In vivo modulation of endogenous gene expression via CRISPR/Cas9-mediated 3'UTR editing.

The 3' untranslated regions (UTRs) modulate gene expression levels by regulating mRNA stability and translation. We previously showed that the replacement of the negative regulatory elements from the 3'UTR of glial cell line-derived neurotrophic factor (GDNF) resulted in increased endogenous GDNF expression while retaining its normal spatiotemporal expression pattern. Here, we have developed a methodology for the generation of in vivo hyper- and hypomorphic alleles via 3'UTR targeting using the CRISPR/Cas9 system. We demonstrate that CRISPR/Cas9-mediated excision of a long inhibitory sequence from Gdnf native 3'UTR in mouse zygotes increases the levels of endogenous GDNF with similar phenotypic alterations in embryonic kidney development as we described in GDNF constitutive and conditional hypermorphic mice. Furthermore, we show that CRISPR/Cas9-mediated targeting of 3'UTRs in vivo allows the modulation of the expression levels of two other morphogens, Gdf11 and Bdnf. Together, our work demonstrates the power of in vivo 3'UTR editing using the CRISPR/Cas9 system to create hyper- and hypomorphic alleles, suggesting wide applicability in studies on gene function and potentially, in gene therapy.

Increased Physiological GDNF Levels Have No Effect on Dopamine Neuron Protection and Restoration in a Proteasome Inhibition Mouse Model of Parkinson's Disease.

Parkinson's disease (PD) is a progressive neurodegenerative disease that comprises a range of motor and nonmotor symptoms. Glial cell line-derived neurotrophic factor (GDNF) promotes the survival of dopamine neurons in vitro and in vivo, and intracranial delivery of GDNF has been tested in six clinical trials for treating PD. However, clinical trials with ectopic GDNF have yielded variable results, which could in part result from abnormal expression site and levels caused by ectopic overexpression. Therefore, an important open question is whether an increase in endogenous GDNF expression could be potent in reversing PD progression. Here, we tested the therapeutic potential of endogenous GDNF using mice in which endogenous GDNF can be conditionally upregulated specifically in cells that express GDNF naturally (conditional GDNF hypermorphic mice; GdnfcHyper ). We analyzed the impact of endogenous GDNF upregulation in both neuroprotection and neurorestoration procedures, and for both motor and nonmotor symptoms in the proteasome inhibitor lactacystin (LC) model of PD. Our results showed that upregulation of endogenous GDNF in the adult striatum is not protective in LC-induced PD model in mice. Since age is the largest risk factor for PD, we also analyzed the effect of deletion of endogenous GDNF in aged Gdnf conditional knock-out mice. We found that GDNF deletion does not increase susceptibility to LC-induced damage. We conclude that endogenous GDNF does not impact the outcome in the LC-induced proteasome inhibition mouse model of Parkinson's disease.

Elevated endogenous GDNF induces altered dopamine signalling in mice and correlates with clinical severity in schizophrenia.

Presynaptic increase in striatal dopamine is the primary dopaminergic abnormality in schizophrenia, but the underlying mechanisms are not understood. Here, we hypothesized that increased expression of endogenous GDNF could induce dopaminergic abnormalities that resemble those seen in schizophrenia. To test the impact of GDNF elevation, without inducing adverse effects caused by ectopic overexpression, we developed a novel in vivo approach to conditionally increase endogenous GDNF expression. We found that a 2-3-fold increase in endogenous GDNF in the brain was sufficient to induce molecular, cellular, and functional changes in dopamine signalling in the striatum and prefrontal cortex, including increased striatal presynaptic dopamine levels and reduction of dopamine in prefrontal cortex. Mechanistically, we identified adenosine A2a receptor (A2AR), a G-protein coupled receptor that modulates dopaminergic signalling, as a possible mediator of GDNF-driven dopaminergic abnormalities. We further showed that pharmacological inhibition of A2AR with istradefylline partially normalised striatal GDNF and striatal and cortical dopamine levels in mice. Lastly, we found that GDNF levels are increased in the cerebrospinal fluid of first episode psychosis patients, and in post-mortem striatum of schizophrenia patients. Our results reveal a possible contributor for increased striatal dopamine signalling in a subgroup of schizophrenia patients and suggest that GDNF-A2AR crosstalk may regulate dopamine function in a therapeutically targetable manner.

Postnatal prolongation of mammalian nephrogenesis by excess fetal GDNF.

Nephron endowment, defined during the fetal period, dictates renal and related cardiovascular health throughout life. We show here that, despite its negative effects on kidney growth, genetic increase of GDNF prolongs the nephrogenic program beyond its normal cessation. Multi-stage mechanistic analysis revealed that excess GDNF maintains nephron progenitors and nephrogenesis through increased expression of its secreted targets and augmented WNT signaling, leading to a two-part effect on nephron progenitor maintenance. Abnormally high GDNF in embryonic kidneys upregulates its known targets but also Wnt9b and Axin2, with concomitant deceleration of nephron progenitor proliferation. Decline of GDNF levels in postnatal kidneys normalizes the ureteric bud and creates a permissive environment for continuation of the nephrogenic program, as demonstrated by morphologically and molecularly normal postnatal nephron progenitor self-renewal and differentiation. These results establish that excess GDNF has a bi-phasic effect on nephron progenitors in mice, which can faithfully respond to GDNF dosage manipulation during the fetal and postnatal period. Our results suggest that sensing the signaling activity level is an important mechanism through which GDNF and other molecules contribute to nephron progenitor lifespan specification.

