Aging and Apolipoprotein E in HIV Infection

Alzheimer's disease as a viral disease: Revisiting the infectious hypothesis

Alzheimer's disease (AD) represents the most frequent type of dementia in elderly people. Two major forms of the disease exist: sporadic - the causes of which have not yet been fully understood - and familial - inherited within families from generation to generation, with a clear autosomal dominant transmission of mutations in Presenilin 1 (PSEN1), 2 (PSEN2) or Amyloid Precursors Protein (APP) genes. The main hallmark of AD consists of extracellular deposits of amyloid-beta (Aβ) peptide and intracellular deposits of the hyperphosphorylated form of the tau protein. An ever-growing body of research supports the viral infectious hypothesis of sporadic forms of AD. In particular, it has been shown that several herpes viruses (i.e., HHV-1, HHV-2, HHV-3 or varicella zoster virus, HHV-4 or Epstein Barr virus, HHV-5 or cytomegalovirus, HHV-6A and B, HHV-7), flaviviruses (i.e., Zika virus, Dengue fever virus, Japanese encephalitis virus) as well as Human Immunodeficiency Virus (HIV), hepatitis viruses (HAV, HBV, HCV, HDV, HEV), SARS-CoV2, Ljungan virus (LV), Influenza A virus and Borna disease virus, could increase the risk of AD. Here, we summarized and discussed these results. Based on these findings, significant issues for future studies are also put forward.

Neuropathologic Findings in Elderly HIV-Positive Individuals

The elderly HIV-positive population is growing due to the widespread use of combination antiretroviral therapy (cART), but the effects of longstanding HIV infection on brain aging are unknown. A significant proportion of HIV-positive individuals develop HIV-associated neurocognitive disorder (HAND) even on cART, but the pathogenesis of HAND is unknown. Although neuroinflammation is postulated to play an important role in aging and neurodegenerative diseases such as Alzheimer disease (AD), it is unclear whether HIV accelerates aging or increases the risk for AD. We examined the brains of 9 elderly HIV-positive subjects on cART without co-infection by hepatitis C virus compared to 7 elderly HIV-negative subjects. Microglial and astrocyte activation and AD pathologic change in association with systemic comorbidities and neurocognitive assessment were evaluated. There was no difference in microglial or astrocyte activation between our HIV-positive and HIV-negative cohorts. One HIV-positive subject and 2 HIV-negative subjects demonstrated significant amyloid deposition, predominantly in the form of diffuse senile plaques, but these individuals were cognitively normal. Neurofibrillary tangles were sparse in the HIV-positive cohort. There was a high prevalence of cardiovascular comorbidities in all subjects. These findings suggest that multiple factors likely contribute to aging and cognitive impairment in elderly HIV-positive individuals on cART.

An exploratory pilot study on the involvement of APOE, HFE, C9ORF72 variants and comorbidities in neurocognitive and physical performance in a group of HIV-infected people

Cognitive decline of aging is modulated by chronic inflammation and comorbidities. In people with HIV-infection (PWH) it may also be affected by HIV-induced inflammation, lifestyle and long-term effects of antiretroviral therapies (ART). The role of genetics in the susceptibility to HIV-associated neurocognitive disorders (HAND) is not fully understood. Here we explored the possible relations among variants in 3 genes involved in inflammation and neurodegenerative disorders (APOE: ε2/ε3/ε4; HFE: H63D; C9ORF72: hexanucleotide expansions ≥ 9 repeats), cognitive/functional impairment (MiniMental State Examination MMSE, Clock Drawing Test CDT, Short Physical Performance Battery SPPB), comorbidities and HIV-related variables in a cohort of > 50 years old PWH (n = 60) with at least 10 years efficient ART. Patients with diabetes or hypertension showed significantly lower MMSE (p = .031) or SPPB (p = .010) scores, respectively, while no relations between HIV-related variables and cognitive/functional scores were observed. Patients with at least one APOEε3 allele had higher CDT scores (p = .019), APOEε2/ε4 patients showing the lowest scores in all tests. Patients with HFE-H63D variant showed more frequently hypertriglyceridemia (p = .023) and those harboring C9ORF72 expansions > 9 repeats had higher CD4⁺-cell counts (p = .032) and CD4% (p = .041). Multiple linear regression analysis computed to verify possible associations among cognitive/functional scores and all variables further suggested positive association between higher CDT scores and the presence of at least one APOEε3 allele (2,2; 95% CI [0,03 0,8]; p = .037), independent of other variables, although the model did not reach the statistical significance (p = .14). These data suggest that in PWH on efficient ART cognitive abilities and physical performances may be partly associated with comorbidities and genetic background. However, further analyses are needed to establish whether they could be also dependent and influenced by comorbidities and genetic background.

