The menopausal mouse: a new neural paradigm of a distressing human condition

Nanoparticle-Based and Bioengineered Probes and Sensors to Detect Physiological and Pathological Biomarkers in Neural Cells

Nanotechnology, a rapidly evolving field, provides simple and practical tools to investigate the nervous system in health and disease. Among these tools are nanoparticle-based probes and sensors that detect biochemical and physiological properties of neurons and glia, and generate signals proportionate to physical, chemical, and/or electrical changes in these cells. In this context, quantum dots (QDs), carbon-based structures (C-dots, grapheme, and nanodiamonds) and gold nanoparticles are the most commonly used nanostructures. They can detect and measure enzymatic activities of proteases (metalloproteinases, caspases), ions, metabolites, and other biomolecules under physiological or pathological conditions in neural cells. Here, we provide some examples of nanoparticle-based and genetically engineered probes and sensors that are used to reveal changes in protease activities and calcium ion concentrations. Although significant progress in developing these tools has been made for probing neural cells, several challenges remain. We review many common hurdles in sensor development, while highlighting certain advances. In the end, we propose some future directions and ideas for developing practical tools for neural cell investigations, based on the maxim "Measure what is measurable, and make measurable what is not so" (Galileo Galilei).

B Cell Production of Both OPG and RANKL is Significantly Increased in Aged Mice

Aging is a risk factor for osteoclastic bone loss and bone fracture. Receptor activator of NF-κB ligand (RANKL) is the key effector cytokine for osteoclastogenesis and bone resorption, and is moderated by its decoy receptor osteoprotegerin (OPG). The development of an inflammatory environment during aging leads to increased bone resorption and loss of bone mineral density (BMD). Interestingly, animal and clinical studies show that OPG is actually increased in aging but fails to fully compensate for endogenous RANKL. Osteoblast- and B-lineage cells are significant sources of physiological OPG, however osteoblast OPG production declines with age, suggesting that elevated OPG in aging may be a consequence of changes in B cell function. In this study we examined BMD and indices of trabecular bone structure during aging, and B cell production of both RANKL and OPG in young and aged mice. Our data reveal significant loss of BMD and trabecular structure with age commensurate with significantly elevated concentrations of both OPG and RANKL in aged mice, and a decline in B cell populations in aged animals. Taken together our data suggest that B cells may be responsible for the elevated concentrations of OPG during aging and are essential to counteract excessive age-associated bone resorption. Paradoxically, B cells themselves likely contribute RANKL in aging and the loss of B cells with age may further contribute to the imbalance in OPG relative to RANKL that predisposes age-associated bone loss.

A novel mouse model of Alzheimer's disease with chronic estrogen deficiency leads to glial cell activation and hypertrophy

The role of estrogens in Alzheimer's disease (AD) involving β-amyloid (Aβ) generation and plaque formation was mostly tested in ovariectomized mice with or without APP mutations. The aim of the present study was to explore the abnormalities of neural cells in a novel mouse model of AD with chronic estrogen deficiency. These chimeric mice exhibit a total FSH-R knockout (FORKO) and carry two transgenes, one expressing the β-amyloid precursor protein (APPsw, Swedish mutation) and the other expressing presenilin-1 lacking exon 9 (PS1Δ9). The most prominent changes in the cerebral cortex and hippocampus of these hypoestrogenic mice were marked hypertrophy of both cortical neurons and astrocytes and an increased number of activated microglia. There were no significant differences in the number of Aβ plaques although they appeared less compacted and larger than those in APPsw/PS1Δ9 control mice. Similar glia abnormalities were obtained in wild-type primary cortical neural cultures treated with letrozole, an aromatase inhibitor. The concordance of results from APPsw/PS1Δ9 mice with or without FSH-R deletion and those with letrozole treatment in vitro (with and without Aβ treatment) of primary cortical/hippocampal cultures suggests the usefulness of these models to explore molecular mechanisms involved in microglia and astrocyte activation in hypoestrogenic states in the central nervous system.

