Experimental heart transplantation: effect of cyclosporine on expression and activity of metzincins.

Metzincins, such as matrix metalloproteases (MMP), and extracellular matrix (ECM) proteins are differentially regulated in inflammation. We hypothesised that metzincins are also dysregulated in experimental acute cardiac allograft rejection. We investigated the Dark Agouti-to-Lewis (DA-to-Lew) rat model of acute cardiac allograft rejection. Cyclosporine (CsA) (7.5 mg/kg/d) was given from transplantation to sacrifice (day +5). At that time, mRNA levels were analysed by Affymetrix genechip and quantitative reverse transcription polymerase chain reaction (qRTPCR). MMP protein and activities were analysed by immunohistology, fluorometry, zymography and Western blots. In untreated rejected DA allografts, mRNA levels of MMP-2/-7/-9/-/12-/14, a disintegrin and metalloprotease (ADAM)-17, tissue inhibitor of metalloprotease (TIMP)-1/-3 were increased, whereas MMP-11/-16/-24 and TIMP-2/-4 were lowered compared to native DA hearts. With respect to these untreated allografts, CsA lowered mRNA levels of MMP-7, TIMP-1/-3 (TIMP-2/-4 remained relatively low) and ADAM17, but augmented mRNA levels of MMP-11/-16/-23 and of many ECM genes. Immunohistology showed increased staining of MMP-2 in acute rejection (AR). Overall MMP activity was augmented in both transplanted groups, but CsA reduced MMP-9 activity and MMP-14 production. Taken together, MMP and TIMP were upregulated during acute AR. CsA ameliorated histology of rejection but showed potential pro-fibrotic effects. Thus, MMP and TIMP may play a role in acute cardiac allograft rejection, and beneficial modification of the MMP-ECM balance requires interventions beyond CsA.

Differential effects of TNF and LTalpha in the host defense against M. bovis BCG.

Signaling via TNF receptor type 1 (TNFR1) was shown to be crucial in host defense against the intracellular pathogens L. monocytogenes, M. tuberculosis and M. bovis. To investigate the function of TNF and LTalpha in host defense against M. bovis, mice double deficient for TNF and LTalpha (TNF / LTalpha (- / -)), TNF / LTalpha (- / -) mice complemented with a murine LTalpha transgene (TNF(- / -)) and LTalpha (- / -) mice were infected with BCG and the ensuing pathology was investigated. Control mice showed a normal host defense with early clearance of bacteria. The granulomatous reaction in the liver was accompanied by recruitment of activated macrophages characterized by their acid phosphatase positivity and differentiation into epithelioid cells as well as a coordinated expression of proinflammatory transcripts. In contrast, TNF / LTalpha (- / -) mice showed no comparable recruitment of activated macrophages in the liver. Furthermore, these mice showed extensive necrotic pulmonary lesions with massive growth of acid fast bacilli. Reintroduction of LTalpha as a transgene into TNF / LTalpha (- / -) mice prolonged survival but did not restore resistance to BCG. This, at least partially protective role of LTalpha was further supported by data demonstrating that LTalpha -deficient mice as well were susceptible to BCG infection. In contrast to the deleterious effect of TNF / LTalpha deficiency in BCG infection, BCG-infected TNF / LTalpha (- / -) mice were tolerant to LPS-induced shock. These results demonstrate that TNF as well as LTalpha are involved in murine host defense against BCG and that absence of TNF / LTalpha protects BCG-infected mice from LPS mediated shock.

IL-12-dependent, INF-gamma-independent experimental glomerulonephritis.

