Higher buccal mitochondrial DNA and mitochondrial common deletion number are associated with markers of neurodegeneration and inflammation in cerebrospinal fluid.

Human immunodeficiency virus (HIV) infection is potentially associated with premature aging, but demonstrating this is difficult due to a lack of reliable biomarkers. The mitochondrial (mt) DNA "common deletion" mutation (mtCDM) is a 4977-bp deletion associated with aging and neurodegenerative diseases. We examined how mtDNA and mtCDM correlate with markers of neurodegeneration and inflammation in people with and without HIV (PWH and PWOH). Data from 149 adults were combined from two projects involving PWH (n = 124) and PWOH (n = 25). We measured buccal mtDNA and mtCDM by digital droplet PCR and compared them to disease and demographic characteristics and soluble biomarkers in cerebrospinal fluid (CSF) and blood measured by immunoassay. Participants had a median age of 52 years, with 53% white and 81% men. Median mtDNA level was 1,332 copies/cell (IQR 1,201-1,493) and median mtCDM level was 0.36 copies × 102/cell (IQR 0.31-0.42); both were higher in PWH. In the best model adjusting for HIV status and demographics, higher mtDNA levels were associated with higher CSF amyloid-ß 1-42 and 8-hydroxy-2'-deoxyguanosine and higher mtCDM levels were associated with higher plasma soluble tumor necrosis factor receptor II. The differences in mtDNA markers between PWH and PWOH support potential premature aging in PWH. Our findings suggest mtDNA changes in oral tissues may reflect CNS processes, allowing the use of inexpensive and easily accessible buccal biospecimens as a screening tool for CSF inflammation and neurodegeneration. Confirmatory and mechanistic studies on mt genome alterations by HIV and ART may identify interventions to prevent or treat neurodegenerative complications.

Effects of innate immune receptor stimulation on extracellular α-synuclein uptake and degradation by brain resident cells.

Synucleinopathies are age-related neurological disorders characterized by the progressive deposition of α-synuclein (α-syn) aggregates and include Parkinson's disease (PD) and dementia with Lewy bodies (DLB). Although cell-to-cell α-syn transmission is thought to play a key role in the spread of α-syn pathology, the detailed mechanism is still unknown. Neuroinflammation is another key pathological feature of synucleinopathies. Previous studies have identified several immune receptors that mediate neuroinflammation in synucleinopathies, such as Toll-like receptor 2 (TLR2). However, the species of α-syn aggregates varies from study to study, and how different α-syn aggregate species interact with innate immune receptors has yet to be addressed. Therefore, we investigated whether innate immune receptors can facilitate the uptake of different species of α-syn aggregates. Here, we examined whether stimulation of TLRs could modulate the cellular uptake and degradation of α-syn fibrils despite a lack of direct interaction. We observed that stimulation of TLR2 in vitro accelerated α-syn fibril uptake in neurons and glia while delaying the degradation of α-syn in neurons and astrocytes. Internalized α-syn was rapidly degraded in microglia regardless of whether TLR2 was stimulated. However, cellular α-syn uptake and degradation kinetics were not altered by TLR4 stimulation. In addition, upregulation of TLR2 expression in a synucleinopathy mouse model increased the density of Lewy-body-like inclusions and induced morphological changes in microglia. Together, these results suggest that cell type-specific modulation of TLR2 may be a multifaceted and promising therapeutic strategy for synucleinopathies; inhibition of neuronal and astroglial TLR2 decreases pathogenic α-syn transmission, but activation of microglial TLR2 enhances microglial extracellular α-syn clearance.

Nucleic acid oxidation is associated with biomarkers of neurodegeneration in CSF in people with HIV.

