Renal tubular epithelial cell apoptosis by Fas-FasL–dependent self-injury can augment renal allograft injury

The role of Fas-FasL interactions in kidney allograft injury may be complex as renal tubular epithelial cells (TEC) express both Fas and FasL. The role and regulation of TEC self-injury has not been investigated. In co-cultures of TEC, FasL-bearing, Fas-null TEC was demonstrated to induce apoptosis of TEC-bearing Fas. Co-culturing effector lpr-TEC (M3.1-lpr) with target WT-TEC (CS3.7) at a ratio of 10:1 (E/T) induced 15.2 +/- 2.4% of target apoptosis as compared to its basal level of 2.6 +/- 0.3%. Similarly lpr-TEC induced apoptosis in gld-TEC (MRM-gld) from a basal level of 3.7 +/- 0.2% to 6.4 +/- 0.3%. Expression of kidney Fas-FasL on injury was tested in a renal transplant model. C57BL/6 (B6) mice were transplanted with Fas-deficient C3H-lpr/lpr or FasL mutation C3H-gld/gld kidneys as compared to normal (wild-type [WT]) C3H/Hej donors. Survival of both lpr and gld recipient was improved compared to WT donors (P <.05) as was function of lpr and gld kidneys indicated by a lower serum creatinine (LPR: 41 +/- 8 micromol/L; GLD: 52 +/- 7 micromol/L) as compared to the WT donors (84 +/- 8 micromol/L, P <.001). These results demonstrate that activated TEC may commit a novel and previously unreported form of self-injury (fractricide) through Fas-FasL. These results suggest that inhibition of renal Fas or FasL might be a useful strategy to prevent TEC loss during rejection.

Development of an XTT tetrazolium salt-based assay for detection of specific hyperthermia sensitizers in a high-flux screening programme

It is now possible to search for new drugs using high-throughput screening of chemical libraries accumulated over the past few years. To detect potential new hyperthermia sensitizers, we are screening for chemical inhibitors of thermotolerance. For the screening of a large chemical library, a rapid and simple assay based on the XTT-tetrazolium salt with the addition of intermediate electron acceptor, phenazine methosulphate (PMS) as a promoter, was developed. It was found that the sensitivity of the XTT/PMS assay is sufficient for assessing thermal cell killing and thermotolerance, although it was highly dependent on cell number and type. When the formazan assay system was challenged with the bioflavonoid drug quercetin (up to 25mm) and validated against the clonogenic cell survival assay, significant decreases in thermotolerant cell viability were observed, directly reflecting inhibition of thermotolerance. Although short-term assays can, in some instances, underestimate overall cell killing, the dose dependency of inhibition of thermotolerance by quercetin recorded in this study by clonogenic and XTT/PMS assays was similar. Application of the XTT/PMS assay in chemical library screening was highly effective in differentiating potential thermotolerance inhibitors from both chemicals with lack of efficacy and from toxic compounds. Taken together, these results show that the XTT/PMS assay, when carried out under careful conditions, is well suited for primary high-flux screen of many thousands of compounds, thus opening up new areas for discovery of hyperthermia sensitizers.

Thymic re-entry of mature activated T cells and increased negative selection in vascularized allograft recipients

Transplantation tolerance is a dynamic state that involves several homeostatic mechanisms intrinsic to the host. One of these mechanisms is activation-induced T cell death (AICD). However, it is unclear where AICD takes place during alloreactive responses. Since activated T cells can re-enter the thymus, we hypothesized that mature T cells activated by an allograft could be deleted upon re-entry into the thymus. To test this hypothesis, we used wild-type or 2C TCR transgenic mice receiving syngeneic or allogeneic heterotopic, vascularized heart grafts. First, we demonstrated that ex vivo CFSE-labelled T cells re-entered the thymus when transferred into allograft recipients but not when transferred into isograft recipients. Next, we compared the changes in cell subset numbers and incidence of apoptosis in the thymi and spleens of allograft or isograft recipients. Seven days after transplantation, at a time in which all the allografts were undergoing rejection, cells expressing donor-MHC class II molecules had migrated to the thymus and to the spleen. In the thymus of allograft recipients, overall cellularity was significantly reduced by 40% and associated with an increase in the number of double negative (CD4-CD8-) thymocytes and a decrease in double positive (CD4+CD8+) thymocytes, consistent with increased negative selection of thymocytes. Additionally, thymi of allograft recipients showed an increase in the number of recently activated, mature T cells (TCRhi, CD25+, CD44+) and a significant increase in the number of apoptotic cells, especially in the thymic medulla, that involved mature T cells as indicated by the TCRhi, CD44+, CD4 or CD8 single positive phenotype. Spleens of allograft recipients were increased in size and cellularity but did not show any of the changes in cell subsets seen in the thymi. Our data show that after allografting there is an increase in apoptotic cell death that is associated with negative selection of developing thymocytes as well as of alloreactive mature T cells that have re-entered the thymus upon activation in the periphery. This may occur upon migration of graft-derived antigen-presenting cells to the thymus.