Using plasma proteomics to investigate viral infections of the central nervous system including patients with HIV-associated neurocognitive disorders

State-of-the-art liquid chromatography/mass spectrometry (LC/MS)-based proteomic technologies, using microliter amounts of patient plasma, can detect and quantify several hundred plasma proteins in a high throughput fashion, allowing for the discovery of clinically relevant protein biomarkers and insights into the underlying pathobiological processes. Using such an in-house developed high throughput plasma proteomics allowed us to identify and quantify > 400 plasmas proteins in 15 min per sample, i.e., a throughput of 100 samples/day. We demonstrated the clinical applicability of our method in this pilot study by mapping the plasma proteomes from patients infected with human immunodeficiency virus (HIV) or herpes virus, both groups with involvement of the central nervous system (CNS). We found significant disease-specific differences in the plasma proteomes. The most notable difference was a decrease in the levels of several coagulation-associated proteins in HIV vs. herpes virus, among other dysregulated biological pathways providing insight into the differential pathophysiology of HIV compared to herpes virus infection. In a subsequent analysis, we found several plasma proteins associated with immunity and metabolism to differentiate patients with HIV-associated neurocognitive disorders (HAND) compared to cognitively normal people with HIV (PWH), suggesting the presence of plasma-based biomarkers to distinguishing HAND from cognitively normal PWH. Overall, our high-throughput plasma proteomics pipeline enables the identification of distinct proteomic signatures of HIV and herpes virus, which may help illuminate divergent pathophysiology behind virus-associated neurological disorders.

Apolipoprotein E Genetic Variation and Its Association With Cognitive Function in Rural-Dwelling Older South Africans

Apolipoprotein E (APOE) 𝜀4 allele carrier status is well known for its association with an increased likelihood of developing Alzheimer’s disease, but its independent role in cognitive function is unclear. APOE genetic variation is understudied in African populations; hence, this cross-sectional study in a rural South African community examined allele and genotype frequencies, and their associations with cognitive function. Cognitive function was assessed using two different screening methods to produce a total cognition score and four domain-specific cognition scores for verbal episodic memory, executive function, language, and visuospatial ability. Cognitive phenotype and APOE genotype data were used to determine whether APOE variation was significantly associated with cognitive function in this population. Observed allele frequencies for 1776 participants from the HAALSI study [age 40–80years (mean=56.19); 58.2% female] were 58.1% (𝜀3), 25.4% (𝜀4) and 16.5% (𝜀2). Allele distributions were similar to the African super population, but different from all non-African super populations from the 1,000 Genomes Project. The 𝜀3 homozygous genotype was most common (34.9%) and used as the base genotype for comparison in regression models. Four models were tested for each of the five cognitive phenotypes to explore association of APOE variation with cognitive function. In the first model assessing association with all genotypes for all individuals, marginally significant associations were observed for 𝜀2 homozygotes where executive function scored higher by ~0.5 standard deviations (p=0.037, SE=0.23), and for 𝜀3/𝜀4 heterozygotes where visuospatial ability scores were lower (p=0.046, SE=0.14). These did not survive correction for multiple testing. Regional African population differences were observed at the APOE locus. Marginally, significant associations between APOE genotype, and executive function and visuospatial ability indicate the need for larger studies to better examine these associations in African populations. Furthermore, longitudinal data could shed light on APOE genetic association with rate of change, or decline, in cognitive function.