OBJECTIVE: To determine whether oxidative stress in virologically suppressed people with HIV (PWH) may contribute to or result from neurodegeneration, we measured 7,8-dihydro-8-oxoguanine (8-oxo-dG), a marker of DNA damage due to oxidative stress, and markers of age-related neurodegeneration, specifically, reduced levels of CSF Aß-42, and elevated CSF total tau and neurofilament light (NFL). METHODS: This cross-sectional study prospectively enrolled participants at 6 US centers in the CNS HIV Antiretroviral Effects Research study. Inclusion criteria included HIV+ with a plasma level of HIV RNA ≤50 copies/mL. Exclusions included significant CNS confounding conditions. Measurements of total tau and Aß-42 were performed by bead suspension array. NFL and 8-oxo-dG were measured using ELISA. RESULTS: Participants were 53 PWH, mean age 55 (±9.3) years, 19% women, and 48% non-Hispanic White. Higher 8-oxo-dG correlated with markers of AD-related neurodegeneration including lower CSF Aß-42 (r = -0.34; p = 0.012) and higher CSF NFL (r = 0.39; p = 0.0091) and total tau (r = 0.6696; p < 0.0001). Relationships remained after adjusting for demographic variables. Levels of protein carbonyls, a marker of protein oxidation, were not related to neurodegeneration markers. CONCLUSIONS: Among virologically suppressed PWH, nucleic acid oxidation was associated with standard CSF biomarkers of neurodegeneration. Potential sources of oxidative stress in PWH include low-level HIV replication, inflammation, mitochondrial dysfunction, and specific antiretroviral drugs. Results suggest that the higher levels of oxidative stress among PWH may play a role in neurodegeneration. CLASSIFICATION OF EVIDENCE: This study provides Class II evidence that among virologically suppressed PWH, nucleic acid oxidation is associated with standard CSF biomarkers of neurodegeneration.

Antiretroviral drug concentrations in brain tissue of adult decedents.

OBJECTIVE: Determine concentrations of antiretroviral therapy (ART) drugs in the human brain. DESIGN: Cohort study of persons with HIV who consented to antemortem assessment and postmortem autopsy. METHODS: Eleven persons with HIV who were taking ART at the time of death and had detectable concentrations of at least one ART drug in intracardiac aspirate at autopsy were evaluated. Autopsies were performed within 24 h of death and brain tissue was stored at -80 °C. Concentrations of 11 ART drugs were measured in three brain regions (globus pallidus, cortical gray matter, white matter) by HPLC tandem mass spectrometry with a lower limit of quantification of 25 ng/ml. RESULTS: Participants were mostly men (82%) with a mean age of 40.4 years. Drug concentrations in brain tissue were highly variable and exceeded published concentrations in cerebrospinal fluid for several drugs, including for tenofovir, efavirenz, and lopinavir. Drug concentrations correlated most strongly between cortical gray matter and globus pallidus (rho = 0.70) but less well between globus pallidus and white matter (rho = 0.43). Combining all drugs and brain regions (n = 89), higher drug concentrations in brain were associated with longer estimated duration of HIV infection (P = 0.015), lower HIV RNA in plasma (P = 0.0001), lower nadir CD4 T-cell count (P = 0.053), and worse neurocognitive performance (P = 0.017). CONCLUSION: This is the first analysis of ART drug concentrations in human brain tissue. Concentrations of several drugs in this analysis were similar to published concentrations in cerebrospinal fluid but others exceeded published concentrations. The association between higher drug concentrations in the brain and worse neurocognitive performance may indicate ART neurotoxicity.

Predictors of worsening neuropathy and neuropathic pain after 12 years in people with HIV.

