Sustained Gq-Protein Signaling Disrupts Striatal Circuits via JNK

The multimodal action of G alpha q in coordinating growth and homeostasis in the Drosophila wing imaginal disc

Background

G proteins mediate cell responses to various ligands and play key roles in organ development. Dysregulation of G-proteins or Ca ²⁺ signaling impacts many human diseases and results in birth defects. However, the downstream effectors of specific G proteins in developmental regulatory networks are still poorly understood.

Methods

We employed the Gal4/UAS binary system to inhibit or overexpress Gαq in the wing disc, followed by phenotypic analysis. Immunohistochemistry and next-gen RNA sequencing identified the downstream effectors and the signaling cascades affected by the disruption of Gαq homeostasis.

Results

Here, we characterized how the G protein subunit Gαq tunes the size and shape of the wing in the larval and adult stages of development. Downregulation of Gαq in the wing disc reduced wing growth and delayed larval development. Gαq overexpression is sufficient to promote global Ca ²⁺ waves in the wing disc with a concomitant reduction in the Drosophila final wing size and a delay in pupariation. The reduced wing size phenotype is further enhanced when downregulating downstream components of the core Ca ²⁺ signaling toolkit, suggesting that downstream Ca ²⁺ signaling partially ameliorates the reduction in wing size. In contrast, Gαq -mediated pupariation delay is rescued by inhibition of IP ₃ R, a key regulator of Ca ²⁺ signaling. This suggests that Gαq regulates developmental phenotypes through both Ca ²⁺ -dependent and Ca ²⁺ -independent mechanisms. RNA seq analysis shows that disruption of Gαq homeostasis affects nuclear hormone receptors, JAK/STAT pathway, and immune response genes. Notably, disruption of Gαq homeostasis increases expression levels of Dilp8, a key regulator of growth and pupariation timing.

Conclusion

Gαq activity contributes to cell size regulation and wing metamorphosis. Disruption to Gαq homeostasis in the peripheral wing disc organ delays larval development through ecdysone signaling inhibition. Overall, Gαq signaling mediates key modules of organ size regulation and epithelial homeostasis through the dual action of Ca ²⁺ -dependent and independent mechanisms.

Lack of adipocyte purinergic P2Y6 receptor greatly improves whole body glucose homeostasis

Uridine diphosphate (UDP)-activated purinergic receptor P2Y₆ (P2Y₆R) plays a crucial role in controlling energy balance through central mechanisms. However, P2Y₆R's roles in peripheral tissues regulating energy and glucose homeostasis remain unexplored. Here, we report the surprising finding that adipocyte-specific deletion of P2Y₆R protects mice from diet-induced obesity, improving glucose tolerance and insulin sensitivity with reduced systemic inflammation. These changes were associated with reduced JNK signaling and enhanced expression and activity of PPARα affecting downstream PGC1α levels leading to beiging of white fat. In contrast, P2Y₆R deletion in skeletal muscle reduced glucose uptake, resulting in impaired glucose homeostasis. Interestingly, whole body P2Y₆R knockout mice showed metabolic improvements similar to those observed with mice lacking P2Y₆R only in adipocytes. Our findings provide compelling evidence that P2Y₆R antagonists may prove useful for the treatment of obesity and type 2 diabetes.

Inhibition of striatonigral autophagy as a link between cannabinoid intoxication and impairment of motor coordination

The use of cannabis is rapidly expanding worldwide. Thus, innovative studies aimed to identify, understand and potentially reduce cannabis-evoked harms are warranted. Here, we found that Δ⁹-tetrahydrocannabinol, the psychoactive ingredient of cannabis, disrupts autophagy selectively in the striatum, a brain area that controls motor behavior, both in vitro and in vivo. Boosting autophagy, either pharmacologically (with temsirolimus) or by dietary intervention (with trehalose), rescued the Δ⁹-tetrahydrocannabinol-induced impairment of motor coordination in mice. The combination of conditional knockout mouse models and viral vector-mediated autophagy-modulating strategies in vivo showed that cannabinoid CB₁ receptors located on neurons belonging to the direct (striatonigral) pathway are required for the motor-impairing activity of Δ⁹-tetrahydrocannabinol by inhibiting local autophagy. Taken together, these findings identify inhibition of autophagy as an unprecedented mechanistic link between cannabinoids and motor performance, and suggest that activators of autophagy might be considered as potential therapeutic tools to treat specific cannabinoid-evoked behavioral alterations.

