined. Cyst-lining epithelial cells derived from a polycystic kidney were successfully grown in culture and designated MZ-PKD-1 cells. By linkage analysis, the related pedigree of the nephrectomized patient could be linked to the PKD1 gene on chromosome 16p. Thus, these cells exhibit the genotype of a mutated PKD1 gene and represent an in vitro culture model for ADPKD involving chromosome 16p. The antigenic phenotype was characterized immunohistologically by epithelial differentiation antigens and markers of individual nephron segments. An essentially identical antigenic pattern of proximal tubular cells was observed both in vitro and in fresh frozen tissue. Electron microscopy showed the formation of a microvillous-like coating. During growth phases in vitro successive changes in the cell shape were observed. MZ-PKD-1 cells exhibited a limited lifespan ending in replicative senescence. Northern blot analysis of kidney-growth-related genes, c-myc, TGF-alpha, TGF-beta 1, and EGF receptor revealed abundant expression of all of these genes in MZ-PKD-1 cells.

Expressions of receptor gene for hepatocyte growth factor in kidney after unilateral nephrectomy and renal injury

The renal expressions of the receptor gene (c-met) for hepatocyte growth factor (HGF) were examined in unilateral nephrectomy (UNX), renal ischemia or folic acid administration. The levels of c-met mRNA were increased rapidly in all rat models at 6h after the operations. On the other hand, the expression of c-met mRNA in a kidney cell line (MDCK cells) was down-regulated for 8 h after HGF addition, indicating that c-met mRNA induction in rat models may be independent of the stimulated production of HGF. The stimulated expression of c-met in these models suggest that HGF may play an important role in renal hypertrophy after UNX and regeneration after ischemic or nephrotoxic injury.

C-fos expression is hypersensitive to serum-stimulation in cultured cystic kidney cells from the C57BL/6J-cpk mouse

Cystic kidneys of the C57BL/6J-cpk murine model of polycystic kidney disease show a marked overexpression of the proto-oncogenes c-fos, c-myc, and c-Ki-ras, consistent with an increased rate of cell proliferation and an altered state of differentiation. To determine if cystic cells have increased responsiveness to stimulation with mitogenic agents, quiescent primary cultures from normal and cystic cpk kidneys were treated with fetal bovine serum (FBS), 8-bromo-cAMP (cAMP), or epidermal growth factor (EGF). The level of c-fos induction following stimulation by FBS was found to be dramatically higher in cystic cells than in normal cells; whereas induction by cAMP or EGF was essentially the same in both cell types and much less than that seen in FBS-stimulated cells. To determine if this serum hypersensitivity reflects an increased proliferative state in vivo, c-fos induction was examined in cultures derived from normal kidneys stimulated to regenerate by folic acid-induced acute renal injury. As with cystic kidneys, the folic acid-injured kidneys showed increased c-fos responsiveness to FBS in cell culture. These experiments suggest that cystic and regenerating kidneys have an altered phenotypic state in vivo that is manifested in cell culture by serum hypersensitivity. However, whereas the folic acid-injured kidneys ultimately reestablish normal kidney function, cystic kidneys further progress to renal failure, suggesting that cystic epithelial cells are locked in this altered state of differentiation.

Localization of overexpressed c-myc mRNA in polycystic kidneys of the cpk mouse

The C57BL/6J-cpk mouse has a form of autosomal-recessive polycystic kidney disease characterized by the rapid growth of large collecting duct cysts and the development of severe renal failure usually by three to four weeks of age. Previous studies had shown higher steady-state levels of proto-oncogene mRNA in these cystic kidneys. It is now shown using nuclear run-on transcription that the c-fos and c-myc proto-oncogenes are transcribed at higher rates in cystic kidneys, and thus that increased transcription, in part, may account for the increased mRNA levels. c-myc mRNA was detected by in situ hybridization in nephron anlagen and elongating tubules of normal and cystic kidneys during late fetal and early neonatal kidney development. Localization of c-myc expression in the normal kidney decreased with age over the three-week postnatal period. By contrast, c-myc mRNA was found in cysts as early as three days of age, with increased levels at two and three weeks. c-myc expression was also elevated in apparently normal, non-dividing proximal tubules in three-week-old cystic animals. On the basis of these findings, we suggest that c-myc expression is linked to the proliferation of cells engaged in the primary cystogenic process, and that expression of this gene in proximal tubule cells of severely azotemic animals reflects the compensatory response of residual tubular epithelial cells to progressive renal dysfunction.

