Clinical and Genetic Analysis of Patients With TK2 Deficiency.

Objectives: Thymidine kinase 2 deficiency (TK2d) is a rare autosomal recessive disorder that stems from a perturbation of the mitochondrial DNA maintenance. Nucleoside treatment has recently shown promise as a disease-modifying therapy. TK2d was initially associated with rapidly progressive fatal myopathy in children featuring mitochondrial DNA depletion. Subsequently, less severe variants of the disease were described, with onset of symptoms during adolescence or adulthood and associated with the presence of multiple mtDNA deletions. These less severe phenotypes have been reported in only 15% of the approximately 120 patients described worldwide. However, some reports suggest that these juvenile and adult-onset presentations may be more common. The objective of this study was to describe the clinical phenotype in a sample of patients from Spain. Methods: This study includes 53 patients harboring biallelic TK2 pathogenic variants, compiling data retrospectively from 7 Spanish centers. We analyzed allele frequency, investigated the most recent common ancestor of core haplotypes, and used the Runs of Homozygosity approach to investigate variant coalescence. Results: Symptom onset distribution revealed that 32 patients (60%) experienced symptoms beyond 12 years of age. Approximately 30% of patients died of respiratory insufficiency, while 56% of surviving patients needed mechanical ventilation. Genetic analysis identified 16 distinct variants in TK2. Two variants, p.Lys202del and p.Thr108Met, exhibited significantly higher prevalence in the Spanish population than that reported in gnomAD database (86-fold and 13-fold, respectively). These variants are estimated to have originated approximately 16.8 generations ago for p.Thr108Met and 95.2 generations ago for p.Lys202del within the Spanish population, with the increase in frequency attributed to various forms of inbreeding. In late-onset cases, 46.9% carried the p.Lys202del variant. Discussion: The higher frequency of TK2d in Spain can be partially attributed to the increased prevalence of 2 variants and consanguinity. Notably, in 60% of the cohort, the disease was late-onset, emphasizing the potential underdiagnosis of this subgroup of patients in other regions. Raising awareness of this potentially treatable disorder is of utmost importance because early interventions can significantly affect the quality of life and survival of affected individuals.

Coupling of D2R Short but not D2R Long receptor isoform to the Rho/ROCK signaling pathway renders striatal neurons vulnerable to mutant huntingtin.

Huntington's disease, an inherited neurodegenerative disorder, results from abnormal polyglutamine extension in the N-terminal region of the huntingtin protein. This mutation causes preferential degeneration of striatal projection neurons. We previously demonstrated, in vitro, that dopaminergic D2 receptor stimulation acted in synergy with expanded huntingtin to increase aggregates formation and striatal death through activation of the Rho/ROCK signaling pathway. In vivo, in a lentiviral-mediated model of expanded huntingtin expression in the rat striatum, we found that the D2 antagonist haloperidol protects striatal neurons against expanded huntingtin-mediated toxicity. Two variant transcripts are generated by alternative splicing of the of D2 receptor gene, the D2R-Long and the D2R-Short, which are thought to play different functional roles. We show herein that overexpression of D2R-Short, but not D2R-Long in cell lines is associated with activation of the RhoA/ROCK signaling pathway. In striatal neurons in culture, the selective D2 agonist Quinpirole triggers phosphorylation of cofilin, a downstream effector of ROCK, which is abrogated by siRNAs that knockdown both D2R-Long and D2R-Short, but not by siRNAs targeting D2R-Long alone. Aggregate formation and neuronal death induced by expanded huntingtin, were potentiated by Quinpirole. This D2 agonist-mediated effect was selectively inhibited by the siRNA targeting both D2R-Long and D2R-Short but not D2R-Long alone. Our data provide evidence for a specific coupling of D2R-Short to the RhoA/ROCK/cofilin pathway, and its involvement in striatal vulnerability to expanded huntingtin. A new route for targeting Rho-ROCK signaling in Huntington's disease is unraveled with our findings.

Elk-1 a transcription factor with multiple facets in the brain.