Anti-CD45RB monoclonal antibody-mediated transplantation tolerance

Currently, lifelong immunosuppression is required for organ transplant recipients. The majority of transplant recipients will eventually develop chronic rejection with resultant graft loss, despite treatment with powerful immunosuppressive agents. These agents are also associated with numerous toxicities including reduced immunity against infection and malignancy. Therefore, the central goal in transplant science is to devise tolerance strategies in an attempt to establish a state of prolonged non-reactivity against the allograft, accompanied with preservation of an intact immune system. Although predictable tolerance induction has been elusive, we found that short course of the novel immunomodulatory agent, anti-CD45RB monoclonal antibody, leads to indefinite acceptance of renal allografts in mice, and has been shown to markedly prolong allograft survival in primates. We review the current state of development of this antibody, and the progress made in defining its mechanism of action.

Spleen autotransplantation in mice: a novel experimental model for immunology study

The aim of the experimental model to develop a spleen transplant model in mice to study the role of spleen in autoimmune and transplant rejection. After a midline incision, splenectomy was performed. Four tiny segments were cut from the removed spleen and were rinsed at room temperature in physiological salt solution. The greater omentum was lifted and four omental pockets were created; four thin segments were then placed into the "nests," subsequently marked, and fixed using 8-0 suture. The abdomen was then closed. The duration of the survival time was different among the nine groups (n = 3-3). Tissue samples were taken from the marked areas for histological examination stained with hematoxylin and eosin (H&E). H&E staining demonstrated large, well-circumscribed splenic nests with lymphoid zone and red pulp and well-formed trabecules in the spleen. Among the possible applications of this novel model is the ability to study the role of spleen in autoimmune and organ rejection.

Caffeoyl coenzyme A O-methyltransferase and lignin biosynthesis

Lignin, a complex phenylpropanoid compound, is polymerized from the monolignols p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol. These three monolignols differ only by the 3- and 5-methoxyl groups. Therefore, enzymatic reactions controlling the methylations of the 3- and 5-hydroxyls of monolignol precursors are critical to determine the lignin composition. Recent biochemical and transgenic studies have indicated that the methylation pathways in monolignol biosynthesis are much more complicated than we have previously envisioned. It has been demonstrated that caffeoyl CoA O-methyltransferase plays an essential role in the synthesis of guaiacyl lignin units as well as in the supply of substrates for the synthesis of syringyl lignin units. Caffeic acid O-methyltransferase has been found to essentially control the biosynthesis of syringyl lignin units. These new findings have greatly enriched our knowledge on the methylation pathways in monolignol biosynthesis.

A short course of high-dose cyclophosphamide induces long-term survival of intestinal allografts in mice

Several transplant programs have recently added cyclophosphamide (CyP) to their immune suppression protocols in an attempt to reduce intestinal graft rejection rates. The present study was undertaken to confirm the benefits of this drug in a murine small bowel transplant model. A short course of monotherapy with CyP 20 mg/kg per dose resulted in a mean survival time (MST) of 17.5 +/- 3.6 days, compared with a MST of 7.5 +/- 0.7 days in the untreated controls (P < 0.01). Cyclosporin A (CsA) 30 mg/kg per day produced comparable survival rates when used as monotherapy (MST: 14.2 +/- 1.3 days) or in combination with CyP 20 mg/kg per dose (MST: 21.3 +/- 5.1 days). Treatment with high dose CyP (40 mg/kg per dose) completely prevented graft loss in 8 of 10 animals (MST: 72.5 +/- 5.3 days, P < 0.01). However, adding CsA abrogated the induction of long-term survival achieved by CyP alone (MST: 23 +/- 0.4 days). These data have important implications for the use of CyP in clinical transplantation.