Higher CSF Ferritin Heavy-Chain (Fth1) and Transferrin Predict Better Neurocognitive Performance in People with HIV

HIV-associated neurocognitive disorder (HAND) remains prevalent despite antiretroviral therapy and involves white matter damage in the brain. Although iron is essential for myelination and myelin maintenance/repair, its role in HAND is largely unexplored. We tested the hypotheses that cerebrospinal fluid (CSF) heavy-chain ferritin (Fth1) and transferrin, proteins integral to iron delivery and myelination, are associated with neurocognitive performance in people with HIV (PWH). Fth1, transferrin, and the pro-inflammatory cytokines TNF-α and IL-6 were quantified in CSF at baseline (entry) in 403 PWH from a prospective observational study who underwent serial, comprehensive neurocognitive assessments. Associations of Fth1 and transferrin with Global Deficit Score (GDS)-defined neurocognitive performance at baseline and 30-42 months of follow-up were evaluated by multivariable regression. While not associated with neurocognitive performance at baseline, higher baseline CSF Fth1 predicted significantly better neurocognitive performance over 30 months in all PWH (p < 0.05), in PWH aged < 50 at 30, 36, and 42 months (all p < 0.05), and in virally suppressed PWH at all three visit time-points (all p < 0.01). Higher CSF transferrin was associated with superior neurocognitive performance at all visits, primarily in viremic individuals (all p < 0.05). All associations persisted after adjustment for neuro-inflammation. In summary, higher CSF Fth1 is neuroprotective over prolonged follow-up in all and virally suppressed PWH, while higher CSF transferrin may be most neuroprotective during viremia. We speculate that higher CSF levels of these critical iron-delivery proteins support improved myelination and consequently, neurocognitive performance in PWH, providing a rationale for investigating their role in interventions to prevent and/or treat HAND.

Influence of APOE locus on poor prognosis of COVID-19

The COVID-19 pandemic has infected over 25 million of people worldwide, 5% of whom evolved to death and, among of the active cases, more than 60 thousand are classified as critical or severe. Recent studies revealed that ApoE, a protein encoded by APOE gene, may increase the risk of severe COVID-19 cases. ApoE has been involved with prevention of tissue damage and promotion of adaptative immune response in the lungs. This study investigated frequencies distribution of alleles that alter the ApoE expression in lung tissues to trace a profile of these variants and associate them to COVID-19 clinical outcomes. Data about APOE expression levels was obtained from the Genotype-Tissue Expression Project and the allele frequencies of APOE variants was acquired from the populations included in the phase 3 release of the 1000 Genomes Project. A total of 128 variants showed a significant impact on the APOE expression in lung tissues (p < 0.0001). Linkage Disequilibrium analysis revealed that 98 variants were closely grouped into seven distinct haplotype blocks, of which six were composed of variants that significantly decrease APOE gene expression in the lungs. Most of the haplotypes with higher impact on APOE expression showed greater frequencies in Europeans and lower in Africans, which implies that European populations might be more susceptible to SARS-CoV-2 infection. The present study indicates a potential genetic contribution of APOE expression-modifying variants in modulating the prognosis of COVID-19.

