Engineered AAV capsid transport mutants overcome transduction deficiencies in the aged CNS.

Adeno-associated virus (AAV)-based gene therapy has enjoyed great successes over the past decade, with Food and Drug Administration-approved therapeutics and a robust clinical pipeline. Nonetheless, barriers to successful translation remain. For example, advanced age is associated with impaired brain transduction, with the diminution of infectivity depending on anatomical region and capsid.

Advancing age and the rs6265 BDNF SNP are permissive to graft-induced dyskinesias in parkinsonian rats.

The rs6265 single nucleotide polymorphism (SNP) in the gene for brain-derived neurotrophic factor is a common variant that alters therapeutic outcomes for individuals with Parkinson's disease (PD). We previously investigated the effects of this SNP on the experimental therapeutic approach of neural grafting, demonstrating that young adult parkinsonian rats carrying the variant Met allele exhibited enhanced graft function compared to wild-type rats and also exclusively developed aberrant graft-induced dyskinesias (GID). Aging is the primary risk factor for PD and reduces graft efficacy.

Advancing Age and the rs6265 BDNF SNP are Permissive to Graft-induced Dyskinesias in Parkinsonian Rats.

The rs6265 single nucleotide polymorphism (SNP) in the gene for brain-derived neurotrophic factor is a common variant that alters therapeutic outcomes for individuals with Parkinson's disease (PD). We previously investigated the effects of this SNP on the experimental therapeutic approach of neural grafting, demonstrating that young adult parkinsonian rats carrying the variant Met allele exhibited enhanced graft function compared to wild-type rats, and also exclusively developed aberrant graft-induced dyskinesias (GID). Aging is the primary risk factor for PD and reduces graft efficacy.

Neuroinflammatory gene expression profiles of reactive glia in the substantia nigra suggest a multidimensional immune response to alpha synuclein inclusions.

Parkinson's disease (PD) pathology is characterized by alpha-synuclein (α-syn) aggregates, degeneration of dopamine neurons in the substantia nigra pars compacta (SNpc), and neuroinflammation. The presence of reactive glia correlates with deposition of pathological α-syn in early-stage PD. Thus, understanding the neuroinflammatory response of microglia and astrocytes to synucleinopathy may identify therapeutic targets.

Quinpirole inhibits levodopa-induced dyskinesias at structural and behavioral levels: Efficacy negated by co-administration of isradipine.

Dopamine depletion associated with parkinsonism induces plastic changes in striatal medium spiny neurons (MSN) that are maladaptive and associated with the emergence of the negative side-effect of standard treatment: the abnormal involuntary movements termed levodopa-induced dyskinesia (LID). Prevention of MSN dendritic spine loss is hypothesized to diminish liability for LID in Parkinson's disease. Blockade of striatal CaV1.

A comparison of machine learning approaches for the quantification of microglial cells in the brain of mice, rats and non-human primates.

Microglial cells are brain-specific macrophages that swiftly react to disruptive events in the brain. Microglial activation leads to specific modifications, including proliferation, morphological changes, migration to the site of insult, and changes in gene expression profiles. A change in inflammatory status has been linked to many neurodegenerative diseases such as Parkinson's disease and Alzheimer's disease.

Downregulation of striatal Ca1.3 inhibits the escalation of levodopa-induced dyskinesia in male and female parkinsonian rats of advanced age.

In the past 25 years, the prevalence of Parkinson's disease (PD) has nearly doubled. Age remains the primary risk factor for PD and as the global aging population increases this trend is predicted to continue. Even when treated with levodopa, the gold standard dopamine (DA) replacement therapy, individuals with PD frequently develop therapeutic side effects.

The Role of Striatal Cav1.3 Calcium Channels in Therapeutics for Parkinson's Disease.

Parkinson's disease (PD) is a relentlessly progressive neurodegenerative disorder with typical motor symptoms that include rigidity, tremor, and akinesia/bradykinesia, in addition to a host of non-motor symptoms. Motor symptoms are caused by progressive and selective degeneration of dopamine (DA) neurons in the SN pars compacta (SNpc) and the accompanying loss of striatal DA innervation from these neurons. With the exception of monogenic forms of PD, the etiology of idiopathic PD remains unknown.

New Frontiers in Neurodegeneration and Regeneration Associated with Brain-Derived Neurotrophic Factor and the rs6265 Single Nucleotide Polymorphism.

