PPARgamma and LXR signaling inhibit dendritic cell-mediated HIV-1 capture and trans-infection

Cholesterol Metabolism in Antigen-Presenting Cells and HIV-1 Trans-Infection of CD4+ T Cells

Antiretroviral therapy (ART) provides an effective method for managing HIV-1 infection and preventing the onset of AIDS; however, it is ineffective against the reservoir of latent HIV-1 that persists predominantly in resting CD4+ T cells. Understanding the mechanisms that facilitate the persistence of the latent reservoir is key to developing an effective cure for HIV-1. Of particular importance in the establishment and maintenance of the latent viral reservoir is the intercellular transfer of HIV-1 from professional antigen-presenting cells (APCs-monocytes/macrophages, myeloid dendritic cells, and B lymphocytes) to CD4+ T cells, termed trans-infection. Whereas virus-to-cell HIV-1 cis infection is sensitive to ART, trans-infection is impervious to antiviral therapy. APCs from HIV-1-positive non-progressors (NPs) who control their HIV-1 infection in the absence of ART do not trans-infect CD4+ T cells. In this review, we focus on this unique property of NPs that we propose is driven by a genetically inherited, altered cholesterol metabolism in their APCs. We focus on cellular cholesterol homeostasis and the role of cholesterol metabolism in HIV-1 trans-infection, and notably, the link between cholesterol efflux and HIV-1 trans-infection in NPs.

Glycolysis-cholesterol metabolic axis in immuno-oncology microenvironment: emerging role in immune cells and immunosuppressive signaling

Cell proliferation and function require nutrients, energy, and biosynthesis activity to duplicate repertoires for each daughter. It is therefore not surprising that tumor microenvironment (TME) metabolic reprogramming primarily orchestrates the interaction between tumor and immune cells. Tumor metabolic reprogramming affords bioenergetic, signaling intermediates, and biosynthesis requirements for both malignant and immune cells. Different immune cell subsets are recruited into the TME, and these manifestations have distinct effects on tumor progression and therapeutic outcomes, especially the mutual contribution of glycolysis and cholesterol metabolism. In particularly, glycolysis-cholesterol metabolic axis interconnection plays a critical role in the TME modulation, and their changes in tumor metabolism appear to be a double-edged sword in regulating various immune cell responses and immunotherapy efficacy. Hence, we discussed the signature manifestation of the glycolysis-cholesterol metabolic axis and its pivotal role in tumor immune regulation. We also highlight how hypothetical combinations of immunotherapy and glycolysis/cholesterol-related metabolic interventions unleash the potential of anti-tumor immunotherapies, as well as developing more effective personalized treatment strategies.

The role of DC-SIGN as a trans-receptor in infection by MERS-CoV

DC-SIGN is a C-type lectin expressed in myeloid cells such as immature dendritic cells and macrophages. Through glycan recognition in viral envelope glycoproteins, DC-SIGN has been shown to act as a receptor for a number of viral agents such as HIV, Ebola virus, SARS-CoV, and SARS-CoV-2. Using a system of Vesicular Stomatitis Virus pseudotyped with MERS-CoV spike protein, here, we show that DC-SIGN is partially responsible for MERS-CoV infection of dendritic cells and that DC-SIGN efficiently mediates trans-infection of MERS-CoV from dendritic cells to susceptible cells, indicating a potential role of DC-SIGN in MERS-CoV dissemination and pathogenesis.

Lipid metabolism in dendritic cell biology

Dendritic cells (DCs) are innate immune cells that detect and process environmental signals and communicate them with T cells to bridge innate and adaptive immunity. Immune signals and microenvironmental cues shape the function of DC subsets in different contexts, which is associated with reprogramming of cellular metabolic pathways. In addition to integrating these extracellular cues to meet bioenergetic and biosynthetic demands, cellular metabolism interplays with immune signaling to shape DC-dependent immune responses. Emerging evidence indicates that lipid metabolism serves as a key regulator of DC responses. Here, we summarize the roles of fatty acid and cholesterol metabolism, as well as selective metabolites, in orchestrating the functions of DCs. Specifically, we highlight how different lipid metabolic programs, including de novo fatty acid synthesis, fatty acid β oxidation, lipid storage, and cholesterol efflux, influence DC function in different contexts. Further, we discuss how dysregulation of lipid metabolism shapes DC intracellular signaling and contributes to the impaired DC function in the tumor microenvironment. Finally, we conclude with a discussion on key future directions for the regulation of DC biology by lipid metabolism. Insights into the connections between lipid metabolism and DC functional specialization may facilitate the development of new therapeutic strategies for human diseases.

Antigen Presenting Cell-Mediated HIV-1 Trans Infection in the Establishment and Maintenance of the Viral Reservoir

Despite potent antiretroviral therapy, an HIV-1 reservoir persists that represents a major barrier to a cure. Understanding the mechanisms by which the HIV-1 reservoir is established and maintained is critical for the discovery of effective treatments to significantly reduce or eliminate the viral reservoir. In addition to cis infection, in which HIV-1 directly infects target CD4+ T cells, cell-to-cell transmission, or trans infection, can also occur. HIV-1 trans infection is significantly more efficient than cis infection, mostly due to the occurrence of multiple infections per cell during transfer. Additionally, trans infection is efficient even in the presence of ART and/or neutralizing antibodies. Cell-to-cell transmission is mediated by CD4+ T cells and professional antigen presenting cells (APC). Here we focus on APC, i.e., myeloid dendritic cells, B lymphocytes, and monocytes/macrophages, that bind, internalize, and transfer HIV-1 to target CD4+ T cells via various proposed mechanisms. We assess the potential impact of trans infection on the establishment and maintenance of the HIV-1 reservoir including its role in disease progression. We consider the natural interactions between APC and CD4+ T cells in vivo that HIV-1 may hijack, allowing for the highly efficient trans infection of CD4+ T cells, maintaining the viral reservoirs in tissue despite undetectable plasma viral loads in peripheral blood. We propose that these modes of viral pathogenesis need to be addressed in potential cure strategies to ensure eradication of the viral reservoir.

The Role of Transcription Factor PPAR-γ in the Pathogenesis of Psoriasis, Skin Cells, and Immune Cells

The peroxisome proliferator-activated receptor PPAR-γ is one of three PPAR nuclear receptors that act as ligand-activated transcription factors. In immune cells, the skin, and other organs, PPAR-γ regulates lipid, glucose, and amino acid metabolism. The receptor translates nutritional, pharmacological, and metabolic stimuli into the changes in gene expression. The activation of PPAR-γ promotes cell differentiation, reduces the proliferation rate, and modulates the immune response. In the skin, PPARs also contribute to the functioning of the skin barrier. Since we know that the route from identification to the registration of drugs is long and expensive, PPAR-γ agonists already approved for other diseases may also represent a high interest for psoriasis. In this review, we discuss the role of PPAR-γ in the activation, differentiation, and proliferation of skin and immune cells affected by psoriasis and in contributing to the pathogenesis of the disease. We also evaluate whether the agonists of PPAR-γ may become one of the therapeutic options to suppress the inflammatory response in lesional psoriatic skin and decrease the influence of comorbidities associated with psoriasis.

Dendritic Cells and Their Immunotherapeutic Potential for Treating Type 1 Diabetes

Type 1 diabetes (T1D) results from the destruction of pancreatic beta cells through a process that is primarily mediated by T cells. Emerging evidence suggests that dendritic cells (DCs) play a crucial role in initiating and developing this debilitating disease. DCs are professional antigen-presenting cells with the ability to integrate signals arising from tissue infection or injury that present processed antigens from these sites to naïve T cells in secondary lymphoid organs, thereby triggering naïve T cells to differentiate and modulate adaptive immune responses. Recent advancements in our knowledge of the various subsets of DCs and their cellular structures and methods of orchestration over time have resulted in a better understanding of how the T cell response is shaped. DCs employ various arsenal to maintain their tolerance, including the induction of effector T cell deletion or unresponsiveness and the generation and expansion of regulatory T cell populations. Therapies that suppress the immunogenic effects of dendritic cells by blocking T cell costimulatory pathways and proinflammatory cytokine production are currently being sought. Moreover, new strategies are being developed that can regulate DC differentiation and development and harness the tolerogenic capacity of these cells. Here, in this report, we focus on recent advances in the field of DC immunology and evaluate the prospects of DC-based therapeutic strategies to treat T1D.

