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Clinical application of the molecular diagnosis of spinal muscular atrophy: deletions of neuronal apoptosis inhibitor protein and survival motor neuron genes.

The molecular genetic diagnosis of spinal muscular atrophy (SMA) has recently been complicated by the identification of two candidate genes, which are often deleted in affected individuals but are also occasionally deleted in apparently unaffected carriers. We present a compilation of genotypes, from our laboratory and recent reports, for the survival motor neuron (SMN) and neuronal apoptosis inhibitor protein (NAIP) genes. Bayesian analyses were used to generate probabilities for SMA when deletions are present or absent in SMN. We found that when the SMN(T) exon 7 is deleted, the probability of SMA can reach greater than 98% in some populations, and when SMN(T) is present, the probability of SMA is approximately 17 times less than the prior population risk. Deletion of NAIP exon 5, as well as SMN(T) exon 7, is associated with a 5-fold increased risk of type I SMA. Case studies are used to illustrate differing disease risks for pre- and postnatal testing, depending on the presence of information about clinical status or molecular results. These analyses demonstrate that deletion screening of candidate genes can be a powerful tool in the diagnosis of SMA.

Cyclic AMP Response Element-Binding Protein↗

Distribution of neuronal apoptosis inhibitory protein-like immunoreactivity in the rat central nervous system.

We have recently shown that spinal muscular atrophy (SMA), an autosomal recessive disorder characterized by motor neuron loss, is associated with deletion of a gene that encodes the neuronal apoptosis inhibitory protein (NAIP). In the present study, we have examined the distribution of NAIP-like immunoreactivity (NAIP-LI) in the rat central nervous system (CNS) by using an affinity-purified polyclonal antibody against NAIP. In the forebrain, immunoreactive neurons were detected in the cortex, the hippocampus (pyramidal cells, dentate granule cells, and interneurons), the striatum (cholinergic interneurons), the basal forebrain (ventral pallidum, medial septal nucleus, and diagonal band), the thalamus (lateral and ventral nuclei), the habenula, the globus pallidus, and the entopenduncular nucleus. In the midbrain, NAIP-LI was located primarily within neurons of the red nucleus, the substantia nigra pars compacta, the oculomotor nucleus, and the trochlear nucleus. In the brainstem, neurons containing NAIP-LI were observed in cranial nerve nuclei (trigeminal, facial, vestibular, cochlear, vagus, and hypoglossal nerves) and in relay nuclei (pontine, olivary, lateral reticular, cuneate, gracile nucleus, and locus coeruleus). In the cerebellum, NAIP-LI was found within both Purkinje and nuclear cells (interposed and lateral nuclei). Finally, within the spinal cord, NAIP-LI was detected in Clarke's column and in motor neurons. Taken together, these results indicate that NAIP-LI is distributed broadly in the CNS. However, high levels of NAIP-LI were restricted to those neuronal populations that have been reported to degenerate in SMA. This anatomical correspondence provides additional evidence for NAIP involvement in the neurodegeneration observed in acute SMA.

Animals↗

[Detection of SMN gene deletions in spinal muscular atrophy].

OBJECTIVE: Survival motor neuron gene(SMN) and neuronal apoptosis inhibitory protein gene (NAIP) have been identified as the candidates of progressive spinal muscular atrophy (SMA)-determining genes. The aims of this study were to investigate the absence of SMN gene exon 7 in Chinese SMA patients, to confirm the relationship between the deletion of the SMN and SMA further, and to establish methods for gene diagnosis and prenatal diagnosis of SMA. METHODS: PCR-SSCP with silver staining method was used to detect the genomic DNA of 37 SMA patients and 30 normal individuals for deletions of SMN exon 7. RESULTS: Homozygous deletion of the SMN exon 7 was identified in 86.7%(13/15) of type I SMA patients and 86.4%(19/22) of type II patients. In the 88 controls (including parents of patients and normal individuals), homozygous absence of SMA exon 7 was only found in a mother of a patient. CONCLUSION: The data support that homozygous absence of SMN exon 7 is strongly associated with SMA. The percentage of homozygous deletions in this study is almost as high as that reported by other researchers. This method is useful, reliable and effective for gene diagnosis and prenatal diagnosis of SMA.

Cyclic AMP Response Element-Binding Protein↗

Spinal muscular atrophy: untangling the knot?

