Immunological and microbial shifts in the aging rhesus macaque lung during nontuberculous mycobacterial infection

Nontuberculous mycobacteria (NTM) are environmentally ubiquitous organisms that predominately cause NTM pulmonary disease (NTMPD) in individuals over the age of 65. The incidence of NTMPD has increased in the U.S., exceeding that of Mycobacterium tuberculosis. However, the mechanisms leading to higher susceptibility and severity of NTMPD with aging are poorly defined in part due to the lack of animal models that accurately recapitulate human disease. Here, we compared bacterial load, microbial communities, and host responses longitudinally between three young (two female and one male) and two aged (two female) rhesus macaques inoculated with Mycobacterium avium subsp. hominissuis (MAH) in the right caudal lobe. Unilateral infection resulted in a low bacterial load in both young and aged animals confined to the infected side. Although a robust inflammatory response was only observed in the inoculated lung, immune cell infiltration and antigen-specific T cells were detected in both lungs. Computed tomography, gross pathology, and histopathology revealed increased disease severity and persistence of bacterial DNA in aged animals. Additional analyses showed the translocation of gut and oral-pharyngeal bacterial DNA into the lower respiratory microbiome. Finally, single-cell RNA sequencing revealed a heightened inflammatory response to MAH infection by alveolar macrophages in aged animals. These data are consistent with the model that increased disease severity in the aged is mediated by a dysregulated macrophage response that may be sustained through persistent antigen presence.

IMPORTANCE

Nontuberculous mycobacteria (NTM) are emerging as pathogens of high consequence, as cases of NTM pulmonary disease (NTMPD) have exceeded those of Mycobacterium tuberculosis. NTMPD can be debilitating, particularly in patients over 65 years of age, as it causes chronic cough and fatigue requiring prolonged treatments with antibiotics. The underlying mechanisms of this increased disease severity with age are poorly understood, hampering the development of therapeutics and vaccines. Here, we use a rhesus macaque model to investigate the impact of age on host-NTM interactions. This work shows that aging is associated with increased disease severity and bacterial persistence in aged rhesus macaques, thus providing a preclinical model to develop and test novel therapeutics and interventions.

Modulation of neural gene networks by estradiol in old rhesus macaque females

The postmenopausal decrease in circulating estradiol (E2) levels has been shown to contribute to several adverse physiological and psychiatric effects. To elucidate the molecular effects of E2 on the brain, we examined differential gene expression and DNA methylation (DNAm) patterns in the nonhuman primate brain following ovariectomy (Ov) and subsequent subcutaneous bioidentical E2 chronic treatment. We identified several dysregulated molecular networks, including MAPK signaling and dopaminergic synapse response, that are associated with ovariectomy and shared across two different brain areas, the occipital cortex (OC) and prefrontal cortex (PFC). The finding that hypomethylation (p = 1.6 × 10-51) and upregulation (p = 3.8 × 10-3) of UBE2M across both brain regions provide strong evidence for molecular differences in the brain induced by E2 depletion. Additionally, differential expression (p = 1.9 × 10-4; interaction p = 3.5 × 10-2) of LTBR in the PFC provides further support for the role E2 plays in the brain, by demonstrating that the regulation of some genes that are altered by ovariectomy may also be modulated by Ov followed by hormone replacement therapy (HRT). These results present real opportunities to understand the specific biological mechanisms that are altered with depleted E2. Given E2's potential role in cognitive decline and neuroinflammation, our findings could lead to the discovery of novel therapeutics to slow cognitive decline. Together, this work represents a major step toward understanding molecular changes in the brain that are caused by ovariectomy and how E2 treatment may revert or protect against the negative neuro-related consequences caused by a depletion in estrogen as women approach menopause.

Age-related increase in the expression of 11β-hydroxysteroid dehydrogenase type 1 in the hippocampus of male rhesus macaques

Introduction

The hippocampus is especially susceptible to age-associated neuronal pathologies, and there is concern that the age-associated rise in cortisol secretion from the adrenal gland may contribute to their etiology. Furthermore, because 11β-hydroxysteroid dehydrogenase type 1 (HSD11B1) catalyzes the reduction of cortisone to the active hormone cortisol, it is plausible that an increase in the expression of this enzyme enhances the deleterious impact of cortisol in the hippocampus and contributes to the neuronal pathologies that underlie cognitive decline in the elderly.

Methods

Rhesus macaques were used as a translational animal model of human aging, to examine age-related changes in gene and protein expressions of (HSD11B1/HSD11B1) in the hippocampus, a region of the brain that plays a crucial role in learning and memory.

Results

Older animals showed significantly (p < 0.01) higher base-line cortisol levels in the circulation. In addition, they showed significantly (p < 0.05) higher hippocampal expression of HSD11B1 but not NR3C1 and NR3C2 (i.e., two receptor-encoding genes through which cortisol exerts its physiological actions). A similar age-related significant (p < 0.05) increase in the expression of the HSD11B1 was revealed at the protein level by western blot analysis.

Discussion

The data suggest that an age-related increase in the expression of hippocampal HSD11B1 is likely to raise cortisol concentrations in this cognitive brain area, and thereby contribute to the etiology of neuropathologies that ultimately lead to neuronal loss and dementia. Targeting this enzyme pharmacologically may help to reduce the negative impact of elevated cortisol concentrations within glucocorticoid-sensitive brain areas and thereby afford neuronal protection.

Effect of hormone replacement therapy on amyloid beta (Aβ) plaque density in the rhesus macaque amygdala

Background

Amyloid beta (Aβ) plaque density was examined in the amygdala of rhesus macaques, to elucidate the influence of age, diet and hormonal environment.

Methods

Luminex technology was used to measure cerebrospinal fluid (CSF) concentrations of Aβ40 and Aβ42 across three decades, while immunohistochemistry was used to examine Aβ plaque density in the amygdala.

Results

Aβ40 was found to be the predominant isoform of Aβ in the CSF, but neither Aβ40 or Aβ42 concentrations showed an age-related change, and the ratio of Aβ42 to Aβ40 showed only a marginal increase. Significantly fewer Aβ plaques were detected in the amygdala of old ovariectomized animals if they received estradiol HRT (p < 0.001); similar results were obtained regardless of whether they had been maintained on a regular monkey chow for ∼48 months or on a high-fat, high-sugar, Western-style diet for ∼30 months.

Conclusion

The results demonstrate that HRT involving estrogen can reduce Aβ plaque load in a cognitive brain region of aged non-human primates. The results from this translational animal model may therefore have clinical relevance to the treatment of AD in post-menopausal women, whether used alone, or as a supplement to current pharmacological and monoclonal antibody-based interventions.

Pathological Markers of Alzheimer's Disease and Related Dementia in the Rhesus Macaque Amygdala

Rhesus macaques develop amyloid-β (Aβ) plaques during old age, but it is unclear how extensively they express other pathological hallmarks of dementia. Here we used immunohistochemistry to examine expression of phosphorylated tau (pTau) protein and cytoplasmic inclusions of TAR DNA binding protein 43 kDa (TDP-43) within the amygdala of young and old males, and also in old surgically-menopausal females that were maintained on regular or obesogenic diets. Only one animal, a 23-year-old female, showed pTau expression and none showed TDP-43 inclusions. What genetic and/or environmental factors protect macaques from expressing more severe human neuro-pathologies remains an interesting unresolved question.