New Insights of CCR7 Signaling in Dendritic Cell Migration and Inflammatory Diseases

CCR7, collaborated with its ligands CCL19 and CCL21, controls extensive migratory events in the immune system. CCR7-bearing dendritic cells can swarm into T-cell zones in lymph nodes, initiating the antigen presentation and T-cell response. Abnormal expression of CCR7 in dendritic cells will cause a series of inflammatory diseases due to the chaotic dendritic cell trafficking. In this review, we take an in-depth look at the structural–functional domains of CCR7 and CCR7-bearing dendritic cell trajectory to lymph nodes. Then, we summarize the regulatory network of CCR7, including transcriptional regulation, translational and posttranslational regulation, internalization, desensitization, and recycling. Furthermore, the potential strategies of targeting the CCR7 network to regulate dendritic cell migration and to deal with inflammatory diseases are integrated, which not only emphasizes the possibility of CCR7 to be a potential target of immunotherapy but also has an implication on the homing of dendritic cells to benefit inflammatory diseases.

Liver X receptors conserve the therapeutic target potential for the treatment of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic multi-system autoimmune disease with extremely complex pathogenesis. Significantly altered lipid paradox related to the inflammatory burden is reported in RA patients, inducing 50% higher cardiovascular risks. Recent studies have also demonstrated that lipid metabolism can regulate many functions of immune cells in which metabolic pathways have altered. The nuclear liver X receptors (LXRs), including LXRα and LXRβ, play a central role in regulating lipid homeostasis and inflammatory responses. Undoubtedly, LXRs have been considered as an attractive therapeutic target for the treatment of RA. However, there are some contradictory effects of LXRs agonists observed in previous animal studies where both pro-inflammatory role and anti-inflammatory role were revealed for LXRs activation in RA. Therefore, in addition to updating the knowledge of LXRs as the prominent regulators of lipid homeostasis, the purpose of this review is to summarize the effects of LXRs agonists in RA-associated immune cells, to explore the underlying reasons for the contradictory therapeutic effects of LXRs agonists observed in RA animal models, and to discuss future strategy for the treatment of RA with LXRs modulators.

Immunologic Aspects of Dyslipidemia: a Critical Regulator of Adaptive Immunity and Immune Disorders

Dyslipidemia is a major cause of cardiovascular diseases which represent a leading cause of death in humans. Diverse immune cells are known to be involved in the pathogenesis of cardiovascular diseases such as atherosclerosis. Conversely, dyslipidemia is known to be tightly associated with immune disorders in humans, as evidenced by a higher incidence of atherosclerosis in patients with autoimmune diseases including psoriasis, rheumatoid arthritis, and systemic lupus erythematosus. Given that the dyslipidemia-related autoimmune diseases are caused by autoreactive T cells and B cells, dyslipidemia seems to directly or indirectly regulate the adaptive immunity. Indeed, accumulating evidence has unveiled that proatherogenic factors can impact the differentiation and function of CD4⁺ T cells, CD8⁺ T cells, and B cells. This review discusses an updated overview on the regulation of adaptive immunity by dyslipidemia and proposes a potential therapeutic strategy for immune disorders by targeting lipid metabolism.

Metabolic syndrome in Zambian adults with human immunodeficiency virus on antiretroviral therapy: Prevalence and associated factors

Metabolic syndrome (MetS) is a constellation of factors including hypertension, abdominal obesity, dyslipidemia, and insulin resistance that separately and together significantly increase risk for cardiovascular disease (CVD) and diabetes. In sub-Saharan Africa, with a substantial burden of human immunodeficiency virus (HIV) and increasing prevalence of CVD and diabetes, there is a paucity of epidemiological data on demographic, laboratory, and clinical characteristics associated with MetS among people with HIV (people with human [PWH]). Therefore, this study aimed to determine the burden and factors influencing MetS in antiretroviral therapy (ART)-experienced individuals in Zambia.We collected cross-sectional demographic, lifestyle, anthropometric, clinical, and laboratory data in a cohort of ART-experienced (on ART for ≥6 months) adults in 24 urban HIV treatment clinics of Zambia between August, 2016 and May, 2020. MetS was defined as having ≥3 of the following characteristics: low high density lipoprotein cholesterol (HDL-c) (<1.0 mmol/L for men, <1.3 for women), elevated waist circumference (≥94 cm for men, ≥80 cm for women), elevated triglycerides (≥1.7 mmol/L), elevated fasting blood glucose (≥5.6 mmol/L), and elevated blood pressure (BP) (systolic BP ≥130 or diastolic BP ≥85 mm Hg). Virological failure (VF) was defined as HIV viral load ≥1000 copies/mL. The following statistical methods were used: Chi-square test, Wilcoxon rank-sum test, and multivariable logistic regression.Among 1108 participants, the median age (interquartile range [IQR]) was 41 years (34, 49); 666 (60.1%) were females. The prevalence of MetS was 26.3% (95% confidence interval [CI] 23.9-29.1). Age (adjusted odds ratio [OR] 1.07; 95% CI 1.04-1.11), female sex (OR 3.02; 95% CI 1.55-5.91), VF (OR 1.98; 95% CI 1.01-3.87), dolutegravir (DTG)-based regimen (OR 2.10; 95% CI 1.05-4.20), hip-circumference (OR 1.03; 95% CI 1.01-1.05), T-lymphocyte count (OR 2.23; 95% CI 1.44-3.43), high-sensitivity C-reactive protein (hsCRP) (OR 1.14; 95% CI 1.01-1.29), and fasting insulin (OR 1.02; 95% CI 1.01-1.04) were significantly associated with MetS.Metabolic syndrome was highly prevalent among HIV+ adults receiving ART in Zambia and associated with demographic, clinical, anthropometric, and inflammatory characteristics. The association between MetS and dolutegravir requires further investigation, as does elucidation of the impact of MetS on ART outcomes in sub-Saharan African PWH.

Immune metabolism: a bridge of dendritic cells function

An increasing number of researches have shown that cell metabolism regulates cell function. Dendritic cells (DCs), a professional antigen presenting cells, connect innate and adaptive immune responses. The preference of DCs for sugar or lipid affects its phenotypes and functions. In many diseases such as atherosclerosis (AS), diabetes mellitus and tumor, altered glucose or lipid level in microenvironment makes DCs exert ineffective or opposite immune roles, which accelerates the development of these diseases. In this article, we review the metabolism pathways of glucose and cholesterol in DCs, and the effects of metabolic changes on the phenotype and function of DCs. In addition, we discuss the effects of changes in glucose and lipid levels on DCs in the context of different diseases for better understanding the relationship between DCs and diseases. The immune metabolism of DCs may be a potential intervention link to treat metabolic-related immune diseases.

Liver X receptors and skeleton: Current state-of-knowledge

The liver X receptors (LXR) is a nuclear receptor that acts as a prominent regulator of lipid homeostasis and inflammatory response. Its therapeutic effectiveness against various diseases like Alzheimer's disease and atherosclerosis has been investigated in detail. Emerging pieces of evidence now reveal that LXR is also a crucial modulator of bone remodeling. However, the molecular mechanisms underlying the pharmacological actions of LXR on the skeleton and its role in osteoporosis are poorly understood. Therefore, in the current review, we highlight LXR and its actions through different molecular pathways modulating skeletal homeostasis. The studies described in this review propound that LXR in association with estrogen, PTH, PPARγ, RXR hedgehog, and canonical Wnt signaling regulates osteoclastogenesis and bone resorption. It regulates RANKL-induced expression of c-Fos, NFATc1, and NF-κB involved in osteoclast differentiation. Additionally, several studies suggest suppression of RANKL-induced osteoclast differentiation by synthetic LXR ligands. Given the significance of modulation of LXR in various physiological and pathological settings, our findings indicate that therapeutic targeting of LXR might potentially prevent or treat osteoporosis and improve bone quality.

