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.

GABA-A Alpha 2/3 but Not Alpha 1 Receptor Subunit Ligand Inhibits Harmaline and Pimozide-Induced Tremor in Rats.

Treatment of tremors, such as in essential tremor (ET) and Parkinson's disease (PD) is mostly ineffective. Exact tremor pathomechanisms are unknown and relevant animal models are missing. GABA-A receptor is a target for tremorolytic medications, but current non-selective drugs produce side effects and have safety liabilities. The aim of this study was a search for GABA-A subunit-specific tremorolytics using different tremor-generating mechanisms. Two selective positive allosteric modulators (PAMs) were tested. Zolpidem, targeting GABA-A α1, was not effective in models of harmaline-induced ET, pimozide- or tetrabenazine-induced tremulous jaw movements (TJMs), while the novel GABA-A α2/3 selective MP-III-024 significantly reduced both the harmaline-induced ET tremor and pimozide-induced TJMs. While zolpidem decreased the locomotor activity of the rats, MP-III-024 produced small increases. These results provide important new clues into tremor suppression mechanisms initiated by the enhancement of GABA-driven inhibition in pathways controlled by α2/3 but not α1 containing GABA-A receptors. Tremor suppression by MP-III-024 provides a compelling reason to consider selective PAMs targeting α2/3-containing GABA-A receptors as novel therapeutic drug targets for ET and PD-associated tremor. The possibility of the improved tolerability and safety of this mechanism over non-selective GABA potentiation provides an additional rationale to further pursue the selective α2/3 hypothesis.

The influence of preconditioning with low dose of LPS on paraquat-induced neurotoxicity, microglia activation and expression of α-synuclein and synphilin-1 in the dopaminergic system.

BACKGROUND: Prolonged inflammation, oxidative stress, and protein aggregation are important factors contributing to Parkinson's disease (PD) pathology. A known ROS generator, pesticide paraquat (PQ), was indicated as an environmental substance potentially increasing the incidence of PD and is used to model this disease. We investigated if a combination of inflammation and oxidative stress in subthreshold doses would exacerbate the modelled neuropathology. METHODS: We examined the late effects of acute or repeated peripheral inflammation induced by low dose of LPS (10 µg/kg, ip) on PQ toxicity in the rat nigrostriatal dopaminergic pathway, microglial activation markers and expression of major Lewy bodies proteins, α-synuclein and synphilin-1. RESULTS: We observed that LPS increased, while PQ decreased body temperature and microglia CD11b expression in the SN. Single LPS pretreatment, 3 h before repeated weekly PQ injections (4×) slightly aggravated neuronal degeneration in the SN. Moreover, degeneration of dopaminergic neurons after weekly repeated inflammation itself (4×) was observed. Interestingly, repeated LPS administration combined with each PQ dose counteracted such effect. The expression of α-synuclein decreased after repeated LPS injections, while only combined, repeated LPS and PQ treatment lowered the levels of synphilin-1. Therefore, α-synuclein and synphilin-1 expression change was influenced by different mechanisms. Concomitantly, decreased levels of the two proteins correlated with decreased degeneration of dopaminergic neurons and with a normalized microglia activation marker. CONCLUSIONS: Our results indicate that both oxidative insult triggered by PQ and inflammation caused by peripheral LPS injection can individually induce neurotoxicity. Those factors act through different mechanisms that are not additive and not selective towards dopaminergic neurons, probably implying microglia. Repeated, but small insults from oxidative stress and inflammation when administered in significant time intervals can counteract each other and even act protective as a preconditioning effect. The timing of such repetitive insults is also of essence.

Beyond the GFAP-Astrocyte Protein Markers in the Brain.

The idea of central nervous system as one-man band favoring neurons is long gone. Now we all are aware that neurons and neuroglia are team players and constant communication between those various cell types is essential to maintain functional efficiency and a quick response to danger. Here, we summarize and discuss known and new markers of astroglial multiple functions, their natural heterogeneity, cellular interactions, aging and disease-induced dysfunctions. This review is focused on newly reported facts regarding astrocytes, which are beyond the old stereotypes. We present an up-to-date list of marker proteins used to identify a broad spectrum of astroglial phenotypes related to the various physiological and pathological nervous system conditions. The aim of this review is to help choose markers that are well-tailored for specific needs of further experimental studies, precisely recognizing differential glial phenotypes, or for diagnostic purposes. We hope it will help to categorize the functional and structural diversity of the astroglial population and ease a clear readout of future experimental results.

Increased Beta-Hydroxybutyrate Level Is Not Sufficient for the Neuroprotective Effect of Long-Term Ketogenic Diet in an Animal Model of Early Parkinson's Disease. Exploration of Brain and Liver Energy Metabolism Markers.