Impairments of heat shock protein expression and MAPK translocation in the central nervous system of follitropin receptor knockout mice

The central nervous system is exposed to the chronic oxidative stress during aging when the endogenous defence weakens and the load of reactive oxygen species enhances. Sex hormones and heat shock proteins (Hsps) participate in these responses to stress. Their regulation is disturbed in aging. We assessed the expression of Hsps in hippocampus and cortex of follitropin receptor knockout (FORKO) mice, known to exhibit gender and age-dependent imbalance in sex steroids and gonadotropins. These imbalances could contribute to an impaired regulation of Hsps thereby increasing the risk of developing neurodegenerative disorders. Our study shows that, in the hippocampus the expression of Hsp70 and Hsp25 was reduced in 20-month-old FORKO mice. However, in the cortex both Hsps were significantly down regulated only in elderly females. There is a well-established co-regulation between Hsps and mitogen-activated protein kinases (MAPKs). Significant, gender-specific impairments in the translocation of phosphorylated ERK and JNK were found in the CNS structures in aged FORKO mice. Our results suggest that hormonal imbalances lead to a disturbed subcellular distribution of activated MAPKs which contribute to the impairments of signal transduction networks maintaining normal physiological functions in the cortex and hippocampus that are associated with neurodegenerative changes in aging.

Progesterone's effects to reduce anxiety behavior of aged mice do not require actions via intracellular progestin receptors

RATIONALE

Aging is associated with reduced secretion of, and down-regulation of receptors for, progesterone (P); yet, P's effects when administered to younger and older animals have not been systematically investigated. Some of P's antianxiety effects may be due to its conversion to 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP) and its subsequent actions as a positive modulator at GABAA receptor complexes (GBRs).

OBJECTIVES

We investigated whether P administration can decrease anxiety behavior of progestin receptor (PR) knockout (PRKO) or wild-type control mice.

METHODS

P (10 mg/kg) or vehicle (propylene glycol) were administered subcutaneously to intact, female or male wild-type or PRKO mice that were either 9-12 or 18-24 months of age. Behavior in tasks that assess spontaneous activity (activity monitor and roto-rod), free exploration of a novel environment (open field, elevated plus maze, and elevated zero maze), and conflict behavior (mirror chamber, dark-light transition, and punished drinking) were examined 1 h after injection.

RESULTS

P significantly decreased anxiety behavior of both PRKO and wild-type mice. P did not alter motor behavior but increased central entries in the open field, time in the open quadrants of the elevated zero maze, time in the mirrored chamber, time in the light compartment of the dark-light transition, and punished drinking in young and old mice. P-administered mice had higher levels of hippocampal 3alpha,5alpha-THP and GABA-stimulated chloride flux than did vehicle-administered PRKO or wild-type mice.

CONCLUSIONS

The effects of P to decrease anxiety behavior of younger and older mice do not require classic PRs and may involve actions of 3alpha,5alpha-THP at GBRs.

Ovarian aging and menopause: current theories, hypotheses, and research models

Aging of the reproductive system has been studied in numerous vertebrate species. Although there are wide variations in reproductive strategies and hormone cycle components, many of the fundamental changes that occur during aging are similar. Evolutionary hypotheses attempt to explain why menopause occurs, whereas cellular hypotheses attempt to explain how it occurs. It is commonly believed that a disruption in the hypothalamic-pituitary-gonadal axis is responsible for the onset of menopause. Data exist to demonstrate that the first signs of menopause occur at the level of the brain or the ovary. Thus, finding an appropriate and representative animal model is especially important for the advancement of menopause research. In primates, there is a gradual decline in the function of the hypothalamic-pituitary-gonadal (HPG) axis ultimately resulting in irregularities in menstrual cycles and increasingly sporadic incidence of ovulation. Rodents also exhibit a progressive deterioration in HPG axis function; however, they also experience a period of constant estrus accompanied by intermittent ovulations, reduced progesterone levels, and elevated circulating estradiol levels. It is remarkable to observe that females of other classes also demonstrate deterioration in HPG axis function and ovarian failure. Comparisons of aging in various taxa provide insight into fundamental biological mechanisms of aging that could underlie reproductive decline.

