RNAseq-based transcriptome profiling of the Engrailed-1 mouse model of Parkinson’s Disease

Abstract

Background | Motor dysfunction due to progressive nigrostriatal degeneration is a key feature of Parkinson’s disease (PD). Hemizygous loss of Engrailed-1 (En1) induces features reminiscent of PD in mice, such as nigrostriatal axonal degeneration and dopaminergic neuron death in the substantia nigra pars compacta (SNpc) starting at three weeks of age. Interestingly, the neuropathological phenotype is only observed in SwissOF1-En1+/- but not in C57Bl/6-En1+/- mice. Multiple interacting quantitative trait loci (QTL) linked to these PD-like neurodegenerative changes have been reported previously in an F2 intercross between SwissOF1-En1+/- and C57Bl/6J. However, the specific genes underlying these QTLs have yet to be determined. The aim of this study was to identify gene expression profiles associated with dopaminergic neuroprotection in C57Bl/6J-En1+/- mice.

Methods | A combination of histological (stereological count of dopaminergic neurons in SNpc and quantification of striatal axonal swellings), molecular (RNAseq-based transcriptome profiling of SNpc isolated by Laser Capture Microdissection), and bioinformatic (differential gene expression and functional enrichment analysis) methods were used to compare the response to En1 hemizygosity in SwissOF1 and C57Bl/6J mice.

Results | SwissOF1-En1+/- displayed early signs of axonal degeneration and 24% loss of dopaminergic neurons in the SNpc at 16 weeks, while C57Bl/6-En1+/- only showed moderate axonal pathology and no nigral cell loss. Whole transcriptome analysis of 1-week-old SwissOF1-En1+/-, C57Bl/6-En1+/- and the respective wild-type strains revealed specific transgene-induced as well as strain-dependent expression profiles, in which genes involved in mitochondrial activity, axonal guidance, and synaptic function were enriched.

Conclusion | Here we provide further insight into the differences observed in the neuropathological phenotype between En1 hemizygous mice on the C57Bl/6J and SwissOF1 background genomes. The generated transcriptomic data will be used for further functional studies and coupled to the previous QTL analysis to identify genetic factors regulating susceptibility to dopaminergic neurodegeneration, a process of prime biological importance in idiopathic PD risk.

Popular Abstract

Of mice and men: looking for new genetic risk factors in Parkinson’s Disease

Parkinson’s disease (PD) is an incurable and common degenerative brain disorder that affects over 10 million people worldwide. Despite intensive research efforts, the genetic factors underlying the susceptibility to develop PD remain largely unknown. Here, we set out to explore this question using a mouse model of the disease and identified several biological processes that could play an important role in determining the risk of developing this debilitating brain disorder.

PD affects mainly a brain region known as the substantia nigra (SN). More specifically within this region, the cells that produce a substance called dopamine are the ones that die during the course of the disease. This results in the well-known features of PD patients, such as tremor and body rigidity. Importantly, these symptoms often appear at a stage when already 80% of the dopamine-producing cells are gone. Although it is clear that the lack of dopamine is the major cause of these symptoms, why these particular cells are so vulnerable remains an open question.

Mouse models are very useful for dissecting the mechanisms of complex diseases such as PD. In this project, we studied the consequences of losing partially a gene called Engrailed-1 (En1) in mice. This gene is of special interest in PD, as it is involved in the development and survival of the dopamine-producing cells in the SN. In fact, variation in this gene has been associated with PD in humans. Total or partial lack of this gene in mice results in the loss of the very same cells that deteriorate and eventually die in PD patients. However, this is not the case for every mouse. Indeed, there is one mouse strain known as C57Bl/6J that copes with the partial loss of En1 and whose dopamine-producing cells endure. This motivated us to explore the differences between resistant C57Bl/6J mice and a vulnerable strain called SwissOF1 upon partial loss of En1 in order to find biological processes that modify the risk of PD.

We could confirm that C57Bl/6J mice do not lose any dopamine-producing cell in the SN, as opposed to SwissOF1 animals, when they lack En1. Using a laser-based technique to accurately dissect the SN of these mice, we could obtain unique genetic fingerprints caused by En1 loss in both strains. Our results shed light onto why C57Bl/6J dopamine-producing cells are protected.

While alleviating treatments exist, it is hoped that a deeper understanding of the genetic factors that increase the risk of developing PD will facilitate the invention of new therapies that can halt or reverse the disease process.

Master’s Degree Project in Molecular Biology (Molecular Genetics and Biotechnology), 60 credits, 2019
Department of Biology, Lund University

Advisor: Maria Swanberg and Itzia Jiménez-Ferrer
Translational Neurogenetics Unit, Department of Experimental Medical Science, Lund University

• author: Dueñas Rey, Alfredo
• supervisor: Maria Swanberg
• organization: Degree Projects in Molecular Biology
• course: MOBN03 20182
• year: 2019
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 8979408
• date added to LUP: 2019-06-04 14:58:20
• date last changed: 2019-06-04 14:58:20