Sarah M. Neuner

TRPC3 channels critically regulate hippocampal excitability and contextual fear memory

Memory formation requires de novo protein synthesis, and memory disorders may result from misregulated synthesis of critical proteins that remain largely unidentified. Plasma membrane ion channels and receptors are likely candidates given their role in regulating neuron excitability, a candidate memory mechanism. Here we conduct targeted molecular monitoring and quantitation of hippocampal plasma membrane proteins from mice with intact or impaired contextual fear memory to identify putative candidates. Here we report contextual fear memory deficits correspond to increased Trpc3 gene and protein expression, and demonstrate TRPC3 regulates hippocampal neuron excitability associated with memory function. These data provide a mechanistic explanation for enhanced contextual fear memory reported herein following knockdown of TRPC3 in hippocampus. Collectively, TRPC3 modulates memory and may be a feasible target to enhance memory and treat memory disorders.

Hippocampal proteomics defines pathways associated with memory decline and resilience in normal aging and Alzheimer's disease mouse models

GRAPHICAL ABSTRACT Figure. No caption available. HIGHLIGHTSProteomics detects 36 hippocampal proteins associated with AD and normal aging memory deficits.Pathway analysis highlights HDAC4 as global regulator of memory deficits.103 proteins differ specifically in AD mice with intact vs impaired memory.Pathway analysis indicates disease‐specific involvement of REST and Gi signaling.Publically available proteomics resource for hypothesis generation and testing. ABSTRACT Alzheimers disease (AD), the most common form of dementia in the elderly, has no cure. Thus, the identification of key molecular mediators of cognitive decline in AD remains a top priority. As aging is the most significant risk factor for AD, the goal of this study was to identify altered proteins and pathways associated with the development of normal aging and AD memory deficits, and identify unique proteins and pathways that may contribute to AD‐specific symptoms. We used contextual fear conditioning to diagnose 8‐month‐old 5XFAD and non‐transgenic (Ntg) mice as having either intact or impaired memory, followed by liquid chromatography‐tandem mass spectrometry (LC–MS/MS) to quantify hippocampal membrane proteins across groups. Subsequent analysis detected 113 proteins differentially expressed relative to memory status (intact vs impaired) in Ntg mice and 103 proteins in 5XFAD mice. Thirty‐six proteins, including several involved in neuronal excitability and synaptic plasticity (e.g., GRIA1, GRM3, and SYN1), were altered in both normal aging and AD. Pathway analysis highlighted HDAC4 as a regulator of observed protein changes in both genotypes and identified the REST epigenetic regulatory pathway and Gi intracellular signaling as AD‐specific pathways involved in regulating the onset of memory deficits. Comparing the hippocampal membrane proteome of Ntg versus AD, regardless of cognitive status, identified 138 differentially expressed proteins, including confirmatory proteins APOE and CLU. Overall, we provide a novel list of putative targets and pathways with therapeutic potential, including a set of proteins associated with cognitive status in normal aging mice or gene mutations that cause AD.

Systems genetics identifies Hp1bp3 as a novel modulator of cognitive aging

An individuals genetic makeup plays an important role in determining susceptibility to cognitive aging. Identifying the specific genes that contribute to cognitive aging may aid in early diagnosis of at-risk patients, as well as identify novel therapeutics targets to treat or prevent development of symptoms. Challenges to identifying these specific genes in human studies include complex genetics, difficulty in controlling environmental factors, and limited access to human brain tissue. Here, we identify Hp1bp3 as a novel modulator of cognitive aging using a genetically diverse population of mice and confirm that HP1BP3 protein levels are significantly reduced in the hippocampi of cognitively impaired elderly humans relative to cognitively intact controls. Deletion of functional Hp1bp3 in mice recapitulates memory deficits characteristic of aged impaired mice and humans, further supporting the idea that Hp1bp3 and associated molecular networks are modulators of cognitive aging. Overall, our results suggest Hp1bp3 may serve as a potential target against cognitive aging and demonstrate the utility of genetically diverse animal models for the study of complex human disease.

HP1BP3 expression determines maternal behavior and offspring survival.

Maternal care is an indispensable behavioral component necessary for survival and reproductive success in mammals, and postpartum maternal behavior is mediated by an incompletely understood complex interplay of signals including effects of epigenetic regulation. We approached this issue using our recently established mice with targeted deletion of heterochromatin protein 1 binding protein 3 (HP1BP3), which we found to be a novel epigenetic repressor with critical roles in postnatal growth. Here, we report a dramatic reduction in the survival of pups born to Hp1bp3−/− deficient mouse dams, which could be rescued by co‐fostering with wild‐type dams. Hp1bp3−/− females failed to retrieve both their own pups and foster pups in a pup retrieval test, and showed reduced anxiety‐like behavior in the open‐field and elevated‐plus‐maze tests. In contrast, Hp1bp3−/− females showed no deficits in behaviors often associated with impaired maternal care, including social behavior, depression, motor coordination and olfactory capability; and maintained unchanged anxiety‐associated hallmarks such as cholinergic status and brain miRNA profiles. Collectively, our results suggest a novel role for HP1BP3 in regulating maternal and anxiety‐related behavior in mice and call for exploring ways to manipulate this epigenetic process.

