Biomarkers of neuronal injury and amyloid metabolism in the cerebrospinal fluid of patients infected with HIV-1 subtypes B and C

Sex related differences in cognitive deficits: Disrupted Arc/Arg3.1 signaling in an HIV model

Combined and highly active anti-retroviral therapies (cART) have transitioned HIV into a more chronic disease. Roughly half of people living with HIV (PLWH) still experience neurocognitive disorders, albeit less severely than in the pre-cART era. Sex-related effects on memory/cognition remain understudied, although the percentage of PLWH that are female has increased. We utilized a transgenic mouse model of HIV that conditionally expresses HIV-1 Tat1-86 in the CNS to examine cognitive behaviors and the expression of biomarkers related to learning and memory in both sexes. Tat+ males exhibited deficits in spatial learning/memory and object recognition, while Tat+ females showed enhanced fear memory. We investigated the involvement of activity-regulated cytoskeleton-associated protein (Arc), which is induced by novel experience related to learning/memory. We observed hippocampal Arc induction following foot shock in Tat+ females but not Tat+ males. Hippocampal levels of Arc, amyloid β (Aβ) monomers/oligomers and pCREB were altered in a sex-specific manner. CREB activity, which is highly associated with Arc induction, was reduced only in Tat+ males. Tat exposure also decreased Arc expression in cultured human neurons. Thus, HIV-1 Tat effects on CREB/Arc signaling may differ between sexes, contributing to differences in cognitive deficits observed here and in PLWH.

The potential of five c-miRNAs as serum biomarkers for Late-Onset Alzheimer's disease diagnosis: miR-10a-5p, miR-29b-2-5p, miR-125a-5p, miR-342-3p, and miR-708-5p

The nervous system is rich in miRNAs, indicating an important role of these molecules in regulating processes associated with cognition, memory, and others. Therefore, qualitative and quantitative imbalances involving such miRNAs may be involved in dementia contexts, including Late-Onset Alzheimer's Disease (LOAD). To test the viability of circulating miRNAs (c-miRNAs) as biomarkers for LOAD, we proceed accordingly to the following reasoning. The first stage was to discover and identify profile of c-miRNAs by RNA sequencing (RNA-Seq). For this purpose, blood serum samples were used from LOAD patients (n = 5) and cognitively healthy elderly control group (CTRL_CH) (n = 5), all over 70 years old. We identified seven c-miRNAs differentially expressed (p ≤ 0.05) in the serum of LOAD patients compared to CTRL_CH (miR-10a-5p; miR-29b-2-5p; miR-125a-5p; miR-342-3p, miR-708-5p, miR-380-5p and miR-340-3p). Of these, five (p ≤ 0.01) were selected for in silico analysis (miR-10a-5p; miR-29b-2-5p; miR-125a-5p; miR-342-3p, miR-708-5p), for which 44 relevant target genes were found regulated by these c-miRNAs and related to LOAD. Through the analysis of these target genes in databases, it was possible to observe that they have functions related to the development and progress of LOAD, directly or indirectly connecting the different Alzheimer's pathways. Thus, this work found five promising serum c-miRNAs as options for biomarkers contributing to LOAD diagnosis. Our study shows the complex network between these molecules and LOAD, supporting the relevance of studies using c-miRNAs in dementia contexts.

CSF Extracellular Vesicle Aβ42 and Tau/Aβ42 Ratio Are Associated with Cognitive Impairment in Older People with HIV