The ternary complex factor (TCF) Elk-1 is a transcription factor that regulates immediate early gene (IEG) expression via the serum response element (SRE) DNA consensus site. Elk-1 is associated with a dimer of serum response factor (SRF) at the SRE site, and its phosphorylation occurs at specific residues in response to mitogen-activated protein kinases (MAPKs), including c-Jun-N terminal kinase (JNK), p38/MAPK, and extracellular-signal regulated kinase (ERK). This phosphorylation event is critical for triggering SRE-dependent transcription. Although MAPKs are fundamental actors for the instatement and maintenance of memory, and much investigation of their downstream signaling partners have been conducted, no data yet clearly implicate Elk-1 in these processes. This is partly due to the complexity of Elk-1 sub-cellular localization, and hence functions, within neurons. Elk-1 is present in its resting state in the cytoplasm, where it colocalizes with mitochondrial proteins or microtubules. In this particular sub-cellular compartment, overexpression of Elk-1 is toxic for neuronal cells. When phosphorylated by the MAPK/ERK, Elk-1 translocates to the nucleus where it is implicated in regulating chromatin remodeling, SRE-dependent transcription, and neuronal differentiation. Another post-translational modification is the conjugation to SUMO (Small Ubiquitin-like MOdifier), which relocalizes Elk-1 in the cytoplasm. Thus, Elk-1 plays a dual role in neuronal functions: pro-apoptotic within the cytoplasm, and pro-differentiation within the nucleus. To address the role of Elk-1 in the brain, one must be aware of its multiple facets, and design molecular tools that will shut down Elk-1 expression, trafficking, or activation, in specific neuronal compartments. We summarize in this review the known molecular functions of Elk-1, its regulation in neuronal cells, and present evidence of its possible implication in model systems of synaptic plasticity, learning, but also in neurodegenerative diseases.

Dopamine D2 receptor stimulation potentiates PolyQ-Huntingtin-induced mouse striatal neuron dysfunctions via Rho/ROCK-II activation.

BACKGROUND: Huntington's disease (HD) is a polyglutamine-expanded related neurodegenerative disease. Despite the ubiquitous expression of expanded, polyQ-Huntingtin (ExpHtt) in the brain, striatal neurons present a higher susceptibility to the mutation. A commonly admitted hypothesis is that Dopaminergic inputs participate to this vulnerability. We previously showed that D2 receptor stimulation increased aggregate formation and neuronal death induced by ExpHtt in primary striatal neurons in culture, and chronic D2 antagonist treatment protects striatal dysfunctions induced by ExpHtt in a lentiviral-induced model system in vivo. The present work was designed to elucidate the signalling pathways involved, downstream D2 receptor (D2R) stimulation, in striatal vulnerability to ExpHtt. METHODOLOGY/PRINCIPAL FINDINGS: Using primary striatal neurons in culture, transfected with a tagged-GFP version of human exon 1 ExpHtt, and siRNAs against D2R or D1R, we confirm that DA potentiates neuronal dysfunctions via D2R but not D1R stimulation. We demonstrate that D2 agonist treatment induces neuritic retraction and growth cone collapse in Htt- and ExpHtt expressing neurons. We then tested a possible involvement of the Rho/ROCK signalling pathway, which plays a key role in the dynamic of the cytoskeleton, in these processes. The pharmacological inhibitors of ROCK (Y27632 and Hydroxyfasudil), as well as siRNAs against ROCK-II, reversed D2-related effects on neuritic retraction and growth cone collapse. We show a coupling between D2 receptor stimulation and Rho activation, as well as hyperphosphorylation of Cofilin, a downstream effector of ROCK-II pathway. Importantly, D2 agonist-mediated potentiation of aggregate formation and neuronal death induced by ExpHtt, was totally reversed by Y27632 and Hydroxyfasudil and ROCK-II siRNAs. CONCLUSIONS/SIGNIFICANCE: Our data provide the first demonstration that D2R-induced vulnerability in HD is critically linked to the activation of the Rho/ROCK signalling pathway. The inclusion of Rho/ROCK inhibitors could be an interesting therapeutic option aimed at forestalling the onset of the disease.

QF2004B, a potential antipsychotic butyrophenone derivative with similar pharmacological properties to clozapine.

