GnRH protective effects against amyloid β-induced cognitive decline: A potential role of the 17β-estradiol

GnRH protective effects against long-term potentiation impairment induced by AANAT-siRNA

There is an interplay between the gonadotropin-releasing hormone (GnRH) and melatoninergic systems. The key enzyme of melatonin synthesis (arylalkylamine N-acetyltransferase, AANAT), and GnRH receptors are expressed in the hippocampus. While it has been shown that hippocampal AANAT enzyme activity is necessary for proper hippocampal cognitive function, their role in long-term potentiation (LTP) induction is not fully understood. In current study, the impact of GnRH on LTP induction was investigated, while hippocampal melatonin synthesis had been inhibited. The melatonin synthesis was inhibited by AANAT-siRNA administration, and LTP was induced using in vivo field potential electrophysiological recording. Animals were divided into 5 groups: Intact, vehicle, siRNA, GnRH and siRNA+GnRH. All animals, except intact group, experienced the stereotaxic surgery and intra-hippocampal cannulation to receive vehicle agent, AANAT siRNA (0.5 μg/hip), GnRH (1 ng/rat), and AANAT siRNA+GnRH. The recognition memory was assessed by Novel object recognition test. The field potential electrophysiology experiment was conducted by stimulating the Schaffer collateral pathway, and LTP induction was carried out through high-frequency stimulation (HFS). After recording, animals' brain was isolated and quickly frozen for further hippocampal melatonin levels measurement by LC-MS and AANAT mRNA levels by qRT-PCR. GnRH injection in the hippocampus increased local AANAT-mRNA expression and melatonin levels. GnRH-treated animals displayed higher LTP amplitude compared to intact, vehicle and siRNA groups. While the reduction in hippocampal melatonin levels by AANAT-siRNA inhibited LTP and impaired recognition memory, the GnRH prevented these adverse effects. The data suggests that GnRH have protective effects against AANAT-siRNA-induced LTP decline. The protective mechanism at least partially, may be related to the increased expression of local AANAT-mRNA.

Neurotrophic and synaptic effects of GnRH and/or GH upon motor function after spinal cord injury in rats

Thoracic spinal cord injury (SCI) profoundly impairs motor and sensory functions, significantly reducing life quality without currently available effective treatments for neuroprotection or full functional regeneration. This study investigated the neurotrophic and synaptic recovery potential of gonadotropin-releasing hormone (GnRH) and growth hormone (GH) treatments in ovariectomized rats subjected to thoracic SCI. Employing a multidisciplinary approach, we evaluated the effects of these hormones upon gene expression of classical neurotrophins (NGF, BDNF, and NT3) as well as indicative markers of synaptic function (Nlgn1, Nxn1, SNAP25, SYP, and syntaxin-1), together with morphological assessments of myelin sheath integrity (Klüver-Barrera staining and MBP immunoreactivity) and synaptogenic proteins (PSD95, SYP) by immunohystochemistry (IHC) , and also on the neuromotor functional recovery of hindlimbs in the lesioned animals. Results demonstrated that chronic administration of GnRH and GH induced notable upregulation in the expression of several neurotrophic and synaptogenic activity genes. Additionally, the treatment showed a significant impact on the restoration of functional synaptic markers and myelin integrity. Intriguingly, while individual GnRH application induced certain recovery benefits, the combined treatment with GH appeared to inhibit neuromotor recovery, suggesting a complex interplay in hormonal regulation post-SCI. GnRH and GH are bioactive and participate in modulating neurotrophic responses and synaptic restoration under neural damage conditions, offering insights into novel therapeutic approaches for SCI. However, the intricate effects of combined hormonal treatment accentuate the necessity for further investigation that conduce to optimal and novel therapeutic strategies for patients with spinal cord lesions.

Down regulation of the c-Fos/MAP kinase signaling pathway during learning memory processes coincides with low GnRH levels in aluminum chloride-induced Alzheimer's male rats

Aluminum chloride (Al) is associated with Alzheimer's disease (AD) and reproductive disorders. But the relationship between gonadotropin-releasing hormone (GnRH) and c-Fos levels, the end product of MAP-kinase signaling, in AD is unknown, so we aimed to investigate this relationship. We exposed rats to Al dissolved in drinking water (10 and 50 mg/kg) for two and four weeks. The control group received only drinking water. At the end, the blood sample was collected under deep anesthesia and the brain was dissected on ice, and the testicular tissue was fixed in formalin. Amyloid beta (βA) plaques in brain regions and the number of CA1 neurons were evaluated by Congo red staining and cresyl violet staining. Activation of neuronal nitric oxide synthase (nNOS) was studied using NADPH-diaphorase. The levels of c-Fos and testosterone receptors in the target area were examined immunohistochemically. Brain GnRH levels were determined by blotting, and serum levels of gonadotropins and steroids were measured by enzyme-linked immunosorbent assay (ELISA). All data were analyzed using analysis of variance (ANOVA) at α = 0.05 level. The accumulation of βA plaque was observed along with a decrease in the number of CA1 pyramidal neurons and a significant decrease in the levels of c-Fos and GnRH in the brains of rats receiving Al, which was aligned with a significant decrease in serum levels of testosterone and LH. This study, for the first time, showed a link between dementia and a concomitant decrease in brain GnRH and c-Fos levels.