HIV-associated neurocognitive disorders (HAND) remain prevalent despite viral suppression on antiretroviral therapy (ART). Older people with HIV (PWH) are also at risk for amnestic mild cognitive impairment (aMCI) and Alzheimer's disease (AD). β-amyloid (Aβ) and Tau biomarkers are associated with aMCI/AD, but their relationship to HAND is unclear. Given the role of extracellular vesicles (EVs) in age-related neurological disorders, we investigated soluble and EV-associated Aβ42, total Tau, NFL, GFAP, ICAM-1, VCAM-1, and CRP in relation to cognitive impairment in PWH. Plasma and CSF EVs were isolated from 184 participants (98 PWH on ART and 86 HIV- controls). Biomarkers were measured using Meso Scale Discovery assays. The median age of PWH was 53 years, and 52% were diagnosed with mild forms of HAND. PWH had increased plasma NFL (p = 0.04) and CSF Aβ42 (p = 0.0003) compared with HIV- controls but no significant difference in Tau or EV-associated forms of these markers. CSF EV Aβ42 was decreased (p = 0.0002) and CSF EV Tau/Aβ42 ratio was increased (p = 0.001) in PWH with HAND vs. no HAND, while soluble forms of these markers showed no significant differences. Decreased CSF EV Aβ42 (p < 0.0001) and an increased CSF EV Tau/Aβ42 ratio (p = 0.0003) were associated with lower neurocognitive T scores in age-adjusted models; an optimal model included both CSF EV Aβ42 and plasma NFL. Levels of soluble, but not EV-associated, ICAM-1, VCAM-1, and CRP were increased in PWH with HAND vs. no HAND (p < 0.05). These findings suggest that decreased Aβ42 and an increased Tau/Aβ42 ratio in CSF EVs are associated with cognitive impairment in older PWH, and these EV-associated biomarkers may help to distinguish aMCI/AD from HIV-related cognitive disorders in future studies.

Increasing Neuroinflammation Relates to Increasing Neurodegeneration in People with HIV

BACKGROUND

HIV infection causes neuroinflammation and immune activation (NIIA) and systemic inflammation and immune activation (SIIA), which in turn drive neurodegeneration (ND). Cross-sectionally, higher levels of NIIA biomarkers correlate with increased biomarkers of ND. A more convincing confirmation would be a longitudinal demonstration.

METHODS

PWH in the US multisite CHARTER Aging project were assessed at a baseline visit and after 12 years using standardized evaluations. We measured a panel of 14 biomarkers of NIIA, SIIA, and ND in plasma and CSF at two time points and calculated changes from baseline to the 12-year visit. Factor analysis yielded simplified indices of NIIA, SIIA, and ND.

RESULTS

The CSF NIIA factor analysis yielded Factor1 loading on soluble tumor necrosis factor type-2 (sTNFR-II) and neopterin, and Factor2, loading on MCP1, soluble CD14, and IL-6. The SIIA factor analysis yielded Factor1 loading on CRP, D-dimer, and Neopterin; Factor2 loading on sTNFR-II. The ND analysis yielded Factor1 loading on Phosphorylated tau (p-tau) and Aβ42; Factor2 loading on NFL. NIIA Factor1, but not Factor2, correlated with increases in CSF NFL (r = 0.370, p = 0.0002).

CONCLUSIONS

Increases in NIIA and SIIA in PWH were associated with corresponding increases in ND, suggesting that reducing neuro/systemic inflammation might slow or reverse neurodegeneration.

Neuropathogenesis of HIV-1: insights from across the spectrum of acute through long-term treated infection

This review outlines the neuropathogenesis of HIV, from initial HIV entry into the central nervous system (CNS) to chronic infection, focusing on key advancements in the last 5 years. Discoveries regarding acute HIV infection reveal timing and mechanisms of early HIV entry and replication in the CNS, early inflammatory responses, and establishment of genetically distinct viral reservoirs in the brain. Recent studies additionally explore how chronic HIV infection is maintained in the CNS, examining how the virus remains in a latent "hidden" state in diverse cells in the brain, and how this leads to sustained pathological inflammatory responses. Despite viral suppression with antiretroviral therapy, HIV can persist and even replicate in the CNS, and associate with ongoing neuropathology including CD8 + T-lymphocyte mediated encephalitis. Crucial investigation to advance our understanding of the immune mechanisms that both control viral infection and lead to pathological consequences in the brain is necessary to develop treatments to optimize long-term neurologic health in people living with HIV.