Multi-scale study of normal aging predicts novel late-onset Alzheimer's disease risk variants

Background Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by severe memory impairment and accumulation of neuropathological amyloid plaques and tau tangles. By contrast, ‘normal’ age-associated cognitive decline is less severe and generally occurs in the absence of neuropathology. Many believe agingand AD-related memory impairments result from separate etiologies, but this distinction is not entirely consistent with emerging evidence that both are linked to hippocampal dysfunction. As aging is the most significant risk factor for late-onset AD (LOAD), we hypothesize that memory deficits in both ‘normal’ aging and AD are driven in part by some common underlying mechanisms, which are exacerbated in AD by disease-specific insults such as neurodegeneration, neuroinflammation, and neuropathologies. In addition, heritability estimates suggest a strong genetic component (50-80%) in both conditions [1,2]. Thus, elucidating genetic correlates of memory decline in ‘normal’ aging may identify risk factors that influence susceptibility to LOAD.

IDENTIFYING PRESYMPTOMATIC GENE SIGNATURES PREDICTIVE OF RESILIENCE TO ALZHEIMER’S

Background: New genetic and genomic resources are identifying genetic risk factors for late-onset Alzheimer’s disease (LOAD) and characterizing this common dementia at the molecular level. Experimental studies in model organisms can validate these associations and elucidate the links between specific genetic factors and transcriptomic signatures. However, most transgenic animal models are based on rare, early-onset AD genes which may not reflect the full transcriptomic signatures and complete neuropathology of LOAD. Animal models based on LOAD-associated genes are necessary to connect common genetic variation with LOAD transcriptomes, thereby providing novel insights into basic biological mechanisms underlying the disease. Methods: We performed RNA-seq on whole brain samples from a panel of sixmonth-old female mice, each carrying one of the following mutations: homozygous deletions of APOE and CLU; hemizygous deletions of BIN1 and CD2AP; and a transgenic APOEe4. We also included a transgenic APP/PS1 model for comparison to early-onset variants. Weighted gene co-expression network analysis (WGCNA) was used to identify modules of correlated genes and each module was tested for differential expression by strain. We then compared mouse modules with human postmortem brain modules from the Accelerating Medicine’s Partnership for AD (AMP-AD) to determine the AD relevance of risk genes. Results: Mouse modules were significantly enriched in multiple AD-related pathways, including immune response, inflammation, lipid-processing, endocytosis and synaptic-cell-functioning. Various modules were significantly associated with APOE, APOEe4, CLU, andAPP/PS1mouse models.APOE, APOEe4, and APP/PS1 driven modules overlapped with AMP-AD inflammation and microglial modules; CLU driven modules overlapped with synaptic modules; and APP/PS1 modules separately overlapped with lipid-processing and metabolism modules. Furthermore, we found that immune/microglia related genes are up-regulated and synaptic genes are down-regulated in early-onset carriers. Conclusions: This study of LOAD mouse models provides a basis to dissect the role of AD risk genes in relevant AD pathologies. We determined that different genetic perturbations affect different molecular mechanism underlying AD, and mapped specific effects to each risk gene. Our approach provides a platform for further exploration into the causes and progression of AD by assessing animal models at different ages and/or with different combinations of LOAD risk variants.

HYPOTHALAMIC ENERGY BALANCE DYSFUNCTION IN THE ETIOLOGY OF ALZHEIMER’S DISEASE

Background: For a patient diagnosed with Alzheimer’s disease, there exist no treatments to prevent, delay, or halt disease progression. Memory impairment and cognitive decline are hallmarks of AD, thus current research has focused predominantly on CNS regions relevant to learning and memory, such as the hippocampus. However, one of the most consistently reported non-cognitive phenotypes in AD patients is weight loss, which may precede the onset of dementia symptoms by as much as 17 years, raising the possibility that dysfunction in CNS regions regulating energy balance and metabolism, such as the hypothalamus, may represent one of the earliest causative changes associated with AD. We used our novel, genetically diverse AD mouse panel (AD-BXDs), which combines high-risk familial AD mutations on a well-established background of genetic diversity, to investigate the complex interactions between genetic background, age, and energy homeostasis. Methods: To determine the relationship between weight and the onset of cognitive decline, we longitudinally measured body weight and working memory in 25 strains of female AD-BXDs and their nontransgenic littermate controls (Ntg-BXD) and 17 strains of male Ntg/ADBXDs at 2, 4, 6, and 14 months. Working memory was assessed using the Y-maze spontaneous alternation task; the age at which performance dropped below 50% was designated as the age of onset (AAO) for cognitive decline. Results: At 2 months of age, Ntg/ AD-BXDs exhibit similar body weights, but by 6 months of age, AD-BXD mice weigh significantly less than Ntg-BXD. Notably, this phenotype emerged 3 months prior to the average AAO for memory decline across AD-BXDs. We further found that in ADBXDs (but not Ntg-BXDs), body weight at 6 months was significantly correlated with long-term memory performance at 14 months, suggesting this relationship is specific to AD and not a general feature of aging. Conclusions: The hypothalamus is understudied in the context of AD, despite an abundance of evidence pointing to an early role for hypothalamic dysfunction in disease onset and severity. Our results further support this hypothesis. Future studies seek to identify novel hypothalamic biomarkers and therapeutic targets to treat AD in its very earliest stages, prior to cognitive decline.

