Faculty Bibliography

We report that neuronal overexpression of the endogenous inhibitor of calpains, calpastatin (CAST), in a mouse model of human Alzheimer's disease (AD) beta-amyloidosis, the APP23 mouse, reduces beta-amyloid (Abeta) pathology and Abeta levels when comparing aged, double transgenic (tg) APP23/CAST with APP23 mice. Concurrent with Abeta plaque deposition, aged APP23/CAST mice show a decrease in the steady-state brain levels of the amyloid precursor protein (APP) and APP C-terminal fragments (CTFs) when compared with APP23 mice. This CAST-dependent decrease in APP metabolite levels was not observed in single tg CAST mice expressing endogenous APP or in younger, Abeta plaque predepositing APP23/CAST mice. We also determined that the CAST-mediated inhibition of calpain activity in the brain is greater in the CAST mice with Abeta pathology than in non-APP tg mice, as demonstrated by a decrease in calpain-mediated cytoskeleton protein cleavage. Moreover, aged APP23/CAST mice have reduced extracellular signal-regulated kinase 1/2 (ERK1/2) activity and tau phosphorylation when compared with APP23 mice. In summary, in vivo calpain inhibition mediated by CAST transgene expression reduces Abeta pathology in APP23 mice, with our findings further suggesting that APP metabolism is modified by CAST overexpression as the mice develop Abeta pathology. Our results indicate that the calpain system in neurons is more responsive to CAST inhibition under conditions of Abeta pathology, suggesting that in the disease state neurons may be more sensitive to the therapeutic use of calpain inhibitors.

Cytoskeletal protein phosphorylation is frequently altered in neuropathologic states but little is known about changes during normal aging. Here we report that declining protein phosphatase activity, rather than activation of kinases, underlies aging-related neurofilament hyperphosphorylation. Purified PP2A or PP2B dephosphorylated the heavy neurofilament (NFH) subunit or its extensively phorphorylated carboxyl-terminal domain in vitro. In cultured primary hippocampal neurons, inhibiting either phosphatase induced NFH phosphorylation without activating known neurofilament kinases. Neurofilament phosphorylation in the mouse CNS, as reflected by levels of the RT-97 phosphoepitope associated with late axon maturation, more than doubled during the 12-month period after NFH expression plateaued at p21. This was accompanied by declines in levels and activity of PP2A but not PP2B, and no rise in activities of neurofilament kinases (Erk1,2, cdk5 and JNK1,2). Inhibiting PP2A in mice in vivo restored brain RT-97 to levels seen in young mice. Declining PP2A activity, therefore, can account for rising neurofilament phosphorylation in maturing brain, potentially compounding similar changes associated with adult-onset neurodegenerative diseases.

The vulnerability of the olfactory system to Alzheimer's disease (AD) pathology and the high incidence of olfactory perceptual dysfunction in early stages of the disease makes the olfactory system a unique model for understanding mechanisms of synaptic and neural network dysfunction in AD. Here we demonstrate aberrant neural oscillations within the olfactory bulb (OB) and piriform cortex (PCX) of mice overexpressing human mutations of amyloid precursor protein (APP). Network dysfunction was evident starting at 3 months of age in APP mice, prior to the onset of significant behavioral impairments or comparable hippocampal network dysfunction. Coinciding with the onset of behavioral impairments, we found hyperactivity of odor-evoked responses in the PCX and enhanced coherence between the OB and PCX. In contrast, older APP mice with established disease-related pathology were characterized by hyporesponsive PCX odor-evoked activity and impaired behavior which were both recovered by treatment with a Liver-X Receptor (LXR) agonist. These results complement recent findings in other neural networks and suggest that disease-relevant network dysfunction can be transient and region specific, yet with lasting effects on cognition and behavior

Abnormally swollen regions of axons and dendrites (neurites) filled mainly with autophagy-related organelles represent the highly characteristic and widespread form of "neuritic dystrophy" in Alzheimer disease (AD), which implies dysfunction of autophagy and axonal transport. In this punctum, we discuss our recent findings that autophagic/lysosomal degradation is critical to proper axonal transport of autophagic vacuoles (AVs) and lysosomes. We showed that lysosomal protease inhibition induces defective axonal transport of specific cargoes, causing these cargoes to accumulate in axonal swellings that biochemically and morphologically resemble the dystrophic neurites in AD. Our findings suggest that a cargo-specific failure of axonal transport promotes neuritic dystrophy in AD, which involves a mechanism distinct from the global axonal transport deficits seen in some other neurodegenerative diseases.

