F-spondin regulates neuronal survival through activation of disabled-1 in the chicken ciliary ganglion.

The extracellular membrane-associated protein F-spondin has been implicated in cell-matrix and cell-cell adhesion and plays an important role in axonal pathfinding. We report here that F-spondin is expressed in non-neuronal cells in the embryonic chicken ciliary ganglion (CG) and robustly promotes survival of cultured CG neurons. Using deletion constructs of F-spondin we found that the amino-terminal Reelin/Spondin domain cooperates with thrombospondin type 1 repeat (TSR) 6, a functional TGFß-activation domain. In ovo treatment with blocking antibodies raised against the Reelin/Spondin domain or the TSR-domains caused increased apoptosis of CG neurons during the phase of programmed cell death and loss of about 30% of the neurons compared to controls. The Reelin/Spondin domain receptor - APP and its downstream signalling molecule disabled-1 are expressed in CG neurons. F-spondin induced rapid phosphorylation of disabled-1. Moreover, both blocking the central APP domain and interference with disabled-1 signalling disrupted the survival promoting effect of F-spondin. Taken together, our data suggest that F-spondin can promote neuron survival by a mechanism involving the Reelin/Spondin and the TSR domains.

BACE inhibitor treatment of mice induces hyperactivity in a Seizure-related gene 6 family dependent manner without altering learning and memory.

BACE inhibitors, which decrease BACE1 (ß-secretase 1) cleavage of the amyloid precursor protein, are a potential treatment for Alzheimer's disease. Clinical trials using BACE inhibitors have reported a lack of positive effect on patient symptoms and, in some cases, have led to increased adverse events, cognitive worsening and hippocampal atrophy. A potential drawback of this strategy is the effect of BACE inhibition on other BACE1 substrates such as Seizure-related gene 6 (Sez6) family proteins which are known to have a role in neuronal function. Mice were treated with an in-diet BACE inhibitor for 4-8 weeks to achieve a clinically-relevant level of amyloid-ß40 reduction in the brain. Mice underwent behavioural testing and postmortem analysis of dendritic spine number and morphology with Golgi-Cox staining. Sez6 family triple knockout mice were tested alongside wild-type mice to identify whether any effects of the treatment were due to altered cleavage of Sez6 family proteins. Wild-type mice treated with BACE inhibitor displayed hyperactivity on the elevated open field, as indicated by greater distance travelled, but this effect was not observed in treated Sez6 triple knockout mice. BACE inhibitor treatment did not lead to significant changes in spatial or fear learning, reference memory, cognitive flexibility or anxiety in mice as assessed by the Morris water maze, context fear conditioning, or light-dark box tests. Chronic BACE inhibitor treatment reduced the density of mushroom-type spines in the somatosensory cortex, regardless of genotype, but did not affect steady-state dendritic spine density or morphology in the CA1 region of the hippocampus. Chronic BACE inhibition for 1-2 months in mice led to increased locomotor output but did not alter memory or cognitive flexibility. While the mechanism underlying the treatment-induced hyperactivity is unknown, the absence of this response in Sez6 triple knockout mice indicates that blocking ectodomain shedding of Sez6 family proteins is a contributing factor. In contrast, the decrease in mature spine density in cortical neurons was not attributable to lack of shed Sez6 family protein ectodomains. Therefore, other BACE1 substrates are implicated in this effect and, potentially, in the cognitive decline in longer-term chronically treated patients.

Interleukin 13 (IL-13)-regulated expression of the chondroprotective metalloproteinase ADAM15 is reduced in aging cartilage.

OBJECTIVE: The adamalysin metalloproteinase 15 (ADAM15) has been shown to protect against development of osteoarthritis in mice. Here, we have investigated factors that control ADAM15 levels in cartilage. DESIGN: Secretomes from wild-type and Adam15 -/- chondrocytes were compared by label-free quantitative mass spectrometry. mRNA was isolated from murine knee joints, either with or without surgical induction of osteoarthritis on male C57BL/6 mice, and the expression of Adam15 and other related genes quantified by RT-qPCR. ADAM15 in human normal and osteoarthritic cartilage was investigated similarly and by fluorescent immunohistochemistry. Cultured HTB94 chondrosarcoma cells were treated with various anabolic and catabolic stimuli, and ADAM15 mRNA and protein levels evaluated. RESULTS: There were no significant differences in the secretomes of chondrocytes from WT and Adam15 -/- cartilage. Expression of ADAM15 was not altered in either human or murine osteoarthritic cartilage relative to disease-free controls. However, expression of ADAM15 was markedly reduced upon aging in both species, to the extent that expression in joints of 18-month-old mice was 45-fold lower than in that 4.5-month-old animals. IL-13 increased expression of ADAM15 in HTB94 â€‹cells by 2.5-fold, while modulators of senescence and autophagy pathways had no effect. Expression of Il13 in the joint was reduced with aging, suggesting this cytokine may control ADAM15 levels in the joint. CONCLUSION: Expression of the chondroprotective metalloproteinase ADAM15 is reduced in aging human and murine joints, possibly due to a concomitant reduction in IL-13 expression. We thus propose IL-13 as a novel factor contributing to increased osteoarthritis risk upon aging.

