Adam C. Kaufman

Metabotropic Glutamate Receptor 5 Is a Coreceptor for Alzheimer Aβ Oligomer Bound to Cellular Prion Protein

Soluble amyloid-β oligomers (Aβo) trigger Alzheimers disease (AD) pathophysiology and bind with high affinity to cellular prion protein (PrP(C)). At the postsynaptic density (PSD), extracellular Aβo bound to lipid-anchored PrP(C) activates intracellular Fyn kinase to disrupt synapses. Here, we screened transmembrane PSD proteins heterologously for the ability to couple Aβo-PrP(C) with Fyn. Only coexpression of the metabotropic glutamate receptor, mGluR5, allowed PrP(C)-bound Aβo to activate Fyn. PrP(C) and mGluR5 interact physically, and cytoplasmic Fyn forms a complex with mGluR5. Aβo-PrP(C) generates mGluR5-mediated increases of intracellular calcium in Xenopus oocytes and in neurons, and the latter is also driven by human AD brain extracts. In addition, signaling by Aβo-PrP(C)-mGluR5 complexes mediates eEF2 phosphorylation and dendritic spine loss. For mice expressing familial AD transgenes, mGluR5 antagonism reverses deficits in learning, memory, and synapse density. Thus, Aβo-PrP(C) complexes at the neuronal surface activate mGluR5 to disrupt neuronal function.

Fyn inhibition rescues established memory and synapse loss in Alzheimer mice

Currently no effective disease‐modifying agents exist for the treatment of Alzheimer disease (AD). The Fyn tyrosine kinase is implicated in AD pathology triggered by amyloid‐ß oligomers (Aßo) and propagated by Tau. Thus, Fyn inhibition may prevent or delay disease progression. Here, we sought to repurpose the Src family kinase inhibitor oncology compound, AZD0530, for AD.

Prion-Protein-interacting Amyloid-β Oligomers of High Molecular Weight Are Tightly Correlated with Memory Impairment in Multiple Alzheimer Mouse Models

Background: Amyloid-β (Aβ) oligomers are key in Alzheimer disease (AD) but are diverse and poorly characterized. Results: Multiple Aβ forms were measured across the life span of AD model mice and human AD brain. Conclusion: Aβ species interacting with prion protein were tightly linked to behavioral impairment. Significance: An Aβ oligomer subset with defined biochemical properties is present in multiple AD-relevant samples. Alzheimer disease (AD) is characterized by amyloid-β accumulation, with soluble oligomers (Aβo) being the most synaptotoxic. However, the multivalent and unstable nature of Aβo limits molecular characterization and hinders research reproducibility. Here, we characterized multiple Aβo forms throughout the life span of various AD mice and in post-mortem human brain. Aβo exists in several populations, where prion protein (PrPC)-interacting Aβo is a high molecular weight Aβ assembly present in multiple mice and humans with AD. Levels of PrPC-interacting Aβo match closely with mouse memory and are equal or superior to other Aβ measures in predicting behavioral impairment. However, Aβo metrics vary considerably between mouse strains. Deleting PrPC expression in mice with relatively low PrPC-interacting Aβo (Tg2576) results in partial rescue of cognitive performance as opposed to complete recovery in animals with a high percentage of PrPC-interacting Aβo (APP/PSEN1). These findings highlight the relative contributions and interplay of Aβo forms in AD.

Anti‐CD3 mAbs for treatment of type 1 diabetes

The use of anti‐CD3 monoclonal antibodies (mAbs) has moved from the bench to the bedside. The experience with the anti‐human CD3 mAb OKT3 for treatment of transplant rejection identified limitations that were largely overcome with the creation of humanized non‐FcR binding antibodies: Teplizumab, Otelixizumab and Visilizumab. Preclinical studies showed the ability of the drugs to reverse hyperglycaemia in diabetic non‐obese diabetic (NOD) mice providing rationale for clinical trials with the agents. The former two drugs have been tested in subjects with new onset type 1 diabetes. They have both shown, in randomized clinical trials, an ability to reduce the loss of insulin production over the first 2 years of the disease. In addition, the need for exogenous insulin to maintain glucose control has been reduced. However, these agents alone do not restore normal glucose control, and future approaches will likely require combinations of agents with complementary immune or metabolic activity. Copyright

Metabotropic glutamate receptor 5 couples cellular prion protein to intracellular signalling in Alzheimer’s disease