Endocytic system dysfunction is one of the earliest disturbances that occur in Alzheimer's disease (AD), and may underlie the selective vulnerability of cholinergic basal forebrain (CBF) neurons during the progression of dementia. Herein we report that genes regulating early and late endosomes are selectively upregulated within CBF neurons in mild cognitive impairment (MCI) and AD. Specifically, upregulation of rab4, rab5, rab7, and rab27 was observed in CBF neurons microdissected from postmortem brains of individuals with MCI and AD compared to age-matched control subjects with no cognitive impairment (NCI). Upregulated expression of rab4, rab5, rab7, and rab27 correlated with antemortem measures of cognitive decline in individuals with MCI and AD. qPCR validated upregulation of these select rab GTPases within microdissected samples of the basal forebrain. Moreover, quantitative immunoblot analysis demonstrated upregulation of rab5 protein expression in the basal forebrain of subjects with MCI and AD. The elevation of rab4, rab5, and rab7 expression is consistent with our recent observations in CA1 pyramidal neurons in MCI and AD. These findings provide further support that endosomal pathology accelerates endocytosis and endosome recycling, which may promote aberrant endosomal signaling and neurodegeneration throughout the progression of AD

Autophagy, the major degradative pathway for organelles and long-lived proteins, is essential for the survival of neurons. Mounting evidence has implicated defective autophagy in the pathogenesis of several major neurodegenerative diseases, particularly Alzheimer's disease (AD). A continuum of abnormalities of the lysosomal system has been identified in neurons of the AD brain, including pathological endocytic pathway responses at the very earliest disease stage and a progressive disruption of autophagy leading to the massive buildup of incompletely digested substrates within dystrophic axons and dendrites. In this review, we examine research on autophagy in AD and evaluate evidence addressing the specific step or steps along the autophagy pathway that may be defective. Current evidence strongly points to disruption of substrate proteolysis within autolysosomes for the principal mechanism underlying autophagy failure in AD. In the most common form of familial early onset AD, mutant presenilin 1 disrupts autophagy directly by impeding lysosomal proteolysis while, in other forms of AD, autophagy impairments may involve different genetic or environmental factors. Attempts to restore more normal lysosomal proteolysis and autophagy efficiency in mouse models of AD pathology have yielded promising therapeutic effects on neuronal function and cognitive performance, demonstrating the relevance of autophagy failure to the pathogenesis of AD and the potential of autophagy modulation as a therapeutic strategy

Ethanol administration to neonatal animals leads to a significant loss of cells in various regions of the brain, including the hippocampus, and impairs long-term potentiation (LTP), which is a physiological correlate of memory. Chromatin remodeling by histone modification plays an important role in several aspects of long-term cellular plasticity, including neuronal differentiation, learning and memory, drug addiction and neurodegeneration. Dimethylation of histone-3 Lys 9 (H3K9me2) correlates with transcriptional silencing, and trimethylation of histone-3 Lys 4 (H3K4me3) is linked to active transcription. Recently, histone (H3) methylation was implicated in the regulation of chromatin remodeling in the nervous system and the process of long-term memory storage. Postnatal ethanol-induces neurodegeneration in rodents, although the molecular mechanisms by which this occurs and physiological consequences are largely limited. In the current study, we show the participation of specific histone methyl transferase mediated dimethylation of histone-3 at lysine 4 in neonatal one or more brain regions. The results suggest that postnatal ethanol-induces robust apoptotic neurodegeneration as indicated by enhanced active caspase-3 immunoreactivity as well as electron microscope ultra structural features in hippocampus, cortex and cerebellum. These conditions resulted in enhanced expression of H3K9 specific histone methyl transferase (G9a/ b) mRNA and protein in a dose and time dependent manner. This is followed by enhanced dimethylation of H3K9 in hippocampus, cortex and cerebellum, although dual immunofluorescence histochemistry reveals that active caspase-3 positive neurons show diminishing immunoreactivity against H3K9me2. The results collectively suggest that developmental ethanol not only induces neurodegeneration but also enhances H3K9 dimethylation through histone methyl transferase, G9a/b. The current finding highlights the histone methylation mediated epigenetic modification as a valuable target in the therapy for fetal alcohol spectrum disorders

