Tomoko Wakabayashi

CLAC: a novel Alzheimer amyloid plaque component derived from a transmembrane precursor, CLAC‐P/collagen type XXV

We raised monoclonal antibodies against senile plaque (SP) amyloid and obtained a clone 9D2, which labeled amyloid fibrils in SPs and reacted with ∼50/100 kDa polypeptides in Alzheimers disease (AD) brains. We purified the 9D2 antigens and cloned a cDNA encoding its precursor, which was a novel type II transmembrane protein specifically expressed in neurons. This precursor harbored three collagen‐like Gly–X–Y repeat motifs and was partially homologous to collagen type XIII. Thus, we named the 9D2 antigen as CLAC (collagen‐like Alzheimer amyloid plaque component), and its precursor as CLAC‐P/collagen type XXV. The extracellular domain of CLAC‐P/collagen type XXV was secreted by furin convertase, and the N‐terminus of CLAC deposited in AD brains was pyroglutamate modified. Both secreted and membrane‐tethered forms of CLAC‐P/collagen type XXV specifically bound to fibrillized Aβ, implicating these proteins in β‐amyloidogenesis and neuronal degeneration in AD.

Chronic Optogenetic Activation Augments Aβ Pathology in a Mouse Model of Alzheimer Disease

In vivo experimental evidence indicates that acute neuronal activation increases Aβ release from presynaptic terminals, whereas long-term effects of chronic synaptic activation on Aβ pathology remain unclear. To address this issue, we adopted optogenetics and transduced stabilized step-function opsin, a channelrhodopsin engineered to elicit a long-lasting neuronal hyperexcitability, into the hippocampal perforant pathway of APP transgenic mice. In vivo microdialysis revealed a ∼24% increase in the hippocampal interstitial fluid Aβ42 levels immediately after acute light activation. Five months of chronic optogenetic stimulation increased Aβ burden specifically in the projection area of the perforant pathway (i.e., outer molecular layer of the dentate gyrus) of the stimulated side by ∼2.5-fold compared with that in the contralateral side. Epileptic seizures were observed during the course of chronic stimulation, which might have partly contributed to the Aβ pathology. These findings implicate functional abnormalities of specific neuronal circuitry in Aβ pathology and Alzheimer disease.

RNA binding mediates neurotoxicity in the transgenic Drosophila model of TDP-43 proteinopathy

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by progressive and selective loss of motor neurons. The discovery of mutations in the gene encoding an RNA-binding protein, TAR DNA-binding protein of 43 kD (TDP-43), in familial ALS, strongly implicated abnormalities in RNA processing in the pathogenesis of ALS, although the mechanisms whereby TDP-43 leads to neurodegeneration remain elusive. To clarify the mechanism of degeneration caused by TDP-43, we generated transgenic Drosophila melanogaster expressing a series of systematically modified human TDP-43 genes in the retinal photoreceptor neurons. Overexpression of wild-type TDP-43 resulted in vacuolar degeneration of the photoreceptor neurons associated with thinning of the retina, which was significantly exacerbated by mutations of TDP-43 linked to familial ALS or disrupting its nuclear localization signal (NLS). Remarkably, these degenerative phenotypes were completely normalized by addition of a mutation or deletion of the RNA recognition motif that abolishes the RNA binding ability of TDP-43. Altogether, our results suggest that RNA binding is key to the neurodegeneration caused by overexpression of TDP-43, and that abnormalities in RNA processing may be crucial to the pathogenesis of TDP-43 proteinopathy.

Mostly Separate Distributions of CLAC- versus Aβ40- or Thioflavin S-Reactivities in Senile Plaques Reveal Two Distinct Subpopulations of β-Amyloid Deposits

Collagenous Alzheimer amyloid plaque component (CLAC) is a unique non-Abeta amyloid component of senile plaques (SP) derived from a transmembrane collagen termed CLAC-precursor. Here we characterize the chronological and spatial relationship of CLAC with other features of SP amyloid in the brains of patients with Alzheimers disease (AD), Down syndrome (DS), and of PSAPP transgenic mice. In AD and DS cerebral cortex, CLAC invariably colocalized with Abeta42 but often lacked Abeta40- or thioflavin S (thioS)-reactivities. Immunoelectron microscopy of CLAC-positive SP showed labeling of fibrils that are more loosely dispersed compared to typical amyloid fibrils in CLAC-negative SP. In DS cerebral cortex, diffuse plaques in young patients were negative for CLAC, whereas a subset of SP became CLAC-positive in patients aged 35 to 50 years, before the appearance of Abeta40. In DS cases over 50 years of age, Abeta40-positive SP dramatically increased, whereas CLAC burden remained at a constant level. In PSAPP transgenic mice, CLAC was positive in the diffuse Abeta deposits surrounding huge-cored plaques. Thus, CLAC and Abeta40 or thioS exhibit mostly separate distribution patterns in SP, suggesting that CLAC is a relatively early component of SP in human brains that may have inhibitory effects against the maturation of SP into beta-sheet-rich amyloid deposits.