Alzheimers disease-related phenotypes in mice can be rescued by blockade of either cellular prion protein or metabotropic glutamate receptor 5. We sought genetic and biochemical evidence that these proteins function cooperatively as an obligate complex in the brain. We show that cellular prion protein associates via transmembrane metabotropic glutamate receptor 5 with the intracellular protein mediators Homer1b/c, calcium/calmodulin-dependent protein kinase II, and the Alzheimers disease risk gene product protein tyrosine kinase 2 beta. Coupling of cellular prion protein to these intracellular proteins is modified by soluble amyloid-β oligomers, by mouse brain Alzheimers disease transgenes or by human Alzheimers disease pathology. Amyloid-β oligomer-triggered phosphorylation of intracellular protein mediators and impairment of synaptic plasticity in vitro requires Prnp-Grm5 genetic interaction, being absent in transheterozygous loss-of-function, but present in either single heterozygote. Importantly, genetic coupling between Prnp and Grm5 is also responsible for signalling, for survival and for synapse loss in Alzheimers disease transgenic model mice. Thus, the interaction between metabotropic glutamate receptor 5 and cellular prion protein has a central role in Alzheimers disease pathogenesis, and the complex is a potential target for disease-modifying intervention.

Brivaracetam, but not ethosuximide, reverses memory impairments in an Alzheimer's disease mouse model.

IntroductionRecent studies have shown that several strains of transgenic Alzheimer’s disease (AD) mice overexpressing the amyloid precursor protein (APP) have cortical hyperexcitability, and their results have suggested that this aberrant network activity may be a mechanism by which amyloid-β (Aβ) causes more widespread neuronal dysfunction. Specific anticonvulsant therapy reverses memory impairments in various transgenic mouse strains, but it is not known whether reduction of epileptiform activity might serve as a surrogate marker of drug efficacy for memory improvement in AD mouse models.MethodsTransgenic AD mice (APP/PS1 and 3xTg-AD) were chronically implanted with dural electroencephalography electrodes, and epileptiform activity was correlated with spatial memory function and transgene-specific pathology. The antiepileptic drugs ethosuximide and brivaracetam were tested for their ability to suppress epileptiform activity and to reverse memory impairments and synapse loss in APP/PS1 mice.ResultsWe report that in two transgenic mouse models of AD (APP/PS1 and 3xTg-AD), the presence of spike-wave discharges (SWDs) correlated with impairments in spatial memory. Both ethosuximide and brivaracetam reduce mouse SWDs, but only brivaracetam reverses memory impairments in APP/PS1 mice.ConclusionsOur data confirm an intriguing therapeutic role of anticonvulsant drugs targeting synaptic vesicle protein 2A across AD mouse models. Chronic ethosuximide dosing did not reverse spatial memory impairments in APP/PS1 mice, despite reduction of SWDs. Our data indicate that SWDs are not a reliable surrogate marker of appropriate target engagement for reversal of memory dysfunction in APP/PS1 mice.

Opposing effects of progranulin deficiency on amyloid and tau pathologies via microglial TYROBP network

Progranulin (PGRN) is implicated in Alzheimer’s disease (AD) as well as frontotemporal lobar degeneration. Genetic studies demonstrate an association of the common GRN rs5848 variant that results in reduced PGRN levels with increased risk for AD. However, the mechanisms by which PGRN reduction from the GRN AD risk variant or mutation exacerbates AD pathophysiology remain ill defined. Here, we show that the GRN AD risk variant has no significant effects on florbetapir positron emission tomographic amyloid imaging and cerebrospinal fluid (CSF) Aβ levels, whereas it is associated with increased CSF tau levels in human subjects of the Alzheimer’s disease neuroimaging initiative studies. Consistent with the human data, subsequent analyses using the APPswe/PS1ΔE9 (APP/PS1) mouse model of cerebral amyloidosis show that PGRN deficiency has no exacerbating effects on Aβ pathology. In contrast and unexpectedly, PGRN deficiency significantly reduces diffuse Aβ plaque growth in these APP/PS1 mice. This protective effect is due, at least in part, to enhanced microglial Aβ phagocytosis caused by PGRN deficiency-induced expression of TYROBP network genes (TNG) including an AD risk factor Trem2. PGRN-deficient APP/PS1 mice also exhibit less severe axonal dystrophy and partially improved behavior phenotypes. While PGRN deficiency reduces these amyloidosis-related phenotypes, other neuronal injury mechanisms are increased by loss of PGRN, revealing a multidimensional interaction of GRN with AD. For example, C1q complement deposition at synapses is enhanced in APP/PS1 mice lacking PGRN. Moreover, PGRN deficiency increases tau AT8 and AT180 pathologies in human P301L tau-expressing mice. These human and rodent data suggest that global PGRN reduction induces microglial TNG expression and increases AD risk by exacerbating neuronal injury and tau pathology, rather than by accelerating Aβ pathology.

