Brain immunoreactive gonadotropin-releasing hormone in Huntington's chorea and in non-choreic subjects

IKKβ signaling mediates metabolic changes in the hypothalamus of a Huntington disease mouse model

Huntington disease (HD) is a neurodegenerative disorder caused by a CAG repeat expansion in the huntingtin (HTT) gene. Metabolic changes are associated with HD progression, but underlying mechanisms are not fully known. As the IKKβ/NF-κB pathway is an essential regulator of metabolism, we investigated the involvement of IKKβ, the upstream activator of NF-κB in hypothalamus-specific HD metabolic changes. We expressed amyloidogenic N-terminal fragments of mutant HTT (mHTT) in the hypothalamus of mice with brain-specific ablation of IKKβ (Nestin/IKKβ^lox/lox) and control mice (IKKβ^lox/lox). We assessed effects on body weight, metabolic hormones, and hypothalamic neuropathology. Hypothalamic expression of mHTT led to an obese phenotype only in female mice. CNS-specific inactivation of IKKβ prohibited weight gain in females, which was independent of neuroprotection and microglial activation. Our study suggests that mHTT in the hypothalamus causes metabolic imbalance in a sex-specific fashion, and central inhibition of the IKKβ pathway attenuates the obese phenotype.

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Mutant huntingtin in the hypothalamus causes sex-specific metabolic imbalance

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CNS-specific inactivation of the IKKβ pathway prevents the obese phenotype

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IKKβ inactivation leads to an increased number of mutant huntingtin inclusions

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IKKβ inactivation does not prevent orexin or A13 TH neuron loss

Matching of the postmortem hypothalamus from patients and controls

The quality of postmortem hypothalamus research depends strongly on a thorough clinical investigation and documentation of the patient's disorder and therapies. In addition, a systematic and professional neuropathological investigation of the entire brain of both the cases and the controls is absolutely crucial. In the experience of the Netherlands Brain Bank (NBB), about 20% of the clinical neurological diagnoses, despite being made in first rate clinics, have to be revised or require extra diagnoses after a complete and thorough neuropathologic review by the NBB. The neuropathology examination may reveal for instance that the elderly "controls" already have preclinical neurodegenerative alterations. In postmortem studies, the patient and control groups must be matched for as many as possible of the known confounding factors. This is necessary to make the groups as similar as possible, except for the topic being investigated. Confounding factors are present (i) before, (ii) during, and (iii) after death. They are, respectively: (i) genetic background, systemic diseases, duration and gravity of illness, medicines and addictive compounds used, age, sex, gender identity, sexual orientation, clock- and seasonal time of death, and lateralization; (ii) agonal state, stress of dying; and (iii) postmortem delay, freezing procedures, fixation, and storage time. Agonal state is generally estimated by measuring the pH of the brain. However, there are disorders in which pH is lower as a part of the disease process. Because of the large number of potentially confounding factors that differ according to, for instance, brain area and disease, a brain bank should have a large number of controls at its disposal for appropriate matching. If matching fails for some confounders, the influence of the confounders may be determined by statistical methods, such as analysis of variance or the regression models.

The art of matching brain tissue from patients and controls for postmortem research

The quality of postmortem research depends strongly on a thorough clinical investigation and documentation of the patient's disorder and therapies. In addition, a systematic and professional neuropathologic investigation of both cases and controls is absolutely crucial. In the experience of the Netherlands Brain Bank (NBB), about 20% of clinical neurologic diagnoses, despite being made in first-rate clinics, have to be revised or require an extra diagnosis after a complete and thorough review by the NBB. The neuropathology examination may reveal for instance that the "controls" already have preclinical neurodegenerative alterations. In postmortem studies the patient and control groups must be matched for as many of the known confounding factors as possible. This is necessary to make the groups as similar as possible, except for the topic being investigated. Confounding factors are present before, during, and after death. They are respectively: (1) genetic background, systemic diseases, duration and gravity of illness, medicines and addictive compounds used, age, sex, gender identity, sexual orientation, circadian and seasonal fluctuations, lateralization; (2) agonal state, stress of dying; and (3) postmortem delay, freezing procedures, fixation and storage time. Consequently, a brain bank should have a large number of controls at its disposal for appropriate matching. If matching fails for some confounders, then their influence may be determined by statistical methods such as analysis of variance or regression models.