Prevalence of low high-density lipoprotein among young adults receiving antiretroviral therapy in Zambia: An opportunity to consider non-communicable diseases in resource-limited settings

Background

With the introduction of effective antiretroviral therapy (ART), people living with HIV (PLWH) are surviving longer and are at risk for developing metabolic abnormalities that contribute to cardiovascular disease (CVD). In Sub-Saharan Africa (SSA), there is a paucity of epidemiological data on lipid profiles among young adults receiving ART. This study aimed to estimate the prevalence of low high-density lipoprotein cholesterol (HDL-c), a cardioprotective lipid class, and whether it differed by age among adults on ART in Livingstone, Zambia.

Methods

From April to December 2019, we conducted a cross-sectional study of 597 PLWH [n = 58 aged 18–24 years (young adults); n = 539 aged ≥25 years (adults)] on ART for ≥6 months. Data collected included demographic and lifestyle information, anthropometrics, viral load (VL), CD4 count, blood pressure, lipid profiles and fasting/random blood glucose. Clinical measures were defined as: low HDL-c [<1.0 mmol/L for men, <1.3 for women], increased waist circumference (WC) [≥94 cm for men, ≥80 cm for women], high triglycerides (TG) [≥1.7 mmol/l], and virological failure (VF) [VL ≥1000 copies/μl]. We used logistic regression to examine the association between age and low HDL-c after adjusting for multiple variables.

Results

Among the young adults, 60% (35/58) were women, median (25^th, 75^th percentile) age 21 years (18, 23), and median time on ART 116 months (60, 144). Among adults, 63% (342/539) were women, median age 46 years (40, 53) and median time on ART 108 months (60, 144). Young adults had a lower CD4 count compared to adults (median, 492 vs. 568 cells/μL, p = 0.010) and higher prevalence of VF (29% vs. 17%, p = 0.016). In young adults, prevalence of low HDL-c was significantly higher than in adults (63 vs. 38%, p<0.001). A high proportion of young adults (75%) and adults (58%) with low HDL-c were on dolutegravir (DTG)-based ART regimens. After adjusting for sex, duration on ART, WC, body mass index, ART regimen, VF, CD4 count, low density lipoprotein cholesterol, blood pressure and smoking, young adults were significantly more likely than adults to have low HDL-c (odds ratio 2.93; 95% confidence interval 1.46–5.86).

Conclusion

Low HDL-c is highly prevalent among young adult with HIV in SSA independent of other risk factors for metabolic derangements. Lipid abnormalities among young PLWH may contribute to the early development of cardiovascular diseases in this population. This highlights the need to consider low HDL-c in the quest to reduce CVD risk among young adults on ART in SSA.

Liver X Receptor Activation Impairs Neutrophil Functions and Aggravates Sepsis

BACKGROUND

Liver X receptors (LXRs) are nuclear receptors activated by oxidized lipids and were previously implicated in several metabolic development and inflammatory disorders. Although neutrophils express both LXR-α and LXR-β, the consequences of their activation, particularly during sepsis, remain unknown.

METHODS

We used the model of cecal ligation and puncture (CLP) to investigate the role of LXR activation during sepsis.

RESULTS

In this study, we verified that LXR activation reduces neutrophil chemotactic and killing abilities in vitro. Mice treated with LXR agonists showed higher sepsis-induced mortality, which could be associated with reduced neutrophil infiltration at the infectious foci, increased bacteremia, systemic inflammatory response, and multiorgan failure. In contrast, septic mice treated with LXR antagonist showed increased number of neutrophils in the peritoneal cavity, reduced bacterial load, and multiorgan dysfunction. More important, neutrophils from septic patients showed increased ABCA1 messenger ribonucleic acid levels (a marker of LXR activation) and impaired chemotactic response toward CXCL8 compared with cells from healthy individuals.

CONCLUSIONS

Therefore, our findings suggest that LXR activation impairs neutrophil functions, which might contribute to poor sepsis outcome.

Pharmacological Inhibition of PPARy Boosts HIV Reactivation and Th17 Effector Functions, While Preventing Progeny Virion Release and de novo Infection

The frequency and functions of Th17-polarized CCR6⁺RORyt⁺CD4⁺ T cells are rapidly compromised upon HIV infection and are not restored with long-term viral suppressive antiretroviral therapy (ART). In line with this, Th17 cells represent selective HIV-1 infection targets mainly at mucosal sites, with long-lived Th17 subsets carrying replication-competent HIV-DNA during ART. Therefore, novel Th17-specific therapeutic interventions are needed as a supplement of ART to reach the goal of HIV remission/cure. Th17 cells express high levels of peroxisome proliferator-activated receptor gamma (PPARy), which acts as a transcriptional repressor of the HIV provirus and the rorc gene, which encodes for the Th17-specific master regulator RORyt. Thus, we hypothesized that the pharmacological inhibition of PPARy will facilitate HIV reservoir reactivation while enhancing Th17 effector functions. Consistent with this prediction, the PPARy antagonist T0070907 significantly increased HIV transcription (cell-associated HIV-RNA) and RORyt-mediated Th17 effector functions (IL-17A). Unexpectedly, the PPARy antagonism limited HIV outgrowth from cells of ART-treated people living with HIV (PLWH), as well as HIV replication in vitro. Mechanistically, PPARy inhibition in CCR6⁺CD4⁺ T cells induced the upregulation of transcripts linked to Th17-polarisation (RORyt, STAT3, BCL6 IL-17A/F, IL-21) and HIV transcription (NCOA1-3, CDK9, HTATIP2). Interestingly, several transcripts involved in HIV-restriction were upregulated (Caveolin-1, TRIM22, TRIM5α, BST2, miR-29), whereas HIV permissiveness transcripts were downregulated (CCR5, furin), consistent with the decrease in HIV outgrowth/replication. Finally, PPARy inhibition increased intracellular HIV-p24 expression and prevented BST-2 downregulation on infected T cells, suggesting that progeny virion release is restricted by BST-2-dependent mechanisms. These results provide a strong rationale for considering PPARy antagonism as a novel strategy for HIV-reservoir purging and restoring Th17-mediated mucosal immunity in ART-treated PLWH.

Integrating the roles of liver X receptors in inflammation and infection: mechanisms and outcomes

Liver X receptors (LXRs) are transcription factors from the nuclear receptor family that can be pharmacologically activated by high-affinity agonists. LXR activation exerts a combination of metabolic and anti-inflammatory actions that result in the modulation of immune responses and in the amelioration of inflammatory disorders. In addition, LXR agonists modulate the metabolism of infected cells and limit the infectivity and/or growth of several pathogens. This review gives an overview of the recent advances in understanding the complexity of the mechanisms through which the LXR pathway controls inflammation and host-cell pathogen interaction.

Saikosaponin A protects chickens against pullorum disease via modulation of cholesterol

The worsening problem of antibiotic resistance prompts the need for alternative strategies that do not directly target bacteria. Virulent Salmonella pullorum strains can invade macrophages and lead to a systemic infection. Saikosaponin A (SSa), a bioactive saponin isolated from Radix bupleuri, has been demonstrated to exhibit anti-inflammatory, hepatoprotective, and cholesterol regulatory activity. The aim of this study was to investigate the effects of SSa on Salmonella-induced pullorum disease in chickens and clarify the possible mechanism. A S. pullorum-induced pullorum disease chicken model was used to confirm the protective effect of SSa in vivo. The model of HD11 cells infected with S. pullorum was used to investigate the molecular mechanism of SSa in vitro. In vivo, SSa prolonged the survival time and decreased the liver bacterial burdens in the pullorum disease model. In vitro, SSa dose-dependently suppressed the invasion of HD11 cells by S. pullorum. SSa depleted cholesterol in the lipid rafts, disrupted the formation of lipid rafts, and promoted the transcription of LXRα, ABCA1, and ABCG1. Moreover, the addition of water-soluble cholesterol and inhibition of LXRα with the LXRα antagonist geranylgeranyl pyrophosphate reversed the inhibitory effects of SSa on the invasion of HD11 cells by S. pullorum. In conclusion, the protective effect of SSa against S. pullorum infection is associated with the upregulation of the LXRα-ABCG1/ABCA1 pathway, which results in a decrease in cholesterol in the lipid rafts of HD11 cells, thereby suppressing the invasion of HD11 cells by S. pullorum. These results validate SSa as a host-target drug for the prevention of bacterial diseases, including those caused by S. pullorum.

