Sex-Dependent Effects of Chronic Circadian Disruption in AßPP/PS1 Mice.

BACKGROUND: Chronic disruption of the circadian timing system, often reflected as a loss of restful sleep, also includes myriad other pathophysiological effects. OBJECTIVE: The current study examined how chronic circadian disruption (CD) could contribute to pathology and rate of progression in the AßPP/PS1 mouse model of Alzheimer's disease (AD). METHODS: A chronic CD was imposed until animals reached 6 or 12 months of age in AßPP/PS1 and C57BL/6J control mice. Home cage activity was monitored for a period of 3-4 weeks prior to the endpoint along with a single timepoint measure of glucose sensitivity. To assess long term effects of CD on the AD phenotype, animals were re-entrained to a no disruption (ND) schedule just prior to the endpoint, after which a Morris water maze (MWM) was used to assess spatial learning and memory. RESULTS: Dampening of nighttime activity levels occurred in disrupted animals, and female animals demonstrated a greater adaptability to CD. Diminished arginine vasopressin (AVP) and vasoactive intestinal peptide (VIP) levels in the suprachiasmatic nucleus (SCN) of 12-month male AßPP/PS1 exposed to the CD paradigm were observed, potentially accounting for the diminished re-entrainment response. Similarly, CD worsened performance in the MWM in 12-month male AßPP/PS1 animals, whereas no effect was seen in females. CONCLUSIONS: Collectively, these findings show that exposure to chronic CD impairs circadian behavioral patterns and cognitive phenotypes of AßPP/PS1 mouse model in a sex-dependent manner.

Assessing Sex-Specific Circadian, Metabolic, and Cognitive Phenotypes in the AßPP/PS1 and APPNL-F/NL-F Models of Alzheimer's Disease.

BACKGROUND: Circadian disruption has long been recognized as a symptom of Alzheimer's disease (AD); however, emerging data suggests that circadian dysfunction occurs early on in disease development, potentially preceding any noticeable cognitive deficits. OBJECTIVE: This study compares the onset of AD in male and female wild type (C57BL6/J), transgenic (AßPP/PS1), and knock-in (APPNL-F/NL-F) AD mouse models from the period of plaque initiation (6 months) through 12 months. METHODS: Rhythmic daily activity patterns, glucose sensitivity, cognitive function (Morris water maze, MWM), and AD pathology (plaques formation) were assessed. A comparison was made across sexes. RESULTS: Sex-dependent hyperactivity in AßPP/PS1 mice was observed. In comparison to C57BL/6J animals, 6-month-old male AßPP/PS1 demonstrated nighttime hyperactivity, as did 12-month-old females. Female AßPP/PS1 animals performed significantly worse on a MWM task than AßPP/PS1 males at 12 months and trended toward increased plaque pathology. APPNL-F/NL-F 12-month-old males performed significantly worse on the MWM task compared to 12-month-old females. Significantly greater plaque pathology occurred in AßPP/PS1 animals as compared to APPNL-F/NL-F animals. Female AßPP/PS1 animals performed significantly worse than APPNL-F/NL-F animals in spatial learning and memory tasks, though this was reversed in males. CONCLUSION: Taken together, this study provides novel insights into baseline sex differences, as well as characterizes baseline diurnal activity variations, in the AßPP/PS1 and APPNL-F/NL-F AD mouse models.

Riluzole attenuates glutamatergic tone and cognitive decline in AßPP/PS1 mice.

We have previously demonstrated hippocampal hyperglutamatergic signaling occurs prior to plaque accumulation in AßPP/PS1 mice. Here, we evaluate 2-Amino-6-(trifluoromethoxy) benzothiazole (riluzole) as an early intervention strategy for Alzheimer's disease (AD), aimed at restoring glutamate neurotransmission prior to substantial Beta amyloid (Aß) plaque accumulation and cognitive decline. Male AßPP/PS1 mice, a model of progressive cerebral amyloidosis, were treated with riluzole from 2-6 months of age. Morris water maze, in vivo electrochemistry, and immunofluorescence were performed to assess cognition, glutamatergic neurotransmission, and pathology, respectively, at 12 months. Four months of prodromal riluzole treatment in AßPP/PS1 mice resulted in long-lasting procognitive effects and attenuated glutamatergic tone that was observed six months after discontinuing riluzole treatment. Riluzole-treated AßPP/PS1 mice had significant improvement in long-term memory compared to vehicle-treated AßPP/PS1 mice that was similar to normal aging C57BL/6J control mice. Furthermore, basal glutamate concentration and evoked-glutamate release levels, which were elevated in vehicle-treated AßPP/PS1 mice, were restored to levels observed in age-matched C57BL/6J mice in AßPP/PS1 mice receiving prodromal riluzole treatment. Aß plaque accumulation was not altered with riluzole treatment. This study supports that interventions targeting the glutamatergic system during the early stages of AD progression have long-term effects on disease outcome, and importantly may prevent cognitive decline. Our observations provide preclinical support for targeting glutamate neurotransmission in patients at risk for developing AD. Read the Editorial Highlight for this article on page 399.

LY379268 Does Not Have Long-Term Procognitive Effects nor Attenuate Glutamatergic Signaling in AßPP/PS1 Mice.

Chronically elevated basal glutamate levels are hypothesized to attenuate detection of physiological signals thereby inhibiting memory formation and retrieval, while inducing excitotoxicity-mediated neurodegeneration observed in Alzheimer's disease (AD). However, current medication targeting the glutamatergic system, such as memantine, shows limited efficacy and is unable to decelerate disease progression, possibly because it modulates postsynaptic N-methyl-D-aspartate receptors rather than glutamate release or clearance. To determine if decreasing presynaptic glutamate release leads to long-term procognitive effects, we treated AßPP/PS1 mice with LY379268 (3.0 mg/kg; i.p.), a metabotropic glutamate receptor (mGluR)2/3 agonist from 2-6 months of age when elevated glutamate levels are first observed but cognition is unaffected. C57BL/6J genetic background control mice and another cohort of AßPP/PS1 mice received normal saline (i.p.) as vehicle controls. After 6 months off treatment, mice receiving LY379268 did not show long-term improvement as assessed by the Morris water maze (MWM) spatial learning and memory paradigm. Following MWM, mice were isoflurane anesthetized and a glutamate selective microelectrode was used to measure in vivo basal and stimulus-evoked glutamate release and clearance independently from the dentate, CA3, and CA1 hippocampal subregions. Immunohistochemistry was used to measure hippocampal astrogliosis and plaque pathology. Similar to previous studies, we observed elevated basal glutamate, stimulus evoked glutamate release, and astrogliosis in AßPP/PS1 vehicle mice versus C57BL/6J mice. Treatment with LY379268 did not attenuate these responses nor diminish plaque pathology. The current study builds upon previous research demonstrating hyperglutamatergic hippocampal signaling in AßPP/PS1 mice; however, long-term therapeutic efficacy of LY379268 in AßPP/PS1 was not observed.