The role of Foxo3a in neuron-mediated cognitive impairment

Cognitive impairment (COI) is a prevalent complication across a spectrum of brain disorders, underpinned by intricate mechanisms yet to be fully elucidated. Neurons, the principal cell population of the nervous system, orchestrate cognitive processes and govern cognitive balance. Extensive inquiry has spotlighted the involvement of Foxo3a in COI. The regulatory cascade of Foxo3a transactivation implicates multiple downstream signaling pathways encompassing mitochondrial function, oxidative stress, autophagy, and apoptosis, collectively affecting neuronal activity. Notably, the expression and activity profile of neuronal Foxo3a are subject to modulation via various modalities, including methylation of promoter, phosphorylation and acetylation of protein. Furthermore, upstream pathways such as PI3K/AKT, the SIRT family, and diverse micro-RNAs intricately interface with Foxo3a, engendering alterations in neuronal function. Through several downstream routes, Foxo3a regulates neuronal dynamics, thereby modulating the onset or amelioration of COI in Alzheimer's disease, stroke, ischemic brain injury, Parkinson's disease, and traumatic brain injury. Foxo3a is a potential therapeutic cognitive target, and clinical drugs or multiple small molecules have been preliminarily shown to have cognitive-enhancing effects that indirectly affect Foxo3a. Particularly noteworthy are multiple randomized, controlled, placebo clinical trials illustrating the significant cognitive enhancement achievable through autophagy modulation. Here, we discussed the role of Foxo3a in neuron-mediated COI and common cognitively impaired diseases.

Functional GnRH receptor signaling regulates striatal cholinergic neurons in neonatal but not in adult mice

Reproduction in mammals is controlled by hypothalamic gonadotropin-releasing hormone (GnRH) neurons. Recent studies from our laboratory established that the basal ganglia of the human brain contain additional large populations of GnRH synthesizing neurons which are absent in adult mice. Such extrahypothalamic GnRH neurons mostly occur in the putamen where they correspond to subsets of the striatal cholinergic interneurons (ChINs) and express GnRHR autoreceptors. In an effort to establish a mouse model for functional studies of striatal GnRH/GnRHR signaling, we carried out electrophysiological experiments on acute brain slices from male transgenic mice. Using PN4-7 neonatal mice, half of striatal ChINs responded with transient hyperpolarization and decreased firing rate to 1.2 µM GnRH, whereas medium spiny projection neurons remained unaffected. GnRH acted on its specific receptor because no response was observed in the presence of the GnRHR antagonist Antide. Addition of the membrane-impermeable G protein-coupled receptor inhibitor GDP-β-S to the internal electrode solution eliminated the effect of GnRH. Further, GnRH was able to inhibit ChINs in presence of tetrodotoxin which blocked action potential mediated events. Collectively, these data indicated that the receptor underlying the effects of GnRH in neonatal mice is localized within ChINs. GnRH responsiveness of ChINs was transient and entirely disappeared in adult mice. These results raise the possibility to use neonatal transgenic mice as a functional model to investigate the role of GnRH/GnRHR signaling discovered earlier in adult human ChINs.

GV1001 modulates neuroinflammation and improves memory and behavior through the activation of gonadotropin-releasing hormone receptors in a triple transgenic Alzheimer's disease mouse model

GV1001 protects neural cells from amyloid-β (Aβ) toxicity and other stressors in in vitro studies and demonstrates clinically beneficial effects in patients with moderate to severe Alzheimer's disease (AD). Here, we investigated the protective effects and mechanism of action of GV1001 in triple transgenic AD (3xTg-AD) mice. We found that GV1001 improved memory and cognition in middle- and old-aged 3xTg-AD mice. Additionally, it reduced Aβ oligomer and phospho-tau (Ser202 and Thr205) levels in the brain, and mitigated neuroinflammation by promoting a neuroprotective microglial and astrocyte phenotype while diminishing the neurotoxic ones. In vitro, GV1001 bound to gonadotropin releasing hormone receptors (GnRHRs) with high affinity. Levels of cyclic adenosine monophosphate, a direct downstream effector of activated GnRHRs, increased after GV1001 treatment. Furthermore, inhibition of GnRHRs blocked GV1001-induced effects. Thus, GV1001 might improve cognitive and memory functions of 3xTg-AD mice by suppressing neuroinflammation and reducing Aβ oligomers levels and phospho-tau by activating GnRHRs and their downstream signaling pathways.

