Single-cell transcriptomics reveals colonic immune perturbations during amyloid-ß driven Alzheimer's disease in mice.

The "gut-brain axis" is emerging as an important target in Alzheimer's disease (AD). However, immunological mechanisms underlying this axis remain poorly understood. Using single-cell RNA sequencing of the colon immune compartment in the 5XFAD amyloid-ß (Aß) mouse model, we uncovered AD-associated changes in ribosomal activity, oxidative stress, and BCR/plasma cell activity. Strikingly, levels of colon CXCR4 + antibody secreting cells (ASCs) were significantly reduced. This corresponded with accumulating CXCR4 + B cells and gut-specific IgA + cells in the brain and dura mater, respectively. Consistently, a chemokine ligand for CXCR4, CXCL12, was expressed at higher levels in 5XFAD glial cells and in in silico analyzed human brain studies, supporting altered neuroimmune trafficking. An inulin prebiotic fiber diet attenuated AD markers including Aß plaques and overall frailty. These changes corresponded to an expansion of gut IgA + cells and rescued peripheral T regs levels. Our study points to a key glia-gut axis and potential targets against AD. Study Highlights: AD is associated with altered immune parameters in the gut of 5XFAD mice. 5 XFAD colon has reduced ASCs, including CXCR4 + cells with a migratory gene signature. 5XFAD brain gliosis includes increased CXCL12 expression. CXCR4 + B cells and gut-specific IgA + ASCs accumulate in the 5XFAD brain and/or dura mater. Inulin diet attenuates AD disease parameters while boosting IgA + cell and T reg levels.

A drug-like molecule engages nuclear hormone receptor DAF-12/FXR to regulate mitophagy and extend lifespan.

Autophagy-lysosomal function is crucial for maintaining healthy lifespan and preventing age-related diseases. The transcription factor TFEB plays a key role in regulating this pathway. Decreased TFEB expression is associated with various age-related disorders, making it a promising therapeutic target. In this study, we screened a natural product library and discovered mitophagy-inducing coumarin (MIC), a benzocoumarin compound that enhances TFEB expression and lysosomal function. MIC robustly increases the lifespan of Caenorhabditis elegans in an HLH-30/TFEB-dependent and mitophagy-dependent manner involving DCT-1/BNIP3 while also preventing mitochondrial dysfunction in mammalian cells. Mechanistically, MIC acts by inhibiting ligand-induced activation of the nuclear hormone receptor DAF-12/FXR, which, in turn, induces mitophagy and extends lifespan. In conclusion, our study uncovers MIC as a promising drug-like molecule that enhances mitochondrial function and extends lifespan by targeting DAF-12/FXR. Furthermore, we discovered DAF-12/FXR as a previously unknown upstream regulator of HLH-30/TFEB and mitophagy.

Taurine deficiency as a driver of aging.

Aging is associated with changes in circulating levels of various molecules, some of which remain undefined. We find that concentrations of circulating taurine decline with aging in mice, monkeys, and humans. A reversal of this decline through taurine supplementation increased the health span (the period of healthy living) and life span in mice and health span in monkeys. Mechanistically, taurine reduced cellular senescence, protected against telomerase deficiency, suppressed mitochondrial dysfunction, decreased DNA damage, and attenuated inflammaging. In humans, lower taurine concentrations correlated with several age-related diseases and taurine concentrations increased after acute endurance exercise. Thus, taurine deficiency may be a driver of aging because its reversal increases health span in worms, rodents, and primates and life span in worms and rodents. Clinical trials in humans seem warranted to test whether taurine deficiency might drive aging in humans.

Urolithin A reduces amyloid-beta load and improves cognitive deficits uncorrelated with plaque burden in a mouse model of Alzheimer's disease.