Brain-derived neurotrophic factor is an extensively studied neurotrophin implicated in the pathology of multiple neurodegenerative and psychiatric disorders including, but not limited to, Parkinson's disease, Alzheimer's disease, Huntington's disease, traumatic brain injury, major de-pressive disorder, and schizophrenia. Here we provide a brief summary of current knowledge on the role of BDNF and the common human single nucleotide polymorphism, rs6265, in driving the pathogenesis and rehabilitation in these disorders, as well as the status of BDNF-targeted therapies. A common trend has emerged correlating low BDNF levels, either detected within the central nervous system or peripherally, to disease states, suggesting that BDNF replacement therapies may hold clinical promise.

Beta2-adrenoreceptor agonist clenbuterol produces transient decreases in alpha-synuclein mRNA but no long-term reduction in protein.

β2-adrenoreceptor (β2AR) agonists have been associated with a decreased risk of developing Parkinson's disease (PD) and are hypothesized to decrease expression of both alpha-synuclein mRNA (Snca) and protein (α-syn). Effects of β2AR agonist clenbuterol on the levels of Snca mRNA and α-syn protein were evaluated in vivo (rats and mice) and in rat primary cortical neurons by two independent laboratories. A modest decrease in Snca mRNA in the substantia nigra was observed after a single acute dose of clenbuterol in rats, however, this decrease was not maintained after multiple doses.

Induction and Assessment of Levodopa-induced Dyskinesias in a Rat Model of Parkinson's Disease.

Levodopa (L-DOPA) remains the gold-standard therapy used to treat Parkinson's disease (PD) motor symptoms. However, unwanted involuntary movements known as L-DOPA-induced dyskinesias (LIDs) develop with prolonged use of this dopamine precursor. It is estimated that the incidence of LIDs escalates to approximately 90% of individuals with PD within 10-15 years of treatment.

α-Synuclein antisense oligonucleotides as a disease-modifying therapy for Parkinson's disease.

Parkinson's disease (PD) is a prevalent neurodegenerative disease with no approved disease-modifying therapies. Multiplications, mutations, and single nucleotide polymorphisms in the SNCA gene, encoding α-synuclein (aSyn) protein, either cause or increase risk for PD. Intracellular accumulations of aSyn are pathological hallmarks of PD.

Striatal Afferent BDNF Is Disrupted by Synucleinopathy and Partially Restored by STN DBS.

Preclinical studies show a link between subthalamic nucleus (STN) deep brain stimulation (DBS) and neuroprotection of nigrostriatal dopamine (DA) neurons, potentially through brain-derived neurotrophic factor (BDNF) signaling. However, the question of whether DBS of the STN can be disease-modifying in Parkinson's disease (PD) remains unanswered. In particular, the impact of STN DBS on α-synuclein (α-syn) aggregation, inclusion-associated neuroinflammation, and BDNF levels has yet to be examined in the context of synucleinopathy.

The BDNF Val66Met polymorphism (rs6265) enhances dopamine neuron graft efficacy and side-effect liability in rs6265 knock-in rats.

Prevalent in approximately 20% of the worldwide human population, the rs6265 (also called 'Val66Met') single nucleotide polymorphism (SNP) in the gene for brain-derived neurotrophic factor (BDNF) is a common genetic variant that can alter therapeutic responses in individuals with Parkinson's disease (PD). Possession of the variant Met allele results in decreased activity-dependent release of BDNF. Given the resurgent worldwide interest in neural transplantation for PD and the biological relevance of BDNF, the current studies examined the effects of the rs6265 SNP on therapeutic efficacy and side-effect development following primary dopamine (DA) neuron transplantation.

Preclinical evidence in support of repurposing sub-anesthetic ketamine as a treatment for L-DOPA-induced dyskinesia.

Parkinson's disease (PD) is the second most common neurodegenerative disease. Pharmacotherapy with L-DOPA remains the gold-standard therapy for PD, but is often limited by the development of the common side effect of L-DOPA-induced dyskinesia (LID), which can become debilitating. The only effective treatment for disabling dyskinesia is surgical therapy (neuromodulation or lesioning), therefore effective pharmacological treatment of LID is a critical unmet need.

Striatal Nurr1, but not FosB expression links a levodopa-induced dyskinesia phenotype to genotype in Fisher 344 vs. Lewis hemiparkinsonian rats.

Numerous genes, and alterations in their expression, have been identified as risk factors for developing levodopa-induced dyskinesia (LID). However, our understanding of the complexities of molecular changes remains insufficient for development of clinical treatment. In the current study we used gene array, in situ hybridization, immunohistochemistry, and microdialysis to provide a unique compare and contrast assessment of the relationship of four candidate genes to LID, employing three genetically distinct rat strains (Sprague-Dawley (SD), Fischer-344 (F344) and Lewis-RT.

