A toolbox for the longitudinal assessment of healthspan in aging mice.

The number of people aged over 65 is expected to double in the next 30 years. For many, living longer will mean spending more years with the burdens of chronic diseases such as Alzheimer's disease, cardiovascular disease, and diabetes. Although researchers have made rapid progress in developing geroprotective interventions that target mechanisms of aging and delay or prevent the onset of multiple concurrent age-related diseases, a lack of standardized techniques to assess healthspan in preclinical murine studies has resulted in reduced reproducibility and slow progress. To overcome this, major centers in Europe and the United States skilled in healthspan analysis came together to agree on a toolbox of techniques that can be used to consistently assess the healthspan of mice. Here, we describe the agreed toolbox, which contains protocols for echocardiography, novel object recognition, grip strength, rotarod, glucose tolerance test (GTT) and insulin tolerance test (ITT), body composition, and energy expenditure. The protocols can be performed longitudinally in the same mouse over a period of 4-6 weeks to test how candidate geroprotectors affect cardiac, cognitive, neuromuscular, and metabolic health.

A paternal methyl donor-rich diet altered cognitive and neural functions in offspring mice.

Dietary intake of methyl donors, such as folic acid and methionine, shows considerable intra-individual variation in human populations. While it is recognized that maternal departures from the optimum of dietary methyl donor intake can increase the risk for mental health issues and neurological disorders in offspring, it has not been explored whether paternal dietary methyl donor intake influences behavioral and cognitive functions in the next generation. Here, we report that elevated paternal dietary methyl donor intake in a mouse model, transiently applied prior to mating, resulted in offspring animals (methyl donor-rich diet (MD) F1 mice) with deficits in hippocampus-dependent learning and memory, impaired hippocampal synaptic plasticity and reduced hippocampal theta oscillations. Gene expression analyses revealed altered expression of the methionine adenosyltransferase Mat2a and BK channel subunit Kcnmb2, which was associated with changes in Kcnmb2 promoter methylation in MD F1 mice. Hippocampal overexpression of Kcnmb2 in MD F1 mice ameliorated altered spatial learning and memory, supporting a role of this BK channel subunit in the MD F1 behavioral phenotype. Behavioral and gene expression changes did not extend into the F2 offspring generation. Together, our data indicate that paternal dietary factors influence cognitive and neural functions in the offspring generation.

Gestational immune activation and Tsc2 haploinsufficiency cooperate to disrupt fetal survival and may perturb social behavior in adult mice.

Approximately 40-50% of individuals affected by tuberous sclerosis (TSC) develop autism spectrum disorders (ASDs). One possible explanation for this partial penetrance is an interaction between TSC gene mutations and other risk factors such as gestational immune activation. In this study, we report the interactive effects of these two ASD risk factors in a mouse model of TSC. Combined, but not single, exposure had adverse effects on intrauterine survival. Additionally, provisional results suggest that these factors synergize to disrupt social approach behavior in adult mice. Moreover, studies in human populations are consistent with an interaction between high seasonal flu activity in late gestation and TSC mutations in ASD. Taken together, our studies raise the possibility of a gene × environment interaction between heterozygous TSC gene mutations and gestational immune activation in the pathogenesis of TSC-related ASD.

Neuronal glucose transporter isoform 3 deficient mice demonstrate features of autism spectrum disorders.

Neuronal glucose transporter (GLUT) isoform 3 deficiency in null heterozygous mice led to abnormal spatial learning and working memory but normal acquisition and retrieval during contextual conditioning, abnormal cognitive flexibility with intact gross motor ability, electroencephalographic seizures, perturbed social behavior with reduced vocalization and stereotypies at low frequency. This phenotypic expression is unique as it combines the neurobehavioral with the epileptiform characteristics of autism spectrum disorders. This clinical presentation occurred despite metabolic adaptations consisting of an increase in microvascular/glial GLUT1, neuronal GLUT8 and monocarboxylate transporter isoform 2 concentrations, with minimal to no change in brain glucose uptake but an increase in lactate uptake. Neuron-specific glucose deficiency has a negative impact on neurodevelopment interfering with functional competence. This is the first description of GLUT3 deficiency that forms a possible novel genetic mechanism for pervasive developmental disorders, such as the neuropsychiatric autism spectrum disorders, requiring further investigation in humans.

From mTOR to cognition: molecular and cellular mechanisms of cognitive impairments in tuberous sclerosis.

BACKGROUND: Tuberous sclerosis (TSC) is a multi-system disorder caused by heterozygous mutations in the TSC1 or TSC2 gene and is often associated with neuropsychiatric symptoms, including intellectual disability, specific neuropsychological deficits, autism, other behavioural disorders and epilepsy. METHOD: Here, we review evidence from animal models of TSC for the role of specific molecular and cellular processes in the pathogenesis of cognitive, developmental and epilepsy-related manifestations seen in the disorder. RESULTS: Recent evidence shows that, in animal models, disinhibited mTOR (mammalian target of rapamycin) signalling substantially contributes to neuropsychiatric phenotypes, including cognitive deficits and seizures. We discuss potential pathogenetic mechanisms involved in the cognitive phenotypes of TSC and present implications regarding mTOR inhibitor-based treatments for TSC-related neuropsychiatric features. CONCLUSIONS: Results suggest that reversing the underlying molecular deficits of TSC with rapamycin or other mTOR inhibitors could result in clinically significant improvements of cognitive function and neurological symptoms, even if treatments are started in adulthood.

Paradoxical effects of learning the Morris water maze on adult hippocampal neurogenesis in mice may be explained by a combination of stress and physical activity.

Studies in rats that assessed the relation of hippocampus-dependent learning and adult hippocampal neurogenesis suggested a direct regulatory effect of learning on neurogenesis, whereas a similar study in mice had not found such causal link. We here report a substantial decrease of BrdU-positive cells and other measures of adult hippocampal neurogenesis in mice trained in the hidden (HID) or cued version (VIS) of the Morris water maze as compared to untrained animals (CTR). Particularly, cells on advanced stages of neuronal development contributed to this decrease, whereas earlier progenitors (type 2 cells) were not diminished in HID, but were diminished in VIS as compared to CTR. The differential regulation of type 2 cells in HID and VIS may have been caused by a different degree of physical activity, given that a time-yoked control group did not differ from HID, and type 2 cells reportedly constitute the proliferative dentate gyrus population that primarily responds to physical activity. The decrease of hippocampal neurogenesis by water maze training was reversible by pre-exposing animals to the water maze prior to training, suggesting that stress associated with training may have caused the acute downregulation of adult neurogenesis. We propose that in mice the Morris water maze does not provide a pure enough learning stimulus to study the presumed effects of 'learning' on adult neurogenesis. In addition, however, our data show that physical activity that is intricately linked to many cognitive tasks in rodents might play an important role in explaining effects of learning on cellular hippocampal plasticity.