Peroxisome Proliferator-Activated Receptor-gamma agonists exhibit anti-inflammatory and antiviral effects in an EcoHIV mouse model

The widespread use of combination antiretroviral therapy (cART) has resulted in significantly reduced deaths from HIV-1 associated complications and opportunistic infections. However, it is estimated that up to 50% of HIV-1 infected individuals still develop HIV-1 associated neurocognitive disorders (HAND). With no treatment currently available for patients, there is a critical need to identify therapeutic approaches that can treat this disorder. Evidence suggests that targeting Peroxisome Proliferator-Activated Receptor-gamma (PPARγ) can be anti-inflammatory in neurological disorders. Here we show that treatment with PPARγ agonists (rosiglitazone or pioglitazone) in primary cultures of mouse glial cells reversed EcoHIV-induced inflammatory genes (TNFα, IL-1β, CCL2, CCL3, CXCL10) and indicator of oxidative stress (iNOS). Furthermore, in vivo, mice administered with EcoHIV through intracranial injection resulted in upregulation of inflammatory genes (TNFα, IL-1β, IFNγ, CCL2, CCL3, CXCL10) and oxidative stress marker (iNOS) in the brain which was reversed through intraperitoneal administration of PPARγ agonists (rosiglitazone or pioglitazone). Finally, we demonstrated that treatment with these compounds in vivo reduced EcoHIV p24 protein burden in the brain. Our results suggest that treatment with PPARγ agonists are anti-inflammatory and antiviral in an in vivo model of EcoHIV infection. These drugs hold promise as potential candidates for HAND treatment in the future.

Regulating Innate and Adaptive Immunity for Controlling SIV Infection by 25-Hydroxycholesterol

Persistent inflammation and extensive immune activation have been associated with HIV-1/SIV pathogenesis. Previously, we reported that cholesterol-25-hydroxylase (CH25H) and its metabolite 25-hydroxycholesterol (25-HC) had a broad antiviral activity in inhibiting Zika, Ebola, and HIV-1 infection. However, the underlying immunological mechanism of CH25H and 25-HC in inhibiting viral infection remains poorly understood. We report here that 25-HC effectively regulates immune responses for controlling viral infection. CH25H expression was interferon-dependent and induced by SIV infection in monkey-derived macrophages and PBMC cells, and 25-HC inhibited SIV infection both in permissive cell lines and primary monkey lymphocytes. 25-HC also strongly inhibited bacterial lipopolysaccharide (LPS)-stimulated inflammation and restricted mitogen-stimulated proliferation in primary monkey lymphocytes. Strikingly, 25-HC promoted SIV-specific IFN-γ-producing cellular responses, but selectively suppressed proinflammatory CD4+ T lymphocytes secreting IL-2 and TNF-α cytokines in vaccinated mice. In addition, 25-HC had no significant immunosuppressive effects on cytotoxic CD8+ T lymphocytes or antibody-producing B lymphocytes. Collectively, 25-HC modulated both innate and adaptive immune responses toward inhibiting HIV/SIV infection. This study provides insights into improving vaccination and immunotherapy regimes against HIV-1 infection.

Microenvironmental derived factors modulating dendritic cell function and vaccine efficacy: the effect of prostanoid receptor and nuclear receptor ligands

Dendritic cells (DCs) are widely used in DC-based immunotherapies because of their capacity to steer immune responses. So far treatment success is limited and more functional knowledge on how DCs initiate and stably drive specific responses is needed. Many intrinsic and extrinsic factors contribute to how DCs skew the immune response towards immunity or tolerance. The origin and type of DC, its maturation status, but also factors they encounter in the in vitro or in vivo microenvironment they reside in during differentiation and maturation affect this balance. Treatment success of DC vaccines will, therefore, also depend on the presence of these factors during the process of vaccination. Identification and further knowledge of natural and pharmacological compounds that modulate DC differentiation and function towards a specific response may help to improve current DC-based immunotherapies. This review focuses on factors that could improve the efficacy of DC vaccines in (pre-)clinical studies to enhance DC-based immunotherapy, with a particular emphasis on compounds acting on prostanoid or nuclear receptor families.

Impact of cocaine use on protease inhibitor-associated dyslipidemia in HIV-infected adults

Previous studies have demonstrated a link between protease inhibitor (PI)-based therapy and lipid dysregulation. The main objective of this study was to examine whether cocaine use may modify PI-associated dyslipidemia in adults. Between June 2003 and June 2014, 957 human immunodeficiency virus (HIV)-infected participants in Baltimore, Maryland were enrolled in a study that investigated HIV/antiretroviral therapy-associated comorbidities. Multiple linear and logistic regression models were fitted to examine the associations between PI therapy and lipid profiles for the pooled sample and cocaine use subgroups, respectively. Total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), TC/high-density lipoprotein cholesterol (HDL-C) ratio, and atherogenic index of plasma (AIP) levels were positively associated with duration of PI-based therapy in long-term cocaine users (all p < 0.05). However, longer-term PI therapy was significantly associated with increased HDL-C in non-chronic cocaine users (β = 0.109, SE = 0.042, p < 0.05). The participants who received PI therapy ≥12 months and used cocaine ≥15 years were more likely to have hypertriglyceridemia (OR = 2.82, 95% CI = 1.63, 4.88) and abnormal AIP (OR = 1.73, 95% CI = 1.08, 2.79) as compared to their counterparts. Our findings showed that long-term cocaine use may exacerbate adverse effects of PI therapy on lipid metabolism, suggesting that reduced cocaine use may be considered an alternative approach to managing PI-associated dyslipidemia in chronic cocaine users with HIV infection.

The Biology of Monocytes and Dendritic Cells: Contribution to HIV Pathogenesis

Myeloid cells such as monocytes, dendritic cells (DC) and macrophages (MΦ) are key components of the innate immune system contributing to the maintenance of tissue homeostasis and the development/resolution of immune responses to pathogens. Monocytes and DC, circulating in the blood or infiltrating various lymphoid and non-lymphoid tissues, are derived from distinct bone marrow precursors and are typically short lived. Conversely, recent studies revealed that subsets of tissue resident MΦ are long-lived as they originate from embryonic/fetal precursors that have the ability to self-renew during the life of an individual. Pathogens such as the human immunodeficiency virus type 1 (HIV-1) highjack the functions of myeloid cells for viral replication (e.g., MΦ) or distal dissemination and cell-to-cell transmission (e.g., DC). Although the long-term persistence of HIV reservoirs in CD4+ T-cells during viral suppressive antiretroviral therapy (ART) is well documented, the ability of myeloid cells to harbor replication competent viral reservoirs is still a matter of debate. This review summarizes the current knowledge on the biology of monocytes and DC during homeostasis and in the context of HIV-1 infection and highlights the importance of future studies on long-lived resident MΦ to HIV persistence in ART-treated patients.

Association of a 3' untranslated region polymorphism in proprotein convertase subtilisin/kexin type 9 with HIV viral load and CD4+ levels in HIV/hepatitis C virus coinfected women

OBJECTIVE

To assess variation in genes that regulate cholesterol metabolism in relation to the natural history of HIV infection.

DESIGN

Cross-sectional and longitudinal analysis of the Women's Interagency HIV Study.

METHODS

We examined 2050 single nucleotide polymorphisms (SNPs) in 19 genes known to regulate cholesterol metabolism in relation to HIV viral load and CD4 T-cell levels in a multiracial cohort of 1066 antiretroviral therapy-naive women.