Vascular smooth muscle cells of recipient origin mediate intimal expansion after aortic allotransplantation in mice

Intimal expansion by vascular smooth muscle cells (SMCs) is a characteristic feature of graft vascular disease. Whether graft intimal SMCs arise from donor or recipient tissue is not well established but has important pathogenetic implications. We examined for the presence of male cells in the expanded intima of sex-mismatched mouse aortic allografts (C57BL/6-to-BALB/c) at 30 or 60 days after transplant by in situ hybridization using a Y-chromosome probe. Study groups included male-to-female allografts, female-to-male allografts, and female-to-female allografts in recipients previously engrafted with male bone marrow. Although intimal expansion developed in all allografts, male-to-female allografts lacked Y-chromosome-positive intimal cells. In contrast, such cells were abundant in female-to-male allografts and most of these cells co-labeled for smooth muscle alpha-actin by immunostain. Female-to-female allografts in recipients with male bone marrow showed a limited number of intimal Y-chromosome-positive cells. However, none of these clearly co-labeled for smooth muscle alpha-actin and their numbers declined throughout time, consistent with graft-infiltrating inflammatory cells. We conclude that intimal expansion of mouse aortic allografts is mediated by SMCs that originated from the recipient. There was little evidence of their derivation from the bone marrow, suggesting instead the adjacent host aorta as the primary source of intimal SMCs.

Alteration of auxin polar transport in the Arabidopsis ifl1 mutants

The INTERFASCICULAR FIBERLESS/REVOLUTA (IFL1/REV) gene is essential for the normal differentiation of interfascicular fibers and secondary xylem in the inflorescence stems of Arabidopsis. It has been proposed that IFL1/REV influences auxin polar flow or the transduction of auxin signal, which is required for fiber and vascular differentiation. Assay of auxin polar transport showed that the ifl1 mutations dramatically reduced auxin polar flow along the inflorescence stems and in the hypocotyls. The null mutant allele ifl1-2 was accompanied by a significant decrease in the expression level of two putative auxin efflux carriers. The ifl1 mutants remained sensitive to auxin and an auxin transport inhibitor. The ifl1-2 mutant exhibited visible phenotypes associated with defects in auxin polar transport such as pin-like inflorescence, reduced numbers of cauline branches, reduced numbers of secondary rosette inflorescence, and dark green leaves with delayed senescence. The visible phenotypes displayed by the ifl1 mutants could be mimicked by treatment of wild-type plants with an auxin polar transport inhibitor. In addition, the auxin polar transport inhibitor altered the normal differentiation of interfascicular fibers in the inflorescence stems of wild-type Arabidopsis. Taken together, these results suggest a correlation between the reduced auxin polar transport and the alteration of cell differentiation and morphology in the ifl1 mutants.

[Effect of pentoxifylline on promoter activity of human alpha 1(I) procollagen gene]

OBJECTIVE

To study the effect of pentoxifylline (PTX) on promoter activity of human alpha 1(I) procollagen (COL1A1) gene and the influence of PTX on the promoter activity induced by insulin-like growth factor 1 and insulin.

METHODS

The constructs of pCOLH2.5 containing -2483 approximately +42bp of the procollagen gene and chloramphenicol acetyltransferase (CAT) as reporter gene were transiently transfected into human skin fibroblasts. The cells were subsequently treated with PTX or IGF-1 or insulin, or PTX plus IGF-1 or insulin. The CAT activity was assessed 24h after PTX and the cytokines added.

RESULTS

PTX of 0.4 mmol/L, 2 mmol/L, and 10 mmol/L decreased the CAT activity of pCOLH 2.5 to 82%+/-9%, 58%+/-8%, and 32%+/-13% of the control level, respectively. IGF-1 and insulin increased the activity of the construct. PTX could inhibit the CAT activity of pCOLH2.5 induced by IGF-1 and insulin.

CONCLUSIONS

These studies indicate that PTX downregulates the promoter activity of the human COL1A1 gene, while IGF-1 and insulin upregulates it. PTX can inhibit the promoter activity induced by IGF-1 and insulin.

A katanin-like protein regulates normal cell wall biosynthesis and cell elongation

Fibers are one of the mechanical tissues that provide structural support to the plant body. To understand how the normal mechanical strength of fibers is regulated, we isolated an Arabidopsis fragile fiber (fra2) mutant defective in the mechanical strength of interfascicular fibers in the inflorescence stems. Anatomical and chemical analyses showed that the fra2 mutation caused a reduction in fiber cell length and wall thickness, a decrease in cellulose and hemicellulose contents, and an increase in lignin condensation, indicating that the fragile fiber phenotype of fra2 is a result of alterations in fiber cell elongation and cell wall biosynthesis. In addition to the effects on fibers, the fra2 mutation resulted in a remarkable reduction in cell length and an increase in cell width in all organs, which led to a global alteration in plant morphology. The FRA2 gene was shown to encode a protein with high similarity to katanin (hence FRA2 was renamed AtKTN1), a protein shown to be involved in regulating microtubule disassembly by severing microtubules. Consistent with the putative function of AtKTN1 as a microtubule-severing protein, immunolocalization demonstrated that the fra2 mutation caused delays in the disappearance of perinuclear microtubule array and in the establishment of transverse cortical microtubule array in interphase and elongating cells. Together, these results suggest that AtKTN1, a katanin-like protein, is essential not only for normal cell wall biosynthesis and cell elongation in fiber cells but also for cell expansion in all organs.