This review critically examines progress in understanding the link between Alzheimer's disease (AD) molecular pathogenesis and behavior, with an emphasis on the impact of amyloid-beta. We present the argument that the AD research field requires more multifaceted analyses into the impacts of Alzheimer's pathogenesis which combine simultaneous molecular-, circuit-, and behavior-level approaches. Supporting this argument is a review of particular research utilizing similar, 'systems-level' methods in mouse models of AD. Related to this, a critique of common physiological and behavioral models is made-highlighting the likely usefulness of more refined and specific tools in understanding the relationship between candidate molecular pathologies and behavioral dysfunction. Finally, we propose challenges for future research which, if met, may greatly extend our current understanding of how AD molecular pathology impacts neural network function and behavior and possibly may lead to refinements in disease therapeutics

The unique vulnerability of the olfactory system to Alzheimer's disease (AD) provides a quintessential translational tool for understanding mechanisms of synaptic dysfunction and pathological progression in the disease. Using the Tg2576 mouse model of beta-amyloidosis, we show that aberrant, hyperactive olfactory network activity begins early in life, before detectable behavioral impairments or comparable hippocampal dysfunction and at a time when amyloid-beta (Abeta) deposition is restricted to the olfactory bulb (OB). Hyperactive odor-evoked activity in the piriform cortex (PCX) and increased OB-PCX functional connectivity emerged at a time coinciding with olfactory behavior impairments. This hyperactive activity persisted until later in life when the network converted to a hyporesponsive state. This conversion was Abeta-dependent, because liver-X receptor agonist treatment to promote Abeta degradation rescued the hyporesponsive state and olfactory behavior. These data lend evidence to a novel working model of olfactory dysfunction in AD and, complimentary to other recent works, suggest that disease-relevant network dysfunction is highly dynamic and region specific, yet with lasting effects on cognition and behavior

The extensive autophagic-lysosomal pathology in Alzheimer disease (AD) brain has revealed a major defect: in the proteolytic clearance of autophagy substrates. Autophagy failure contributes on several levels to AD pathogenesis and has become an important therapeutic target for AD and other neurodegenerative diseases. We recently observed broad therapeutic effects of stimulating autophagic-lysosomal proteolysis in the TgCRND8 mouse model of AD that exhibits defective proteolytic clearance of autophagic substrates, robust intralysosomal amyloid-beta peptide (Abeta) accumulation, extracellular beta-amyloid deposition and cognitive deficits. By genetically deleting the lysosomal cysteine protease inhibitor, cystatin B (CstB), to selectively restore depressed cathepsin activities, we substantially cleared Abeta, ubiquitinated proteins and other autophagic substrates from autolysosomes/lysosomes and rescued autophagic-lysosomal pathology, as well as reduced total Abeta40/42 levels and extracellular amyloid deposition, highlighting the underappreciated importance of the lysosomal system for Abeta clearance. Most importantly, lysosomal remediation prevented the marked learning and memory deficits in TgCRND8 mice. Our findings underscore the pathogenic significance of autophagic-lysosomal dysfunction in AD and demonstrate the value of reversing this dysfunction as an innovative therapeautic strategy for AD