RESULTS

Six SNPs were associated with both HIV viral load and CD4 T-cell levels at a false discovery rate of 0.01. Bioinformatics tools did not predict functional activity for five SNPs, located in introns of nuclear receptor corepressor 2, retinoid X receptor alpha (RXRA), and tetratricopeptide repeat domain 39B. Rs17111557 located in the 3' untranslated region of proprotein convertase subtilisin/kexin type 9 (PCSK9) putatively affects binding of hsa-miR-548t-5p and hsa-miR-4796-3p, which could regulate PCSK9 expression levels. Interrogation of rs17111557 revealed stronger associations in the subset of women with HIV/hepatitis C virus (HCV) coinfection (n = 408, 38% of women). Rs17111557 was also associated with low-density lipoprotein cholesterol levels in HIV/HCV coinfected (β: -10.4; 95% confidence interval: -17.9, -2.9; P = 0.007), but not in HIV monoinfected (β:1.2; 95% confidence interval: -6.3, 8.6; P = 0.76) women in adjusted analysis.

CONCLUSION

PCSK9 polymorphism may affect HIV pathogenesis, particularly in HIV/HCV coinfected women. A likely mechanism for this effect is PCSK9-mediated regulation of cholesterol metabolism. Replication in independent cohorts is needed to clarify the generalizability of the observed associations.

Association of NR1I2 gene polymorphisms and time of progression to AIDS

BACKGROUND

The time of progression towards AIDS can vary greatly among seropositive patients, and may be associated with host genetic variation. The NR1I2 (PXR) gene, a ligand-activated transcription factor, regulates the transcription immune pathway genes and can therefore be targets of viral replication mechanisms influencing time of progression to AIDS.

OBJECTIVE

To verify the association of single nucleotide polymorphisms (SNPs) rs3814057, rs6785049, rs7643645, and rs2461817 in the NR1I2 (PXR) gene with progression to AIDS in HIV-1 infected patients.

METHODS

Blood samples were obtained from 96 HIV-1 positive individuals following informed consent. DNA was isolated and genotyped through real time polymerase chain reaction (PCR) for the presence of SNPs in the NR1I2. Questionnaires on socio-demographic features and behaviors were answered and time of progression to AIDS was estimated based on medical chart analysis.

FINDINGS

Patients with the GG genotype for rs7643645 were shown to be related with a more rapid disease progression when compared to GA and AA genotypes. This result was maintained by the Multivariate Cox Regression considering sex, ethnicity, and presence of HLA-B*57, HLA-B*27, and CCR5del32 polymorphisms.

MAIN CONCLUSIONS

Recent studies reported the expression of the nuclear receptors in T-Lymphocytes, suggesting their possible role in the immune response. In addition, nuclear receptors have been shown to inhibit the HIV replication, although no such mechanism has been thoroughly elucidated to date. This is the first time an association between NR1I2 polymorphism and time of progression to AIDS is reported and supports an apparent relationship between the gene in the immune response and identifies another genetic factor influencing AIDS progression.

HELZ2 Is an IFN Effector Mediating Suppression of Dengue Virus

Flaviviral infections including dengue virus are an increasing clinical problem worldwide. Dengue infection triggers host production of the type 1 IFN, IFN alpha, one of the strongest and broadest acting antivirals known. However, dengue virus subverts host IFN signaling at early steps of IFN signal transduction. This subversion allows unbridled viral replication which subsequently triggers ongoing production of IFN which, again, is subverted. Identification of downstream IFN antiviral effectors will provide targets which could be activated to restore broad acting antiviral activity, stopping the signal to produce endogenous IFN at toxic levels. To this end, we performed a targeted functional genomic screen for IFN antiviral effector genes (IEGs), identifying 56 IEGs required for antiviral effects of IFN against fully infectious dengue virus. Dengue IEGs were enriched for genes encoding nuclear receptor interacting proteins, including HELZ2, MAP2K4, SLC27A2, HSP90AA1, and HSP90AB1. We focused on HELZ2 (Helicase With Zinc Finger 2), an IFN stimulated gene and IEG which encodes a promiscuous nuclear factor coactivator that exists in two isoforms. The two unique HELZ2 isoforms are both IFN responsive, contain ISRE elements, and gene products increase in the nucleus upon IFN stimulation. Chromatin immunoprecipitation-sequencing revealed that the HELZ2 complex interacts with triglyceride-regulator LMF1. Mass spectrometry revealed that HELZ2 knockdown cells are depleted of triglyceride subsets. We thus sought to determine whether HELZ2 interacts with a nuclear receptor known to regulate immune response and lipid metabolism, AHR, and identified HELZ2:AHR interactions via co-immunoprecipitation, found that AHR is a dengue IEG, and that an AHR ligand, FICZ, exhibits anti-dengue activity. Primary bone marrow derived macrophages from HELZ2 knockout mice, compared to wild type controls, exhibit enhanced dengue infectivity. Overall, these findings reveal that IFN antiviral response is mediated by HELZ2 transcriptional upregulation, enrichment of HELZ2 protein levels in the nucleus, and activation of a transcriptional program that appears to modulate intracellular lipid state. IEGs identified in this study may serve as both (1) potential targets for host directed antiviral design, downstream of the common flaviviral subversion point, as well as (2) possible biomarkers, whose variation, natural, or iatrogenic, could affect host response to viral infections.

PPAR-γ agonist pioglitazone regulates dendritic cells immunogenicity mediated by DC-SIGN via the MAPK and NF-κB pathways

Dendritic cell-specific ICAM-3 grabbing non-integrin (DC-SIGN) is a dendritic cell-specific lectin which participates in dendritic cell (DC) trafficking, antigen uptake and DC-T cell interactions at the initiation of immune responses. This study investigated whether peroxisome proliferator-activated receptor-gamma (PPAR-γ) activation in human DCs regulates the immunogenicity of DCs mediated by DC-SIGN and exploited the possible molecular mechanisms, especially focused on the signaling pathways of mitogen-activated protein kinases (MAPK) and nuclear factor-κB (NF-κB). Here, we show that the PPAR-γ agonist pioglitazone decreased DC adhesion and transmigration, and DC stimulation of T cell proliferation mediated by DC-SIGN dependent on activation of PPAR-γ, although it increased DC endocytosis independent of PPAR-γ activation. Furthermore, PPAR-γ activation by pioglitazone in DCs down-regulated the expression of DC-SIGN, which was mediated by modulating the balance of the signaling pathways of extracellular signal-regulated kinase, c-Jun N-terminal kinase and NF-κB, but not p38 MAPK. Therefore, we conclude that PPAR-γ activation in human DCs regulates the immunogenicity of DCs mediated by DC-SIGN via the pathways of MAPK and NF-κB. These findings may support the important role of these mediators in the regulation of DC-mediated inflammatory and immunologic processes.

Detection and Functional Analysis of Tumor-Derived LXR Ligands

There is growing evidence highlighting the ability of nuclear receptors to control not only metabolism, but also inflammation and cancer progression. In particular liver X receptors (LXRs), the nuclear receptors physiologically involved in cholesterol homeostasis, have been shown to regulate innate and adaptive immune responses in many pathological conditions, including cancer.We have recently demonstrated that LXR ligands (oxysterols) released by tumor cells may have an immunomodulatory role, affecting the immune cells involved in the antitumor immune response. Indeed, oxysterols inhibit the expression of the chemokine receptor CCR7 on dendritic cells (DC) in an LXR-dependent manner, thus impairing DC migration to secondary lymphoid organs, and therefore dampening the induction of successful antitumor responses.We have resorted to direct (i.e., luciferase-based LXR activation assay) and indirect (i.e., activation of LXR target genes in dendritic cells) methods in order to assess the presence of LXR ligands (oxysterols) in tumor-conditioned media.These two methods are also suitable to study strategies to block oxysterol release by tumor cells.