An update in toxicology of ageing

The field of ageing research has been rapidly advancing in recent decades and it had provided insight into the complexity of ageing phenomenon. However, as the organism-environment interaction appears to significantly affect the organismal pace of ageing, the systematic approach for gerontogenic risk assessment of environmental factors has yet to be established. This puts demand on development of effective biomarker of ageing, as a relevant tool to quantify effects of gerontogenic exposures, contingent on multidisciplinary research approach. Here we review the current knowledge regarding the main endogenous gerontogenic pathways involved in acceleration of ageing through environmental exposures. These include inflammatory and oxidative stress-triggered processes, dysregulation of maintenance of cellular anabolism and catabolism and loss of protein homeostasis. The most effective biomarkers showing specificity and relevancy to ageing phenotypes are summarized, as well. The crucial part of this review was dedicated to the comprehensive overview of environmental gerontogens including various types of radiation, certain types of pesticides, heavy metals, drugs and addictive substances, unhealthy dietary patterns, and sedentary life as well as psychosocial stress. The reported effects in vitro and in vivo of both recognized and potential gerontogens are described with respect to the up-to-date knowledge in geroscience. Finally, hormetic and ageing decelerating effects of environmental factors are briefly discussed, as well.

Nusinersen Modulates Proteomics Profiles of Cerebrospinal Fluid in Spinal Muscular Atrophy Type 1 Patients

Spinal muscular atrophy (SMA) type 1 is a severe infantile autosomal-recessive neuromuscular disorder caused by a survival motor neuron 1 gene (SMN1) mutation and characterized by progressive muscle weakness. Without supportive care, SMA type 1 is rapidly fatal. The antisense oligonucleotide nusinersen has recently improved the natural course of this disease. Here, we investigated, with a functional proteomic approach, cerebrospinal fluid (CSF) protein profiles from SMA type 1 patients who underwent nusinersen administration to clarify the biochemical response to the treatment and to monitor disease progression based on therapy. Six months after starting treatment (12 mg/5 mL × four doses of loading regimen administered at days 0, 14, 28, and 63), we observed a generalized reversion trend of the CSF protein pattern from our patient cohort to that of control donors. Notably, a marked up-regulation of apolipoprotein A1 and apolipoprotein E and a consistent variation in transthyretin proteoform occurrence were detected. Since these multifunctional proteins are critically active in biomolecular processes aberrant in SMA, i.e., synaptogenesis and neurite growth, neuronal survival and plasticity, inflammation, and oxidative stress control, their nusinersen induced modulation may support SMN improved-expression effects. Hence, these lipoproteins and transthyretin could represent valuable biomarkers to assess patient responsiveness and disease progression.

Brain amyloid in virally suppressed HIV-associated neurocognitive disorder

Objective

To determine whether virally suppressed HIV neuropathogenesis, a chronic neuroinflammatory state, promotes abnormal brain amyloid deposition.

Methods

A total of 10 men with virally suppressed HIV-associated neurocognitive disorder (HAND), aged 46–68 years, underwent ¹¹C-labeled Pittsburgh compound B PET. Data from the Australian Imaging, Biomarkers and Lifestyle (AIBL), including 39 cognitively normal individuals (aged 60–74 years), 7 individuals with mild cognitive impairment (MCI) (aged 64–71 years), and 11 individuals with Alzheimer disease (AD) (aged 55–74 years), were used as reference. Apart from more women, the AIBL cohort was demographically comparable with the HIV sample. Also, the AIBL PET data did not differ by sex. Cerebellum standardized uptake value ratio amyloid values within 22 regions of interest were estimated. In the HIV sample, apolipoprotein E (APOE) was available in 80%, CSF biomarkers in 60%, and 8–10 years of long-term health outcomes in 100%.

Results

HAND and the AIBL group with no cognitive deficits had similar amyloid deposition, which was lower than that in both the MCI and AD groups. At the individual level, one HAND case showed high amyloid deposition consistent with AD. This case also had a CSF-AD–like profile and an E4/E4 for APOE. Clinically, this case declined over 18 years with mild HAND symptoms first, followed by progressive memory decline 8–9 years after the study PET, then progression to severe dementia within 2–3 years, and lived a further 6 years. Another HAND case showed increased amyloid deposition restricted to the hippocampi. Two other HAND cases showed abnormally decreased amyloid in subcortical areas.