The Role of Pannexin-1 Channels in HIV and NeuroHIV Pathogenesis

The human immunodeficiency virus-1 (HIV) enters the brain shortly after infection, leading to long-term neurological complications in half of the HIV-infected population, even in the current anti-retroviral therapy (ART) era. Despite decades of research, no biomarkers can objectively measure and, more importantly, predict the onset of HIV-associated neurocognitive disorders. Several biomarkers have been proposed; however, most of them only reflect late events of neuronal damage. Our laboratory recently identified that ATP and PGE2, inflammatory molecules released through Pannexin-1 channels, are elevated in the serum of HIV-infected individuals compared to uninfected individuals and other inflammatory diseases. More importantly, high circulating ATP levels, but not PGE2, can predict a decline in cognition, suggesting that HIV-infected individuals have impaired ATP metabolism and associated signaling. We identified that Pannexin-1 channel opening contributes to the high serological ATP levels, and ATP in the circulation could be used as a biomarker of HIV-associated cognitive impairment. In addition, we believe that ATP is a major contributor to chronic inflammation in the HIV-infected population, even in the anti-retroviral era. Here, we discuss the mechanisms associated with Pannexin-1 channel opening within the circulation, as well as within the resident viral reservoirs, ATP dysregulation, and cognitive disease observed in the HIV-infected population.

Soluble CD14 is subtype-dependent in serum but not in cerebrospinal fluid in people with HIV

Monocytes and macrophages activation are crucial in human immunodeficiency virus (HIV) central nervous system (CNS) infection and HIV associated neurocognitive disorders (HAND) pathogenesis. The soluble form of CD14 (sCD14) is a marker of monocyte activation. We hypothesized that sCD14 levels would be lower in people with HIV-1 subtype C (HIV-1C) than in HIV-1B owing to a variant Tat cysteine dimotif (C30S31) with reduced chemotactic activity. A total of 68 paired cerebrospinal fluid (CSF) and blood samples from people with HIV (PWH); 27 samples of the HIV-1B subtype and 40 of the non-B HIV-1 subtypes (including 26,HIV-1C), and 18 HIV-negative controls were included. sCD14 levels were quantified using a high-sensitivity enzyme-linked immunosorbent assay. sCD14 increase in serum, but not in CSF, was higher in samples from HIV-1B than HIV-1C (p = 0.002; Cohen's d, 0.7). CSF or serum sCD14 values were not correlated with global deficit score or specific cognitive domains. The impact of HIV-1 on monocyte stimulation biomarkers evaluated by sCD14 in serum was subtype-dependent, higher in HIV-1B than HIV-1C, consistent with reduced chemotactic activity as hypothesized.

Higher Cerebrospinal Fluid Soluble Urokinase-type Plasminogen Activator Receptor, But Not Interferon γ-inducible Protein 10, Correlate With Higher Working Memory Deficits

BACKGROUND

We hypothesized that the induction of monocyte activation biomarkers, especially soluble urokinase-type plasminogen activator receptor (suPAR) and interferon γ-inducible protein 10 (IP-10), is lower in HIV-1C than HIV-1B, owing to a defective Tat cysteine dimotif (C30S).

METHODS

A total of 68 paired cerebrospinal fluid (CSF) and blood samples from people with HIV (PWH), free of CNS opportunistic infections, from a Southern Brazil outpatient HIV clinic were evaluated such as HIV-1B subtype (n = 27), HIV-1C (n = 26), other (n = 15), and 19 HIV-negative controls. The levels of suPAR, IP-10, neopterin, and β2 microglobulin (β2m) in the CSF and serum were quantified using different immunoassays.