CCR7 Receptor Expression in Mono-MAC-1 Cells: Modulation by Liver X Receptor α Activation and Prostaglandin E 2

Cell migration via chemokine receptor CCR7 expression is an essential function of the immune system. We previously showed that prostaglandin E₂ (PGE₂), an important immunomodulatory molecule, increases CCR7 expression and function in monocytes. Here, we explore the role of the liver X receptor α (LXRα) activation on CCR7 expression in Mono-Mac-1 (MM-1) cells in the presence of PGE₂. To do this, MM-1 cells were stimulated with the LXRα synthetic agonist T0901317 in the presence or absence of PGE₂. CCR7 mRNA transcription was measured using quantitative RT-PCR and protein expression was examined using flow cytometry. CCR7 function was analyzed using migration assays in response to CCL19/CCL21, which are natural ligands for CCR7. Our results show that agonist-mediated activation of LXRα in the presence of PGE₂ increases CCR7 mRNA transcription and MM-1 cell migratory capacity in response to CCL19/21. In addition, our results demonstrate that engagement of the E-prostanoids 2 and 4 (EP₂/EP₄) receptors present on MM-1 cells is responsible for the observed increase in CCR7 mRNA expression and function during LXRα activation. Examination of monocyte migration in response to lipid derivatives such as PGE₂ and oxysterols that are produced at sites of chronic inflammation would contribute to understanding the excessive monocyte migration that characterizes atherosclerosis.

Liver X receptors in immune cell function in humans

The liver X receptors (LXRs), LXRα and LXRβ, are transcription factors with well-established roles in the regulation of lipid metabolism and cholesterol homeostasis. In addition, LXRs influence innate and adaptive immunity, including responses to inflammatory stimuli, proliferation and differentiation, migration, apoptosis and survival. However, the majority of work describing the role of LXRs in immune cells has been carried out in mouse models, and there are a number of known species-specific differences concerning LXR function. Here we review what is known about the role of LXRs in human immune cells, demonstrating the importance of these receptors in the integration of lipid metabolism and immune function, but also highlighting the need for a better understanding of the species, isoform, and cell-type specific effects of LXR activation.

Liver X receptors contribute to periodontal pathogen-elicited inflammation and oral bone loss

Periodontal diseases are chronic oral inflammatory diseases that are polymicrobial in nature. The presence of specific bacteria in subgingival plaque such as Porphyromonas gingivalis is associated with microbial dysbiosis and the modulation of host immune response. Bacterially elicited innate immune activation and inflammation are key elements implicated in the destruction of soft and hard tissues supporting the teeth. Liver X receptors (LXRs) are nuclear hormone receptors with important function in lipid homeostasis, inflammation, and host response to infection; however, their contribution to chronic inflammatory diseases such as periodontal disease is not understood. The aim of this study was to define the contribution of LXRs in the development of immune response to P. gingivalis and to assess the roles that LXRs play in infection-elicited oral bone loss. Employing macrophages, we observed that P. gingivalis challenge led to reduced LXRα and LXRβ gene expression compared with that observed with unchallenged wild-type cells. Myeloid differentiation primary response gene 88 (MyD88)-independent, Toll/interleukin-1 receptor-domain-containing adapter-inducing interferon-β (TRIF)-dependent signaling affected P. gingivalis-mediated reduction in LXRα expression, whereas neither pathway influenced the P. gingivalis effect on LXRβ expression. Employing LXR agonist and mice deficient in LXRs, we observed functional effects of LXRs in the development of a P. gingivalis-elicited cytokine response at the level of the macrophage, and participation of LXRs in P. gingivalis-elicited oral bone loss. These findings identify novel importance for LXRs in the pathogenesis of P. gingivalis infection-elicited inflammation and oral bone loss.

Impact of antiretroviral therapy on lipid metabolism of human immunodeficiency virus-infected patients: Old and new drugs

For human immunodeficiency virus (HIV)-infected patients, the 1990s were marked by the introduction of highly active antiretroviral therapy (HAART) representing a new perspective of life for these patients. The use of HAART was shown to effectively suppress the replication of HIV-1 and dramatically reduce mortality and morbidity, which led to a better and longer quality of life for HIV-1-infected patients. Apart from the substantial benefits that result from the use of various HAART regimens, laboratory and clinical experience has shown that HAART can induce severe and considerable adverse effects related to metabolic complications of lipid metabolism, characterized by signs of lipodystrophy, insulin resistance, central adiposity, dyslipidemia, increased risk of cardiovascular disease and even an increased risk of atherosclerosis. New drugs are being studied, new therapeutic strategies are being implemented, and the use of statins, fibrates, and inhibitors of intestinal cholesterol absorption have been effective alternatives. Changes in diet and lifestyle have also shown satisfactory results.

A mechanistic overview of dendritic cell-mediated HIV-1 trans infection: the story so far

Despite progress in antiretroviral therapy, HIV-1 rebound after cessation of antiretroviral therapy suggests that establishment of long-term cellular reservoirs of virus is a significant barrier to functional cure. There is considerable evidence that dendritic cells (DCs) play an important role in systemic virus dissemination. Although productive infection of DCs is inefficient, DCs capture HIV-1 and transfer-captured particles to CD4+ T cells, a mechanism of DC-mediated HIV-1 trans infection. Recent findings suggest that DC-mediated trans infection of HIV-1 is dependent on recognition of GM3, a virus-particle-associated host-derived ligand, by CD169 expressed on DCs. In this review, we describe mechanisms of DC-mediated HIV-1 trans infection and discuss specifically the role of CD169 in establishing infection in CD4+ T cells.

Frienemies of infection: A chronic case of host nuclear receptors acting as cohorts or combatants of infection

Macrophages and dendritic cells provide critical effector functions to efficiently resist and promptly eliminate infection. Pattern recognition receptors signaling operative in these cell types is imperative for their innate properties. However, it is now emerging that besides these conventional signaling pathways, nuclear receptors coupled gene regulation and transrepression pathways assemble immune regulatory networks. A couple of these networks associated with members of nuclear receptor superfamily decide heterogeneity in macrophages and dendritic cells population and thereby play decisive role in determining protective immunity against bacteria, viruses, fungi, protozoa and helminths. Pathogens also direct shift in the expression of nuclear receptors and their target genes and this is proclaimed to be a sui generis mechanism whereby microbes disconnect the genomic component from the peripheral immune response. Many endogenous and synthetic nuclear receptor ligands have been tested in various in vitro and in vivo infection models to study their effect on pathogen burden. Here, we discuss current advances in our understanding of the composite interactions between nuclear receptor and pathogens and their implications on the causatum infectious diseases.

Development of therapeutic polymeric nanoparticles for the resolution of inflammation

Liver X receptors (LXRs) attenuate inflammation by modulating the expression of key inflammatory genes, making LXRs and their ligands particularly attractive candidates for therapeutic intervention in cardiovascular, metabolic, and/or inflammatory diseases. Herein, enhanced proresolving activity of polymeric nanoparticles (NPs) containing the synthetic LXR agonist GW3965 (LXR-NPs) is demonstrated, developed from a combinatorial library of more than 70 formulations with variations in critical physicochemical parameters. In vitro studies on peritoneal macrophages confirm that LXR-NPs are significantly more effective than the free agonist at downregulating pro-inflammatory mediators (MCP-1 and TNFα), as well as inducing the expression of LXR target genes (ABCA1 and SREBP1c). Through a zymosan-induced acute peritonitis in vivo model, LXR-NPs are found to be more efficient than free GW3965 at limiting the recruitment of polymononuclear neutrophils (50% vs 17%), suppressing the gene expression and secretion of pro-inflammatory factors MCP-1 and TNFα in peritoneal macrophages, and decreasing the resolution interval up to 4 h. Furthermore, LXR-NPs suppress the secretion of MCP-1 and TNFα by monocytes and macrophages more efficiently than the commercial drug dexamethasone. Overall, these findings demonstrate that LXR-NPs are capable of promoting resolution of inflammation and highlight the prospect of LXR-based nanotherapeutics for inflammatory diseases.

