Epigenetic Therapy in Parkinson´s Disease

ORDER	DESCRIPTION
Title	Epigenetic regulation in Parkinson’s disease
Epigenetic mechanism	Ideally, the main desired outcome would be downregulation of a specific pathogenic gene like SNCA or upregulation of gatekeeper genes or both. An Epigenetic mechanism that helps doing this, is DNA methylation. Several molecules can affect DNA methylation but their effects are highly unspecific. Another approach to specifically downregulate or knockdown genes of interest, uses RNA molecules as particularly interesting therapeutic strategies. Specifically, with the use of small interfering RNAs (siRNA), that are short (20–25bp) double-stranded RNA molecules complementary to a specific mRNA region. Finally, mirtrons are a specific class of miRNAs that are encoded in the introns of genes. They have been shown to silence certain genes in both in vitro and in vivo PD models.
How was it done	About DNA Methylation L-dopa appears to increase SNCA methylation in vitro and in vivo. However, its long-term use induces dyskinesia, which appears to be correlated to increased H4 deacetylation. Similar to molecules involved in methylation, the effects of HDACs inhibitors are wide ranging. About siRNA Unstable in their native form, siRNA are often coupled to a vector for transfection into cells. Non-viral vectors specific for neuronal cells can cross the blood-brain barrier rapidly and deliver SNCA-specific siRNAs to neurons knocking down α-synuclein protein expression, thereby preventing PD-like symptoms in in vitro and in vivo experimental models. Pretreatment of M17 cells with a vector/siRNA complex in in vitro models resulted in a greater survival rate when exposed to MPP+ toxin, than untreated M17 cells. About Mirtrons They have been shown to silence certain genes in both in vitro and in vivo PD models. Specially, artificial mirtrons created based on miR-1224 to target LRRK2 and SNCA.
Results	Pretreatment of M17 cells with a vector/siRNA complex in in vitro models resulted in a greater survival rate when exposed to MPP+ toxin, than untreated M17 cells. Additionally, in MPTP mouse models, the release of these vector/siRNAs complexes improved the motor symptoms generated by the MPP+ toxin via downregulation of SNCA. The inhibition SIRT2, a deacetylase, can also rescue α-synuclein toxicity in a cellular model of PD. In fact, when transfecting human neuroglioma cells (H4) with SNCA and synthetic siRNA against SIRT2 or SIRT3, only those transfected with SIRT2 siRNA were rescued from α-synuclein toxicity. Mirtrons achieved an 85% LRRK2 gene expression reduction in HEK293 cells cotransfected with artificial mirtrons and exogenous LRRK2, but the reduction of endogenous LRRK2 was only 36% in SH-SY5Y cells. A similar assay targeting SNCA could only achieve a 26% reduction in expression, suggesting that artificial mirtrons may have therapeutic uses but optimization is needed. However, the off-target effects of a miR could seriously damage normal cell machinery. For RNAbased epigenetic treatments to be successful, specific neurons, as opposed to every cell in a tissue have to be targeted. For this purpose, the chosen delivery system is of utmost importance. MiRs have to: 1) cross the blood brain barrier 2) enter the targeted neurons and 3) remain in the brain long enough to perform their actions. Another aspect to be considered is the potential effects of therapeutic miRs on different isoforms that could lead to undesirable results. Additional experiments need to be carried out to identify which gene isoforms need to be downregulated to improve PD symptoms and delay pathological effects and which ones should be upregulated in neurons so that they perform their expected role to maintain normal neuronal function.

Reference:

1. Labbé C, Lorenzo-Betancor O, Ross O. Epigenetic regulation in Parkinson’s disease. Acta Neuropathologica. 2016;132(4):515-530.

2. Lewis J, Melrose H, Bumcrot D, Hope A, Zehr C, Lincoln S et al. In vivo silencing of alpha-synuclein using naked siRNA. Molecular Neurodegeneration. 2008;3(1):19.

3. Javed H, Menon S, Al-Mansoori K, Al-Wandi A, Majbour N, Ardah M et al. Development of Nonviral Vectors Targeting the Brain as a Therapeutic Approach For Parkinson's Disease and Other Brain Disorders. Molecular Therapy. 2016;24(4):746-758.

Técnicas de Edición de Acidos Nucléicos en Parkinson´s Disease

Repression of SNCA expression by reducing its mRNA level through the use of nucleic acid medicine may lead to suppression of α-synuclein protein levels and prevention of neurodegeneration (1).

Type of editing and Target Organ	New techniques of drug delivery have been attempted to downregulate α-synuclein expression in the brain have been done using ex vivo experiments in rat models.
Administration and Technique	The technique per se, consists in systemic injection of modified exosomes expressing Rabies virus glycoprotein loaded with siRNA targeting SNCA into the mouse tail vein resulted in widespread distribution of siRNA in the brain and around 50% reduction of SNCA mRNA and protein expression in the midbrain and striatum.
Directed To	These approaches are delivered to experimental models that, if successfully work, will be applied to human brains.
Directed By	These experiments are supported by the Michael J. Fox Foundation for Parkinson’s Research, the American Parkinson Disease Association, and the New Jersey Health Foundation/Nicholson Foundation, and by grants from the US National Institutes of Health.
Short-Mid-Long Term Results	However, none of these approaches has produced ideal outcomes, and achieving long-term effects has proven challenging due to intracellular instability of these RNA-based nucleic acid compounds. Additionally, AAV-mediated expression of shRNA-SNCA can have negative effects such as increased inflammatory response, reduced TH expression, and nigrostriatal degeneration.

Reference:
1. Nakamori M, Junn E, Mochizuki H, Mouradian M. Nucleic Acid–Based Therapeutics for Parkinson’s Disease. Neurotherapeutics. 2019;16(2):287-298.

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