Metabolic and behavioral effects of mutant huntingtin deletion in Sim1 neurons in the BACHD mouse model of Huntington's disease

Hypothalamic pathology, metabolic dysfunction and psychiatric symptoms are part of Huntington disease (HD), which is caused by an expanded CAG repeat in the huntingtin (HTT) gene. Inactivation of mutant HTT selectively in the hypothalamus prevents the development of metabolic dysfunction and depressive-like behavior in the BACHD mouse model. The hypothalamic paraventricular nucleus (PVN) is implicated in metabolic and emotional control, therefore we here tested whether inactivation of mutant HTT in the PVN affects metabolic and psychiatric manifestations of HD in BACHD mice. BACHD mice were crossed with mice expressing Cre-recombinase under the Sim1 promoter (Sim1-Cre) to inactivate mutant HTT in Sim1 expressing cells, i.e. the PVN of the hypothalamus. We found that inactivation of mutant HTT in Sim1 cells had a sex-specific effect on both the metabolic and the psychiatric phenotype, as these phenotypes were no longer different in male BACHD/Sim1-Cre mice compared to wild-type littermates. We also found a reduced number of GnRH neurons specifically in the anterior hypothalamus and an increased testes weight in male BACHD mice compared to wild-type littermates. Taken together, expression of mutant HTT in Sim1 cells may play a role for the development of metabolic dysfunction and depressive-like behavior in male BACHD mice.

Relationship satisfaction and sexuality in Huntington's disease

Huntington's disease (HD) is a chronic disabling disease that inflicts a considerable burden on patients and their families for a variety of reasons. These reasons include cognitive impairment and motor dysfunction, personality changes, and knowledge of possible genetic transmission of the disease to their children. Thus, the decision to take a genetic test for individuals at risk for HD is often associated with family planning and relationship stress. However, for most individuals, a positive genetic test does not alter family planning with regard to their decision to have children. HD has also been associated with abnormal sexual behaviors, although only a few studies have explored sexuality and sexual dysfunction in HD. Up to 85% of men and 75% of women experience sexual problems, including hypoactive sexual disorder in some cases and increased sexual interest and paraphilia in others. Psychologic support should involve the communication of realistic expectations about the progression of the disorder and potential consequences on the children.

Androgen function in the pathophysiology and treatment of male Huntington's disease patients

Low concentrations of circulating testosterone have been associated with dementia manifesting with advancing age and in neurodegenerative conditions. Huntington's disease (HD) is a dominantly inherited neurodegenerative disease with an invariably fatal outcome. Severe motor symptoms, psychosis and dementia are symptomatic hallmarks of the progression of HD that result from the dysfunction and death of neocortical and basal ganglia neurones. Treatments are directed toward manifest symptoms, although they are largely ineffectual in slowing or preventing disease progression. Emerging data have identified hypothamic pathologies in HD that result in endocrine disturbances. Clinically defined primary or secondary hypogonadism elicit low circulating testosterone concentrations and have been linked to the development of Alzheimer's disease in men. Examining similar neuroendocrine dysfunction in HD including the nature of manifest hypogonadism in male patients could allow an elucidation of the complex pathophysiology of HD and provide an impetus for hitherto untested testosterone replacement therapy.

Changes in key hypothalamic neuropeptide populations in Huntington disease revealed by neuropathological analyses

Huntington disease (HD) is a fatal neurodegenerative disorder caused by expansion of a CAG repeat in the HD gene. Degeneration concentrating in the basal ganglia has been thought to account for the characteristic psychiatric symptoms, cognitive decline and motor dysfunction. However, the homeostatic control of emotions and metabolism are disturbed early in HD, and focused studies have identified a loss of orexin (hypocretin) neurons in the lateral hypothalamus in HD patients. There has been limited assessment of other hypothalamic cell populations that may be involved. In this study, we quantified the neuropeptide-expressing hypothalamic neurons known to regulate metabolism and emotion in patients with HD compared to healthy controls using unbiased stereological methods. We confirmed the loss of orexin-expressing neurons in HD and revealed substantial differences in the peptide expression of other neuronal populations in the same patients. Both oxytocin- and vasopressin-expressing neurons were decreased by 45 and 24%, respectively, while the number of cocaine- and amphetamine-regulated transcript (CART)-expressing neurons was increased by 30%. The increased expression of CART in the hypothalamus is consistent with a previous study showing increased CART levels in cerebrospinal fluid from HD patients. There was no difference in the numbers of neuropeptide Y-expressing neurons. These results show significant and specific alterations in the peptide expression of hypothalamic neurons known to regulate metabolism and emotion. They may be important in the development of psychiatric symptoms and metabolic disturbances in HD, and may provide potential targets for therapeutic interventions.