A katanin-like protein regulates normal cell wall biosynthesis and cell elongation

Fibers are one of the mechanical tissues that provide structural support to the plant body. To understand how the normal mechanical strength of fibers is regulated, we isolated an Arabidopsis fragile fiber (fra2) mutant defective in the mechanical strength of interfascicular fibers in the inflorescence stems. Anatomical and chemical analyses showed that the fra2 mutation caused a reduction in fiber cell length and wall thickness, a decrease in cellulose and hemicellulose contents, and an increase in lignin condensation, indicating that the fragile fiber phenotype of fra2 is a result of alterations in fiber cell elongation and cell wall biosynthesis. In addition to the effects on fibers, the fra2 mutation resulted in a remarkable reduction in cell length and an increase in cell width in all organs, which led to a global alteration in plant morphology. The FRA2 gene was shown to encode a protein with high similarity to katanin (hence FRA2 was renamed AtKTN1), a protein shown to be involved in regulating microtubule disassembly by severing microtubules. Consistent with the putative function of AtKTN1 as a microtubule-severing protein, immunolocalization demonstrated that the fra2 mutation caused delays in the disappearance of perinuclear microtubule array and in the establishment of transverse cortical microtubule array in interphase and elongating cells. Together, these results suggest that AtKTN1, a katanin-like protein, is essential not only for normal cell wall biosynthesis and cell elongation in fiber cells but also for cell expansion in all organs.

Endothelin-1, endothelin-3 and their receptors (endothelin(A) and endothelin(B)) in chronic renal transplant rejection in rats

Endothelins (ET) are a family of vasoactive peptides that play an important role in several disorders affecting kidneys. In this study we investigated the expressions of ET-1, ET-3, and their receptors, ET(A) and ET(B), in a rat chronic renal transplant rejection model. Renal allografts were performed (F344 --> Lewis) with bilateral nephrectomy in recipients. For isograft control, lewis --> lewis transplantations were performed. All recipients were sacrificed 140 days after transplantation and the grafts were analyzed histologically. ET-1 and ET-3 protein expression in grafts was measured by immunohistochemistry and ELISA. Semiquantitative RT-PCR methods were used for mRNA levels of ET-1, ET-3, ET(A) and ET(B). No evidence of chronical rejection was manifested in isografts. The allografted rats showed proteinuria and increased serum creatinine levels. Histologically, renal allografts showed atrophy and sclerosis of the glomeruli, cortical scarring and vascular intimal thickening. Immunohistochemically, ET-1 and ET-3 were localized in the convoluted tubules, collecting ducts, endothelium and smooth muscle cells of the large blood vessels. Significantly increased staining for ET-1 and ET-3 were found in allografts compared to isografts. Simultaneously, ELISA for ET-1 and ET-3 showed elevated protein concentrations in allografts compared to isografts. Allografts showed significantly increased ET-1- and ET-3 mRNA compared to isografts. On the other hand, a significant down regulation of the ET(A) mRNA was noted, and the ET(B) mRNA remained unchanged. The data from the present study suggest that alteration of ET system may be of importance in the pathogenesis of chronic renal transplant rejection.

Fragmentation of N-oxides (deoxygenation) in atmospheric pressure ionization: investigation of the activation process

The diagnostic fragmentation of N-oxides resulting from loss of the oxygen atom (MH+ --> MH+-O) in electrospray and atmospheric pressure chemical ionization (APCI) mass spectra was investigated. When the temperature of the heated capillary tube was elevated, the ratio of the intensity of the [MH+ -16] fragment to the precursor ion (MH+) increased. This 'deoxygenation' process was associated with thermal activation and did not result from collisional activation in the desolvation region of the API source. Although the extent of 'deoxygenation' is compound-dependent, it can provide evidence for the presence of an N-oxide in a sample and can be used to distinguish N-oxides from hydroxylated metabolites (Ramanathan et al. Anal. Chem. 2000; 72: 1352). To demonstrate the practical application of thermal fragmentation of N-oxides, liquid chromatography (LC)/APCI-MS was used to distinguish an N-oxide drug from its hydroxylated metabolite in an unprocessed rat urine sample, despite the fact that the drug and its metabolite were not fully resolved by HPLC.

