Ribosomal Protein s15 Phosphorylation Mediates LRRK2 Neurodegeneration in Parkinson’s Disease

SummaryMutations in leucine-rich repeat kinase 2 (LRRK2) are a common cause of familial and sporadic Parkinson’s disease (PD). Elevated LRRK2 kinase activity and neurodegeneration are linked, but the phosphosubstrate that connects LRRK2 kinase activity to neurodegeneration is not known. Here, we show that ribosomal protein s15 is a key pathogenic LRRK2 substrate in Drosophila and human neuron PD models. Phosphodeficient s15 carrying a threonine 136 to alanine substitution rescues dopamine neuron degeneration and age-related locomotor deficits in G2019S LRRK2 transgenic Drosophila and substantially reduces G2019S LRRK2-mediated neurite loss and cell death in human dopamine and cortical neurons. Remarkably, pathogenic LRRK2 stimulates both cap-dependent and cap-independent mRNA translation and induces a bulk increase in protein synthesis in Drosophila, which can be prevented by phosphodeficient T136A s15. These results reveal a novel mechanism of PD pathogenesis linked to elevated LRRK2 kinase activity and aberrant protein synthesis in vivo

Meta-Analysis of the Alzheimer\u27s Disease Human Brain Transcriptome and Functional Dissection in Mouse Models.

We present a consensus atlas of the human brain transcriptome in Alzheimer\u27s disease (AD), based on meta-analysis of differential gene expression in 2,114 postmortem samples. We discover 30 brain coexpression modules from seven regions as the major source of AD transcriptional perturbations. We next examine overlap with 251 brain differentially expressed gene sets from mouse models of AD and other neurodegenerative disorders. Human-mouse overlaps highlight responses to amyloid versus tau pathology and reveal age- and sex-dependent expression signatures for disease progression. Human coexpression modules enriched for neuronal and/or microglial genes broadly overlap with mouse models of AD, Huntington\u27s disease, amyotrophic lateral sclerosis, and aging. Other human coexpression modules, including those implicated in proteostasis, are not activated in AD models but rather following other, unexpected genetic manipulations. Our results comprise a cross-species resource, highlighting transcriptional networks altered by human brain pathophysiology and identifying correspondences with mouse models for AD preclinical studies

MOLECULAR MECHANISMS OF DEREGULATED TRANSLATION IN PARKINSON’S DISEASE-LINKED G2019S LEUCINE-RICH REPEAT KINASE 2 (LRRK2) NEURONS

Parkinson’s disease (PD) is a neurodegenerative disorder affecting approximately 1.5% of the population over 65 years of age (Lees, Hardy, & Revesz, 2009). Pathologically, PD is characterized by a selective loss of dopamine neurons in the substantia nigra pars compacta and subsequently reduced dopamine signaling in the central nervous system. Over the last two decades, genetic studies have revealed a number of genes that can cause familial forms of PD when mutated. Among the PD-linked genes, G2019S missense mutation in leucine- rich repeat kinase 2 (LRRK2) gene is the most common disease-causing mutation in familial PD. The G2019S mutation is known to increase its kinase activity (Greggio et al., 2006; Smith et al., 2006). Recent studies have suggested that the increased kinase activity can cause translational abnormality, however, the mechanistic relationship between LRRK2 kinase activity and translation has not yet been established (Imai et al., 2008; Martin, Kim, Lee, et al., 2014). Our laboratory has previously identified the ribosomal small subunit protein S15 as a pathogenic substrate of G2019S LRRK2. In this study, we revealed that global translation is increased in G2019S LRRK2 expressing Drosophila brain, and that the increased translation is important for its neurotoxicity. To gain a deeper understanding of the increased translation, we performed ribosome profiling experiments with LRRK2 mammalian models. We found that mRNAs harboring complex 5’ untranslated region (UTR) secondary structure are preferentially translated in the presence of G2019S LRRK2, and it is dependent on phosphorylation of S15. Structured 5’UTR-mediated alteration in translation was observed in G2019S LRRK2 transgenic mice, LRRK2 knockout mice, and in human dopamine neurons differentiated from G2019S LRRK2 PD patient-derived induced pluripotent stem cells. Notably, translation of CaV1.2 L-type voltage-gated Ca2+ channel, which is continuously active in substantia nigra pars compacta dopamine neurons, is enhanced through its 5’UTR in G2019S LRRK2 neurons. This increased expression leads to the elevation of neuronal Ca2+ influx and intracellular Ca2+ concentration in dopamine neurons. This study provides a novel finding between deregulated translation and increased Ca2+ influx, which may be crucial to understand progressive and selective dopamine neuronal death

Protocol for measurement of calcium dysregulation in human induced pluripotent stem cell-derived dopaminergic neurons

Summary: Calcium regulation is a critical process in neurons, and Ca2+ signaling is a major contributor to neurological disorders including Parkinson’s disease (PD). Here, combining calcium imaging with whole-cell Ca2+ current recording, we provide a detailed protocol for measuring Ca2+ homeostasis in dopaminergic (DA) neurons derived from human induced pluripotent stem cells (hiPSCs). This approach can be applied to investigate the role of Ca2+ homeostasis in neuronal functionality as well as in disease processes.For complete details on the use and execution of this protocol, please refer to Kim et al. (2020)

PINK1 Primes Parkin-Mediated Ubiquitination of PARIS in Dopaminergic Neuronal Survival

Mutations in PTEN-induced putative kinase 1 (PINK1) and parkin cause autosomal-recessive Parkinson’s disease through a common pathway involving mitochondrial quality control. Parkin inactivation leads to accumulation of the parkin interacting substrate (PARIS, ZNF746) that plays an important role in dopamine cell loss through repression of proliferator-activated receptor gamma coactivator-1-alpha (PGC-1α) promoter activity. Here, we show that PARIS links PINK1 and parkin in a common pathway that regulates dopaminergic neuron survival. PINK1 interacts with and phosphorylates serines 322 and 613 of PARIS to control its ubiquitination and clearance by parkin. PINK1 phosphorylation of PARIS alleviates PARIS toxicity, as well as repression of PGC-1α promoter activity. Conditional knockdown of PINK1 in adult mouse brains leads to a progressive loss of dopaminergic neurons in the substantia nigra that is dependent on PARIS. Altogether, these results uncover a function of PINK1 to direct parkin-PARIS-regulated PGC-1α expression and dopaminergic neuronal survival

Meta-Analysis of the Alzheimer’s Disease Human Brain Transcriptome and Functional Dissection in Mouse Models

We present a consensus atlas of the human brain transcriptome in Alzheimer’s disease (AD), based on meta-analysis of differential gene expression in 2,114 postmortem samples. We discover 30 brain coexpression modules from seven regions as the major source of AD transcriptional perturbations. We next examine overlap with 251 brain differentially expressed gene sets from mouse models of AD and other neurodegenerative disorders. Human-mouse overlaps highlight responses to amyloid versus tau pathology and reveal age- and sex-dependent expression signatures for disease progression. Human coexpression modules enriched for neuronal and/or microglial genes broadly overlap with mouse models of AD, Huntington’s disease, amyotrophic lateral sclerosis, and aging. Other human coexpression modules, including those implicated in proteostasis, are not activated in AD models but rather following other, unexpected genetic manipulations. Our results comprise a cross-species resource, highlighting transcriptional networks altered by human brain pathophysiology and identifying correspondences with mouse models for AD preclinical studies