CLAC-P/Collagen Type XXV Is Required for the Intramuscular Innervation of Motoneurons during Neuromuscular Development

Formation of proper neuromuscular connections is a process coordinated by both motoneuron-intrinsic and target-dependent programs. Under these programs, motoneurons innervate target muscles, escape programmed cell death during fetal development, and form neuromuscular junctions (NMJ). Although a number of studies have revealed molecules involved in axon guidance to target muscles and NMJ formation, little is known about the molecular mechanisms linking intramuscular innervation and target-derived trophic factor-dependent prevention of motoneuron apoptosis. Here we studied the physiological function of CLAC-P/collagen XXV, a transmembrane-type collagen originally identified as a component of senile plaque amyloid of Alzheimers disease brains, by means of generating Col25a1-deficient (KO) mice. Col25a1 KO mice died immediately after birth of respiratory failure. In Col25a1 KO mice, motor axons projected properly toward the target muscles but failed to elongate and branch within the muscle, followed by degeneration of axons. Failure of muscular innervation in Col25a1 KO mice led to excessive apoptosis during development, resulting in almost complete and exclusive loss of spinal motoneurons and immaturity in skeletal muscle development. Bax deletion in Col25a1 KO mice rescued motoneurons from apoptosis, although motor axons remained halted around the muscle entry site. Furthermore, these motoneurons were positive for phosphorylated c-Jun, an indicator of insufficient supply of target-derived survival signals. Together, these observations indicate that CLAC-P/collagen XXV is a novel essential factor that regulates the initial phase of intramuscular motor innervation, which is required for subsequent target-dependent motoneuron survival and NMJ formation during development.

Familial Amyotrophic Lateral Sclerosis-linked Mutations in Profilin 1 Exacerbate TDP-43-induced Degeneration in the Retina of Drosophila melanogaster through an Increase in the Cytoplasmic Localization of TDP-43

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive and selective loss of motor neurons. Causative genes for familial ALS (fALS), e.g. TARDBP or FUS/TLS, have been found, among which mutations within the profilin 1 (PFN1) gene have recently been identified in ALS18. To elucidate the mechanism whereby PFN1 mutations lead to neuronal death, we generated transgenic Drosophila melanogaster overexpressing human PFN1 in the retinal photoreceptor neurons. Overexpression of wild-type or fALS mutant PFN1 caused no degenerative phenotypes in the retina. Double overexpression of fALS mutant PFN1 and human TDP-43 markedly exacerbated the TDP-43-induced retinal degeneration, i.e. vacuolation and thinning of the retina, whereas co-expression of wild-type PFN1 did not aggravate the degenerative phenotype. Notably, co-expression of TDP-43 with fALS mutant PFN1 increased the cytoplasmic localization of TDP-43, the latter remaining in nuclei upon co-expression with wild-type PFN1, whereas co-expression of TDP-43 lacking the nuclear localization signal with the fALS mutant PFN1 did not aggravate the retinal degeneration. Knockdown of endogenous Drosophila PFN1 did not alter the degenerative phenotypes of the retina in flies overexpressing wild-type TDP-43. These data suggest that ALS-linked PFN1 mutations exacerbate TDP-43-induced neurodegeneration in a gain-of-function manner, possibly by shifting the localization of TDP-43 from nuclei to cytoplasm.

Self-assembly of FUS through its low-complexity domain contributes to neurodegeneration

Aggregation of fused in sarcoma (FUS) protein, and mutations in FUS gene, are causative to a range of neurodegenerative disorders including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia. To gain insights into the molecular mechanism whereby FUS causes neurodegeneration, we generated transgenic Drosophila melanogaster overexpressing human FUS in the photoreceptor neurons, which exhibited mild retinal degeneration. Expression of familial ALS-mutant FUS aggravated the degeneration, which was associated with an increase in cytoplasmic localization of FUS. A carboxy-terminally truncated R495X mutant FUS also was localized in cytoplasm, whereas the degenerative phenotype was diminished. Double expression of R495X and wild-type FUS dramatically exacerbated degeneration, sequestrating wild-type FUS into cytoplasmic aggregates. Notably, replacement of all tyrosine residues within the low-complexity domain, which abolished self-assembly of FUS, completely eliminated the degenerative phenotypes. Taken together, we propose that self-assembly of FUS through its low-complexity domain contributes to FUS-induced neurodegeneration.

Two distinct pathways leading to retinal degeneration in transgenic Drosophila melanogaster overexpressing human FUS

tau phosphorylation.Results: Six months high fat diet increased Abeta40 in the brains ofB6C wild type mice. On the other hand, high fat diet increased plasma Abeta levels in APP/PS1 mice, but not in wild type mice. Moreover, tau phosphorylation was highly increased in the brains of 18 months old APP+ ob/obmice.Conclusions:Tau phosphorylation is increased by diabetes in APP mice, suggesting that Abeta i s prerequisite, but insufficient to cause tau phosphorylation in vivo. A beta accumulation, insulin signaling and tau phosphorylation might play essential roles in the pathological interaction between AD and diabetes. Of note, a vicious cycle likely underlie the interaction between AD and diabetes. High fat diet-induced elevation of plasma Abeta level might be involved in this interaction between AD and diabetes.