Expression of differentiation antigens and growth-related genes in normal kidney, autosomal dominant polycystic kidney disease, and renal cell carcinoma

Cellular differentiation and mRNA levels of genes involved in kidney growth were investigated in normal kidney cells, cyst-lining epithelial cells of polycystic kidney disease, and renal carcinoma cells (RCC). All cells comparatively studied exhibited an antigenic phenotype of proximal tubular cells as shown by the expression of a panel of brush border membrane enzymes and kidney-associated cell surface antigens. The epithelial developmental antigen Exo-1 was expressed in 50% to 80% of cyst-lining epithelia in polycystic kidney tissue and in 20% to 30% of polycystic kidney cells cultured in vitro. Normal kidney cells and RCC were negative under identical culture conditions. The expression of antigen Exo-1 is associated with hyperproliferation in an epithelial tissue compartment composed of cells which have not yet reached their terminal differentiation state. Increased amounts of mRNA of the growth factor receptor system of epidermal growth factor (EGF) receptor and its ligand transforming growth factor (TGF)-alpha were associated with the malignant phenotype of RCC. Increased expression of EGF receptor and TGF-alpha, although less prominent, were also observed in polycystic kidney cells compared with normal kidney cells. In conclusion, the expression of Exo-1 in cyst-lining epithelial cells of autosomal dominant polycystic kidney disease (ADPKD) and the altered regulation of TGF-alpha and EGF receptor in these cells contribute to the hypothesis that hyperproliferation is an underlying pathogenic mechanism of ADPKD.

Molecular mechanisms of tubulointerstitial hypertrophy and hyperplasia

Adult kidneys, which are principally composed of tubulointerstitium, do not normally regenerate or expand their working pool of functional cells at a very high rate. Loss of kidney tissue, however, can lead to some compensatory renal enlargement. The catalytic forces initiating such exchanges have not been fully articulated by current experimental endeavors. Increasing evidence, nevertheless, does suggest that factors other than simple changes in renal hemodynamics may be involved in this process. Different cellular elements in the tubulointerstitial microenvironment probably modulate changes in tubular enlargement or size through a complex cytokine network. Autocrine and paracrine stimulation of enlargement by different local growth factors also seem to play a pivotal role. After binding to cellular receptors, these factors activate signal transduction pathways resulting in expression of immediate early genes, which by themselves can synchronize the expression of subsequent genes through the medium of transacting factors. The renal enlargement response can also be modified by endocrine hormones that can activate such genes directly and/or stimulate other adjunctive processes, like receptor expression for the regional binding of growth factors. Furthermore, renal enlargement is under negative feedback of inhibitory factors like TGF beta. It is possible, for example, that special genes exist which are only expressed to arrest enlargement. It has been further suggested that activation of the Na+/H+ antiporter is a common denominator in renal enlargement. Recent findings, however, indicate that the activation of this antiporter is not always necessary, and might rather be a parallel event rather than a key phenomena in tubular enlargement. G0/G1 transition of tubular cells seems to involve similar factors in tubular hypertrophy and hyperplasia. The factors which are responsible for the final determination of the enlargement pattern (hypertrophy vs. proliferation) are unknown. The separation between hypertrophy and hyperplasia, although suggested by striking differences in cellular regulation, may be somewhat artificial, since responses leading to tubular enlargement also exist in circumstances where hyperplasia and hypertrophy are combined events. Recently it has been proposed that growth factors stimulate gluconeogenesis in proximal tubular cells producing hyperplasia, whereas factors inhibiting gluconeogenesis might induce hypertrophy. Whether the common pathway message of this intriguing hypothesis is correct still requires further validation.(ABSTRACT TRUNCATED AT 400 WORDS)

Defective epidermal growth factor gene expression in mice with polycystic kidney disease

The C57BL/6J-cpk mouse has an inheritable form of polycystic kidney disease similar to the autosomal recessive disorder seen in humans. Between approximately 1 and 3 weeks of age, affected cpk mice develop numerous large cysts in the collecting tubule segment of kidney nephrons. The present study examined the ontogeny of renal and submandibular gland prepro-epidermal growth factor (preproEGF) gene expression in the cpk mouse using Northern blot hybridization and immunohistochemistry. There was a virtual absence of renal preproEGF gene expression in cystic kidneys over the 3-week postnatal period, during which time renal preproEGF mRNA and proEGF/EGF protein normally reach significant levels. PreproEGF mRNA was expressed in salivary glands of cystic mice; however, this mRNA could not be further elevated with testosterone suggesting that there are abnormalities in the regulation of the preproEGF gene in the submandibular gland, as well as in the kidney. Since renal preproEGF expression during the early postnatal period occurs when collecting duct cysts form, it is possible that a deficiency in renal proEGF or EGF contributes to the rapid development of collecting duct cysts and the concomitant renal failure in the C57BL/6J-cpk cystic mouse.

Relation between toxicity and carcinogenesis in the kidney: an heuristic hypothesis

Cellular toxicity and cellular carcinogenesis are closely linked. In the kidney, this relationship has been emphasized by the recent discovery of a number of putatively non-mutagenic chemicals that result in acute and chronic toxicity and ultimately in carcinogenesis, especially in the male rat. Many, but not all such compounds, result in renal PTE phagolysosomal overload. At the same time, known metabolites of other carcinogens, e.g., HCBD and FBPA, result in acute renal injury and/or necrosis, followed by chronic tubular disease, interstitial nephritis, and ultimately carcinogenesis. A series of cell mechanisms have been suggested that lead from acute cell injury to altered control of cell division. These mechanisms appear to involve ion deregulation, (especially [Ca2+]i) resulting from a variety of continued injuries, (e.g., oxidative stress from inflammatory cells) and ultimately leading to altered gene expression.