Effects of high fat diet on metabolic health vary by age of menopause onset.

Menopause accelerates metabolic dysfunction, including (pre-)diabetes, obesity and visceral adiposity. However, the effects of endocrine vs. chronological aging in this progression are poorly understood. We hypothesized that menopause, especially in the context of middle-age, would exacerbate the metabolic effects of a high fat diet. Using young-adult and middle-aged C57BL/6J female mice, we modeled diet-induced obesity via chronic administration of high fat (HF) diet vs. control diet. We modeled peri-menopause/menopause via injections of 4-vinylcyclohexene diepoxide, which accelerates ovarian failure vs. vehicle. We performed glucose tolerance tests 2.5 and 7 months after diet onset, during the peri-menopausal and menopausal phases, respectively. Peri-menopause increased the severity of glucose intolerance and weight gain in middle-aged, HF-fed mice. Menopause increased weight gain in all mice regardless of age and diet, while chronological aging drove changes in adipose tissue distribution towards more visceral vs. subcutaneous adiposity. These data are in line with clinical data showing that post-menopausal women are more susceptible to metabolic dysfunction and suggest that greater chronological age exacerbates the effects of endocrine aging (menopause). This work highlights the importance of considering both chronological and endocrine aging in studies of metabolic health.

Androgen regulation of behavioral stress responses and the hypothalamic-pituitary-adrenal axis.

Testosterone is a powerful steroid hormone that can impact the brain and behavior in various ways, including regulating behavioral and neuroendocrine (hypothalamic-pituitary-adrenal (HPA) axis) stress responses. Early in life androgens can act to alter development of brain regions associated with stress regulation, which ultimately impacts the display of stress responses later in life. Adult circulating androgens can also influence the expression of distinct genes and proteins that regulate stress responses. These changes in the brain are hypothesized to underlie the potent effects of androgens in regulating behaviors related to stress and stress-induced activation of the HPA axis. Androgens can induce alterations in these functions through direct binding to the androgen receptor (AR) or following conversion to estrogens and subsequent binding to estrogen receptors including estrogen receptor alpha (ERα), beta (ERß), and G protein-coupled estrogen receptor 1 (GPER1). In this review, we focus on the role of androgens in regulating behavioral and neuroendocrine stress responses at different stages of the lifespan and the sex hormone receptors involved in regulating these effects. We also review the specific brain regions and cell phenotypes upon which androgens are proposed to act to regulate stress responses with an emphasis on hypothalamic and extended amygdala subregions. This knowledge of androgen effects on these neural systems is critical for understanding how sex hormones regulate stress responses.

Treatment with brain specific estrogen prodrug ameliorates cognitive effects of surgical menopause in mice.

Menopause is an endocrine shift leading to increased vulnerability for cognitive impairment and dementia risk factors, in part due to loss of neuroprotective circulating estrogens. Systemic replacement of estrogen post-menopause has limitations, including risk for estrogen-sensitive cancers. A promising therapeutic approach therefore might be to deliver estrogen only to the brain. We examined whether we could enhance cognitive performance by delivering estrogen exclusively to the brain in ovariectomized mice (a surgical menopause model). We treated mice with the prodrug 10ß,17ß-dihydroxyestra-1,4-dien-3-one (DHED), which can be administered systemically but is converted to 17ß-estradiol only in the brain. Young and middle-aged C57BL/6 J mice received ovariectomy and subcutaneous implant containing vehicle or DHED and underwent cognitive testing to assess memory after 1-3.5 months of treatment. Low and medium doses of DHED did not alter metabolic status in middle-aged mice. In both age groups, DHED treatment improved spatial memory in ovariectomized mice. Additional testing in middle-aged mice showed that DHED treatment improved working and recognition memory in ovariectomized mice. These results lay the foundation for future studies determining if this intervention is as efficacious in models of dementia with comorbid risk factors.

The role of innate lymphocytes in regulating brain and cognitive function.