OBJECTIVE: Distal sensory polyneuropathy (DSP) and neuropathic pain are important clinical concerns in virally suppressed people with HIV. We determined how these conditions evolved, what factors influenced their evolution, and their clinical impact. METHODS: Ambulatory, community-dwelling HIV seropositive individuals were recruited at six research centers. Clinical evaluations at baseline and 12 years later determined neuropathy signs and distal neuropathic pain (DNP). Additional assessments measured activities of daily living and quality of life (QOL). Factors potentially associated with DSP and DNP progression included disease severity, treatment, demographics, and co-morbidities. Adjusted odds ratios were calculated for follow-up neuropathy outcomes. RESULTS: Of 254 participants, 21.3% were women, 57.5% were non-white. Mean baseline age was 43.5 years. Polyneuropathy prevalence increased from 25.7% to 43.7%. Of 173 participants initially pain-free, 42 (24.3%) had incident neuropathic pain. Baseline risk factors for incident pain included unemployment (OR [95% CI], 5.86 [1.97, 17.4]) and higher baseline body mass index (BMI) (1.78 [1.03, 3.19] per 10-units). Participants with neuropathic pain at follow-up had significantly worse QOL and greater dependence in activities of daily living than those who remained pain-free. INTERPRETATION: HIV DSP and neuropathic pain increased in prevalence and severity over 12 years despite high rates of viral suppression. The high burden of neuropathy included disability and poor life quality. However, substantial numbers remained pain-free despite clear evidence of neuropathy on exam. Protective factors included being employed and having a lower BMI. Implications for clinical practice include promotion of lifestyle changes affecting reversible risk factors.

Effects of HIV-1 TAT protein and methamphetamine exposure on visual discrimination and executive function in mice.

Mild neurocognitive impairments are common in people with human immunodeficiency virus (HIV) infection. HIV-encoded proteins, such as trans-activator of transcription (TAT), contribute to neuropathology and cognitive function in medicated subjects. The combination of TAT and comorbid methamphetamine use may further impair neurocognitive function in HIV-positive individuals by affecting dopaminergic systems in the brain. The current study examined the effects of TAT protein expression and methamphetamine exposure on cognitive function and dopamine systems in mice. Transgenic mice with inducible brain expression of the TAT protein were exposed to a binge methamphetamine regimen. TAT expression was induced via a doxycycline-containing diet during the final stage of the regimen and maintained throughout cognitive testing. Learning and executive function were assessed using an operant visual discrimination protocol, with a strategy switch and reversal. TAT expression and methamphetamine exposure improved visual discrimination learning. Combined TAT expression and methamphetamine exposure increased perseverative errors during reversal learning. TAT expression altered reversal learning by improving early stage, but impairing late stage, learning. TAT expression was also associated with an increase in dopamine transporter expression in the caudate putamen. These results highlight that TAT expression and methamphetamine exposure likely affect a range of selective cognitive processes, with some potentially improving function under certain conditions.

Human immunodeficiency virus Tat impairs mitochondrial fission in neurons.

Human immunodeficiency virus-1 (HIV) infection of the central nervous system promotes neuronal injury that culminates in HIV-associated neurocognitive disorders. Viral proteins, including transactivator of transcription (Tat), have emerged as leading candidates to explain HIV-mediated neurotoxicity, though the mechanisms remain unclear. Tat transgenic mice or neurons exposed to Tat, which show neuronal loss, exhibit smaller mitochondria as compared to controls. To provide an experimental clue as to which mechanisms are used by Tat to promote changes in mitochondrial morphology, rat cortical neurons were exposed to Tat (100 nM) for various time points. Within 30 min, Tat caused a significant reduction in mitochondrial membrane potential, a process that is regulated by fusion and fission. To further assess whether Tat changes these processes, fission and fusion proteins dynamin-related protein 1 (Drp1) and mitofusin-2 (Mfn2), respectively, were measured. We found that Drp1 levels increased beginning at 2 h after Tat exposure while Mfn2 remained unchanged. Moreover, increased levels of an active form of Drp1 were found to be present following Tat exposure. Furthermore, Drp1 and calcineurin inhibitors prevented Tat-mediated effects on mitochondria size. These findings indicate that mitochondrial fission is likely the leading factor in Tat-mediated alterations to mitochondrial morphology. This disruption in mitochondria homeostasis may contribute to the instability of the organelle and ultimately neuronal cell death following Tat exposure.

Transgenic mice expressing HIV-1 envelope protein gp120 in the brain as an animal model in neuroAIDS research.