Spinal muscular atrophy (SMA), a clinically and genetically heterogeneous group of neuromuscular diseases, is a disorder of motor neurones characterised by degeneration of spinal cord anterior horn cells and muscular atrophy. SMA is an autosomal recessive disorder with a carrier frequency of about 1150. Three candidate genes, the survival motor neurone (SMN) gene, the neuronal inhibitory protein (NAIP) gene, and the p44 (subunit of basal transcription factor TFIIH) gene, have been considered as genes involved in this condition. The region spanning these genes has a complex organisation including duplications, repetitive sequences, truncated genes, and pseudogenes, which makes molecular analysis of this condition difficult. Although deletions have been found in the majority of SMA patients, a few microrearrangements (like duplications, missense mutations, microdeletions, and gene conversions) localised in the telomeric form of the SMN gene have also been reported. The function of the protein encoded by the SMN gene is still not fully understood but recent studies have indicated that it is found intracellularly in gems, novel nuclear structures. Its interaction with other proteins suggests a role in mRNA processing and metabolism. Whether the NAIP gene protein and other apoptosis associated proteins are directly involved in the initial stages of neurone degeneration and apoptosis, or acting downstream on the pathological pathway, has been difficult to determine. Further studies will be required to elucidate possible functional interactions between these proteins.

Autoantigens↗

Congenital club foot with survival of motor neuron 1, telomeric (SMN1) gene deletion.

A boy with nonreducible bilateral congenital talipes equinovarus had delayed milestones with early-onset generalized hypotonia and muscular weakness. The condition remained stable until he was 8 years old. A slow worsening of motor abilities, with myopathic signs, was observed thereafter. A homozygous deletion of exons 7 and 8 of the survival of motor neuron 1, telomeric (SMN1) gene was found, without neuronal apoptosis inhibitory protein (NAIP) gene deletion, leading to the diagnosis of spinal muscular atrophy. Independent ambulation was lost when he was 13 years old. The occurrence of congenital clubfoot with early onset of neurologic signs, but with a very slowly progressive course, has not been reported in spinal muscular atrophy until now.

Adolescent↗

NAIP protects the nigrostriatal dopamine pathway in an intrastriatal 6-OHDA rat model of Parkinson's disease.

Parkinson's disease (PD) is a progressive neurodegenerative disorder of the basal ganglia, associated with the inappropriate death of dopaminergic neurons of the substantia nigra pars compacta (SNc). Here, we show that adenovirally mediated expression of neuronal apoptosis inhibitor protein (NAIP) ameliorates the loss of nigrostriatal function following intrastriatal 6-OHDA administration by attenuating the death of dopamine neurons and dopaminergic fibres in the striatum. In addition, we also addressed the role of the cysteine protease caspase-3 activity in this adult 6-OHDA model, because a role for caspases has been implicated in the loss of dopamine neurons in PD, and because NAIP is also a reputed inhibitor of caspase-3. Although caspase-3-like proteolysis was induced in the SNc dopamine neurons of juvenile rats lesioned with 6-OHDA and in adult rats following axotomy of the medial forebrain bundle, caspase-3 is not induced in the dopamine neurons of adult 6-OHDA-lesioned animals. Taken together, these results suggest that therapeutic strategies based on NAIP may have potential value for the treatment of PD.

Amphetamine↗

[Apoptotic cell death in child-onset neurodegenerative disorders].

Apoptotic cell death was examined in autopsied brains with Werdnig Hoffmann disease, hereditary DNA repair disorders (xeroderma pigmentosum and Cockayne syndrome) and neuronal ceroid lipofuscinosis, using in situ nick end labeling (TUNEL) and immunohistochemistry for cell death-related proteins. TUNEL-positive cells were found in the thalamus, cerebellum and/or hippocampus in each disorder. The expression of cell death-related proteins in the cerebellum of hereditary DNA repair disorders and the hippocampus of neuronal ceroid-lipofuscinosis suggested the involvement of apoptotic process in neurodegeneration in these disorders. On the other hand, TUNEL-reactivity without the altered expression of cell death-related proteins might reflect neuronal changes preceding the thalamic degeneration in Werdnig-Hoffmann disease.

Adolescent↗

Comparative study of gene expression by cDNA microarray in human colorectal cancer tissues and normal mucosa.

