Takako Niikura

A rescue factor abolishing neuronal cell death by a wide spectrum of familial Alzheimer's disease genes and Aβ

Through functional expression screening, we identified a gene, designated Humanin (HN) cDNA, which encodes a short polypeptide and abolishes death of neuronal cells caused by multiple different types of familial Alzheimers disease genes and by Aβ amyloid, without effect on death by Q79 or superoxide dismutase-1 mutants. Transfected HN cDNA was transcribed to the corresponding polypeptide and then was secreted into the cultured medium. The rescue action clearly depended on the primary structure of HN. This polypeptide would serve as a molecular clue for the development of new therapeutics for Alzheimers disease targeting neuroprotection.

Interaction between the Alzheimer's survival peptide humanin and insulin-like growth factor-binding protein 3 regulates cell survival and apoptosis

Insulin-like growth factor-binding protein-3 (IGFBP-3) regulates IGF bioactivity and also independently modulates cell growth and survival. By using a yeast two-hybrid screen to identify IGFBP-3-interacting proteins, we cloned humanin (HN) as an IGFBP-3-binding partner. HN is a 24-aa peptide that has been shown to specifically inhibit neuronal cell death induced by familial Alzheimers disease mutant genes and amyloid-β (Aβ). The physical interaction of HN with IGFBP-3 was determined to be of high affinity and specificity and was confirmed by yeast mating, displaceable pull-down experiments with (His)-6-tagged HN, and ligand blot experiments. Coimmunoprecipitation of IGFBP-3 and HN from mouse testes confirmed the interaction in vivo. In cross-linking experiments, HN bound IGFBP-3 but did not compete with IGF-I–IGFBP-3 binding; competitive ligand dot blot experiments revealed the 18-aa heparin-binding domain of IGFBP-3 as the binding site for HN. Alanine scanning determined that F6A-HN mutant does not bind IGFBP-3. HN but not F6A-HN inhibited IGFBP-3-induced apoptosis in human glioblastoma-A172. In contrast, HN did not suppress IGFBP-3 response in SH-SY5Y neuroblastoma and mouse cortical primary neurons. In primary neurons, IGFBP-3 markedly potentiated HN rescue ability from Aβ1–43 toxicity. In summary, we have identified an interaction between the survival peptide HN and IGFBP-3 that is pleiotrophic in nature and is capable of both synergistic and antagonistic interaction. This interaction may prove to be important in neurological disease processes and could provide important targets for drug development.

Evidence for in vivo production of Humanin peptide, a neuroprotective factor against Alzheimer's disease-related insults

An unbiased functional screening with brain cDNA library from an Alzheimers disease (AD) brain identified a novel 24-residue peptide Humanin (HN), which suppresses AD-related neurotoxicity. As the 1567-base cDNA containing the open reading frame (ORF) of HN is 99% identical to mitochondrial 16S ribosomal RNA as well as registered human mRNA, it was elusive whether HN is produced in vivo. Here, we raised anti-HN antibody and found that long cDNAs containing the ORF of HN (HN-ORF) produced the HN peptide in mammalian cells, dependent on the presence of full-length HN-ORF. Immunoblot analysis detected a 3-kDa protein with HN immunoreactivity in the testis and the colon in 3-week-old mice and in the testis in 12-week-old mice. HN immunoreactivity was also detected in an AD brain, but little in normal brains. This study suggests that HN peptide could be produced in vivo, and would provide a novel insight into the pathophysiology of AD.

Involvement of c-Jun N-terminal kinase in amyloid precursor protein-mediated neuronal cell death

Amyloid precursor protein (APP), the precursor of Aβ, has been shown to function as a cell surface receptor that mediates neuronal cell death by anti‐APP antibody. The c‐Jun N‐terminal kinase (JNK) can mediate various neurotoxic signals, including Aβ neurotoxicity. However, the relationship of APP‐mediated neurotoxicity to JNK is not clear, partly because APP cytotoxicity is Aβ independent. Here we examined whether JNK is involved in APP‐mediated neuronal cell death and found that: (i) neuronal cell death by antibody‐bound APP was inhibited by dominant‐negative JNK, JIP‐1b and SP600125, the specific inhibitor of JNK, but not by SB203580 or PD98059; (ii) constitutively active (ca) JNK caused neuronal cell death and (iii) the pharmacological profile of caJNK‐mediated cell death closely coincided with that of APP‐mediated cell death. Pertussis toxin (PTX) suppressed APP‐mediated cell death but not caJNK‐induced cell death, which was suppressed by Humanin, a newly identified neuroprotective factor which inhibits APP‐mediated cytotoxicity. In the presence of PTX, the PTX‐resistant mutant of Gαo, but not that of Gαi, recovered the cytotoxic action of APP. These findings demonstrate that JNK is involved in APP‐mediated neuronal cell death as a downstream signal transducer of Go.

