Sex- and age-related P75 neurotrophin receptor expression in the human supraoptic nucleus

Ageing restructures the transcriptome of the hypothalamic supraoptic nucleus and alters the response to dehydration

Ageing is associated with altered neuroendocrine function. In the context of the hypothalamic supraoptic nucleus, which makes the antidiuretic hormone vasopressin, ageing alters acute responses to hyperosmotic cues, rendering the elderly more susceptible to dehydration. Chronically, vasopressin has been associated with numerous diseases of old age, including type 2 diabetes and metabolic syndrome. Bulk RNAseq transcriptome analysis has been used to catalogue the polyadenylated supraoptic nucleus transcriptomes of adult (3 months) and aged (18 months) rats in basal euhydrated and stimulated dehydrated conditions. Gene ontology and Weighted Correlation Network Analysis revealed that ageing is associated with alterations in the expression of extracellular matrix genes. Interestingly, whilst the transcriptomic response to dehydration is overall blunted in aged animals compared to adults, there is a specific enrichment of differentially expressed genes related to neurodegenerative processes in the aged cohort, suggesting that dehydration itself may provoke degenerative consequences in aged rats.

The supraoptic and paraventricular nuclei in healthy aging and neurodegeneration

The supraoptic (SON) and paraventricular (PVN) nuclei of the hypothalamus undergo structural and functional changes over the course of healthy aging. These nuclei and their connections are also heterogeneously affected by several different neurodegenerative diseases. This chapter reviews the involvement of the SON and PVN, the hypothalamic-pituitary axes, and the peptide hormones produced in both nuclei in healthy aging and in neurodegeneration, with a focus on Alzheimer's disease (AD), frontotemporal dementia (FTD), amyotrophic lateral sclerosis, progressive supranuclear palsy, Parkinson's disease (PD), dementia with Lewy bodies (DLB), multiple system atrophy, and Huntington's disease. Although age-related changes occur in several regions of the hypothalamus, the SON and PVN are relatively preserved during aging and in many neurodegenerative disorders. With aging, these nuclei do undergo some sexually dimorphic changes including changes in size and levels of vasopressin and corticotropin-releasing hormone, likely due to age-related changes in sex hormones. In contrast, oxytocinergic cells and circulating levels of thyrotropin-releasing hormone remain stable. A relative resistance to many forms of neurodegenerative pathology is also observed, in comparison to other hypothalamic and brain regions. Mirroring the pattern observed in aging, pathologic hallmarks of AD, and some subtypes of FTD are observed in the PVN, though to a milder degree than are observed in other brain regions, while the SON is relatively spared. In contrast, the SON appears more vulnerable to alpha-synuclein pathology of DLB and PD. The consequences of these alterations may help to inform several of the physiologic changes observed in aging and neurodegenerative disease.

Increased neuronal metabolic activity and estrogen receptors in the vertical limb of the diagonal band of Broca in Alzheimer's disease: relation to sex and aging

Changes in the interaction between sex hormones and the cholinergic system are presumed to play a role in cognitive decline in aging and Alzheimer's disease (AD). The hippocampus is one of the most strongly affected brain structures in AD and the vertical limb of the diagonal band of Broca (VDB) is its major source of innervation. In the present study we found, surprisingly, for the first time that the neuronal metabolic activity as measured by the size of the Golgi apparatus in the VDB gradually increases after the age of 50 years in controls and that this process starts earlier and is more pronounced in Alzheimer's disease patients. Neuronal metabolic activity in the VDB was significantly higher in AD than in control patients younger than 70 years of age and was higher in control patients over 70 years than in control patients younger than 70 years of age. The activation of VDB neurons during aging was accompanied by an increased nuclear estrogen receptor (ER) beta staining, which was stronger in patients over 70 years of age than in younger subjects (in both controls and AD patients). Interestingly, as in the nucleus basalis of Meynert, nuclear ERalpha expression was markedly enhanced in AD patients compared to controls independent of age. In addition, evidence was found for the influence of APOE genotype on ERalpha and ERbeta staining in the human VDB in aging and in AD. APOE genotype was positively correlated (epsilon 2 < epsilon 3 < epsilon 4) with the percentage of cytoplasm ERalpha-positive VDB neurons in elderly control male and female subjects and with both nuclear and cytoplasm ERbeta-positive neurons in control women. In conclusion, the VDB is compensatory activated and shows more nuclear ER expression in aging and AD in a sex- and APOE genotype-dependent way. So neither global degeneration or a strongly decreased neuronal metabolism nor a lack of sex hormone receptors in the VDB seems to contribute to the decline in cognition in aging or AD in which the hippocampus plays such a crucial role.