There is evidence that crescentic glomerulonephritis initiated in rodents by heterologous antibodies against the glomerular basement membrane (anti-GBM glomerulonephritis) depends on a Th1-type immune reaction. Interleukin 12 (IL-12) is crucial for the development of Th1 helper cells, and interferon gamma (IFN-gamma) is a major proinflammatory product of these cells. In order to test the role of the two cytokines in anti-GBM glomerulonephritis we used mice lacking either the p40 chain of IL-12 (IL-12-/-) or the IFN-gamma receptor (IFN-gammaR-/-). Glomerulonephritis was induced by injecting a rabbit anti-GBM serum in mice preimmunized against rabbit IgG. Glomerulonephritis was assessed on the basis of proteinuria, immunofluorescence findings and histology. IL-12-/- mice were completely protected against glomerulonephritis. In contrast, IFN-gammaR-/- mice were more severely affected than wild-type mice. Similarly, cutaneous delayed-type hypersensitivity, a typical Th1 response, was abolished in the IL-12-/-, mice but increased in the IFN-gammaR-/- mice. The data obtained in IL-12-/- mice support the view that crescentic glomerulonephritis in this model represents a Th1 response. Since IFN-gamma is not required, other products of Th1 cells are likely to mediate glomerulonephritis.

A Th1 response is essential for induction of crescentic glomerulonephritis in mice.

Crescentic glomerulonephritis can be induced in rodents by injection of heterologous antibodies against the glomerular basement membrane. There is evidence that glomerular inflammation in that model represents a delayed-type hypersensitivity response to the heterologous immunoglobulin, whereas the antibody response is not important. The aim of the present study was to test this hypothesis. Delayed-type hypersensitivity is mediated by T cells with the Th1 phenotype. We compared mice immunized with rabbit immunoglobulin G in complete Freund's adjuvant or in incomplete Freund's adjuvant, producing, respectively, Th1- or Th2-biased responses to the antigen. Intravenous injection of rabbit antimouse glomerular basement membrane serum provoked proteinuria, infiltration with T cells and macrophages, as well as profound histological damage in the group treated with complete Freund's adjuvant. There was no evidence of glomerulonephritis in the group which received incomplete Freund's adjuvant. Deposits of mouse IgG along the glomerular basement membrane were similar in both groups. Thus, a Th1 response appears to be essential for the induction of glomerulonephritis in this model.

A syndrome resembling human systemic sclerosis (scleroderma) in MRL/lpr mice lacking interferon-gamma (IFN-gamma) receptor (MRL/lprgammaR-/-).

MRL/lpr mice develop a systemic autoimmune disease characterized by autoantibodies and inflammatory lesions in various organs. The main cause of early mortality is glomerulonephritis. We previously found that MRL/lprgammaR-/- mice are protected from glomerulonephritis and have an increased life span compared with their MRL/lprgammaR+/+ littermates. We now carried out a histopathological study of a selection of organs of MRL/lprgammaR-/- mice. Mice were killed as soon as they showed clinical signs of disease. In the majority of animals skin lesions were the first apparent pathology. Mononuclear cell infiltrates were frequent in skin, lungs and kidneys, and they occurred also in liver, salivary glands and heart. In infiltrated areas there was an abnormal accumulation of bundles of collagen. In the lungs of MRL/lprgammaR-/- mice, and occasionally in other organs, small and middle-sized arteries and veins showed intimal proliferation, resulting in a narrowed lumen. Alveolitis was widespread. Mononuclear cell infiltrates and excessive production of collagen in the skin and several visceral organs, thickening of vascular intima and autoantibodies are characteristic features of human systemic sclerosis. Thus, MRL/lprgammaR-/- mice might represent a model for that disease.

Correction of the TNF-LT alpha-deficient phenotype by bone marrow transplantation.

Mice with inactivated TNF-LT alpha genes have profound abnormalities of the immune system with hypoimmunoglobulinaemia, lack of lymph nodes, undifferentiated spleen, and defective Ig class switch. Transplantation of bone marrow cells from wild-type mice restored the synthesis of TNF, corrected the splenic microarchitecture, repopulated the lamina propria with IgA-producing plasma cells, and normalized the serum immunoglobulin levels of TNF-LT alpha deficient mice. Furthermore, the formation of germinal centers in the spleen and the defective Ig class switch in response to a T-cell-dependent antigen is corrected. These data demonstrate that most TNF-producing cells are bone-marrow-derived, and that the immunodeficiency due to TNF-LT alpha deletion can be corrected to a large extent by normal bone marrow, cell transplantation.

