Mossy fiber long-term potentiation deficits in BACE1 knock-outs can be rescued by activation of alpha7 nicotinic acetylcholine receptors.

ß-Site amyloid precursor protein-cleaving enzyme 1 (BACE1)-the neuronal ß-secretase responsible for producing ß-amyloid (Aß) peptides-emerged as one of the key therapeutic targets of Alzheimer's disease (AD). Although complete ablation of the BACE1 gene prevents Aß formation, we reported that BACE1 knock-out mice display severe presynaptic deficits at mossy fiber (MF)-to-CA3 synapses in the hippocampus, a major locus of BACE1 expression. We also found that the deficits are likely due to abnormal presynaptic Ca(2+) regulation. Cholinergic system has been implicated in AD, in some cases involving Ca(2+)-permeable α7-nicotinic acetylcholine receptors (nAChRs). Here we report that brief application of nicotine, via α7-nAChRs, can restore MF long-term potentiation in BACE1 knock-outs. Our data suggest that activating α7-nAChRs can recover the presynaptic deficits in BACE1 knock-outs.

Elevated levels of neutrophil gelatinase-associated lipocalin in bile from patients with malignant pancreatobiliary disease.

OBJECTIVES: Accurate differentiation between benign and malignant causes of biliary obstruction remains challenging and reliable biomarkers are urgently needed. Bile is a potential source of such biomarkers. Our aim was to apply a proteomic approach to identify a potential biomarker in bile that differentiates between malignant and benign disease, and to assess its diagnostic accuracy. Neutrophil gelatinase-associated lipocalin (NGAL) is multi-functional protein, released from activated neutrophils, with roles in inflammation, immune function, and carcinogenesis. It has not previously been described in bile. METHODS: Bile, urine, and serum were collected prospectively from 38 patients undergoing endoscopic retrograde cholangiopancreatography ("discovery" cohort); 22 had benign and 16 had malignant pancreatobiliary disease. Initially, label-free proteomics and immunoblotting were performed in samples from a subset of these patients. Enzyme-linked immunosorbent assay was then performed for NGAL as a potential biomarker on all samples in this cohort. The diagnostic performance of biliary NGAL was then validated in a second, independent group ("validation" cohort) of 21 patients with pancreatobiliary disease (benign n=14, malignant n=7). RESULTS: NGAL levels were significantly raised in bile from the malignant disease group, compared with bile from the benign disease group in the discovery cohort (median 1,556 vs. 480 ng/ml, P=0.007). Biliary NGAL levels had a receiver operating characteristic area under curve of 0.76, sensitivity 94%, specificity 55%, positive predictive value 60%, and negative predictive value 92% for distinguishing malignant from benign causes. Biliary NGAL was independent of serum biochemistry and carbohydrate antigen 19-9 (CA 19-9) in differentiating between underlying benign and malignant disease. No significant differences in serum and urine NGAL levels were found between benign and malignant disease. Combining biliary NGAL and serum CA 19-9 improved diagnostic accuracy for malignancy (sensitivity 85%, specificity 82%, positive predictive value 79%, and negative predictive value 87%). The diagnostic accuracy of biliary NGAL was confirmed in the second independent validation cohort. CONCLUSIONS: NGAL in bile is a novel potential biomarker to help distinguish benign from malignant biliary obstruction.

BACE1 knock-outs display deficits in activity-dependent potentiation of synaptic transmission at mossy fiber to CA3 synapses in the hippocampus.

beta-Amyloid precursor protein cleavage enzyme 1 (BACE1) has been identified as a major neuronal beta-secretase critical for the formation of beta-amyloid (Abeta) peptide, which is thought responsible for the pathology of Alzheimer's disease (AD). Therefore, BACE1 is one of the key therapeutic targets that can prevent the progression of AD. Previous studies showed that knocking out the BACE1 gene prevents Abeta formation, but results in behavioral deficits and specific synaptic dysfunctions at Schaffer collateral to CA1 synapses. However, BACE1 protein is most highly expressed at the mossy fiber projections in CA3. Here, we report that BACE1 knock-out mice display reduced presynaptic function, as measured by an increase in paired-pulse facilitation ratio. More dramatically, mossy fiber long-term potentiation (LTP), which is normally expressed via an increase in presynaptic release, was eliminated in the knock-outs. Although long-term depression was slightly larger in the BACE1 knock-outs, it could not be reversed. The specific deficit in mossy fiber LTP was upstream of cAMP signaling and could be "rescued" by transiently elevating extracellular Ca2+ concentration. These results suggest that BACE1 may play a critical role in regulating presynaptic function, especially activity-dependent strengthening of presynaptic release, at mossy fiber synapses.

Motor neuron disease occurring in a mutant dynactin mouse model is characterized by defects in vesicular trafficking.

Amyotrophic lateral sclerosis (ALS), a fatal and progressive neurodegenerative disorder characterized by weakness, muscle atrophy, and spasticity, is the most common adult-onset motor neuron disease. Although the majority of ALS cases are sporadic, approximately 5-10% are familial, including those linked to mutations in SOD1 (Cu/Zn superoxide dismutase). Missense mutations in a dynactin gene (DCTN1) encoding the p150(Glued) subunit of dynactin have been linked to both familial and sporadic ALS. To determine the molecular mechanism whereby mutant dynactin p150(Glued) causes selective degeneration of motor neurons, we generated and characterized mice expressing either wild-type or mutant human dynactin p150(Glued). Neuronal expression of mutant, but not wild type, dynactin p150(Glued) causes motor neuron disease in these animals that are characterized by defects in vesicular transport in cell bodies of motor neurons, axonal swelling and axo-terminal degeneration. Importantly, we provide evidence that autophagic cell death is implicated in the pathogenesis of mutant p150(Glued) mice. This novel mouse model will be instrumental for not only clarifying disease mechanisms in ALS, but also for testing therapeutic strategies to ameliorate this devastating disease.