Estrogen signaling via estrogen receptor alpha and its implications for neurodegeneration associated with Alzheimer's disease in aging women

Estrogen receptor alpha (ERα) is a transcription factor activated by estrogenic hormones to regulate gene expression in certain organs, including the brain. In the brain, estrogen signaling pathways are central for maintaining cognitive functions. Herein, we review the neuroprotective effects of estrogens mediated by ERα. The estrogen/ERα pathways are affected by the reduction of estrogens in menopause, and this event may be a risk factor for neurodegeneration associated with Alzheimer's disease in women. Thus, developing a better understanding of estrogen/ERα signaling may be critical for defining new biomarkers and potential therapeutic targets for Alzheimer's disease in women.

Roles of traditional chinese medicine regulating neuroendocrinology on AD treatment

The incidence of sporadic Alzheimer's disease (AD) is increasing in recent years. Studies have shown that in addition to some genetic abnormalities, the majority of AD patients has a history of long-term exposure to risk factors. Neuroendocrine related risk factors have been proved to be strongly associated with AD. Long-term hormone disorder can have a direct detrimental effect on the brain by producing an AD-like pathology and result in cognitive decline by impairing neuronal metabolism, plasticity and survival. Traditional Chinese Medicine(TCM) may regulate the complex process of endocrine disorders, and improve metabolic abnormalities, as well as the resulting neuroinflammation and oxidative damage through a variety of pathways. TCM has unique therapeutic advantages in treating early intervention of AD-related neuroendocrine disorders and preventing cognitive decline. This paper reviewed the relationship between neuroendocrine and AD as well as the related TCM treatment and its mechanism. The advantages of TCM intervention on endocrine disorders and some pending problems was also discussed, and new insights for TCM treatment of dementia in the future was provided.

The roles of GnRH in the human central nervous system

It is widely known that GnRH plays a role in facilitating reproductive function via the HPG axis, and this was once believed to be its only function. However, over the last several decades important neuromodulatory roles of GnRH in multiple brain functions have been elucidated. Multiple GnRH isoforms and receptors have been detected outside the HPG-axis across different species. In this review, we focus on the human CNS where GnRH I and II isoforms and a functional GnRH I receptor have been isolated. We first describe the traditional understanding of GnRH within the hypothalamus and the pituitary and current clinical use of GnRH analogues. We then review the location and function of GnRH-producing neurons and receptors located outside the HPG axis. We next review the GnRH I and II neuron location and quantity and GnRH I receptor gene expression throughout the human brain, using the Allen Brain Map Atlas. This analysis demonstrates a wide expression of GnRH throughout the brain, including prominent expression in the basal forebrain and cerebellum. Lastly, we examine the potential role of GnRH in aging and inflammation and its therapeutic potential for neurodegenerative disease and spinal cord lesions.

Exploring the role of sex differences in Alzheimer's disease pathogenesis in Down syndrome

Women are disproportionately affected by Alzheimer's disease (AD), yet little is known about sex-specific effects on the development of AD in the Down syndrome (DS) population. DS is caused by a full or partial triplication of chromosome 21, which harbors the amyloid precursor protein (APP) gene, among others. The majority of people with DS in their early- to mid-40s will accumulate sufficient amyloid-beta (Aβ) in their brains along with neurofibrillary tangles (NFT) for a neuropathological diagnosis of AD, and the triplication of the APP gene is regarded as the main cause. Studies addressing sex differences with age and impact on dementia in people with DS are inconsistent. However, women with DS experience earlier age of onset of menopause, marked by a drop in estrogen, than women without DS. This review focuses on key sex differences observed with age and AD in people with DS and a discussion of possible underlying mechanisms that could be driving or protecting from AD development in DS. Understanding how biological sex influences the brain will lead to development of dedicated therapeutics and interventions to improve the quality of life for people with DS and AD.

Assessment of lipophilic fluorescence products in β-amyloid-induced cognitive decline: A parallel track in hippocampus, CSF, plasma and erythrocytes

BACKGROUND

Oxidative stress implicates in Alzheimer's disease (AD) pathophysiology, and associates with the creation of end products of free radical reactions, are known as lipophilic fluorescent products (LFPs). This study aimed to evaluate the probable parallel alterations in the spectral properties of the LFPs in the hippocampus tissues, cerebrospinal fluid (CSF), plasma, and erythrocytes during AD model induction by intra-cerebroventricular (ICV) amyloid β-protein fragment 25-35 (Aβ) injection.