IFN-gamma receptor deletion prevents autoantibody production and glomerulonephritis in lupus-prone (NZB x NZW)F1 mice.

(NZB x NZW)F1 female (BW) mice spontaneously develop an autoimmune disease, characterized by the production of autoantibodies (autoAbs) and glomerulonephritis, which can be delayed by neutralizing IFN-gamma Abs and accelerated by IFN-gamma injections. To define the role of IFN-gamma in the pathogenesis of glomerulonephritis, we established a population of BW mice deficient in IFN-gammaR (BWgammaR[-/-]) by repeated crossing; these mice were compared with BWgammaR(+/+) and +/- littermates. Of the BWgammaR(+/+) and +/- mice, 50% showed immune complex glomerulonephritis with heavy proteinuria at 8 mo of age, while only 10% of the BWgammaR(-/-) mice were affected at 14 mo. The serum concentration of anti-dsDNA and anti-histone Abs was dramatically reduced in BWgammaR(-/-) mice. The role of IFN-gamma in promoting class switch to IgG2a and IgG3 could not fully account for the impaired production of anti-dsDNA in BWgammaR(-/-) animals since, IgM and IgG1 levels were also reduced. There was a high incidence of B cell lymphoma in the BWgammaR(-/-) mice, which might be related to the suppression of autoAb production. Thus, the absence of glomerulonephritis in BWgammaR(-/-) mice is likely due to a dramatic yet unexplained effect of the inactivation of IFN-gamma signaling on autoAb production.

Prevention of crescentic glomerulonephritis induced by anti-glomerular membrane antibody in tumor necrosis factor-deficient mice.

Tumor necrosis factor (TNF) is a proinflammatory cytokine playing a central role in the expression of endothelial adhesion molecules required for the recruitment of inflammatory cells. Proliferative glomerulonephritis induced by anti-glomerular basement membrane (GBM) antibody is characterized by the recruitment of inflammatory cells in the glomerulus followed by capillary damage and crescent formation. The glomerular pathology may be due to a large extent to TNF induction. We therefore tested this hypothesis in TNF-deficient mice. Anti-GBM antibody administration in sensitized wild-type mice resulted in deposition of immune complexes, followed by increased intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) expression, as well as the influx of polymorphonuclear neutrophils (PMNs), lymphocytes, and macrophages. Distinct proteinuria preceded proliferative glomerulonephritis characterized by crescent formation. In the absence of TNF, the development of proteinuria was delayed and the formation of crescents was almost completely prevented. Although the deposition of immune complexes in glomeruli was comparable in both groups, the up-regulation of ICAM-1 and VCAM-1, as well as the influx of PMNs and lymphocytes, but not of monocytes, was dramatically reduced in TNF-deficient mice. Therefore, we conclude that TNF plays a key role in the recruitment of inflammatory cells and in the subsequent development of proliferative glomerulonephritis.

Failure to induce anti-glomerular basement membrane glomerulonephritis in TNF alpha/beta deficient mice.

TNF is a key proinflammatory cytokine playing a central role in the expression of endothelial adhesion molecules required for the recruitment of inflammatory cells. Proliferative glomerulonephritis induced by anti-GBM antibody is characterized by the recruitment of inflammatory cells into the glomerulus and capillary damage followed by regeneration with crescent formation. The glomerular pathology may be due to TNF induction and we therefore tested this hypothesis in TNF alpha/beta deficient mice. Anti-GBM antibody administration in sensitised wild-type mice resulted in deposition of immune complexes and complement factor 3, followed by increased ICAM-1 and VCAM-1 expression and influx of polymorphonuclear leucocytes. Distinct proteinuria precedes proliferative glomerulonephritis with glomerular crescent formation, which is fully developed at 10 days. By contrast, no glomerulonephritis developed in TNF alpha/beta deficient mice. Comparable antibody complex deposits are found, but the upregulation of ICAM-1 and VCAM-1, the influx of inflammatory cells and the subsequent tissue damage is absent in TNF alpha/beta deficient mice. Therefore, we conclude that TNF plays a key role for the recruitment of inflammatory cells by preventing the upregulation of endothelial adhesion molecule and the subsequent development of proliferative glomerulonephritis.