Astroglial monoacylglycerol lipase controls mutant huntingtin-induced damage of striatal neurons

Cannabinoids exert neuroprotection in a wide array of preclinical models. A number of these studies has focused on cannabinoid CB₁ receptors in striatal medium spiny neurons (MSNs) and the most characteristic MSN-degenerative disease, Huntington's disease (HD). Accruing evidence supports that astrocytes contribute to drive HD progression, and that they express CB₁ receptors, degrade endocannabinoids, and modulate endocannabinergic transmission. However, the possible role of the astroglial endocannabinoid system in controlling MSN integrity remains unknown. Here, we show that JZL-184, a selective inhibitor of monoacylglycerol lipase (MGL), the key enzyme that deactivates the endocannabinoid 2-arachidonoylglycerol, prevented the mutant huntingtin-induced up-regulation of the pro-inflammatory cytokine tumor necrosis factor-α in primary mouse striatal astrocytes via CB₁ receptors. To study the role of astroglial MGL in vivo, we injected stereotactically into the mouse dorsal striatum viral vectors that encode mutant or normal huntingtin under the control of the glial fibrillary acidic protein promoter. We observed that, in wild-type mice, pharmacological blockade of MGL with JZL-184 (8 mg/kg/day, i.p.) conferred neuroprotection against mutant huntingtin-induced striatal damage, as evidenced by the prevention of MSN loss, astrogliosis, and motor coordination impairment. We next found that conditional mutant mice bearing a genetic deletion of MGL selectively in astroglial cells (MGL^{floxed/floxed;GFAP-Cre/+} mice) were resistant to mutant huntingtin-induced MSN loss, astrogliosis, and motor coordination impairment. Taken together, these data support that astroglial MGL controls the availability of a 2-arachidonoylglycerol pool that ensues protection of MSNs in the mouse striatum in vivo, thus providing a potential druggable target for reducing striatal neurodegeneration.

Modulating Dopamine Signaling and Behavior with Chemogenetics: Concepts, Progress, and Challenges

For more than 60 years, dopamine (DA) has been known as a critical modulatory neurotransmitter regulating locomotion, reward-based motivation, and endocrine functions. Disturbances in DA signaling have been linked to an array of different neurologic and psychiatric disorders, including Parkinson's disease, schizophrenia, and addiction, but the underlying pathologic mechanisms have never been fully elucidated. One major obstacle limiting interpretation of standard pharmacological and transgenic interventions is the complexity of the DA system, which only appears to widen as research progresses. Nonetheless, development of new genetic tools, such as chemogenetics, has led to an entirely new era for functional studies of neuronal signaling. By exploiting receptors that are engineered to respond selectively to an otherwise inert ligand, so-called Designer Receptors Exclusively Activated by Designer Drugs (DREADDs), chemogenetics enables pharmacological remote control of neuronal activity. Here we review the recent, extensive application of this technique to the DA field and how its use has advanced the study of the DA system and contributed to our general understanding of DA signaling and related behaviors. Moreover, we discuss the challenges and pitfalls associated with the chemogenetic technology, such as the metabolism of the DREADD ligand clozapine N-oxide (CNO) to the D2 receptor antagonist clozapine. We conclude that despite the recent concerns regarding CNO, the chemogenetic toolbox provides an exceptional approach to study neuronal function. The huge potential should promote continued investigations and additional refinements to further expound key mechanisms of DA signaling and circuitries in normal as well as maladaptive behaviors.

Pathway-Specific Control of Striatal Neuron Vulnerability by Corticostriatal Cannabinoid CB1 Receptors

The vast majority of neurons within the striatum are GABAergic medium spiny neurons (MSNs), which receive glutamatergic input from the cortex and thalamus, and form two major efferent pathways: the direct pathway, expressing dopamine D1 receptor (D1R-MSNs), and the indirect pathway, expressing dopamine D2 receptor (D2R-MSNs). While molecular mechanisms of MSN degeneration have been identified in animal models of striatal damage, the molecular factors that dictate a selective vulnerability of D1R-MSNs or D2R-MSNs remain unknown. Here, we combined genetic, chemogenetic, and pharmacological strategies with behavioral and neurochemical analyses, and show that the pool of cannabinoid CB1 receptor (CB1R) located on corticostriatal terminals efficiently safeguards D1R-MSNs, but not D2R-MSNs, from different insults. This cell-specific response relies on the regulation of glutamatergic signaling, and is independent from the CB1R-dependent control of astroglial activity in the striatum. These findings define cortical CB1R as a pivotal synaptic player in dictating a differential vulnerability of D1R-MSNs versus D2R-MSNs, and increase our understanding of the role of coordinated cannabinergic-glutamatergic signaling in establishing corticostriatal circuits and its dysregulation in neurodegenerative diseases.