Conclusions

Relative to cognitively normal older controls, brain amyloid burden does not differ in virally suppressed HAND at the group level. However, individual analyses show that abnormally high and low amyloid burden occur.

A candidate gene study of intermediate histopathological phenotypes in HIV-associated neurocognitive disorders

HIV-associated neurocognitive disorders (HAND) describe a spectrum of neuropsychological impairment caused by HIV-1 infection. While the sequence of cellular and physiological events that lead to HAND remains obscure, it likely involves chronic neuroinflammation. Host genetic markers that increase the risk for HAND have been reported, but replication of such studies is lacking, possibly due to inconsistent application of a behavioral phenotype across studies. In the current study, we used histopathologic phenotypes in order to validate putative risk alleles for HAND. The National NeuroAIDS Tissue Consortium, a longitudinal study of the neurologic manifestations of HIV. Data and specimens were obtained from 175 HIV-infected adults. After determining several potential covariates of neurocognitive functioning, we quantified levels of six histopathological markers in the frontal lobe in association with neurocognitive functioning: SYP, MAP 2, HLA-DR, Iba1, GFAP, and β-amyloid. We then determined alleles of 15 candidate genes for their associations with neurocognitive functioning and histopathological markers. Finally, we identified the most plausible causal pathway based on our data using a multi-stage linear regression-based mediation analysis approach. None of the genetic markers were associated with neurocognitive functioning. Of the histopathological markers, only MAP 2 and SYP were associated with neurocognitive functioning; however, MAP 2 and SYP did not vary as a function of genotype. Mediation analysis suggests a causal pathway in which presynaptic degeneration (SYP) leads to somatodendritic degeneration (MAP 2) and ultimately neurocognitive impairment. This study did not support the role of host genotype in the histopathology underlying HAND. The findings lend further support for synaptodendritic degeneration as the proximal underlying neuropathological substrate of HAND.

Beyond the CNS: The many peripheral roles of APOE

Apolipoprotein E (APOE) is a multifunctional protein synthesized and secreted by multiple mammalian tissues. Although hepatocytes contribute about 75% of the peripheral pool, APOE can also be expressed in adipose tissue, the kidney, and the adrenal glands, among other tissues. High levels of APOE production also occur in the brain, where it is primarily synthesized by glia, and peripheral and brain APOE pools are thought to be distinct. In humans, APOE is polymorphic, with three major alleles (ε2, ε3, and ε4). These allelic forms dramatically alter APOE structure and function. Historically, the vast majority of research on APOE has centered on the important role it plays in modulating risk for cardiovascular disease and Alzheimer's disease. However, the established effects of this pleiotropic protein extend well beyond these two critical health challenges, with demonstrated roles across a wide spectrum of biological conditions, including adipose tissue function and obesity, metabolic syndrome and diabetes, fertility and longevity, and immune function. While the spectrum of biological systems in which APOE plays a role seems implausibly wide at first glance, there are some potential unifying mechanisms that could tie these seemingly disparate disorders together. In the current review, we aim to concisely summarize a wide breadth of APOE-associated pathologies and to analyze the influence of APOE in the development of several distinct disorders in order to provide insight into potential shared mechanisms implied in these various pathophysiological processes.

