Expression of interleukin-22 in rheumatoid arthritis: potential role as a proinflammatory cytokine

OBJECTIVE

Interleukin-22 (IL-22) is a novel cytokine of the IL-10 family. Although its pathophysiologic function is largely unknown, induction of acute-phase responses by IL-22 has suggested proinflammatory properties. In this study, we sought to examine whether IL-22 plays a role in the pathogenesis of rheumatoid arthritis (RA).

METHODS

Expression of IL-22 and IL-22 receptor 1 (IL-22R1) was examined by reverse transcription-polymerase chain reaction (RT-PCR), Western blot, and immunohistochemical analysis. The effects of recombinant IL-22 (rIL-22) on cultured synovial fibroblasts derived from RA patients (RASF), with regard to the proliferation of synovial fibroblasts and production of monocyte chemoattractant protein 1 (MCP-1), were examined by alamer blue assay and enzyme-linked immunosorbent assay, respectively.

RESULTS

IL-22 messenger RNA was detected by RT-PCR in RA synovial tissues and mononuclear cells isolated from RA synovial fluid samples. High levels of IL-22 were expressed both in the lining and the sublining layers of RA synovial tissues. Staining for vimentin and CD68, as markers of synovial fibroblasts and macrophages, respectively, showed that the majority of IL-22-positive cells were synovial fibroblasts and macrophages. IL-22R1 was also expressed in both the lining and the sublining layers of RA synovial tissues. The majority of cells expressing IL-22R1 were positive for vimentin, but not for CD68. Expression of IL-22 and IL-22R1 in RASF was confirmed by RT-PCR and Western blot analysis. In vitro, rIL-22 significantly increased proliferation of RASF and production of MCP-1 by RASF above the value of medium controls. Moreover, MAPK activation was induced in RASF in response to IL-22 stimulation.

CONCLUSION

These data suggest that IL-22, produced by synovial fibroblasts and macrophages, promotes inflammatory responses in RA synovial tissues by inducing the proliferation and chemokine production of synovial fibroblasts.

Widespread crystalline inclusions affecting podocytes, tubular cells and interstitial histiocytes in the myeloma kidney

Numerous crystalline inclusions were observed in glomerular and tubular epithelial cells in a 46-year-old female patient with multiple myeloma and renal dysfunction. On light microscopy, epithelial cells were filled with homogenous materials and were remarkably swollen. Infiltrations of histiocytes with expanded cytoplasm were also seen in the interstitium of the kidney and bone marrow. On electron microscopy, cytoplasmic inclusions had crystalline structure showing rhomboid and oval shapes. Immunofluorescence study revealed that these cells were positive for IgG-kappa. The combination chemotherapy followed by autologous stem cell transplantation led to a partial resolution of her renal dysfunction, continued by a slight reduction in the number of crystalline-containing podocytes at the second renal biopsy. Crystal inclusions in the kidney are rarely found and cause renal impairment in multiple myeloma.

Water intoxication associated with moderate dose of cyclophosphamide pulse therapy in an elderly patient: a case report and literature review

Intravenous high-dose cyclophosphamide infusion, usually performed to treat malignant neoplasms, is known to cause water intoxication. Intravenous cyclophosphamide pulse therapy (IVCY) is increasingly being employed for the treatment of rheumatic diseases as well. Recently, water intoxication has been reported to occur even after low-to-moderate doses of IVCY. In the present paper, we describe a case of polyarteritis nodosa in a patient in whom water intoxication developed after IVCY at a moderate dose. Hydration is usually performed to maintain sufficient urine flow to avoid cystitis. Based on our case and a review of the literature, it is recommended that hydration should be carefully performed during IVCY in order to avoid water intoxication, especially when treating elderly patients.

Secretion of parathyroid hormone oscillates depending on the change in serum ionized calcium during hemodialysis and may affect bone metabolism

BACKGROUND

The current study was undertaken to clarify the dynamic response of parathyroid hormone (PTH) during hemodialysis and to determine whether or not such dynamic change of PTH affects bone turnover.