Systems genetics identifies modifiers of Alzheimer's disease risk and resilience

Identifying genes that modify symptoms of Alzheimer’s disease (AD) will provide novel therapeutic strategies to prevent, cure or delay AD. To discover genetic modifiers of AD, we combined a mouse model of AD with a genetically diverse reference panel to generate F1 mice harboring identical ‘high-risk’ human AD mutations but which differ across the remainder of their genome. We first show that genetic variation profoundly modifies the impact of causal human AD mutations and validate this panel as an AD model by demonstrating a high degree of phenotypic, transcriptomic, and genetic overlap with human AD. Genetic mapping was used to identify candidate modifiers of cognitive deficits and amyloid pathology, and viral-mediated knockdown was used to functionally validate Trpc3 as a modifier of AD. Overall, work here introduces a ‘humanized’ mouse population as an innovative and reproducible resource for the study of AD and identifies Trpc3 as a novel therapeutic target. Highlights New transgenic mouse population enables mapping of AD risk and resilience factors Transcriptomic and phenotypic profiles in diverse AD mice parallel those in humans Apoe genotype and expression correlate with cognitive symptoms in mice Trpc3 is a novel target to reduce amyloid load and cognitive symptoms in AD

Corrigendum to “TRPC3 channels critically regulate hippocampal excitability and contextual fear memory” Behav. Brain Res. 281(March) 2015, 69–77

a Dept. of Anatomy and Neurobiology, The University of Tennessee Health Science Center, Memphis, TN, United States b Dept. of Biotechnology and Bioengineering, Medical College of Wisconsin, Milwaukee, WI, United States c Hydra Biosciences, Cambridge, MA,United States d Laboratory of Neurobiology, National Institute of Environmental Health Sciences, Research Triangle Park, NC, United States e Dept. of Physiology, The University of Tennessee Health Science Center, Memphis, TN, United States f Dept. of Pediatrics, The University of Chicago, Chicago, IL, United States g Dept. of Physiology, Medical College of Wisconsin, Milwaukee, WI, United States h Dept. of Physiology, Northwestern Fienberg School of Medicine, Chicago, IL, United States

Advances at the intersection of normal brain aging and Alzheimer’s disease

Alzheimer’s disease (AD) is a neurodegenerative disorder charcterized by severe memory impairment and the accumulation of europathological beta-amyloid plaques and tau tangles. In conrast, normal age-associated cognitive decline is less severe and enerally occurs in the absence of neuropathology (NIA Alzheimer’s isease Fact Sheet). As aging is the most significant risk factor or AD, many believe agingand AD-related memory impairments re driven by common underlying mechanisms, which are exacrbated in AD by disease-specific insults such as neuropathologies, euroinflammation, and neurodegeneration – culminating in worsned cognitive impairment [1–5]. Therefore, it is imperative that e determine to what extent normal agingand AD-related memry impairments result from similar or separate etiologies to design ffective therapies to treat memory decline in our aging population s well as to identify biomarkers to facilitate earlier diagnosis. The initial articles in this Special Issue of Behavioural Brain esearch examine the similarities and differences of mechanisms nderlying cognitive function in aging and AD. The review by ullinger and Puglielli provides an overview of age-related changes n the hippocampus at multiple levels (e.g. structural, molecular, nd functional). They discuss the increasingly evident commonlities between aging and AD, which provide ample support for he notion that a better understanding of aging biology is likely to ield therapeutic targets to prevent or delay cognitive decline in oth conditions [6]. The review by Yu and associates focuses on a pecific subset of age-related changes in the hippocampus, particlarly those that impact the critical memory-relevant transcription actor cAMP response element binding protein (CREB). Given that ownregulation of CREB is associated with decreased neuronal xcitability and impaired cognitive function in aged rodents, the uthors suggest enhancement of endogenous CREB (or downtream genes/ion channels) may provide therapeutic benefits in ging patients [7]. A CREB-centric approach has been proposed for epairing neuronal network activity, synaptic dysfunction, and cogitive deficits in AD, providing another example whereby changes