Hypothalamic dysfunction and neuroendocrine and metabolic alterations in Huntington's disease: clinical consequences and therapeutic implications

Huntington's disease (HD) is a hereditary neurodegenerative disorder characterized by cognitive, psychiatric, behavioural and motor disturbances. Although the course of HD is also frequently complicated by unintended weight loss, sleep disturbances and autonomic nervous system dysfunction, the aetiology of these signs and symptoms remains largely unknown. In recent years, many novel findings from both animal and human studies have emerged that indicate considerable hypothalamic, endocrine and metabolic alterations in HD. However, a comprehensive overview of these findings is lacking and their precise clinical significance is far from clear. Therefore, in this review we attempt to put these recent developments in the field into perspective by integrating them with previous findings in a comprehensible manner, and by discussing their clinical relevance, with a special focus on body weight, sleep and autonomic functions in HD, which will also allow for the identification of future lines of research in this area.

Testicular degeneration in Huntington disease

Huntington disease (HD) is an adult onset, neurodegenerative disorder that results from CAG expansion in the HD gene. Recent work has demonstrated testicular degeneration in mouse models of HD and alterations in the hypothalamic-pituitary-gonadal (HPG) axis in HD patients. Here, we show that HD patients have specific testicular pathology with reduced numbers of germ cells and abnormal seminiferous tubule morphology. In the YAC128 mouse model, testicular degeneration develops prior to 12 months of age, but at 12 months, there is no evidence for decreased testosterone levels or loss of GnRH neurons in the hypothalamus. This suggests that testicular pathology results from a direct toxic effect of mutant huntingtin in the testis and is supported by the fact that huntingtin is highly expressed in the affected cell populations in the testis. Understanding the pathogenesis of HD in the testis may reveal common critical pathways which lead to degeneration in both the brain and testis.

Hypothalamic-endocrine aspects in Huntington's disease

Huntington's disease (HD) is a hereditary and fatal disorder caused by an expanded CAG triplet repeat in the HD gene, resulting in a mutant form of the protein huntingtin. Wild-type and mutant huntingtin are expressed in most tissues of the body but the normal function of huntingtin is not fully known. In HD, the neuropathology is characterized by intranuclear and cytoplasmic inclusions of huntingtin aggregates, and cell death primarily in striatum and cerebral cortex. However, hypothalamic atrophy occurs at early stages of HD with loss of orexin- and somatostatin-containing cell populations. Several symptoms of HD such as sleep disturbances, alterations in circadian rhythm, and weight loss may be due to hypothalamic dysfunction. Endocrine changes including increased cortisol levels, reduced testosterone levels and increased prevalence of diabetes are found in HD patients. In HD mice, alterations in the hypothalamic-pituitary-adrenal axis occurs as well as pancreatic beta-cell and adipocyte dysfunction. Increasing evidence points towards important pathology of the hypothalamus and the endocrine system in HD. As many neuroendocrine factors are secreted into the cerebrospinal fluid, blood and urine, it is possible that their levels may reflect the disease state in the central nervous system. Investigating neuroendocrine changes in HD opens up the possibility of finding biomarkers to evaluate future therapies for HD, as well as of identifying novel targets for therapeutic interventions.

Reduction of GnRH and infertility in the R6/2 mouse model of Huntington's disease

Reductions in testosterone and luteinizing hormone levels and reduced sexual functions have been reported in Huntington's disease (HD) patients. Atrophy of the reproductive organs and loss of fertility have also been observed in the R6/2 mouse, which is currently the most studied transgenic model of HD. In an effort to define the cause of infertility we studied the expression of gonadotropin-releasing hormone (GnRH) in the medial septum, diagonal band of Broca and hypothalamus of R6/2 male mice during sexual maturation. We found a progressive reduction in the numbers of GnRH-immunoreactive neurons in the analysed brain areas of R6/2 mice starting at 5 weeks of age and becoming statistically significant with only 10% of the neurons remaining by 9 weeks of age. Atrophy of testes and seminal vesicles combined with a significant reduction in serum and testicular testosterone levels were detected in 12-week-old R6/2mice. These results suggest that infertility in the R6/2 males is due either to death of GnRH neurons or to a reduction in GnRH expression leading to a downstream impairment of the gonadotropic hormones. Gonadotropic hormone replacement did not mitigate weight loss or restore motor function in R6/2 males.