In the present study, we investigated the effects of urolithin A (UA), a metabolite generated from ellagic acid via its metabolism by gut bacteria, as an autophagy activator with potential neuroprotective activity. WT and 3xTg-AD mice were administered long-term intermittent dietary supplementation with UA. UA was found to prevent deficits in spatial memory, cued fear response, and exploratory behavior in this model. It also decreased the Aß plaque burden in areas of the hippocampus where these protein deposits are prominent in the model. Interestingly, correlation analyses demonstrate that Aß plaque burden positively correlates with enhanced spatial memory in 3xTg-AD mice on a control diet but not in those supplemented with UA. In contrast, Aß42 abundance in cortical and hippocampal homogenates negatively correlate with spatial memory in UA-fed mice. Our data suggest that plaque formation may be a protective mechanism against neurodegeneration and cognitive decline and that targeting the generation of proteotoxic Aß species might be a more successful approach in halting disease progression. UA was also found to extend lifespan in normal aging mice. Mechanistically, we demonstrate that UA is able to induce autophagy and to increase Aß clearance in neuronal cell lines. In summary, our studies reveal UA, likely via its actions as a autophagy inducer, is capable of removing Aß from neurons and its dietary administration prevents the onset of cognitive deficits associated with pathological Aß deposition in the 3xTg-AD mouse model as well as extending lifespan in normal aging mice.

Potassium-chelating drug sodium polystyrene sulfonate enhances lysosomal function and suppresses proteotoxicity.

Lysosomes are crucial for degradation and recycling of damaged proteins and cellular components. Therapeutic strategies enhancing lysosomal function are a promising approach for aging and age-related neurodegenerative diseases. Here, we show that an FDA approved drug sodium polystyrene sulfonate (SPS), used to reduce high blood potassium in humans, enhances lysosomal function both in C. elegans and in human neuronal cells. Enhanced lysosomal function following SPS treatment is accompanied by the suppression of proteotoxicity caused by expression of the neurotoxic peptides Aß and TAU. Additionally, treatment with SPS imparts health benefits as it significantly increases lifespan in C. elegans. Overall our work supports the potential use of SPS as a prospective geroprotective intervention.

Trimethylamine modulates dauer formation, neurodegeneration, and lifespan through tyra-3/daf-11 signaling in Caenorhabditis elegans.

In the nematode Caenorhabditis elegans, signals derived from bacteria in the diet, the animal's major nutrient source, can modulate both behavior and healthspan. Here we describe a dual role for trimethylamine (TMA), a human gut flora metabolite, which acts as a nutrient signal and a neurotoxin. TMA and its associated metabolites are produced by the human gut microbiome and have been suggested to serve as risk biomarkers for diabetes and cardiovascular diseases. We demonstrate that the tyramine receptor TYRA-3, a conserved G protein-coupled receptor (GPCR), is required to sense TMA and mediate its responses. TMA activates guanylyl cyclase DAF-11 signaling through TYRA-3 in amphid neurons (ASK) and ciliated neurons (BAG) to mediate food-sensing behavior. Bacterial mutants deficient in TMA production enhance dauer formation, extend lifespan, and are less preferred as a food source. Increased levels of TMA lead to neural damage in models of Parkinson's disease and shorten lifespan. Our results reveal conserved signaling pathways modulated by TMA in C. elegans that are likely to be relevant for its effects in mammalian systems.

Microdose lithium reduces cellular senescence in human astrocytes - a potential pharmacotherapy for COVID-19?

Cell senescence is a process that causes growth arrest and the release of a senescence associated secretory phenotype (SASP), characterized by secretion of chemokines, cytokines, cell growth factors and metalloproteases, leading to a tissue condition that may precipitate cancers and neurodegenerative processes. With the recent pandemic of coronavirus, senolytic drugs are being considered as possible therapeutic tools to reduce the virulence of SARS-CoV-2. In the last few years, our research group showed that lithium carbonate at microdose levels was able to stabilize memory and change neuropathological characteristics of Alzheimer's disease (AD). In the present work, we present evidence that low-dose lithium can reduce the SASP of human iPSCs-derived astrocytes following acute treatment, suggesting that microdose lithium could protect cells from senescence and development of aging-related conditions. With the present findings, a perspective of the potential use of low-dose lithium in old patients from the "high risk group" for COVID-19 (with hypertension, diabetes and chronic obstructive pulmonary disease) is presented.

Gedunin Inhibits Oligomeric Aß1-42-Induced Microglia Activation Via Modulation of Nrf2-NF-κB Signaling.