LXR-dependent and -independent effects of oxysterols on immunity and tumor growth

Oxysterols are involved in maintaining cellular cholesterol levels. Recently, oxysterols have been demonstrated to modulate the function of immune cells and tumor growth. These effects can be dependent on the activation of the oxysterol-binding liver X receptors (LXRs) or, as recently demonstrated for T and B cells, DCs and neutrophils, can be independent of LXR activation. LXR-dependent oxysterol effects can be ascribed to the activation of LXRα, LXRβ or LXRαβ isoforms, which induces transcriptional activation or trans-repression of target genes. The prevalent activation of one isoform seems to be cell-, tissue-, or context-specific, as shown in some pathologic processes, i.e., infectious diseases, atherosclerosis, and autoimmunity. Oxysterol-LXR signaling has recently been shown to inhibit antitumor immune responses, as well as to modulate tumor cell growth. Here, we review the mechanisms that link oxysterols to tumor growth, and discuss possible networks at the basis of LXR-dependent and -independent oxysterol effects on immune cells and tumor development.

New clues to understanding HIV nonprogressors: low cholesterol blocks HIV trans infection

A small percentage of HIV-infected subjects (2 to 15%) are able to control disease progression for many years without antiretroviral therapy. Years of intense studies of virologic and immunologic mechanisms of disease control in such individuals yielded a number of possible host genes that could be responsible for the preservation of immune functions, from immune surveillance genes, chemokines, or their receptors to anti-HIV restriction factors. A recent mBio paper by Rappocciolo et al. (G. Rappocciolo, M. Jais, P. Piazza, T. A. Reinhart, S. J. Berendam, L. Garcia-Exposito, P. Gupta, and C. R. Rinaldo, mBio 5:e01031-13, 2014) describes another potential factor controlling disease progression: cholesterol levels in antigen-presenting cells. In this commentary, we provide a brief background of the role of cholesterol in HIV infection, discuss the results of the study by Rappocciolo et al., and present the implications of their findings.

Alterations in cholesterol metabolism restrict HIV-1 trans infection in nonprogressors

HIV-1-infected nonprogressors (NP) inhibit disease progression for years without antiretroviral therapy. Defining the mechanisms for this resistance to disease progression could be important in determining strategies for controlling HIV-1 infection. Here we show that two types of professional antigen-presenting cells (APC), i.e., dendritic cells (DC) and B lymphocytes, from NP lacked the ability to mediate HIV-1 trans infection of CD4⁺ T cells. In contrast, APC from HIV-1-infected progressors (PR) and HIV-1-seronegative donors (SN) were highly effective in mediating HIV-1 trans infection. Direct cis infection of T cells with HIV-1 was comparably efficient among NP, PR, and SN. Lack of HIV-1 trans infection in NP was linked to lower cholesterol levels and an increase in the levels of the reverse cholesterol transporter ABCA1 (ATP-binding cassette transporter A1) in APC but not in T cells. Moreover, trans infection mediated by APC from NP could be restored by reconstitution of cholesterol and by inhibiting ABCA1 by mRNA interference. Importantly, this appears to be an inherited trait, as it was evident in APC obtained from NP prior to their primary HIV-1 infection. The present study demonstrates a new mechanism wherein enhanced lipid metabolism in APC results in remarkable control of HIV-1 trans infection that directly relates to lack of HIV-1 disease progression.

HIV-1 can be captured by antigen-presenting cells (APC) such as dendritic cells and transferred to CD4 helper T cells, which results in greatly enhanced viral replication by a mechanism termed trans infection. A small percentage of HIV-1-infected persons are able to control disease progression for many years without antiretroviral therapy. In our study, we linked this lack of disease progression to a profound inability of APC from these individuals to trans infect T cells. This effect was due to altered lipid metabolism in their APC, which appears to be an inherited trait. These results provide a basis for therapeutic interventions to control of HIV-1 infection through modulation of cholesterol metabolism.

Transcriptional profiling reveals molecular signatures associated with HIV permissiveness in Th1Th17 cells and identifies peroxisome proliferator-activated receptor gamma as an intrinsic negative regulator of viral replication

BACKGROUND

We previously demonstrated that primary Th1Th17 cells are highly permissive to HIV-1, whereas Th1 cells are relatively resistant. Molecular mechanisms underlying these differences remain unknown.

RESULTS

Exposure to replication competent and single-round VSV-G pseudotyped HIV strains provide evidence that superior HIV replication in Th1Th17 vs. Th1 cells was regulated by mechanisms located at entry and post-entry levels. Genome-wide transcriptional profiling identified transcripts upregulated (n = 264) and downregulated (n = 235) in Th1Th17 vs. Th1 cells (p-value < 0.05; fold change cut-off 1.3). Gene Set Enrichment Analysis revealed pathways enriched in Th1Th17 (nuclear receptors, trafficking, p38/MAPK, NF-κB, p53/Ras, IL-23) vs. Th1 cells (proteasome, interferon α/β). Differentially expressed genes were classified into biological categories using Gene Ontology. Th1Th17 cells expressed typical Th17 markers (IL-17A/F, IL-22, CCL20, RORC, IL-26, IL-23R, CCR6) and transcripts functionally linked to regulating cell trafficking (CEACAM1, MCAM), activation (CD28, CD40LG, TNFSF13B, TNFSF25, PTPN13, MAP3K4, LTB, CTSH), transcription (PPARγ, RUNX1, ATF5, ARNTL), apoptosis (FASLG), and HIV infection (CXCR6, FURIN). Differential expression of CXCR6, PPARγ, ARNTL, PTPN13, MAP3K4, CTSH, SERPINB6, PTK2, and ISG20 was validated by RT-PCR, flow cytometry and/or confocal microscopy. The nuclear receptor PPARγ was preferentially expressed by Th1Th17 cells. PPARγ RNA interference significantly increased HIV replication at levels post-entry and prior HIV-DNA integration. Finally, the activation of PPARγ pathway via the agonist Rosiglitazone induced the nuclear translocation of PPARγ and a robust inhibition of viral replication.

CONCLUSIONS

Thus, transcriptional profiling in Th1Th17 vs. Th1 cells demonstrated that HIV permissiveness is associated with a superior state of cellular activation and limited antiviral properties and identified PPARγ as an intrinsic negative regulator of viral replication. Therefore, triggering PPARγ pathway via non-toxic agonists may contribute to limiting covert HIV replication and disease progression during antiretroviral treatment.

Dendritic cells in progression and pathology of HIV infection

Although the major targets of HIV infection are CD4⁺ T cells, dendritic cells (DCs) represent a crucial subset in HIV infection because they influence viral transmission and target cell infection and presentation of HIV antigens. DCs are potent antigen-presenting cells that can modulate antiviral immune responses. Through secretion of inflammatory cytokines and interferons (IFNs), DCs also alter T cell proliferation and differentiation, participating in the immune dysregulation characteristic of chronic HIV infection. Their wide distribution in close proximity with the mucosal epithelia makes them one of the first cell types to encounter HIV during sexual transmission. We discuss here the multiple roles that DCs play at different stages of HIV infection, emphasizing their relevance to HIV pathology and progression.

Sterols and oxysterols in immune cell function

Intermediates in the cholesterol-biosynthetic pathway and oxysterol derivatives of cholesterol regulate diverse cellular processes. Recent studies have expanded the appreciation of their roles in controlling the functions of cells of the innate and adaptive immune systems. Here we review recent literature reporting on the biological functions of sterol intermediates and oxysterols, acting through transcription factors such as the liver X receptors (LXRs), sterol regulatory element-binding proteins (SREBPs) and the G protein-coupled receptor EBI2, in regulating the differentiation and population expansion of cells of the innate and adaptive immune systems, their responses to inflammatory mediators, their effects on the phagocytic functions of macrophages and their effects on antiviral activities and the migration of immune cells. Such findings have raised many new questions about the production of endogenous bioactive sterols and oxysterols and their mechanisms of action in the immune system.