Serum dehydroepiandrosterone and cortisol measurements in Huntington's chorea

Serum levels of dehydroepiandrosterone sulfate (DHEAS), known to antagonize metabolic effects of glucocorticoids in animals, and cortisol (CRT), already shown to be related to cognitive dysfunction in man and animals, were measured in 11 drug-free male subjects with definite Huntington's chorea (HC) and in 25 age-matched male normal controls. Statistical difference was found between DHEAS serum levels (p < 0.05), CRT levels (p < 0.05) and the DHEAS/CRT ratio (p < 0.01) of HC subjects and normal individuals. These findings may indicate a dysfunction of the hypothalamic-pituitary-adrenal axis (HPAA) and possibly suggest a role of DHEAS as an antiglucocorticoid in HC.

The posttranslational processing of beta-endorphin in human hypothalamus

beta-Endorphin is posttranslationally processed to six derivatives, which, although structurally similar, produce distinctly different biological effects. beta-Endorphin 1-31 is a potent opioid receptor agonist, but beta-endorphin 1-27 exhibits antagonist properties, and beta-endorphin 1-26 and the alpha-N-acetyl derivatives of all three peptides lack opioid receptor activity. In the present study, we identified the beta-endorphin peptides synthesized in human hypothalamus using cation exchange HPLC. First, we tested whether postmortem changes occur by storing rat hypothalami at 4 degrees C. This demonstrated that relative amounts of the six beta-endorphin forms did not change for up to 24 h, although total beta-endorphin immunoreactivity significantly declined after 6 h. HPLC analysis of human hypothalami revealed that beta-endorphin 1-31 was the principal form, constituting 58.4 +/- 5.4% of total immunoreactivity. Substantial amounts of beta-endorphin 1-27 (13.4 +/- 1.2%) and beta-endorphin 1-26 (13.1 +/- 1.6%) were also present, but alpha-N-acetylated forms were quantitatively minor, each comprising approximately 5% of total beta-endorphin. A similar processing pattern occurred in preoptic and suprachiasmatic areas of the hypothalamus. These results show that, despite differences in primary sequence, beta-endorphin is processed similarly in both rat and human hypothalamus. Opiate-active beta-endorphin 1-31 is the principal form in both species.

Somatostatin in multiple sclerosis

The detection of somatostatin, a 14 aminoacid peptide, in human brain and cerebrospinal fluid (CSF) initiated examinations by radioimmunoassay and immunocytochemical technique to elucidate its origin, localization, function, and possible significance in central nervous system disorders. The present survey deals with these aspects with special reference to multiple sclerosis (MS) and to correlation between disease activity and somatostatin content and variations in CSF.

Immunocytochemical localization of somatostatin in human brain

The distribution of somatostatin (SRIF) was examined in normal human forebrain, using thick vibratome cut sections. The unlabeled antibody enzyme method of immunocytochemistry revealed a widespread distribution of SRIF immunoreactive neurons and fibers throughout the septum, diencephalon and corpus striatum. Within the septum SRIF neurons and fibers were observed in the medial and lateral septal nuclei, the nucleus of the diagonal band, the nucleus accumbens and the bed nucleus of the stria terminalis. SRIF neurons and fibers were found in several hypothalamic and anterior thalamic nuclei as well as all regions of the corpus striatum. An interesting collection of SRIF immunoreactive neurons and processes were observed forming a wide band extending anteriorly from the lateral preoptic area through the lateral hypothalamus and substantia innominata posteriorly. This report on the localization of immunoreactive SRIF in the human forebrain extends previous anatomical findings and lends morphological support to recent biochemical studies.

Transmissible and non-transmissible neurodegenerative disease: similarities in age of onset and genetics in relation to aetiology

In only a few cases is transmissible dementia known to have been acquired by infection from a source outside the individual; the remaining cases can be classified as sporadic, loosely familial, or autosomal dominant. Each group has a characteristic mean age of onset. A range of neurodegenerative diseases (including Alzheimer-type dementia and amyotrophic lateral sclerosis) can also be classified in this way, with similar characteristic mean ages of onset. The emergence of these diseases in later middle age, and the interdependence of age of onset and the type of familial occurrence suggest that these pathological processes are related to those genetic mechanisms which determine senescence. It is argued that the majority of cases of transmissible dementia arise, not from infection, but from the expression of endogenous virogene sequences as part of the aging processes.