Alzheimer's disease (AD) is a neurodegenerative disorder and the leading cause of dementia in aged populations worldwide. The deposition of toxic protein aggregates such as amyloid beta (Aß) is a hallmark of AD, and there is growing awareness that a key driver of AD pathogenesis is the neuroinflammatory cascade triggered and sustained by these proteins. Consequently, interventions that suppress prolonged neuroinflammation represent viable therapeutic approaches for AD. In this context, we tested the natural product gedunin which is an anti-inflammatory molecule, found in the seeds of the neem tree (Azadirachta indica), whose mechanism of action remains to be fully elucidated. Using a mouse microglia cell line (IMG), we show that gedunin suppresses neuroinflammation arising from Aß1-42 oligomer exposure. Our results demonstrate that gedunin suppresses Aß1-42-induced NF-κB activation and its targets, including nitric oxide (NO) and IL-1ß, known proinflammatory molecules. Further, we show that gedunin inhibits neuroinflammation by activating nuclear factor 2 erythroid-related factor 2 (Nrf2) and its downstream targets γ-glutamylcysteine synthetase, heme oxygenase 1, and NADPH quinone dehydrogenase 1, which are involved in quenching reactive oxygen and nitrogen species (NO) generated by NF-κB activation. Nrf2 activation appears essential for the anti-inflammatory effect because when silenced, the proinflammatory effects of Aß1-42 are enhanced and the protective effect of gedunin against NO production is reduced. Additionally, using human neuronal cells (SH-SY5Y), we show that gedunin prevents neurotoxicity secondary to Aß-induced microglial activation. In conclusion, our findings highlight a potential therapeutic role of gedunin in neurodegenerative diseases.

Cellular Senescence Is Induced by the Environmental Neurotoxin Paraquat and Contributes to Neuropathology Linked to Parkinson's Disease.

Exposure to the herbicide paraquat (PQ) is associated with an increased risk of idiopathic Parkinson's disease (PD). Therapies based on PQ's presumed mechanisms of action have not, however, yielded effective disease therapies. Cellular senescence is an anticancer mechanism that arrests proliferation of replication-competent cells and results in a pro-inflammatory senescence-associated secretory phenotype (SASP) capable of damaging neighboring tissues. Here, we demonstrate that senescent cell markers are preferentially present within astrocytes in PD brain tissues. Additionally, PQ was found to induce astrocytic senescence and an SASP in vitro and in vivo, and senescent cell depletion in the latter protects against PQ-induced neuropathology. Our data suggest that exposure to certain environmental toxins promotes accumulation of senescent cells in the aging brain, which can contribute to dopaminergic neurodegeneration. Therapies that target senescent cells may constitute a strategy for treatment of sporadic PD, for which environmental exposure is a major risk factor.

Hsp90 Co-chaperone p23 contributes to dopaminergic mitochondrial stress via stabilization of PHD2: Implications for Parkinson's disease.

The heat shock factor 90 (hsp90) complex has long been associated with neuropathological phenotypes linked to Parkinson's disease (PD) and its inhibition is neuroprotective in disease models. Hsp90 is conventionally believed to act by suppressing induction of hsp70. Here, we report a novel hsp70-independent mechanism by which Hsp90 may also contribute to PD-associated neuropathology. We previously reported that inhibition of the enzyme prolyl hydroxylase domain 2 (PHD2) in conjunction with increases in hypoxia-inducible factor 1 alpha (HIF1α) results in protection of vulnerable dopaminergic substantia nigra pars compacta (DAergic SNpc) neurons in in vitro and in vivo models of PD. We discovered an increased interaction between PHD2 and the p23:Hsp90 chaperone complex in response to mitochondrial stress elicited by the mitochondrial neurotoxin 1-methyl-4-phenylpyridine (MPP+) within cultured DAergic cells. Genetic p23 knockdown was found to result in decreases in steady-state PHD2 protein and activity and reduced susceptibility to MPP+ neurotoxicity. Administration of the p23 inhibitor gedunin was also neuroprotective in these cells as well as in human induced pluripotent stem cell (iPSC)-derived neurons. Our data suggests that mitochondrial stress-mediated elevations in PHD2 interaction with the p23-hsp90 complex have detrimental effects on the survival of DAergic neurons, while p23 inhibition is neuroprotective. We propose that neurotoxic effects are tied to enhanced PHD2 stabilization by the hsp90-p23 chaperone complex that is abrogated by p23 inhibition. This demonstrates a novel connection between two independent pathways previously linked to PD, hsp90 and PHD2-HIF1α, which could have important implications for here-to-fore unexplored mechanisms underlying PD neuropathology.