HIV-1 infection causes injury to the central nervous system (CNS) and is often associated with neurocognitive disorders. One model for brain damage seen in AIDS patients is the transgenic (tg) mouse expressing a soluble envelope protein gp120 of HIV-1 LAV in the brain in astrocytes under the control of the promoter of glial fibrillary acidic protein. These GFAP-gp120tg mice manifest several key neuropathological features observed in AIDS brains, such as decreased synaptic and dendritic density, increased numbers of activated microglia, and pronounced astrocytosis. Several recent studies show that brains of GFAP-gp120tg mice and neurocognitively impaired HIV patients share also a significant number of differentially regulated genes, activation of innate immunity and other cellular signaling pathways, disturbed neurogenesis, and learning deficits. These findings support the continued relevance of the GFAP-gp120tg mouse as a useful model to investigate neurodegenerative mechanisms and develop therapeutic strategies to mitigate the consequences associated with HIV infection of the CNS, neuroAIDS, and HAND.

Human Immunodeficiency Virus Promotes Mitochondrial Toxicity.

Combined antiretroviral therapies (cART) have had remarkable success in reducing morbidity and mortality among patients infected with human immunodeficiency virus (HIV). However, mild forms of HIV-associated neurocognitive disorders (HAND), characterized by loss of synapses, remain. cART may maintain an undetectable HIV RNA load but does not eliminate the expression of viral proteins such as trans-activator of transcription (Tat) and the envelope glycoprotein gp120 in the brain. These two viral proteins are known to promote synaptic simplifications by several mechanisms, including alteration of mitochondrial function and dynamics. In this review, we aim to outline the many targets and pathways used by viral proteins to alter mitochondria dynamics, which contribute to HIV-induced neurotoxicity. A better understanding of these pathways is crucial for the development of adjunct therapies for HAND.

Inhibition of the mitochondrial pyruvate carrier protects from excitotoxic neuronal death.

Glutamate is the dominant excitatory neurotransmitter in the brain, but under conditions of metabolic stress it can accumulate to excitotoxic levels. Although pharmacologic modulation of excitatory amino acid receptors is well studied, minimal consideration has been given to targeting mitochondrial glutamate metabolism to control neurotransmitter levels. Here we demonstrate that chemical inhibition of the mitochondrial pyruvate carrier (MPC) protects primary cortical neurons from excitotoxic death. Reductions in mitochondrial pyruvate uptake do not compromise cellular energy metabolism, suggesting neuronal metabolic flexibility. Rather, MPC inhibition rewires mitochondrial substrate metabolism to preferentially increase reliance on glutamate to fuel energetics and anaplerosis. Mobilizing the neuronal glutamate pool for oxidation decreases the quantity of glutamate released upon depolarization and, in turn, limits the positive-feedback cascade of excitotoxic neuronal injury. The finding links mitochondrial pyruvate metabolism to glutamatergic neurotransmission and establishes the MPC as a therapeutic target to treat neurodegenerative diseases characterized by excitotoxicity.

The anticancer drug sunitinib promotes autophagyand protects from neurotoxicity in an HIV-1 Tat model of neurodegeneration.

Despite the success of antiretroviral therapies to control systemic HIV-1 infection, the prevalence of HIV-associated neurocognitive disorders (HANDs) has not decreased among aging patients with HIV. Autophagy pathway alterations, triggered by HIV-1 proteins including gp120, Tat, and Nef, might contribute to the neurodegenerative process in aging patients with HAND. Although no treatments are currently available to manage HAND, we have previously shown that sunitinib, an anticancer drug that blocks receptor tyrosine-kinase and cyclin kinase pathways, might be of interest. Studies in cancer models suggest that sunitinib might also modulate autophagy, which is dysregulated in our models of Tat-induced neurotoxicity. We evaluated the efficacy of sunitinib to promote autophagy in the CNS and ameliorate neurodegeneration using LC3-GFP-expressing neuronal cells challenged with low concentrations of Tat and using inducible Tat transgenic mice. In neuronal cultures challenged with low levels of Tat, sunitinib increased markers of autophagy such as LC3-II and reduced p62 accumulation in a dose-dependent manner. In vivo, sunitinib treatment restored LC3-II, p62, and endophilin B1 (EndoB1) levels in doxycycline-induced Tat transgenic mice. Moreover, in these animals, sunitinib reduced the hyperactivation of CDK5, tau hyperphosphorylation, and p35 cleavage to p25. Restoration of CDK5 and autophagy were associated with reduced neurodegeneration and behavioral alterations. Alterations in autophagy in the Tat tg mice were associated with reduced levels of a CDK5 substrate, EndoB1, and levels of total EndoB1 were normalized by sunitinib treatment. We conclude that sunitinib might ameliorate Tat-mediated autophagy alterations and may decrease neurodegeneration in aging patients with HAND.