Modulation of neural gene networks by estradiol in old rhesus macaque females

The postmenopausal decrease in circulating estradiol (E2) levels has been shown to contribute to several adverse physiological and psychiatric effects. To elucidate the molecular effects of E2 on the brain, we examined differential gene expression and DNA methylation (DNAm) patterns in the nonhuman primate brain following ovariectomy (Ov) and subsequent E2 treatment. We identified several dysregulated molecular networks, including MAPK signaling and dopaminergic synapse response, that are associated with ovariectomy and shared across two different brain areas, the occipital cortex (OC) and prefrontal cortex (PFC). The finding that hypomethylation (p=1.6×10-51) and upregulation (p=3.8×10-3) of UBE2M across both brain regions, provide strong evidence for molecular differences in the brain induced by E2 depletion. Additionally, differential expression (p=1.9×10-4; interaction p=3.5×10-2) of LTBR in the PFC, provides further support for the role E2 plays in the brain, by demonstrating that the regulation of some genes that are altered by ovariectomy may also be modulated by Ov followed by hormone replacement therapy (HRT). These results present real opportunities to understand the specific biological mechanisms that are altered with depleted E2. Given E2's potential role in cognitive decline and neuroinflammation, our findings could lead to the discovery of novel therapeutics to slow cognitive decline. Together, this work represents a major step towards understanding molecular changes in the brain that are caused by ovariectomy and how E2 treatment may revert or protect against the negative neuro-related consequences caused by a depletion in estrogen as women approach menopause.

Brain volumetrics across the lifespan of the rhesus macaque

The rhesus macaque is a long-lived nonhuman primate (NHP) with a brain structure similar to humans, which may represent a valuable translational animal model in which to study human brain aging. Previous magnetic resonance imaging (MRI) studies of age in rhesus macaque brains have been prone to low statistical power, unbalanced sex ratio and lack of a complete age range. To overcome these problems, the current study surveyed structural T1-weighted magnetic resonance imaging scans of 66 animals, 34 females (aged 6-31 years) and 32 males (aged 5-27 years). Differences observed in older animals, included enlargement of the lateral ventricles and a smaller volume in the frontal cortex, caudate, putamen, hypothalamus, and thalamus. Unexpected, greater volume, were measured in older animals in the hippocampus, amygdala, and globus pallidus. There were also numerous differences between males and females with respect to age in both white and gray matter regions. As an apparent model of normative human aging, the macaque is ideal for studying induction and mitigation of neurodegenerative disease.

A class of anti-inflammatory lipids decrease with aging in the central nervous system

Lipids contribute to the structure, development, and function of healthy brains. Dysregulated lipid metabolism is linked to aging and diseased brains. However, our understanding of lipid metabolism in aging brains remains limited. Here we examined the brain lipidome of mice across their lifespan using untargeted lipidomics. Co-expression network analysis highlighted a progressive decrease in 3-sulfogalactosyl diacylglycerols (SGDGs) and SGDG pathway members, including the potential degradation products lyso-SGDGs. SGDGs show an age-related decline specifically in the central nervous system and are associated with myelination. We also found that an SGDG dramatically suppresses LPS-induced gene expression and release of pro-inflammatory cytokines from macrophages and microglia by acting on the NF-κB pathway. The detection of SGDGs in human and macaque brains establishes their evolutionary conservation. This work enhances interest in SGDGs regarding their roles in aging and inflammatory diseases and highlights the complexity of the brain lipidome and potential biological functions in aging.

A macaque clonal hematopoiesis model demonstrates expansion of TET2-disrupted clones and utility for testing interventions

Individuals with age-related clonal hematopoiesis (CH) are at greater risk for hematologic malignancies and cardiovascular diseases. However, predictive preclinical animal models to recapitulate the spectrum of human CH are lacking. Through error-corrected sequencing of 56 human CH/myeloid malignancy genes, we identified natural CH driver mutations in aged rhesus macaques matching genes somatically mutated in human CH, with DNMT3A mutations being the most frequent. A CH model in young adult macaques was generated via autologous transplantation of clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9-mediated gene-edited hematopoietic stem and progenitor cells (HSPCs), targeting the top human CH genes with loss-of-function (LOF) mutations. Long-term follow-up revealed reproducible and significant expansion of multiple HSPC clones with heterozygous TET2 LOF mutations, compared with minimal expansion of clones bearing other mutations. Although the blood counts of these CH macaques were normal, their bone marrows were hypercellular and myeloid-predominant. TET2-disrupted myeloid colony-forming units isolated from these animals showed a distinct hyperinflammatory gene expression profile compared with wild type. In addition, mature macrophages purified from the CH macaques showed elevated NLRP3 inflammasome activity and increased interleukin-1β (IL-1β) and IL-6 production. The model was used to test the impact of IL-6 blockage by tocilizumab, documenting a slowing of TET2-mutated expansion, suggesting that interruption of the IL-6 axis may remove the selective advantage of mutant HSPCs. These findings provide a model for examining the pathophysiology of CH and give insights into potential therapeutic interventions.

MRI characteristics of Japanese macaque encephalomyelitis: Comparison to human diseases

BACKGROUND AND PURPOSE

To describe MRI findings in Japanese macaque encephalomyelitis (JME) with emphasis on lesion characteristics, lesion evolution, normal-appearing brain tissue, and similarities to human demyelinating disease.

METHODS

MRI data were obtained from 114 Japanese macaques, 30 presenting neurological signs of JME. All animals were screened for presence of T2 -weighted white matter signal hyperintensities; animals with behavioral signs of JME were additionally screened for contrast-enhancing lesions. Whole-brain quantitative T1 maps were collected, and histogram analysis was performed with regression across age to evaluate microstructural changes in normal appearing brain tissue in JME and neurologically normal animals. Quantitative estimates of blood-brain-barrier (BBB) permeability to gadolinium-based-contrast agent (GBCA) were obtained in acute, GBCA-enhancing lesions. Longitudinal imaging data were acquired for 15 JME animals.

RESULTS

One hundred and seventy-three focal GBCA-enhancing lesions were identified in 30 animals demonstrating behavioral signs of neurological dysfunction. JME GBCA-enhancing lesions were typically focal and ovoid, demonstrating highest BBB GBCA permeability in the lesion core, similar to acute, focal multiple sclerosis lesions. New GBCA-enhancing lesions arose rapidly from normal-appearing tissue, and BBB permeability remained elevated for weeks. T1 values in normal-appearing tissue were significantly associated with age, but not with sex or disease.

CONCLUSIONS

Intense, focal neuroinflammation is a key MRI finding in JME. Several features of JME compare directly to human inflammatory demyelinating diseases. Investigation of JME combined with the development and validation of noninvasive imaging biomarkers offers substantial potential to improve diagnostic specificity and contribute to the understanding of human demyelinating diseases.

Myelin-specific T cells in animals with Japanese macaque encephalomyelitis

Objective

To determine whether animals with Japanese macaque encephalomyelitis (JME), a spontaneous demyelinating disease similar to multiple sclerosis (MS), harbor myelin‐specific T cells in their central nervous system (CNS) and periphery.

Methods

Mononuclear cells (MNCs) from CNS lesions, cervical lymph nodes (LNs) and peripheral blood of Japanese macaques (JMs) with JME, and cervical LN and blood MNCs from healthy controls or animals with non‐JME conditions were analyzed for the presence of myelin‐specific T cells and changes in interleukin 17 (IL‐17) and interferon gamma (IFNγ) expression.

Results

Demyelinating JME lesions contained CD4⁺ T cells and CD8⁺ T cells specific to myelin oligodendrocyte glycoprotein (MOG), myelin basic protein (MBP), and/or proteolipid protein (PLP). CD8⁺ T‐cell responses were absent in JME peripheral blood, and in age‐ and sex‐matched controls. However, CD4⁺ Th1 and Th17 responses were detected in JME peripheral blood versus controls. Cervical LN MNCs from eight of nine JME animals had CD3⁺ T cells specific for MOG, MBP, and PLP that were not detected in controls. Mapping myelin epitopes revealed a heterogeneity in responses among JME animals. Comparison of myelin antigen sequences with those of JM rhadinovirus (JMRV), which is found in JME lesions, identified six viral open reading frames (ORFs) with similarities to myelin antigen sequences. Overlapping peptides to these JMRV ORFs did not induce IFNγ responses.

Interpretations

JME possesses an immune‐mediated component that involves both CD4⁺ and CD8⁺ T cells specific for myelin antigens. JME may shed new light on inflammatory demyelinating disease pathogenesis linked to gamma‐herpesvirus infection.