The benefits of a ketogenic diet in childhood epilepsy steered up hope for neuroprotective effects of hyperketonemia in Parkinson's disease (PD). There are multiple theoretical reasons but very little actual experimental proof or clinical trials. We examined the long-term effects of the ketogenic diet in an animal model of early PD. A progressive, selective dopaminergic medium size lesion was induced by 6-OHDA injection into the medial forebrain bundle. Animals were kept on the stringent ketogenic diet (1% carbohydrates, 8% protein, 70% fat) for 3 weeks prior and 4 weeks after the brain operation. Locomotor activity, neuron count, dopaminergic terminal density, dopamine level, and turnover were analyzed at three time-points post-lesion, up to 4 weeks after the operation. Energy metabolism parameters (glycogen, mitochondrial complex I and IV, lactate, beta-hydroxybutyrate, glucose) were analyzed in the brain and liver or plasma. Protein expression of enzymes essential for gluconeogenesis (PEPCK, G6PC) and glucose utilization (GCK) was analyzed in the liver. Despite long-term hyperketonemia pre- and post-lesion, the ketogenic diet did not protect against 6-OHDA-induced dopaminergic neuron lesions. The ketogenic diet only tended to improve locomotor activity and normalize DA turnover in the striatum. Rats fed 7 weeks in total with a restrictive ketogenic diet maintained normoglycemia, and neither gluconeogenesis nor glycogenolysis in the liver was responsible for this effect. Therefore, potentially, the ketogenic diet could be therapeutically helpful to support the late compensatory mechanisms active via glial cells but does not necessarily act against the oxidative stress-induced parkinsonian neurodegeneration itself. A word of caution is required as the stringent ketogenic diet itself also carries the risk of unwanted side effects, so it is important to study the long-term effects of such treatments. More detailed metabolic long-term studies using unified diet parameters are required, and human vs. animal differences should be taken under consideration.

Overview of General and Discriminating Markers of Differential Microglia Phenotypes.

Inflammatory processes and microglia activation accompany most of the pathophysiological diseases in the central nervous system. It is proven that glial pathology precedes and even drives the development of multiple neurodegenerative conditions. A growing number of studies point out the importance of microglia in brain development as well as in physiological functioning. These resident brain immune cells are divergent from the peripherally infiltrated macrophages, but their precise in situ discrimination is surprisingly difficult. Microglial heterogeneity in the brain is especially visible in their morphology and cell density in particular brain structures but also in the expression of cellular markers. This often determines their role in physiology or pathology of brain functioning. The species differences between rodent and human markers add complexity to the whole picture. Furthermore, due to activation, microglia show a broad spectrum of phenotypes ranging from the pro-inflammatory, potentially cytotoxic M1 to the anti-inflammatory, scavenging, and regenerative M2. A precise distinction of specific phenotypes is nowadays essential to study microglial functions and tissue state in such a quickly changing environment. Due to the overwhelming amount of data on multiple sets of markers that is available for such studies, the choice of appropriate markers is a scientific challenge. This review gathers, classifies, and describes known and recently discovered protein markers expressed by microglial cells in their different phenotypes. The presented microglia markers include qualitative and semi-quantitative, general and specific, surface and intracellular proteins, as well as secreted molecules. The information provided here creates a comprehensive and practical guide through the current knowledge and will facilitate the choosing of proper, more specific markers for detailed studies on microglia and neuroinflammatory mechanisms in various physiological as well as pathological conditions. Both basic research and clinical medicine need clearly described and validated molecular markers of microglia phenotype, which are essential in diagnostics, treatment, and prevention of diseases engaging glia activation.

The role of glia in Parkinson's disease: Emerging concepts and therapeutic applications.

Originally believed to primarily affect neurons, Parkinson's disease (PD) has recently been recognized to also affect the functions and integrity of microglia and astroglia, two cell categories of fundamental importance to brain tissue homeostasis, defense, and repair. Both a loss of glial supportive-defensive functions and a toxic gain of glial functions are implicated in the neurodegenerative process. Moreover, the chronic treatment with L-DOPA may cause maladaptive glial plasticity favoring a development of therapy complications. This chapter focuses on the pathophysiology of PD from a glial point of view, presenting this rapidly growing field from the first discoveries made to the most recent developments. We report and compare histopathological and molecular findings from experimental models of PD and human studies. We moreover discuss the important role played by astrocytes in compensatory adaptations taking place during presymptomatic disease stages. We finally describe examples of potential therapeutic applications stemming from an increased understanding of the important roles of glia in PD.

Increased energetic demand supported by mitochondrial electron transfer chain and astrocyte assistance is essential to maintain the compensatory ability of the dopaminergic neurons in an animal model of early Parkinson's disease.

Partial degeneration of dopaminergic neurons in the substantia nigra (SN), induces locomotor disability in animals but with time it is spontaneously compensated for by neurons surviving in the tissue by increasing their functional efficiency. Such compensation probably increases energy requirements and astrocyte support could be essential for this ability. We studied the effect of degeneration of dopaminergic neurons induced by the selective toxin 6-hydroxydopamine and/or death of 30% of astrocytes induced by chronic infusion of the glial toxin fluorocitrate on functioning of the mitochondrial electron transfer chain (ETC) complexes (Cxs) I, II, IV and their higher assembled forms, supercomplexes in the rat SN. Astrocyte death decreased Cx I and IV performance, while significantly increased the amount of Cx II protein SDHA, indicating system adaptation. After death of 50% of dopaminergic neurons in the SN, we observed increased mitochondrial Cxs performing, especially Cx I and IV in the remaining cells. It corresponded with reduction of behavioural deficits. Those results support the hypothesis that the compensatory ability of surviving neurons requires meeting their higher energetic demand by ETC. When astrocytes were defective, the neurons remaining after partial lesion were not able to enhance their functioning anymore and compensate for deficits. It proves in vivo that astrocytic support is important for compensatory potential of neurons in the SN. Neuro-glia cooperation is fundamental for compensation for early deficits in the nigrostriatal system.