METHODS

Serum ionized calcium (iCa) and intact PTH (iPTH) were measured in 66 dialysis patients before (basal) and after each hemodialysis. The changes of iCa (DeltaiCa) and iPTH (DeltaiPTH) were defined as [postdialysis iCa -basal iCa] mM, and [(postdialysis iPTH - basal iPTH)/basal iPTH] x 100%, respectively. We also investigated the data of the patients divided into four groups based on their basal iPTH levels; group 1 (iPTH < 60 pg/ml, n = 17), 2 (> or = 60 to < 150, n = 20), 3 (> or = 150 to < 300, n = 15), and 4 (> or = 300, n = 14).

RESULTS

While iCa and iPTH changed variably during each hemodialysis procedure, there was a highly significant inverse correlation between DeltaiCa and DeltaiPTH (r = -0.761, p < 0.0001). Regression coefficients between DeltaiPTH and DeltaiCa were -519.1, -311.2, -268.1, and -194.6%/mM in groups 1-4, respectively. The difference in the regression coefficient was statistically significant between group 1 and 2 (F = 3.69, p < 0.05, ANCOVA), group 1 and 3 (F = 5.599, p < 0.05), and group 1 and 4 (F = 10.853, p < 0.005). This suggested that patients with higher basal iPTH responded poorly to modulate serum PTH levels by sensing the change of iCa. However, after an intensified oral calcitriol therapy to reduce iPTH, the PTH response in group 4 patients was restored to levels comparable with those observed in patients having lower basal iPTH. We also demonstrate that the DeltaiPTH of patients of group 1 but not of other groups was significantly correlated with serum markers for bone metabolism; osteocalcin (r = 0.535, p < 0.05) and collagen type I C-terminal telopeptide (r = -0.575, p < 0.05).

CONCLUSIONS

Our findings suggest that secretion of PTH is dynamically regulated by DeltaiCa during hemodialysis and such oscillated PTH secretion may affect bone metabolism in a subset of dialysis patients.

Mesangial cells stimulate differentiation of endothelial cells to form capillary-like networks in a three-dimensional culture system

BACKGROUND

There are conflicting results regarding the role of periendothelial mural cells in angiogenesis. In the current study, we investigated the role of mesangial cells (MCs) in endothelial vascularization by using a three-dimensional co-culture system in basement-membrane reconstruct gel (Matrigel).

METHODS

Human umbilical vein endothelial cells (ECs) and human MCs were used. In the contact co-culture system, ECs and MCs were mixed and then plated together onto Matrigel. In the non-contact co-culture system, MCs were cultured within an intercup chamber, which prevented direct physical contact with the ECs on the Matrigel but allowed both cell types to share culture medium. To visualize ECs and MCs, the cells were labelled with two different fluorescent dyes prior to the co-culture. A capillary-like network formation was observed under a fluorescent microscope and confocal microscope, and the length of the network formation was quantified by the image analyzer.

RESULTS

ECs barely formed capillary-like networks when cultured alone in growth factor-free medium. However, ECs cultured with MCs in a contact condition remarkably formed capillary-like networks (9.10+/-0.96 vs 0.20+/-0.07 mm/mm2 at 6 h, contact vs ECs alone, P<0.001). Direct contact between ECs and MCs was clearly demonstrated by confocal microscopy. Differentiation into branching capillary-like structures was also observed in the non-contact co-culture system (3.02+/-1.21 mm/mm2 at 6 h, P<0.001 vs ECs alone), but less prominently than in the contact co-culture condition. Vascular endothelial growth factor (VEGF) was secreted from MCs, as determined by enzyme-linked immunosorbent assay and immunofluorescent study. Adding neutralizing antibodies against VEGF into the co-culture system partially inhibited capillary network formation.

CONCLUSIONS

Our data indicate that MCs help ECs differentiate toward vascularization, in which the direct cell-cell contact between ECs and MCs plays an important role. VEGF is a mediator in this process.