White Matter Abnormalities Linked to Interferon, Stress Response, and Energy Metabolism Gene Expression Changes in Older HIV-Positive Patients on Antiretroviral Therapy

Neurocognitive impairment (NCI) remains a significant cause of morbidity in human immunodeficiency virus (HIV)-positive individuals despite highly active antiretroviral therapy (HAART). White matter abnormalities have emerged as a key component of age-related neurodegeneration, and accumulating evidence suggests they play a role in HIV-associated neurocognitive disorders. Viral persistence in the brain induces chronic inflammation associated with lymphocytic infiltration, microglial proliferation, myelin loss, and cerebrovascular lesions. In this study, gene expression profiling was performed on frontal white matter from 34 older HIV+ individuals on HAART (18 with NCI) and 24 HIV-negative controls. We used the NanoString nCounter platform to evaluate 933 probes targeting inflammation, interferon and stress responses, energy metabolism, and central nervous system-related genes. Viral loads were measured using single-copy assays. Compared to HIV- controls, HIV+ individuals exhibited increased expression of genes related to interferon, MHC-1, and stress responses, myeloid cells, and T cells and decreased expression of genes associated with oligodendrocytes and energy metabolism in white matter. These findings correlated with increased white matter inflammation and myelin pallor, suggesting interferon (IRFs, IFITM1, ISG15, MX1, OAS3) and stress response (ATF4, XBP1, CHOP, CASP1, WARS) gene expression changes are associated with decreased energy metabolism (SREBF1, SREBF2, PARK2, TXNIP) and oligodendrocyte myelin production (MAG, MOG), leading to white matter dysfunction. Machine learning identified a 15-gene signature predictive of HIV status that was validated in an independent cohort. No specific gene expression patterns were associated with NCI. These findings suggest therapies that decrease chronic inflammation while protecting mitochondrial function may help to preserve white matter integrity in older HIV+ individuals.

The Iowa Gambling Task on HIV-infected subjects

HIV-associated neurocognitive disorders (HAND) are characterized by cognitive, behavioral, and motor dysfunctions, which impact daily functioning and are predictive of poor survival among patients. The diagnosis of HAND is marked by clinically significant declines in multiple domains of neurocognitive functioning. Some patients diagnosed with HAND have social problem; however, higher brain dysfunction is not detected in general neuropsychological assessments and the intelligence quotient may remain unchanged. Impaired decision-making may reduce social and occupational qualities of life. The Iowa Gambling Task (IGT) has been developed as a task to evaluate risk predictions at the time of decision-making. In the present study, 38 HIV-infected patients enrolled in our hospital performed IGT and we investigated whether the results obtained are associated with HAND. The median net IGT score of all HIV-infected subjects was significantly lower than that of healthy controls. Patients diagnosed with HAND accounted for 43.8% of the negative net score group. We elucidated the relationship between the net IGT score and HAND for the first time. We think that IGT is a good tool to detect decision-making impairment for ANI and MND. Careful follow-ups of the progression of HAND and increased awareness among HIV-infected patients and medical care workers of the risk of social behavioral disorders, which negatively impact daily life before they are detected, are needed in order to prevent deteriorations in the quality of life of these patients.

Pathogenesis of age-related HIV neurodegeneration

People over the age of 50 are the fastest growing segment of the HIV-infected population in the USA. Although antiretroviral therapy has remarkable success controlling the systemic HIV infection, HIV-associated neurocognitive disorder (HAND) prevalence has increased or remained the same among this group, and cognitive deficits appear more severe in aged patients with HIV. The mechanisms of HAND in the aged population are not completely understood; a leading hypothesis is that aged individuals with HIV might be at higher risk of developing Alzheimer's disease (AD) or one of the AD-related dementias (ADRD). There are a number of mechanisms through which chronic HIV disease alone or in combination with antiretroviral therapy and other comorbidities (e.g., drug use, hepatitis C virus (HCV)) might be contributing to HAND in individuals over the age of 50 years, including (1) overlapping pathogenic mechanisms between HIV and aging (e.g., decreased proteostasis, DNA damage, chronic inflammation, epigenetics, vascular), which could lead to accelerated cellular aging and neurodegeneration and/or (2) by promoting pathways involved in AD/ADRD neuropathogenesis (e.g., triggering amyloid β, Tau, or α-synuclein accumulation). In this manuscript, we will review some of the potential common mechanisms involved and evidence in favor and against a role of AD/ADRD in HAND.