Neuropeptides in aging and dementia

Although senile dementia of the Alzheimer's type (SDAT) is a common disease associated with advancing age, recent studies have suggested that SDAT should not be considered synonymous with old age but a disease process separate from normal aging. This study examined the morphology of two neurochemically-defined neuronal populations (i.e., neurophysin, somatostatin) in the cortex and hypothalamus to determine if structural changes in these neuropeptide systems associated with advancing age are similar to those seen with SDAT. Our findings suggest that morphological changes consistent with neuronal degeneration occur in somatostatin but not neurophysin-containing neurons in cases diagnosed to have SDAT, and these structural changes are different from those seen in aged brain without central nervous system disease. These data support the concept that senile dementia of the Alzheimer's type is not a single neurochemical related disease, but may be associated with anatomical lesions and biochemical imbalances among a number of neuropeptide and neurotransmitter systems.

Implications of neuropeptides in neurological diseases

Neuropeptides are sufficiently stable to allow valid radioimmunoassay of peptide concentrations in post-mortem human nervous tissue and in human cerebrospinal fluid. Studies have now documented abnormalities of peptide concentrations in degenerative diseases of the brain. Somatostatin concentration is reduced in the hippocampus and neocortex of patients dying with Alzheimer's type dementia. In Huntington's disease, there are reduced concentrations of substance P, met-enkephalin and cholecystokinin in the basal ganglia; in contrast the concentrations of somatostatin and TRH are increased. Immunocytochemical and experimental lesion studies are underway in an attempt to localize the peptide-containing cells affected by these disorders; and the potential role of alterations in neuropeptide function in the pathogenesis, clinical manifestations and therapy of these illnesses is of great interest. Although alterations of CSF peptide concentrations have been reported in a variety of human diseases, interpretation of these results requires knowledge of the origin and disposition of CSF peptides. Future research into the pathology of peptidergic systems will depend on the development of specific peptide antagonists to probe dynamic aspects of peptide function and on the application of the tools of molecular biology, such as specific mRNA assays, to human material.

The regional distribution of somatostatin, substance P and neurotensin in human brain

The regional distribution of somatostatin-, substance P- and neurotensin-like immunoreactivity was determined in 41 areas of 10 human brains. Each peptide is distributed widely in the human central nervous system and for each the pattern of distribution is unique. No significant relationship was found between peptide levels and patient age, interval between death and autopsy, and tissue storage time prior to assay. The regional distribution of these peptides is similar to that seen in several animal species and the pattern of this distribution is consistent with the idea that peptides function as neurotransmitters within the central nervous system. The problems of using human post-mortem material for peptide assay are discussed.

Regional and subcellular localization of luteinizing hormone releasing hormone in the adult human brain

The localization of luteinizing hormone releasing hormone (LHRH) in the post mortem adult human brain was investigated. LHRH was highly concentrated in medial basal hypothalamic tissue (1.14 ng/mg protein); lower levels of LHRH were present in tissue from the optic chiasm (0.05 ng/mg protein) and mammillary bodies (0.07 ng/mg protein). The concentrations of LHRH in hypothalamic tissue of men and women were similar. LHRH was undetectable (< 0.001 ng/mg protein) in the frontal cerebral cortex and cerebellum. When homogenates of the medial basal hypothalamus were fractionated on continuous or discontinuous sucrose density gradients, LHRH was found to be associated with subcellular particles. Upon examination by transmission electron microscopy, we found that these subcellular particles resembled isolated neuron terminals, i.e., synaptosomes. Low to undetectable amounts of LHRH were found in the cytosol or the myelin + microsome fraction of the gradients. The results of these studies are supportive of the view that LHRH is highly concentrated in neuron terminals of the adult human brain and may, therefore, be a central neurotransmitter or neuromodulator in the human.

Growth hormone and prolactin response to bromocriptine in patients with Huntington's chorea

The growth hormone (hGH) and prolactin (hPRL) responses to oral bromocriptine were studied in two groups of patients with Huntington's chorea and in seven healthy control subjects. The patients included six patients who had previously been treated with phenothiazines and six patients who had not received phenothiazine treatment. All medication was stopped 72 hours before the investigation which involved taking blood samples for up to 210 minutes after taking bromocriptine (2.5 mg). Plasma samples were analysed for hGH and hPRL. There was no significant difference in basal hGH concentrations between the patients and control subjects. The hGH response to bromocriptine varied in the individual patients but the concentrations were significantly lower in the patients compared with the controls between 160 and 210 minutes. The basal concentrations of hPRL were also not different, apart from the findings of elevated hPRL concentrations in three patients previously treated with phenothiazines. The patients and control subjects showed a consistent fall in hPRL concentrations after taking bromocriptine. The lower peak hGH response to bromocriptine found in the patients suggests that there may be an alteration of dopaminergic neurones mediating hGH release.