Sembragiline: A Novel, Selective Monoamine Oxidase Type B Inhibitor for the Treatment of Alzheimer's Disease.

Monoamine oxidase B (MAO-B) has been implicated in the pathogenesis of Alzheimer's disease (AD) and other neurodegenerative disorders. Increased MAO-B expression in astroglia has been observed adjacent to amyloid plaques in AD patient brains. This phenomenon is hypothesized to lead to increased production of hydrogen peroxide and reactive oxygen species (ROS), thereby contributing to AD pathology. Therefore, reduction of ROS-induced oxidative stress via inhibition of MAO-B activity may delay the progression of the disease. In the present study we report the pharmacological properties of sembragiline, a novel selective MAO-B inhibitor specifically developed for the treatment of AD, and on its effect on ROS-mediated neuronal injury and astrogliosis in MAO-B transgenic animals. Sembragiline showed potent and long-lasting MAO-B-selective inhibition and did not inhibit MAO-A at doses where full inhibition of MAO-B was observed. Such selectivity should translate into a favorable clinical safety profile. Indeed, sembragiline neither induced the serotonin syndrome when administered together with the serotonin precursor l-5-hydroxytryptophan in combination with antidepressants such as fluoxetine, nor potentiated the pressor effect of tyramine. Additionally, in experiments using a transgenic animal model conditionally overexpressing MAO-B in astroglia, sembragiline protected against neuronal loss and reduced both ROS formation and reactive astrogliosis. Taken together, these findings warrant further investigation of the potential therapeutic benefit of MAO-B inhibitors in patients with AD and other neurologic disorders.

Anti-Inflammatory and Neuroprotective Role of Natural Product Securinine in Activated Glial Cells: Implications for Parkinson's Disease.

Glial activation and subsequent release of neurotoxic proinflammatory factors are believed to play an important role in the pathogenesis of several neurological disorders including Parkinson's disease (PD). Inhibition of glial activation and inflammatory processes may represent a therapeutic target to alleviate neurodegeneration. Securinine, a major natural alkaloid product from the root of the plant Securinega suffruticosa, has been reported to have potent biological activity and is used in the treatment of neurological conditions such as amyotrophic lateral sclerosis, poliomyelitis, and multiple sclerosis. In this study, we explored the underlying mechanisms of neuroprotection elicited by securinine, particularly its anti-inflammatory effects in glial cells. Our results demonstrate that securinine significantly and dose-dependently suppressed the nitric oxide production in microglia and astrocytic cultures. In addition, securinine inhibited the activation of the inflammatory mediator NF-κB, as well as mitogen-activated protein kinases in lipopolysaccharide- (LPS-) stimulated BV2 cells. Additionally, securinine also inhibited interferon-γ- (IFN-γ-) induced nitric oxide levels and iNOS mRNA expression. Furthermore, conditioned media (CM) from securinine pretreated BV2 cells significantly reduced mesencephalic dopaminergic neurotoxicity compared with CM from LPS stimulated microglia. These findings suggest that securinine may be a potential candidate for the treatment of neurodegenerative diseases related to neuroinflammation.

Detrimental effects of oxidative losses in parkin activity in a model of sporadic Parkinson's disease are attenuated by restoration of PGC1alpha.