Essential role of caffeoyl coenzyme A O-methyltransferase in lignin biosynthesis in woody poplar plants

Caffeoyl coenzyme A O-methyltransferase (CCoAOMT) has recently been shown to participate in lignin biosynthesis in herbacious tobacco plants. Here, we demonstrate that CCoAOMT is essential in lignin biosynthesis in woody poplar (Populus tremula x Populus alba) plants. In poplar stems, CCoAOMT was found to be expressed in all lignifying cells including vessel elements and fibers as well as in xylem ray parenchyma cells. Repression of CCoAOMT expression by the antisense approach in transgenic poplar plants caused a significant decrease in total lignin content as detected by both Klason lignin assay and Fourier-transform infrared spectroscopy. The reduction in lignin content was the result of a decrease in both guaiacyl and syringyl lignins as determined by in-source pyrolysis mass spectrometry. Fourier-transform infrared spectroscopy indicated that the reduction in lignin content resulted in a less condensed and less cross-linked lignin structure in wood. Repression of CCoAOMT expression also led to coloration of wood and an elevation of wall-bound p-hydroxybenzoic acid. Taken together, these results indicate that CCoAOMT plays a dominant role in the methylation of the 3-hydroxyl group of caffeoyl CoA, and the CCoAOMT-mediated methylation reaction is essential to channel substrates for 5-methoxylation of hydroxycinnamates. They also suggest that antisense repression of CCoAOMT is an efficient means for genetic engineering of trees with low lignin content.

Synthetic peptides which inhibit the interaction between C1q and immunoglobulin and prolong xenograft survival

BACKGROUND

Acute vascular xenograft rejection (AVXR), also termed delayed xenograft rejection (DXR), occurs when hyperacute rejection (HAR) is prevented by strategies directed at xenoreactive natural antibodies and/or complement activation. We have hypothesized that AVXR/DXR is initiated in part by early components of the complement cascade, notably C1q. We have developed synthetic peptides (termed CBP2 and WY) that interfere with the interaction between C1q and antibody.

METHODS

CBP2 and the WY-conjugates were used as inhibitors of immunoglobulin aggregate binding to solid phase C1q. Inhibition of complement activation by the peptides of the classical system was determined using lysis assays with sensitized sheep red blood cells or porcine aortic endothelial cells as targets and of the alternate complement pathway using guinea pig red blood cells as targets. Two transplant models were used to study the effects of administering peptides to recipients: rat heart transplant to presensitized mouse, and guinea heart transplant to PVG C6-deficient rats.

RESULTS

CBP2 and WY-conjugates inhibited immunoglobulin aggregate binding to C1q. The peptides also inhibited human complement-mediated lysis of sensitized sheep red blood cells and porcine aortic endothelial cells in a dose-dependent manner and the WY-conjugates prevented activation of the alternate complement pathway as shown by inhibition of guinea pig red blood cells lysis with human serum. In addition, the use of the peptides and conjugates resulted in significant prolongation of xenograft survival.

CONCLUSIONS

The CBP2 and WY peptides exhibit the functional activity of inhibition of complement activation. These peptides also prolong xenograft survival and thus provide reagents for the study of the importance of C1q and other complement components in transplant rejection mechanisms.

Animal models in xenotransplantation

The severe shortage of donor organs has provided a strong impetus to push the investigation into the use of animal organs for humans. Xenotransplantation will not only benefit patients, but also represents a unique and potentially profitable business opportunity. However, there are many barriers to successful clinical xenotransplantation, including immunological barriers, physiological incompatibility, zoonosis and ethical concerns. This overview will focus on currently available animal models used in attempts to break through the immunological barriers to xenotransplantation. There are many advantages to using small animal, namely rodent, models in xenotransplantation research. For example, the use of the mouse model allows the use of knockout mice and careful dissection of rejection mechanisms at the molecular level. The following models can be used to study hyperacute rejection (HAR): guinea-pig-to-rat, mouse-to-rabbit, guinea-pig-to-mouse, rat-to-presensitised mouse and rat-to-alpha-Gal knockout mouse. The hamster-to-rat, mouse-to-rat and rat-to-mouse models are commonly used to study acute vascular rejection. Large animal models are complex and expensive, but they are more relevant to clinical xenotransplantation. Based on experiments using transgenic pig-to-primate models, HAR can be overcome. However, acute vascular rejection remains a major barrier at the present time. A pig cartilage-to-monkey model has been developed to study chronic rejection. Other novel models such as pig venous segment-to-monkey model and rat-to-primate model may represent viable options to study immunological barriers following xenotransplantation. Like many other medical breakthroughs, animal research will continue to make enormous contributions towards the eventual success of xenotransplantation.