Mounting evidence indicates complex interaction between the immune system and the nervous system, challenging the traditional view about the immune privilege of the brain. Innate lymphoid cells (ILCs) and innate-like T cells are unique families of immune cells that functionally mirror traditional T cells but may function via antigen- and T cell antigen receptor (TCR)-independent mechanisms. Recent work indicates that various ILCs and innate-like T cell subsets are present in the brain barrier tissue, where they play important roles in regulating brain barrier integrity, brain homeostasis and cognitive function. In this review, we discuss recent advances in understanding the intricate roles for innate and innate-like lymphocytes in regulating brain and cognitive function.

Changes in Corticotropin-Releasing Factor Receptor Type 1, Co-Expression with Tyrosine Hydroxylase and Oxytocin Neurons, and Anxiety-Like Behaviors across the Postpartum Period in Mice.

INTRODUCTION: Corticotropin-releasing factor and its primary receptor (CRFR1) are critical regulators of behavioral and neuroendocrine stress responses. CRFR1 has also been associated with stress-related behavioral changes in postpartum mice. Our previous studies indicate dynamic changes in CRFR1 levels and coupling of CRFR1 with tyrosine hydroxylase (TH) and oxytocin (OT) neurons in postpartum mice. In this study, we aimed to determine the time course of these changes during the postpartum period. METHODS: Using a CRFR1-GFP reporter mouse line, we compared postpartum mice at five time points with nulliparous mice. We performed immunohistochemistry to assess changes in CRFR1 levels and changes in co-expression of TH/CRFR1-GFP and OT/CRFR1-GFP across the postpartum period. Mice were also assessed for behavioral stress responses in the open field test. RESULTS: Relative to nulliparous mice, CRFR1 levels were elevated in the anteroventral periventricular nucleus (AVPV/PeN) but were decreased in the medial preoptic area from postpartum day 1 (P1) through P28. In the paraventricular hypothalamus (PVN), there is a transient decline in CRFR1 mid-postpartum with a nadir at P7. Co-localization of CRFR1 with TH-expressing neurons was also altered with a transient decrease found in the AVPV/PeN at P7 and P14. Co-expression of CRFR1 and OT neurons of the PVN and supraoptic nucleus was dramatically altered with virtually no co-expression found in nulliparous mice, but levels increased shortly after parturition and peaked near P21. A transient decrease in open field center time was found at P7, indicating elevated anxiety-like behavior. CONCLUSION: This study revealed various changes in CRFR1 across the postpartum period, which may contribute to stress-related behavior changes in postpartum mice.

High-fat diet exacerbates cognitive decline in mouse models of Alzheimer's disease and mixed dementia in a sex-dependent manner.

BACKGROUND: Approximately 70% of Alzheimer's disease (AD) patients have co-morbid vascular contributions to cognitive impairment and dementia (VCID); this highly prevalent overlap of dementia subtypes is known as mixed dementia (MxD). AD is more prevalent in women, while VCID is slightly more prevalent in men. Sex differences in risk factors may contribute to sex differences in dementia subtypes. Unlike metabolically healthy women, diabetic women are more likely to develop VCID than diabetic men. Prediabetes is 3× more prevalent than diabetes and is linked to earlier onset of dementia in women, but not men. How prediabetes influences underlying pathology and cognitive outcomes across different dementia subtypes is unknown. To fill this gap in knowledge, we investigated the impact of diet-induced prediabetes and biological sex on cognitive function and neuropathology in mouse models of AD and MxD. METHODS: Male and female 3xTg-AD mice received a sham (AD model) or unilateral common carotid artery occlusion surgery to induce chronic cerebral hypoperfusion (MxD model). Mice were fed a control or high fat (HF; 60% fat) diet from 3 to 7 months of age. In both sexes, HF diet elicited a prediabetic phenotype (impaired glucose tolerance) and weight gain. RESULTS: In females, but not males, metabolic consequences of a HF diet were more severe in AD or MxD mice compared to WT. In both sexes, HF-fed AD or MxD mice displayed deficits in spatial memory in the Morris water maze (MWM). In females, but not males, HF-fed AD and MxD mice also displayed impaired spatial learning in the MWM. In females, but not males, AD or MxD caused deficits in activities of daily living, regardless of diet. Astrogliosis was more severe in AD and MxD females compared to males. Further, AD/MxD females had more amyloid beta plaques and hippocampal levels of insoluble amyloid beta 40 and 42 than AD/MxD males. In females, but not males, more severe glucose intolerance (prediabetes) was correlated with increased hippocampal microgliosis. CONCLUSIONS: High-fat diet had a wider array of metabolic, cognitive, and neuropathological consequences in AD and MxD females compared to males. These findings shed light on potential underlying mechanisms by which prediabetes may lead to earlier dementia onset in women.