Loss of parkin E3 ligase activity as a result of parkin gene mutation in rare familial forms of Parkinson's disease (PD) has been shown to be detrimental to mitochondrial function and to contribute to ensuing neurodegeneration. This has been shown by ourselves and others to be in part due to reductions in parkin-mediated ubiquitination of the transcriptional repressor PARIS, limiting the protein's subsequent degradation by the proteasome. Subsequent elevations in PARIS protein levels result in reduced expression of the master mitochondrial regulator PGC-1α, impacting in turn on mitochondrial function. Here, we report that oxidatively-mediated reductions in parkin solubility and function in a mouse model of age-related sporadic PD coincides with increased PARIS levels and reduced PGC-1α signaling. Furthermore, restoration of PGC-1α expression was found to abrogate losses in mitochondrial function and degeneration of dopaminergic (DAergic) neurons within the substantia nigra pars compacta (SNpc) associated with this particular model. These findings suggest that the PGC-1α signaling pathway constitutes a viable therapeutic target for the treatment of not only familial PD, but also more common sporadic forms of the disorder.

Regulation of ATP13A2 via PHD2-HIF1α Signaling Is Critical for Cellular Iron Homeostasis: Implications for Parkinson's Disease.

We previously reported that pharmacological inhibition of a class of enzymes known as prolyl hydroxylase domain proteins (PHDs) has neuroprotective effects in various in vitro and in vivo models of Parkinson's disease (PD). We hypothesized that this was due to inhibition of the PHD2 isoform, preventing it from hydroxylating the transcription factor hypoxia inducible factor 1 α (HIF1α), targeting it for eventual proteasomal degradation. HIF1α itself induces the transcription of various cellular stress genes, including several involved in iron metabolism. Although all three isoforms of PHD are expressed within vulnerable dopaminergic (DAergic) substantia nigra pars compacta neurons, only select downregulation of the PHD2 isoform was found to protect against in vivo neurodegenerative effects associated with the mitochondrial neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. These findings were corroborated in induced pluripotent stem cell-derived neurons, providing validation in a pertinent human cell model. PHD2 inhibition was found to result in increased expression of ATP13A2, mutation of which is responsible for a rare juvenile form of PD known as Kufor-Rakeb syndrome. Knockdown of ATP13A2 expression within human DAergic cells was found to abrogate restoration of cellular iron homeostasis and neuronal cell viability elicited by inhibition of PHD2 under conditions of mitochondrial stress, likely via effects on lysosomal iron storage. These data suggest that regulation of ATP13A2 by the PHD2-HIF1α signaling pathway affects cellular iron homeostasis and DAergic neuronal survival. This constitutes a heretofore unrecognized process associated with loss of ATP13A2 function that could have wide-ranging implications for it as a therapeutic target for PD and other related conditions. SIGNIFICANCE STATEMENT: Reductions in PHD2 activity within dopaminergic neurons in vivo and in cultured human induced pluripotent stem cell-derived neurons protects against mitochondrial stress-induced neurotoxicity. Protective effects are dependent on downstream HIF-1α expression. Knockdown of ATP13A2, a gene linked to a rare juvenile form of Parkinson's disease and recently identified as a novel HIF1α target, was found to abrogate maintenance of cellular iron homeostasis and neuronal viability elicited by PHD2 inhibition in vivo and in cultured dopaminergic cells under conditions of mitochondrial stress. Mechanistically, this was due to ATP13A2's role in maintaining lysosomal iron stores. This constitutes a novel mechanism by which alterations in ATP13A2 activity may be driving PD-related neuropathology.

Mitochondrial Quality Control via the PGC1α-TFEB Signaling Pathway Is Compromised by Parkin Q311X Mutation But Independently Restored by Rapamycin.