Cyclin-dependent kinase 5 is a regulator of podocyte differentiation, proliferation, and morphology

Podocytes are highly specialized and terminally differentiated glomerular cells that play a vital role in renal physiology, including the prevention of proteinuria. Cyclin-dependent kinase 5 (CDK5) has been shown to influence several cellular processes in other terminally differentiated cells, in particular neurons. In this study, we examined the role of CDK5 in podocyte differentiation, proliferation, and morphology. In conditionally immortalized mouse podocytes in culture, CDK5 increased in association with podocyte differentiation. During mouse glomerulogenesis in vivo, CDK5 expression was predominantly detected in podocytes from the capillary loop stage to maturation and persisted in the podocytes of adult glomeruli. In contrast, CDK5 was markedly decreased in the proliferating and dedifferentiated podocytes of mice with anti-glomerular basement membrane nephritis and in human immunodeficiency virus transgenic mice. p35, the activator of CDK5, was also detected in podocytes and the p35/CDK5 complex was active. Cell fractionation studies showed that active p35/CDK5 was mainly localized to the plasma membrane. Specific inhibition of CDK5 in differentiated cultured podocytes, either pharmacologically or with siRNA, induced shape changes, with cellular elongation and loss of process formation compared to the characteristic arborized phenotype. These data suggest a role for CDK5 as a regulator of podocyte differentiation, proliferation, and morphology.

Aplastic anemia associated with initiation of nizatidine therapy in a hemodialysis patient

We report on a hemodialysis (HD) patient in whom fatal aplastic anemia developed after the administration of nizatidine, a histamine 2 (H2)-receptor antagonist. The patient was a 55-year old Japanese woman and had been on HD for 2 years due to endstage diabetic nephropathy. The patient had a hemorrhagic duodenal ulcer and had been treated with lansoprazole, a proton pump inhibitor, for 2 months. After improvement, lansoprozole was discontinued and she was subsequently treated with nizatidine. Twelve days after initiation of nizatidine treatment, the patient developed a high-grade fever with symptoms suggestive of upper respiratory infection. Hematological tests showed severe pancytopenia, and drug-induced aplastic anemia was diagnosed. Nizatidine was suggested as the causal drug. Despite intensive therapies, the patient died on the 23rd hospital day from generalized fungal infections. Although hematological adverse events have been reported in HD patients receiving H2-receptor antagonists, few studies of fatal aplastic anemia associated with these drugs have been reported. This case emphasized that careful observation is required after the initiation of H2-receptor antagonist treatment in HD patients.

Differential expression of d-type cyclins in podocytes in vitro and in vivo

The proliferative response of podocytes to injury determines the histological phenotype. Moreover, an apparent lack of podocyte proliferation may underlie the development of glomerulosclerosis. Podocyte proliferation is closely linked with its state of differentiation. However, the mechanisms regulating these processes are not fully elucidated. Because D-type cyclins have been shown to be important in the regulation of proliferation and differentiation, we examined their expression in podocytes in vitro and in vivo. The glomerular expression of cyclins D1 and D3 was examined in vitro in cultured immortalized podocytes by immunostaining and Western blot analysis, and in embryonic mice and rats, the passive Heymann nephritis model of experimental membranous nephropathy in rats, and human immunodeficiency virus (HIV)-transgenic mice. Kidneys from cyclin D1 knockout mice were also examined. Cyclin D1 was abundant in cultured proliferating podocytes, but not in quiescent differentiated podocytes. In contrast, cyclin D3 was abundant in differentiated, but not proliferating podocytes. Cyclin D1 was expressed in embryonic mouse and rat glomeruli during the S- and comma-shaped stages, and was absent in podocytes at the capillary loop stage and in mature rodent glomeruli. Cyclin D1 protein increased after injury in passive Heymann nephritis rats and in HIV-transgenic mice. Cyclin D3 was constitutively and specifically expressed in podocytes in normal rodent glomeruli, and decreases during dedifferentiation and proliferation in HIV-transgenic mice. Kidneys from cyclin D1-/- mice were normal with the podocytes expressing specific differentiation markers. Cyclin D1 is not necessary for the terminal differentiation of podocytes, and expression coincides with cell-cycle entry. In contrast, cyclin D3 expression coincides with podocyte differentiation and quiescence.

