Stephan Gehrke

All Publications

• The bantam microRNA acts through Numb to exert cell growth control and feedback regulation of Notch in tumor-forming stem cells in the Drosophila brain. PLoS genetics Wu, Y., Lee, K., Song, Y., Gehrke, S., Lu, B. 2017; 13 (5)

  Abstract

  Notch (N) signaling is central to the self-renewal of neural stem cells (NSCs) and other tissue stem cells. Its deregulation compromises tissue homeostasis and contributes to tumorigenesis and other diseases. How N regulates stem cell behavior in health and disease is not well understood. Here we show that N regulates bantam (ban) microRNA to impact cell growth, a process key to NSC maintenance and particularly relied upon by tumor-forming cancer stem cells. Notch signaling directly regulates ban expression at the transcriptional level, and ban in turn feedback regulates N activity through negative regulation of the Notch inhibitor Numb. This feedback regulatory mechanism helps maintain the robustness of N signaling activity and NSC fate. Moreover, we show that a Numb-Myc axis mediates the effects of ban on nucleolar and cellular growth independently or downstream of N. Our results highlight intricate transcriptional as well as translational control mechanisms and feedback regulation in the N signaling network, with important implications for NSC biology and cancer biology.

  View details for DOI 10.1371/journal.pgen.1006785

  View details for PubMedID 28520736

• PINK1 and Parkin Control Localized Translation of Respiratory Chain Component mRNAs on Mitochondria Outer Membrane. Cell metabolism Gehrke, S., Wu, Z., Klinkenberg, M., Sun, Y., Auburger, G., Guo, S., Lu, B. 2015; 21 (1): 95-108

  Abstract

  Mitochondria play essential roles in many aspects of biology, and their dysfunction has been linked to diverse diseases. Central to mitochondrial function is oxidative phosphorylation (OXPHOS), accomplished by respiratory chain complexes (RCCs) encoded by nuclear and mitochondrial genomes. How RCC biogenesis is regulated in metazoans is poorly understood. Here we show that Parkinson's disease (PD)-associated genes PINK1 and Parkin direct localized translation of certain nuclear-encoded RCC (nRCC) mRNAs. Translationally repressed nRCC mRNAs are localized in a PINK1/Tom20-dependent manner to mitochondrial outer membrane, where they are derepressed and activated by PINK1/Parkin through displacement of translation repressors, including Pumilio and Glorund/hnRNP-F, a Parkin substrate, and enhanced binding of activators such as eIF4G. Inhibiting the translation repressors rescued nRCC mRNA translation and neuromuscular-degeneration phenotypes of PINK1 mutant, whereas inhibiting eIF4G had opposite effects. Our results reveal previously unknown functions of PINK1/Parkin in RNA metabolism and suggest new approaches to mitochondrial restoration and disease intervention.

  View details for DOI 10.1016/j.cmet.2014.12.007

  View details for PubMedID 25565208

• RNA metabolism in the pathogenesis of Parkinson's disease BRAIN RESEARCH Lu, B., Gehrke, S., Wu, Z. 2014; 1584: 105-115

  Abstract

  Neurodegenerative diseases such as Parkinson's disease are progressive disorders of the nervous system that affect the function and maintenance of specific neuronal populations. While most disease cases are sporadic with no known cause, a small percentage of disease cases is caused by inherited genetic mutations. The identification of genes associated with the familial forms of the diseases and subsequent studies of proteins encoded by the disease genes in cellular or animals models have offered much-needed insights into the molecular and cellular mechanisms underlying disease pathogenesis. Recent studies of the familial Parkinson's disease genes have emphasized the importance of RNA metabolism, particularly mRNA translation, in the disease process. It is anticipated that continued studies on the role of RNA metabolism in Parkinson's disease will offer unifying mechanisms for understanding the cause of neuronal dysfunction and degeneration and facilitate the development of novel and rational strategies for treating this debilitating disease.