3-D motion capture for long-term tracking of spontaneous locomotor behaviors and circadian sleep/wake rhythms in mouse

BACKGROUND

Locomotor activity provides an index of an animal's behavioral state. Here, we report a reliable and cost-effective method that allows long-term (days to months) simultaneous tracking of locomotion in mouse cohorts (here consisting of 24 animals).

NEW METHOD

The technique is based on a motion capture system used mainly for human movement study. A reflective marker was placed on the head of each mouse using a surgical procedure and labeled animals were returned to their individual home cages. Camera-recorded data of marker displacement resulting from locomotor movements were then analyzed with custom built software. To avoid any data loss, data files were saved every hour and automatically concatenated. Long-term recordings (up to 3 months) with high spatial (<1mm) and temporal (up to 100Hz) resolution of animal movements were obtained.

RESULTS

The system was validated by analyzing the spontaneous activity of mice from post-natal day 30-90. Daily motor activity increased up to 70days in correspondence with maturational changes in locomotor performance. The recorded actigrams also permitted analysis of circadian and ultradian rhythms in cohort sleep/wake behavior.

COMPARISON WITH EXISTING METHOD(S)

In contrast to traditional session-based experimental approaches, our technique allows locomotor activity to be recorded with minimal experimenter manipulation, thereby minimizing animal stress.

CONCLUSIONS

Our method enables the continuous long-term (up to several months) monitoring of tens of animals, generating manageable amounts of data at minimal costs without requiring individual dedicated devices. The actigraphic data collected allows circadian and ultradian analysis of sleep/wake behaviors to be performed.

Optogenetic approaches for dissecting neuromodulation and GPCR signaling in neural circuits

Optogenetics has revolutionized neuroscience by providing means to control cell signaling with spatiotemporal control in discrete cell types. In this review, we summarize four major classes of optical tools to manipulate neuromodulatory GPCR signaling: opsins (including engineered chimeric receptors); photoactivatable proteins; photopharmacology through caging-photoswitchable molecules; fluorescent protein based reporters and biosensors. Additionally, we highlight technologies to utilize these tools in vitro and in vivo, including Cre dependent viral vector expression and two-photon microscopy. These emerging techniques targeting specific members of the GPCR signaling pathway offer an expansive base for investigating GPCR signaling in behavior and disease states, in addition to paving a path to potential therapeutic developments.

Gene therapy approaches in the non-human primate model of Parkinson's disease

The field of gene therapy has recently witnessed a number of major conceptual changes. Besides the traditional thinking that comprises the use of viral vectors for the delivery of a given therapeutic gene, a number of original approaches have been recently envisaged, focused on using vectors carrying genes to further modify basal ganglia circuits of interest. It is expected that these approaches will ultimately induce a therapeutic potential being sustained by gene-induced changes in brain circuits. Among others, at present, it is technically feasible to use viral vectors to (1) achieve a controlled release of neurotrophic factors, (2) conduct either a transient or permanent silencing of any given basal ganglia circuit of interest, (3) perform an in vivo cellular reprogramming by promoting the conversion of resident cells into dopaminergic-like neurons, and (4) improving levodopa efficacy over time by targeting aromatic L-amino acid decarboxylase. Furthermore, extensive research efforts based on viral vectors are currently ongoing in an attempt to better replicate the dopaminergic neurodegeneration phenomena inherent to the progressive intraneuronal aggregation of alpha-synuclein. Finally, a number of incoming strategies will soon emerge over the horizon, these being sustained by the underlying goal of promoting alpha-synuclein clearance, such as, for instance, gene therapy initiatives based on increasing the activity of glucocerebrosidase. To provide adequate proof-of-concept on safety and efficacy and to push forward true translational initiatives based on these different types of gene therapies before entering into clinical trials, the use of non-human primate models undoubtedly plays an instrumental role.