Influence of the post-ovariectomy time frame on the experimental anxiety and the behavioural actions of some anxiolytic agents

This study analyzes the long-term effects of ovariectomy on the basal experimental anxiety of rats and the influence of this condition on the anxiolytic properties of diazepam and the 5-HT(1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT). Rats ovariectomized 3, 6 and 12 weeks previously, were tested in the burying behaviour paradigm and in an automatic activity counter. The highest values of time spent burying were observed in the 12-week group. In general, the 12-week group was more responsive to diazepam than the 3-week group, while 8-OH-DPAT showed similar effects on time spent burying, independently of how long ago the ovariectomy was done. Detection of anxiogenic-like behaviours by the shock-probe burying test in rats after chronic absence of gonadal hormones could help in the understanding of mood changes associated with human menopause.

What have we learned about gonadotropin function from gonadotropin subunit and receptor knockout mice?

A number of biochemical and physiological studies elucidated the roles of pituitary and placental glycoprotein hormones. Advances in the past two decades in manipulating the mouse genome by random or site-specific mutagenesis have heralded a new dimension to our understanding of the biology of gonadotropins. It is now possible to model many human reproductive disorders involving gonadotropins/gonadotropin-signaling in the mouse. Mutant mice selectively lacking either FSH or LH or their cognate receptors have been generated. The gonadotropin ligand and the corresponding receptor knockout mice mostly phenocopy each other. Analyses with these genetic models confirmed earlier physiological studies; in addition they also revealed novel roles for gonadotropins previously unrecognized. While FSH action seems dispensable for male but not female fertility, absence of LH causes infertility in both the sexes. While Sertoli cell number and germ cell carrying capacity of the Sertoli cells in compromised in FSH mutants, both somatic and germ cell lineages are affected in the LH mutants resulting in complete male infertility. FSH mutant females demonstrate a preantral stage block in folliculogenesis and FSH alone is not sufficient to promote full folliculogenesis in the absence of LH. Pre-ovulatory stage follicles do not form and most of the follicles undergo apoptosis in the absence of LH. Many extra-gonadal phenotypes have been described for the receptor knockout mice and whether these bear any resemblances to those in patients with similar inactivating mutations in the receptors for FSH and LH remains an open question. Thus the in vivo models will continue to have a significant impact in understanding gonadotropin physiology and pathophysiology and serve as novel genetic tools to study signaling mechanisms in the gonads.

Perspectives on reproductive senescence and biological aging: studies in genetically altered follitropin receptor knockout [FORKO] mice

Increased life expectancy leads to increased age-associated health issues in both sexes. For menopausal women the most important of these appear to result from the severe estrogen deficiency caused by ovarian dysfunction. The consequences among others include hot flashes, osteoporosis, obesity, impaired memory, higher incidence of Alzheimer's disease and cardiovascular disease. Ovarian function and steroidogenesis are influenced by pituitary gonadotropins, including follicle-stimulating hormone (FSH), whose actions are mediated through ovarian receptors. This article highlights our recent data pertinent to aging as derived from a novel genetically modified animal model [the FORKO mouse (FOllitropin Receptor KnockOut) lacking the FSH receptor. FORKO female mice experience a chronic depletion of estrogen (E2) from early development, and have phenotypes similar to aging women, with ovarian failure, obesity, skeletal changes, and ovarian tumors. A variety of findings support the conclusion that E2 deficiency in FORKO mice is responsible for their neural impairments associated with glial cell hypertrophy, region-specific brain cells loss, and abnormal behavior. Findings from mice with FSH receptor haploinsufficiency mice ('menopausal mice') are also shedding light on the molecular basis of menopausal conditions that include degeneration of the hippocampus. Many phenotypes noted in the null condition also occur in +/- females but in an age related manner. Thus, the FORKO mouse becomes an excellent model to investigate mechanisms underlying age-related changes especially when these events are accelerated, as in menopausal women. Opportunities abound to assess the potential benefits/adverse effects of hormone replacement regimen on various targets.