  View details for DOI 10.1016/j.brainres.2014.03.003

  View details for Web of Science ID 000343838400012

• RNA metabolism in the pathogenesis of Parkinson?s disease. Brain research Lu, B., Gehrke, S., Wu, Z. 2014; 1584: 105-115

  Abstract

  Neurodegenerative diseases such as Parkinson's disease are progressive disorders of the nervous system that affect the function and maintenance of specific neuronal populations. While most disease cases are sporadic with no known cause, a small percentage of disease cases is caused by inherited genetic mutations. The identification of genes associated with the familial forms of the diseases and subsequent studies of proteins encoded by the disease genes in cellular or animals models have offered much-needed insights into the molecular and cellular mechanisms underlying disease pathogenesis. Recent studies of the familial Parkinson's disease genes have emphasized the importance of RNA metabolism, particularly mRNA translation, in the disease process. It is anticipated that continued studies on the role of RNA metabolism in Parkinson's disease will offer unifying mechanisms for understanding the cause of neuronal dysfunction and degeneration and facilitate the development of novel and rational strategies for treating this debilitating disease.

  View details for DOI 10.1016/j.brainres.2014.03.003

  View details for PubMedID 24631951

• The synaptic function of LRRK2 BIOCHEMICAL SOCIETY TRANSACTIONS Lee, S., Imai, Y., Gehrke, S., Liu, S., Lu, B. 2012; 40: 1047-1051

  Abstract

  Mutations in LRRK2 (leucine-rich repeat kinase 2) are the most frequent genetic lesions so far found in familial as well as sporadic forms of PD (Parkinson's disease), a neurodegenerative disease characterized by the dysfunction and degeneration of dopaminergic and other neuronal types. The molecular and cellular mechanisms underlying LRRK2 action remain poorly defined. Synaptic dysfunction has been increasingly recognized as an early event in the pathogenesis of major neurological disorders. Using Drosophila as a model system, we have shown that LRRK2 controls synaptic morphogenesis. Loss of dLRRK (Drosophila LRRK2) results in synaptic overgrowth at the Drosophila neuromuscular junction synapse, whereas overexpression of wild-type dLRRK, hLRRK2 (human LRRK2) or the pathogenic hLRRK2-G2019S mutant has the opposite effect. Alteration of LRRK2 activity also affects synaptic transmission in a complex manner. LRRK2 exerts its effects on synaptic morphology by interacting with distinct downstream effectors at the pre- and post-synaptic compartments. At the postsynapse, LRRK2 functionally interacts with 4E-BP (eukaryotic initiation factor 4E-binding protein) and the microRNA machinery, both of which negatively regulate protein synthesis. At the presynapse, LRRK2 phosphorylates and negatively regulates the microtubule-binding protein Futsch and functionally interacts with the mitochondrial transport machinery. These results implicate compartment-specific synaptic dysfunction caused by altered protein synthesis, cytoskeletal dynamics and mitochondrial transport in LRRK2 pathogenesis and offer a new paradigm for understanding and ultimately treating LRRK2-related PD.

  View details for DOI 10.1042/BST20120113

  View details for Web of Science ID 000309513200021

  View details for PubMedID 22988863

• Pathogenic LRRK2 negatively regulates microRNA-mediated translational repression NATURE Gehrke, S., Imai, Y., Sokol, N., Lu, B. 2010; 466 (7306): 637-U9

  Abstract

  Gain-of-function mutations in leucine-rich repeat kinase 2 (LRRK2) cause familial as well as sporadic Parkinson's disease characterized by age-dependent degeneration of dopaminergic neurons. The molecular mechanism of LRRK2 action is not known. Here we show that LRRK2 interacts with the microRNA (miRNA) pathway to regulate protein synthesis. Drosophila e2f1 and dp messenger RNAs are translationally repressed by let-7 and miR-184*, respectively. Pathogenic LRRK2 antagonizes these miRNAs, leading to the overproduction of E2F1/DP, previously implicated in cell cycle and survival control and shown here to be critical for LRRK2 pathogenesis. Genetic deletion of let-7, antagomir-mediated blockage of let-7 and miR-184* action, transgenic expression of dp target protector, or replacement of endogenous dp with a dp transgene non-responsive to let-7 each had toxic effects similar to those of pathogenic LRRK2. Conversely, increasing the level of let-7 or miR-184* attenuated pathogenic LRRK2 effects. LRRK2 associated with Drosophila Argonaute-1 (dAgo1) or human Argonaute-2 (hAgo2) of the RNA-induced silencing complex (RISC). In aged fly brain, dAgo1 protein level was negatively regulated by LRRK2. Further, pathogenic LRRK2 promoted the association of phospho-4E-BP1 with hAgo2. Our results implicate deregulated synthesis of E2F1/DP caused by the miRNA pathway impairment as a key event in LRRK2 pathogenesis and suggest novel miRNA-based therapeutic strategies.