Activation of a local tissue angiotensin system in podocytes by mechanical strain11See Editorial by Kriz, p. 333

BACKGROUND

Glomerular capillary hypertension, a common denominator in various forms of progressive glomerular disease, results in mechanical distention of the capillary tuft, and subsequent injury of the overlying podocyte layer. The mechanisms by which elevated intraglomerular pressure is translated into a maladaptive podocyte response remain poorly understood. Angiotensin II plays a central role in the pathogenesis of chronic renal injury, largely through its actions on the subtype 1 receptor. Accordingly, we have tested the hypothesis that mechanical strain up-regulates local angiotensin II in podocytes, thereby resulting in a progressive reduction in podocyte number.

METHODS

Conditionally immortalized mouse podocytes were subjected to cyclical stretch of 10% amplitude. Nonstretched podocytes served as controls. Angiotensin II levels were measured in whole cell lysate by competitive enzyme-linked immunosorbent assay (ELISA). Expression of angiotensin II receptors (AT1R, AT2R) was measured by quantitative polymerase chain reaction (PCR) and Western blot analysis. Apoptosis was measured by Hoechst staining. Immunostaining for AT1R was performed in tissue sections from rats with 5/6 remnant kidney disease, a model of glomerular hypertension.

RESULTS

Mechanical strain increased angiotensin II production in podocytes at 24, 48, and 72 hours (P < 0.05 vs. nonstretched controls). Stretching podocytes resulted in a fivefold increase in AT1R mRNA expression at 24 hours and a twofold increase in protein levels vs. controls (P < 0.05), and also an increase in transforming growth hormone-beta (TGF-beta) mRNA expression. AT1R staining was increased in a podocyte distribution in the 5/6 remnant kidney, consistent with our in vitro findings. Mechanical strain resulted in a 2.5-fold increase in apoptosis (P < 0.001 vs. nonstretched controls) in an angiotensin II-dependent fashion.

CONCLUSION

Mechanical strain leads to up-regulation of the AT1R and increased angiotensin II production in conditionally immortalized podocytes. The resulting activation of a local tissue angiotensin system leads to an increase in podocyte apoptosis, mainly in an AT1R-mediated fashion.

Podocytes that detach in experimental membranous nephropathy are viable

BACKGROUND

Podocyte loss contributes to the development of glomerulosclerosis. Although podocytes have been detected in the urine in certain glomerular diseases, the viability of detached cells is not known.

METHODS

Urine was collected from rats with experimental membranous nephropathy [passive Heymann nephritis (PHN) model], centrifuged, and following resuspension in tissue culture media, cells were seeded onto collagen-coated tissue culture plates. Cells were grown under typical cell culture conditions. Cell number was measured, the cell type was identified by immunostaining with specific antibodies, and cell morphology was assessed by light and electron microscopy.

RESULTS

Cells obtained in the urine from PHN rats were positive for synaptopodin, nephrin, podocin, WT-1, and GLEPP1 (podocyte-specific antigens). When grown ex vivo under cell culture conditions, cells obtained in the urine from PHN rats adhered to tissue culture plates, and expressed podocyte-specific proteins at the mRNA [reverse transcription-polymerase chain reaction (RT-PCR)] and protein (immunostaining) level. Cells did not stain with antibodies to mesangial (OX-7), tubular (Tamm-Horsfall protein) and endothelial (RECA) cells. Electron microscopy showed the presence of foot processes, and podocytes from PHN rats stained positive for C5b-9. Although podocyte number increased transiently during the first 5 days ex vivo, apoptosis increased significantly thereafter, reducing overall cell number.

