Female Sex and Brain-Selective Estrogen Benefit α-Synuclein Tetramerization and the PD-like Motor Syndrome in 3K Transgenic Mice

Reducing the lipase LIPE in mutant α-synuclein mice improves Parkinson-like deficits and reveals sex differences in fatty acid metabolism

Impaired lipid metabolism is a risk factor for Parkinson's disease (PD) and dementia with Lewy bodies (DLB) and can shift the physiological α-synuclein (αS) tetramer-monomer (T:M) ratio toward aggregation prone monomers. A resultant increase in phospho-serine 129+ αS monomers associating with excess mono- and polyunsaturated fatty acids contributes to the αS aggregation. We previously reported that decreasing the release of monounsaturated fatty acids (MUFAs) by reducing or inhibiting the hormone sensitive lipase (LIPE) reversed pathologic αS phosphorylation and improved soluble αS homeostasis in cultured αS triplication PD neurons and reduced DAergic neurodegeneration in a C.elegans αS model. However, assessing LIPE as a potential therapeutic target for progressive PD motor phenotypes has not been investigated. 3K αS mice, representing a biochemical and neuropathological amplification of the E46K fPD-causing mutation, have decreased αS T:M ratios, lipidic aggregates, and a L-DOPA responsive PD-like motor syndrome. Here, we reduced LIPE by crossings of 3K mice with LIPE null mice, which attenuated motor deficits in male LIPE+/- knockdown (LKD)-3K mice. Heterozygous LIPE reduction was associated with an improved αS T:M ratio, and dopaminergic neurotransmitter levels and fiber densities. In female 3K-LKD mice, an increase in pS129+ and larger lipid droplets (LDs) likely decreased the benefits seen in males. Reducing LIPE decreased MUFA release from neutral lipid storage, thereby reducing MUFA in phospholipid membranes with which αS interacts. Our study highlights fatty acid turnover as a therapeutic target for Lewy body diseases and support LIPE as a promising target in males. LIPE regulation represents a novel approach to mitigate PD and DLB risk and treat disease.

Haploinsufficiency of the Parkinson's disease gene synaptojanin1 is associated with abnormal responses to psychomotor stimulants and mesolimbic dopamine signaling

The synaptojanin-1 (SYNJ1) gene is known to be important for dopamine-related disorders. Recent evidence has demonstrated that Synj1 deficient mice (Synj1 +/-) have impairments in dopaminergic synaptic vesicular recycling. However, less is known about how Synj1 deficits affect the mesolimbic system, reward processing, and motivated behavior. To examine the role of the Synj1 gene in motivated behavior, we subjected male and female Synj1 +/- and Synj1 +/+ mice to a battery of behavioral tests evaluating hedonic responses, effortful responding, and responses to psychomotor stimulants. We observed that Synj1 +/- mice exhibit few differences in reward processing and motivated behavior, with normal hedonic responses and motivated responding for sucrose. However, male but not female Synj1 +/- demonstrated an attenuated conditioned place preference for cocaine that could not be attributed to deficits in spatial memory. To further understand the dopamine signaling underlying the attenuated response to cocaine in these mutant mice, we recorded nucleus accumbens dopamine in response to cocaine and observed that Synj1 +/- male and female mice took longer to reach peak dopamine release following experimenter-administered cocaine. However, female mice also showed slower decay in accumbens dopamine that appear to be linked to differences in cocaine-induced DAT responses. These findings demonstrate that SYNJ1 deficiencies result in abnormal mesolimbic DA signaling which has not previously been demonstrated. Our work also highlights the need to develop targeted therapeutics capable of restoring deficits in DAT function, which may be effective for reversing the pathologies associated with Synj1 mutations.

Sex-dependent effects of monomeric α-synuclein on calcium and cell death of lateral hypothalamic mouse neurons are altered by orexin

Parkinson's Disease (PD) patients experience sleeping disorders in addition to the disease-defining symptomology of movement dysfunctions. The prevalence of PD is sex-based and presence of sleeping disorders in PD also shows sex bias with a stronger phenotype in males. In addition to loss of dopamine-containing neurons in the striatum, arousal-related, orexin-containing neurons in the lateral hypothalamus (LH) are lost in PD, which could contribute to state-related disorders. As orexin has been shown to be involved in sleeping disorders and to have neuroprotective effects, we asked whether orexin could protect sleep-related LH neurons from damage putatively from the protein α-synuclein (α-syn), which is found at high levels in the PD brain and that we have shown is associated with putatively excitotoxic rises in intracellular calcium in brainstem sleep-controlling nuclei, especially in males. Accordingly, we monitored intracellular calcium transients induced by α-syn and whether concurrent exposure to orexin affected those transients in LH cells of the mouse brain slice using calcium imaging. Further, we used an assay of cell death to determine whether LH cell viability was influenced when α-syn and orexin were co-applied when compared to exposure to α-syn alone. We found that excitatory calcium events induced by α-syn were reduced in amplitude and frequency when orexin was co-applied, and when data were evaluated by sex, this effect was found to be greater in females. In addition, α-syn exposure was associated with cell death that was higher in males, and interestingly, reduced cell death was noted when orexin was present, which did not show a sex bias. We interpret our findings to indicate that orexin is protective to α-syn-mediated damage to hypothalamic neurons, and the actions of orexin on α-syn-induced cellular effects differ between sexes, which could underlie sex-based differences in sleeping disorders in PD.