RESULTS

Overall, in PWH, increases in CSF suPAR, CSF/serum suPAR, and CSF/serum β2m correlated with worse working memory deficits (r = 0.303, 0.353, and 0.289, respectively, all P < 0.05). The medians of IP-10, suPAR, neopterin, and β2m in CSF and serum and the CSF/serum ratio and suPAR index were comparable between the HIV-1B and HIV-1C subtypes. CSF IP-10 and neopterin and serum IP-10 and suPAR levels were higher in PWH than the HIV-negative controls (P = 0.015, P = 0.001, P < 0.0001, and P < 0.001, respectively). The serum β2m level was higher in HIV-associated dementia than neuropsychologically normal or asymptomatic (P = 0.024).

DISCUSSION

We observed that higher levels of CSF suPAR and the suPAR quotient correlated with worse working memory deficit. Elevated levels of monocyte activation were similar in both HIV-1 B and C subtypes, providing no evidence of reduced neuropathogenicity of HIV-1 subtype C Tat compared with subtype B.

Patterns of Cerebrospinal Fluid Alzheimer’s Dementia Biomarkers in People Living with HIV: Cross-Sectional Study on Associated Factors According to Viral Control, Neurological Confounders and Neurocognition

People living with HIV (PLWH) age with an excess burden of comorbidities that may increase the incidence of age-related complications. There is controversy surrounding the hypothesis that HIV can accelerate neurodegeneration and Alzheimer’s dementia (AD). We performed a retrospective study to analyze the distribution of cerebrospinal fluid (CSF) AD biomarkers (beta amyloid 1–42 fragment, tau, and phosphorylated tau) in adult PLWH (on cART with undetectable viremia, n = 136, with detectable viremia, n = 121, and with central nervous system CNS disorders regardless of viremia, n = 72) who underwent a lumbar puncture between 2008 to 2018; HIV-negative controls with AD were included (n = 84). Five subjects (1.5%) presented CSF biomarkers that were compatible with AD: one was diagnosed with AD, whereas the others showed HIV encephalitis, multiple sclerosis, cryptococcal meningitis, and neurotoxoplasmosis. Regardless of confounders, 79.6% of study participants presented normal CSF AD biomarkers. Isolated abnormalities in CSF beta amyloid 1–42 (7.9%) and tau (10.9%) were associated with age, biomarkers of intrathecal injury, and inflammation, although no HIV-specific feature was associated with abnormal CSF patterns. CSF levels of AD biomarkers very poorly overlapped between HIV-positive clinical categories and AD controls. Despite the correlations with neurocognitive performance, the inter-relationship between amyloid and tau proteins in PLWH seem to differ from that observed in AD subjects; the main driver of the isolated increase in tau seems represented by non-specific CNS inflammation, whereas the mechanisms underlying isolated amyloid consumption remain unclear.

IgG intrathecal synthesis in HIV-associated neurocognitive disorder (HAND) according to the HIV-1 subtypes and pattern of HIV RNA in CNS and plasma compartments

We hypothesized that humoral immunity stimulation in the CNS in HIV-1C patients would be lower than that in HIV-1B due to a defective Tat chemokine dimotif (C30C31) that might influence cellular trafficking and CNS inflammation. Sixty-eight paired CSF and blood samples from people with HIV (PWH), free of CNS opportunistic infections, were included, HIV-1B (n = 27), HIV-1C (n = 26), and HIV negative (n = 25). IgG intrathecal synthesis was assayed using quantitative and qualitative methods. IgG oligoclonal bands (OCB) in CSF were observed in 51% of PWH, comparable between HIV-1B and HIV-1C, as well as the medians of IgG intrathecal synthesis formulas. The group with HIV infection aviremic in CSF and blood showed 75% of OCB. There was a poor positive correlation between the IgG quotient and GDS. The impact of HIV-1 on IgG intrathecal production was not subtype dependent. Low-grade CNS intrathecal IgG production persists in HIV CNS infection even in PWH with CSF and blood HIV RNA controlled.