The aim of the present work was to characterize a lead compound displaying relevant multi-target interactions, and with an in vivo behavioral profile predictive of atypical antipsychotic activity. Synthesis, molecular modeling and in vitro and in vivo pharmacological studies were carried out for 2-[4-(6-fluorobenzisoxazol-3-yl)piperidinyl]methyl-1,2,3,4-tetrahydro-carbazol-4-one (QF2004B), a conformationally constrained butyrophenone analogue. This compound showed a multi-receptor profile with affinities similar to those of clozapine for serotonin (5-HT2A, 5-HT1A, and 5-HT2C), dopamine (D1, D2, D3 and D4), alpha-adrenergic (alpha1, alpha2), muscarinic (M1, M2) and histamine H1 receptors. In addition, QF2004B mirrored the antipsychotic activity and atypical profile of clozapine in a broad battery of in vivo tests including locomotor activity (ED50 = 1.19 mg/kg), apomorphine-induced stereotypies (ED50 = 0.75 mg/kg), catalepsy (ED50 = 2.13 mg/kg), apomorphine- and DOI (2,5-dimethoxy-4-iodoamphetamine)-induced prepulse inhibition (PPI) tests. These results point to QF2004B as a new lead compound with a relevant multi-receptor interaction profile for the discovery and development of new antipsychotics.

Role for dopamine neurons of the rostral linear nucleus and periaqueductal gray in the rewarding and sensitizing properties of heroin.

There is a mesencephalic dopaminergic network outside the ventral tegmental area (VTA), including structures such as the rostral linear nucleus (RLi) and periaqueductal gray (PAG). These nuclei project to neural areas implicated in reinforcing effects of drugs, indicating that they could participate in opiate reward. The objectives were to study the morphological characteristics of the dopamine network of the RLi/PAG region, and to discern its role on rewarding and sensitizing effects of heroin in rats, following dopamine depletion or local injection of dopaminergic antagonists. The findings indicated that this network is composed of small cells in the RLi/ventral PAG, large multipolar dopamine PAG neurons, and periaqueductal PAG neurons. Following repeated heroin, large PAG neurons and small RLi/ventral PAG cells (not periaqueductal neurons) were activated, since tyrosine-hydroxylase was adaptively induced, without changes in protein kinase Aalpha. After dopamine depletion, small RLi/ventral PAG neurons and large cells of the PAG (not periaqueductal ones) were selectively affected by the neurotoxin. Dopamine neurons of the nearby VTA and dorsal raphe were not affected, as revealed by cell counting. After lesion, 'anxiety-like' responses and basal locomotion were not altered. However, conditioned place preference to heroin was found to be abolished, as well as heroin-induced motor sensitization. Following infusions of dopaminergic antagonists into RLi/PAG, D(2) (not D(1)) receptor blocking dose-dependently abolished heroin-induced reward. The present study provides evidence that dopamine neurons of the RLi/PAG region (excluding PAG periaqueductal cells) show adaptive biochemical changes after heroin, and mediate the rewarding and sensitizing effects of this drug. D(2) dopamine receptors within the RLi/PAG region participate in these effects.

Cells of the sympathoadrenal lineage: biological properties as donor tissue for cell-replacement therapies for Parkinson's disease.

Sympathoadrenal (SA) cell lineage encompasses neural crest derivatives such as sympathetic neurons, small intensely fluorescent (SIF) cells of sympathetic ganglia and adrenal medulla, and chromaffin cells of adrenal medulla and extra-adrenal paraganglia. SA autografts have been used for transplantation in Parkinson's disease (PD) for three reasons: (i) as autologous donor tissue avoids graft rejection and the need for immunosuppressant therapy, (ii) SA cells express dopaminotrophic factors such as GNDF and TGFbetas, and (iii) although most of SA cells release noradrenaline, some of them are able to produce and release dopamine. Adrenal chromaffin cells were the first SA transplanted cells in both animal models of PD and PD patients. However, these autografts have met limited success because long-term cell survival is very poor, and this approach is no longer pursued clinically. Sympathetic neurons from the superior cervical ganglion have been also grafted in PD animal models and PD patients. Poor survival into brain parenchyma of grafted tissue is a serious disadvantage for its clinical application. However, cultured sympathetic cell grafts present a better survival rate, and they reduce the need for levodopa medication in PD patients by facilitating the conversion of exogenous levodopa. SA extra-adrenal chromaffin cells are located on paraganglia (i.e., the Zuckerkandl's organ), and have been used for grafting in a rodent model of PD. Preliminary results indicate that long-term survival of these cells is better than for other SA cells, exerting a more prolonged restorative neurotrophic action on denervated host striatum. The ability of SA extra-adrenal cells to respond to hypoxia, differently to SA sympathetic neurons or adrenal medulla cells, could explain their good survival rate after brain transplantation.