Tamoxifen in breast cancer and risk of Parkinson's disease: A meta-analysis

BACKGROUND

Tamoxifen is widely used for hormone-sensitive breast cancer, achieved by modulating the estrogen receptor activity in a tissue-specific manner. There is evidence to support the protective effects of estrogen against Parkinson's disease (PD), a common neurodegenerative condition. Some epidemiologic studies suggest the use of tamoxifen may modulate the PD risk. We conducted a meta-analysis to examine the association between tamoxifen and risk of PD.

METHODS

A search of PubMed using search terms synonymous with "tamoxifen" and "Parkinson's disease" was conducted. Outcomes of interest were the odds ratio (OR) of PD comparing tamoxifen-exposed to -unexposed women, as well as the incidence rate of PD in tamoxifen-exposed women.

RESULTS

A total of 37,932 subjects with breast cancer, comprising 17,233 tamoxifen-exposed subjects and 20,699 tamoxifen-unexposed subjects, satisfied the inclusion criteria. The exposure to tamoxifen ranged from 30-96 months. Using the common-effect model, the pooled OR of PD was 2.4, with (95% CI 1.91-3.01, P < 0.0001), with high heterogeneity (I2 = 81.5%, Cochran's Q test P = 0.001). Pooling 28,640 tamoxifen-exposed patients under the common-effect model found an incidence rate of 5.86 events per 10,000 person-years (95% CI 4.82-7.12) with minimal heterogeneity (I2 = 26%, Cochran's Q test P = 0.258).

CONCLUSIONS

Our meta-analysis suggests that tamoxifen use may be associated with an increased PD risk in women. However, due to heterogeneity and potential limitations of some of the studies, further clinical and functional validation will be needed. Longitudinal studies supported by imaging and biomarkers evaluation will be useful to identify the mechanisms linking tamoxifen and PD risk.

Young human alpha synuclein transgenic (BAC-SNCA) mice display sex- and gene-dose-dependent phenotypic disturbances

Parkinson's disease (PD) is a common neurodegenerative movement disorder, characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta and the accumulation of aggregated alpha synuclein (aSyn). The disease often presents with early prodromal non-motor symptoms and later motor symptoms. Diagnosing PD based purely on motor symptoms is often too late for successful intervention, as a significant neuronal loss has already occurred. Furthermore, the lower prevalence of PD in females is not well understood, highlighting the need for a better understanding of the interaction between sex and aSyn, the crucial protein for PD pathogenesis. Here, we conducted a comprehensive phenotyping study in 1- to 5-month-old mice overexpressing human aSyn gene (SNCA) in a bacterial artificial chromosome (BAC-SNCA). We demonstrate a SNCA gene-dose-dependent increase of human aSyn and phosphorylated aSyn, as well as a decrease in tyrosine hydroxylase expression in BAC-SNCA mice, with more pronounced effects in male mice. Phosphorylated aSyn was already found in the dorsal motor nucleus of the vagus nerve of 2-month-old mice. This was time-wise associated with significant gait altrations in BAC-SNCA mice as early as 1 and 3 months of age using CatWalk gait analysis. Furthermore, anxiety-related behavioral tests revealed an increase in anxiety levels in male BAC-SNCA mice. Finally, 5-month-old male BAC-SNCA mice exhibited a SNCA gene-dose-dependent elevation in energy expenditure in automated home-cage monitoring. For the first time, these findings describe early-onset, sex- and gene-dose-dependent, aSyn-mediated disturbances in BAC-SNCA mice, providing a model for sex-differences, early-onset neuropathology, and prodromal symptoms of PD.

Sensorimotor dysfunction due to developmental manganese exposure is less severe in adult female than male rats and partially improved by acute methylphenidate treatment

Epidemiological studies have reported associations between elevated manganese (Mn) exposure and poorer psychomotor performance in children. Our studies in adult male rats have established that this relationship is causal and that prolonged methylphenidate (MPH) treatment is efficacious in treating this area of dysfunction. However, it is unclear if sensitivity to these Mn deficits differs between females and males, and whether existing pharmacological therapies are efficacious in improving sensorimotor dysfunction in females. To address these questions, we used our rat model of childhood environmental Mn exposure and the Montoya staircase test to determine whether 1) there are sex differences in the lasting sensorimotor dysfunction caused by developmental Mn exposure, and 2) MPH treatment is efficacious in ameliorating the sensorimotor deficits in females. Female and male neonates were treated orally with Mn (50 mg Mn/kg/d) from postnatal day 1 to 21 and evaluated for skilled forelimb sensorimotor performance as adults. Subsequently, the efficacy of acute oral MPH treatment (doses of 0, 0.5, and 3.0 mg MPH/kg/d) was assessed in females using a within-subject MPH treatment design. Developmental postnatal Mn exposure produced lasting sensorimotor reaching and grasping deficits that were milder in females than in males. Acute MPH treatment of Mn-exposed females with the 0.5 mg/kg/d dose attenuated the reaching dysfunction without alleviating grasping dysfunction. These findings show sex-based variations in sensitivity to the sensorimotor impairment caused by developmental Mn exposure, and they are consistent with prior studies showing less vulnerability of females to Mn-induced dysfunction in other functional domains, possibly due to the protective effects of estrogen. Given our previous work showing the efficacy of MPH treatment to alleviate Mn-induced inattention, impulsiveness, and sensorimotor dysfunctions in adult male rats, they also highlight the need for further research into sex-based differences in cognitive and behavioral areas of brain function, and the efficacy of therapeutics in treating behavioral dysfunction in females. Supported by NIEHS R01ES028369.