METHODS

Male rats received an intra-ICV injection of Aβ. Hippocampus, CSF, plasma, and erythrocytes were harvested at 5, 14, and 21 days after Aβ injection. The fluorescent intensity of LFPs was assessed by spectrofluorimetry using synchronous fluorescence spectra 25 (SYN 25) and 50 (SYN 50) in the range of 250-500 nm. Hippocampal tissue malondialdehyde (MDA) and superoxide dismutase (SOD) were also measured. Cognitive alterations were evaluated using Morris water maze (MWM) test.

RESULTS

The parallel significant rise in the fluorescence intensity of LFPs was detected in the hippocampus, CSF, plasma, and erythrocytes, 14, and 21 days after ICV-Aβ injection. These alterations were found in both types of synchronous spectra 25, and 50, and were coincided with hippocampal cognitive decline, the MDA rise, and decrease of SOD activity. There was a positive correlation between hippocampus homogenate, and plasma or CSF rise in fluorescence intensity.

CONCLUSION

Data showed that the Aβ increased hippocampal MDA, and decreased SOD activity, led to a higher rate of oxidative products and subsequently resulted in an increase in LFPs fluorescence intensity during the development of cognitive decline. LFPs' alterations reflect a comprehensive view of tissue redox status. The fluorescence properties of LFPs indicate their composition, which may pave the way to trace the different pathological states.

Brain-derived estrogen and neural function

Although classically known as an endocrine signal produced by the ovary, 17β-estradiol (E₂) is also a neurosteroid produced in neurons and astrocytes in the brain of many different species. In this review, we provide a comprehensive overview of the localization, regulation, sex differences, and physiological/pathological roles of brain-derived E₂ (BDE₂). Much of what we know regarding the functional roles of BDE₂ has come from studies using specific inhibitors of the E₂ synthesis enzyme, aromatase, as well as the recent development of conditional forebrain neuron-specific and astrocyte-specific aromatase knockout mouse models. The evidence from these studies support a critical role for neuron-derived E₂ (NDE₂) in the regulation of synaptic plasticity, memory, socio-sexual behavior, sexual differentiation, reproduction, injury-induced reactive gliosis, and neuroprotection. Furthermore, we review evidence that astrocyte-derived E₂ (ADE₂) is induced following brain injury/ischemia, and plays a key role in reactive gliosis, neuroprotection, and cognitive preservation. Finally, we conclude by discussing the key controversies and challenges in this area, as well as potential future directions for the field.

Single-Molecule Imaging Reveals Rapid Estradiol Action on the Surface Movement of AMPA Receptors in Live Neurons

Gonadal steroid 17β-estradiol (E2) exerts rapid, non-genomic effects on neurons and strictly regulates learning and memory through altering glutamatergic neurotransmission and synaptic plasticity. However, its non-genomic effects on AMPARs are not well understood. Here, we analyzed the rapid effect of E2 on AMPARs using single-molecule tracking and super-resolution imaging techniques. We found that E2 rapidly decreased the surface movement of AMPAR via membrane G protein-coupled estrogen receptor 1 (GPER1) in neurites in a dose-dependent manner. The cortical actin network played a pivotal role in the GPER1 mediated effects of E2 on the surface mobility of AMPAR. E2 also decreased the surface movement of AMPAR both in synaptic and extrasynaptic regions on neurites and increased the synaptic dwell time of AMPARs. Our results provide evidence for understanding E2 action on neuronal plasticity and glutamatergic neurotransmission at the molecular level.

The cryptic gonadotropin-releasing hormone neuronal system of human basal ganglia

Human reproduction is controlled by ~2000 hypothalamic gonadotropin-releasing hormone (GnRH) neurons. Here, we report the discovery and characterization of additional ~150,000–200,000 GnRH-synthesizing cells in the human basal ganglia and basal forebrain. Nearly all extrahypothalamic GnRH neurons expressed the cholinergic marker enzyme choline acetyltransferase. Similarly, hypothalamic GnRH neurons were also cholinergic both in embryonic and adult human brains. Whole-transcriptome analysis of cholinergic interneurons and medium spiny projection neurons laser-microdissected from the human putamen showed selective expression of GNRH1 and GNRHR1 autoreceptors in the cholinergic cell population and uncovered the detailed transcriptome profile and molecular connectome of these two cell types. Higher-order non-reproductive functions regulated by GnRH under physiological conditions in the human basal ganglia and basal forebrain require clarification. The role and changes of GnRH/GnRHR1 signaling in neurodegenerative disorders affecting cholinergic neurocircuitries, including Parkinson’s and Alzheimer’s diseases, need to be explored.