Following its activation by PINK1, parkin is recruited to depolarized mitochondria where it ubiquitinates outer mitochondrial membrane proteins, initiating lysosomal-mediated degradation of these organelles. Mutations in the gene encoding parkin, PARK2, result in both familial and sporadic forms of Parkinson's disease (PD) in conjunction with reductions in removal of damaged mitochondria. In contrast to what has been reported for other PARK2 mutations, expression of the Q311X mutation in vivo in mice appears to involve a downstream step in the autophagic pathway at the level of lysosomal function. This coincides with increased PARIS expression and reduced expression of a reciprocal signaling pathway involving the master mitochondrial regulator peroxisome proliferator-activated receptor-gamma coactivator (PGC1α) and the lysosomal regulator transcription factor EB (TFEB). Treatment with rapamycin was found to independently restore PGC1α-TFEB signaling in a manner not requiring parkin activity and to abrogate impairment of mitochondrial quality control and neurodegenerative features associated with this in vivo model. Losses in PGC1α-TFEB signaling in cultured rat DAergic cells expressing the Q311X mutation associated with reduced mitochondrial function and cell viability were found to be PARIS-dependent and to be independently restored by rapamycin in a manner requiring TFEB. Studies in human iPSC-derived neurons demonstrate that TFEB induction can restore mitochondrial function and cell viability in a mitochondrially compromised human cell model. Based on these data, we propose that the parkin Q311X mutation impacts on mitochondrial quality control via PARIS-mediated regulation of PGC1α-TFEB signaling and that this can be independently restored via upregulation of TFEB function. SIGNIFICANCE STATEMENT: Mutations in PARK2 are generally associated with loss in ability to interact with PINK1, impacting on autophagic initiation. Our data suggest that, in the case of at least one parkin mutation, Q311X, detrimental effects are due to inhibition at the level of downstream lysosomal function. Mechanistically, this involves elevations in PARIS protein levels and subsequent effects on PGC1α-TFEB signaling that normally regulates mitochondrial quality control. Treatment with rapamycin independently restores PGC1α-TFEB signaling in a manner not requiring parkin activity and abrogates subsequent mitochondrial impairment and neuronal cell loss. Taken in total, our data suggest that the parkin Q311X mutation impacts on mitochondrial quality control via PARIS-mediated regulation of PGC1α-TFEB signaling and that this can be independently restored via rapamycin.

The combination of lithium and l-Dopa/Carbidopa reduces MPTP-induced abnormal involuntary movements (AIMs) via calpain-1 inhibition in a mouse model: Relevance for Parkinson׳s disease therapy.

Lithium has recently been suggested to have neuroprotective effects in several models of neurodegenerative disease including Parkinson׳s disease (PD). Levodopa (l-Dopa) replacement therapy remains the most common and effective treatment for PD, although it induces the complication of l-Dopa induced dyskinesia after years of use. Here we examined the potential use of lithium in combination with l-Dopa/Carbidopa for both reducing MPTP-induced abnormal involuntary movements (AIMs) as well as protecting against cell death in MPTP-lesioned mice. Chronic lithium administration (0.127% LiCl in the feed) in the presence of daily l-Dopa/Carbidopa injection for a period of 2 months was sufficient to effectively reduce MPTP-induced AIMs in mice. Mechanistically, lithium was found to suppress MPTP-induced calpain activities in vivo coinciding with down-regulation of calpain-1 but not calpain-2 expression in both the striatum (ST) and the brain stem (BS). Calpain inhibition has previously been associated with increased levels of the rate-limiting enzyme in dopamine synthesis, tyrosine hydroxylase (TH), which is probably mediated by the up-regulation of the transcription factors MEF-2A and 2D. Lithium was found to induce up-regulation of TH expression in the ST and the BS, as well as in N27 rat dopaminergic cells. Further, histone acetyltransferase (HAT) expression was substantially up-regulated by lithium treatment in vitro. These results suggest the potential use of lithium in combination with l-Dopa/Carbidopa not only as a neuroprotectant, but also for reducing AIMs and possibly alleviating potential side-effects associated with the current treatment for PD.

Cellular senescence and the aging brain.

Cellular senescence is a potent anti-cancer mechanism that arrests the proliferation of mitotically competent cells to prevent malignant transformation. Senescent cells accumulate with age in a variety of human and mouse tissues where they express a complex 'senescence-associated secretory phenotype' (SASP). The SASP includes many pro-inflammatory cytokines, chemokines, growth factors and proteases that have the potential to cause or exacerbate age-related pathology, both degenerative and hyperplastic. While cellular senescence in peripheral tissues has recently been linked to a number of age-related pathologies, its involvement in brain aging is just beginning to be explored. Recent data generated by several laboratories suggest that both aging and age-related neurodegenerative diseases are accompanied by an increase in SASP-expressing senescent cells of non-neuronal origin in the brain. Moreover, this increase correlates with neurodegeneration. Senescent cells in the brain could therefore constitute novel therapeutic targets for treating age-related neuropathologies.