Generation of G51D and 3D mice reveals decreased α-synuclein tetramer-monomer ratios promote Parkinson's disease phenotypes

Mutations in the α-Synuclein (αS) gene promote αS monomer aggregation that causes neurodegeneration in familial Parkinson's disease (fPD). However, most mouse models expressing single-mutant αS transgenes develop neuronal aggregates very slowly, and few have dopaminergic cell loss, both key characteristics of PD. To accelerate neurotoxic aggregation, we previously generated fPD αS E46K mutant mice with rationally designed triple mutations based on the α-helical repeat motif structure of αS (fPD E46K→3 K). The 3 K variant increased αS membrane association and decreased the physiological tetramer:monomer ratio, causing lipid- and vesicle-rich inclusions and robust tremor-predominant, L-DOPA responsive PD-like phenotypes. Here, we applied an analogous approach to the G51D fPD mutation and its rational amplification (G51D → 3D) to generate mutant mice. In contrast to 3 K mice, G51D and 3D mice accumulate monomers almost exclusively in the cytosol while also showing decreased αS tetramer:monomer ratios. Both 1D and 3D mutant mice gradually accumulate insoluble, higher-molecular weight αS oligomers. Round αS neuronal deposits at 12 mos immunolabel for ubiquitin and pSer129 αS, with limited proteinase K resistance. Both 1D and 3D mice undergo loss of striatal TH+ fibers and midbrain dopaminergic neurons by 12 mos and a bradykinesia responsive to L-DOPA. The 3D αS mice have decreased tetramer:monomer equilibria and recapitulate major features of PD. These fPD G51D and 3D mutant mice should be useful models to study neuronal αS-toxicity associated with bradykinetic motor phenotypes.

Differences in brain aging between sexes in Parkinson's disease

Parkinson's disease (PD) is linked to faster brain aging. Male sex is associated with higher prevalence, severe symptoms, and a faster progression rate in PD. There remains a significant gap in understanding the function of sex in the process of brain aging in PD. The structural T1-weighted MRI-driven brain-predicted age difference (i.e., Brain-PAD: the actual age subtracted from the brain-predicted age) was computed in a group of 373 people with PD (mean age ± SD: 61.37 ± 9.81, age range: 33-85, 34% female) from the Parkinson's Progression Marker Initiative database using a robust brain-age estimation framework that was trained on 949 healthy subjects. Linear regression models were used to investigate the association between Brain-PAD and clinical variables in PD, stratified by sex. Males with Parkinson's disease (PD-M) exhibited a significantly higher mean Brain-PAD than their female counterparts (PD-F) (t(256) = 2.50, p = 0.012). In the propensity score-matched PD-M group (PD-M*), Brain-PAD was found to be associated with a decline in general cognition, a worse degree of sleep behavior disorder, reduced visuospatial acuity, and caudate atrophy. Conversely, no significant links were observed between these factors and Brain-PAD in the PD-F group. Having 'older' looking brains in PD-M than PD-F supports the idea that sex plays a vital function in PD, such that the PD mechanism may be different in males and females. This study has the potential to broaden our understanding of dissimilarities in brain aging between sexes in the context of PD.

Neuroactive steroids and Parkinson's disease: Review of human and animal studies

The greater prevalence and incidence of Parkinson's disease (PD) in men suggest a beneficial effect of sex hormones. Neuroactive steroids have neuroprotective activities thus offering interesting option for disease-modifying therapy for PD. Neuroactive steroids are also neuromodulators of neurotransmitter systems and may thus help to control PD symptoms and side effect of dopamine medication. Here, we review the effect on sex hormones (estrogen, androgen, progesterone and its metabolites) as well as androstenediol, pregnenolone and dehydroepiandrosterone) in human studies and in animal models of PD. The effect of neuroactive steroids is reviewed by considering sex and hormonal status to help identify specifically for women and men with PD what might be a preventive approach or a symptomatic treatment. PD is a complex disease and the pathogenesis likely involves multiple cellular processes. Thus it might be useful to target different cellular mechanisms that contribute to neuronal loss and neuroactive steroids provide therapeutics options as they have multiple mechanisms of action.

Increased palmitoylation improves estrogen receptor alpha-dependent hippocampal synaptic deficits in a mouse model of synucleinopathy

Parkinson's disease (PD) is characterized by conversion of soluble α-synuclein (αS) into intraneuronal aggregates and degeneration of neurons and neuronal processes. Indications that women with early-stage PD display milder neurodegenerative features suggest that female sex partially protects against αS pathology. We previously reported that female sex and estradiol improved αS homeostasis and PD-like phenotypes in E46K-amplified (3K) αS mice. Here, we aimed to further dissect mechanisms that drive this sex dimorphism early in disease. We observed that synaptic abnormalities were delayed in females and improved by estradiol, mediated by local estrogen receptor alpha (ERα). Aberrant ERα distribution in 3K compared to wild-type mice was paired with its decreased palmitoylation. Treatment with ML348, a de-palmitoylation inhibitor, increased ERα availability and soluble αS homeostasis, ameliorating synaptic plasticity and cognitive and motor phenotypes. Our finding that sex differences in early-disease αS-induced synaptic impairment in 3KL mice are in part mediated by palmitoylated ERα may have functional and pathogenic implications for clinical PD.