Amyloidosis increase is not attenuated by long-term calorie restriction or related to neuron density in the prefrontal cortex of extremely aged rhesus macaques

As human lifespan increases and the population ages, diseases of aging such as Alzheimer's disease (AD) are a major cause for concern. Although calorie restriction (CR) as an intervention has been shown to increase healthspan in many species, few studies have examined the effects of CR on brain aging in primates. Using postmortem tissue from a cohort of extremely aged rhesus monkeys (22-44 years old, average age 31.8 years) from a longitudinal CR study, we measured immunohistochemically labeled amyloid beta plaques in Brodmann areas 32 and 46 of the prefrontal cortex, areas that play key roles in cognitive processing, are sensitive to aging and, in humans, are also susceptible to AD pathogenesis. We also evaluated these areas for cortical neuron loss, which has not been observed in younger cohorts of aged monkeys. We found a significant increase in plaque density with age, but this was unaffected by diet. Moreover, there was no change in neuron density with age or treatment. These data suggest that even in the oldest-old rhesus macaques, amyloid beta plaques do not lead to overt neuron loss. Hence, the rhesus macaque serves as a pragmatic animal model for normative human aging but is not a complete model of the neurodegeneration of AD. This model of aging may instead prove most useful for determining how even the oldest monkeys are protected from AD, and this information may therefore yield valuable information for clinical AD treatments.

Lack of effect of short-term DHEA supplementation on the perimenopausal ovary†

Dehydroepiandrosterone (DHEA) hormonal supplementation can improve oocyte quality in women with diminished ovarian function. However, it is unclear whether DHEA supplementation can also enhance ovarian function during the perimenopause (i.e., when the number of follicles in the ovary has undergone a marked reduction). To address this question, we examined the impact of 2.5-months of daily 5-mg oral DHEA supplementation on the number of ovarian follicles and the concentration of anti-Müllerian hormone (AMH) in perimenopausal rhesus macaques. Like women, these long-lived nonhuman primates have ~ 28-day menstrual cycles and eventually undergo menopause. They also show similar age-related neuroendocrine changes, including a marked decrease in circulating concentrations of DHEA and DHEA sulfate (DHEAS). Our experimental design involved the following three groups of animals (N = 6 per group): Young adult (mean age = 11.6 years), Old control (mean age = 23.1 years), and Old DHEA-treated (mean age = 23.5 years). Histological examination of the ovaries revealed a significant age-related decrease in the mean number of primordial follicles despite DHEA supplementation. Moreover, AMH concentrations within the ovaries and circulation, assessed by Western analysis and ELISA, respectively, showed significant age-related decreases that were not attenuated by DHEA supplementation. Taken together, these results fail to show a clear effect of short-term physiological DHEA supplementation on the perimenopausal ovary. However, they do not exclude the possibility that alternative DHEA supplementation paradigms (e.g., involving an earlier start date, longer duration and using pharmacological doses) may extend reproductive potential during aging.

Longitudinal Effects of Immediate and Delayed Estradiol on Cognitive Performance in a Spatial Maze and Hippocampal Volume in Menopausal Macaques Under an Obesogenic Diet

The consumption of a diet high in fat and refined sugars has several health risks, including the development of cognitive decline and neurodegeneration. For women, menopause carries additional health risks that may interact with a high-fat diet in negative ways. Some symptoms of menopause, including cognitive impairments, can be modulated by hormone replacement therapy (HRT), but the hormonal formulation and the timing of the treatment relative to the onset of menopause are critical factors determining its efficacy. Little is known about how obesogenic, high-fat, high-sugar diets interact with HRT in menopause to affect cognition and neurodegeneration. Given the high prevalence of the consumption of an obesogenic Western-style diet, understanding how the effects of HRT are modulated by an obesogenic diet is critical for developing optimized therapeutic strategies for peri- and post-menopausal women. In this study, we investigated by magnetic resonance imaging (MRI) the effects of either immediate or delayed estradiol hormone therapy on cognition and neuroanatomy following ovo-hysterectomy (OvH) of aged, female rhesus macaques on an obesogenic diet. The macaques were followed for 2.5 years after ovo-hysterectomy, with four time points at which anatomical MRIs were acquired. Analysis of hippocampal volumes revealed an interaction between time point and treatment; hippocampal volumes in the delayed estrogen group, but not the immediate estrogen group, increased over time compared to those in untreated controls. Performance on a hippocampal-dependent spatial maze task showed improved performance in estrogen treated animals compared to OvH macaques given placebo. These results indicate that HRT may contribute to beneficial cognitive outcomes after menopause under an obesogenic diet.

Gene expression profiling of the SCN in young and old rhesus macaques

In mammals, the suprachiasmatic nucleus (SCN) is the location of a master circadian pacemaker. It receives photic signals from the environment via the retinal hypothalamic tract, which play a key role in synchronizing the body's endogenously generated circadian rhythms with the 24-h rhythm of the environment. Therefore, it is plausible that age-related changes within the SCN contribute to the etiology of perturbed activity-rest cycles that become prevalent in humans during aging. To test this hypothesis, we used gene arrays and quantitative RT-PCR to profile age-related gene expression changes within the SCN of male rhesus macaques - a pragmatic translational animal model of human aging, which similarly displays an age-related attenuation of daytime activity levels. As expected, the SCN showed high expression of arginine vasopressin, vasoactive intestinal polypeptide, calbindin and nuclear receptor subfamily 1, group D, member 1 (NR1D1) (also known as reverse strand of ERBA (REV-ERBα), both at the mRNA and protein level. However, no obvious difference was detected between the SCNs of young (7-12 years) and old animals (21-26 years), in terms of the expression of core clock genes or genes associated with SCN signaling and neurotransmission. These data demonstrate the resilience of the primate SCN to normal aging, at least at the transcriptional level and, at least in males, suggest that age-related disruption of activity-rest cycles in humans may instead stem from changes within other components of the circadian system, such as desynchronization of subordinate oscillators in other parts of the body.

Discovery of a CLN7 model of Batten disease in non-human primates

We have identified a natural Japanese macaque model of the childhood neurodegenerative disorder neuronal ceroid lipofuscinosis, commonly known as Batten Disease, caused by a homozygous frameshift mutation in the CLN7 gene (CLN7^−/−). Affected macaques display progressive neurological deficits including visual impairment, tremor, incoordination, ataxia and impaired balance. Imaging, functional and pathological studies revealed that CLN7^−/− macaques have reduced retinal thickness and retinal function early in disease, followed by profound cerebral and cerebellar atrophy that progresses over a five to six-year disease course. Histological analyses showed an accumulation of cerebral, cerebellar and cardiac storage material as well as degeneration of neurons, white matter fragmentation and reactive gliosis throughout the brain of affected animals. This novel CLN7^−/− macaque model recapitulates key behavioral and neuropathological features of human Batten Disease and provides novel insights into the pathophysiology linked to CLN7 mutations. These animals will be invaluable for evaluating promising therapeutic strategies for this devastating disease.

Age-associated gene expression changes in the arcuate nucleus of male rhesus macaques

The hypothalamic arcuate nucleus (ARC) represents a major component of the neuroendocrine reproductive axis and plays an important role in controlling the onset of puberty as well as age-associated reproductive senescence. Although significant gene expression changes have been observed in the ARC during sexual maturation, it is unclear what changes occur during aging, especially in males. Therefore, in the present study, we profiled the expression of reproduction-related genes in the ARC of young and old male rhesus macaques, as well as old males that had received 6 months of hormone supplementation (HS) in the form of daily testosterone and dehydroepiandrosterone; we also compared morning vs night ARC gene expression in the old males. Using Affymetrix gene microarrays, we found little evidence for age-associated expression changes for genes associated with the neuroendocrine reproductive axis, whereas using qRT-PCR, we detected a similar age-associated decrease in PGR (progesterone receptor) that we previously observed in postmenopausal females. We also detected a sex-steroid-dependent and age-associated decrease in androgen receptor (AR) expression, with highest AR levels being expressed at night (i.e., coinciding with the natural peak in daily testosterone secretion). Finally, unlike previous observations made in females, we did not find a significant age-associated increase in KISS1 (Kisspeptin) or TAC3 (Neurokinin B) expression in the ARC of males, most likely because the attenuation of circulating sex-steroid levels in the males was much less than that in postmenopausal females. Taken together, the data highlight some similarities and differences in ARC gene expression between aged male and female nonhuman primates.