Depletion of NK Cells Improves Cognitive Function in the Alzheimer Disease Mouse Model.

Despite mounting evidence suggesting the involvement of the immune system in regulating brain function, the specific role of immune and inflammatory cells in neurodegenerative diseases remain poorly understood. In this study, we report that depletion of NK cells, a type of innate lymphocytes, alleviates neuroinflammation, stimulates neurogenesis, and improves cognitive function in a triple-transgenic Alzheimer disease (AD) mouse model. NK cells in the brains of triple-transgenic AD mouse model (3xTg-AD) mice exhibited an enhanced proinflammatory profile. Depletion of NK cells by anti-NK1.1 Abs drastically improved cognitive function of 3xTg-AD mice. NK cell depletion did not affect amyloid ß concentrations but enhanced neurogenesis and reduced neuroinflammation. Notably, in 3xTg-AD mice depleted of NK cells, microglia demonstrated a homeostatic-like morphology, decreased proliferative response and reduced expression of neurodestructive proinflammatory cytokines. Together, our results suggest a proinflammatory role for NK cells in 3xTg-AD mice and indicate that targeting NK cells might unlock novel strategies to combat AD.

Group 2 innate lymphoid cells are numerically and functionally deficient in the triple transgenic mouse model of Alzheimer's disease.

BACKGROUND: The immune pathways in Alzheimer's disease (AD) remain incompletely understood. Our recent study indicates that tissue-resident group 2 innate lymphoid cells (ILC2) accumulate in the brain barriers of aged mice and that their activation alleviates aging-associated cognitive decline. The regulation and function of ILC2 in AD, however, remain unknown. METHODS: In this study, we examined the numbers and functional capability of ILC2 from the triple transgenic AD mice (3xTg-AD) and control wild-type mice. We investigated the effects of treatment with IL-5, a cytokine produced by ILC2, on the cognitive function of 3xTg-AD mice. RESULTS: We demonstrate that brain-associated ILC2 are numerically and functionally defective in the triple transgenic AD mouse model (3xTg-AD). The numbers of brain-associated ILC2 were greatly reduced in 7-month-old 3xTg-AD mice of both sexes, compared to those in age- and sex-matched control wild-type mice. The remaining ILC2 in 3xTg-AD mice failed to efficiently produce the type 2 cytokine IL-5 but gained the capability to express a number of proinflammatory genes. Administration of IL-5, a cytokine produced by ILC2, transiently improved spatial recognition and learning in 3xTg-AD mice. CONCLUSION: Our results collectively indicate that numerical and functional deficiency of ILC2 might contribute to the cognitive impairment of 3xTg-AD mice.

Sex-specific effects of high-fat diet on cognitive impairment in a mouse model of VCID.

Mid-life metabolic disease (ie, obesity, diabetes, and prediabetes) causes vascular dysfunction and is a risk factor for vascular contributions to cognitive impairment and dementia (VCID), particularly in women. Using middle-aged mice, we modeled metabolic disease (obesity/prediabetes) via chronic high-fat (HF) diet and modeled VCID via unilateral common carotid artery occlusion. VCID impaired spatial memory in both sexes, but episodic-like memory in females only. HF diet caused greater weight gain and glucose intolerance in middle-aged females than males. HF diet alone impaired episodic-like memory in both sexes, but spatial memory in females only. Finally, the combination of HF diet and VCID elicited cognitive impairments in all tests, in both sexes. Sex-specific correlations were found between metabolic outcomes and memory. Notably, both visceral fat and the pro-inflammatory cytokine tumor necrosis factor alpha correlated with spatial memory deficits in middle-aged females, but not males. Overall, our data show that HF diet causes greater metabolic impairment and a wider array of cognitive deficits in middle-aged females than males. The combination of HF diet with VCID elicits deficits across multiple cognitive domains in both sexes. Our data are in line with clinical data, which shows that mid-life metabolic disease increases VCID risk, particularly in females.