Childhood trauma interacts with ApoE to influence neurocognitive function in women living with HIV

HIV-associated neurocognitive disorder (HAND) describes a spectrum of behavioural, motor and cognitive disturbances that can occur secondary to HIV infection. Less severe forms of the disorder persist despite advances in antiretroviral medication efficacy and availability. Childhood trauma (CT) may predispose individuals to developing HAND. As genetic variation in human apolipoprotein E (ApoE) has been implicated in cognitive decline and may mediate the development of long-term health outcomes following CT, we investigated the influence of ApoE and CT on cognitive function in the context of HIV. One hundred twenty-eight HIV-positive Xhosa women completed the Childhood Trauma Questionnaire-Short Form (CTQ-SF) as well as the HIV Neurobehavioural Research Center neurocognitive test battery. rs7412 and rs429358 were genotyped using KASP assays, and this data was used to determine the ApoE isoform. Baseline differences in demographic and clinical variables according to CT exposure were calculated. Analysis of covariance was used to assess the contributions of CT and ApoE variants, as well as their interaction, to cognitive function. Eighty-eight participants reported experiencing CT. The rs7412 C allele protected against the harmful effect of CT on motor scores using an additive model. The interaction of ApoE ε4 and CT was associated with worse attention/working memory scores. ApoE ε4, alone and in combination with CT, is associated with poorer cognitive function. Further research into this gene-environment interaction may assist in identifying at-risk individuals for targeted interventions.

The Genetic Variability of APOE in Different Human Populations and Its Implications for Longevity

Human longevity is a complex phenotype resulting from the combinations of context-dependent gene-environment interactions that require analysis as a dynamic process in a cohesive ecological and evolutionary framework. Genome-wide association (GWAS) and whole-genome sequencing (WGS) studies on centenarians pointed toward the inclusion of the apolipoprotein E (APOE) polymorphisms ε2 and ε4, as implicated in the attainment of extreme longevity, which refers to their effect in age-related Alzheimer's disease (AD) and cardiovascular disease (CVD). In this case, the available literature on APOE and its involvement in longevity is described according to an anthropological and population genetics perspective. This aims to highlight the evolutionary history of this gene, how its participation in several biological pathways relates to human longevity, and which evolutionary dynamics may have shaped the distribution of APOE haplotypes across the globe. Its potential adaptive role will be described along with implications for the study of longevity in different human groups. This review also presents an updated overview of the worldwide distribution of APOE alleles based on modern day data from public databases and ancient DNA samples retrieved from literature in the attempt to understand the spatial and temporal frame in which present-day patterns of APOE variation evolved.

Risk Factors and Pathogenesis of HIV-Associated Neurocognitive Disorder: The Role of Host Genetics

Neurocognitive impairments associated with human immunodeficiency virus (HIV) infection remain a considerable health issue for almost half the people living with HIV, despite progress in HIV treatment through combination antiretroviral therapy (cART). The pathogenesis and risk factors of HIV-associated neurocognitive disorder (HAND) are still incompletely understood. This is partly due to the complexity of HAND diagnostics, as phenotypes present with high variability and change over time. Our current understanding is that HIV enters the central nervous system (CNS) during infection, persisting and replicating in resident immune and supporting cells, with the subsequent host immune response and inflammation likely adding to the development of HAND. Differences in host (human) genetics determine, in part, the effectiveness of the immune response and other factors that increase the vulnerability to HAND. This review describes findings from studies investigating the role of human host genetics in the pathogenesis of HAND, including potential risk factors for developing HAND. The similarities and differences between HAND and Alzheimer's disease are also discussed. While some specific variations in host genes regulating immune responses and neurotransmission have been associated with protection or risk of HAND development, the effects are generally small and findings poorly replicated. Nevertheless, a few specific gene variants appear to affect the risk for developing HAND and aid our understanding of HAND pathogenesis.