Moderate reduction of gamma-secretase attenuates amyloid burden and limits mechanism-based liabilities.

Although gamma-secretase is recognized as a therapeutic target for Alzheimer's disease, side effects associated with strong inhibition of this aspartyl protease raised serious concerns regarding this therapeutic strategy. However, it is not known whether moderate inhibition of this enzyme will allow dissociation of beneficial effects in the CNS from mechanism-based toxicities in the periphery. We tested this possibility by using a series of mice with genetic reduction of gamma-secretase (levels ranging from 25 to 64% of control mice). Here, we document that even 30% reduction of gamma-secretase can effectively ameliorate amyloid burden in the CNS. However, global reduction of this enzyme below a threshold level increased the risk of developing squamous cell carcinoma as well as abnormal proliferation of granulocytes in a gamma-secretase dosage-dependent manner. Importantly, we demonstrate that there exists a critical gamma-secretase level that reduces the risk of amyloidosis in the CNS and limits tumorigenesis in epithelia. Our findings suggest that moderate inhibition of gamma-secretase represents an attractive anti-amyloid therapy for Alzheimer's disease.

Progressive behavioral deficits in DJ-1-deficient mice are associated with normal nigrostriatal function.

Loss-of-function mutations in the DJ-1 gene account for an autosomal recessive form of Parkinson's disease (PD). To investigate the physiological functions of DJ-1 in vivo, we generated DJ-1 knockout (DJ-1(-/-)) mice. Younger (<1 year) DJ-1(-/-) mice were hypoactive and had mild gait abnormalities. Older DJ-1(-/-), however, showed decreased body weight and grip strength and more severe gait irregularities compared to wild-type littermates. The basal level of extracellular dopamine, evoked dopamine release and dopamine receptor D2 sensitivity appeared normal in the striatum of DJ-1(-/-) mice, which was consistent with similar results between DJ-1(-/-) and controls in behavioral paradigms specific for the dopaminergic system. An examination of spinal cord, nerve and muscle tissues failed to identify any pathological changes that were consistent with the noted motor deficits. Taken together, our findings suggest that loss of DJ-1 leads to progressive behavioral changes without significant alterations in nigrostriatal dopaminergic and spinal motor systems.

BACE1, a major determinant of selective vulnerability of the brain to amyloid-beta amyloidogenesis, is essential for cognitive, emotional, and synaptic functions.

A transmembrane aspartyl protease termed beta-site APP cleavage enzyme 1 (BACE1) that cleaves the amyloid-beta precursor protein (APP), which is abundant in neurons, is required for the generation of amyloid-beta (Abeta) peptides implicated in the pathogenesis of Alzheimer's disease (AD). We now demonstrate that BACE1, enriched in neurons of the CNS, is a major determinant that predisposes the brain to Abeta amyloidogenesis. The physiologically high levels of BACE1 activity coupled with low levels of BACE2 and alpha-secretase anti-amyloidogenic activities in neurons is a major contributor to the accumulation of Abeta in the CNS, whereas other organs are spared. Significantly, deletion of BACE1 in APPswe;PS1DeltaE9 mice prevents both Abeta deposition and age-associated cognitive abnormalities that occur in this model of Abeta amyloidosis. Moreover, Abeta deposits are sensitive to BACE1 dosage and can be efficiently cleared from the CNS when BACE1 is silenced. However, BACE1 null mice manifest alterations in hippocampal synaptic plasticity as well as in performance on tests of cognition and emotion. Importantly, memory deficits but not emotional alterations in BACE1(-/-) mice are prevented by coexpressing APPswe;PS1DeltaE9 transgenes, indicating that other potential substrates of BACE1 may affect neural circuits related to emotion. Our results establish BACE1 and APP processing pathways as critical for cognitive, emotional, and synaptic functions, and future studies should be alert to potential mechanism-based side effects that may occur with BACE1 inhibitors designed to ameliorate Abeta amyloidosis in AD.

Loss of ALS2 function is insufficient to trigger motor neuron degeneration in knock-out mice but predisposes neurons to oxidative stress.

Amyotrophic lateral sclerosis (ALS), the most common motor neuron disease, is caused by a selective loss of motor neurons in the CNS. Mutations in the ALS2 gene have been linked to one form of autosomal recessive juvenile onset ALS (ALS2). To investigate the pathogenic mechanisms of ALS2, we generated ALS2 knock-out (ALS2(-/-)) mice. Although ALS2(-/-) mice lacked obvious developmental abnormalities, they exhibited age-dependent deficits in motor coordination and motor learning. Moreover, ALS2(-/-) mice showed a higher anxiety response in the open-field and elevated plus-maze tasks. Although they failed to recapitulate clinical or neuropathological phenotypes consistent with motor neuron disease by 20 months of age, ALS2(-/-) mice or primary cultured neurons derived from these mice were more susceptible to oxidative stress compared with wild-type controls. These observations suggest that loss of ALS2 function is insufficient to cause major motor deficits or motor neuron degeneration in a mouse model but predisposes neurons to oxidative stress.