Effects of obesogenic diet and estradiol on dorsal raphe gene expression in old female macaques

The beneficial effects of bioidentical ovarian steroid hormone therapy (HT) during the perimenopause are gaining recognition. However, the positive effects of estrogen (E) plus or minus progesterone (P) administration to ovariectomized (Ovx) lab animals were recognized in multiple systems for years before clinical trials could adequately duplicate the results. Moreover, very large numbers of women are often needed to find statistically significant results in clinical trials of HT; and there are still opposing results being published, especially in neural and cardiovascular systems. One of the obvious differences between human and animal studies is diet. Laboratory animals are fed a diet that is low in fat and refined sugar, but high in micronutrients. In the US, a large portion of the population eats what is known as a "western style diet" or WSD that provides calories from 36% fat, 44% carbohydrates (includes 18.5% sugars) and 18% protein. Unfortunately, obesity and diabetes have reached epidemic proportions and the percentage of obese women in clinical trials may be overlooked. We questioned whether WSD and obesity could decrease the positive neural effects of estradiol (E) in the serotonin system of old macaques that were surgically menopausal. Old ovo-hysterectomized female monkeys were fed WSD for 2.5 years, and treated with placebo, Immediate E (ImE) or Delayed E (DE). Compared to old Ovx macaques on primate chow and treated with placebo or E, the WSD-fed monkeys exhibited greater individual variance and blunted responses to E-treatment in the expression of genes related to serotonin neurotransmission, CRH components in the midbrain, synapse assembly, DNA repair, protein folding, ubiquitylation, transport and neurodegeneration. For many of the genes examined, transcript abundance was lower in WSD-fed than chow-fed monkeys. In summary, an obesogenic diet for 2.5 years in old surgically menopausal macaques blunted or increased variability in E-induced gene expression in the dorsal raphe. These results suggest that with regard to function and viability in the dorsal raphe, HT may not be as beneficial for obese women as normal weight women.

DNA-PK Promotes the Mitochondrial, Metabolic, and Physical Decline that Occurs During Aging

Hallmarks of aging that negatively impact health include weight gain and reduced physical fitness, which can increase insulin resistance and risk for many diseases, including type 2 diabetes. The underlying mechanism(s) for these phenomena is poorly understood. Here we report that aging increases DNA breaks and activates DNA-dependent protein kinase (DNA-PK) in skeletal muscle, which suppresses mitochondrial function, energy metabolism, and physical fitness. DNA-PK phosphorylates threonines 5 and 7 of HSP90α, decreasing its chaperone function for clients such as AMP-activated protein kinase (AMPK), which is critical for mitochondrial biogenesis and energy metabolism. Decreasing DNA-PK activity increases AMPK activity and prevents weight gain, decline of mitochondrial function, and decline of physical fitness in middle-aged mice and protects against type 2 diabetes. In conclusion, DNA-PK is one of the drivers of the metabolic and fitness decline during aging, and therefore DNA-PK inhibitors may have therapeutic potential in obesity and low exercise capacity.

Effect of caloric restriction on plasma melatonin levels in aged rhesus macaques

In this study, we examined the 24-hour plasma melatonin patterns of young adult (∼11 years of age) and old (∼24 years of age) rhesus macaques, and determined how they would be influenced by 30% caloric restriction (CR). Well-defined 24-hour plasma melatonin rhythms were observed in all the males but only the old animals showed significant attenuation of night-time melatonin levels. Moreover, 4.5 years of CR failed to prevent the age-associated decline in plasma melatonin levels in the old males and caused a significant decrease in the young adult males. Similar plasma melatonin rhythms were also observed in all the females but no age-related decline was detected, and 2 years of CR had no obvious effect on plasma melatonin levels. If anything, there was a trend for the CR to decrease melatonin levels in the young adult females. Taken together, the results fail to show any clear benefit of CR on plasma melatonin levels in old rhesus macaques and may even be detrimental to plasma melatonin levels in young adults.

Effect of short-term DHEA supplementation on serum and hippocampal estrogen concentrations in perimenopausal female rhesus macaques

The hippocampus of rhesus macaques expresses genes that encode key enzymes involved in the intracrine conversion of dehydroepiandrosterone (DHEA) to estradiol. Therefore, it is plausible that supplementary DHEA may enhance hippocampal estradiol concentrations and help to compensate for the marked postmenopausal attenuation of circulating estrogen levels. To test this hypothesis, we used LC-MS/MS to measure estradiol and estrone concentrations in the serum and hippocampus of young and old perimenopausal female rhesus macaques, as well as old perimenopausal females that received daily DHEA (5 mg) oral supplementation for 1 week. Despite lower concentrations of these estrogens in the serum of the older animals, their concentrations in the hippocampus did not show any obvious differences due to age or to DHEA supplementation. The results suggest that de novo estrogen synthesis in the brain may compensate for the perimenopausal loss of estrogens in the circulation even without supplemental DHEA.

Cognition in aged rhesus monkeys: effect of DHEA and correlation with steroidogenic gene expression

Estradiol supplementation has been shown to enhance cognitive performance in old ovariectomized rhesus macaques (Macaca mulatta). To determine if similar benefits could be achieved in perimenopausal animals using alternative hormonal supplements, we administered dehydroepiandrosterone (DHEA) to old ovary-intact female rhesus macaques for ∼2.5 months. Using computerized touch screen memory tasks, including delayed response (DR) and delayed matching-to-sample (DMS), we observed improved performance with time in all of the animals but failed to detect a significant effect of DHEA. On the other hand, gene expression profiling disclosed a significant correlation between cognitive performance and the expression of several steroidogenic and steroid-responsive genes. The DR performance was positively correlated with hippocampal expression of AKR1C3 and STAR and negatively correlated with the expression of SDRD5A1. A positive correlation was also found between DMS performance and prefrontal cortical expression of AKR1C3 and a negative correlation with STAR, as well as a negative correlation with the hippocampal expression of HSD11B1 and NR3C1. Taken together, the results suggest that steroidogenic gene regulation within the brain may help to maintain cognitive function during the perimenopausal transition period, despite a decline in sex-steroid levels in the circulation.

Effect of Ovarian Hormone Therapy on Cognition in the Aged Female Rhesus Macaque

Studies of the effect of hormone therapy on cognitive function in menopausal women have been equivocal, in part due to differences in the type and timing of hormone treatment. Here we cognitively tested aged female rhesus macaques on (1) the delayed response task of spatial working memory, (2) a visuospatial attention task that measured spatially and temporally cued reaction times, and (3) a simple reaction time task as a control for motor speed. After task acquisition, animals were ovariectomized (OVX). Their performance was compared with intact controls for 2 months, at which time no group differences were found. The OVX animals were then assigned to treatment with either a subcutaneous sham implant (OVX), 17-β estradiol (E) implant (OVX+E) or E implant plus cyclic oral progesterone (OVX+EP). All groups were then tested repeatedly over 12 months. The OVX+E animals performed significantly better on the delayed response task than all of the other groups for much of the 12 month testing period. The OVX+EP animals also showed improved performance in the delayed response task, but only at 30 s delays and with performance levels below that of OVX+E animals. The OVX+E animals also performed significantly better in the visuospatial attention task, particularly in the most challenging invalid cue condition; this difference also was maintained across the 12 month testing period. Simple reaction time was not affected by hormonal manipulation. These data demonstrate that chronic, continuous administration of E can exert multiple beneficial cognitive effects in aged, OVX rhesus macaque females.