Neurocytoskeleton Proteins in Cerebrospinal Fluid of People With HIV-1 Subtypes B and C

BACKGROUND

The objective was to compare the effect of HIV-1C and HIV-1B subtypes on neurofilament light (NfL) cerebrospinal fluid (CSF) levels and ratios of NfL to tau proteins. Additional comparisons were performed between people with HIV (PWH), participants with Alzheimer disease (AD), and HIV-negative controls (HIV-). We also calculated the diagnostic characteristics of CSF NfL and its ratios in HIV-associated neurocognitive disorder (HAND) diagnosis.

METHODS

CSF NfL, T-tau, and P-tau181 concentrations were measured using immunoassays in a total of 108 CSF samples, including PWH (n = 68), HIV- (n = 16), and participants with AD (n = 24). These proteins were compared between HIV-1B (n = 27) and HIV-1C (n = 26) using multiple linear regression adjusted for nadir CD4 and plasma viral load suppression. Comparisons between PWH, HIV-, and participants with AD were adjusted for gender and age.

RESULTS

CSF neurocytoskeleton proteins and their ratios were comparable in HIV-1B and HIV-1C. However, the HIV-1C group had a higher proportion of samples of CSF NfL above the reference value (n = 14, 53.85%) than the HIV-1B group (n = 8, 29.63%), P = 0.098. The values of CSF NfL were higher in the AD group [2578 (1864; 3500) pg/mL] than those in PWH [683 (500; 1197) pg/mL, P < 0.001] and control [660 (539; 802) pg/mL, P = 0.012] groups. The value of CSF NfL and its ratios for HAND diagnosis were poor.

CONCLUSION

The effects of HIV-1B and HIV-1C on CSF NfL and tau ratios were comparable. The differences in CSF neurocytoskeleton proteins between PWH and individuals with AD suggested they might not share the same mechanisms of impairment. Further research is necessary to evaluate CSF NfL on the differential diagnoses of HAND with AD.

Cerebrospinal fluid pleocytosis as a predictive factor for CSF and plasma HIV RNA discordance and escape

The aims of this study were to investigate the frequency of HIV-1 RNA level discordance between the cerebrospinal fluid (CSF) and plasma and of CSF viral escape (CVE) in patients with HIV-1 subtype C on antiretroviral therapy, and evaluate the CSF white blood cell (WBC) performance characteristics in predicting CSF discordance in HIV+ group and the frequency of cognitive impairment in individuals with CSF HIV discordance or escape. HIV-1 RNA levels were assessed in plasma and CSF samples from 68 HIV+ participants without opportunistic infection. CSF discordance was found in 7.4% and CVE in 10%, with comparable frequencies between HIV-1B and C. Twenty samples (29%) showed increased CSF WBC counts. This group had higher CSF and plasma HIV-1 RNA levels than the group with normal WBC counts (p < 0.0001 and 0.006, respectively). The odds of CSF discordance were 18 times higher for a person with CSF WBC count of > 5 cells/mm3 than the group with normal CSF WBC count. CSF WBC counts (cut-off of 15 cells/mm3) showed high-performance characteristics as a predictive biomarker of CSF discordance (AUC the ROC curve 0.98). The frequency of cognitive impairment for CSF escape or discordance was 83% and 80%. The odds of cognitive impairment in these groups were 19 and 15 times higher than those for an HIV(-) person. Viral discordance or escape in the CNS occurs at a comparable frequency for HIV-1C and HIV-1B. The CSF WBC count was effective as a predictive biomarker of CSF and plasma discordance.