Combination of alpha-synuclein immunotherapy with anti-inflammatory treatment in a transgenic mouse model of multiple system atrophy.

Multiple system atrophy (MSA) is a fatal neurodegenerative disorder characterized by the pathological accumulation of alpha-synuclein (α-syn) in oligodendrocytes. Therapeutic efforts to stop or delay the progression of MSA have yielded suboptimal results in clinical trials, and there are no efficient treatments currently available for MSA patients. We hypothesize that combining therapies targeting different aspects of the disease may lead to better clinical outcomes. To test this hypothesis, we combined the use of a single-chain antibody targeting α-syn modified for improved central nervous system penetration (CD5-D5) with an unconventional anti-inflammatory treatment (lenalidomide) in the myelin basic protein (MBP)-α-syn transgenic mouse model of MSA. While the use of either CD5-D5 or lenalidomide alone had positive effects on neuroinflammation and/or α-syn accumulation in this mouse model of MSA, the combination of both approaches yielded better results than each single treatment. The combined treatment reduced astrogliosis, microgliosis, soluble and aggregated α-syn levels, and partially improved behavioral deficits in MBP-α-syn transgenic mice. These effects were associated with an activation of the Akt signaling pathway, which may mediate cytoprotective effects downstream tumor necrosis factor alpha (TNFα). These results suggest that a strategic combination of treatments may improve the therapeutic outcome in trials for MSA and related neurodegenerative disorders.

Neuroprotective effects of the immunomodulatory drug FK506 in a model of HIV1-gp120 neurotoxicity.

BACKGROUND: HIV-associated neurocognitive disorders (HAND) continue to be a common morbidity associated with chronic HIV infection. It has been shown that HIV proteins (e.g., gp120) released from infected microglial/macrophage cells can cause neuronal damage by triggering inflammation and oxidative stress, activating aberrant kinase pathways, and by disrupting mitochondrial function and biogenesis. Previous studies have shown that FK506, an immunophilin ligand that modulates inflammation and mitochondrial function and inhibits calcineurin, is capable of rescuing the neurodegenerative pathology in models of Parkinson's disease, Alzheimer's disease, and Huntington's disease. In this context, the main objective of this study was to evaluate if FK506 could rescue the neuronal degeneration and mitochondrial alterations in a transgenic (tg) animal model of HIV1-gp120 neurotoxicity. METHODS: GFAP-gp120 tg mice were treated with FK506 and analyzed for neuropathology, behavior, mitochondrial markers, and calcium flux by two-photon microscopy. RESULTS: We found that FK506 reduced the neuronal cell loss and neuro-inflammation in the gp120 tg mice. Moreover, while vehicle-treated gp120 tg mice displayed damaged mitochondria and increased neuro-inflammatory markers, FK506 rescued the morphological mitochondrial alterations and neuro-inflammation while increasing levels of optic atrophy 1 and mitofusin 1. By two-photon microscopy, calcium levels were not affected in the gp120 tg mice and no effects of FK506 were detected. However, at a functional level, FK506 ameliorated the gp120 tg mice hyperactivity in the open field. CONCLUSIONS: Together, these results suggest that FK506 might be potentially neuroprotective in patients with HAND by mitigating inflammation and mitochondrial alterations.