Role of sex and high-fat diet in metabolic and hypothalamic disturbances in the 3xTg-AD mouse model of Alzheimer's disease.

BACKGROUND: Hypothalamic dysfunction occurs early in the clinical course of Alzheimer's disease (AD), likely contributing to disturbances in feeding behavior and metabolic function that are often observed years prior to the onset of cognitive symptoms. Late-life weight loss and low BMI are associated with increased risk of dementia and faster progression of disease. However, high-fat diet and metabolic disease (e.g., obesity, type 2 diabetes), particularly in mid-life, are associated with increased risk of AD, as well as exacerbated AD pathology and behavioral deficits in animal models. In the current study, we explored possible relationships between hypothalamic function, diet/metabolic status, and AD. Considering the sex bias in AD, with women representing two-thirds of AD patients, we sought to determine whether these relationships vary by sex. METHODS: WT and 3xTg-AD male and female mice were fed a control (10% fat) or high-fat (HF 60% fat) diet from ~ 3-7 months of age, then tested for metabolic and hypothalamic disturbances. RESULTS: On control diet, male 3xTg-AD mice displayed decreased body weight, reduced fat mass, hypoleptinemia, and mild systemic inflammation, as well as increased expression of gliosis- and inflammation-related genes in the hypothalamus (Iba1, GFAP, TNF-α, IL-1ß). In contrast, female 3xTg-AD mice on control diet displayed metabolic disturbances opposite that of 3xTg-AD males (increased body and fat mass, impaired glucose tolerance). HF diet resulted in expected metabolic alterations across groups (increased body and fat mass; glucose intolerance; increased plasma insulin and leptin, decreased ghrelin; nonalcoholic fatty liver disease-related pathology). HF diet resulted in the greatest weight gain, adiposity, and glucose intolerance in 3xTg-AD females, which were associated with markedly increased hypothalamic expression of GFAP and IL-1ß, as well as GFAP labeling in several hypothalamic nuclei that regulate energy balance. In contrast, HF diet increased diabetes markers and systemic inflammation preferentially in AD males but did not exacerbate hypothalamic inflammation in this group. CONCLUSIONS: These findings provide further evidence for the roles of hypothalamic and metabolic dysfunction in AD, which in the 3xTg-AD mouse model appears to be dependent on both sex and diet.

Sex differences in the metabolic effects of diet-induced obesity vary by age of onset.

Sex differences in the effect of diet-induced obesity (DIO) have been reported in juvenile mice. However, thorough side by side comparisons of the effects of DIO in males and females at different ages of onset have yet to be examined. We hypothesized that aged females would lose their protection, relative to males, from the effects of DIO. We examined the effect of DIO on body weight and glucose tolerance in juvenile, young adult, and middle-aged male and female mice. Our data show DIO in juvenile mice causes a greater increase in body weight and greater impairment in glucose tolerance in males than females. However, if the diet is initiated in young adult mice, these sex differences are absent. Further, if the diet is initiated in middle-aged mice, the sex difference is reversed, and females gain more weight and have greater impairment in glucose tolerance than males. Our data show that sex differences in the effect of DIO vary by age of onset; thus highlighting the importance of both age and sex as biological variables in DIO research.

Protective role of p450 epoxyeicosanoids in subarachnoid hemorrhage.