SIGNIFICANCE STATEMENT

Hormone therapy after menopause is controversial. We tested the effects of hormone replacement in aged rhesus macaques, soon after surgically-induced menopause [ovariectomy (OVX)], on tests of memory and attention. Untreated ovarian-intact and OVX animals were compared with OVX animals receiving estradiol (E) alone or E with progesterone (P). E was administered in a continuous fashion via subcutaneous implant, whereas P was administered orally in a cyclic fashion. On both tests, E-treated animals performed better than the other 3 experimental groups across 1 year of treatment. Thus, in this monkey model, chronic E administered soon after the loss of ovarian hormones had long-term benefits for cognitive function.

Immunopathology of Japanese macaque encephalomyelitis is similar to multiple sclerosis

Japanese macaque encephalomyelitis (JME) is an inflammatory demyelinating disease that occurs spontaneously in a colony of Japanese macaques (JM) at the Oregon National Primate Research Center. Animals with JME display clinical signs resembling multiple sclerosis (MS), and magnetic resonance imaging reveals multiple T2-weighted hyperintensities and gadolinium-enhancing lesions in the central nervous system (CNS). Here we undertook studies to determine if JME possesses features of an immune-mediated disease in the CNS. Comparable to MS, the CNS of animals with JME contain active lesions positive for IL-17, CD4+ T cells with Th1 and Th17 phenotypes, CD8+ T cells, and positive CSF findings.

Ovarian steroids regulate gene expression in the dorsal raphe of old female macaques

With extended life spans in modern humans, menopause has become a significant risk factor for depression, anxiety, loss of cognitive functions, weight gain, metabolic disease, osteoporosis, cardiovascular disease, and neurodegenerative diseases. Clinical studies have found beneficial neural effects of ovarian steroid hormone therapy (HT) during the menopausal transition and data are emerging that it can be continued long term. To further understand molecular underpinnings of the clinical studies, we used quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) to examine gene expression in the serotonergic dorsal raphe of old (>18 years) rhesus macaques, focusing on genes related to depression, cellular resilience, and neurodegenerative diseases. The animals were ovariectomized (Ovx, surgically menopausal) and subjected to either estradiol or estradiol plus progesterone HT, or to placebo, starting 2 months after Ovx and continuing for ∼ 4 years. Significant changes were observed in 36 of 48 genes examined that encode proteins supporting serotonin neurotransmission, synapse assembly, glutamate neurotransmission, DNA repair, chaperones, ubiquinases and transport motors, as well as genes encoding proteins that have potential to delay the onset of neuropathologies. The data reveal important gene targets for chronic HT that contribute to neural health. Alternatively, the loss of ovarian steroids may lead to loss of functions at the gene level that contribute to many of the observable neural deficits after menopause.

3D structure tensor analysis of light microscopy data for validating diffusion MRI

Diffusion magnetic resonance imaging (d-MRI) is a powerful non-invasive and non-destructive technique for characterizing brain tissue on the microscopic scale. However, the lack of validation of d-MRI by independent experimental means poses an obstacle to accurate interpretation of data acquired using this method. Recently, structure tensor analysis has been applied to light microscopy images, and this technique holds promise to be a powerful validation strategy for d-MRI. Advantages of this approach include its similarity to d-MRI in terms of averaging the effects of a large number of cellular structures, and its simplicity, which enables it to be implemented in a high-throughput manner. However, a drawback of previous implementations of this technique arises from it being restricted to 2D. As a result, structure tensor analyses have been limited to tissue sectioned in a direction orthogonal to the direction of interest. Here we describe the analytical framework for extending structure tensor analysis to 3D, and utilize the results to analyze serial image "stacks" acquired with confocal microscopy of rhesus macaque hippocampal tissue. Implementation of 3D structure tensor procedures requires removal of sources of anisotropy introduced in tissue preparation and confocal imaging. This is accomplished with image processing steps to mitigate the effects of anisotropic tissue shrinkage, and the effects of anisotropy in the point spread function (PSF). In order to address the latter confound, we describe procedures for measuring the dependence of PSF anisotropy on distance from the microscope objective within tissue. Prior to microscopy, ex vivo d-MRI measurements performed on the hippocampal tissue revealed three regions of tissue with mutually orthogonal directions of least restricted diffusion that correspond to CA1, alveus and inferior longitudinal fasciculus. We demonstrate the ability of 3D structure tensor analysis to identify structure tensor orientations that are parallel to d-MRI derived diffusion tensors in each of these three regions. It is concluded that the 3D generalization of structure tensor analysis will further improve the utility of this method for validation of d-MRI by making it a more flexible experimental technique that closer resembles the inherently 3D nature of d-MRI measurements.

Androgen supplementation during aging: development of a physiologically appropriate protocol

Men show an age-related decline in the circulating levels of testosterone (T) and dehydroepiandrosterone sulfate (DHEAS). Consequently, there is interest in developing androgen supplementation paradigms for old men that replicate the hormone profiles of young adults. In the present study, we used old (21-26 years old) male rhesus monkeys as a model to examine the efficacy of an androgen supplementation paradigm that comprised oral T administration (12 mg/kg body weight, dissolved in sesame oil/chocolate) in the evening, and two oral DHEA administrations, 3 hr apart (0.04 mg/kg body weight, dissolved in sesame oil/chocolate) in the morning. After 5 days of repeated hormone supplementation, serial blood samples were remotely collected from each animal hourly across the 24-hr day, and assayed for cortisol, DHEAS, T, 5α-dihydrotestosterone (DHT), estrone (E1), and 17β-estradiol (E2). Following androgen supplementation, T levels were significantly elevated and this was associated with a more sustained nocturnal elevation of T's primary bioactive metabolites, DHT and E1 and E2. Plasma DHEAS levels were also significantly elevated after androgen supplementation; DHEAS levels rose in the early morning and gradually declined during the course of the day, closely mimicking the profiles observed in young adults (7-12 years old); in contrast, cortisol levels were unaltered by the supplementation. Together the data demonstrate a non-invasive androgen supplementation paradigm that restores youthful circulating androgen levels in old male primates. Because this paradigm preserves the natural circulating circadian hormone patterns, we predict that it will produce fewer adverse side effects, such as perturbed sleep or cognitive impairment.

Impact of moderate calorie restriction on testicular morphology and endocrine function in adult rhesus macaques (Macaca mulatta)

We previously reported that moderate calorie restriction (CR) has minimal impact on testicular gene expression in young adult rhesus macaques, and no obvious negative impact on semen quality or plasma testosterone levels. We now extend these findings by examining the influence of CR on various aspects of the reproductive axis of older males, including 24-h circulating testosterone levels, testicular gene expression, and testicular morphology. Young adult and old adult male rhesus macaques were subjected to either 30 % CR for 5-7 years, or were fed a standard control diet. Analysis of the 24-h plasma testosterone profiles revealed a significant age-associated decline, but no evidence for CR-induced suppression in either the young or old males. Similarly, expression profiling of key genes associated with testosterone biosynthesis and Leydig cell maintenance showed no significant CR-induced changes in either the young or old animals. The only evidence for CR-associated negative effects on the testis was detected in the old animals at the histological level; when old CR animals were compared with their age-matched controls, there was a modest decrease in seminiferous tubule diameter and epithelium height, with a concomitant increase in the number of depleted germ cell lines. Reassuringly, data from this study and our previous study suggest that moderate CR does not negatively impact 24-h plasma testosterone profiles or testicular gene expression. Although there appear to be some minor CR-induced effects on testicular morphology in old animals, it is unclear if these would significantly compromise fertility.

Changes in spontaneous activity assessed by accelerometry correlate with extent of cerebral ischemia-reperfusion injury in the nonhuman primate

The use of accelerometry to monitor activity in human stroke patients has revealed strong correlations between objective activity measurements and subjective neurological findings. The goal of our study was to assess the applicability of accelerometry-based measurements in experimental animals undergoing surgically-induced cerebral ischemia. Using a nonhuman primate cortical stroke model, we demonstrate for the first time that monitoring locomotor activity prior to and following cerebrovascular ischemic injury using an accelerometer is feasible in adult male rhesus macaques and that the measured activity outcomes significantly correlate with severity of brain injury. The use of accelerometry as an unobtrusive, objective preclinical efficacy determinant could complement standard practices involving subjective neurological scoring and magnetic resonance imaging in nonhuman primates. Similar activity monitoring devices to those employed in this study are currently in use in human clinical studies, underscoring the feasibility of this approach for assessing the clinical potential of novel treatments for cerebral ischemia.