CONCLUSION

Rats with experimental membranous nephropathy shed podocytes into the urine that attach to tissue culture plates ex-vivo, and proliferate. These results suggest that detached podocytes are viable. These results add new perspectives into our understanding of podocyte loss in the development of glomerulosclerosis.

Activin A induces cell proliferation of fibroblast-like synoviocytes in rheumatoid arthritis

OBJECTIVE

To investigate the expression of activin A and its receptors in rheumatoid arthritis (RA) synovial tissues, and to determine the effect of activin A on cultured fibroblast-like synoviocytes (FLS).

METHODS

The localization of activin A and activin type II receptor (ARII) in synovial tissues of RA patients was analyzed by immunohistochemistry. The expression of activin A and activin receptors in human cultured FLS was examined by reverse transcriptase-polymerase chain reaction and Western blotting. Enzyme-linked immunosorbent assay was used to measure activin A in culture supernatants. The cell growth of FLS was determined by (3)H-thymidine incorporation and MTT assay.

RESULTS

Immunohistochemical analysis confirmed the up-regulation of activin A in rheumatoid synovium as compared with osteoarthritis or normal joint tissues. CD68+ macrophage-lineage cells and vimentin-positive FLS were identified as activin-producing cells in rheumatoid synovium. Both cell types also expressed ARII. The expression of activin A and ARII on cultured FLS was confirmed at the protein and messenger RNA levels. Interleukin-1 beta (IL-1 beta), tumor necrosis factor alpha, and transforming growth factor beta activated FLS to secrete activin A. Recombinant activin A accelerated the proliferation of FLS, while follistatin, an endogenous activin antagonist, partially inhibited FLS proliferation induced by IL-1 beta.

CONCLUSION

These results suggest that activin A acts as a growth factor of FLS in RA.

DNA damage is a novel response to sublytic complement C5b-9-induced injury in podocytes

In response to Ab-complement-mediated injury, podocytes can undergo lysis, apoptosis, or, when exposed to sublytic (<5% lysis) amounts of C5b-9, become activated. Following the insertion of sublytic quantities of C5b-9, there is an increase in signaling pathways and growth factor synthesis and release of proteases, oxidants, and other molecules. Despite an increase in DNA synthesis, however, sublytic C5b-9 is associated with a delay in G(2)/M phase progression in podocytes. Here we induced sublytic C5b-9 injury in vitro by exposing cultured rat podocytes or differentiated postmitotic mouse podocytes to Ab and a complement source; we also studied the passive Heymann nephritis model of experimental membranous nephropathy in rats. A major finding was that sublytic C5b-9-induced injury caused an increase in DNA damage in podocytes both in vitro and in vivo. This was associated with an increase in protein levels for p53, the CDK inhibitor p21, growth-arrest DNA damage-45 (GADD45), and the checkpoint kinases-1 and -2. Sublytic C5b-9 increased extracellular signal-regulated kinase-1 and -2 (ERK-1 and -2), and inhibiting ERK-1 and -2 reduced the increase in p21 and GADD45 and augmented the DNA damage response to sublytic C5b-9-induced injury. These results show that sublytic C5b-9 induces DNA damage in vitro and in vivo and may explain why podocyte proliferation is limited following immune-mediated injury.

Mitotic cell cycle proteins increase in podocytes despite lack of proliferation

BACKGROUND

Podocyte proliferation is an uncommon response to glomerular injury and its lack may underlie the development of glomerulosclerosis. However, whether podocytes have the capacity to enter and finish mitosis and cytokinesis is not known.

METHODS

The expression of mitotic cell cycle proteins (phosphorylated Histone 3, Cdc2, cyclin B1 and B2) was examined by immunohistochemistry in kidneys of embryonal mice, transgenic HIV-mice, and rats with experimental membranous nephropathy (passive Heymann nephritis, PHN). Mitotic proteins also were measured by Western blot in glomerular protein from PHN-rats and the activity of mitotic cyclins was quantified by histone kinase assay.