The role of lipid-activated nuclear receptors in shaping macrophage and dendritic cell function: From physiology to pathology

Nuclear receptors are ligand-activated transcription factors linking lipid signaling to the expression of the genome. There is increasing appreciation of the involvement of this receptor network in the metabolic programming of macrophages and dendritic cells (DCs), essential members of the innate immune system. In this review we focus on the role of retinoid X receptor, retinoic acid receptor, peroxisome proliferator-associated receptor γ, liver X receptor, and vitamin D receptor in shaping the immune and metabolic functions of macrophages and DCs. We also provide an overview of the contribution of macrophage- and DC-expressed nuclear receptors to various immunopathologic conditions, such as rheumatoid arthritis, inflammatory bowel disease, systemic lupus erythematosus, asthma, and some others. We suggest that systematic analyses of the roles of these receptors and their activating lipid ligands in immunopathologies combined with complementary and focused translational and clinical research will be crucial for the development of new therapies using the many molecules available to target nuclear receptors.

Targeting liver X receptors in inflammation

INTRODUCTION

The two oxysterol receptors, 'liver X receptors (LXRs)' LXRα and LXRβ, are amongst the emerging newer drug targets within the nuclear receptor family and targeting LXRs represents novel strategies needed for prevention and treatment of diseases where current therapeutics is inadequate.

AREAS COVERED

This review discusses the current understanding of LXR biology with an emphasis on the molecular aspects of LXR signalling establishing their potential as drug targets. Recent advances of their transcriptional mechanisms in inflammatory pathways and their physiological roles in inflammation and immunity are described.

EXPERT OPINION

The new discoveries of LXR-regulated inflammatory pathways have ignited new promises for LXRs as drug targets. The broad physiological roles of LXRs involve a high risk of unwanted side effects. Recent insights into LXR biology of the brain indicate a highly important role in neuronal development and a clinical trial testing an LXR agonist reported adverse neurological side effects. This suggests that drug development must focus on limiting the range of LXR signalling - possibly achieved through subtype, tissue specific, promoter specific or pathway specific activation of LXRs where a successful candidate drug must be carefully studied for its effect in the central nervous system.

HIV-1 Trans Infection of CD4(+) T Cells by Professional Antigen Presenting Cells

Since the 1990s we have known of the fascinating ability of a complex set of professional antigen presenting cells (APCs; dendritic cells, monocytes/macrophages, and B lymphocytes) to mediate HIV-1 trans infection of CD4(+) T cells. This results in a burst of virus replication in the T cells that is much greater than that resulting from direct, cis infection of either APC or T cells, or trans infection between T cells. Such APC-to-T cell trans infection first involves a complex set of virus subtype, attachment, entry, and replication patterns that have many similarities among APC, as well as distinct differences related to virus receptors, intracellular trafficking, and productive and nonproductive replication pathways. The end result is that HIV-1 can sequester within the APC for several days and be transmitted via membrane extensions intracellularly and extracellularly to T cells across the virologic synapse. Virus replication requires activated T cells that can develop concurrently with the events of virus transmission. Further research is essential to fill the many gaps in our understanding of these trans infection processes and their role in natural HIV-1 infection.

Control of the immune system by oxysterols and cancer development

Oxysterols/oxysterol receptors have been shown to modulate several immune cell subsets, such as macrophages, T-cells and B-cells, neutrophils and dendritic cells (DCs). They participate in the control of several pathologic processes, that is, infectious diseases, atherosclerosis and autoimmunity. Moreover, some oxysterols have also been shown to favor tumor progression by dampening the antitumor immune response. The cellular responses generated by oxysterols depend on the engagement of Liver X Receptor (LXR) α and/or β isoforms, which induce activation of target genes or trans-repression of pro-inflammatory gene transcription. Recently, some reports have described a different mechanism of action of oxysterols, mediated by the engagement of G-Protein Coupled Receptors. Here, we summarize LXR-dependent and LXR-independent responses of oxysterols on immune cells with possible effects on tumor development.

Liver X receptors, atherosclerosis and inflammation

Liver X receptors (LXRs) belong to the nuclear receptor superfamily of ligand-dependent transcription factors. LXRs are activated by oxysterols, metabolites of cholesterol, and therefore act as intracellular sensors of this lipid. There are two LXR genes (α and β) that display distinct tissue/cell expression profiles. LXRs interact with regulatory sequences in target genes as heterodimers with retinoid X receptor. Such direct targets of LXR actions include important genes implicated in the control of lipid homeostasis, particularly reverse cholesterol transport. In addition, LXRs attenuate the transcription of genes associated with the inflammatory response indirectly by transrepression. In this review, we describe recent evidence that both highlights the key roles of LXRs in atherosclerosis and inflammation and provides novel insights into the mechanisms underlying their actions. In addition, we discuss the major limitations of LXRs as therapeutic targets for the treatment of atherosclerosis and how these are being addressed.

The effect of human immunodeficiency virus-1 on monocyte-derived dendritic cell maturation and function

Dendritic cells (DC) are mediators of the adaptive immune response responsible for antigen presentation to naive T cells in secondary lymph organs. Human immunodeficiency virus (HIV-1) has been reported to inhibit the maturation of DC, but a clear link between maturation and function has not been elucidated. To understand further the effects of HIV-1 on DC maturation and function, we expanded upon previous investigations and assessed the effects of HIV-1 infection on the expression of surface molecules, carbohydrate endocytosis, antigen presentation and lipopolysaccharide (LPS) responsiveness over the course of maturation. In vitro infection with HIV-1 resulted in an increase in the expression of DC-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) as well as decreases in maturation-induced CCR7 and major histocompatibility complex (MHC)-II expression. Retention of endocytosis that normally occurs with DC maturation as well as inhibition of antigen presentation to CD8(+) T cells was also observed. Mitogen-activated protein kinase (MAPK) responsiveness to LPS as measured by phosphorylation of p38, c-Jun N-terminal kinase (JNK) and extracellular-regulated kinase (ERK)1/2 was not affected by HIV-1 infection. In summary, in-vitro HIV-1 impairs DC maturation, as defined by cell surface protein expression, with selective alterations in mature DC function. Understanding the mechanisms of DC dysfunction in HIV infection will provide further insight into HIV immune pathogenesis.

Retinoic acid and liver X receptor agonist synergistically inhibit HIV infection in CD4+ T cells by up-regulating ABCA1-mediated cholesterol efflux

Background

Retinoic acids regulate the reverse cholesterol transport by inducing the ATP binding cassette transporter A1 (ABCA1) dependent cholesterol efflux in macrophages, neuronal as well as intestine cells. In the present study, we aim to test the effect of all trans retinoic acid (ATRA) on ABCA1 expression in human CD4+ T cells and the involvement of cholesterol in ATRA mediated anti-HIV effect.

Results

Treatment with ATRA dramatically up-regulated ABCA1 expression in CD4+ T cells in a time and dose dependent manner. The expression of ABCA1 paralleled with increased ABCA1-dependent cholesterol efflux. This induction was dependent on T cell receptor (TCR) signaling and ATRA failed to induce ABCA1 expression in resting T cells. Moreover, ATRA and liver X receptor (LXR) agonist-TO-901317 together had synergistic effect on ABCA1 expression as well as cholesterol efflux. Increased ABCA1 expression was associated with lower cellular cholesterol staining. Cells treated with either ATRA or TO-901317 were less vulnerable to HIV-1 infection. Combination of retinoic acid and TO-901317 further inhibited HIV-1 entry and their inhibitory effects could be reversed by cholesterol replenishment.

Methods

ABCA1 RNA and protein were determined by real-time PCR and immuno blot methods in cells treated with ATRA. Cholesterol efflux rate was measured in cells treated with ATRA and TO-901317.

Conclusions

ATRA up-regulates ABCA1 expression and cholesterol efflux in CD4+ T cells and combination of ATRA and liver X receptor (LXR) agonist further enhanced these effects. Increased cholesterol efflux contributed to reduced HIV-1 entry, suggesting that anti-HIV effect of ATRA is mediated through ABCA1.