Sex and Age Differences in a Progressive Synucleinopathy Mouse Model

The mutation and overexpression of the alpha-synuclein protein (αSyn), described as synucleinopathy, is associated with Parkinson's disease (PD)-like pathologies. A higher prevalence of PD is documented for men versus women, suggesting female hormones' implication in slowing PD progression. The nigrostriatal dopamine (DA) neurons in rodent males are more vulnerable to toxins than those in females. The effect of biological sex on synucleinopathy remains poorly described and was investigated using mice knocked out for murine αSyn (SNCA-/-) and also overexpressing human αSyn (SNCA-OVX) compared to wildtype (WT) mice. All the mice showed decreased locomotor activity with age, and more abruptly in the male than in the female SNCA-OVX mice; anxiety-like behavior increased with age. The SNCA-OVX mice had an age-dependent accumulation of αSyn. Older age was associated with the loss of nigral DA neurons and decreased striatal DA contents. The astrogliosis, microgliosis, and cytokine concentrations increased with aging. More abrupt nigrostriatal DA decreases and increased microgliosis were observed in the male SNCA-OVX mice. Human αSyn overexpression and murine αSyn knockout resulted in behavioral dysfunctions, while only human αSyn overexpression was toxic to DA neurons. At 18 months, neuroprotection was lost in the female SNCA-OVX mice, with a likely loss of estrus cycles. In conclusion, sex-dependent αSyn toxicity was observed, affecting the male mice more significantly.

Association of women-specific health factors in the severity of Parkinson's disease

Parkinson's disease (PD) is an age-related neurological disorder known for the observational differences in its risk, progression, and severity between men and women. While estrogen has been considered to be a protective factor in the development of PD, there is little known about the role that fluctuations in hormones and immune responses from sex-specific health experiences have in the disease's development and severity. We sought to identify women-specific health experiences associated with PD severity, after adjusting for known PD factors, by developing and distributing a women-specific questionnaire across the United States and creating multivariable models for PD severity. We created a questionnaire that addresses women's specific experiences and their PD clinical history and deployed it through The Parkinson's Foundation: PD Generation. To determine the association between women-specific health factors and PD severity, we constructed multivariable logistic regression models based on the MDS-UPDRS scale and the participants' questionnaire responses, genetics, and clinical data. For our initial launch in November 2021, we had 304 complete responses from PD GENEration. Univariate and multivariate logistic modeling found significant associations between major depressive disorder, perinatal depression, natural childbirth, LRRK2 genotype, B12 deficiency, total hysterectomy, and increased PD severity. This study is a nationally available questionnaire for women's health and PD. It shifts the paradigm in understanding PD etiology and acknowledging how sex-specific experiences may contribute to PD severity. In addition, the work in this study sets the foundation for future research to investigate the factors behind sex differences in PD.

Disruption of α-Synuclein proteostasis in the striatum and midbrain of long-term ovariectomized female mice

Epidemiological studies have demonstrated that women are less susceptible to Parkinson's disease (PD) than men. Estrogen exposure is hypothesized to confer protection against dopaminergic neuronal loss in patients with PD. Although the accumulation and propagation of α-synuclein (α-Syn) are closely linked to the clinical progression of PD, no relevant research has examined whether α-Syn proteostasis in the brain is altered in women after menopause. In this study, we established long-term ovariectomized (OVX) mice to simulate late post-menopause and investigated the expression and aggregation of α-Syn following the ovariectomy procedure. We observed that the OVX mice exhibited a significant increase in the expression and aggregation of α-Syn in the striatum and midbrain accompanied by impaired motor performance at 3 months after ovariectomy. The accumulation of α-Syn did not result in a significant loss of nigral dopaminergic neurons but did enhance autophagy and neuroglial activation. These findings imply that menopause may disrupt α-Syn proteostasis and exacerbate the accumulation of α-Syn in the basal ganglia circuit.

Sex and Brain: The Role of Sex Chromosomes and Hormones in Brain Development and Parkinson's Disease

Sex hormones and genes on the sex chromosomes are not only key factors in the regulation of sexual differentiation and reproduction but they are also deeply involved in brain homeostasis. Their action is crucial for the development of the brain, which presents different characteristics depending on the sex of individuals. The role of these players in the brain is fundamental in the maintenance of brain function during adulthood as well, thus being important also with respect to age-related neurodegenerative diseases. In this review, we explore the role of biological sex in the development of the brain and analyze its impact on the predisposition toward and the progression of neurodegenerative diseases. In particular, we focus on Parkinson's disease, a neurodegenerative disorder that has a higher incidence in the male population. We report how sex hormones and genes encoded by the sex chromosomes could protect from the disease or alternatively predispose toward its development. We finally underline the importance of considering sex when studying brain physiology and pathology in cellular and animal models in order to better understand disease etiology and develop novel tailored therapeutic strategies.

Can accelerated ageing models inform us on age-related tauopathies?

Ageing is the greatest risk factor of late-onset neurodegenerative diseases. In the realm of sporadic tauopathies, modelling the process of biological ageing in experimental animals forms the foundation of searching for the molecular origin of pathogenic tau and developing potential therapeutic interventions. Although prior research into transgenic tau models offers valuable lessons for studying how tau mutations and overexpression can drive tau pathologies, the underlying mechanisms by which ageing leads to abnormal tau accumulation remains poorly understood. Mutations associated with human progeroid syndromes have been proposed to be able to mimic an aged environment in animal models. Here, we summarise recent attempts in modelling ageing in relation to tauopathies using animal models that carry mutations associated with human progeroid syndromes, or genetic elements unrelated to human progeroid syndromes, or have exceptional natural lifespans, or a remarkable resistance to ageing-related disorders.