RESULTS

Mitotic proteins were increased in embryonal mouse glomeruli during the S- and comma-shaped stages and were absent at the capillary loop stage and in mature rodent glomeruli. There was an increase in podocyte expression of Cdc2, cyclin B1 and B2 and phosphorylated histone 3 in PHN rats, and in HIV transgenic mice.

CONCLUSIONS

Podocytes have the ability to increase cell cycle proteins required for mitosis. Without obvious differences in the expression of the major mitotic proteins in PHN- and HIV-nephropathy, a regulatory disturbance in cytokinesis might be responsible for the development of polynucleated cells and a lack of podocyte proliferation in experimental glomerular disease.

The hypertrophic effect of transforming growth factor-beta is reduced in the absence of cyclin-dependent kinase-inhibitors p21 and p27

Transforming growth factor-beta (TGF-beta) has both antiproliferative and hypertrophic effects on mesangial cells (MC). However, it is not known if these processes are independent or if they share common signaling pathways. Proliferation and hypertrophy are regulated by specific cell-cycle regulatory proteins, where the cyclin-dependent kinase (CDK) inhibitors inhibit target cyclin-CDK complexes. This study examined whether the growth regulatory effects of TGF-beta were determined by the CDK inhibitors p21 and p27. Accordingly, cultured MC from wild type (+/+) and single and double null (-/-) p21 and p27 mice were grown in 5% serum in the presence or absence of TGF-beta1 (2 ng/ml). Proliferation ([(3)H]-thymidine incorporation, cell number, cell cycle) and hypertrophy ([(3)H]-leucine incorporation, total protein content, forward light scatter) were measured after 24 h, 48 h, and 96 h. TGF-beta inhibited proliferation in +/+ and p21/p27 double -/- MC to a similar extent. TGF-beta induced hypertrophy in +/+ MC (18.0% increase at 48 h), and to lesser extent in p21 -/- (12.8%) and p27 -/- MC (11.5%) measured by forward light scatter analysis. In p21/p27 double -/-, the hypertrophic effects of TGF-beta were significantly reduced (3.9% at 48 h). Similar results were obtained by measuring hypertrophy by total protein and [(3)H]-leucine incorporation. In conclusion, the CDK inhibitors p21 and p27 are not required for the antiproliferative effects of TGF-beta. However, the hypertrophic growth effects of TGF-beta are reduced in the absence of both p21 and p27. These data suggest that the regulation of the antiproliferative and hypertrophic effects of TGF-beta may be distinct processes.

Insulin is a potent survival factor in mesangial cells: role of the PI3-kinase/Akt pathway

BACKGROUND

Elucidating the mechanisms of apoptosis is important for understanding the molecular mechanisms underlying glomerular disease. The phosphatidylinositol 3 kinase (PI3-kinase)/Akt pathway is essential for survival signaling in non-renal cells. However, little is known about the anti-apoptotic effect of insulin and the role of the PI3-kinase/Akt pathway in mesangial cells (MC) apoptosis.

METHODS

Apoptosis was induced in wild type, p27Kip1 (p27) -/- and p21Cip1/Waf1 (p21) -/- mouse MC by survival factor withdrawal, actinomycin D, ultraviolet (UV)-B irradiation and cycloheximide in the presence or absence of insulin (1 micromol/L) or insulin-like growth factor-I (IGF-I; 100 ng/mL). The activation and levels of Akt, extracellular signal regulated kinase (ERK) and specific cell cycle proteins were determined by Western blot analysis.

RESULTS

Insulin and IGF-I inhibited wild-type MC apoptosis induced by survival factor withdrawal, actinomycin D, ultraviolet-B irradiation and cycloheximide and in p27 -/- MC when apoptosis was induced by survival factor withdrawal. Akt was activated by insulin and IGF-I during apoptosis. Blocking PI3-kinase with LY294002 reduced Akt activation and abrogated the anti-apoptotic effect of insulin. ERK was activated during apoptosis and blocking ERK activation with U0126 or PD98059 partially rescued MC from apoptosis. Moreover, insulin also suppressed ERK activation during apoptosis. Our results also showed that the CDK-inhibitor p21 was increased by insulin and that p21 up-regulation was PI3-kinase/Akt pathway dependent. Furthermore, p21 -/- MC apoptosis induced by survival factor withdrawal was not rescued by insulin in contrast to the wild-type and p27 -/- MC. These data suggest that p21 may have a critical role in the anti-apoptotic effect of insulin.