BACKGROUND: Patients recovering from aneurysmal subarachnoid hemorrhage (SAH) are at risk for developing delayed cerebral ischemia (DCI). Experimental and human studies implicate the vasoconstrictor P450 eicosanoid 20-hydroxyeicosatetraenoic acid (20-HETE) in the pathogenesis of DCI. To date, no studies have evaluated the role of vasodilator epoxyeicosatrienoic acids (EETs) in DCI. METHODS: Using mass spectrometry, we measured P450 eicosanoids in cerebrospinal fluid (CSF) from 34 SAH patients from 1 to 14 days after admission. CSF eicosanoid levels were compared in patients who experienced DCI versus those who did not. We then studied the effect of EETs in a model of SAH using mice lacking the enzyme soluble epoxide hydrolase (sEH), which catabolizes EETs into their inactive diol. To assess changes in vessel morphology and cortical perfusion in the mouse brain, we used optical microangiography, a non-invasive coherence-based imaging technique. RESULTS: Along with increases in 20-HETE, we found that CSF levels of 14,15-EET were elevated in SAH patients compared to control CSF, and levels were significantly higher in patients who experienced DCI compared to those who did not. Mice lacking sEH had elevated 14,15-EET and were protected from the delayed decrease in microvascular cortical perfusion after SAH, compared to wild type mice. CONCLUSIONS: Our findings suggest that P450 eicosanoids play an important role in the pathogenesis of DCI. While 20-HETE may contribute to the development of DCI, 14,15-EET may afford protection against DCI. Strategies to enhance 14,15-EET, including sEH inhibition, should be considered as part of a comprehensive approach to prevent DCI.

Role of aromatase in sex-specific cerebrovascular endothelial function in mice.

Stroke risk and outcome are strongly modified by estrogen. In addition to ovaries, estrogen is produced locally in peripheral tissue by the enzyme aromatase, and extragonadal synthesis becomes the major source of estrogen after menopause. Aromatase gene deletion in female mice exacerbates ischemic brain damage after stroke. However, it is not clear which cell type is responsible for this effect, since aromatase is expressed in multiple cell types, including cerebrovascular endothelium. We tested the hypothesis that cerebrovascular aromatase contributes to sex differences in cerebrovascular endothelial function. Cerebrocortical microvascular responses to the endothelium-dependent vasodilator ACh were compared between male and female wild-type (WT) and aromatase knockout (ArKO) mice by measuring laser-Doppler perfusion in vivo through a closed cranial window. Additional studies were performed in WT mice treated with the aromatase inhibitor fadrozole or vehicle. WT female mice had significantly greater responses to ACh compared with WT males (P < 0.001), which was associated with higher aromatase expression in female compared with male cerebral vessels (P < 0.05). ACh responses were significantly lower in ArKO compared with WT females (P < 0.05) and in WT females treated with fadrozole versus vehicle (P < 0.001). Conversely, ACh responses were significantly higher in ArKO versus WT males (P < 0.05). Levels of phosphorylated endothelial nitric oxide synthase (eNOS) were lower in ArKO versus WT female brains, but were not altered by aromatase deletion in males. We conclude that cerebrovascular endothelial aromatase plays an important and sexually dimorphic role in cerebrovascular function and that aromatase inhibitors in clinical use may have cardiovascular consequences in both males and females.

A transient brain endothelial translatome response to endotoxin is associated with mild cognitive changes post-shock in young mice.

Sepsis-associated encephalopathy (SAE) is associated with increased risk of long-term cognitive impairment. SAE is driven, at least in part, by brain endothelial dysfunction in response to systemic cytokine signaling. However, the mechanisms driving SAE and its consequences remain largely unknown. Here, we performed translating ribosome affinity purification and RNA-sequencing (TRAP-seq) from the brain endothelium to determine the transcriptional changes after an acute endotoxemic (LPS) challenge. LPS induced a strong acute transcriptional response in the brain endothelium that partially correlates with the whole brain transcriptional response and suggested an endothelial-specific hypoxia response. Consistent with a crucial role for IL-6, loss of the main regulator of this pathway, SOCS3, leads to a broadening of the population of genes responsive to LPS, suggesting that an overactivation of the IL-6/JAK/STAT3 pathway leads to an increased transcriptional response that could explain our prior findings of severe brain injury in these mice. To identify any potential sequelae of this acute response, we performed brain TRAP-seq following a battery of behavioral tests in mice after apparent recovery. We found that the transcriptional response returns to baseline within days post-challenge, but reductions in gene expression regulating protein translation and respiratory electron transport remained. We observed that mice that recovered from the endotoxemic shock showed mild, sex-dependent cognitive impairment, suggesting that the acute brain injury led to sustained effects. A better understanding of the transcriptional and non-transcriptional changes in response to shock is needed in order to prevent and/or revert the devastating consequences of septic shock.