Testosterone increases circulating dehydroepiandrosterone sulfate levels in the male rhesus macaque

The adrenal steroid dehydroepiandrosterone (DHEA) and its sulfate (DHEAS) are two of the most abundant hormones in the human circulation. Furthermore, they are released in a circadian pattern and show a marked age-associated decline. Adult levels of DHEA and DHEAS are significantly higher in males than in females, but the reason for this sexual dimorphism is unclear. In the present study, we administered supplementary androgens [DHEA, testosterone and 5α-dihydrotestosterone (DHT)] to aged male rhesus macaques (Macaca mulatta). While this paradigm increased circulating DHEAS immediately after DHEA administration, an increase was also observed following either testosterone or DHT administration, resulting in hormonal profiles resembling levels observed in young males in terms of both amplitude and circadian pattern. This stimulatory effect was limited to DHEAS, as an increase in circulating cortisol was not observed. Taken together, these data demonstrate an influence of the hypothalamo-pituitary-testicular axis on adrenal function in males, possibly by sensitizing the zona reticularis to the stimulating action of adrenocorticopic hormone. This represents a plausible mechanism to explain sex differences in circulating DHEA and DHEAS levels, and may have important implications in the development of hormone therapies designed for elderly men and women.

Intrahepatic lipid, not visceral or muscle fat, is correlated with insulin resistance in older, female rhesus macaques

OBJECTIVE

Little is known of the effect of body composition on glucose metabolism in the aging female non-human primate. These variables in older female Rhesus macaques were studied.

DESIGN AND METHODS

Female Rhesus macaques (Macaca mulatta, n = 19, age range 23-30 years) underwent magnetic resonance imaging and (1) H spectroscopy to quantify total abdominal fat, visceral fat (VF), subcutaneous fat (SF) area, extramyocellular lipid (EMCL), intramyocellular lipid (IMCL) and intrahepatic lipid (IHL) content, and DEXA scan for whole body composition. A subgroup (n = 12) underwent a fasting blood draw and intravenous glucose tolerance test.

RESULTS

SF correlated with homeostatic model assessment of insulin resistance (HOMAIR ) and quantitative insulin sensitivity check index (QUICKI), but not after adjustment for fat mass. IHL demonstrated the strongest correlation with HOMAIR , QUICKI and calculated insulin sensitivity index (CSI ), and remained significant after adjustment for fat mass. VF, IMCL, and EMCL did not correlate with any of our measures of insulin sensitivity.

CONCLUSIONS

Despite a greater amount of VF compared to SF, VF was not associated with markers of insulin resistance (IR) in the older female monkey. Instead, IHL is a marker for IR in the fasting and post-prandial state in these animals.

Age-related changes in human and non-human primate white matter: from myelination disturbances to cognitive decline

The cognitive decline associated with normal aging was long believed to be due primarily to decreased synaptic density and neuron loss. Recent studies in both humans and non-human primates have challenged this idea, pointing instead to disturbances in white matter (WM) including myelin damage. Here, we review both cross-sectional and longitudinal studies in humans and non-human primates that collectively support the hypothesis that WM disturbances increase with age starting at middle age in humans, that these disturbances contribute to age-related cognitive decline, and that age-related WM changes may occur as a result of free radical damage, degenerative changes in cells in the oligodendrocyte lineage, and changes in microenvironments within WM.

Hormone supplementation during aging: how much and when?

Circulating levels of dehydroepiandrosterone, a major adrenal steroid, show a marked age-related decrease in both humans and nonhuman primates. Because this decrease has been implicated in age-related cognitive decline, we administered supplementary dehydroepiandrosterone to perimenopausal rhesus macaques (Macaca mulatta) to test for cognitive benefits. Although recognition memory improved, there was no benefit to spatial working memory. To address the limitations of this study we developed a hormone supplementation regimen in aged male macaques that more accurately replicates the 24-hr androgen profiles of young animals. We hypothesize that this more comprehensive physiological hormone replacement paradigm will enhance cognitive function in the elderly.

Association of microtubule associated protein-2, synaptophysin, and apolipoprotein E mRNA and protein levels with cognition and anxiety levels in aged female rhesus macaques

The dendritic protein microtubule associated protein 2 (MAP-2), the presynaptic marker synaptophysin (SYN), and apolipoprotein E (APOE), a protein which plays a role in lipid transport and metabolism and affects synaptic activity show changes with age. We analyzed post-mortem tissue from aged female rhesus macaques cognitively tested in a spatial maze and classified as good spatial performers (GSP) or poor spatial performers (PSP) and behaviorally tested in a playroom and classified as bold or reserved animals. MAP2, SYN, and APOE mRNA and protein levels in the prefrontal cortex (PFC), hippocampus, and amygdala, were assessed using qRT-PCR and western blot. In the amygdala, bold monkeys had higher levels of MAP2 and SYN mRNA than reserved monkeys. MAP2 mRNA correlated positively with amygdala size on the right, left, and combined left and right sides, while SYN mRNA levels correlated positively with the size of the right amygdala. In the hippocampus, SYN and APOE protein levels were higher in GSP than PSP animals. Thus, in aged nonhuman primates, classification of measures of anxiety is associated with differences in selected mRNA, but not protein, levels. In contrast, classification of cognitive performance is associated with differences in selected protein, but not mRNA, levels.

Mitochondrial DNA deletions and differential mitochondrial DNA content in Rhesus monkeys: implications for aging

The purpose of this study was to determine the relationship between mitochondrial DNA (mtDNA) deletions, mtDNA content and aging in rhesus monkeys. Using 2 sets of specific primers, we amplified an 8 kb mtDNA fragment covering a common 5.7 kb deletion and the entire 16.5 kb mitochondrial genome in the brain and buffy-coats of young and aged monkeys. We studied a total of 66 DNA samples: 39 were prepared from a buffy-coat and 27 were prepared from occipital cortex tissues. The mtDNA data were assessed using a permutation test to identify differences in mtDNA, in the different monkey groups. Using real-time RT-PCR strategy, we also assessed both mtDNA and nuclear DNA levels for young, aged and male and female monkeys. We found a 5.7 kb mtDNA deletion in 81.8% (54 of 66) of the total tested samples. In the young group of buffy-coat DNA, we found 5.7 kb deletions in 7 of 17 (41%), and in the aged group, we found 5.7 kb deletions in 12 of 22 (54%), suggesting that the prevalence of mtDNA deletions is related to age. We found decreased mRNA levels of mtDNA in aged monkeys relative to young monkeys. The increases in mtDNA deletions and mtDNA levels in aged rhesus monkeys suggest that damaged DNA accumulates as rhesus monkeys age and these altered mtDNA changes may have physiological relevance to compensate decreased mitochondrial function.

Accelerated immune senescence and reduced response to vaccination in ovariectomized female rhesus macaques

Aging is associated with a general dysregulation in immune function, commonly referred to as "immune senescence". Several studies have shown that female sex steroids can modulate the immune response. However, the impact of menopause-associated loss of estrogen and progestins on immune senescence remains poorly understood. To help answer this question, we examined the effect of ovariectomy on T-cell homeostasis and function in adult and aged female rhesus macaques. Our data show that in adult female rhesus macaques, ovariectomy increased the frequency of naïve CD4 T cells. In contrast, ovariectomized (ovx) aged female rhesus macaques had increased frequency of terminally differentiated CD4 effector memory T cells and inflammatory cytokine-secreting memory T cells. Moreover, ovariectomy reduced the immune response (T-cell cytokine and IgG production) following vaccination with modified vaccinia ankara in both adult and aged female rhesus macaques compared to ovary-intact age-matched controls. Interestingly, hormone therapy (estradiol alone or in conjunction with progesterone) partially improved the T-cell response to vaccination in aged ovariectomized female rhesus macaques. These data suggest that the loss of ovarian steroids, notably estradiol and progesterone, may contribute to reduced immune function in post-menopausal women and that hormone therapy may improve immune response to vaccination in this growing segment of the population.