A tripartite motif protein TRIM11 binds and destabilizes Humanin, a neuroprotective peptide against Alzheimer's disease‐relevant insults

Humanin (HN) is a newly identified neuroprotective peptide that specifically suppresses Alzheimers disease (AD)‐related neurotoxicity. HN peptide has been detected in the human AD brain as well as in mouse testis and colon by immunoblot and immunohistochemical analyses. By means of yeast two‐hybrid screening, we identified TRIM11 as a novel HN‐interacting protein. TRIM11, which is a member of protein family containing a tripartite motif (TRIM), is composed of a RING finger domain, which is a putative E3 ubiquitin ligase, a B‐box domain, a coiled‐coil domain and a B30.2 domain. Deletion of the B30.2 domain in TRIM11 abolished the interaction with HN, whereas the B30.2 domain alone did not interact with HN. For their interaction, at least the coiled‐coil domain was indispensable together with the B30.2 domain. The intracellular level of glutathione S‐transferase‐fused or EGFP‐fused HN peptides or plain HN was drastically reduced by the coexpression of TRIM11. Disruption of the RING finger domain by deleting the first consensus cysteine or proteasome inhibitor treatment significantly diminished the effect of TRIM11 on the intracellular level of HN. These results suggest that TRIM11 plays a role in the regulation of intracellular HN level through ubiquitin‐mediated protein degradation pathways.

Characterization of the toxic mechanism triggered by Alzheimer's amyloid‐β peptides via p75 neurotrophin receptor in neuronal hybrid cells

Neuronal pathology of the brain with Alzheimers disease (AD) is characterized by numerous depositions of amyloid‐β peptides (Aβ). Aβ binding to the 75‐kDa neurotrophin receptor (p75NTR) causes neuronal cell death. Here we report that Aβ causes cell death in neuronal hybrid cells transfected with p75NTR, but not in nontransfected cells, and that p75NTRL401K cannot mediate Aβ neurotoxicity. We analyzed the cytotoxic pathway by transfecting pertussis toxin (PTX)‐resistant G protein α subunits in the presence of PTX and identified that Gαo, but not Gαi, proteins are involved in p75NTR‐mediated Aβ neurotoxicity. Further investigation suggested that Aβ neurotoxicity via p75NTR involved JNK, NADPH oxidase, and caspases‐9/3 and was inhibited by activity‐dependent neurotrophic factor, insulin‐like growth factor‐I, basic fibroblast growth factor, and Humanin, as observed in primary neuron cultures. Understanding the Aβ neurotoxic mechanism would contribute significantly to the development of anti‐AD therapies.

Multiple Mechanisms Underlie Neurotoxicity by Different Types of Alzheimer's Disease Mutations of Amyloid Precursor Protein

We examined a neuronal cell system in which single-cell expression of either familial Alzheimers disease (FAD) gene V642I-APP or K595N/M596L-APP (NL-APP) in an inducible plasmid was controlled without affecting transfection efficiency. This system revealed that (i) low expression of both mutants exerted toxicity sensitive to both Ac-DEVD-CHO (DEVD) and glutathione ethyl ester (GEE), whereas wild-type APP (wtAPP) only at higher expression levels caused GEE/DEVD-resistant death to lesser degrees; (ii) toxicity by the V642I mutation was entirely GEE/DEVD sensitive; and (iii) toxicity by higher expression of NL-APP was GEE/DEVD resistant. The GEE/DEVD-sensitive death was sensitive to pertussis toxin and was due to Go-interacting His657-Lys676 domain. The GEE/DEVD-resistant death was due to C-terminal Met677-Asn695. APP mutants lacking either domain unraveled elaborate intracellular cross-talk between these domains. E618Q-APP, responsible for non-AD type of a human disease, only exerted GEE/DEVD-resistant death at higher expression. Therefore, (i) different FAD mutations in APP cause neuronal cell death through different cytoplasmic domains via different sets of mechanisms; (ii) expression levels of FAD genes are critical in activating specific death mechanisms; and (iii) toxicity by low expression of both mutants most likely reflects the pathogenetic mechanism of FAD.