  View details for DOI 10.1038/nature09191

  View details for Web of Science ID 000280412100056

  View details for PubMedID 20671708

  View details for PubMedCentralID PMC3049892

• Leucine-rich repeat kinase 2 interacts with Parkin, DJ-1 and PINK-1 in a Drosophila melanogaster model of Parkinson's disease HUMAN MOLECULAR GENETICS Venderova, K., Kabbach, G., Abdel-Messih, E., Zhang, Y., Parks, R. J., Imai, Y., Gehrke, S., Ngsee, J., LaVoie, M. J., Slack, R. S., Rao, Y., Zhang, Z., Lu, B., Haque, M. E., Park, D. S. 2009; 18 (22): 4390-4404

  Abstract

  Mutations in the LRRK2 gene are the most common genetic cause of familial Parkinson's disease (PD). However, its physiological and pathological functions are unknown. Therefore, we generated several independent Drosophila lines carrying WT or mutant human LRRK2 (mutations in kinase, COR or LRR domains, resp.). Ectopic expression of WT or mutant LRRK2 in dopaminergic neurons caused their significant loss accompanied by complex age-dependent changes in locomotor activity. Overall, the ubiquitous expression of LRRK2 increased lifespan and fertility of the flies. However, these flies were more sensitive to rotenone. LRRK2 expression in the eye exacerbated retinal degeneration. Importantly, in double transgenic flies, various indices of the eye and dopaminergic survival were modified in a complex fashion by a concomitant expression of PINK1, DJ-1 or Parkin. This evidence suggests a genetic interaction between these PD-relevant genes.

  View details for DOI 10.1093/hmg/ddp394

  View details for Web of Science ID 000271107300015

  View details for PubMedID 19692353

• Neuroprotective effects of compounds with antioxidant and anti-inflammatory properties in a Drosophila model of Parkinson's disease BMC NEUROSCIENCE Faust, K., Gehrke, S., Yang, Y., Yang, L., Beal, M. F., Lu, B. 2009; 10

  Abstract

  Parkinson's disease (PD) is the most common movement disorder. Extrapyramidal motor symptoms stem from the degeneration of the dopaminergic pathways in patient brain. Current treatments for PD are symptomatic, alleviating disease symptoms without reversing or retarding disease progression. Although the cause of PD remains unknown, several pathogenic factors have been identified, which cause dopaminergic neuron (DN) death in the substantia nigra (SN). These include oxidative stress, mitochondrial dysfunction, inflammation and excitotoxicity. Manipulation of these factors may allow the development of disease-modifying treatment strategies to slow neuronal death. Inhibition of DJ-1A, the Drosophila homologue of the familial PD gene DJ-1, leads to oxidative stress, mitochondrial dysfunction, and DN loss, making fly DJ-1A model an excellent in vivo system to test for compounds with therapeutic potential.In the present study, a Drosophila DJ-1A model of PD was used to test potential neuroprotective drugs. The drugs applied are the Chinese herb celastrol, the antibiotic minocycline, the bioenergetic amine coenzyme Q10 (coQ10), and the glutamate antagonist 2,3-dihydroxy-6-nitro-7-sulphamoylbenzo[f]-quinoxaline (NBQX). All of these drugs target pathogenic processes implicated in PD, thus constitute mechanism-based treatment strategies. We show that celastrol and minocycline, both having antioxidant and anti-inflammatory properties, confer potent dopaminergic neuroprotection in Drosophila DJ-1A model, while coQ10 shows no protective effect. NBQX exerts differential effects on cell survival and brain dopamine content: it protects against DN loss but fails to restore brain dopamine level.The present study further validates Drosophila as a valuable model for preclinical testing of drugs with therapeutic potential for neurodegenerative diseases. The lower cost and amenability to high throughput testing make Drosophila PD models effective in vivo tools for screening novel therapeutic compounds. If our findings can be further validated in mammalian PD models, they would implicate drugs combining antioxidant and anti-inflammatory properties as strong therapeutic candidates for mechanism-based PD treatment.