Hippocampal M1 receptor function associated with spatial learning and memory in aged female rhesus macaques

Of the acetylcholine muscarinic receptors, the type 1 (M1) and type 2 (M2) receptors are expressed at the highest levels in the prefrontal cortex (PFC) and hippocampus, brain regions important for cognition. As equivocal findings of age-related changes of M1 and M2 in the nonhuman primate brain have been reported, we first assessed age-related changes in M1 and M2 in the PFC and hippocampus using saturation binding assays. Maximum M1 receptor binding, but not affinity of M1 receptor binding, decreased with age. In contrast, the affinity of M2 receptor binding, but not maximum M2 receptor binding, increased with age. To determine if in the elderly cognitive performance is associated with M1 or M2 function, we assessed muscarinic function in elderly female rhesus macaques in vivo using a scopolamine challenge pharmacological magnetic resonance imaging and in vitro using saturation binding assays. Based on their performance in a spatial maze, the animals were classified as good spatial performers (GSP) or poor spatial performers (PSP). In the hippocampus, but not PFC, the GSP group showed a greater change in T(2)*-weighted signal intensity after scopolamine challenge than the PSP group. The maximum M1 receptor binding and receptor binding affinity was greater in the GSP than the PSP group, but no group difference was found in M2 receptor binding. Parameters of circadian activity positively correlated with the difference in T(2)*-weighted signal intensity before and after the challenge, the maximum M1 receptor binding, and the M1 receptor binding affinity. Thus, while in rhesus macaques, there are age-related decreases in M1 and M2 receptor binding, in aged females, hippocampal M1, but not M2, receptor function is associated with spatial learning and memory and circadian activity.

Astrocytes in aged nonhuman primate brain gray matter synthesize excess hyaluronan

The glycosaminoglycan hyaluronan (HA) accumulates in central nervous system lesions where it limits astrogliosis but also inhibits oligodendrocyte progenitor cell (OPC) maturation. The role of hyaluronan in normative brain aging has not been previously investigated. Here, we tested the hypothesis that HA accumulates in the aging nonhuman primate brain. We found that HA levels significantly increase with age in the gray matter of rhesus macaques. HA accumulation was linked to age-related increases in the transcription of HA synthase-1 (HAS1) expressed by reactive astrocytes but not changes in the expression of other HAS genes or hyaluronidases. HA accumulation was accompanied by increased expression of CD44, a transmembrane HA receptor. Areas of gray matter with elevated HA in older animals demonstrated increased numbers of olig2(+) OPCs, consistent with the notion that HA may influence OPC expansion or maturation. Collectively, these data indicate that HAS1 and CD44 are transcriptionally upregulated in astrocytes during normative aging and are linked to HA accumulation in gray matter.

Perimenopausal regulation of steroidogenesis in the nonhuman primate

Human aging is characterized by a marked decrease in circulating levels of dehydroepiandrosterone (DHEA) and DHEA-sulfate (DHEAS), hormonal changes associated with cognitive decline. Despite beneficial effects of DHEA supplementation in rodents, studies in elderly humans have generally failed to show cognitive improvement after treatment. In the present study we evaluate the effects of age and estradiol supplementation on expression of genes involved in the de novo synthesis of DHEA and its conversion to estradiol in the rhesus macaque hippocampus. Using reverse transcription polymerase chain reaction (RT-PCR) we demonstrate the expression of genes associated with this synthesis in several areas of the rhesus brain. Furthermore, real-time PCR reveals an age-related attenuation of hippocampal expression level of the genes CYP17A1, STS, and 3BHSD1/2. Additionally, short-term administration of estradiol is associated with decreased expression of CYP17A1, STS, SULT2B1, and AROMATASE, consistent with a downregulation not only of estrogen synthesis from circulating DHEA, but also of de novo DHEA synthesis within the hippocampus. These findings suggest a decline in neurosteroidogenesis may account for the inefficacy of DHEA supplementation in elderly humans, and that central steroidogenesis may be a function of circulating hormones and menopausal status.

Japanese macaque encephalomyelitis: a spontaneous multiple sclerosis-like disease in a nonhuman primate

OBJECTIVE

To describe Japanese macaque encephalomyelitis (JME), a spontaneous inflammatory demyelinating disease occurring in the Oregon National Primate Research Center's (ONPRC) colony of Japanese macaques (JMs, Macaca fuscata).

METHODS

JMs with neurologic impairment were removed from the colony, evaluated, and treated with supportive care. Animals were humanely euthanized and their central nervous systems (CNSs) were examined.

RESULTS

ONPRC's JM colony was established in 1965 and no cases of JME occurred until 1986. Since 1986, 57 JMs spontaneously developed a disease characterized clinically by paresis of 1 or more limbs, ataxia, or ocular motor paresis. Most animals were humanely euthanized during their initial episode. Three recovered, later relapsed, and were then euthanized. There was no gender predilection and the median age for disease was 4 years. Magnetic resonance imaging of 8 cases of JME revealed multiple gadolinium-enhancing T(1) -weighted hyperintensities in the white matter of the cerebral hemispheres, brainstem, cerebellum, and cervical spinal cord. The CNS of monkeys with JME contained multifocal plaque-like demyelinated lesions of varying ages, including acute and chronic, active demyelinating lesions with macrophages and lymphocytic periventricular infiltrates, and chronic, inactive demyelinated lesions. A previously undescribed gamma-herpesvirus was cultured from acute JME white matter lesions. Cases of JME continue to affect 1% to 3% of the ONPRC colony per year.

INTERPRETATION

JME is a unique spontaneous disease in a nonhuman primate that has similarities with multiple sclerosis (MS) and is associated with a novel simian herpesvirus. Elucidating the pathogenesis of JME may shed new light on MS and other human demyelinating diseases.

Spatial Memory Performance Associated with Measures of Immune Function in Elderly Female Rhesus Macaques

We recently reported that in aged female rhesus macaques, spatial learning and memory correlates with circadian sleep-wake measures and hippocampal muscarinic type 1 (M(1)) receptor binding. To investigate if spatial memory also correlates with measures of immune function, we now assessed the magnitude of the adaptive immune response to vaccination in the same old female rhesus macaques. Cognitively characterized animals were classified as good spatial performers (GSP) or poor spatial performers (PSP) based on performance in the Spatial Foodport maze. The GSP group had higher frequency of CD8, but not CD4, interferon-γ (IFN-γ) producing cells following vaccination compared to the PSP group, suggesting a stronger CD8 T cell response in the GSP group. In addition, the number of CD-8 IFN-γ positive cells correlated with measures of sleep quality. Interestingly, the PSP group had a significantly higher antibody titer compared to the GSP group, and antibody titer negatively correlated with day-time activity. Thus, in aged female rhesus macaques, superior cognitive performance is correlated with a more robust CD8 T cell response but a reduced antibody response to vaccination.

Age-related decreases in SYN levels associated with increases in MAP-2, apoE, and GFAP levels in the rhesus macaque prefrontal cortex and hippocampus

Loss of synaptic integrity in the hippocampus and prefrontal cortex (PFC) may play an integral role in age-related cognitive decline. Previously, we showed age-related increases in the dendritic marker microtubule associated protein 2 (MAP-2) and the synaptic marker synaptophysin (SYN) in mice. Similarly, apolipoprotein E (apoE), involved in lipid transport and metabolism, and glial fibrillary acidic protein (GFAP), a glia specific marker, increase with age in rodents. In this study, we assessed whether these four proteins show similar age-related changes in a nonhuman primate, the rhesus macaque. Free-floating sections from the PFC and hippocampus from adult, middle-aged, and aged rhesus macaques were immunohistochemically labeled for MAP-2, SYN, apoE, and GFAP. Protein levels were measured as area occupied by fluorescence using confocal microscopy as well as by Western blot. In the PFC and hippocampus of adult and middle-aged animals, the levels of SYN, apoE, and GFAP immunoreactivity were comparable but there was a trend towards higher MAP-2 levels in middle-aged than adult animals. There was significantly less SYN and more MAP-2, apoE, and GFAP immunoreactivity in the PFC and hippocampus of aged animals compared to adult or middle-aged animals. Thus, the age-related changes in MAP-2, apoE, and GFAP levels were similar to those previously observed in rodents. On the other hand, the age-related changes in SYN levels were not, but were similar to those previously observed in the aging human brain. Taken together, these data emphasize the value of the rhesus macaque as a pragmatic translational model for human brain aging.