IFN-gamma is essential for the development of autoimmune glomerulonephritis in MRL/Ipr mice.

MRL/lpr mice develop lymphoproliferation and accelerated autoimmune glomerulonephritis from which they ultimately die. To investigate the role of IFN-gamma in the manifestation of the disease, we generated MRL/lpr mice lacking the IFN-gamma receptor (MRL/lpr gammaR -/-). The absence of IFN-gamma signaling had no effect on generalized lymphoproliferation, expansion of CD4- CD8- double-negative T cells, or hypergammaglobulinemia. By contrast, glomerulonephritis as detected by proteinuria and histology was absent in MRL/lpr gammaR -/- mice. While serum IgG1 anti-dsDNA Abs were increased in all three strains of MRL/lpr mice (gammaR +/+, +/-, -/-), those of the IgG2a and IgG3 isotypes were low in MRL/lpr gammaR -/- mice. Immune complexes and C3 deposition were dramatically reduced in the glomerular capillaries of MRL/lpr gammaR -/- mice compared with MRL/lpr gammaR +/+ and +/- mice. Therefore, IFN-gamma plays a key regulatory role in the development of nephritis in MRL/lpr mice. Low levels of IFN-gamma-dependent IgG2a and IgG3 autoantibodies in MRL/lpr gammaR -/- mice might protect them from the pathogenic features of IgG3 cryoglobulins and complement-activating IgG2a and IgG3.

Lack of type 2 T cell-independent B cell responses and defect in isotype switching in TNF-lymphotoxin alpha-deficient mice.

TNF is implicated in in vitro Ig production, but its role in vivo is not clearly defined. Our previous studies had shown that TNF-LT alpha double-deficient mice have defective IgM and IgG primary Ab responses to the T cell-dependent (TD) Ag SRBC. We now extend these studies to secondary responses and to T cell-independent (TI) B cell responses. Injections of the TD Ag SRBC did not induce germinal center formation in the spleen of TNF-LT alpha-deficient mice. Associated with the morphologic defect, there was a defective IgG Ab response and a secondary hyper-IgM response to the TD Ag in TNF-LT alpha-deficient mice. The response to the TI Ag type 2 DNP-alanyl-glycyl-glycyl-Ficoll was essentially absent in TNF-LT alpha-deficient mice, while that to the TI Ag type 1 TNP-LPS was significantly reduced only for IgG2b isotype. Transplantation of bone marrow cells from wild-type mice into irradiated TNF-LT alpha-deficient mice restored the formation of splenic germinal centers and corrected the IgM and IgG responses to both TD and TI Ags. These data suggest that TNF and/or LT alpha signaling are critically required for germinal center formation and for the IgM and IgG responses to both TD and TI type 2 Ags.

Thiazide treatment of rats provokes apoptosis in distal tubule cells.

We studied the effects of inhibition of apical NaCl entry on the structural correlates for electrolyte transport in the distal convoluted tubule (DCT) of rats. Thiazide diuretics were used to block NaCl entry specifically in the DCT. Metolazone or hydrochlorothiazide (HCTZ) were applied for three days subcutaneously via osmotic minipumps. The renal epithelial structure of control and treated rats was studied by light and electron microscopy. Distribution of the thiazide-sensitive NaCl cotransporter (rTSC1), calbindin D28K and Ca(2+)-Mg(2+)-ATPase was examined by immunohistochemistry, and the content of rTSC1 transcripts by Northern blot and in situ hybridization. In treated rats the DCT epithelium had lost the structural characteristics of electrolyte transporting epithelia and the cells were in different stages of apoptosis. In damaged cells calbindin D28K and Ca(2+)-Mg(2+)-ATPase were strongly decreased; the rTSC1 was shifted from the luminal membrane to the basal cell half and was found additionally in small membrane vesicles in intercellular and peritubular spaces. Transcripts of rTSC1 were drastically reduced in homogenates of kidney cortex and almost absent in damaged DCT cells. All other tubular segments were unaffected by the treatment. Focal inflammatory infiltrates were found to be specifically surrounding DCT profiles. Thus, inhibition by thiazides of apical NaCl entry into DCT cells is associated with apoptosis of DCT cells and focal peritubular inflammation.