A humanin derivative, S14G-HN, prevents amyloid-β-induced memory impairment in mice

Humanin (HN) is a 24‐amino acid peptide that protects neuronal cells from death caused by Alzheimers disease (AD)‐related genes and amyloid‐β (Aβ). Multiple studies have revealed its biochemical and neuroprotective characteristics in vitro; however, little has been known regarding whether HN is effective in vivo in AD model systems. We examined the effect of S14G‐HN, a 1,000‐fold more potent derivative of HN in vitro, on amnesia induced by Aβ25–35 in mice. The Y‐maze test revealed that at least 50 pmol of S14G‐HN by intracerebroventricular injection prevented Aβ‐induced impairment of short‐term/spatial working memory; however, 5 nmol of S14A‐HN, a neuroprotection‐defective mutant in vitro, did not prevent Aβ‐induced amnesia. These results are in agreement with the structure–function correlation shown previously in vitro. In the water‐finding task, S14G‐HN prevented prolongation of finding latency (the time to find water) observed in Aβ‐amnesic mice, indicating that S14G‐HN also blocked Aβ‐induced impairment of latent learning. In accordance with these observations, immunohistochemical analysis showed that S14G‐HN sustained the number of cholinergic neurons in the basal forebrain and the striata nearly to the normal level. Furthermore, genistein, a specific inhibitor of tyrosine kinases, blocked recovery from scopolamine‐induced amnesia by S14G‐HN, suggesting that certain tyrosine kinase(s) are involved in the inhibitory function of S14G‐HN in vivo. Taking these findings together, we conclude that S14G‐HN has rescue activity against memory impairment caused by AD‐related insults in vivo by activating the same intracellular neuroprotective machinery as elucidated previously in vitro.

Antibody-regulated neurotoxic function of cell-surface β-amyloid precursor protein

APP is a transmembrane precursor of beta-amyloid, and its mutations cause early-onset familial Alzheimers disease. We report a toxic function of normal wild-type APP (wtAPP). Treatment of neuronal F11 cells, immortalized embryonic day 13 neurons, overexpressing wtAPP with anti-APP antibodies caused death. Death was not induced by antibody in parental F11 cells. Death by antibody occurred through cell-surface APP, not through secreted APP, in a pertussis toxin-sensitive manner and was typical apoptosis, not observed in primary astrocytes or glioma cells overexpressing wtAPP, but observed in primary cortical neurons. Cell-surface APP thus performs a toxic function as an extracellularly controllable regulator of neuronal death. This study provides a novel insight into the normal and pathological functions of cell-surface wtAPP.

Identification of essential amino acids in Humanin, a neuroprotective factor against Alzheimer's disease-relevant insults.

Humanin (HN) is a secretory peptide that inhibits neurotoxicity by various Alzheimers disease-relevant insults. We have so far identified that the substitution of Leu9 for Arg nullifies the extracellular secretion of HN. Here we comprehensively investigate the amino acid requirement of HN essential for its secretion and for its neuroprotective function. Intracellulary expressed HN-EGFP (EGFP N-terminally fused with HN) was extracellularly secreted, whereas neither EGFP nor (L9R)HN-EGFP was secreted at all. While Ala substitution of neither residue affected HN secretion, Arg substitution revealed that the two structures-Leu9-Leu11 and Pro19-Va120-were essential for the secretion of full-length HN. In the Leu9-Leu11 domain, the Leu10 residue turned out to play a central role in this function, because the Asp substitution of Leu10, but not Leu9 or Leu11, nullified the secretion of HN. Utilizing Ala-scanned HN constructs, we also investigated a comprehensive structure-function relationship for the neuroprotective function of full-length HN, which revealed (i) that Pro3, Ser7, Cys8, Leu9, Leu12, Thr13, Ser14, and Pro19 were essential for this function and (ii) that Ser7 and Leu9 were essential for self-dimerization of HN. These findings indicate that HN has activity similar to a signal peptide, for which the Leu9-Leu11 region, particularly Leu10, functions as a core domain, and suggest that self-dimerization of HN is a process essential for its neuroprotective function.