The Parkinson-Associated Toxin Paraquat Shifts Physiological α-Synuclein Tetramers toward Monomers That Can Be Calpain-Truncated and Form Oligomers

Abnormal aggregation of α-synuclein (αS) is thought to initiate neuronal dysfunction and death in Parkinson disease (PD). In addition to higher-molecular-weight, oligomeric, and polymeric forms of αS associated with neurotoxicity and disease, recent findings indicate the occurrence of physiological tetrameric assemblies in healthy neurons in culture and in brain. Herein, the PD-associated neurotoxin paraquat reduced physiological tetramers and led to calpain-truncated monomers and an approximately 70-kDa apparent oligomer different in size from physiological αS multimers. These truncated and oligomeric forms could also be generated by calpain cleavage of pure, recombinant human αS in vitro. Moreover, they were detected in the brains of tetramer-abrogating, E46K-amplified (3K) mice that model PD. These results indicate that paraquat triggers membrane damage and aberrant calpain activity that can induce a pathologic shift of tetramers toward an excess of full-length and truncated monomers, the accumulation of αS oligomers, and insoluble cytoplasmic αS puncta. The findings suggest that an environmental precipitant of PD can alter αS tetramer/monomer equilibrium, as already shown for several genetically caused forms of PD.

Sex Differences in Dopaminergic Vulnerability to Environmental Toxicants - Implications for Parkinson's Disease

PURPOSE OF REVIEW

Sex dimorphism in Parkinson's disease (PD) is an ostensible feature of the neurological disorder, particularly as men are 1.5-2 times more likely to develop PD than women. Clinical features of the disease, such as presentation at onset, most prevalent symptoms, and response to treatment, are also affected by sex. Despite these well-known sex differences in PD risk and phenotype, the mechanisms that impart sex dimorphisms in PD remain poorly understood.

RECENT FINDINGS

As PD incidence is influenced by environmental factors, an intriguing pattern has recently emerged in research studies suggesting a male-specific vulnerability to dopaminergic neurodegeneration caused by neurotoxicant exposure, with relative protection in females. These new experimental data have uncovered potential mechanisms that provide clues to the source of sex differences in dopaminergic neurodegeneration and other PD pathology such as alpha-synuclein toxicity. In this review, we discuss the emerging evidence of increased male sensitivity to neurodegeneration from environmental exposures. We examine mechanisms underlying dopaminergic neurodegeneration and PD-related pathologies with evidence supporting the roles of estrogen, SRY expression, the vesicular glutamate transporter VGLUT2, and the microbiome as prospective catalysts for male vulnerability. We also highlight the importance of including sex as a biological variable, particularly when evaluating dopaminergic neurotoxicity in the context of PD.

Ca2+ Dyshomeostasis Links Risk Factors to Neurodegeneration in Parkinson’s Disease

Parkinson’s disease (PD), a common neurodegenerative disease characterized by motor dysfunction, results from the death of dopaminergic neurons in the substantia nigra pars compacta (SNc). Although the precise causes of PD are still unknown, several risk factors for PD have been determined, including aging, genetic mutations, environmental factors, and gender. Currently, the molecular mechanisms underlying risk factor-related neurodegeneration in PD remain elusive. Endoplasmic reticulum stress, excessive reactive oxygen species production, and impaired autophagy have been implicated in neuronal death in the SNc in PD. Considering that these pathological processes are tightly associated with intracellular Ca²⁺, it is reasonable to hypothesize that dysregulation of Ca²⁺ handling may mediate risk factors-related PD pathogenesis. We review the recent findings on how risk factors cause Ca²⁺ dyshomeostasis and how aberrant Ca²⁺ handling triggers dopaminergic neurodegeneration in the SNc in PD, thus putting forward the possibility that manipulation of specific Ca²⁺ handling proteins and subcellular Ca²⁺ homeostasis may lead to new promising strategies for PD treatment.

Brain region-specific susceptibility of Lewy body pathology in synucleinopathies is governed by α-synuclein conformations

The protein α-synuclein, a key player in Parkinson’s disease (PD) and other synucleinopathies, exists in different physiological conformations: cytosolic unfolded aggregation-prone monomers and helical aggregation-resistant multimers. It has been shown that familial PD-associated missense mutations within the α-synuclein gene destabilize the conformer equilibrium of physiologic α-synuclein in favor of unfolded monomers. Here, we characterized the relative levels of unfolded and helical forms of cytosolic α-synuclein in post-mortem human brain tissue and showed that the equilibrium of α-synuclein conformations is destabilized in sporadic PD and DLB patients. This disturbed equilibrium is decreased in a brain region-specific manner in patient samples pointing toward a possible “prion-like” propagation of the underlying pathology and forms distinct disease-specific patterns in the two different synucleinopathies. We are also able to show that a destabilization of multimers mechanistically leads to increased levels of insoluble, pathological α-synuclein, while pharmacological stabilization of multimers leads to a “prion-like” aggregation resistance. Together, our findings suggest that these disease-specific patterns of α-synuclein multimer destabilization in sporadic PD and DLB are caused by both regional neuronal vulnerability and “prion-like” aggregation transmission enabled by the destabilization of local endogenous α-synuclein protein.