The causative molecular pathways underlying the pathogenesis of colorectal cancer (CRC) need to be better characterized. The purpose of our study was to better understand the genetic mechanism of oncogenesis for human colorectal cancer and to identify new potential tumor markers of use in clinical practice. We used cDNA microarrays to compare gene expression profiles of colorectal biopsies from 25 CRC patients and 13 normal mucosa from adjacent non-cancerous tissues. Findings were validated by real-time PCR; in addition, western blotting and immunochemistry analysis were carried out as further confirmation of differential expression at a protein level. Comparing cancerous tissues with normal colonic mucosa we identified 584 known genes differentially expressed to a significant degree (p<0.001). Many of the transcripts that were more abundant in tumors than in non-neoplastic tissues appear to reflect important events for colon carcinogenesis. For example, a significant number of these genes serve as apoptotic inhibitors (e.g. BFAR, BIRC1, BIRC6). Furthermore, we observed the simultaneous up-regulation of HLA-E and the down-regulation of beta2-microglobulin; these genes strongly support a potential tumor escape strategy from immune surveillance in colon cancer tissues. Our study provides new gene candidates in the pathogenesis of human CRC disease. From our results we hypothesize that CRC cells escape immune surveillance through a specific gene expression alteration; moreover, over-expression of several survival genes seems to confer a more anti-apoptotic phenotype. These genes are involved in pathways not previously implicated in CRC pathogenesis and they may provide new targets for therapy.

Adaptor Proteins, Signal Transducing↗

Antitumor effects of the novel NF-kappaB inhibitor dehydroxymethyl-epoxyquinomicin on human hepatic cancer cells: analysis of synergy with cisplatin and of possible correlation with inhibition of pro-survival genes and IL-6 production.

We tested the novel NF-kappaB inhibitor dehydroxymethylepoxyquinomicin (DHMEQ) in the hepatic cancer (HCC) HepG2, HA22T/VGH and HuH-6 cells. The sensitivity to the cell growth inhibitory and apoptotic effects of the agent increased along with the levels of constitutively activated NF-kappaB, which were low in HepG2 and higher in HA22T/VGH and HuH-6. In HA22T/VGH, DHMEQ exhibited synergy with cisplatin. In the same cells, DHMEQ exerted dose-dependent decreases in the nuclear levels of activated NF-kappaB and attenuated NF-kappaB activation by cisplatin. It down-regulated Bcl-XL mRNA in a dose-dependent manner and up-regulated that of Bcl-XS. It also decreased interleukin 6 (IL-6), NAIP and, after 16 h of exposure to the higher concentration tested (10 microg/ml), c-IAP-1 mRNA levels. At 10 microg/ml it caused significant increase in Bax, XIAP, cyclin D1 and beta-catenin mRNAs. The combination of DHMEQ with cisplatin produced unexpected significant decrease in c-IAP-2 and Bcl-XS mRNAs as well as additive decrease (IL-6, NAIP and, after 16 h, Bcl-XL) or increase (XIAP at 8 h) in gene expression. HA22T/VGH produce IL-6; in agreement with the results on mRNA, DHMEQ inhibited such a process. HA22T/VGH lack the IL-6 receptor alpha chain, ruling out that in these cells the antitumor effects of DHMEQ may be attributed to an interference with a growth stimulatory autocrine loop based on IL-6. However, the use of DHMEQ in HCC might be beneficial to contrast the adverse systemic effects of the released cytokine.

Antineoplastic Agents↗

Evolutionary relationships of vertebrate NACHT domain-containing proteins.

Phylogenetic analyses of conserved [neuronal apoptosis inhibitory protein (NAIP), MHC class II transcription activator (CIITA), incompatibility locus protein from Podospora anserina (HET-E), and telomerase-associated protein (TP1)] (NACHT) domains were used to reconstruct the evolutionary history of vertebrate NACHT-containing proteins. The results supported the hypothesis that NOD3 is basal to the other NACHT-containing proteins found in tetrapods. The latter formed two strongly supported clusters or subfamilies, here designated NALP and nucleotide-binding oligomerization domain (NOD). The presence of apparent bony fish orthologs of NOD3 and CIITA supported the hypothesis that the origin of these molecules predates the origin of tetrapods, and the presence of avian sequences in both NALP and NOD clusters supported the origin of these subfamilies before the bird-mammal divergence. However, the extensive diversification of the NALP subfamily seen in mammals evidently occurred within the mammalian lineage. Both NALP and NOD subfamilies include members with differential expression in the antigen-presenting cells of the immune system, and the phylogenetic analyses supported the hypothesis that this expression pattern has evolved independently more than once in each of these subfamilies.

Adaptor Proteins, Signal Transducing↗

TLRS in the gut. II. Flagellin-induced inflammation and antiapoptosis.