Cannabinoid CB1 antagonists possess antiparkinsonian efficacy only in rats with very severe nigral lesion in experimental parkinsonism.

We have observed that systemic administration of cannabinoid CB1 antagonists exerts antiparkinsonian effects in rats with very severe nigral lesion (>95% cell loss), but not in rats with less severe lesion (85-95% cell loss). Local injections into denervated striatum and corresponding globus pallidus reduced parkinsonian asymmetry. Infusions into lesioned substantia nigra enhanced motor asymmetries, but this effect was absent after very severe nigral lesion. At the striatal level, CB1 antagonists act enhancing dopamine D1 receptor function and reducing D2 receptor function. Striatal dopaminergic denervation did not affect cannabinoid CB1 receptor coupling to G proteins. These results suggest that (i) systemic administration of CB1 antagonists in rats with severe nigral degeneration is ineffective because striatopallidal-mediated motor effects are antagonized by nigra-mediated activity, and (ii) CB1 antagonists exert antiparkinsonian effects after very severe nigral degeneration because nigra-mediated inhibition disappears. CB1 receptor antagonists that lack psychoactive effects might be of therapeutic value in the control of very advanced stage of Parkinson's disease in humans.

Opiate anti-nociception is attenuated following lesion of large dopamine neurons of the periaqueductal grey: critical role for D1 (not D2) dopamine receptors.

The periaqueductal grey (PAG) area is involved in pain modulation as well as in opiate-induced anti-nociceptive effects. The PAG possess dopamine neurons, and it is likely that this dopaminergic network participates in anti-nociception. The objective was to further study the morphology of the PAG dopaminergic network, along with its role in nociception and opiate-induced analgesia in rats, following either dopamine depletion with the toxin 6-hydroxydopamine or local injection of dopaminergic antagonists. Nociceptive responses were studied through the tail-immersion (spinal reflex) and the hot-plate tests (integrated supraspinal response), establishing a cut-off time to further minimize animal suffering. Heroin and morphine were employed as opiates. Histological data indicated that the dopaminergic network of the PAG is composed of two types of neurons: small rounded cells, and large multipolar neurons. Following dopamine depletion of the PAG, large neurons (not small ones) were selectively affected by the toxin (61.9% dopamine cell loss, 80.7% reduction of in vitro dopaminergic peak), and opiate-induced analgesia in the hot-plate test (not the tail-immersion test) was reliably attenuated in lesioned rats (P < 0.01). After infusions of dopaminergic ligands into the PAG, D(1) (not D(2)) receptor antagonism attenuated opiate-induced analgesia in a dose-dependent manner in the hot-plate test. The present study provides evidence that large neurons of the dopaminergic network of the PAG participate in supraspinal (not spinal) nociceptive responses after opiates through the involvement of D(1) dopamine receptors. This dopaminergic system should be included as another network within the PAG involved in opiate-induced anti-nociception.

Effects on turning of microinjections into basal ganglia of D(1) and D(2) dopamine receptors agonists and the cannabinoid CB(1) antagonist SR141716A in a rat Parkinson's model.