CONCLUSIONS

Insulin is a potent survival factor for MC in response to a number of different apoptotic triggers, and this effect is mediated through the PI3-kinase/Akt pathway. Moreover, ERK and p21 may be involved in anti-apoptotic effect of insulin in MC.

The subcellular localization of cyclin dependent kinase 2 determines the fate of mesangial cells: role in apoptosis and proliferation

Apoptosis is closely linked to proliferation. In this study we showed that inducing apoptosis in mouse mesangial cells with ultraviolet (UV) irradiation was associated with increased cyclin A-cyclin dependent kinase (CDK) 2 activity. Inhibiting CDK2 activity with Roscovitine or dominant negative mutant reduced apoptosis. Because apoptosis typically begins in the cytoplasm, we tested the hypothesis that the subcellular localization of CDK2 determines the proliferative or apoptotic fate of the cell. Our results showed that cyclin A-CDK2 was nuclear in proliferating cells. However, inducing apoptosis in proliferating cells with UV irradiation was associated with a decrease in nuclear cyclin A and CDK2 protein levels. This coincided with an increase in protein and kinase activity for cyclin A-CDK2 in the cytoplasm. Translocation of cyclin A-CDK2 also occurred in p53-/- mesangial cells. Finally, we showed that caspase-3 activity was significantly reduced by inhibiting CDK2 activity with Roscovitine. In summary, our results show that apoptosis is associated with an increase in cytoplasmic cyclin A-CDK2 activity, which is p53 independent and upstream of caspase-3. We propose that the subcellular localization of CDK2 determines the proliferative or apoptotic fate of the cell.

Mechanical stress reduces podocyte proliferation in vitro

BACKGROUND

Mechanical stretch, a consequence of capillary glomerular hypertension, is thought to be the common final pathway for glomerulosclerosis in systemic hypertension, diabetes, reduced nephron number and focal segmental glomerulosclerosis. However, the effects of stretch on podocyte growth and the mechanisms that underlie this have not been elucidated.

METHODS

Mouse podocyte growth (3H-thymidine, MTT-assay, FACS) was measured following the application of mechanical stretch created by vacuum. The expression of specific cell cycle regulatory proteins was examined by RNAse protection assay and Western blot analysis. Control cells were grown under similar conditions, but were not exposed to stretch.

RESULTS

Mechanical stretch decreased DNA-synthesis (3H-thymidine incorporation) and cell number (MTT-assay) in podocytes at 24, 48 and 72 hours (P < 0.001 vs. control non-stretched cells), which was not due to apoptosis (Hoechst staining) nor cell detachment. Stretch decreased the mRNA and protein levels of cyclins D1, A and B1 within 24 hours. Stretching cells decreased the activity of Cdk2 (measured by histone H1 kinase assay) at 48 and 72 hours and Cdc2 at 72 hours. In contrast, stretch increased the protein levels of the cyclin dependent kinase inhibitors (CKI) p21Cip/Kip/Waf (p21) and p27Kip1 (p27) within the first 24 hours, and increased the mRNA levels of p57Kip2 (p57) at 72 hours. To examine the role of p21 in inhibiting proliferation induced by stretch, we studied p21-/- podocytes in culture. Stretch did not reduce proliferation in p21-/- podocytes (P> 0.05 vs. non-stretched podocytes; P < 0.001 vs. stretched p21+/+ podocytes).

CONCLUSIONS

In contrast to mesangial cells, mechanical stretch decreases the growth of podocytes. This effect is mediated through the regulation of specific cell cycle regulatory proteins. These events may explain the apparent lack of podocyte proliferation in diseases correlated with capillary glomerular hypertension.

