Inhibition of nuclear translocation of calcineurin suppresses T-cell activation and prevents acute rejection of donor hearts.

BACKGROUND: Inhibition of calcineurin (CnA) activity by cyclosporine A (CsA) is the mainstay in immunosuppressive therapy. CsA inhibits the phosphatase activity of the cytosolic phosphatase CnA and, therefore, prevents the dephosphorylation and subsequently nuclear translocation of the transcription factor nuclear factor of activated T cells (NFAT). However, CsA has multiple other targets within the cell and is, therefore, not specific. We developed a new approach to inhibit CnA/NFAT signaling. This synthetic peptide prevented CnA nuclear translocation in vitro. The purpose of this study was to demonstrate that this novel approach could potentially inhibit T-cell function in vitro and in vivo. METHODS: T-cell activation (Jurkat T cells, naïve rat T cells, and peripheral human T cells) was assessed by protein synthesis, interleukin (IL)-2 promoter activity, and IL-2 levels after T-cell activation. Immunohistological stainings for CnA were performed to investigate nuclear localization of CnA. The immunosuppressive effects in vivo of the synthetic peptide were investigated in rats with heterotopic transplanted hearts. RESULTS: The nuclear localization signal peptide significantly decreased alloantigen-specific T-lymphocyte proliferation, IL-2 promoter activity, and IL-2 production (338% ± 27% vs. 149% ± 11%, n=8, P<0.05) in cultured T cells by inhibition of CnA nuclear translocation. The synthetic peptide also significantly decreased the number of graft infiltrating CD8 T lymphocytes. Moreover, treatment with the synthetic inhibitory inhibited acute graft rejection (5 ± 0.6 days vs. 12 ± 2 days, n=10, P<0.05). CONCLUSIONS: Inhibition of nuclear translocation of CnA is a novel approach to inhibit the activation of the CnA/NFAT signaling cascade. Further studies have to demonstrate the long-term use of this principle in vivo.

Conditional overexpression of neuronal nitric oxide synthase is cardioprotective in ischemia/reperfusion.

BACKGROUND: We previously demonstrated that conditional overexpression of neuronal nitric oxide synthase (nNOS) inhibited L-type Ca2+ channels and decreased myocardial contractility. However, nNOS has multiple targets within the cardiac myocyte. We now hypothesize that nNOS overexpression is cardioprotective after ischemia/reperfusion because of inhibition of mitochondrial function and a reduction in reactive oxygen species generation. METHODS AND RESULTS: Ischemia/reperfusion injury in wild-type mice resulted in nNOS accumulation in the mitochondria. Similarly, transgenic nNOS overexpression caused nNOS abundance in mitochondria. nNOS translocation into the mitochondria was dependent on heat shock protein 90. Ischemia/reperfusion experiments in isolated hearts showed a cardioprotective effect of nNOS overexpression. Infarct size in vivo was also significantly reduced. nNOS overexpression also caused a significant increase in mitochondrial nitrite levels accompanied by a decrease of cytochrome c oxidase activity. Accordingly, O(2) consumption in isolated heart muscle strips was decreased in nNOS-overexpressing nNOS(+)/αMHC-tTA(+) mice already under resting conditions. Additionally, we found that the reactive oxygen species concentration was significantly decreased in hearts of nNOS-overexpressing nNOS(+)/αMHC-tTA(+) mice compared with noninduced nNOS(+)/αMHC-tTA(+) animals. CONCLUSION: We demonstrated that conditional transgenic overexpression of nNOS resulted in myocardial protection after ischemia/reperfusion injury. Besides a reduction in reactive oxygen species generation, this might be caused by nitrite-mediated inhibition of mitochondrial function, which reduced myocardial oxygen consumption already under baseline conditions.

Inhibition of the calcineurin-NFAT signalling cascade in the treatment of heart failure.

Calcineurin (Cn), a serine/threonine phosphatase, plays a crucial role in the development of myocardial hypertrophy. Cn is a cytosolic phosphatase which dephosphorylates various target molecules, e.g. the transcriptional factor nuclear factor of activated T cells (NFAT), thereby enabling its nuclear translocation. Recently, it was demonstrated that not only NFAT, but also Cn is translocated into the nucleus. The nuclear coexistence of Cn and NFAT is important for the full transcriptional activity of the Cn-NFAT signalling cascade. Once Cn and NFAT have entered the nucleus of cardiomyocytes, the transcription of genes characteristic for myocardial hypertrophy (e.g. BNP, ANP) is initiated. The nuclear localization sequence (NLS), a region spanning amino acids 172-183 of calcineurin Abeta (CnAbeta) is essential for recognition and shuttling of Cn into the nucleus by importinbeta (1). A synthetic import blocking peptide (IBP) that mimics the NLS of Cn was tested recently. The NLS analogon IBP saturates the Cn binding site of importinbeta(1) thereby preventing binding of Cn and importin. This inhibits the translocation of Cn into the nucleus. Inhibiting the Cn/importin interaction with competing synthetic peptides is one of several new approaches to prevent the development of myocardial hypertrophy. Several patents have also been filed on molecules related to inhibition of Cn-NFAT signalling.

Medullary cystic kidney disease type 1: mutational analysis in 37 genes based on haplotype sharing.

