Elsevier

Neurobiology of Disease

Volume 56, August 2013, Pages 104-115
Neurobiology of Disease

Adhesion molecule L1 binds to amyloid beta and reduces Alzheimer's disease pathology in mice

https://doi.org/10.1016/j.nbd.2013.04.014Get rights and content

Highlights

  • We overexpressed adhesion molecule L1 in the brain of an Alzheimer's disease mouse.

  • L1 overexpression decreases amyloid plaque load, levels of Aβ42, and Aβ42/40 ratio.

  • L1 overexpression in a mouse model of Alzheimer's disease reduces astrogliosis.

  • L1, unlike its close homolog (CHL1), binds Aβ42 and Aβ40 peptides.

  • L1 prevents in vitro amyloid aggregation.

Abstract

Alzheimer's disease (AD) is a devastating neurodegenerative disorder and the most common cause of elderly dementia. In an effort to contribute to the potential of molecular approaches to reduce degenerative processes we have tested the possibility that the neural adhesion molecule L1 ameliorates some characteristic cellular and molecular parameters associated with the disease in a mouse model of AD. Three-month-old mice overexpressing mutated forms of amyloid precursor protein and presenilin-1 under the control of a neuron-specific promoter received an injection of adeno-associated virus encoding the neuronal isoform of full-length L1 (AAV-L1) or, as negative control, green fluorescent protein (AAV-GFP) into the hippocampus and occipital cortex. Four months after virus injection, the mice were analyzed for histological and biochemical parameters of AD. AAV-L1 injection decreased the Aβ plaque load, levels of Aβ42, Aβ42/40 ratio and astrogliosis compared with AAV-GFP controls. AAV-L1 injected mice also had increased densities of inhibitory synaptic terminals on pyramidal cells in the hippocampus when compared with AAV-GFP controls. Numbers of microglial cells/macrophages were similar in both groups, but numbers of microglial cells/macrophages per plaque were increased in AAV-L1 injected mice. To probe for a molecular mechanism that may underlie these effects, we analyzed whether L1 would directly and specifically interact with Aβ. In a label-free binding assay, concentration dependent binding of the extracellular domain of L1, but not of the close homolog of L1 to Aβ40 and Aβ42 was seen, with the fibronectin type III homologous repeats 1–3 of L1 mediating this effect. Aggregation of Aβ42 in vitro was reduced in the presence of the extracellular domain of L1. The combined observations indicate that L1, when overexpressed in neurons and glia, reduces several histopathological hallmarks of AD in mice, possibly by reduction of Aβ aggregation. L1 thus appears to be a candidate molecule to ameliorate the pathology of AD, when applied in therapeutically viable treatment schemes.

Introduction

Alzheimer's disease (AD) is the most common cause of dementia in elderly individuals. In AD patients brain regions involved in learning, memory and emotions are reduced in size due to neuronal cell death, astrogliosis and synaptic degeneration (Albert, 2011, Hardy, 2006, Jucker and Walker, 2011, Mattson, 2004). Pathological hallmarks of AD are intracellular neurofibrillary tangles and extracellular aggregates composed of amyloid beta peptides (Aβ) (Ittner and Götz, 2011). Treatments restoring neuronal function and keeping AD pathology at bay are therefore of prime importance. Beneficial adhesion molecules that prevent neuronal cell death and spare imperiled synapses represent potential venues for treatment. The neural cell adhesion molecule L1 is one of such molecules and has attracted our attention in the context of AD, since elevated levels of L1 were detected in the cerebrospinal fluid of patients with AD, vascular dementia and dementia of mixed type (Strekalova et al., 2006). We hypothesized that L1 may beneficially influence the adverse symptoms in an animal model of AD, because L1 has improved the negative symptoms in several animal models of acute and chronic neurological disorders: Infusion of L1 into the injured spinal cord of rats promoted regeneration (Roonprapunt et al., 2003) and L1-transfected embryonic stem cells as well as Schwann cells improved regeneration after spinal cord injury in mice (Chen et al., 2005, Lavdas et al., 2009); expression of L1 in the spinal cord injured mouse via adeno-associated-virus (AAV) resulted in improved locomotor recovery, regrowth/sprouting and sparing of severed axons, and reduced reactive astrogliosis, by limiting astrocyte proliferation and migration, when injected both acutely and in a sub-chronic phase of injury (Chen et al., 2007, Lee et al., 2012); in a mouse model of Parkinson's disease, embryonic stem cell-derived L1 overexpressing neural aggregates enhanced survival and migration of transplanted cells, differentiation into dopaminergic neurons, survival of endogenous dopaminergic neurons and behavioral recovery (Cui et al., 2010); neural stem cells expressing L1 upon differentiation into astrocytes promoted host–donor cell interactions when transplanted in a mouse model of Parkinson's disease (Ourednik et al., 2009); in a mouse model of Huntington's disease, transplanted L1 overexpressing embryonic stem cells showed preferential neuronal over glial cell differentiation, increased yield of γ-aminobutyric acid (GABA)-ergic neurons, concomitant with behavioral improvement (Bernreuther et al., 2006). Noteworthy in the context of AD is the observation that L1 increases the levels of choline acetyltransferase in the developing and injured central nervous system (Cui et al., 2011a, Lee et al., 2012).