Flagellin is bacterial protein that serves as a danger signal across a wide variety of eukaryotes and is a potent inducer of inflammatory effector responses in the mammalian gut. Recent findings utilizing purified flagellin and flagellate/aflagellate bacteria in in vitro and in vivo systems have revealed the important roles played by flagellin in the initial encounter between mucosa and flagellate bacteria, specifically in the modulation of apoptotic responses.

Animals↗

Autophagy and inflammatory cell death, partners of innate immunity.

By law in the evolutionary jungle, any host defense mechanism that efficiently kills microbes also exerts a strong selective pressure for tolerant variants to emerge. As a consequence, pathogens can be exploited as powerful tools to examine host defense mechanisms. Recent studies of the confrontation between macrophages and the opportunistic pathogen Legionella pneumophila have revealed a regulatory mechanism that may link autophagy to pyroptosis, a type of programmed cell death. Building from the extensive literature on autophagy, cell death, and innate immunity, we propose here a testable model in which the NOD-LRR protein Naip5 dictates whether murine macrophages elevate autophagy or pyroptosis as a barrier to infection.

Animals↗

The Birc1e cytosolic pattern-recognition receptor contributes to the detection and control of Legionella pneumophila infection.

Baculovirus inhibitor of apoptosis repeat-containing 1 (Birc1) proteins have homology to several germline-encoded receptors of the innate immune system. However, their function in immune surveillance is not clear. Here we describe a Birc1e-dependent signaling pathway that restricted replication of the intracellular pathogen Legionella pneumophila in mouse macrophages. Translocation of bacterial products into host-cell cytosol was essential for Birc1e-mediated control of bacterial replication. Caspase-1 was required for Birc1e-dependent antibacterial responses ex vivo in macrophages and in a mouse model of Legionnaires' disease. The interleukin 1beta converting enzyme-protease-activating factor was necessary for L. pneumophila growth restriction, but interleukin 1beta was not required. These results establish Birc1e as a nucleotide-binding oligomerization-leucine-rich repeat protein involved in the detection and control of intracellular L. pneumophila.

Animals↗

Flagellin-deficient Legionella mutants evade caspase-1- and Naip5-mediated macrophage immunity.

Macrophages from C57BL/6J (B6) mice restrict growth of the intracellular bacterial pathogen Legionella pneumophila. Restriction of bacterial growth requires caspase-1 and the leucine-rich repeat-containing protein Naip5 (Birc1e). We identified mutants of L. pneumophila that evade macrophage innate immunity. All mutants were deficient in expression of flagellin, the primary flagellar subunit, and failed to induce caspase-1-mediated macrophage death. Interestingly, a previously isolated flagellar mutant (fliI) that expresses, but does not assemble, flagellin did not replicate in macrophages, and induced macrophage death. Thus, flagellin itself, not flagella or motility, is required to initiate macrophage innate immunity. Immunity to Legionella did not require MyD88, an essential adaptor for toll-like receptor 5 (TLR5) signaling. Moreover, flagellin of Legionella and Salmonella induced cytotoxicity when delivered to the macrophage cytosol using Escherichia coli as a heterologous host. It thus appears that macrophages sense cytosolic flagellin via a TLR5-independent pathway that leads to rapid caspase-1-dependent cell death and provides defense against intracellular bacterial pathogens.

Animals↗

The mouse region syntenic for human spinal muscular atrophy lies within the Lgn1 critical interval and contains multiple copies of Naip exon 5.

Spinal muscular atrophy (SMA) is a relatively common, autosomal recessively inherited neurodegenerative disorder that maps to human chromosome 5q13. This region of the human genome has an intricate genomic structure that has complicated the evaluation of SMA candidate genes. We have chosen to study the mouse region syntenic for human SMA in the hope that the homologous mouse interval would contain the same genes as human 5q13 on a simpler genomic background. Here, we report the mapping of such a region to mouse chromosome 13 and to the critical interval for Lgn1, a mouse locus responsible for modulating the intracellular replication and pathogenicity of the bacterium Legionella pneumophila. We have generated a mouse YAC contig across the Lgn1/Sma interval and have mapped the two flanking gene markers for the human SMA locus, MAP1B and CCNB1, onto this contig. In addition, we have localized the two SMA candidate genes, SMN and NAIP, to the Lgn1 critical region, making these two genes candidates for the Lgn1 phenotype. Upon subcloning of the YAC contig into P1s and BACs, we have detected a large, low copy number repeat that contains at least one copy of Naip exon 5. Identification of the Lgn1 gene will either provide a novel function for SMN or NAIP or reveal the existence of another, yet uncharacterized gene in the SMA critical region. Mutations in such a gene might help to explain some of the phenotypic variability among the human SMAs.