A transient brain endothelial translatome response to endotoxin is associated with mild cognitive changes post-shock in young mice.

Sepsis-associated encephalopathy (SAE) is a common manifestation in septic patients that is associated with increased risk of long-term cognitive impairment. SAE is driven, at least in part, by brain endothelial dysfunction in response to systemic cytokine signaling. However, the mechanisms driving SAE and its consequences remain largely unknown. Here, we performed translating ribosome affinity purification and RNA-sequencing (TRAP-seq) from the brain endothelium to determine the transcriptional changes after an acute endotoxemic (LPS) challenge. LPS induced a strong acute transcriptional response in the brain endothelium that partially correlates with the whole brain transcriptional response and suggested an endothelial-specific hypoxia response. Consistent with a crucial role for IL-6, loss of the main regulator of this pathway, SOCS3, leads to a broadening of the population of genes responsive to LPS, suggesting that an overactivation of the IL-6/JAK/STAT3 pathway leads to an increased transcriptional response that could explain our prior findings of severe brain injury in these mice. To identify any potential sequelae of this acute response, we performed brain TRAP-seq following a battery of behavioral tests in mice after apparent recovery. We found that the transcriptional response returns to baseline within days post-challenge. Despite the transient nature of the response, we observed that mice that recovered from the endotoxemic shock showed mild, sex-dependent cognitive impairment, suggesting that the acute brain injury led to sustained, non-transcriptional effects. A better understanding of the transcriptional and non-transcriptional changes in response to shock is needed in order to prevent and/or revert the devastating consequences of septic shock.

Effects of High Fat Diet on Metabolic Health Vary by Age of Menopause Onset.

Menopause accelerates metabolic dysfunction, including (pre-)diabetes, obesity and visceral adiposity. However, the effects of endocrine vs. chronological aging in this progression are poorly understood. We hypothesize that menopause, especially in the context of middle-age, will exacerbate the metabolic effects of a high fat diet. Using young-adult and middle-aged C57BL/6J female mice, we modeled diet-induce obesity via chronic administration of high fat (HF) diet vs. control diet. We modeled peri-menopause/menopause via injections of 4-vinylcyclohexene diepoxide, which accelerates ovarian failure vs. vehicle. We performed glucose tolerance tests 2.5 and 7 months after diet onset, during the peri-menopausal and menopausal phases, respectively. Peri-menopause increased the severity of glucose intolerance and weight gain in middle-aged, HF-fed mice. Menopause increased weight gain in all mice regardless of age and diet, while chronological aging drove changes in adipose tissue distribution towards more visceral vs. subcutaneous adiposity. These data are in line with clinical data showing that post-menopausal women are more susceptible to metabolic dysfunction and suggest that greater chorological age exacerbates the effects of endocrine aging (menopause). This work highlights the importance of considering both chronological and endocrine aging in studies of metabolic health.

Effects of Menopause and High Fat Diet on Metabolic Outcomes in a Mouse Model of Alzheimer's Disease.

Background: About two-thirds of those with Alzheimer's disease (AD) are women, most of whom are post-menopausal. Menopause accelerates dementia risk by increasing the risk for metabolic, cardiovascular, and cerebrovascular diseases. Mid-life metabolic disease (obesity, diabetes/prediabetes) is a well-known risk factor for dementia. A high fat diet can lead to poor metabolic health in both humans and rodents. Objective: Our goal was to determine the effects of a high fat diet on metabolic outcomes in the AppNL-F knock-in mouse model of AD and assess the effects of menopause. Methods: First, 3-month-old AppNL-F and WT female mice were placed on either a control or a high fat diet until 10 months of age then assessed for metabolic outcomes. Next, we did a more extensive assessment in AppNL-F mice that were administered VCD (4-vinylcyclohexene diepoxide) or vehicle (oil) and placed on a control or high fat diet for 7 months. VCD was used to model menopause by causing accelerated ovarian failure. Results: Compared to WT controls, AD female mice had worse glucose intolerance. Menopause led to metabolic impairment (weight gain and glucose intolerance) and further exacerbated obesity in response to a high fat diet. There were interactions between diet and menopause on some metabolic health serum biomarkers and the expression of hypothalamic markers related to energy balance. Conclusions: This work highlights the need to model endocrine aging in animal models of dementia and will contribute to further understanding the interaction between menopause and metabolic health in the context of AD.