  View details for DOI 10.1186/1471-2202-10-109

  View details for Web of Science ID 000270558900001

  View details for PubMedID 19723328

  View details for PubMedCentralID PMC3152779

• Phosphorylation of 4E-BP by LRRK2 affects the maintenance of dopaminergic neurons in Drosophila EMBO JOURNAL Imai, Y., Gehrke, S., Wang, H., Takahashi, R., Hasegawa, K., Oota, E., Lu, B. 2008; 27 (18): 2432-2443

  Abstract

  Dominant mutations in leucine-rich repeat kinase 2 (LRRK2) are the most frequent molecular lesions so far found in Parkinson's disease (PD), an age-dependent neurodegenerative disorder affecting dopaminergic (DA) neuron. The molecular mechanisms by which mutations in LRRK2 cause DA degeneration in PD are not understood. Here, we show that both human LRRK2 and the Drosophila orthologue of LRRK2 phosphorylate eukaryotic initiation factor 4E (eIF4E)-binding protein (4E-BP), a negative regulator of eIF4E-mediated protein translation and a key mediator of various stress responses. Although modulation of the eIF4E/4E-BP pathway by LRRK2 stimulates eIF4E-mediated protein translation both in vivo and in vitro, it attenuates resistance to oxidative stress and survival of DA neuron in Drosophila. Our results suggest that chronic inactivation of 4E-BP by LRRK2 with pathogenic mutations deregulates protein translation, eventually resulting in age-dependent loss of DA neurons.

  View details for DOI 10.1038/emboj.2008.163

  View details for Web of Science ID 000259260100008

  View details for PubMedID 18701920

  View details for PubMedCentralID PMC2543051

• LRRK2 regulates protein translation via eIF4E/4E-BP pathway and influences dopaminergic neuron maintenance Imai, Y., Gehrke, S., Lu, B. ELSEVIER IRELAND LTD. 2008: S71

  View details for Web of Science ID 000261548100421

• Mitochondrial pathology and muscle and dopaminergic neuron degeneration caused inactivation of Drosophila Pink1 is rescued by by Parkin PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Yang, Y., Gehrke, S., Imai, Y., Huang, Z., Ouyang, Y., Wang, J., Yang, L., Beal, M. F., Vogel, H., Lu, B. 2006; 103 (28): 10793-10798

  Abstract

  Mutations in Pink1, a gene encoding a Ser/Thr kinase with a mitochondrial-targeting signal, are associated with Parkinson's disease (PD), the most common movement disorder characterized by selective loss of dopaminergic neurons. The mechanism by which loss of Pink1 leads to neurodegeneration is not understood. Here we show that inhibition of Drosophila Pink1 (dPink1) function results in energy depletion, shortened lifespan, and degeneration of select indirect flight muscles and dopaminergic neurons. The muscle pathology was preceded by mitochondrial enlargement and disintegration. These phenotypes could be rescued by the wild type but not the pathogenic C-terminal deleted form of human Pink1 (hPink1). The muscle and dopaminergic phenotypes associated with dPink1 inactivation show similarity to that seen in parkin mutant flies and could be suppressed by the overexpression of Parkin but not DJ-1. Consistent with the genetic rescue results, we find that, in dPink1 RNA interference (RNAi) animals, the level of Parkin protein is significantly reduced. Together, these results implicate Pink1 and Parkin in a common pathway that regulates mitochondrial physiology and cell survival in Drosophila.