A Brain-Penetrant Stearoyl-CoA Desaturase Inhibitor Reverses α-Synuclein Toxicity

Increasing evidence has shown that Parkinson's disease (PD) impairs midbrain dopaminergic, cortical and other neuronal subtypes in large part due to the build-up of lipid- and vesicle-rich α-synuclein (αSyn) cytotoxic inclusions. We previously identified stearoyl-CoA desaturase (SCD) as a potential therapeutic target for synucleinopathies. A brain-penetrant SCD inhibitor, YTX-7739, was developed and has entered Phase 1 clinical trials. Here, we report the efficacy of YTX-7739 in reversing pathological αSyn phenotypes in various in vitro and in vivo PD models. In cell-based assays, YTX-7739 decreased αSyn-mediated neuronal death, reversed the abnormal membrane interaction of amplified E46K ("3K") αSyn, and prevented pathological phenotypes in A53T and αSyn triplication patient-derived neurospheres, including dysregulated fatty acid profiles and pS129 αSyn accumulation. In 3K PD-like mice, YTX-7739 crossed the blood-brain barrier, decreased unsaturated fatty acids, and prevented progressive motor deficits. Both YTX-7739 treatment and decreasing SCD activity through deletion of one copy of the SCD1 gene (SKO) restored the physiological αSyn tetramer-to-monomer ratio, dopaminergic integrity, and neuronal survival in 3K αSyn mice. YTX-7739 efficiently reduced pS129 + and PK-resistant αSyn in both human wild-type αSyn and 3K mutant mice similar to the level of 3K-SKO. Together, these data provide further validation of SCD as a PD therapeutic target and YTX-7739 as a clinical candidate for treating human α-synucleinopathies.

Targeting the non-classical estrogen pathway in neurodegenerative diseases and brain injury disorders

Estrogens can alter the biology of various tissues and organs, including the brain, and thus play an essential role in modulating homeostasis. Despite its traditional role in reproduction, it is now accepted that estrogen and its analogues can exert neuroprotective effects. Several studies have shown the beneficial effects of estrogen in ameliorating and delaying the progression of neurodegenerative diseases, including Alzheimer's and Parkinson's disease and various forms of brain injury disorders. While the classical effects of estrogen through intracellular receptors are more established, the impact of the non-classical pathway through receptors located at the plasma membrane as well as the rapid stimulation of intracellular signaling cascades are still under active research. Moreover, it has been suggested that the non-classical estrogen pathway plays a crucial role in neuroprotection in various brain areas. In this mini-review, we will discuss the use of compounds targeting the non-classical estrogen pathway in their potential use as treatment in neurodegenerative diseases and brain injury disorders.

Female Rats Are Resistant to Cognitive, Motor and Dopaminergic Deficits in the Reserpine-Induced Progressive Model of Parkinson's Disease

Parkinson’s disease (PD) is the second most common neurodegenerative disease. The main symptoms are motor signs such as resting tremor and difficulty in initializing movements. Non-motor alterations, such as cognitive deficits, can precede the motor symptoms. PD is more frequent in men than women. The mechanisms related to this difference are not completely understood. There is evidence that females present distinct characteristics in dopaminergic function compared to males. While the severity of motor impairments is often compared between sexes, little is known about sex differences in the prodromal stage. Most animal models of PD present acute severe motor impairment, which precludes the study of non-motor symptoms. Our research group have proposed an adaptation of the classic reserpine protocol, using low doses in a chronic treatment. This method allows the observation of progressive motor impairment as well as premotor deficits. Here we investigate possible behavioral and neuronal sex differences in the effects of the repeated treatment with a low dose of reserpine in rats. Male and female Wistar rats received 10–15 injections of reserpine (0.1 mg/kg) or vehicle, on alternate days. We followed-up the estrous cycle phases and conducted motor and cognitive assessments (catalepsy, open field, oral movements and object recognition tests). The euthanasia occurred 48 h after the 10th or 15th injections, with the collection of blood for the quantification of sex hormones and brains for tyrosine hydroxylase (TH) immunohistochemistry in the substantia nigra pars compact (SNpc). Reserpine induced progressive catalepsy, involuntary oral movements and cognitive deficits in male rats. The behavioral effects of reserpine were attenuated (motor) or absent (cognitive) in females. Reserpine decreased TH immunoreactivity in males, but not in females. Estrogen levels in females negatively correlated with catalepsy duration. Our findings show that females present a delay and/or a prevention in the reserpine-induced motor alterations in the progressive PD model, compatible with the lower prevalence of this disease in women. Further, females were protected from the deficit in object recognition at the prodromal stage. The absence of reserpine-induce decrease in TH immunoreactivity suggests that differences in dopaminergic function/plasticity are related to this protection in female sex.

Neurodegenerative Disease: Roles for Sex, Hormones, and Oxidative Stress

Neurodegenerative diseases cause severe impairments in cognitive and motor function. With an increasing aging population and the onset of these diseases between 50 and 70 years, the consequences are bound to be devastating. While age and longevity are the main risk factors for neurodegenerative diseases, sex is also an important risk factor. The characteristic of sex is multifaceted, encompassing sex chromosome complement, sex hormones (estrogens and androgens), and sex hormone receptors. Sex hormone receptors can induce various signaling cascades, ranging from genomic transcription to intracellular signaling pathways that are dependent on the health of the cell. Oxidative stress, associated with aging, can impact the health of the cell. Sex hormones can be neuroprotective under low oxidative stress conditions but not in high oxidative stress conditions. An understudied sex hormone receptor that can induce activation of oxidative stress signaling is the membrane androgen receptor (mAR). mAR can mediate nicotinamide adenine dinucleotide-phosphate (NADPH) oxidase (NOX)-generated oxidative stress that is associated with several neurodegenerative diseases, such as Alzheimer disease. Further complicating this is that aging can alter sex hormone signaling. Prior to menopause, women experience more estrogens than androgens. During menopause, this sex hormone profile switches in women due to the dramatic ovarian loss of 17β-estradiol with maintained ovarian androgen (testosterone, androstenedione) production. Indeed, aging men have higher estrogens than aging women due to aromatization of androgens to estrogens. Therefore, higher activation of mAR-NOX signaling could occur in menopausal women compared with aged men, mediating the observed sex differences. Understanding of these signaling cascades could provide therapeutic targets for neurodegenerative diseases.