Atrazine inhibits pulsatile gonadotropin-releasing hormone (GnRH) release without altering GnRH messenger RNA or protein levels in the female rat.

Atrazine (ATR) is a commonly used pre-emergence/early postemergence herbicide. Previous work has shown that exposure to high doses of ATR in rats results in blunting of the hormone-induced luteinizing hormone (LH) surge and inhibition of pulsatile LH release without significantly reducing pituitary sensitivity to a gonadotropin-releasing hormone (GnRH) agonist. Accompanying the reduction in the LH surge was an attenuation of GnRH neuronal activation. These findings suggest that ATR exposure may be acting to inhibit GnRH release. In this study, we examined GnRH directly to determine the effect of high doses of ATR on GnRH pulsatile release, gene expression, and peptide levels in the female rat. Ovariectomized adult female Wistar rats were treated with ATR (200 mg/kg) or vehicle for 4 days via gavage. Following the final treatment, GnRH release was measured from ex vivo hypothalamic explants for 3 h. In another experiment, animals were administered either vehicle or ATR (50, 100, or 200 mg/kg) daily for 4 days. Following treatment, in situ hybridization was performed to examine total GnRH mRNA and the primary GnRH heterogeneous nuclear RNA transcript. Finally, GnRH immunoreactivity and total peptide levels were measured in hypothalamic tissue of treated animals. ATR treatment resulted in no changes to GnRH gene expression, peptide levels, or immunoreactivity but a reduction in GnRH pulse frequency and an increased pulse amplitude. These findings suggest that ATR acts to inhibit the secretory dynamics of GnRH pulses without interfering with GnRH mRNA and protein synthesis.

Sex differences in metabolic phenotype and hypothalamic inflammation in the 3xTg-AD mouse model of Alzheimer's disease.

BACKGROUND: Alzheimer's disease (AD) is notably associated with cognitive decline resulting from impaired function of hippocampal and cortical areas; however, several other domains and corresponding brain regions are affected. One such brain region is the hypothalamus, shown to atrophy and develop amyloid and tau pathology in AD patients. The hypothalamus controls several functions necessary for survival, including energy and glucose homeostasis. Changes in appetite and body weight are common in AD, often seen several years prior to the onset of cognitive symptoms. Therefore, altered metabolic processes may serve as a biomarker for AD, as well as a target for treatment, considering they are likely both a result of pathological changes and contributor to disease progression. Previously, we reported sexually dimorphic metabolic disturbances in ~ 7-month-old 3xTg-AD mice, accompanied by differences in systemic and hypothalamic inflammation. METHODS: In the current study, we investigated metabolic outcomes and hypothalamic inflammation in 3xTg-AD males and females at 3, 6, 9, and 12 months of age to determine when these sex differences emerge. RESULTS: In agreement with our previous study, AD males displayed less weight gain and adiposity, as well as reduced blood glucose levels following a glucose challenge, compared to females. These trends were apparent by 6-9 months of age, coinciding with increased expression of inflammatory markers (Iba1, GFAP, TNF-α, and IL-1ß) in the hypothalamus of AD males. CONCLUSIONS: These findings provide additional evidence for sex-dependent effects of AD pathology on energy and glucose homeostasis, which may be linked to hypothalamic inflammation.