Increased p75(NTR) expression in hippocampal neurons containing hyperphosphorylated tau in Alzheimer patients

p75(NTR), a low-affinity neurotrophin receptor, may be involved in the pathogenesis of Alzheimer's disease (AD). The aim of present study was to detect the relationship between p75(NTR)-containing neurons and the pretangles consisting of hyperphosphorylated tau stained by Alz-50 in the hippocampus of AD patients. Samples of hippocampus of 10 female AD patients and 10 nondemented female controls matched for age and postmortem delay were investigated immunocytochemically, and the stainings were quantified using an image analysis system. The results showed that: (i) p75(NTR) was present in about half of the pyramidal neurons of the CA1-CA4 subfields of hippocampus. No difference was observed in the number of p75(NTR) immunoreactive neurons in the CA1-CA4 subfields between the two groups. Interestingly, the ratio of p75(NTR) expressing neurons to the total number of neurons as staining with thionin was significantly higher in the CA1 and CA2 subfields of AD hippocampus than in controls. (ii) There were a large number of Alz-50 neurons and double-labeled neurons containing p75(NTR) and Alz-50 in the CA1 and CA2 subfields of AD patients. These results suggest that p75(NTR) may be involved in the formation of tangles in the Alzheimer process.

Sex differences in estrogen receptor α and β expression in vasopressin neurons of the supraoptic nucleus in elderly and Alzheimer’s disease patients: no relationship with cytoskeletal alterations

In various hypothalamic and adjacent brain regions we have previously found a remarkable increase in nuclear estrogen receptor staining in Alzheimer's disease (AD). In order to see whether this was a general phenomenon or rather specific for those areas that are affected by the AD process we investigated ERalpha and ERbeta expression in the arginine-vasopressin (AVP) neurons of the human dorsolateral suparoptic nucleus (dl-SON), that is the major source of plasma AVP. These neurons remain exceptionally intact in AD. Changes in ER expression were studied in relation to early Alzheimer changes (i.e. hyperphosphorylated tau) and neuronal metabolism in AD as determined by the size of the Golgi apparatus (GA) or cell size. No difference in neuronal metabolism (i.e. GA size or cell size) of AVP neurons was observed between AD and control patients and no early cytoskeletal AD alterations were found confirming the resistance of the dl-SON to AD. While no differences between AD and control patients were present for ERalpha and ERbeta staining except for a lower proportion of nuclear ERbeta AVP-positive neurons in AD subjects, complex sex differences not directly related to AD were observed within each group. The main finding of the present study is that in the dl-SON, that remains active and spared of AD changes, the increase in nuclear ERs seen in adjacent affected areas in AD patients does not occur. This indicates that a rise of nuclear ERs is not a generally occurring phenomenon but rather related to the pathogenetic alterations of the AD process.