Systems Analysis Reveals Ageing-Related Perturbations in Retinoids and Sex Hormones in Alzheimer's and Parkinson's Diseases

Neurodegenerative diseases, including Alzheimer's (AD) and Parkinson's diseases (PD), are complex heterogeneous diseases with highly variable patient responses to treatment. Due to the growing evidence for ageing-related clinical and pathological commonalities between AD and PD, these diseases have recently been studied in tandem. In this study, we analysed transcriptomic data from AD and PD patients, and stratified these patients into three subclasses with distinct gene expression and metabolic profiles. Through integrating transcriptomic data with a genome-scale metabolic model and validating our findings by network exploration and co-analysis using a zebrafish ageing model, we identified retinoids as a key ageing-related feature in all subclasses of AD and PD. We also demonstrated that the dysregulation of androgen metabolism by three different independent mechanisms is a source of heterogeneity in AD and PD. Taken together, our work highlights the need for stratification of AD/PD patients and development of personalised and precision medicine approaches based on the detailed characterisation of these subclasses.

Wild-type GBA1 increases the α-synuclein tetramer-monomer ratio, reduces lipid-rich aggregates, and attenuates motor and cognitive deficits in mice

The mechanisms responsible for brain α-synuclein (αS) dyshomeostasis, caused by Gaucher’s GBA1 mutations that increase Parkinson’s disease (PD) risk, are largely unknown. We previously showed that abrogating physiological αS tetramers by a familial PD-E46K–amplified 3K mutation produces PD-like syndrome in mice and that treatment with stearoyl-CoA desaturase inhibitors increased a portion of the αS tetramers, benefitting the motor phenotypes. Here, we show that—similar to previous findings in GBA1-mutant PD culture—GCase elevation prolonged the stabilization of wild-type and 3K mutant αS tetramers in wtGBA1–transduced mouse brains, improving lysosomal integrity and motor and cognitive phenotypes. These data help elucidating lipid modulators that impact the αS physiological state in vivo and the development of PD therapeutic approaches.

Loss-of-function mutations in acid beta-glucosidase 1 (GBA1) are among the strongest genetic risk factors for Lewy body disorders such as Parkinson’s disease (PD) and Lewy body dementia (DLB). Altered lipid metabolism in PD patient–derived neurons, carrying either GBA1 or PD αS mutations, can shift the physiological α-synuclein (αS) tetramer–monomer (T:M) equilibrium toward aggregation-prone monomers. A resultant increase in pSer129+ αS monomers provides a likely building block for αS aggregates. 3K αS mice, representing a neuropathological amplification of the E46K PD–causing mutation, have decreased αS T:M ratios and vesicle-rich αS+ aggregates in neurons, accompanied by a striking PD-like motor syndrome. We asked whether enhancing glucocerebrosidase (GCase) expression could benefit αS dyshomeostasis by delivering an adeno-associated virus (AAV)–human wild-type (wt) GBA1 vector into the brains of 3K neonates. Intracerebroventricular AAV-wtGBA1 at postnatal day 1 resulted in prominent forebrain neuronal GCase expression, sustained through 6 mo. GBA1 attenuated behavioral deficits both in working memory and fine motor performance tasks. Furthermore, wtGBA1 increased αS solubility and the T:M ratio in both 3K-GBA mice and control littermates and reduced pS129+ and lipid-rich aggregates in 3K-GBA. We observed GCase distribution in more finely dispersed lysosomes, in which there was increased GCase activity, lysosomal cathepsin D and B maturation, decreased perilipin-stabilized lipid droplets, and a normalized TFEB translocation to the nucleus, all indicative of improved lysosomal function and lipid turnover. Therefore, a prolonged increase of the αS T:M ratio by elevating GCase activity reduced the lipid- and vesicle-rich aggregates and ameliorated PD-like phenotypes in mice, further supporting lipid modulating therapies in PD.

Altered conformation of α-synuclein drives dysfunction of synaptic vesicles in a synaptosomal model of Parkinson's disease

While misfolding of alpha-synuclein (αSyn) is central to the pathogenesis of Parkinson's disease (PD), fundamental questions about its structure and function at the synapse remain unanswered. We examine synaptosomes from non-transgenic and transgenic mice expressing wild-type human αSyn, the E46K fPD-causing mutation, or an amplified form of E46K ("3K"). Synaptosomes from mice expressing the 3K mutant show reduced Ca²⁺-dependent vesicle exocytosis, altered synaptic vesicle ultrastructure, decreased SNARE complexes, and abnormal levels of certain synaptic proteins. With our intra-synaptosomal nuclear magnetic resonance (NMR) method, we reveal that WT αSyn participates in heterogeneous interactions with synaptic components dependent on endogenous αSyn and synaptosomal integrity. The 3K mutation markedly alters these interactions. The synaptic microenvironment is necessary for αSyn to reach its native conformations and establish a physiological interaction network. Its inability to populate diverse conformational ensembles likely represents an early step in αSyn dysfunction that contributes to the synaptotoxicity observed in synucleinopathies.

Potential roles of natural products in the targeting of proteinopathic neurodegenerative diseases

Defective proteostasis is associated with the gradual accumulations of misfolded proteins and is a hallmark of many age-associated neurodegenerative diseases. In the aged brain, maintenance of the proteostasis network presents a substantial challenge, and its loss contributes to the onset and progression of neurological diseases associated with cognitive decline due to the generation of toxic protein aggregates, a process termed 'proteinopathy'. Emerging evidence suggests that reversing proteinopathies by boosting proteostasis might provide an effective means of preventing neurodegeneration. From this perspective, phytochemicals may play significant roles as potent modulators of the proteostasis network, as previous reports have suggested they can interact with various network components to modify pathologies and confer neuroprotection. This review focuses on some potent phytochemicals that directly or indirectly modulate the proteostasis network and on their possible molecular targets. In addition, we propose strategies for the natural product-based modulation of proteostasis machinery that target proteinopathies.