Lithium prevents parkinsonian behavioral and striatal phenotypes in an aged parkin mutant transgenic mouse model.

Lithium has long been used as a treatment for the psychiatric disease bipolar disorder. However, previous studies suggest that lithium provides neuroprotective effects in neurodegenerative diseases such as Parkinson's disease (PD) and Alzheimer's disease. The exact mechanism by which lithium exerts these effects still remains unclear. In the present study, we evaluated the effects of low-dose lithium treatment in an aged mouse model expressing a parkin mutation within dopaminergic neurons. We found that low-dose lithium treatment prevented motor impairment as demonstrated by the open field test, pole test, and rearing behavior. Furthermore, lithium prevented dopaminergic striatal degeneration in parkin animals. We also found that parkin-induced striatal astrogliosis and microglial activation were prevented by lithium treatment. Our results further corroborate the use of this parkin mutant transgenic mouse line as a model for PD for testing novel therapeutics. The findings of the present study also provide further validation that lithium could be re-purposed as a therapy for PD and suggest that anti-inflammatory effects may contribute to its neuroprotective mechanisms.

Age-related behavioral phenotype of an astrocytic monoamine oxidase-B transgenic mouse model of Parkinson's disease.

We have previously shown that increases in astrocytic monoamine oxidase-B (MAO-B) expression, mimicking that which occurs with aging and in neurodegenerative disease, in a doxycycline (dox)-inducible transgenic mouse model evokes neuropathological similarities to what is observed in the human parkinsonian brain. Additional behavioral and neuropathological studies could provide further validation for its usage as a model for Parkinson's disease (PD). In the present study, we utilized a battery of behavioral tests to evaluate age-related phenotype in this model. In the open field test, we found that dox-induction impaired motor ability with decreases in movement and ambulatory function as well as diminished stereotypical, repetitive movement episodes in both young and old mice. Older mice also showed decreased motor performance in the pole test when compared to younger mice. Furthermore, dox-induced older mice displayed severe hindlimb clasping and the most significant loss of dopamine (DA) in the striatum when compared to young and non-induced animals. Additionally, increased MAO-B activity significantly correlated with decreased expression of striatal DA. The results of our study further confirms that the dox-inducible astrocytic MAO-B transgenic mouse displays similar age-related behavioral and neuropathological features to other models of PD, and could serve as a useful tool to study PD pathophysiology and for the evaluation of therapeutic interventions.

Mitochondrial DNA damage is associated with reduced mitochondrial bioenergetics in Huntington's disease.

Oxidative stress and mitochondrial dysfunction have been implicated in the pathology of HD; however, the precise mechanisms by which mutant huntingtin modulates levels of oxidative damage in turn resulting in mitochondrial dysfunction are not known. We hypothesize that mutant huntingtin increases oxidative mtDNA damage leading to mitochondrial dysfunction. We measured nuclear and mitochondrial DNA lesions and mitochondrial bioenergetics in the STHdhQ7 and STHdhQ111 in vitro striatal model of HD. Striatal cells expressing mutant huntingtin show higher basal levels of mitochondrial-generated ROS and mtDNA lesions and a lower spare respiratory capacity. Silencing of APE1, the major mammalian apurinic/apyrimidinic (AP) endonuclease that participates in the base excision repair (BER) pathway, caused further reductions of spare respiratory capacity in the mutant huntingtin-expressing cells. Localization experiments show that APE1 increases in the mitochondria of wild-type Q7 cells but not in the mutant huntingtin Q111 cells after treatment with hydrogen peroxide. Moreover, these results are recapitulated in human HD striata and HD skin fibroblasts that show significant mtDNA damage (increased lesion frequency and mtDNA depletion) and significant decreases in spare respiratory capacity, respectively. These data suggest that mtDNA is a major target of mutant huntingtin-associated oxidative stress and may contribute to subsequent mitochondrial dysfunction and that APE1 (and, by extension, BER) is an important target in the maintenance of mitochondrial function in HD.