Medullary cystic kidney disease type 1 (MCKD1) is an autosomal dominant, tubulo-interstitial nephropathy that causes renal salt wasting and end-stage renal failure in the fourth to seventh decade of life. MCKD1 was localized to chromosome 1q21. We demonstrated haplotype sharing and confirmed the telomeric border by a recombination of D1S2624 in a Belgian kindred. Since the causative gene has been elusive, high resolution haplotype analysis was performed in 16 kindreds. Clinical data and blood samples of 257 individuals (including 75 affected individuals) from 26 different kindreds were collected. Within the defined critical region mutational analysis of 37 genes (374 exons) in 23 MCKD1 patients was performed. In addition, for nine kindreds RT-PCR analysis for the sequenced genes was done to screen for mutations activating cryptic splice sites. We found consistency with the haplotype sharing hypothesis in an additional nine kindreds, detecting three different haplotype subsets shared within a region of 1.19 Mb. Mutational analysis of all 37 positional candidate genes revealed sequence variations in 3 different genes, AK000210, CCT3, and SCAMP3, that were segregating in each affected kindred and were not found in 96 healthy individuals, indicating, that a single responsible gene causing MCKD1 remains elusive. This may point to involvement of different genes within the MCKD1 critical region.

Mapping a new suggestive gene locus for autosomal dominant nephrolithiasis to chromosome 9q33.2-q34.2 by total genome search for linkage.

BACKGROUND: Nephrolithiasis is a complex, multifactorial disease resulting from genetic and environmental interaction. The pathogenesis of nephrolithiasis is far from being understood. So far, no gene locus for autosomal dominant nephrolithiasis only has been described. We here identified a new suggestive gene locus for autosomal dominant nephrolithiasis by a genome-wide search for linkage in a Spanish kindred with nephrolithiasis. METHODS: Clinical data, blood and urine samples of 18 individuals from a Spanish kindred with nephrolithiasis were collected. We performed a genome-wide search for linkage using 380 polymorphic microsatellite markers. RESULTS: Nephrolithiasis segregated in this Spanish kindred in a pattern compatible with autosomal dominant inheritance. The total genome search yielded the highest two-point LOD score of Z(max) = 1.99 (theta = 0) for marker D9S159 on chromosome 9q33.2-q34.2. Multipoint analysis of 24 polymorphic markers used for further fine mapping resulted in a LOD score of Z(max) = 2.7 (theta = 0) for markers D9S1881-D9S164, thereby identifying a new gene locus for autosomal dominant nephrolithiasis (NPL1). Two recombination events define D9S1850 as the centromeric flanking marker and D9S1818 as the telomeric flanking marker, restricting the NPL1 locus to a 14 Mb interval. CONCLUSION: We here identified a new suggestive gene locus (NPL1) for autosomal dominant nephrolithiasis. It is localized on chromosome 9q33.2-q34.2. The identification of the responsible gene will provide new insights into the molecular basis of nephrolithiasis.

Expression and phenotype analysis of the nephrocystin-1 and nephrocystin-4 homologs in Caenorhabditis elegans.

Nephronophthisis (NPHP), an autosomal-recessive cystic kidney disease, is the most frequent genetic cause of end-stage renal failure in children. NPHP types 1 and 4 are caused by mutations in NPHP1 and NPHP4, encoding the proteins nephrocystin-1 and nephrocystin-4, respectively. Nephrocystin-1 and nephrocystin-4 are expressed in primary cilia of renal epithelial cells. NPHP1 and NPHP4 are highly conserved in Caenorhabditis elegans. However, this species does not have a kidney but an excretory system that consists of an excretory cell, an excretory gland cell, a duct cell, and a pore cell. Therefore, cell type-specific expression pattern and function of the nephrocystin homologs in C. elegans were of interest. Expression of green fluorescence protein fusion constructs that contain the C. elegans promoter regions for nph-1 and nph-4 was not found in the excretory system but in ciliated sensory neurons of the head (amphid neurons) and the tail in hermaphrodites (phasmid neurons) and males (sensory ray neurons). As the knockout phenotype for the PKD homologs lov-1 and pkd-2 shows impaired male mating behavior, RNAi knockdown animals were analyzed for this phenotype. A similar phenotype was found in the nph-1 and nph-4 RNAi knockdown animals compared with the lov-1 and pkd-2 knockout phenotype. Thus, it is suggested that renal cyst-causing genes may be part of a shared functional module, highly conserved in evolution. The NPHP homologs may be necessary for initial assembly of the cilium, whereas the polycystic kidney disease homologs may function as sensory transducers.

Telomeric refinement of the MCKD1 locus on chromosome 1q21.

BACKGROUND: Autosomal-dominant medullary cystic kidney disease type 1 (MCKD1) is a tubulointerstitial nephropathy that causes renal salt wasting and end-stage renal failure in the sixth decade of life. The chromosomal locus for MCKD1 was localized to chromosome 1q21 in a Cyprotic kindred. In this report we describe further refinement of the critical genetic region by a recombination in a Belgian kindred. METHODS: Clinical data and blood samples of 33 individuals from a large Belgian kindred were collected and high-resolution haplotype analysis was performed. RESULTS: In the Belgian kindred linkage to the MCKD1 locus on chromosome 1q21 was found with a logarithm of odds (LOD) score significant for linkage. A recombination in individual III:7 for marker D1S2624 refines the critical genetic region to 2.1 Mb. In this kindred a wide variety of clinical symptoms and age of onset of renal failure was detected. CONCLUSION: We confirm the MCKD1 locus on chromosome 1q21 and show further refinement of the MCKD1 locus to 2.1 Mb. This allowed us to exclude another 17 genes as positional candidate genes.