Alzheimer's disease (AD), often associated with memory loss, can also affect other parts of the brain and body, resulting in several other symptoms. Changes in appetite and body weight are commonly seen in people with AD, often before they start showing signs of memory loss. These metabolism-related changes are likely due in part to AD affecting a part of the brain called the hypothalamus, which controls important functions like energy balance (calories in vs. calories out) and blood sugar levels. This study aimed to examine whether changes in metabolism and the hypothalamus could serve as early signs of AD, and even help in treating the disease. We also wanted to see if these changes were influenced by biological sex, as two-thirds of AD patients are women, and our previous studies showed many differences between males and females. In this study, we observed male and female mice at different ages to see when these changes began to appear. We found that male AD mice gained less weight, had less body fat, and had better blood sugar control, compared to female AD mice. These differences became noticeable at the same age that we noticed signs of increased inflammation in the hypothalamus of male mice. These findings suggest that AD affects males and females differently, particularly in terms of energy balance and blood sugar control, and this might be related to inflammation in the hypothalamus. This research could provide valuable insights into understanding, diagnosing, and treating Alzheimer's disease.

Menopause causes metabolic and cognitive impairments in a chronic cerebral hypoperfusion model of vascular contributions to cognitive impairment and dementia.

BACKGROUND: The vast majority of women with dementia are post-menopausal. Despite clinical relevance, menopause is underrepresented in rodent models of dementia. Before menopause, women are less likely than men to experience strokes, obesity, and diabetes-known risk factors for vascular contributions to cognitive impairment and dementia (VCID). During menopause, ovarian estrogen production stops and the risk of developing these dementia risk factors spikes. Here, we aimed to determine if menopause worsens cognitive impairment in VCID. We hypothesized that menopause would cause metabolic dysfunction and increase cognitive impairment in a mouse model of VCID. METHODS: We performed a unilateral common carotid artery occlusion surgery to produce chronic cerebral hypoperfusion and model VCID in mice. We used 4-vinylcyclohexene diepoxide to induce accelerated ovarian failure and model menopause. We evaluated cognitive impairment using behavioral tests including novel object recognition, Barnes maze, and nest building. To assess metabolic changes, we measured weight, adiposity, and glucose tolerance. We explored multiple aspects of brain pathology including cerebral hypoperfusion and white matter changes (commonly observed in VCID) as well as changes to estrogen receptor expression (which may mediate altered sensitivity to VCID pathology post-menopause). RESULTS: Menopause increased weight gain, glucose intolerance, and visceral adiposity. VCID caused deficits in spatial memory regardless of menopausal status. Post-menopausal VCID specifically led to additional deficits in episodic-like memory and activities of daily living. Menopause did not alter resting cerebral blood flow on the cortical surface (assessed by laser speckle contrast imaging). In the white matter, menopause decreased myelin basic protein gene expression in the corpus callosum but did not lead to overt white matter damage (assessed by Luxol fast blue). Menopause did not significantly alter estrogen receptor expression (ERα, ERß, or GPER1) in the cortex or hippocampus. CONCLUSIONS: Overall, we have found that the accelerated ovarian failure model of menopause caused metabolic impairment and cognitive deficits in a mouse model of VCID. Further studies are needed to identify the underlying mechanism. Importantly, the post-menopausal brain still expressed estrogen receptors at normal (pre-menopausal) levels. This is encouraging for any future studies attempting to reverse the effects of estrogen loss by activating brain estrogen receptors.

Nearly all women with dementia are menopausal. Reduced blood flow to the brain, resulting from damaged blood vessels, can lead to vascular dementia. Vascular dementia is the second most common cause of dementia. Before menopause, women are less likely than men to experience strokes, obesity, and diabetes­known risk factors for vascular dementia. During menopause, estrogen levels drop and the risk of developing these dementia risk factors increases. The goal of this study was to determine how menopause impacts risk factors (obesity, diabetes), memory and brain pathology in vascular dementia. This study used mouse models of vascular dementia and menopause. Menopause increased weight gain and other indicators of poor metabolic health. In mice with vascular dementia, menopausal mice had worse memory than pre-menopausal mice. After menopause, the brain still expressed estrogen receptors at normal (pre-menopausal) levels. This is encouraging for any future studies attempting to reverse the effects of estrogen loss by activating brain estrogen receptors.