Lipopolysaccharide-induced glomerulonephritis develops in the absence of interferon-gamma signaling.

IFN gamma is a costimulator of macrophage activation and it plays an important role as a proinflammatory cytokine by upregulation of adhesion molecules and MHC antigens. In this study we tested the role of IFN gamma in a model of endotoxin-induced glomerulonephritis. A systemic lupus-like disease was induced by injection of 50 micrograms bacterial LPS twice a week for 4 weeks in wild-type and in IFN gamma receptor-deficient (IFN gamma R-/-) mice. The renal cortex was examined by immunofluorescence and by light microscopy. LPS treatment induced an increase in serum levels of IgG and anti-dsDNA antibodies. A mild glomerulonephritis was characterized morphologically, but proteinuria was not observed. The main histological features of glomerulonephritis were an increase in ICAM-1 expression, deposition of immune complexes and of complement in the glomeruli, increased mesangial matrix and mesangial hypercellularity. The number of intraglomerular leukocytes, detected by MHC class-II and LFA-1 expression increased roughly 4-fold. All those alterations took place in a similar manner in wild-type and in IFN gamma R-/-mice. Therefore it is concluded that IFN gamma does not play an important role in the development of endotoxic glomerulonephritis.

Differentiation of follicular dendritic cells and full antibody responses require tumor necrosis factor receptor-1 signaling.

Using mice double deficient for tumor necrosis factor (TNF) and lymphotoxin alpha (LT alpha), we demonstrated that TNF and/or LT alpha are necessary for development of a normal splenic microarchitecture and for isotype switch after immunization with sheep red blood cells (SRBC). In the present study, we extended these observations by determining which TNF receptor (TNFR) is involved in morphological and functional differentiation of the spleen. Spleen morphology and antibody response were investigated in wild-type, TNFR1-/-, TNFR2-/- and TNF/LT alpha-/- mice immunized with SRBC. TNF/LT alpha-/- mice, which have a complete disruption of the TNF/LT alpha signaling system including the LT beta-receptor pathway, displayed an abnormal microarchitecture, and isotype switch did not take place. TNFR1-/- and TNFR2-/- mice displayed a normal spleen microarchitecture and mounted an IgM and IgG antibody response to SRBC. However, the IgG production in TNFR1-/- mice was minimal, with citers leveling off 6 d after immunization. In this strain, immunofluorescence revealed a lack of follicular dendritic cells (FDC) network, detected with FDC-M1 as well as anti-CR1, and a lack of germinal centers, detected with peanut agglutinin. In conclusion, whereas normal splenic microarchitecture and isotype switch might require the LT beta receptor, differentiation of FDC network, development of germinal centers, and full IgG response depend on signaling via TNFR1.

Morphology of interstitial cells in the healthy kidney.