Influence of age and 17beta-estradiol on kisspeptin, neurokinin B, and prodynorphin gene expression in the arcuate-median eminence of female rhesus macaques

The neuropeptides kisspeptin, neurokinin B, and dynorphin A (collectively abbreviated as KNDy) are, respectively, encoded by KiSS-1, NKB, and PDYN and are coexpressed by neurons of the hypothalamic arcuate nucleus (ARC). Here, using quantitative real-time PCR, we examined age-related changes in the expression of genes encoding KNDy and associated receptors G protein-coupled receptor 54 (encoded by GPR54), neurokinin 3 receptor (encoded by NK3), and kappa-opioid receptor (encoded by KOR), in the female rhesus macaque ARC-median eminence (ARC-ME). Expression of KiSS-1 and NKB was highly elevated in old perimenopausal compared with young or middle-aged premenopausal animals. To test whether these age-related changes could be attributed to perimenopausal loss of sex steroids, we then examined KNDy, GPR54, NK3, and KOR expression changes in response to ovariectomy (OVX) and exposure to 17beta-estradiol (E(2)). Short-term (7 months) OVX (with or without 1 month of estrogen replacement) failed to modulate the expression of any of the KNDy-related genes. In contrast, long-term ( approximately 4 yr) OVX significantly increased KiSS-1 and NKB expression, and this was reversed by E(2) administration. Finally, we examined the expression of KNDy-related genes in young adult females during the early follicular, late follicular, or midluteal phases of their menstrual cycle but found no difference. Together, the results suggest that short-term alterations in circulating E(2) levels, such as those occurring during the menstrual cycle, may have little effect on the ARC-ME expression of KNDy and associated receptors. Nevertheless, they clearly demonstrate that loss of ovarian steroid negative feedback that occurs during perimenopause plays a major role in modulating the activity of KNDy circuits of the aging primate ARC-ME.

Microarray analysis of relative gene expression stability for selection of internal reference genes in the rhesus macaque brain

Background

Normalization of gene expression data refers to the comparison of expression values using reference standards that are consistent across all conditions of an experiment. In PCR studies, genes designated as "housekeeping genes" have been used as internal reference genes under the assumption that their expression is stable and independent of experimental conditions. However, verification of this assumption is rarely performed. Here we assess the use of gene microarray analysis to facilitate selection of internal reference sequences with higher expression stability across experimental conditions than can be expected using traditional selection methods.

We recently demonstrated that relative gene expression from qRT-PCR data normalized using GAPDH, ALG9 and RPL13A expression values mirrored relative expression using quantile normalization in Robust Multichip Analysis (RMA) on the Affymetrix^® GeneChip^® rhesus Macaque Genome Array.

Having shown that qRT-PCR and Affymetrix^® GeneChip^® data from the same hormone replacement therapy (HRT) study yielded concordant results, we used quantile-normalized gene microarray data to identify the most stably expressed among probe sets for prospective internal reference genes across three brain regions from the HRT study and an additional study of normally menstruating rhesus macaques (cycle study). Gene selection was limited to 575 previously published human "housekeeping" genes. Twelve animals were used per study, and three brain regions were analyzed from each animal. Gene expression stabilities were determined using geNorm, NormFinder and BestKeeper software packages.

Results

Sequences co-annotated for ribosomal protein S27a (RPS27A), and ubiquitin were among the most stably expressed under all conditions and selection criteria used for both studies. Higher annotation quality on the human GeneChip^® facilitated more targeted analysis than could be accomplished using the rhesus GeneChip^®. In the cycle study, multiple probe sets annotated for actin, gamma 1 (ACTG1) showed high signal intensity and were among the most stably expressed.

Conclusions

Using gene microarray analysis, we identified genes showing high expression stability under various sex-steroid environments in different regions of the rhesus macaque brain. Use of quantile-normalized microarray gene expression values represents an improvement over traditional methods of selecting internal reference genes for PCR analysis.

Effect of caloric restriction on base-excision repair (BER) in the aging rat brain

Apyrimidinic/apurinic endonuclease (APE) is a key protein involved in the base-excision DNA repair (BER) pathway of oxidative DNA lesions. Using a novel oligonucleotide substrate, we demonstrate that APE activity in the frontal/parietal cortex (F/PCTX), cerebellum, brainstem, midbrain and hypothalamus declined with age in rats on an ad libitum (AL) diet. In contrast, APE activity for these brain regions was approximately 1.5-3 times higher in young, caloric restricted (CR) rats. Despite continuous CR treatment in all animals since six weeks of age, APE activity in the CR group started to decline by middle-age and continued into old age. However, CR maintained APE activity at a level that was significantly higher than that in AL rats across age and in the brain regions examined. Because Western analysis of APE, DNA polymerase beta and DNA ligase III levels in the F/PCTX of both CR and AL rats remained unchanged with age, this suggests that the increased APE activity in CR rats is the result of differential post-translational modification of APE.

Influence of 17beta-estradiol and progesterone on GABAergic gene expression in the arcuate nucleus, amygdala and hippocampus of the rhesus macaque

Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the brain, and the responsiveness of neurons to GABA can be modulated by sex steroids. To better understand how ovarian steroids influence the GABAergic system in the primate brain, we evaluated the expression of genes encoding GABA receptor subunits, glutamic acid decarboxylase (GAD) and a GABA transporter in the brains of female rhesus macaques. Ovariectomized adults were subjected to a hormone replacement paradigm involving either 17beta-estradiol (E), or E plus progesterone (E+P). Untreated animals served as controls. Using GeneChip microarray analysis and real-time RT-PCR (qPCR), we examined gene expression differences within and between the amygdala (AMD), hippocampus (HPC) and arcuate nuclei of the medial basal hypothalamus (MBH). The results from PCR corresponded with results from representative GeneChip probesets, and showed similar effects of sex steroids on GABA receptor subunit gene expression in the AMD and HPC, and a more pronounced expression than in the MBH. Exposure to E+P attenuated GAD1, GAD2 and SLC32A1 gene expression in the AMD and HPC, but not in the MBH. GABA receptor subunit gene expression was generally higher in the AMD and HPC than in the MBH, with the exception of receptor subunits epsilon and gamma 2. Taken together, the data demonstrate differential regulation of GABA receptor subunits and GABAergic system components in the MBH compared to the AMD and HPC of rhesus macaques. Elevated epsilon and reduced delta subunit expression in the MBH supports the hypothesis that the hypothalamic GABAergic system is resistant to the modulatory effects of sex steroids.

Gene expression profiling in the rhesus macaque: experimental design considerations

The development of species-specific gene microarrays has greatly facilitated gene expression profiling in nonhuman primates. However, to obtain accurate and physiologically meaningful data from these microarrays, one needs to consider several factors when designing the studies. This article focuses on effective experimental design while the companion article focuses on methodology and data analysis. Biological cycles have a major influence on gene expression, and at least 10% of the expressed genes are likely to show a 24-h expression pattern. Consequently, the time of day when RNA samples are collected can influence detection of significant changes in gene expression levels. Similarly, when photoperiodic species such as the rhesus macaque are housed outdoors, some of their genes show differential expression according to the time of year. In addition, the sex-steroid environment of humans and many nonhuman primates changes markedly across the menstrual cycle, and so phase of the cycle needs to be considered when studying gene expression in adult females.