Brain cannabinoid CB(1) receptors are expressed in neural areas that contribute to movement such as basal ganglia, where they co-localize with dopamine D(1) and D(2) receptors. The objective of the present study was to further study the functional role of CB(1) receptors along with D(1) and D(2) dopamine receptors of basal ganglia by local injections of SR141716A (CB(1) receptor antagonist), SKF-38393 (D(1) agonist), and quinpirole (D(2) agonist), in a rat Parkinson's model. Turning response after amphetamine was considered as the parkinsonian variable for quantifying motor effects of drugs. The findings indicated that, after intrastriatal infusions, both D(1) or D(2) dopamine receptor agonists alone reduced turning in parkinsonian rats. At the pallidal and subthalamic levels, D(1) (not D(2)) receptor stimulation also reduced rotation. Regarding SR141716A-induced effects, CB(1) antagonism reduced motor asymmetry in parkinsonian rats after injections into striatum, globus pallidus, and to a lesser extent, subthalamic nucleus. At the level of dorsal striatum, effects of SR141716A were mediated through an opposite modulation of D(1) and D(2) dopamine receptor function. At the pallidal and subthalamic nucleus levels, motor effects after SR14716A are not associated to modulation of D(1) and D(2) receptor function.

Sensorimotor gating in mice is disrupted after AM404, an anandamide reuptake and degradation inhibitor.

RATIONALE: Prepulse inhibition (PPI) represents a normal sensorimotor gating response that is typically impaired in schizophrenic patients. It is known that cannabinoid CB1 agonists reduce sensorimotor gating in rats, suggesting that the CB1 receptor and the cannabinoid system are involved in sensorimotor gating. OBJECTIVE: The objective was to study the effects of AM404, an anandamide reuptake and degradation inhibitor, on PPI and startle response in Swiss mice. METHODS. AM404 was injected either acutely (0, 2.5 and 5 mg/kg i.p.) or chronically (5 mg/kg daily, 7 days). The PPI protocol was based on standard methodologies using acoustic stimuli (pulse 120 dB; prepulses 70 dB and 80 dB). SR141716A, a CB1 antagonist, was employed for further confirmation of the involvement of CB1 receptors. RESULTS: Acute AM404 (5 mg/kg) disrupted PPI (70-dB prepulse, P<0.05) and enhanced the startle response after the 2.5-mg/kg dose (P<0.01). Chronic AM404 disrupted PPI after both 70-dB (P<0.01) and 80-dB prepulses (P<0.05). These effects were blocked after SR141716A cotreatment. CONCLUSIONS: The data indicate that AM404 (5 mg/kg) acts as a psychodysleptic, altering PPI through stimulation of cannabinoid CB1 receptors, pointing to a possible "psychosis-like" state after enhancement of anandamide bioavailability. The startle response was enhanced only following a lower AM404 dose (2.5 mg/kg), indicating that AM404 induced hyperreactivity at a dose that did not affect PPI, further reinforcing a selective disruption of PPI.

Experimental parkinsonism alters anandamide precursor synthesis, and functional deficits are improved by AM404: a modulator of endocannabinoid function.

Modulation of the endocannabinoid system might be useful in treating Parkinson's disease. Here, we show that systemic administration of N-(4-hydroxyphenyl)-arachidonamide (AM404), a cannabinoid modulator that enhances anandamide (AEA) availability in the biophase, exerts antiparkinsonian effects in 6-hydroxydopamine-lesioned rats. Local injections of AM404 into denervated striata reduced parkinsonian motor asymmetries, these effects being associated with the reduction of D2 dopamine receptor function together with a positive modulation of 5-HT(1B) serotonin receptor function. Stimulation of striatal 5-HT(1B) receptors alone was observed to ameliorate parkinsonian deficits, supporting the fact that AM404 exerts antiparkinsonian effects likely through stimulation of striatal 5-HT(1B) serotonin receptor function. Hence, modulation of cannabinoid function leading to enhancement of AEA in the biophase might be of therapeutic value in the control of symptoms of Parkinson's disease. On the other hand, reduced levels of N-acyl-transferase (AEA precursor synthesizing enzyme), without changes in fatty acid amidohydrolase (AEA degradative enzyme), were detected in denervated striata in comparison with intact striata. This finding reveals the presence of a homeostatic striatal mechanism emerging after dopaminergic denervation likely tending to enhance low dopamine tone.