Neurohypophyseal peptides in aging and Alzheimer's disease

The neurohypophyseal hormones arginine-vasopressin (AVP) and oxytocin (OT) are produced in the neurons of the hypothalamic supraoptic (SON) and paraventricular (PVN) nucleus and in the much smaller cells of the suprachiasmatic (SCN) nucleus. The SON is the main source of plasma AVP. Part of the AVP and OT neurons of the PVN join the hypothalamo-neurohypophyseal tract, whereas others send projections to the median eminence or various brain areas, where AVP and OT are involved in a number of central functions as neurotransmitters/neuromodulators. AVP and OT from the PVN can also regulate via the autonomous innervation endocrine glands and fat tissue. OT is produced for a major part in the PVN but some OT neurons are present in the SON. Moreover, both AVP and OT containing neurons are observed in the "accessory nuclei", i.e. islands situated between the SON and PVN. The SCN is the biological clock, and the number of AVP expressing neurons in the SCN shows both diurnal and seasonal rhythms. In addition to these hypothalamic areas, AVP and OT may be found to a lesser extent in some other brain areas, such as the bed nucleus of the stria terminalis, diagonal band of Broca, nucleus basalis of Meynert, lateral septal nucleus, globus pallidus and the anterior amygdaloid nucleus, as well as in the peripheral tissues. The AVP and OT containing neurons should not be considered as one system. Prominent functional differences exist between the different nuclei. The heterogeneity also becomes clear from the marked differences in the neurohypophyseal peptides containing neurons of the SON, PVN and SCN during aging, and in the most prevalent age-related neurodegenerative diseases, i.e. Alzheimer's disease (AD). For those reasons, we will discuss the SON, PVN and SCN separately.

Hypothalamic NPY and agouti-related protein are increased in human illness but not in Prader-Willi syndrome and other obese subjects

Animal studies have demonstrated the importance of orexigenic NPY and agouti-related protein (AGRP) hypothalamic neurons, which are inhibited by the adipocyte hormone leptin, in the regulation of body weight and neuroendocrine secretion. We have examined NPY and AGRP neurons in postmortem human hypothalami from controls, Prader-Willi syndrome and other obese subjects, using quantitative immunocytochemistry (ICC) and in situ hybridization, to identify causes of leptin resistance in human obesity. Using combined ICC and in situ hybridization, AGRP, but not POMC, was colocalized with NPY in infundibular nucleus neurons. Infundibular nucleus (including median eminence) NPY ICC staining or mRNA expression, and AGRP ICC staining, increased with premorbid illness duration. NPY ICC staining and mRNA expression were reduced in obese subjects, but AGRP ICC staining was unchanged, correcting for illness duration. This suggests normal responses of NPY and AGRP neurons to peripheral signals, such as leptin and insulin, in human illness and obesity. The pathophysiology of obesity and illness-associated anorexia appear to lie in downstream or separate neuronal circuits, but the infundibular neurons may mediate neuroendocrine responses to illness. The implications for pharmacological treatment of human obesity are discussed.

Biological ageing research in the Netherlands

After an introduction on the development of biological ageing research in the Netherlands during the past decades, 606 papers on aging published by Dutch institutes in the period 1991-2000, collected from PubMed, were analysed for their relevance to research into biological ageing. For the period 1996-2000, the total number of research papers on biological ageing amounted to 142, which accounts for 23% of all publications on ageing in that period. The number of publications per year did not change. On the basis of these papers and additional information provided by research groups a comprehensive overview of biological ageing research in the Netherlands is presented, together with an extensive literature list. Ageing of the central nervous system (CNS), of the endocrinological system and of the cardiovascular system are the topics most studied. It is concluded that general biological ageing research has not increased in the Netherlands over the last ten years, and that the infrastructure for basic biological ageing research in the Netherlands is weak.

Increased expression of estrogen receptor α and β in the nucleus basalis of Meynert in Alzheimer’s disease

The human nucleus basalis of Meynert (NBM) is severely affected in Alzheimer's disease (AD). Since estrogens may reduce both the risk and severity of AD, possibly by an action on the cholinergic system, we determined whether estrogen receptors are present in the human NBM and what their changes are in normal aging and in AD. ERalpha was expressed to a higher degree than ERbeta and was localized mainly in the cell nucleus, while ERbeta was mainly confined to the cytoplasm. A significant positive correlation between the percentage of ERalpha nuclear positive neurons and age was found in men but not in women, whereas the proportion of ERbeta cytoplasm positive cells increased during aging in both sexes. In AD the proportion of neurons showing nuclear staining for both ERalpha and beta and cytoplasmic staining for ERbeta was markedly increased. The percentage of ERbeta nuclear positive neurons increased in AD only in women but not in men. The ApoE genotype had no effect on ER expression in the NBM in AD. In conclusion, whereas only minor sex- and age-related changes in both ERs were found in the human NBM, a clear upregulation of ERalpha and beta was observed in AD.