Brain Selective Estrogen Treatment Protects Dopaminergic Neurons and Preserves Behavioral Function in MPTP-induced Mouse Model of Parkinson's Disease

Parkinson's disease (PD) is characterized by progressive degeneration of dopaminergic neurons in the substantia nigra and loss of both motor and non-motor features. Several clinical and preclinical studies have provided evidence that estrogen therapy reduces the risk of PD but have limitations in terms of adverse peripheral effects. Therefore, we examined the potential beneficial effects of the brain-selective estrogen prodrug, 10β, 17β-dihydroxyestra-1,4-dien-3-one (DHED) on nigrostriatal dopaminergic neurodegeneration and behavioral abnormalities in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. Wild-type mice were treated with daily subcutaneous injections of DHED (50 and 100 µg/kg) or vehicle for four weeks. To produce PD-like symptoms, mice were injected with MPTP (18 mg/kg in saline; intraperitoneally) four times at 2-hr intervals for one day. After behavioral examination, mice were sacrificed, and the brains were isolated for neurochemical and morphological examinations. MPTP injected mice exhibited loss of dopaminergic neurons and fibers in substantia nigra and striatum respectively, along with impaired motor function at day 7 post MPTP injection. These phenotypes were associated with significantly increased oxidative stress and inflammatory responses in the striatum regions. DHED treatments significantly mitigated behavioral impairments and dopaminergic neurodegeneration induced by MPTP. We further observed that DHED treatment suppressed oxidative stress and inflammation in the striatum of MPTP treated mice when compared to vehicle treated mice. In conclusions, our findings suggest that DHED protects dopaminergic neurons from MPTP toxicity in mouse model of PD and support a beneficial effect of brain-selective estrogen in attenuating neurodegeneration and motor symptoms in PD-related neurological disorders. Graphical Abstract.

A Stearoyl-Coenzyme A Desaturase Inhibitor Prevents Multiple Parkinson Disease Phenotypes in α-Synuclein Mice

Objective

Parkinson disease (PD) has useful symptomatic treatments that do not slow the neurodegenerative process, and no significant disease‐modifying treatments are approved. A key therapeutic target in PD is α‐synuclein (αS), which is both genetically implicated and accumulates in Lewy bodies rich in vesicles and other lipid membranes. Reestablishing αS homeostasis is a central goal in PD. Based on previous lipidomic analyses, we conducted a mouse trial of a stearoyl–coenzyme A desaturase (SCD) inhibitor (“5b”) that prevented αS‐positive vesicular inclusions and cytotoxicity in cultured human neurons.

Methods

Oral dosing and brain activity of 5b were established in nontransgenic mice. 5b in drinking water was given to mice expressing wild‐type human αS (WT) or an amplified familial PD αS mutation (E35K + E46K + E61K ["3K"]) beginning near the onset of nigral and cortical neurodegeneration and the robust PD‐like motor syndrome in 3K. Motor phenotypes, brain cytopathology, and SCD‐related lipid changes were quantified in 5b‐ versus placebo‐treated mice. Outcomes were compared to effects of crossing 3K to SCD1^−/− mice.

Results

5b treatment reduced αS hyperphosphorylation in E46K‐expressing human neurons, in 3K neural cultures, and in both WT and 3K αS mice. 5b prevented subtle gait deficits in WT αS mice and the PD‐like resting tremor and progressive motor decline of 3K αS mice. 5b also increased αS tetramers and reduced proteinase K‐resistant lipid‐rich aggregates. Similar benefits accrued from genetically deleting 1 SCD allele, providing target validation.

Interpretation

Prolonged reduction of brain SCD activity prevented PD‐like neuropathology in multiple PD models. Thus, an orally available SCD inhibitor potently ameliorates PD phenotypes, positioning this approach to treat human α‐synucleinopathies. ANN NEUROL 2021;89:74–90

A Novel Prodrug Approach for Central Nervous System-Selective Estrogen Therapy

Beneficial effects of estrogens in the central nervous system (CNS) results from the synergistic combination of their well-orchestrated genomic and non-genomic actions, making them potential broad-spectrum neurotherapeutic agents. However, owing to unwanted peripheral hormonal burdens by any currently known non-invasive drug administrations, the development of estrogens as safe pharmacotherapeutic modalities cannot be realized until they are confined specifically and selectively to the site of action. We have developed small-molecule bioprecursor prodrugs carrying the para-quinol scaffold on the steroidal A-ring that are preferentially metabolized in the CNS to the corresponding estrogens. Here, we give an overview of our discovery of these prodrugs. Selected examples are shown to illustrate that, independently of the route of administrations and duration of treatments, these agents produce high concentration of estrogens only in the CNS without peripheral hormonal liability. 10β,17β-Dihydroxyestra-1,4-dien-3-one (DHED) has been the best-studied representative of this novel type of prodrugs for brain and retina health. Specific applications in preclinical animal models of centrally-regulated and estrogen-responsive human diseases, including neurodegeneration, menopausal symptoms, cognitive decline and depression, are discussed to demonstrate the translational potential of our prodrug approach for CNS-selective and gender-independent estrogen therapy with inherent therapeutic safety.