Conditional Deletion of Prnp Rescues Behavioral and Synaptic Deficits after Disease Onset in Transgenic Alzheimer's Disease

Biochemical and genetic evidence implicate soluble oligomeric amyloid-β (Aβo) in triggering Alzheimers disease (AD) pathophysiology. Moreover, constitutive deletion of the Aβo-binding cellular prion protein (PrPC) prevents development of memory deficits in APPswe/PS1ΔE9 mice, a model of familial AD. Here, we define the role of PrPC to rescue or halt established AD endophenotypes in a therapeutic disease-modifying time window after symptom onset. Deletion of Prnp at either 12 or 16 months of age fully reverses hippocampal synapse loss and completely rescues preexisting behavioral deficits by 17 months. In contrast, but consistent with a neuronal function for Aβo/PrPC signaling, plaque density, microgliosis, and astrocytosis are not altered. Degeneration of catecholaminergic neurons remains unchanged by PrPC reduction after disease onset. These results define the potential of targeting PrPC as a disease-modifying therapy for certain AD-related phenotypes after disease onset. SIGNIFICANCE STATEMENT The study presented here further elucidates our understanding of the soluble oligomeric amyloid-β–Aβo-binding cellular prion protein (PrPC) signaling pathway in a familial form of Alzheimers disease (AD) by implicating PrPC as a potential therapeutic target for AD. In particular, genetic deletion of Prnp rescued several familial AD (FAD)-associated phenotypes after disease onset in a mouse model of FAD. This study underscores the therapeutic potential of PrPC deletion given that patients already present symptoms at the time of diagnosis.

Delayed amyloid plaque deposition and behavioral deficits in outcrossed AβPP/PS1 mice.

Alzheimers disease (AD) is a progressive neurodegenerative dementia characterized by amyloid plaque accumulation, synapse/dendrite loss, and cognitive impairment. Transgenic mice expressing mutant forms of amyloid‐β precursor protein (AβPP) and presenilin‐1 (PS1) recapitulate several aspects of this disease and provide a useful model system for studying elements of AD progression. AβPP/PS1 mice have been previously shown to exhibit behavioral deficits and amyloid plaque deposition between 4–9 months of age. We crossed AβPP/PS1 animals with mice of a mixed genetic background (C57BL/6 × 129/SvJ) and investigated the development of AD‐like features in the resulting outcrossed mice. The onset of memory‐based behavioral impairment is delayed considerably in outcrossed AβPP/PS1 mice relative to inbred mice on a C57BL/6 background. While inbred AβPP/PS1 mice develop deficits in radial‐arm water maze performance and novel object recognition as early as 8 months, outcrossed AβPP/PS1 mice do not display defects until 18 months. Within the forebrain, we find that inbred AβPP/PS1 mice have significantly higher amyloid plaque burden at 12 months than outcrossed AβPP/PS1 mice of the same age. Surprisingly, inbred AβPP/PS1 mice at 8 months have low plaque burden, suggesting that plaque burden alone cannot explain the accompanying behavioral deficits. Analysis of AβPP processing revealed that elevated levels of soluble Aβ correlate with the degree of behavioral impairment in both strains. Taken together, these findings suggest that animal behavior, amyloid plaque deposition, and AβPP processing are sensitive to genetic differences between mouse strains. J. Comp. Neurol., 521:1395–1408, 2013.

Role of Cellular Prion Protein in the Amyloid-β Oligomer Pathophysiology of Alzheimer’s Disease

Alzheimer’s disease (AD) is the most common form of dementia affecting millions worldwide. The primary histopathological features of AD are amyloid-beta (Aβ) plaques and neurofibrillary tangles. Aβ oligomers (Aβo) are believed to be essential mediators of the synaptotoxicity and cell death that are characteristic of this illness. For decades, the exact mechanism for how Aβ exerted its toxic effect remained unknown. Recently, it has been shown that the cellular Prion Protein (PrPC) acts as a high-affinity binding partner for Aβo. Moreover, it has been demonstrated that PrPC is necessary for memory loss, impaired long-term potentiation, and neuronal dysfunction in transgenic mouse models of AD. Antagonizing PrPC in AD mouse models has also been shown to reverse memory deficits, so targeting PrPC is a potential avenue for treatment. This chapter will review the evidence connecting PrPC to Aβo pathophysiology.