A novel substrate for analyzing Alzheimer's disease gamma-secretase.

Proteolytic processing of Alzheimer's disease amyloid precursor protein (APP) by beta-secretase leads to A4CT (C99), which is further cleaved by the as yet unknown protease called gamma-secretase. To study the enzymatic properties of gamma-secretase independently of beta-secretase, A4CT together with an N-terminal signal peptide (SPA4CT) may be expressed in eukaryotic cells. However, in all existing SPA4CT proteins the signal peptide is not correctly cleaved upon membrane insertion. Here, we report the generation of a mutated SPA4CT protein that is correctly cleaved by signal peptidase and, thus, identical to the APP-derived A4CT. This novel SPA4CT protein is processed by gamma-secretase in the same manner as APP-derived A4CT and might be valuable for the generation of transgenic animals showing amyloid pathology.

Mutations in the transmembrane domain of APP altering gamma-secretase specificity.

Alzheimer's disease (AD) beta-amyloid peptide (Abeta and betaA4) is derived from the amyloid precursor protein (APP) by the subsequent action of the so-far unidentified beta- and gamma-secretases. gamma-secretase, which generates the C-terminus of Abeta, cleaves within the transmembrane domain of APP, preferentially after Abeta-residue 40 (Abeta 40) but also after residue 42 (Abeta 42). This Abeta 42 represents the major subunit of the plaques in AD. Since the position of gamma-secretase cleavage is crucial for understanding the pathogenic pathway, we investigated the effect of different point mutations at Thr43 on gamma-secretase specificity in SPA4CT (SPC99)-expressing COS7 cells. These constructs only require gamma-cleavage for Abeta release. We observed that all Thr43 mutations altered the specificity of gamma-secretase. Small hydrophobic residues favored the generation of Abeta 42, leading to an increase in the 42/40 ratio of Abeta (1.6-2.8-fold). The increase was even stronger (5.6-5.8-fold) when combined with the familial mutation Val46Phe. Thus, these constructs might be highly valuable for the generation of animal models for AD. Processing of full-length APP or SPA4CT yielded the same 42/40 ratio of Abeta (4. 7%). Both constructs, bearing the familial AD mutation Val46Phe, led to a similar increase in the 42/40 ratio (3.3- versus 3.6-fold). The p3 fragment, produced by alpha- and gamma-secretase, showed 42/40 ratios similar to Abeta when derived from wild-type and mutant proteins. These results suggest that the different Abeta- and p3-species are generated by gamma-cleavage activities with a similar enzymatic mechanism.

Mechanism of the cleavage specificity of Alzheimer's disease gamma-secretase identified by phenylalanine-scanning mutagenesis of the transmembrane domain of the amyloid precursor protein.

Proteolytic processing of the amyloid precursor protein by beta-secretase yields A4CT (C99), which is cleaved further by the as yet unknown gamma-secretase, yielding the beta-amyloid (Abeta) peptide with 40 (Abeta40) or 42 residues (Abeta42). Because the position of gamma-secretase cleavage is crucial for the pathogenesis of Alzheimer's disease, we individually replaced all membrane-domain residues of A4CT outside the Abeta domain with phenylalanine, stably transfected the constructs in COS7 cells, and determined the effect of these mutations on the cleavage specificity of gamma-secretase (Abeta42/Abeta40 ratio). Compared with wild-type A4CT, mutations at Val-44, Ile-47, and Val-50 led to decreased Abeta42/Abeta40 ratios, whereas mutations at Thr-43, Ile-45, Val-46, Leu-49, and Met-51 led to increased Abeta42/Abeta40 ratios. A massive effect was observed for I45F (34-fold increase) making this construct important for the generation of animal models for Alzheimer's disease. Unlike the other mutations, A4CT-V44F was processed mainly to Abeta38, as determined by mass spectrometry. Our data provide a detailed model for the active site of gamma-secretase: gamma-secretase interacts with A4CT by binding to one side of the alpha-helical transmembrane domain of A4CT. Mutations in the transmembrane domain of A4CT interfere with the interaction between gamma-secretase and A4CT and, thus, alter the cleavage specificity of gamma-secretase.

Alzheimer's disease: correlation of the suppression of beta-amyloid peptide secretion from cultured cells with inhibition of the chymotrypsin-like activity of the proteasome.

Peptide aldehyde inhibitors of the chymotrypsin-like activity of the proteasome (CLIP) such as N-acetyl-Leu-Leu-Nle-H (or ALLN) have been shown previously to inhibit the secretion of beta-amyloid peptide (A beta) from cells. To evaluate more fully the role of the proteasome in this process, we have tested the effects on A beta formation of a much wider range of peptide-based inhibitors of CLIP than published previously. The inhibitors tested included several peptide boronates, some of which proved to be the most potent peptide-based inhibitors of beta-amyloid production reported so far. We found that the ability of the peptide aldehyde and boronate inhibitors to suppress A beta formation from cells correlated extremely well with their potency as CLIP inhibitors. Thus, we conclude that the proteasome may be involved either directly or indirectly in A beta formation.