Blood amyloid-β protein isoforms are affected by HIV-1 in a subtype-dependent pattern

This study aimed to compare serum amyloid processing biomarkers among HIV subtype B (n = 25), HIV subtype C (n = 26), healthy HIV-negative controls (n = 18), and patients with Alzheimer's disease (AD; n = 24). Immunoassays were used to measure main soluble Aβ isoforms Aβ38, Aβ40, Aβ42, and Aβ-total in serum and cerebrospinal fluid (CSF). People living with HIV (PLWH) and HIV(-) samples, including AD samples, were compared for gender and age, while HIV subtypes were compared for nadir CD4 and plasma viral load suppression. CSF/serum ratios of Aβ40, Aβ42, and Aβ-total were lower in HIV-1C group than in HIV-1B group (p = 0.020, 0.025, and 0.050, respectively). In serum, these biomarkers were comparable. Serum Aβ isoforms were significantly lower in PLWH than in AD. Serum Aβ42 levels in PLWH were decreased compared to those in control group, thus similar to Aβ42 alterations in CSF; these results were different from those observed in AD. Impaired cellular immunity, low CD4 cell count (nadir or current) influences serum Aβ metabolism in HIV-1B but not HIV-1C. However, in PLWH overall, but not in individual HIV subtype groups, greater CD4 recovery, calculated as the difference between current and nadir CD4, correlated with Aβ42/Aβ40 ratio in serum (rs 0.246; p = 0.0479). No significant correlation was found with global deficit score (GDS), an index of neurocognitive performance, age, or duration of infection. These findings are consistent with those of subtype-dependent amyloid processing in blood in chronic HIV disease.

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.

Linked CSF reduction of phosphorylated tau and IL-8 in HIV associated neurocognitive disorder

HIV-associated neurocognitive disorder (HAND) is a common condition in both developed and developing nations, but its cause is largely unknown. Previous research has inconsistently linked Alzheimer's disease (AD), viral burden, and inflammation to the onset of HAND in HIV-infected individuals. Here we simultaneously measured cerebrospinal fluid (CSF) levels of established amyloid and tau biomarkers for AD, viral copy numbers, and six key cytokines in 41 HIV-infected individuals off combination anti-retroviral therapy (14 with HAND) who underwent detailed clinical and neuropsychological characterization, and compared their CSF patterns with those from young healthy subjects, older healthy subjects with normal cognition, and older people with AD. HAND was associated with the lowest CSF levels of phosphorylated tau (p-Tau181) after accounting for age and race. We also found very high CSF levels of the pro-inflammatory interferon gamma-induced protein 10 (IP-10/CXCL10) in HIV regardless of cognition, but elevated CSF interleukin 8 (IL-8/CXCL8) only in HIV-NC but not HAND. Eleven HIV-infected subjects underwent repeat CSF collection six months later and showed strongly correlated longitudinal changes in p-Tau181 and IL-8 levels (R = 0.841). These data suggest reduced IL-8 relative to IP-10 and reduced p-Tau181 to characterize HAND.

Neprilysin in the Cerebrospinal Fluid and Serum of Patients Infected With HIV1-Subtypes C and B

OBJECTIVE

Neprilysin (NEP) is the dominant Aβ peptide-degrading enzyme in the brain. HIV-1 subtype B transactivator of transcription protein is known to interfere with NEP function, but whether this is true of HIV-1C transactivator of transcription, which has a defective chemokine motif, is not known. This study aimed to analyze the impact of HIV subtype on NEP-mediated cleavage of Aβ by comparing cerebrospinal fluid (CSF) and serum levels of NEP between HIV+ (27 patients with HIV-1B and 26 with HIV-1C), healthy HIV- controls (n = 13), and patients with Alzheimer disease (n = 24).

METHODS

NEP and Aβ oligomers 38, 40, 42 levels were measured in CSF and serum by immunoassays. Ratios between NEP and Aβ-38, 40, 42, and total were calculated in CSF and serum. Comparisons between HIV(+) and HIV(-) were adjusted by linear regression for sex and age; HIV subtype comparisons were adjusted for nadir CD4 and plasma viral load suppression.