Renal interstitial cells play an important role in renal function and renal diseases. We describe the morphology of renal interstitial cells in the healthy kidney. We distinguish within the renal interstitium (1) renal fibroblasts and (2) cells of the immune system. Fibroblasts are in the majority and constitute the scaffold of the kidney; they are interconnected by junctions, and are attached to tubules and vessels. Although the phenotype of fibroblasts shows some variation depending on their location in the kidney and on their functional stage, their recognition as fibroblasts is possible on account of structural features. Among the cell types of the second group, antigen-presenting dendritic cells are the most abundant in in the peritubular interstitial spaces of healthy kidneys. Their incidence is highest in the inner stripe of the outer medulla. They share some morphological features with fibroblasts but lack others--junctional complexes, morphologically defined connections with tubules and vessels, and the prominent layer of actin filaments under the plasma membrane--that are characteristic for fibroblasts. Dendritic cells in healthy kidneys are morphologically different from macrophages, which are characterized by abundant primary and secondary lysosomes. In healthy kidneys macrophages are restricted to the connective tissue of the renal capsule and the pelvic wall, and to the periarterial connective tissue. Lymphocytes are rare in healthy kidneys. The distinction of cell types by morphology is supported by differences of membrane proteins. Among all interstitial cells in the renal cortex, fibroblasts alone exhibit ecto-5'-nucleotidase. Dendritic cells constitutively have a high abundance of MHC class II protein. Both proteins are mutually exclusive. Rat macrophages display the membrane antigen ED 2 and lymphocytes exhibit specific surface antigens, depending on their type and functional stage, e.g., CD4 or CD8.

Correction or transfer of immunodeficiency due to TNF-LT alpha deletion by bone marrow transplantation.

BACKGROUND: Mice with inactivated tumor necrosis factor (TNF) and lymphotoxin alpha (LT alpha) genes have profound abnormalities of the immune system including lymphocytosis, lack of lymph nodes, undifferentiated spleen, hypoimmunoglobulinaemia, and defective Ig class switch. Here, we asked whether this phenotype is due to incompetent lymphohemopoietic progenitors or to a defective environment. MATERIALS AND METHODS: Lethally irradiated TNF-LT alpha-deficient and wild-type mice received bone marrow cells from either TNF-LT alpha-deficient or wild-type mice. The reconstitution and transfer of the phenotype was followed by morphological and functional analyses. RESULTS: Bone marrow cells from wild-type mice restored the synthesis of TNF and LT alpha, corrected the splenic microarchitecture, normalized the lymphocyte counts in the circulation, and repopulated the lamina propria with IgA-producing plasma cells of TNF-LT alpha-deficient mice. Furthermore, the formation of germinal centers in the spleen and the defective Ig class switch in response to a T-cell dependent antigen was corrected, while no lymph nodes were formed. Conversely, the TNF-LT alpha phenotype could be transferred to wild-type mice by bone marrow transplantation after lethal irradiation. CONCLUSIONS: These data demonstrate that most TNF- and LT alpha-producing cells are bone marrow derived and radiosensitive, and that the immunodeficiency due to TNF-LT alpha deletion can be corrected to a large extent by normal bone marrow cell transplantation. The genotype of the donor bone marrow cells determines the functional and structural phenotype of the TNF-LT alpha-deficient adult murine host, with the exception of lymph node formation. These findings may have therapeutic implications for the restoration of genetically defined immunodeficiencies in humans.

Multiple immune abnormalities in tumor necrosis factor and lymphotoxin-alpha double-deficient mice.

To investigate the roles of tumor necrosis factor (TNF) and lymphotoxin (LT)-alpha in the development and function of the immune system, the Tnf and Ltalpha genes were simultaneously inactivated in mice by homologous recombination. These mutant mice are highly susceptible to Listeria monocytogenes infection and resistant to endotoxic shock induced by the combined administration of D-galactosamine (D-GaIN) and lipopolysaccharide (LPS). Their splenic microarchitecture is disorganized, characterized by the loss of the clearly defined marginal zone, ill defined T and B cell areas, and absence of MAdCAM-1 and reduced ICAM-1, VCAM-1 and Mac-1 expression. They are devoid of peripheral lymph nodes and Peyer's patches, and show a strong reduction of IgA+ plasma cells in the intestinal lamina propria. The alymphoplasia is accompanied by a marked B lymphocytosis and reduced basal lg levels. Ig depositions in the renal glomerulus and a strong up-regulation of MHC class I antigen expression on endothelial cells of different tissues are observed. The primary humoral immune response towards sheep red blood cells reveals a defective IgG isotype switch, while that against vesicular stomatitis virus is normal. The cytotoxic T cell responses are attenuated, although still effective, against vaccinia, lymphocytic choriomeningitis virus (LCMV-ARM) and LCMV-WE. In conclusion, the combined inactivation of Tnf and Ltalpha confirms their essential role in the normal development and function of the immune system.