  View details for DOI 10.1073/pnas.0602493103

  View details for PubMedID 16818890

• Modeling Parkinson's disease using RNAi 37th Annual Meeting of the American-Society-for-Neurochemistry Lu, B., Yang, Y., Gehrke, S., Wang, J., Imai, Y., Ouyang, Y., Huang, Z. WILEY-BLACKWELL. 2006: 14–14

  View details for Web of Science ID 000235982900031

• Inactivation of Drosophila DJ-1 leads to impairments of oxidative stress response and phosphatidylinositol 3-kinase/Akt signaling PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Yang, Y. F., Gehrke, S., Haque, M. E., Imai, Y., Kosek, J., Yang, L. C., Beal, M. F., Nishimura, I., Wakarnatsu, K., Ito, S., Takahashi, R., Lu, B. W. 2005; 102 (38): 13670-13675

  Abstract

  Parkinson's disease (PD) is the most common movement disorder characterized by dopaminergic dysfunction and degeneration. The cause of most PD cases is unknown, although postmortem studies have implicated the involvement of oxidative stress. The identification of familial PD-associated genes offers the opportunity to study mechanisms of PD pathogenesis in model organisms. Here, we show that DJ-1A, a Drosophila homologue of the familial PD-associated gene DJ-1, plays an essential role in oxidative stress response and neuronal maintenance. Inhibition of DJ-1A function through RNA interference (RNAi) results in cellular accumulation of reactive oxygen species, organismal hypersensitivity to oxidative stress, and dysfunction and degeneration of dopaminergic and photoreceptor neurons. To identify other genes that may interact with DJ-1A in regulating cell survival, we performed genetic interaction studies and identified components of the phosphatidylinositol 3-kinase (PI3K)/Akt-signaling pathway as specific modulators of DJ-1A RNAi-induced neurodegeneration. PI3K signaling suppresses DJ-1A RNAi phenotypes at least in part by reducing cellular reactive oxygen species levels. Consistent with the genetic interaction results, we also found reduced phosphorylation of Akt in DJ-1A RNAi animals, indicating an impairment of PI3K/Akt signaling by DJ-1A down-regulation. Together with recent findings in mammalian systems, these results implicate impairments of PI3K/Akt signaling and oxidative stress response in DJ-1-associated disease pathogenesis. We also observed impairment of PI3K/Akt signaling in the fly parkin model of PD, hinting at a common molecular event in the pathogenesis of PD. Manipulation of PI3K/Akt signaling may therefore offer therapeutic benefits for the treatment of PD.

  View details for DOI 10.1073/pnas.0504610102

  View details for Web of Science ID 000232115100057

  View details for PubMedID 16155123

  View details for PubMedCentralID PMC1224636

• Chimeric transcriptional control units for improved liver-specific transgene expression GENE Gehrke, S., Jerome, V., Muller, R. 2003; 322: 137-143

  Abstract

  Hepatocyte-directed delivery of therapeutic genes is a major field of gene therapy. An important issue in this context is the availability of promoters units providing for maximum transcriptional activity and specificity. Although a number of liver-specific promoters and transcriptional control elements have been identified and used for gene delivery, no systematic study has been performed to identify the best suitable combination of known liver-specific promoter and enhancer elements. We now report the results of a comparative investigation addressing this issue. We tested a total of 25 synthetic transcriptional control units consisting of either of the four core promoters from liver-specific genes linked in various combinations and configurations to hepatocyte-specific enhancer elements. These constructs were analyzed for transcriptional activity in different cell types in cell culture and in mouse liver in vivo. The data lead to the clear conclusion that a combination of the alcohol dehydrogenase 6 (ADH6) basal promoter linked to two tandem copies of an apoplipoprotein E enhancer element is the transcriptional control unit of choice for the liver-specific expression of transgenes.

  View details for DOI 10.1016/j.gene.2003.08.010

  View details for Web of Science ID 000187253100013

  View details for PubMedID 14644505