Podocyte expression of the CDK-inhibitor p57 during development and disease

BACKGROUND

The mature podocyte is a terminally differentiated cell with a limited proliferative capacity. The precise cell cycle proteins necessary for establishing podocyte quiescence during development or permitting podocyte cell cycle re-entry in disease states have not been fully defined. Accordingly, we studied the role of the cyclin dependent kinase (CDK)-inhibitor p57Kip2 (p57) in modulating these processes.

METHODS

The expression of p57 protein in relation to markers of DNA synthesis was examined in developing mouse kidneys, and in the passive Heymann nephritis (PHN) and anti-glomerular antibody models of glomerular disease by immunohistochemistry. The role of p57 in glomerulogenesis was explored by examining renal tissue from embryonic p57-/- mice, and the expression of p21, p27 and p57 protein and mRNA was examined in podocytes in vitro.

RESULTS

The de novo expression of p57 during glomerulogenesis coincides with the cessation of podocyte proliferation, and the establishment of a mature phenotype, and p57 is expressed exclusively in podocytes in mature glomeruli. However, p57 knockout mice have normal glomerular podocyte development. In addition, mRNA but not protein levels of p57 increased upon differentiation of podocytes in vitro. There was a marked decrease in p57 expression in both animal models of podocyte injury. This was diffuse in PHN, whereas in the murine model, loss of expression of p57 occurred predominantly in proliferating podocytes, expressing proliferating cell nuclear antigen (PCNA).

CONCLUSION

Despite the de novo expression of p57 protein coinciding with the cessation of primitive podocyte proliferation during glomerulogenesis, embryonic p57-/- mice glomeruli were histologically normal. Cultured podocytes did not require changes in p57 protein levels to undergo differentiation. These data suggest that p57 alone is not required for podocyte differentiation, and that other cell cycle regulators may play a role. Furthermore, although injury to mature podocytes in experimental glomerular disease is associated with a decrease in p57, the levels of all three members of the Cip/Kip family of CDK inhibitors appear to determine the capability of podocytes to proliferate.

Platelet-activating factor antagonist, SM-12502, attenuates experimental glomerular thrombosis in rats

Platelet-activating factor (PAF) is involved in many pathologic conditions through its potent proinflammatory and vasoactive effects. Using a specific PAF antagonist, SM-12502, we investigated the role of PAF in rat experimental glomerular thrombosis. In this model, sequential injections of nephrotoxic serum (NTS) and lipopolysaccharide (LPS) selectively induce glomerular fibrin deposition accompanied by neutrophil accumulation. SM-12502, when injected simultaneously with either NTS or LPS, strongly inhibited glomerular fibrin deposition in a dose-dependent manner. In contrast, neutrophil invasion was similar in both SM-12502-injected and uninjected rats, suggesting that the antithrombotic effect was not mediated by inhibition of neutrophil migration. However, serum myeloperoxidase activity, a marker of neutrophil activation, was significantly suppressed by treatment with SM-12502. From a previous finding supporting the indispensable role of neutrophils in this model and the current observations, SM-12502 is suggested to attenuate glomerular thrombosis by inhibiting neutrophil activation. Thus, the present findings suggest an involvement of PAF in this glomerular thrombosis model.

Four cases of anti-myeloperoxidase antibody-related rapidly progressive glomerulonephritis during the course of idiopathic pulmonary fibrosis

We report here 4 cases of rapidly progressive glomerulonephritis (RPGN) which developed during the management of idiopathic pulmonary fibrosis. In each patient, pulmonary disease preceded the onset of nephritis by 1 to 6 years. All patients had a high titer of serum autoantibodies against myeloperoxidase (MPO-ANCA) when the diagnosis of RPGN was made. Although the association of pulmonary fibrosis with ANCA-related glomerulonephritis has been occasionally described in the past literature, the sequence of pulmonary and renal injury has not been well defined. The present report demonstrates that idiopathic pulmonary fibrosis exists as a preceding condition in some patients with MPO-ANCA-related nephritis.