To further explore the therapeutic potential of L1 in neurodegenerative disorders, we used a mouse model for AD with accelerated progression of disease symptoms: the transgenic mouse APPPS1 (Gengler et al., 2010, Radde et al., 2006) which carries the KM670/671NL mutated (“Swedish mutation”) human amyloid precursor protein (APP) and the L166P mutated human presenilin-1 (PS-1). This mouse shows many histological aspects of cerebral amyloidosis, including plaque formation, dystrophic synaptic boutons, hyperphosphorylated tau-positive neuritic structures, astrogliosis and increased numbers of microglia when compared to wild-type mice of the same C57BL/6J inbred genetic background.

In the present study, we injected AAV-L1 or AAV-green fluorescent protein (GFP) as a negative control into the hippocampus and occipital cortex of APPPS1 mice at three months of age, when the first histological abnormalities become apparent. When analyzed four months after injection of virus, overexpression of L1 in neurons and glia led to a reduction of plaque load, astrogliosis and reduced loss of perisomatic inhibitory synapses in the CA1 and CA3 regions of the hippocampus. Direct and specific binding of the extracellular domain of L1 – but not of CHL1, the close homolog of L1 – to Aβ42 reduced aggregation in vitro. Our results indicate that L1 ameliorates the histopathology of AD in a mouse model, probably by directly interacting with Aβ, thus raising the hope that it may become a promising candidate for therapy of AD in humans.

Section snippets

Animals

Three-month-old transgenic male APPPS1 (C57BL/6J-TgN; Thy1-APPKM670/671NL; Thy1-PS1L166P) mice were obtained from a breeding colony at the University of Tübingen, Germany. These mice co-express mutated human APP (Swedish double mutation) and mutated presenilin-1 under the neuron-specific murine Thy-1 promoter element on the C57BL/6J background (Radde et al., 2006). The wild-type C57BL/6J mice were obtained from the breeding colony at the central animal facility of the Universitätsklinikum

AAV-mediated transduction of the occipital cortex and hippocampus

To deliver L1 into the brain, we used AAV serotype 5, which was designed to drive L1 expression under the control of the murine cytomegalovirus immediately early promoter and which has been successfully used to overexpress L1 after spinal cord injury in mice (Chen et al., 2007, Lee et al., 2012). Immunoblot analysis of homogenates of AAV-L1 injected and corresponding non-injected contralateral control hemispheres showed an increase of approximately 20% in the level of L1 expression in the

Discussion

In this study we present evidence that AAV-mediated overexpression of L1 in neurons and astrocytes confers beneficial effects in a mouse model of AD. AD has an intricate and not yet fully understood pathology that would demand a complex therapeutic approach (Herrup, 2010). The positive effects of L1 overexpression in an AD mouse model include the reduction of amyloid plaque load, decreased astrogliosis and better preservation of inhibitory synaptic terminals on pyramidal cell bodies in the

Acknowledgments

We are grateful to Emanuela Szpotowicz for excellent technical assistance, to Isabelle Aubert, Andrey Irintchev, Carsten Schmidt for critical reading of the manuscript, and Southeast Europe Cooperation Hamburg for support. We thank Mathias Jucker for the generous gift of APPPS1 mice. Authors declare no conflict of interest. This work was supported by grants from the New Jersey Commission for Spinal Cord Research and Li Ka-Shing Foundation (to M.S.).

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