MHC antigens in interferon gamma (IFN gamma) receptor deficient mice: IFN gamma-dependent up-regulation of MHC class II in renal tubules.

MHC class II gene products in parenchymal cells, such as tubular epithelial cells in kidney, may play a role in the regulation of autoimmune reactions. Expression of MHC class II in renal tubular cells is normally very low, but it increases considerably under various pathologic conditions. The predominant role of IFN gamma in up-regulation of MHC class II expression has been demonstrated repeatedly. We tested the existence of alternative pathways of MHC class II regulation using IFN gamma receptor-deficient (IFN gamma R-/-) mice. Mutant and wild type mice received 50 micrograms bacterial endotoxin (LPS) i.p. Four days later the kidneys were removed for immunofluorescence examination. In agreement with published results LPS provoked an increase of immunoreactivity for MHC class I and MHC class II in proximal tubules of wild type mice. While MHC class I up-regulation was strictly IFN gamma receptor-dependent, up-regulation of MHC II was still evident in mutant mice, although less than in wild type mice. Since injection of IFN gamma induced proximal tubular MHC class II expression in wild type mice but not in IFN gamma R-/- mice, an alternative signaling pathway for IFN gamma does not seem to exist. Thus, up-regulation of MHC class II expression in renal tubules does not necessarily require IFN gamma. The markedly patchy pattern of immunofluorescence in IFN gamma R-/- mice suggests that induction of MHC class II after LPS injection may represent renal injury due to shock.

In situ detection of cyclosporin A: evidence for nuclear localization of cyclosporine and cyclophilins.

BACKGROUND: The immunosuppressant cyclosporin A (CsA) forms a trimolecular complex with cyclophilin (CPH) and calcineurins (CN) and inhibits CN phosphatase activity. Inhibition of CN phosphatase by CsA prevents the dephosphorylation of a nuclear factor in the cytosol and its nuclear translocation to the nucleus. EXPERIMENTAL DESIGN: The intracellular distribution of CPH and CN was investigated in permeabilized Jurkat T lymphocytes and MRC fibroblasts using biochemical techniques and confocal microscopy. The site of CsA binding was identified in situ using a photoaffinity label derivative of CsA followed by immunodetection. RESULTS: Cyclophilin A (CPH-A) and CN display essentially a cytosolic localization by immunofluorescence, and additional nuclear CPH-A and CN are evidenced by Western blot analysis of purified nuclei and immunofluorescence. By contrast, cyclophilin B (CPH-B) has a punctuate and reticular distribution pattern in cytoplasm, indicating an association with the endoplasmatic reticulum, but its main location is in the nuclear matrix, sparing the nucleolar region. For the in situ detection of CsA binding sites, a photolabile cyclosporine derivative (PL-CS) was used that allowed the detection of covalently bound CsA by Ab. Using the biologically active PL-CS, a punctate cytoplasmatic and nuclear immunoreactivity was obtained, which was specific and competed only with active cyclosporine derivatives. Nuclear CPH-A and -B were labeled by PL-CS, and trimolecular complexes of labeled CPH and CN were obtained by chemically cross-linking nuclear extracts. CONCLUSIONS: We describe herein the accessibility of CsA to the nucleus, the presence and labeling in situ of nuclear CPH and CN. The current models of CsA action predict that CsA-CPH complexes inhibit CN activity in the cytosol. However, our present findings invite the hypothesis that CPH may capture the drug into the nucleus and target regulatory proteins or transcriptional control elements.