Lipase regulation of cellular fatty acid homeostasis as a Parkinson's disease therapeutic strategy

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.

MUFA synthesis and stearoyl-CoA desaturase as a new pharmacological target for modulation of lipid and alpha-synuclein interaction against Parkinson's disease synucleinopathy

Protein pathology spreading within the nervous system, accompanies neurodegeneration and a spectrum of motor and cognitive dysfunctions. Currently available therapies against Parkinson's disease and other synucleinopathies are mostly symptomatic and fail to slow the disease progression in the long term. Modification of α-synuclein (αS) aggregation and toxicity of its pathogenic forms is one of the main goals in neuroprotective approach. Since the discovery of lipid component of Lewy bodies, fatty acids became a crucial, yet little explored target for research. MUFAs (monounsaturated fatty acids) are substrates for lipids, such as phospholipids, triglycerides and cholesteryl esters. They regulate membrane fluidity, take part in signal transduction, cellular differentiation and other fundamental processes. αS and MUFA interactions are essential for Lewy body pathology. αS increases levels of MUFAs, mainly oleic acid, which in turn can enhance αS toxicity and aggregation. Thus, reduction of MUFAs synthesis by inhibition of stearoyl-CoA desaturase (SCD) activity could be the new way to prevent aggravation of αS pathology. Due to the limited distribution in peripheral tissues, SCD5 is a potential target in novel therapies and therefore could be an important starting point in search for disease-modifying neuroprotective therapy. Here we summarize facts about physiology and pathology of αS, explain recently discovered lipid-αS interactions, review SCD function and involved mechanisms, present available SCD inhibitors and discuss their pharmacological potential in disease management. Modulation of MUFA synthesis, decreasing αS and lipid toxicity is clearly essential, but unexplored avenue in pharmacotherapy of Parkinson's disease and synucleinopathies.

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.

Unraveling the Genetic Landscape of Neurological Disorders: Insights into Pathogenesis, Techniques for Variant Identification, and Therapeutic Approaches

Genetic abnormalities play a crucial role in the development of neurodegenerative disorders (NDDs). Genetic exploration has indeed contributed to unraveling the molecular complexities responsible for the etiology and progression of various NDDs. The intricate nature of rare and common variants in NDDs contributes to a limited understanding of the genetic risk factors associated with them. Advancements in next-generation sequencing have made whole-genome sequencing and whole-exome sequencing possible, allowing the identification of rare variants with substantial effects, and improving the understanding of both Mendelian and complex neurological conditions. The resurgence of gene therapy holds the promise of targeting the etiology of diseases and ensuring a sustained correction. This approach is particularly enticing for neurodegenerative diseases, where traditional pharmacological methods have fallen short. In the context of our exploration of the genetic epidemiology of the three most prevalent NDDs-amyotrophic lateral sclerosis, Alzheimer's disease, and Parkinson's disease, our primary goal is to underscore the progress made in the development of next-generation sequencing. This progress aims to enhance our understanding of the disease mechanisms and explore gene-based therapies for NDDs. Throughout this review, we focus on genetic variations, methodologies for their identification, the associated pathophysiology, and the promising potential of gene therapy. Ultimately, our objective is to provide a comprehensive and forward-looking perspective on the emerging research arena of NDDs.

Undetected Association Between Fatty Acids and Dementia with Lewy Bodies: A Bidirectional Two-Sample Mendelian Randomization Study

Background

Although observational studies indicated connections between fatty acids (FAs) and Alzheimer's disease and dementia, uncertainty persists regarding how these relationships extend to dementia with Lewy bodies (DLB).

Objective

To explore the potential causal relationships between FAs and the development of DLB, thus clarifying these associations using genetic instruments to infer causality.

Methods

We applied a two-sample Mendelian randomization (MR) and multivariable Mendelian randomization (MVMR) approach. Genetic data were obtained from a DLB cohort, comprising 2,591 cases and 4,027 controls of European descent. Eight FAs, including linoleic acid, docosahexaenoic acid, monounsaturated fatty acid, omega-3 fatty acid, omega-6 fatty acid, polyunsaturated fatty acid, saturated fatty acid, and total fatty acid, were procured from a comprehensive GWAS of metabolic biomarkers of UK Biobank, conducted by Nightingale Health in 2020 (met-d), involving 114,999 individuals. Our analysis included inverse-variance weighted, MR-Egger, weighted-median, simple mode, and weighted-mode MR estimates. Cochran's Q-statistics, MR-PRESSO, and MR-Egger intercept test were used to quantify the heterogeneity and horizontal pleiotropy of instrumental variables.

Results

Only linoleic acid showed a significant genetic association with the risk of developing DLB in the univariate MR. The odds ratio for linoleic acid was 1.337 with a 95% confidence interval of 1.019-1.756 (pIVW = 0.036). Results from the MVMR showed that no FAs were associated with the incidence of DLB.

Conclusions

The results did not support the hypothesis that FAs could reduce the risk of developing DLB. However, elucidating the relationship between FAs and DLB risk holds potential implications for informing dietary recommendations and therapeutic approaches in DLB.

Microglial REV-ERBα regulates inflammation and lipid droplet formation to drive tauopathy in male mice

Alzheimer's disease, the most common age-related neurodegenerative disease, is characterized by tau aggregation and associated with disrupted circadian rhythms and dampened clock gene expression. REV-ERBα is a core circadian clock protein which also serves as a nuclear receptor and transcriptional repressor involved in lipid metabolism and macrophage function. Global REV-ERBα deletion has been shown to promote microglial activation and mitigate amyloid plaque formation. However, the cell-autonomous effects of microglial REV-ERBα in healthy brain and in tauopathy are unexplored. Here, we show that microglial REV-ERBα deletion enhances inflammatory signaling, disrupts lipid metabolism, and causes lipid droplet (LD) accumulation specifically in male microglia. These events impair microglial tau phagocytosis, which can be partially rescued by blockage of LD formation. In vivo, microglial REV-ERBα deletion exacerbates tau aggregation and neuroinflammation in two mouse tauopathy models, specifically in male mice. These data demonstrate the importance of microglial lipid droplets in tau accumulation and reveal REV-ERBα as a therapeutically accessible, sex-dependent regulator of microglial inflammatory signaling, lipid metabolism, and tauopathy.

Palmitoylation of the Parkinson's disease-associated protein synaptotagmin-11 links its turnover to α-synuclein homeostasis

Synaptotagmin-11 (Syt11) is a vesicle-trafficking protein that is linked genetically to Parkinson's disease (PD). Likewise, the protein α-synuclein regulates vesicle trafficking, and its abnormal aggregation in neurons is the defining cytopathology of PD. Because of their functional similarities in the same disease context, we investigated whether the two proteins were connected. We found that Syt11 was palmitoylated in mouse and human brain tissue and in cultured cortical neurons and that this modification to Syt11 disrupted α-synuclein homeostasis in neurons. Palmitoylation of two cysteines adjacent to the transmembrane domain, Cys39 and Cys40, localized Syt11 to digitonin-insoluble portions of intracellular membranes and protected it from degradation by the endolysosomal system. In neurons, palmitoylation of Syt11 increased its abundance and enhanced the binding of α-synuclein to intracellular membranes. As a result, the abundance of the physiologic tetrameric form of α-synuclein was decreased, and that of its aggregation-prone monomeric form was increased. These effects were replicated by overexpression of wild-type Syt11 but not a palmitoylation-deficient mutant. These findings suggest that palmitoylation-mediated increases in Syt11 amounts may promote pathological α-synuclein aggregation in PD.