Selective targeting of striatal parvalbumin-expressing interneurons for transgene delivery.

PVCre mice--> combined with AAV-FLEX vectors allowed efficient and specific targeting of PV+ interneurons in the striatum. However, diffusion of viral particles to the globus pallidus caused massive transduction of PV+ projection neurons and subsequent anterograde transport of the transgene product to the subthalamic nucleus and the substantia nigra pars reticulata. Different AAV serotypes (1 and 9) and promoters (CBA and human synapsin) were evaluated. The combination of AAV1, a moderate expression level (human synapsin promoter) and a precise adjustment of the stereotaxic coordinates in the anterior and dorsolateral part of the striatum were necessary to avoid transduction of PV+ GP projection neurons. Even in the absence of direct transduction due to diffusion of viral particles, GP PV+ projection neurons could be retrogradely transduced via their terminals present in the dorsal striatum. However, in the absence of diffusion, GP-Str PV+ projection neurons were poorly or not transduced suggesting that retrograde transduction did not significantly impair the selective targeting of striatal PV+ neurons. Finally, a prominent reduction of the number of striatal PV+ interneurons (about 50 %) was evidenced in the presence of the Cre recombinase suggesting that functional effects of AAV-mediated transgene expression in PV+ striatal interneurons in PVCre mice should be analyzed with caution.

Granulocyte-macrophage colony-stimulating factor, a potent adjuvant for polarization to Th-17 pattern: an experience on HIV-1 vaccine model.

Cytokines are mediators for polarization of immune response in vaccines. Studies show that co-immunization of DNA vaccines with granulocyte-macrophage colony-stimulating factor (GM-CSF) can increase immune responses. Here, experimental mice were immunized with HIV-1tat/pol/gag/env DNA vaccine with GM-CSF and boosted with recombinant vaccine. Lymphocyte proliferation with Brdu and CTL activity, IL-4, IFN-γ, IL-17 cytokines, total antibody, and IgG1 and IgG2a isotypes were assessed with ELISA. Results show that GM-CSF as adjuvant in DNA immunization significantly increased lymphocyte proliferation and IFN-γ cytokines, but CTL response was tiny increased. Also GM-CSF as adjuvant decreased IL-4 cytokine vs mere vaccine group. IL-17 in the group that immunized with mixture of DNA vaccine/GM-CSF was significantly increased vs DNA vaccine group. Result of total antibody shows that GM-CSF increased antibody response in which both IgG1 and IgG2a increased. Overall, results confirmed the beneficial effect of GM-CSF as adjuvant to increase vaccine immunogenicity. The hallmark result of this study was to increase IL-17 cytokine with DNA vaccine/GM-CSF immunized group. This study for the first time provides the evidence of the potency of GM-CSF in the induction of IL-17 in response to a vaccine, which is important for control of infection such as HIV-1.

Dampened Amphetamine-Stimulated Behavior and Altered Dopamine Transporter Function in the Absence of Brain GDNF.

Midbrain dopamine neuron dysfunction contributes to various psychiatric and neurological diseases, including drug addiction and Parkinson's disease. Because of its well established dopaminotrophic effects, the therapeutic potential of glial cell line-derived neurotrophic factor (GDNF) has been studied extensively in various disorders with disturbed dopamine homeostasis. However, the outcomes from preclinical and clinical studies vary, highlighting a need for a better understanding of the physiological role of GDNF on striatal dopaminergic function. Nevertheless, the current lack of appropriate animal models has limited this understanding. Therefore, we have generated novel mouse models to study conditional Gdnf deletion in the CNS during embryonic development and reduction of striatal GDNF levels in adult mice via AAV-Cre delivery. We found that both of these mice have reduced amphetamine-induced locomotor response and striatal dopamine efflux. Embryonic GDNF deletion in the CNS did not affect striatal dopamine levels or dopamine release, but dopamine reuptake was increased due to increased levels of both total and synaptic membrane-associated dopamine transporters. Collectively, these results suggest that endogenous GDNF plays an important role in regulating the function of dopamine transporters in the striatum.SIGNIFICANCE STATEMENT Delivery of ectopic glial cell line-derived neurotrophic factor (GDNF) promotes the function, plasticity, and survival of midbrain dopaminergic neurons, the dysfunction of which contributes to various neurological and psychiatric diseases. However, how the deletion or reduction of GDNF in the CNS affects the function of dopaminergic neurons has remained unknown. Using conditional Gdnf knock-out mice, we found that endogenous GDNF affects striatal dopamine homeostasis and regulates amphetamine-induced behaviors by regulating the level and function of dopamine transporters. These data regarding the physiological role of GDNF are relevant in the context of neurological and neurodegenerative diseases that involve changes in dopamine transporter function.