Animals↗

Unique anti-apoptotic activity of EAAC1 in injured motor neurons.

Injured motor neurons of the adult rat can survive, whereas similar axotomy causes gradual motor neuron death in the adult mouse. We report that the decreased expression of the neuronal glutamate transporter excitatory amino-acid carrier 1 (EAAC1) following nerve injury is associated with motor neuron death in the mouse. Glutamate transporters play a crucial role in prevention of neuronal death by suppressing glutamate toxicity. However, the possible functional role of EAAC1 in preventing neuron death has not been resolved as compared with glial glutamate transporters such as GLT-1. Here, we have revealed a unique 'rescue' function of EAAC1, which is independent of removal of extracellular glutamate. During apoptotic stimuli, a mitochondrial protein, holocytochrome c synthetase (HCCS), translocates to outside the mitochondria, binds to and suppresses the X-linked inhibitor of apoptosis protein (XIAP), leading to activation of caspase-3. The N-terminus of EAAC1 can bind to HCCS, which interferes with the HCCS-XIAP association, and thereby maintain XIAP activity. This unique anti-apoptotic mechanism of EAAC1 functions in rescuing PC12 cells and motor neurons from NGF deprivation and nerve injury, respectively.

Animals↗

Cytosolic recognition of flagellin by mouse macrophages restricts Legionella pneumophila infection.

To restrict infection by Legionella pneumophila, mouse macrophages require Naip5, a member of the nucleotide-binding oligomerization domain leucine-rich repeat family of pattern recognition receptors, which detect cytoplasmic microbial products. We report that mouse macrophages restricted L. pneumophila replication and initiated a proinflammatory program of cell death when flagellin contaminated their cytosol. Nuclear condensation, membrane permeability, and interleukin-1beta secretion were triggered by type IV secretion-competent bacteria that encode flagellin. The macrophage response to L. pneumophila was independent of Toll-like receptor signaling but correlated with Naip5 function and required caspase 1 activity. The L. pneumophila type IV secretion system provided only pore-forming activity because listeriolysin O of Listeria monocytogenes could substitute for its contribution. Flagellin monomers appeared to trigger the macrophage response from perforated phagosomes: once heated to disassemble filaments, flagellin triggered cell death but native flagellar preparations did not. Flagellin made L. pneumophila vulnerable to innate immune mechanisms because Naip5+ macrophages restricted the growth of virulent microbes, but flagellin mutants replicated freely. Likewise, after intratracheal inoculation of Naip5+ mice, the yield of L. pneumophila in the lungs declined, whereas the burden of flagellin mutants increased. Accordingly, macrophages respond to cytosolic flagellin by a mechanism that requires Naip5 and caspase 1 to restrict bacterial replication and release proinflammatory cytokines that control L. pneumophila infection.

Adaptor Proteins, Signal Transducing↗

Neuronal apoptosis inhibitory protein is expressed in developing kidney and is regulated by PAX2.

During fetal kidney development, the extent of ureteric bud (UB) branching will determine final nephron endowment for life. Nephron number varies widely among normal humans and those who are born at the low end of the nephron number spectrum may be at risk for essential hypertension in adulthood. Little is known about how nephron number is set. However, we previously showed that the transcription factor, Pax2, suppresses apoptosis in UB cells during kidney development and optimizes branching morphogenesis. Here, we report that PAX2 directly binds to a specific recognition motif in the human neuronal apoptosis inhibitory protein (NAIP) gene promoter. NAIP is an endogenous inhibitor of apoptosis, inactivating caspase-3 and caspase-7 in neuronal tissues. PAX2 activates NAIP gene transcription (7-fold) in vitro and NAIP transcript level is increased fourfold in HEK293 cells stably transfected with PAX2. We show that Naip is expressed in embryonic day 15 (E15) fetal kidney tissue (RT-PCR) and NAIP protein is demonstrated by immunohistochemistry in E15 mouse kidney collecting ducts and P1 proximal tubules. Naip mRNA is significantly reduced (50%) in heterozygous Pax2 mutant mice. Finally, we show that an antisense Naip1 cDNA transfected into murine collecting duct cells doubles caspase-3/7 activity induced by Baxalpha. These observations suggest that the powerful effects of PAX2 on renal branching morphogenesis and final nephron number may be mediated by activation of Naip which then suppresses apoptosis in UB cells.

Animals↗