RESULTS

Levels of NEP and ratios in CSF were comparable for HIV-1C and B subtypes. The ratio of serum NEP/Aβ-40 was lower for HIV1-C than HIV1-B (P = 0.032). The CSF/serum index of NEP/Aβ-40, NEP/Aβ-42, and NEP/Aβ-total were lower for HIV1-B than HIV1-C (P = 0.008, 0.005, and 0.017, respectively), corroborating the findings for serum. CSF NEP was comparable for HIV+, HIV-, and AD.

CONCLUSION

There was impact of HIV subtype on NEP. The ratio of NEP/Aβ-40 on serum was lower on HIV1-C than HIV1-B. These results are consistent with the results of CSF Aβ-42 levels decreased in HIV1-C compared with HIV1-B, suggesting higher amyloid β deposit on HIV1-C than HIV1-B.

HIV and Alzheimer's disease: complex interactions of HIV-Tat with amyloid β peptide and Tau protein

In patients infected with the human immunodeficiency virus (HIV), the HIV-Tat protein may be continually produced despite adequate antiretroviral therapy. As the HIV-infected population is aging, it is becoming increasingly important to understand how HIV-Tat may interact with proteins such as amyloid β and Tau which accumulate in the aging brain and eventually result in Alzheimer's disease. In this review, we examine the in vivo data from HIV-infected patients and animal models and the in vitro experiments that show how protein complexes between HIV-Tat and amyloid β occur through novel protein-protein interactions and how HIV-Tat may influence the pathways for amyloid β production, degradation, phagocytosis, and transport. HIV-Tat may also induce Tau phosphorylation through a cascade of cellular processes that lead to the formation of neurofibrillary tangles, another hallmark of Alzheimer's disease. We also identify gaps in knowledge and future directions for research. Available evidence suggests that HIV-Tat may accelerate Alzheimer-like pathology in patients with HIV infection which cannot be impacted by current antiretroviral therapy.

Diagnostic and prognostic biomarkers for HAND

In 2007, the nosology for HIV-1-associated neurocognitive disorders (HAND) was updated to a primarily neurocognitive disorder. However, currently available diagnostic tools lack the sensitivity and specificity needed for an accurate diagnosis for HAND. Scientists and clinicians, therefore, have been on a quest for an innovative biomarker to diagnose (i.e., diagnostic biomarker) and/or predict (i.e., prognostic biomarker) the progression of HAND in the post-combination antiretroviral therapy (cART) era. The present review examined the utility and challenges of four proposed biomarkers, including neurofilament light (NFL) chain concentration, amyloid (i.e., sAPPα, sAPPβ, amyloid β) and tau proteins (i.e., total tau, phosphorylated tau), resting-state functional magnetic resonance imaging (fMRI), and prepulse inhibition (PPI). Although significant genotypic differences have been observed in NFL chain concentration, sAPPα, sAPPβ, amyloid β, total tau, phosphorylated tau, and resting-state fMRI, inconsistencies and/or assessment limitations (e.g., invasive procedures, lack of disease specificity, cost) challenge their utility as a diagnostic and/or prognostic biomarker for milder forms of neurocognitive impairment (NCI) in the post-cART era. However, critical evaluation of the literature supports the utility of PPI as a powerful diagnostic biomarker with high accuracy (i.e., 86.7-97.1%), sensitivity (i.e., 89.3-100%), and specificity (i.e., 79.5-94.1%). Additionally, the inclusion of multiple CSF and/or plasma markers, rather than a single protein, may provide a more sensitive diagnostic biomarker for HAND; however, a pressing need for additional research remains. Most notably, PPI may serve as a prognostic biomarker for milder forms of NCI, evidenced by its ability to predict later NCI in higher-order cognitive domains with regression coefficients (i.e., r) greater than 0.8. Thus, PPI heralds an opportunity for the development of a brief, noninvasive diagnostic and promising prognostic biomarker for milder forms of NCI in the post-cART era.