Striatal Nurr1 Facilitates the Dyskinetic State and Exacerbates Levodopa-Induced Dyskinesia in a Rat Model of Parkinson's Disease.

The transcription factor Nurr1 has been identified to be ectopically induced in the striatum of rodents expressing l-DOPA-induced dyskinesia (LID). In the present study, we sought to characterize Nurr1 as a causative factor in LID expression. We used rAAV2/5 to overexpress Nurr1 or GFP in the parkinsonian striatum of LID-resistant Lewis or LID-prone Fischer-344 (F344) male rats.

Cell therapy for Parkinson's disease: Why it doesn't work every time.

The clinical experience with cell replacement therapy for advanced PD has yielded notable successes and failures. A recent autopsy case report of an individual that received implants of fetal dopamine neurons 16 years previously, but at no time experienced clinical benefit despite the best documented survival of grafted neurons and most extensive reinnervation of the striatum, raises sobering issues. With good reason, a great deal of effort in cell replacement science continues to focus on optimizing the cell source and implantation procedure.

Genetic silencing of striatal CaV1.3 prevents and ameliorates levodopa dyskinesia.

Background: Levodopa-induced dyskinesias are an often debilitating side effect of levodopa therapy in Parkinson's disease. Although up to 90% of individuals with PD develop this side effect, uniformly effective and well-tolerated antidyskinetic treatment remains a significant unmet need. The pathognomonic loss of striatal dopamine in PD results in dysregulation and disinhibition of striatal CaV1.

Regulation of dopamine neurotransmission from serotonergic neurons by ectopic expression of the dopamine D2 autoreceptor blocks levodopa-induced dyskinesia.

Levodopa-induced dyskinesias (LID) are a prevalent side effect of chronic treatment with levodopa (L-DOPA) for the motor symptoms of Parkinson's disease (PD). It has long been hypothesized that serotonergic neurons of the dorsal raphe nucleus (DRN) are capable of L-DOPA uptake and dysregulated release of dopamine (DA), and that this "false neurotransmission" phenomenon is a main contributor to LID development. Indeed, many preclinical studies have demonstrated LID management with serotonin receptor agonist treatment, but unfortunately, promising preclinical data has not been translated in large-scale clinical trials.

Subthalamic Nucleus Deep Brain Stimulation Does Not Modify the Functional Deficits or Axonopathy Induced by Nigrostriatal α-Synuclein Overexpression.

Subthalamic nucleus deep brain stimulation (STN DBS) protects dopaminergic neurons of the substantia nigra pars compacta (SNpc) against 6-OHDA and MPTP. We evaluated STN DBS in a parkinsonian model that displays α-synuclein pathology using unilateral, intranigral injections of recombinant adeno-associated virus pseudotype 2/5 to overexpress wildtype human α-synuclein (rAAV2/5 α-syn). A low titer of rAAV2/5 α-syn results in progressive forelimb asymmetry, loss of striatal dopaminergic terminal density and modest loss of SNpc dopamine neurons after eight weeks, corresponding to robust human-Snca expression and no effect on rat-Snca, Th, Bdnf or Trk2.

Subthalamic Nucleus Deep Brain Stimulation Employs trkB Signaling for Neuroprotection and Functional Restoration.

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is the most common neurosurgical treatment for Parkinson's disease motor symptoms. In preclinical models, STN DBS provides neuroprotection for substantia nigra (SN) dopamine neurons and increases BDNF in the nigrostriatal system and primary motor cortex. However, whether BDNF signaling in the SN participates in the neuroprotective effects of DBS remains unknown.

Repairing the Aged Parkinsonian Striatum: Lessons from the Lab and Clinic.

The primary risk factor associated with Parkinson's disease (PD) is advanced age. While there are symptomatic therapies for PD, efficacy of these eventually wane and/or side-effects develop over time. An alternative experimental therapy that has received a great deal of attention over the past several decades has been neural transplantation aimed at replacing nigral dopamine (DA) neurons that degenerate in PD.

Impact of age and vector construct on striatal and nigral transgene expression.

Therapeutic protein delivery using viral vectors has shown promise in preclinical models of Parkinson's disease (PD) but clinical trial success remains elusive. This may partially be due to a failure to include advanced age as a covariate despite aging being the primary risk factor for PD. We investigated transgene expression following intracerebral injections of recombinant adeno-associated virus pseudotypes 2/2 (rAAV2/2), 2/5 (rAAV2/5), 2/9 (rAAV2/9), and lentivirus (LV) expressing green fluorescent protein (GFP) in aged versus young adult rats.